Magnetic nanoparticle solid-state composite

Abstract

A magnetic nanoparticle solid-state composite includes a solid matrix and a plurality of magnetic nanoparticles arranged within the solid matrix in a non-random configuration. The non-random configuration of the plurality of magnetic nanoparticles enhances a magnetic property of the composite. The solid matrix provides structural support and stability, while the magnetic nanoparticles enable interaction with external magnetic fields.

Description

MAGNETIC NANOPARTICLE SOLID-STATE COMPOSITESTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention.CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 560,958 (filed March 4, 2024), which is herein incorporated by reference in its entirety.BACKGROUND

[0003] The present invention generally relates to the field of magnetic nanoparticle solid-state composites, and more particularly to techniques for enhancing magnetic properties and modulating magnetic particle imaging (MPI) signals within a solid matrix.

[0004] Magnetic particle imaging (MPI) is a rapidly developing biomedical imaging modality that leverages the unique magnetic properties of nanoparticles to generate high-contrast, real-time images. Unlike traditional imaging techniques such as X-ray computed tomography (CT) or magnetic resonance imaging (MRI), MPI directly detects the concentration and distribution of magnetic nanoparticles, offering significant advantages in sensitivity and specificity. The core principle behind MPI involves exposing magnetic nanoparticles to a time-varying magnetic field and measuring the resulting induced voltage. This induced voltage arises from the nonlinear response of the nanoparticles’ magnetic moment to the applied field, allowing for quantitative imaging of tracer distribution.

[0005] While MPI holds tremendous promise, significant challenges remain in optimizing the performance of magnetic nanoparticle tracers. One key area of research focuses on maximizing the signal -to-noise ratio (SNR) and spatial resolution of MPI images. In liquid suspension, magnetic nanoparticles exhibit both Neel relaxation (rotation of the magnetic moment within the particle) and Brownian relaxation (physical rotation of the particle). However, in solid matrices, Brownian relaxation is suppressed, leading to a reduction in the overall MPI signal. This limitation hinders the application of MPI in scenarios where solid or semi-solid materials are involved, such as in vivo tissue imaging or in the development of solid- state sensors.

[0006] Existing approaches to address this limitation have primarily focused on magnetically aligning nanoparticles within solid matrices. However, conventional alignment techniques typically yield only modest improvements in MPI signal, falling short of the performance achieved with nanoparticles in liquid suspension. Furthermore, controlling the spatial arrangement and stability of aligned nanoparticles within a solid matrix remains a significant challenge. Random orientation of nanoparticles within a matrix is easy to achieve but does not provide as good of a MPI signal output. Achieving a well-defined, stable, and reproducible spatial configuration of nanoparticles in a solid matrix that significantly enhances MPI signal is still an unrealized objective.

[0007] It is therefore an objective of the present invention to provide a magnetic nanoparticle solid-state composite with enhanced magnetic properties and methods for modulating MPI signals within a solid matrix, thereby overcoming the above-mentioned disadvantages of the prior art at least in part. Accordingly, methods and equipment for using magnetic nanoparticle solid-state composites with enhanced magnetic properties, tailored spatial arrangements, and methods for modulating the MPI signal with a non-random alignment of nanoparticles in a solid phase would be advantageous and would be favorably received in the art.BRIEF DESCRIPTION

[0008] One aspect of the present invention relates to a magnetic nanoparticle solid- state composite. A magnetic nanoparticle solid-state composite may be understood as a material system where magnetic nanoparticles are integrated within a solid matrix, combining the properties of both components. Magnetic nanoparticles refer to nanoscale particles exhibiting magnetic behavior, typically composed of materials such as iron oxide, nickel, or cobalt. A solid-state composite may be understood as a multiphase material consisting of distinct solid constituents that are physically combined to achieve desired structural and functional properties.

[0009] It may be provided that the magnetic nanoparticle solid-state composite includes a solid matrix. A solid matrix may be understood as a continuous, solid phase material that serves as a host structure for embedding or dispersing other materials. One advantage of including the solid matrix is to provide mechanical support, structural integrity, and environmental protection for the plurality of magnetic nanoparticles. This arrangement allows for the fabrication of robust and durable materials suitable for a variety of applications, particularly those requiring stability and resistance to degradation. By encapsulating themagnetic nanoparticles within a solid matrix, the mechanical and chemical stability is enhanced.

[0010] It may be provided that the magnetic nanoparticle solid-state composite includes a plurality of magnetic nanoparticles arranged within the solid matrix in a non-random configuration. A plurality of magnetic nanoparticles refers to a collection of numerous nanoscale particles exhibiting magnetic behavior. A non-random configuration may be defined as a deliberate and controlled arrangement of the plurality of magnetic nanoparticles within the solid matrix, deviating from a statistically uniform distribution. One advantage of including the plurality of magnetic nanoparticles is to tailor the magnetic, optical, electrical, or sensing characteristics of the solid-state composite. This arrangement could enable unique properties, such as enhanced magnetic response, directional anisotropy, or controlled interparticle interactions, that would not be achievable with randomly distributed nanoparticles. Arranging the nanoparticles in a non-random way results in improved functionality and enhanced performance.

[0011] It may be provided that the non-random configuration of the plurality of magnetic nanoparticles enhances a magnetic property of the composite. The phrase “enhances a magnetic property” refers to the improvement or amplification of a specific magnetic characteristic of the solid-state composite. This enhancement could manifest in various forms, such as increased magnetization, enhanced magnetic anisotropy, or improved magnetic susceptibility. One advantage of enhancing the magnetic property is enabling improved and novel performance for magnetic particle imaging, as signal improves, the signal output is increased, and thus has better signal and sensitivity that provides the best performance. This leads to a non-obvious solution, provides utility, and has a practical application.

[0012] One aspect of the present invention relates to a process for modulating a magnetic particle imaging (MPI) signal using a magnetic nanoparticle solid-state composite. A process may be understood as a series of actions or steps taken in order to achieve a particular end. Modulating can be understood as controlling or adjusting a property or characteristic of something. “Magnetic Particle Imaging (MPI) signal” refers to the electromagnetic signal emitted by magnetic nanoparticles when subjected to a time-varying magnetic field in the context of MPI.

[0013] It may be provided that this process comprises subjecting a magnetic nanoparticle solid-state composite to an alternating magnetic field. “Subjecting” is defined as exposing or exposing something to a particular condition or influence. “Alternating magnetic field” may be understood as a magnetic field whose direction and magnitude vary periodicallywith time. One advantage of subjecting the solid-state composite to an alternating magnetic field is causing the magnetic nanoparticles to generate a signal readable by the magnetic particle imaging system. Alternating magnetic fields provides improved function and allows for a more reliable function. This signal output produces a solution that is novel and performs accurately.

[0014] It may be provided that this process has a step of modulating a structural characteristic of the magnetic nanoparticle solid-state composite to modify the MPI signal emanating from the solid-state composite in response to the alternating magnetic field. A “structural characteristic” may be understood as a physical property or attribute of a material, relating to its composition, arrangement, or morphology. “To modify the MPI signal” refers to altering or controlling the electromagnetic signal emitted by the magnetic nanoparticles. One advantage is to induce changes in the spatial arrangement of the nanoparticles that enhances the MPI signal or makes it so it can be readable, measurable, and can act as a sensor switch for monitoring environmental conditions. This enables a novel way to measure or sense things by applying an inventive, previously unknown algorithm. By relying on a structural arrangement instead of concentration and a modulated signal from that structure, the composite is now a very useful microsensor tailored for MPI.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following description cannot be considered limiting in any way. Various objectives, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings, in which like reference numerals identify like elements.

[0016] FIG. 1 shows, according to some embodiments, a top schematic illustrating a primary method for producing solid nanocomposites with superior MPI response, and a bottom schematic illustrating another approach for making aligned nanocomposites.

[0017] FIG. 2 shows, according to some embodiments, imaging of aligned polystyrene nanocomposites in 3D printed wells and a sapphire crucible, wherein a 66 mT field is generated by two parallel permanent magnets.

[0018] FIG. 3 shows, according to some embodiments, an MPI signal comparison at different applied field amplitudes at 25 kHz of nanoparticles aligned in a polystyrene nanocomposite compared to the same nanoparticles in toluene (liquid vs. solid environment),wherein a nearly identical response is found at sufficiently high fields and the solid aligned nanocomposites generally show a higher response at low fields.

[0019] FIG. 4 shows, according to some embodiments, an MPI response and DC magnetometry data comparing aligned and randomly oriented nanoparticles on a plastic weighing boat substrate, wherein a volume fraction of polystyrene is different between MPI and DC magnetometry data, such that in the 1 mg / mL to 100 mg / mL range no significant difference in signal was observed.

[0020] FIG. 5 shows, according to some embodiments, a comparison of nanoparticles aligned in polystyrene, layered / laminated in PDMS compared to an approach where the nanoparticles are mixed and aligned or not aligned by a magnetic field in PDMS.

[0021] FIG. 6 shows, according to some embodiments: (a) SEM images of aligned polystyrene wrapped on Si / SiCh; (b) aligned polystyrene wrapped on a plastic weighing boat (C coated for imaging); (c) different sized particles aligned polystyrene wrapped on Si / SiCh; and (d) are identically without application of a magnetic field, wherein (e) is a high-resolution image of (a); (f) is a high-resolution image of (c), and (g) is a high-resolution image of (d).

[0022] FIG. 7 shows, according to some embodiments, data that: (h) compares MPI signal of these samples to a sample of the nanoparticles mixed into a PDMS matrix (harmonics that are close to background signal are removed); (i) includes different direction of MPI field being applied to samples shown in (c / f) and (d / g) in FIG. 6, and compares film-like structures to aligned structures; and (j) shows detection of a low quantity of nanoparticles (about 10 pg) compared to background signal and the ratio showing signal to noise.

[0023] FIG. 8 shows, according to some embodiments: (a) result of swelling which results in modulated signal; (b) compares polystyrene nanocomposites and PDMS layered / laminated structures; and (c) change in signal with swelling using two different solvents (hexanes and acetone), wherein hexanes swell the PDMS more than acetone resulting in a larger change in signal between dried and swollen state.

[0024] FIG. 9 shows, according to some embodiments, (d, e) shows the harmonic spectrum of the cycles between drying and swelling in both hexanes and acetone.

[0025] FIG. 10 shows, according to some embodiments, (a,b,c,d) cross section TEM showing nanoparticles (FesCh) in PDMS fabricated by the mixing and aligning process (low MPI signal); and panels (e,f,g,h) showing nanoparticles (FesCh) in polystyrene deposited on plastic weight boat (high MPI signal).

[0026] FIG. 11 shows, according to some embodiments, aligned layered / laminated nanoparticles between PDMS which show comparable signal to those fabricated by the polystyrene alignment fabrication procedure.

[0027] FIG. 12 shows, according to some embodiments, enlarged views of portions of the composite shown in FIG. 11.

[0028] FIG. 13 shows, according to some embodiments, enlarged views of portions of the composite shown in FIG. 11; aligned layered / laminated nanoparticles between PDMS show similar randomly oriented nanoparticle arrangement within close-packed structure as polystyrene samples.

[0029] FIG. 14 shows, according to some embodiments, an optical image of aligned layered / laminated nanoparticles between PDMS.

[0030] FIG. 15 shows, according to some embodiments, an optical and SEM image of aligned layered / laminated nanoparticles between PDMS.

[0031] The left panel of FIG. 16 shows an MPS response versus drive field amplitude for chaining particles in solution (circles) and in solid nanocomposite (squares). The top right panel shows data for MPS response versus harmonic number at low fields, wherein the nanocomposite sample exhibits superior response at all harmonics. The bottom right panel shows data for MPS response versus harmonic number at high magnetic fields, wherein the fully chained nanoparticles in solution and in nanocomposite exhibit almost identical response at all harmonics.DETAILED DESCRIPTION

[0032] A detailed description of one or more embodiments is presented herein by way of exemplification and not limitation.

[0033] Conventional approaches to magnetic particle imaging (MPI) tracers often suffer from limited signal strength and spatial resolution, particularly when implemented in solid or semi-solid environments. Existing methods for aligning magnetic nanoparticles in solid matrices typically provide only modest improvements in MPI signal, failing to achieve the enhanced performance observed in liquid suspensions. This deficiency stems from the suppression of relaxation in solid matrices and the difficulty in controlling the spatial arrangement and stability of aligned nanoparticles.

[0034] The magnetic nanoparticle solid-state composite overcomes these signal outputs and spatial restrictions. It has been discovered that the magnetic nanoparticle solid- state composite achieves enhanced magnetic properties by combining the benefits of magneticnanoparticles with the stability and structural control afforded by a solid matrix. One advantage of the magnetic nanoparticle solid-state composite lies in its ability to tailor the spatial arrangement of the nanoparticles to enhance specific magnetic properties, enhancing MPI signal in the composite. This results in a strong output with a high resolution. In this way, the magnetic nanoparticle solid-state composite solves a previously unsolved problem and has better performance, novelty, and has a practical utility for magnetic imaging.

[0035] In an embodiment, a magnetic nanoparticle solid-state composite comprises a solid matrix (200) and a plurality of magnetic nanoparticles (201) arranged within the solid matrix (200) in a non-random configuration (202), wherein the non-random configuration (202) of the plurality of magnetic nanoparticles (201) enhances a magnetic property of the composite. In an embodiment, the solid matrix (200) comprises a polymer. In an embodiment, the polymer comprises polydimethylsiloxane (PDMS) or polystyrene. In an embodiment, the plurality of magnetic nanoparticles (201) are arranged in a chain-like structure (203) within the solid matrix (200). In an embodiment, the plurality of magnetic nanoparticles (201) are arranged as a thin film (204) within the solid matrix (200). In an embodiment, the plurality of magnetic nanoparticles (201) comprise iron oxide. In an embodiment, the iron oxide comprises majority magnetite . In an embodiment, a substrate (205) is included, and the solid matrix (200) with the plurality of magnetic nanoparticles (201) is disposed on the substrate (205). In an embodiment, the substrate (205) comprises a non-magnetic material. In an embodiment, the non-random configuration (202) is selected to modulate a magnetic particle imaging (MPI) signal of the composite.

[0036] The magnetic nanoparticle solid-state composite (206) comprises a solid matrix (200). Functionally, the solid matrix (200) provides a structural framework that houses and supports the plurality of magnetic nanoparticles (201). It serves to maintain the desired spatial arrangement of the nanoparticles (201) and protect them from external environmental factors. In terms of implementation, the solid matrix (200) can be composed of various materials, including polymers, ceramics, glasses, or metals, depending on the desired application and performance characteristics. For example, a polymer matrix could be formed from a precursor material that undergoes curing or polymerization to create the solid structure. One benefit of including the solid matrix (200) is to provide a mechanically robust and chemically stable environment for the magnetic nanoparticles (201). Variations of the solid matrix (200) include the use of biodegradable polymers for controlled release applications or stimuli-responsive polymers for dynamic control over the nanoparticle arrangement. As an example of use, the solid matrix (200) could be a crosslinked polymer network that maintainsthe nanoparticles’ relative positions and protects them during exposure to physiological conditions.

[0037] The magnetic nanoparticle solid-state composite (206) further comprises a plurality of magnetic nanoparticles (201) arranged within the solid matrix (200) in a nonrandom configuration (202). Functionally, the plurality of magnetic nanoparticles (201) are the active components that generate a magnetic signal in response to an external magnetic field, enabling the magnetic nanoparticle solid-state composite (206) to function as an MPI tracer or a magnetic sensor. The non-random configuration (202) dictates the collective magnetic behavior of the nanoparticles (201) and influences the strength, shape, and anisotropy of the MPI signal. In implementation, the plurality of magnetic nanoparticles (201) can be composed of materials such as iron oxide (magnetite or maghemite), doped iron oxide (e.g., Zn-doped magnetite), cobalt ferrite, or other suitable magnetic materials. The non-random configuration (202) can be achieved through various techniques, such as applying an external magnetic field during the solidification of the solid matrix (200), self-assembly of nanoparticles (201) with specific surface functionalization, or microfabrication techniques to pattern the arrangement of nanoparticles (201). One benefit is enabling a higher sensitivity and resolution as now we can dictate where the signal output can occur. Variations of the plurality of magnetic nanoparticles (201) include using different sizes, shapes, and compositions of nanoparticles to optimize the MPI signal for specific applications. For example, the plurality of magnetic nanoparticles (201) could be arranged in a chain-like structure (203) to enhance the magnetic anisotropy and increase the MPI signal strength or as a thin film (204) to enhance MPI signal.

[0038] The magnetic nanoparticle solid-state composite (206) is configured such that the non-random configuration (202) of the plurality of magnetic nanoparticles (201) enhances a magnetic property of the composite. Functionally, this enhances a magnetic property to enhance MPI output. One implementation can include selecting a specific nonrandom alignment in one direction but not others to enhance the sensitivity in one axis and disregard sensitivities in other directions. The non-random arrangement helps achieve a previously unknown resolution and MPI output, providing a practical utility.

[0039] In one embodiment, the solid matrix (200) comprises a polymer. Functionally, the polymer provides a flexible and processable matrix for embedding the plurality of magnetic nanoparticles (201). Implementation can involve using a variety of polymers, including both synthetic and natural polymers, depending on the desired mechanical, thermal, and chemical properties. For example, the polymer can be a thermoplastic, a thermoset, or an elastomer. The use of a polymer matrix can enhance the ease of manufacturingthe magnetic nanoparticle solid-state composite (206) and can provide biocompatibility for in vivo applications. A polymer matrix can be varied to use biodegradable polymers to allow controlled release of magnetic nanoparticles.

[0040] In another embodiment, the polymer comprises polydimethylsiloxane (PDMS) or polystyrene. Functionally, PDMS and polystyrene offer distinct advantages as matrix materials due to their unique properties. PDMS is a silicone-based elastomer known for its flexibility, biocompatibility, and chemical inertness. Polystyrene is a rigid thermoplastic polymer with good mechanical strength and ease of processing. Implementation might involve using PDMS for applications requiring flexibility and biocompatibility, such as implantable sensors or drug delivery devices, or using polystyrene for applications where mechanical strength and rigidity are important, such as structural components or microfluidic devices. One benefit is the selection of a matrix material based on the specific application requirements, allowing for optimization of the solid-state composite’s performance. Variations may include using modified PDMS or polystyrene with specific functional groups to enhance the interaction with the magnetic nanoparticles (201) or to impart specific properties to the composite material.

[0041] In another embodiment, the plurality of magnetic nanoparticles (201) are arranged in a chain-like structure (203) within the solid matrix (200). Functionally, a chainlike structure (203) can enhance the magnetic anisotropy and increase the MPI signal strength of the composite (206). Chain-like alignment allows for a more uniform magnetic response to the magnetic field. The implementation can include applying a magnetic field during the solidification of the matrix precursor (215), causing the magnetic nanoparticles (201) to selfassemble into chains (203) aligned with the field. A benefit is generating optimized magnetic anisotropy that enhances the signal response.

[0042] In another embodiment, the plurality of magnetic nanoparticles (201) are arranged as a thin film (204) within the solid matrix (200). The thin film configuration (204) provides a high surface area-to-volume ratio, enabling efficient interaction with an external magnetic field, along with optimized magnetic anisotropy and enhancing the MPI signal response. Implementation may involve depositing a thin layer of the solution (214) containing the magnetic nanoparticles (201) and matrix precursor (215) onto a substrate (205) and then solidifying the matrix. One benefit is to improve the sensitivity and resolution of MPI imaging.

[0043] In another embodiment, the plurality of magnetic nanoparticles (201) comprise iron oxide. Functionally, iron oxide nanoparticles offer a combination of high magnetic susceptibility, biocompatibility, and relatively low cost. Iron oxide enables strong contrast and signal in MPI applications. Implementation can include using iron oxidenanoparticles synthesized by chemical co-precipitation, thermal decomposition, or hydrothermal methods. The choice of synthesis method affects the size, shape, and crystallinity of the nanoparticles, which influences their magnetic properties. A benefit is that iron oxide nanoparticles make the overall product cheaper, and therefore accessible to more end-users.

[0044] In another embodiment, the iron oxide comprises magnetite, maghemite, or doped versions of these materials. Functionally, magnetite (FesCh) and maghemite (y-Fe2O3) are two common forms of iron oxide with distinct magnetic properties. Magnetite is a ferrimagnetic material with a higher saturation magnetization, while maghemite is a ferrimagnetic material with a lower saturation magnetization but greater chemical stability. This provides better thermal stability. Implementation may involve selecting magnetite for applications requiring high magnetic response or maghemite for applications requiring greater stability in harsh chemical environments. A benefit is to be able to fine-tune the magnetic properties of the composite by selecting the appropriate iron oxide phase. Doping magnetite or maghemite with metals such as Zn or Co can tune the magnetic response. For instance, Zn- doped magnetite nanoparticles can exhibit higher saturation magnetization than pure magnetite nanoparticles.

[0045] In another embodiment, the magnetic nanoparticle solid-state composite (206) further comprises a substrate (205), and the solid matrix (200) with the plurality of magnetic nanoparticles (201) is disposed on the substrate (205). Functionally, the substrate (205) provides mechanical support and facilitates handling of the magnetic nanoparticle solid- state composite (206). This makes it easier to control the deposition and provides high utility in applications where the composite needs to be integrated with other devices. Implementation can include various materials, such as silicon, glass, plastic, or sapphire, depending on the application. The solid matrix and nanoparticle component on a substrate helps make the device perform more efficiently, more reliably, and improve on its overall performance.

[0046] In another embodiment, the substrate (205) comprises a non-magnetic material. The presence of magnetic materials in the substrate (205) could interfere with the MPI signal. A non-magnetic substrate increases the accuracy of the system. Implementation can include materials such as silicon, glass, plastic, ceramic, or sapphire. A benefit is enabling accurate and reliable MPI measurements.

[0047] In another embodiment, the non-random configuration (202) is selected to modulate a magnetic particle imaging (MPI) signal of the composite. Functionally, the magnetic particle imaging system can have a wide range of sensitivity with this ability. This implementation involves manipulating the size, shape, composition, effective anisotropy andspatial arrangement of the magnetic nanoparticles to control the MPI signal strength, shape, and anisotropy. One benefit is to enhance the performance of the magnetic nanoparticle solid- state composite (206) as an MPI tracer or sensor. This enables the control of the signal strength output based on the configuration chosen.

[0048] The solid matrix (200) is a solid phase material providing mechanical support and structural integrity to the magnetic nanoparticle solid-state composite (206). Physically, the solid matrix (200) can be a continuous material encasing the plurality of magnetic nanoparticles (201). Interconnectivity with other elements of the solid matrix (200) includes the physical and chemical interactions between the matrix material and the surface of the magnetic nanoparticles (201), ensuring uniform distribution and preventing agglomeration. Its operability and functionality are to provide a stable environment for the magnetic nanoparticles (201) that will withstand external forces and maintain the desired spatial arrangement. Implementation of the solid matrix (200) might use various technologies or algorithms depending on the type of solid.

[0049] The physical construction of the solid matrix (200) can include a polymer network, a ceramic structure, or a glass substrate. Physical interoperability is achieved by selecting materials and processes that allow for the magnetic nanoparticles (201) to be uniformly dispersed and securely embedded. Physical arrangement may involve the solid matrix (200) being cast, molded, or spin-coated onto a substrate (205) to create a thin film or a three-dimensional structure. The physical dimensions and size of the solid matrix (200) are application-dependent. For instance, a thin-film sensor may have a thickness from 100 nm to 10 pm, specifically from 500 nm to 5 pm, and more specifically from 1 pm to 3 pm, while a microscale composite for biomedical applications can be from 1 pm to 500 pm, specifically from 2 pm to 250 pm, and more specifically from 5 pm to 50 pm, and bulk composite for structural applications can be from 1 mm to 10 cm, specifically from 5 mm to 5 cm, and more specifically from 1 cm to 3 cm. The physical shape of the solid matrix (200) can be planar, curved, or complex, as dictated by the device’s geometry. One benefit of the solid matrix (200) is that the magnetic particles are held together.

[0050] The solid matrix (200) provides mechanical support, protects the magnetic nanoparticles (201) from degradation, and can also be selected to modulate the interaction of the nanoparticles (201) with external stimuli, providing improved functionality, reliability, and performance. In one application, the solid matrix (200) is a PDMS material in microfluidic devices. In another application, the solid matrix is a ceramic to help the solid matrix (200) withstand high-impact external conditions.

[0051] It is contemplated that the solid matrix (200) acts as the structural backbone for the magnetic nanoparticle solid-state composite (206), providing mechanical support, chemical protection, and enabling the desired spatial arrangement of the plurality of magnetic nanoparticles (201). The architecture of the solid matrix (200) can be a continuous phase to promote uniform nanoparticle dispersion; layered to induce anisotropic behavior; or porous to facilitate interaction with external stimuli.

[0052] The selection of materials and their composition for the solid matrix (200) hinges on the application’s requirements. Polymers offer processability and potential biocompatibility. Specific examples include polydimethylsiloxane (PDMS), suitable for biomedical and microfluidic devices due to its flexibility, inertness, and biocompatibility; polystyrene (PS), providing mechanical strength and electrical insulation for structural and sensing applications; poly(methyl methacrylate) (PMMA), useful in optical devices and sensors due to its transparency and mechanical robustness; biodegradable polymers such as PLA, PGA, and PLGA, enabling controlled release of nanoparticles in drug delivery and tissue engineering. Ceramics such as silica (SiCh), alumina (AI2O3), and zirconia (ZrCh) can also be matrix materials given their high thermal and chemical resistance. The solid matrix can be formed into a variety of embodiments ranging from the aforementioned thin layers to bulk samples to act as a substrate for the composite.

[0053] The plurality of magnetic nanoparticles (201) are discrete magnetic particles dispersed within the solid matrix (200), contributing to the magnetic properties and enabling the composite’s functionality. The physical structure is such that the physical size, shape, and material composition are carefully controlled to achieve the desired magnetic properties. In an embodiment, the magnetic nanoparticles (201) are dispersed throughout the solid matrix (200) to allow for a uniform magnetic response. In an embodiment, the magnetic nanoparticles (201) are dispersed throughout the solid matrix (200) to allow for a selected non-uniform magnetic response. One operability and functionality is to interact with an external magnetic field, enabling their detection and manipulation for various applications, especially for producing an MPI output. Implementation may include, depending on the desired properties, using a singledomain structure, composition, size, and surface coating of the magnetic nanoparticles (201).

[0054] The physical construction is such that magnetic nanoparticles are created from metals such as iron oxide, cobalt ferrite, or other magnetic materials. Physical interoperability involves chemically or physically bonding to the solid matrix (200). The nanoparticles (201) should have an overall physical arrangement with inter-particle spacings of 1 nm to 100 nm, specifically from 1 nm to 50 nm, and more specifically from 1 nm to 5 nm,to allow dipole-dipole interactions between the magnetic nanoparticles (201). The physical dimension or particle size of the magnetic nanoparticles (201) can be from 5 nm to 100 nm, specifically from 10 nm to 50 nm, and more specifically from 15 nm to 25 nm. The physical shape is spherical, cubic, or rod-shaped to enhance the magnetic response of the composite. One benefit of the magnetic nanoparticles (201) is to provide a source of detectable magnetic signal and allowing magnetic control through an applied magnetic field.

[0055] Variations for the nanoparticles (201) include materials of the core and any coatings, if applicable. Such coatings are for functionalization (surface charges). In one application of a medical device that goes inside a human body, a coating on the iron oxide would provide for better compatibility with the environment. In another application of a microfluidic device, the coating can provide a selected shape to the nanoparticle (201), e.g., cubic, to improve structural properties to be more resistant to environmental factors such as external vibrations.

[0056] It is contemplated that the magnetic nanoparticle (MNP) is a nanoscale particle, typically ranging in size from 1 to 100 nanometers, exhibiting magnetic properties. These particles, often composed of materials like iron oxide (magnetite or maghemite), cobalt, iron, nickel, or their alloys, respond to external magnetic fields, making them valuable in a wide array of applications, including biomedical imaging, drug delivery, data storage, and catalysis. The individual magnetic nanoparticles (201) have a single crystalline structure. This means that each nanoparticle consists of a single crystal lattice, where the atoms are arranged in a highly ordered and periodic manner throughout the entire particle volume. This single crystalline nature contributes to the uniform magnetic properties and minimizes energy loss due to domain wall motion.

[0057] The types of materials used for the magnetic nanoparticle core include, but are not limited to iron oxide, which has relatively high saturation magnetization. Exemplary forms are magnetite (FesCh) that exhibits ferrimagnetism and has a high saturation magnetization and maghemite (y-Fe2O3), which is a defect spinel structure, also ferrimagnetic, and known for its chemical stability.. Other materials such as metallic iron, nickel, zinc / cobalt ferrite, and various alloys thereof can also be used, each offering a unique set of magnetic properties.

[0058] Materials composition refers to the specific arrangement of atoms and elements within the magnetic nanoparticle. For iron oxide nanoparticles, the stoichiometry (ratio of iron to oxygen) is crucial for determining the magnetic properties. Deviations from the ideal stoichiometry can lead to defects and reduced magnetization. The presence of dopantsor impurities can also affect the magnetic properties by altering the crystal structure or electron configuration.

[0059] Size distribution is a critical parameter for controlling the magnetic properties of nanoparticles. A narrow size distribution ensures a more uniform magnetic response across the ensemble of nanoparticles, while a broad distribution can lead to variations in magnetic behavior. The mean diameter of the plurality of magnetic nanoparticles (201) can range from 5 nm to 100 nm, specifically from 10 nm to 50 nm, and more specifically from 15 nm to 25 nm. These ranges can be tailored for the specific application needs. The particles will generally be spherical to allow them to properly align without any angular momentum considerations.

[0060] The magnetic nanoparticles (201) can have a tailored non-magnetic shell (surfactant layer) and the saturation magnetization of the magnetic core. The ratio of nanoparticle diameter to shell affects interparticle dipolar interactions, since they are important for the response behavior. Also, the saturation magnetization of the magnetic core can be optimized for better signal output.

[0061] The non-random configuration (202) is a specific spatial arrangement of the plurality of magnetic nanoparticles (201) within the solid matrix (200), designed to enhance a particular magnetic property of the composite. Physical structure is such that nanoparticles need to be close enough together to interact. Physical construction occurs during the curing, which can either be random, oriented (based on external magnetic field) or close-packed (selfassembly). This has interoperability with the solid matrix (200), and functionality of the composite depends on the non-random configuration chosen. The physical construction for the non-random configuration (202) include arrangements such as chains, layers, or other ordered structures. The magnetic nanoparticles (201) maintain an arrangement to achieve optimized magnetic properties. Non-random alignment is achieved through a magnetic field, conformation to substrate structure, or structural elements. The physical dimensions and size of the magnetic nanoparticles (201) arrangement can be selected to provide a tailored response for MPI. The magnetic nanoparticles (201) can be arranged from 2 to thousands of nanoparticles, specifically from 2 to 100 nanoparticles, and more specifically from 3 to 10 nanoparticles, to align the overall magnetic properties. The shape can be chain-like or a thin film depending on the material used for the solid matrix (200). One benefit of the non-random configuration (202) is allowing an enhanced MPI output.

[0062] Non-random configurations (202) can vary in the specific type or configuration depending on how they are formed. This can be performed by self-assembly,template-guided assembly, field-directed assembly, and the like. For example, rod-shaped selfassembled nanoparticles (201) help increase the magnetic signal output in one direction and minimize the MPI output from the other direction. Using a non-random configuration provides optimized magnetic responses and better efficiency.

[0063] The chain-like structure (203) constitutes a specific non-random configuration (202) within the magnetic nanoparticle solid-state composite (206), wherein the plurality of magnetic nanoparticles (201) are arranged in a substantially linear fashion. This configuration promotes strong dipolar interactions between neighboring nanoparticles (201), leading to enhanced magnetic properties. The chains may be one-dimensional or exhibit some degree of curvature or branching. The individual magnetic nanoparticles (201) in the chainlike structure (203) interact through magnetic dipolar forces, aligning their magnetic moments along the chain axis. This alignment results in a significantly larger effective magnetic moment / optimized magnetic anisotropy for the chain as a whole compared to individual, randomly oriented nanoparticles. The strength of this dipolar interaction depends on the interparticle spacing and the magnetic moment of the individual nanoparticles (201). It allows for a higher sensitivity of the instrument. When exposed to an external magnetic field (207), the chain-like structure (203) exhibits enhanced magnetic anisotropy. The chain’s overall magnetic moment becomes highly sensitive. This arrangement can enable stronger output and higher signal, allowing the system to operate more effectively. This enhancement is particularly relevant for MPI applications, where a strong and anisotropic magnetic response is essential for achieving high sensitivity and spatial resolution. It results in the Neel response to avalanche along the nanoparticles (201) of the chain, creating a response larger than if the particles were not lined up.

[0064] The thin film (204) represents an alternative non-random configuration (202) for the plurality of magnetic nanoparticles (201) within the solid matrix (200), wherein the nanoparticles (201) are arranged as a substantially two-dimensional layer. The thin film (204) configuration offers a high surface area-to-volume ratio, enhancing the interaction between the nanoparticles (201) and an external magnetic field (207). Also, this can enhance specific interactions such as the Neel avalanche. The implementation of the thin film (204) can involve various deposition techniques such as spin coating, drop casting, or Langmuir-Blodgett deposition. These techniques allow for precise control over the thickness and uniformity of the thin film (204), ensuring consistent magnetic properties across the composite material (206). Also, the configuration allows the magnetic nanoparticles (201) to be closely packed. By arranging the nanoparticles (201) in a thin film (204), the magnetic nanoparticle solid-statecomposite (206) exhibits a distinct magnetic anisotropy compared to randomly distributed nanoparticles. If the applied magnetic field (207) is applied to the directions of the film, it will have an enhanced output. This enhancement makes the composite (206) a highly sensitive and spatially accurate output reading, or sensor. This leads to increased performance in medical devices, sensors, and remote control devices. The thickness of the film enables its unique magnetic anisotropy by being between one and one thousand nanometers. In addition, the packing density allows for a higher sensitivity to external magnetic fields.

[0065] The substrate (205) is a supporting material upon which the solid matrix(200) and plurality of magnetic nanoparticles (201) are deposited, providing mechanical support and a defined surface for the composite (206). Its physical structure can be varied depending on application with the following shapes and dimensions. The surface of the substrate (205) can be planar, curved, or textured to influence the morphology of the deposited composite (206). A function of the substrate (205) is to give support, or it might also have more operability and functionality depending on other components in the device. This could involve the use of a non-magnetic, electrically conductive substrate (205) material such as to provide a ground plane for the device. Another example is the deposition of the magnetic nanoparticle solid-state composite (206) for in-vivo use. The non-magnetic aspect is important to avoid any interference from external forces of magnetism. The substrate (205) materials can vary depending on the type of application. Examples include silicon, glass, sapphire, plastic, and the like. These materials can be altered or have functional groups added to their surfaces. As a structural base, the substrate adds improved utility and resistance to external vibrations or movement.

[0066] The magnetic nanoparticle solid-state composite (206) is the final article of manufacture, integrating the solid matrix (200) and the plurality of magnetic nanoparticles(201). Its physical structure combines the physical properties of the matrix and the magnetic properties of the nanoparticles (201), creating a hybrid material with tailored characteristics. The material’s magnetic response can be improved through field-directed assembly, enabling a new application in magnetic particle imaging and providing accurate and reliable readouts. The interconnectivity with other elements means that the solid matrix (200) helps keep the nanoparticles (201) in a non-random configuration (202) that has a high surface area-to-volume ratio. The material is designed to enhance magnetic anisotropy and facilitate strong dipolar interactions for improved performance. The solid-state composite (206) can then be integrated with a substrate to improve physical and structural performance. Its operability and functionality enable many different features and uses. The physical and electromagneticproperties, particularly for medical diagnostic imaging applications, are of utmost importance. The material is sensitive to external magnetic fields (207) and has a quantifiable measurement. By using a known material for the solid matrix (200) and the particles, known electromagnetic qualities can then be applied to the configuration of the nanoparticles. A specific embodiment is for use in microfluidic devices and biosensors, used in drug delivery, for magnetic hyperthermia cancer treatments, and as a sensor for mechanical stress. In applications for in- vivo sensing, the composite’s size can range from several nanometers to several centimeters.

[0067] The alternating magnetic field (207) is an externally applied magnetic field with a periodically varying direction and magnitude. Functionally, it serves as an excitation source to induce a response from the magnetic nanoparticles (201) within the solid matrix (200) in MPI applications. The use of an alternating magnetic field (207) means the device can have time-varying signals that can be detected and analyzed. In implementation, the alternating magnetic field (207) can be generated using various electromagnetic components such as coils, solenoids, or antennas driven by an alternating current (AC) source. It creates magnetic signals with greater performance and sensitivity. The frequency and amplitude of the alternating magnetic field (207) are parameters that can be selected depending on the magnetic properties of the nanoparticles (201) and the specific requirements of the MPI system. This enables the unique properties of the non-random arrangement in the device and provides a new way to control the signal output. Amplitudes can range from 1 mT to 100 mT, specifically from 5 mT to 70 mT, and more specifically from 10 mT to 50 mT. Frequencies may range from 100 Hz to 1 MHz, specifically from 10 kHz to 500 kHz, and more specifically from 20 kHz to 100 kHz.

[0068] The structural characteristic (208) refers to a physical attribute of the magnetic nanoparticle solid-state composite (206) that can be modulated to alter its magnetic properties and, consequently, its MPI signal (209). This modulation forms the basis for sensing or responsive behavior. The physical dimension of the device can be directly manipulated from 10 nm to 100 mm. The inter-connectivity allows it to communicate with the MPI and have a useful readout. Examples of structural characteristics (208) include:Interparticle Spacing: Changing the average distance between the magnetic nanoparticles (201) affects the strength of dipolar interactions and the overall magnetic anisotropy of the composite (206). As they are arranged as a unit, the spatial resolution in the sensor also improves.Chain Alignment: The degree of alignment or orientation of the nanoparticle chains (203) with respect to the applied field (207) influences the magnitude and directionality of the MPI signal (209). This change allows for an MPI signal to be controlled in eachdirection as there is some range of magnetic field, or even zero, where it cannot be recorded.Matrix Swelling / Contraction: Changing the dimensions of the solid matrix (200) through swelling or contraction alters the interparticle spacing and chain alignment, modulating the magnetic properties and MPI signal (209). The amount that the matrix swells and contracts is tailored for maximum performance.

[0069] Implementation can involve various techniques to modulate these structural characteristics (208), such as applying external stimuli (e.g., solvents, temperature, mechanical stress) to the composite material (206). This enables new applications in areas such as remote sensors. The modulated structural arrangement creates a shift that provides better detection, increased reliability, and an overall efficient function.

[0070] The magnetic particle imaging (MPI) signal (209) constitutes the electromagnetic signal emitted by the magnetic nanoparticle solid-state composite (206) in response to the alternating magnetic field (207). As the structure is altered, the change in the signal allows it to act as a sensor. The strength, frequency spectrum, and spatial distribution are what creates the distinct characteristics and how this signal interacts with other components. It is quantifiable with the various sensors and techniques. The MPI signal (209) carries information about the concentration, distribution, temperature, and magnetic properties of the nanoparticles (201) within the composite (206). Its characteristics makes it suited for various sensor readings, particularly for magnetic particle imaging. This function is reliable as long as a proper magnetic signature output is present. Implementation can involve using a receiver coil and signal processing algorithms to detect and analyze the MPI signal (209). Techniques such as Fourier analysis can be employed to extract specific harmonics or spectral components of the MPI signal (209) related to particular parameters, such as temperature or environmental conditions.

[0071] The separation distance (210) refers to the spatial interval between individual magnetic nanoparticles (201) or clusters of nanoparticles within the solid matrix (200). This is a structural characteristic (208) that impacts the collective magnetic behavior. Manipulation of the structure allows for manipulation of the signals. The precise control of the separation distance (210) can range from 0.1 nm to 100 nm, specifically from 1 nm to 50 nm, and more specifically from 1 nm to 20 nm. The separation distance dictates the strength of the magnetic dipole-dipole interactions between neighboring nanoparticles (201), directly influencing the magnetic anisotropy and MPI response of the composite. This means that the inter-connectivity between the particles are carefully modulated. These ranges are achieved byusing specific sizes of core and shells for the magnetic nanoparticles (201) and precise process conditions during fabrication and alignment. Functionality relies on changing the solid matrix(200) volume, which in turn changes the inter-particle distances. Swelling or contracting the solid matrix can increase or decrease the distances. For sensing applications, for example, it may be desirable to alter the solid matrix (200) to determine an analyte concentration. As the separation distances (210) change, the strength or frequency of the magnetic particle imaging (MPI) signal 209 changes too and can be measured, increasing the device’s resolution and sensitivity. The device, through this functional change, also has increased performance, reliability, and robustness.

[0072] Various substances can be used to treat the magnetic nanoparticles, including a solvent, matrix precursor, and the like. The solvent (211) is a liquid substance used to dissolve or disperse the matrix precursor (215) and the plurality of magnetic nanoparticles(201) during the fabrication process. Also, it allows for a solid matrix (200) dimension to be altered by introducing the substance. A liquid with a defined concentration with a chemical mixture would be an example of the material composition. The liquid allows the particles to be dispersed so that the matrix precursor (215) does not cause any unexpected forces. A nonspecific solvent might be used such as distilled water. The solvent (211) facilitates the uniform mixing and dispersion of the nanoparticles (201) within the matrix precursor (215), enabling the formation of a homogeneous composite material (206). After a period of time, or by external forces, the solvent (211) can also be extracted. The selection of a specific solvent (211) depends on the chemical nature of the matrix precursor (215) and the surface properties of the nanoparticles (201). Polar or nonpolar properties can be considered. Solvents can also be selected to provide for a good and controllable extraction rate. For polymer matrix precursors, solvents such as toluene, chloroform, or ethanol can be employed. After applying a magnetic field (207) and solidifying the matrix material, the solvent (211) is removed through evaporation or other suitable means, resulting in the formation of a magnetic nanoparticle solid- state composite (206) with the desired structure and magnetic properties. This can result in lower production costs.

[0073] The magnetic particle imaging (MPI) scanner (212) constitutes a specialized imaging system designed to detect and process the magnetic particle imaging (MPI) signal (209) emitted by the magnetic nanoparticle solid-state composite (206). It performs measurements that would be difficult or impossible using more conventional testing equipment. The MPI scanner (212) applies a time-varying magnetic field (207) to the composite material (206) and measures the resulting induced voltage. The MPI scanner cangenerate tomographic images that can measure how much the signal is changing. MPI is more robust because it can detect a larger magnetic variance, and there is minimal signal from other parts of the subject. The MPI scanner (212) can include a series of gradient coils, drive coils, and receiver coils arranged in a specific configuration to generate the necessary magnetic fields and detect the MPI signal (209). The received signal is amplified, filtered, and digitized for image reconstruction using specialized algorithms. The type and properties will depend on the solid matrix and how much the volume changes. Through the detection of various physical phenomena, better devices that can accurately and reliably produce measurements can be used with this technology.

[0074] The environmental condition (213) refers to a measurable aspect of the surrounding environment that influences the structural characteristics (208) of the magnetic nanoparticle solid-state composite (206) and, consequently, its MPI signal (209). As the structure is altered, there is a quantifiable and reliable measurement as to whatever aspect is being sought. The composition of what is used and measured can vary to cover a wide range of applications. This function enables remote monitoring capabilities in scenarios where traditional sensors may be unsuitable. Instead of requiring a sensor, for example temperature, the magnetic properties are manipulated and provide better remote imaging for medical diagnostics. Implementation can involve selecting a matrix material or surface modification strategy that is sensitive to a particular environmental parameter, for example, a polymer that swells in response to a specific solvent or a receptor molecule that binds to a target analyte. The environmental condition provides the ability to enhance different aspects of environmental conditions that weren’t possible with sensors today.

[0075] The solution (214) is a liquid mixture comprising the solvent (211) and the matrix precursor (215), along with the plurality of magnetic nanoparticles (201). The mixture aids provision of the non-random configurations (202). The physical structure can be based on the type of materials in this medium, and the interoperability will depend on the ratios of materials. The solution enables suspension and uniform distribution of the magnetic nanoparticles (201) within the matrix precursor (215) prior to solidification of the matrix. The solution can have a viscosity low enough to allow the materials to form well-ordered chains and bundles during alignment to obtain a predictable result. The selection of the solution (214) components (solvent (211) and matrix precursor (215)) can depend on the specific materials used and their compatibility with the magnetic nanoparticles (201). The selection of the materials can lead to predictability and reliability. Some examples are a dispersion of iron oxide nanoparticles (201) in a toluene solution (214) containing polystyrene; or a suspension of cobaltferrite nanoparticles (201) in a hexane solution (214) containing uncured PDMS. With well- characterized materials and careful selection, the resulting solution enables a solid-state magnetic nanoparticle (201) with enhanced and customized properties.

[0076] The matrix precursor (215) is a substance that can be converted into a solid matrix (200) through a solidification process. It allows magnetic nanoparticles to be held in a configuration of non-random configurations (202). Material composition can be varied as long as it forms into a solid matrix (200). The characteristics of the solid can depend on the matrix precursor (215). These can include:Polymers. In this instance the solution (214) can include PDMS mixed with a curing agent or an additional polymer that is wrapped around the solid material.Sol-gel precursors: used to make ceramic materials.Pre-ceramic polymers: polymers that pyrolyze to form ceramics.

[0077] The solidification can involve varying methods, which can include chemical curing, evaporation, cooling, and the like. After the solidification happens, the structural arrangement remains fixed to help produce an effective MPI output.

[0078] In certain embodiments, the surface of the magnetic nanoparticles (201) can be modified. Such modifications can achieve colloidal stability, controlling interparticle interactions, and functionalizing the composite for specific applications. Coating or surface treatment of the plurality of magnetic nanoparticles (201) may occur, which can change the dynamics of their interaction. Various coatings might be implemented such as dextran, silica, or polymers. Also, the surface of the substrate (205) can be treated for improved structural support, such as with a surface that promotes the adherence between it and the magnetic particles. A non-continuous coating of the surface can improve adhesion without impacting the magnetic properties of the plurality of magnetic particles (201).

[0079] In addition to the previously described shapes and arrangements, the magnetic nanoparticle solid-state composite (206) and its constituent elements can be fabricated in various geometric forms, tailored to specific applications. The shapes can be selected and provide a customized output based on the geometry chosen. The magnetic nanoparticles (201) can have a variety of shapes, influencing their magnetic properties and assembly behavior:Spheres: Provide isotropic magnetic properties and easy dispersion within the matrix.Cubes: Offer enhanced magnetic anisotropy and packing density in ordered structures. Rods: Promote the formation of chain-like structures and enhance directional magnetic properties.Other Shapes: Core-shell, star-shaped, or hollow nanoparticles can be designed for particular purposes.

[0080] The solid matrix (200) can also take on different forms such as:Planar Thin Films: Exemplary for surface sensors, coatings, and microfluidic devices. Cylindrical Structures: Suitable for implantable devices, catheters, and probes.Spherical Beads or Microparticles: Useful for drug delivery, cell sorting, and magnetic separation.Complex 3D Structures: Fabricated using techniques such as 3D printing or micromachining, enabling customized shapes for specific applications.

[0081] The surface morphology of the solid matrix (200) and its compatibility with any given device enables optimization of performance and can provide improved and reliable utility.

[0082] In an embodiment, a process for modulating a magnetic particle imaging (MPI) signal using a magnetic nanoparticle solid-state composite (206) comprises subjecting a magnetic nanoparticle solid-state composite (206) to an alternating magnetic field (207), the magnetic nanoparticle solid-state composite (206) including a solid matrix (200) and a plurality of magnetic nanoparticles (201) arranged within the solid matrix (200) in a non-random configuration (202); and modulating a structural characteristic (208) of the magnetic nanoparticle solid-state composite (206) to modify a magnetic particle imaging (MPI) signal (209) emanating from the magnetic nanoparticle solid-state composite (206) in response to the alternating magnetic field (207). In an embodiment, modulating the structural characteristic(208) comprises changing a separation distance (210) between the plurality of magnetic nanoparticles (201). In an embodiment, changing the separation distance (210) comprises swelling or contracting the solid matrix (200). In an embodiment, the solid matrix (200) comprises a shape-changing or stretchable polymer. In an embodiment, the shape-changing or stretchable polymer comprises polydimethylsiloxane (PDMS). In an embodiment, the process further comprises exposing the magnetic nanoparticle solid-state composite (206) to a solvent (211) to induce swelling or contraction of the solid matrix (200). In an embodiment, the solvent (211) comprises hexanes or acetone. In an embodiment, the process further comprises detecting the modulated magnetic particle imaging (MPI) signal (209) with a magnetic particle imaging (MPI) scanner (212); and correlating the modulated magnetic particle imaging (MPI) signal(209) to an environmental condition (213). In an embodiment, the environmental condition (213) is selected from the group consisting of solvent concentration, pH, presence of abiomolecule, and temperature. In an embodiment, the non-random configuration (202) is selected from the group consisting of chain-like structures (203) and thin films (204).

[0083] The process for modulating a magnetic particle imaging (MPI) signal using a magnetic nanoparticle solid-state composite (206) overcomes the limitations of traditional MPI tracers, offering enhanced sensitivity and control over the MPI signal. Conventional MPI methods use liquid suspensions of nanoparticles, which limits their applicability in solid or semi-solid environments. The modulation enables highly sensitive detection of subtle changes in the material’s environment or properties, enabling new sensing modalities. The magnetic nanoparticle solid-state composite (206), when subjected to a magnetic field, enhances the signal to noise ratio for improved sensitivity and robustness. The process includes subjecting a magnetic nanoparticle solid-state composite (206) to an alternating magnetic field (207). Functionally, the alternating magnetic field (207) acts as an excitation source, causing the magnetic nanoparticles (201) within the solid matrix (200) to generate a detectable MPI signal (209). Interoperability happens with precise tuning and having the right materials so that signal isn’t obfuscated. Implementation involves placing the magnetic nanoparticle solid-state composite (206) within the MPI scanner (212) and activating the gradient and drive coils to generate a time-varying magnetic field (207). Different magnetic amplitudes can be selected for different purposes from remote controlled sensors to a device implanted in a human. The benefits of this action is a high contrast and enhanced spatial resolution within the MPI signals. The process further includes modulating a structural characteristic (208) of the magnetic nanoparticle solid-state composite (206) to modify a magnetic particle imaging (MPI) signal (209) emanating from the magnetic nanoparticle solid-state composite (206) in response to the alternating magnetic field (207). In this element, the dimensions of the composite are then manipulated. Implementation can be done through applying external stimuli. The environmental data that it is manipulated by gives a specific and well-known correlation to the signal’s characteristics. Variations can include different types of force to change the dimensions which include heat and electrical stimulus. The benefit of this force is the highly sensitive detection of changes and a unique microsensor created for MPI.

[0084] In an embodiment, modulating the structural characteristic (208) comprises changing the separation distance (210) between the plurality of magnetic nanoparticles (201). By modifying the spatial arrangement, and as a result, the device’s properties, there are enhanced qualities with new functionalities. This makes the system more accurate, reliable, and higher in its performance. Implementation can be achieved through swelling or contraction of the matrix material due to temperature, pressure or other external forces that are well known.

[0085] In an embodiment, the process includes changing the separation distance (210) by swelling or contracting the solid matrix (200). This expansion or reduction means the composite matrix (200) can be sensitive to its environment, such as hexanes. The solution offers easy access to the magnetic particles, which makes the magnetic readings more reliable.

[0086] In an embodiment, the solid matrix (200) comprises a shape-changing or stretchable polymer. These provide the best control of the structural characteristics because they are designed to stretch. The structural characteristics (208) can also be very precise.

[0087] In an embodiment, the shape-changing or stretchable polymer comprises polydimethylsiloxane (PDMS). PDMS is chemically inert, thermally stable, and biocompatible, making it suitable for biomedical and microfluidic applications.

[0088] In an embodiment, the process further comprises exposing the magnetic nanoparticle solid-state composite (206) to a solvent (211) to induce swelling or contraction of the solid matrix (200). Adding a known solvent (211) allows the structural characteristics (208) to be a function of its environment.

[0089] In an embodiment, the solvent (211) comprises hexanes or acetone. Hexanes swell the PDMS more than acetone, which makes the dimensions of the solid matrix (200) more responsive to hexanes, in particular.

[0090] In an embodiment, the process further comprises detecting the modulated magnetic particle imaging (MPI) signal (209) with a magnetic particle imaging (MPI) scanner (212); and correlating the modulated magnetic particle imaging (MPI) signal (209) to an environmental condition (213). MPI scanner enables an accurate and reliable reading, as its sensors will respond predictably with the solid state of the sensor as well as the magnetic field. The environmental changes are detected because the volume of the matrix changes (because of the solid reacting to the environment it is in) and the changed signals from magnetic particles give an identifiable and reliable response.

[0091] In an embodiment, the environmental condition (213) comprises solvent concentration, pH, presence of a biomolecule, temperature, or a combination thereof. By knowing what the specific environmental conditions (213), there can be calibration on the device. The selection also helps with the reliability of the device and its repeatability.

[0092] In an embodiment, the non-random configuration (202) comprises chainlike structures (203) and thin films (204). With each configuration, depending on how the system changes, there will be a tailored output. The changes in the shape and composition of the various elements in the system allow it to perform better.

[0093] In certain embodiments, the modulation process is enhanced through the application of feedback mechanisms. A sensor can be incorporated to monitor the MPI signal (209), and the output of the sensor can be utilized in a feedback loop to adjust the alternating magnetic field (207) or other parameters to maintain a desired signal level or response. This active feedback control enables enhanced stability. Also, the process can be modified with a machine learning feedback loop. A camera can be added to observe the size of the solid matrix or measure how the shape has changed based on how it is implemented. A computer or circuitry uses this information to modify either the amplitude of the changing magnetic field or apply some other external environmental conditions. In some embodiments, the magnetic particle imaging (MPI) process for measuring the device can include adding a coating to the device to improve signal to noise. The particular type of coating can be specific and depend on what signal is being measured, but some type of polymer coating or non-conductive material can ensure the device’s electrical properties do not interfere with the measurement.

[0094] In an embodiment, the process involves subjecting a magnetic nanoparticle solid-state composite (206) to an alternating magnetic field (207). This step initiates magnetic polarization and produces a read-out signal. The field is sufficient to acquire appropriate readings, and the frequency of the magnetic field (207) depends on what magnetic properties are desired, which can be known from the material being placed inside the device. To produce a reliable signal to the MRI system, the amplitude can range from 1 mT to 100 mT, specifically from 5 mT to 70 mT, and more specifically from 10 mT to 50 mT. This is done to ensure there is sufficient magnetic saturation.

[0095] The process can include modulating a structural characteristic (208) of the magnetic nanoparticle solid-state composite (206). This process is carefully designed to predictably change the MPI signal (209). Modulating refers to the manipulation of the characteristics of the composite. The method of modulation will affect how this step happens, and this can be due to one of the following: changing the distance between the particles due to environmental changes; using an external source to control the distances; or applying specific levels of magnetic fields (207). This step enhances performance and provides novel, accurate, and reliable information about the material being tested or sensed with magnetic properties.

[0096] The separation distance (210) of the magnetic nanoparticle solid-state composite (206) is modified as the individual magnetic nanoparticles (201) or the structural morphology changes. The dimensions vary with the material, but a high degree of accuracy is required for precision measurement. There are different ways to ensure that this spatial interval meets requirements. The selection of what method to apply for spatial separation depends onthe implementation. For example, the solid matrix (200) can be an elastic membrane or a thermally responsive material, resulting in unique signals being displayed. In any case, creating a separation to the plurality of magnetic nanoparticles (201) can be implemented with the correct selection of materials in an embodiment.

[0097] Modulating a magnetic particle imaging (MPI) signal using a magnetic nanoparticle solid-state composite (206) manifests as a discernible and quantifiable change in the characteristics of the MPI signal (209). This change, directly linked to alterations in the structural characteristic (208) of the composite (206), forms the foundation for diverse sensing and imaging applications. The modulation process induces changes in several key parameters of the MPI signal (209), including its amplitude, frequency spectrum, phase, and spatial distribution, each providing unique insights into the composite’s state and its interaction with the surrounding environment. The relationship has predictable qualities and provides a response to different environments. The MPI signal amplitude is strongly influenced by the effective magnetic anisotropy of the nanoparticle assembly. As the structural arrangement of the nanoparticles changes, a magnetic axis of the composite (206) may reorient, resulting in a corresponding variation in the amplitude of the MPI signal (209). For instance, if the plurality of magnetic nanoparticles (201) are arranged in a chain-like structure (203) and the chain alignment is modulated, a more aligned configuration will exhibit a stronger MPI signal (209) when the applied field is parallel to the chain axis, while a less aligned configuration will result in a weaker signal. The strength of a magnetic field allows this to be carefully measured depending on the material. This amplitude modulation can be calibrated and correlated with the applied stimulus, such as the concentration of a specific analyte or the magnitude of an external force. The change provides good spatial resolution and can be used to determine the location of the source of the reading. The sensitivity and accurate reading of the sensor can depend on the ability to be remote from the device. By using a solid-state composite, this is now feasible as opposed to other methods such as microfluidics.

[0098] The frequency spectrum of the MPI signal (209) can also be modulated by altering the structural characteristic (208) of the composite (206). As different arrangements, thicknesses or concentrations of the magnetic nanoparticles (201) are achieved, different frequencies and signal amplitudes at each frequency appear in the readings. By analyzing the harmonic content and phase relationships of the frequency spectrum, one can distinguish between different scenarios being tested. If the solid matrix (200) is made of a flexible polymer, one can more accurately control how the MPI signal is received and the external conditions of the composite itself. In embodiments where the separation distance (210) betweennanoparticles (201) is modulated, the dipolar interactions between the nanoparticles (201) and the MPI spectrum is changed. Analyzing these changes allow detection of the concentration of nanoparticles used in the device.

[0099] The spatial distribution of the MPI signal (209) within the composite (206) can be further analyzed to provide spatial information about the stimulus or field affecting the device. For instance, if a thin film (204) of magnetic nanoparticles (201) is being used and portions of the film are more excited than other parts, external readings of the substrate can be used to map temperature gradients in the surrounding environment, thereby enhancing the image with better detail. The change in heat signatures from location-to-location in turn create a gradient change in the MPI signal (209). Therefore, the shape and dimensions of the solid matrix (200) can be tailored to provide specific information. Other magnetic components and materials in the composition of the magnetic nanoparticles solid-state composites (206) can produce complex behavior and provide greater utility to the instrument’s user.

[0100] In an embodiment, a process for making a magnetic nanoparticle solid-state composite (206) comprises dispersing a plurality of magnetic nanoparticles (201) in a solution (214), the solution (214) including a solvent (211) and a matrix precursor (215); applying a magnetic field (207) to the solution (214) to induce a non-random configuration (202) of the plurality of magnetic nanoparticles (201); and solidifying the matrix precursor (215) to form a solid matrix (200), thereby fixing the non-random configuration (202) of the plurality of magnetic nanoparticles (201) within the solid matrix (200) to form the magnetic nanoparticle solid-state composite (206). In an embodiment, the matrix precursor (215) comprises a polymer precursor. In an embodiment, the polymer precursor is cured to form a polymer. In an embodiment, the solvent (211) is selected such that a viscosity of the solution (214) allows for the formation of ordered chains or bundles of the plurality of magnetic nanoparticles (201) during application of the magnetic field (207). In an embodiment, the magnetic field (207) has an amplitude equal to or greater than approximately 10 ml. In an embodiment, the process further comprises depositing the solution (214) onto a substrate (205) prior to applying the magnetic field (207). In an embodiment, the non-random configuration (202) comprises arranging the plurality of magnetic nanoparticles (201) in a chain-like structure (203). In an embodiment, the non-random configuration (202) comprises arranging the plurality of magnetic nanoparticles (201) as a thin film (204). In an embodiment, the plurality of magnetic nanoparticles (201) comprise iron oxide. In an embodiment, the process further comprises laminating the plurality of magnetic nanoparticles (201) between layers of a matrix material to form the solid matrix (200).

[0101] The process for making a magnetic nanoparticle solid-state composite (206) synthesizes the material to create a unique functionality that can be tailored for different applications. Traditional methods often rely on manual techniques or haphazard methods, which do not provide for reliable or repeatable results. Also, such methods may not have predictable features for its production. The steps used in the method described herein allow for better reliability, repeatability, and the process is well-suited for large-scale production. In an embodiment, the process comprises dispersing a plurality of magnetic nanoparticles (201) in a solution (214). The process can provide an even distribution. A solution allows for the easy manipulation and movement. To implement this, the particles are selected to be miscible in the solvent. The benefit is that a plurality of magnetic nanoparticles, once in liquid, can then be affected by external forces. The solvent can be any number of things that helps perform the step. As for types, they are numerous but depend on the composition of the matrix precursor (215). The result of this is a solution with the ability to produce better and more reliable outcomes. The solution can include a solvent (211) and a matrix precursor (215), and the application of a magnetic field (207) to the solution helps in creation of the composite. The magnetic field allows for a configuration of the nanoparticles to occur. Solidifying the matrix precursors (215) to form a solid matrix (200) can occur when the matrix locks and confines the plurality of magnetic nanoparticles (201) such that there is reduced Brownian action as the magnetic field freezes the nanoparticles in a select arrangement. Additional steps can be involved such as curing, natural evaporation, or heating.

[0102] The matrix precursor (215) comprises a polymer precursor for easy manipulation, high biocompatibility, and simple manufacturing. For example, the polymer might have one monomer that provides crosslinking. The solidification phase that occurs creates a known structure with a quantifiable measurement of the end result. To form a polymer, the polymer precursor can be cured, resulting in better strength. In cases where chains and bundles of magnetic nanoparticles are made, the viscosity is selected so that the process forms well-ordered chains. The solvent needs to be one that is commonly available, easy to work with, and affordable to create a high utility for a wide range of users. With the use of correct materials and viscosity, better and more reliable chains can be produced. By having the magnetic field be an optimized value for the solid matrix and particles, the application of this external magnetic field can range up to, or above, 10 mT. The magnetic field assists with better alignment, and therefore helps create the structure that provides signal enhancement. In another process step, the solution can be deposited onto a substrate (205) that allows for easier handling of the deposition of the solution. The type of substrate is selected such that it does not interferewith the magnetism, and instead contributes to the overall strength and support for the magnetic process. By forming a chain-like structure (203), and using the proper particles and ratios in the initial set up, there can be significantly enhanced responses and the system provides a high resolution. These can be in various environments ranging from medical products or sensors.

[0103] To better control the magnetic response, an embodiment includes the magnetic nanoparticles disposed in a thin film (204) for enhanced manipulation and sensitivities. This process step allows for the use of known structural techniques for the film. It has a wide range of applications including remote sensing and is useful for non-linear MPI and better power cycling. In certain embodiments, the plurality of magnetic nanoparticles (201) comprise iron oxide. The use of iron oxide improves the bio-compatibility of the device for medical uses. The process can involve laminating the plurality of magnetic nanoparticles (201) between layers. In this manner, the process can create a multi-layered or laminated composite that allows for better efficiency or tailored outputs based on the layering or film techniques used. This can protect various components of the composite.

[0104] The process can involve modifications or additional steps. In polymer curing, crosslinking can involve the use of UV light for a specific period. The UV light source can have a wavelength and intensity so that is does not damage the plurality of magnetic nanoparticles (201). A buffer can be added to the solution or additional treatments can be applied to the external surfaces of the solid matrix. By applying a coating, the surface roughness can increase or decrease.

[0105] In an embodiment, the process for making the composite includes dispersing a plurality of magnetic nanoparticles (201) in a solution (214). This step helps promote an even dispersion and distribution of the magnetic nanoparticles (201). It involves using a selected solvent and magnetic particles to have the correct viscosity. The steps can consider what the magnetic nanoparticle material consists of because certain materials are more easily dispersed than others. Implementation can be achieved with some type of outside force that can aid interaction among the magnetic particles and solvent. Some examples include bath sonication, vortex mixing, magnetic stirring, high-shear mixing, and ultrasonication. The temperature and external conditions (213) can be controlled to ensure a predictable and expected result to the procedure.

[0106] The process for the making the composite includes applying a magnetic field (207) to the solution (214) to organize the particles into the correct non-random configuration (202). Various devices can be used to create the magnetic field such as permanent magnets, electromagnets, superconducting magnets, and the like. The field strength anduniformity will impact this step. In general, the field can have an amplitude above a minimum value of approximately 10 mT and can range from 1 mT to 500 mT, specifically from 10 mT to 100 mT, and more specifically from 20 mT to 70 mT, to cause well-ordered chains and bundles of nanoparticles to form. As a result of the magnetic field (207), the overall characteristics are now more consistent and predictable with a quantifiable and controllable process. This leads to better reproducibility, accuracy, and reliability to the production of the article.

[0107] The process for making the composite can include transforming the matrix precursor (215) into a solid matrix (200). The transformation effectively freezes the nonrandom configurations (202) of the particles in space. After solidification, the external magnetic field (207) is no longer necessary. The new state allows the composite to be useful with a novel implementation and high predictability. This step can be implemented with several different mechanisms such as curing using a curing agent to convert the matrix precursor to a solid; evaporation of solvent; cooling, wherein some matrix precursors are efficiently solidified due to the change in temperature.

[0108] A polymer precursor can be selected as the matrix precursor (215). A wide range of monomers and prepolymers can be selected for a variety of uses that will change the solid matrix (200). Examples precursors include acrylic precursors, epoxy precursors, silicone precursors, and the like. The resulting solid matrix is mechanically robust and easy to work with.

[0109] During the solidification process step, a polymer precursor can be cured to create a more robust state. The functionality of the polymer can also impact the quality of the curing. Also, cross-linking affects the stability of the structural integrity of the solid matrix (200). The temperature for this step depends on what material is used, and certain processes for this step will be preferable for production. A variety of chemical processes can be used to solidify the matrix precursor such as thermal curing, chemical curing, or UV curing. The type of light or other type of curing can depend on the material for the polymer. For example, for an epoxy type structure, UV light can cause cross-linking to happen at a molecular level.

[0110] Selecting the solvent ensures that magnetic forces are more influential during the setting step. It creates well-ordered chains that can be relied upon for repeatability and predictability of the devices that will be used for remote sensors, medical imaging, and the like. The viscosity of the solvent can range from 0.1 mPa s to 100 mPa s, specifically from 1 mPa- s to 50 mPa- s, and more specifically from 5 mPa- s to 20 mPa- s, depending on the material and external environmental forces. This allows the magnetic interactions to better align thematerials. The forces and materials must play together correctly so there has to be testing done to ensure compatibility. The type of materials used can be any liquid solvent and is dependent on the materials used. Different options can be selected and optimized for different magnetic interactions or to produce a new and novel outcome. For example, lower or higher viscosities can be desirable based on what shape the structure takes, or if it is a thin-film or some three- dimensional structure that is desired.

[0111] The amplitude of the applied magnetic field (207) is a parameter for controlling the arrangement of the plurality of magnetic nanoparticles (201) within the solid matrix (200). An applied magnetic field can then have varying intensities or strength based on the needs of the other steps being taken. It provides a way to align the components. Different electromagnetic sources might be implemented to achieve this such as permanent magnets, electromagnets, and the like. A field strength greater than or equal to approximately 10 mT ensures sufficient magnetic force to overcome thermal agitation and induce a non-random configuration. In some other embodiments the force can range from 10 mT to 500 mT, specifically from 20 mT to 100 mT, and more specifically from 30 mT to 70 mT, depending on the materials and method used for the assembly. With this range, better chain configurations can be performed and more reliable results are achieved.

[0112] In the process for making the composite, the deposition of a solution onto a substrate (205) allows a wide variety of implementations for use for the magnetic nanoparticle solid-state composite (206). The enables a reliable scaling for a large number of devices, e.g., by printing the solution with high precision. The step can create improved mechanical stability of the matrix, improved connectivity between the matrix and surface, to reduce the chance of any unwanted motion, provide a heat sink to dissipate the localized heating from the nanoparticles, and the like. Various coating include spin-coating and chemical vapor deposition. The type of materials depends on the solution (214) and the surface properties. For example, a Si / SiC>2 surface may have some properties of high surface-tension to allow for better adherence. The implementation allows for easier handling of the deposition to avoid external or unwanted conditions that impede its usefulness. The implementation also increases reliability and creates more versatility to the uses of the device.

[0113] Creating a chain-like structure (203) by aligning the plurality of magnetic nanoparticles (201) provides the material with enhanced performance and a non-obvious improvement to MPI properties. By precisely manipulating this arrangement, one achieves a high degree of accuracy in the outputted signal. The shape provides a direct effect on the signal. The inter-connectivity also dictates some features such as wherein the structure providinginteractions between nanoparticles that are maximized in the field direction and minimized in the perpendicular direction. Implementation techniques can include magnetic field-induced self-assembly, template-assisted assembly, directed assembly, and the like. The shape can influence the magnetic direction to be used and the magnitude of the output signal. For example, the length of the chain can be from 1 to 100 particles.

[0114] The creation of a thin film (204) is based on its planar geometry, conformality, and thickness of the solid matrix (200). The magnetic field and spatial uniformity can be easier to control as compared to a 3 -dimensional shape. The film can be one or more nanoparticle layers thick. The geometry of the thin film (204) is uniform to enhance the performance of the composite. Forming the thin film can include chemical vapor deposition, thermal treatments, deposition, or another type of material.

[0115] Laminating the magnetic nanoparticles (201) in the solid matrix (200) gives the ability to increase the magnetic effect of the magnetic nanoparticles (201). This configuration also assists in the manipulation of magnetic properties by layering the materials. During the lamination process, the layers of the matrix material can be deposited with precise thicknesses ranging from 1 nm to 100 nm, specifically from 5 nm to 50 nm, and more specifically from 10 nm to 20 nm. This can be achieved by spin-coating and the various layers are built up at the end of the process. The use of lamination provides advantages to the composite. The mechanical robustness is increased as the layers help improve the matrix material integrity. The magnetic particle alignment and density can be higher than other types of distribution. By optimizing both magnetic and structural properties, enhanced performance can be created.

[0116] In an embodiment, with reference to FIG. 1, a process for making the composite includes various steps. FIG. 1 provides two methods for fabricating magnetic nanoparticle solid-state composites. The top portion depicts a method to produce enhanced MPI response that includes a three-stage process. Stage one, “Deposition of Colloidal Particles in Polystyrene Toluene Solution or Toluene,” involves preparing a mixture. A high surface tension droplet of this mixture is formed on a substrate, which can be Si / SiC>2 or dried PDMS, often secured with double-sided tape. This configuration helps the plurality of magnetic nanoparticles (201) organize themselves due to surface tension and viscosity. Stage two, “Evaporation in Magnetic Field,” subjects the droplet to a magnetic field (denoted as poH) during solvent evaporation. The field strength needs to be high enough to correctly align the magnetic nanoparticles (201). This induces the formation of chain-like structures. The drying occurs at a specific rate or over a selected time so that the particles are well-ordered. Stagethree, “Polystyrene Wrapped Structures,” shows the resulting composite, where the polystyrene solidifies around the aligned nanoparticles, creating polystyrene-wrapped structures or PDMS-encapsulated structures, with the final configuration achieving enhanced MPI response.

[0117] The bottom schematic illustrates a fabrication process, wherein “PDMS Mixed with Colloidal Particles in Hexanes” depicts a mixture preparation. The mixture is poured into a beaker. A weight boat plastic is placed inside, which acts as the substrate for the device. “PDMS Allowed to Dry in Magnetic Field” shows the alignment step, where the composite material is subjected to a magnetic field (poH) while drying to promote alignment. Finally, “PDMS with Embedded Structures” shows the final product.

[0118] The articles and processes herein are illustrated further by the following Examples, which are non-limiting.EXAMPLES

[0119] Example 1.

[0120] FIG. 2 provides a setup for fabricating aligned polystyrene nanocomposites, detailing the arrangement of components and the application of a magnetic field (207). The setup shown in FIG. 2 is designed for small-scale fabrication and testing of magnetic nanoparticle solid-state composites (206) with non-random configurations (202). Two images are shown of the experimental setup used to create aligned nanocomposites. The left image is a zoomed-in view of the setup to highlight the components. The right image is a zoomed-out image to show the experimental setup. The setup is compact and easy to operate with components that are readily available. The setup incorporates two parallel permanent magnets, generating a uniform magnetic field (207) of 66 mT in the region between the magnets. The field strength can be varied by adjusting the distance between the magnets and by selecting different magnets. Alignment can also be performed by a commercially available vibrating sample magnetometer (VSM), allowing for better tunability of applied field from mT to T ranges.. This tunability enables optimization of the magnetic field (207) strength for aligning the magnetic nanoparticles (201) during composite fabrication. A fixture comprising two blocks held together by threaded rods and screws provides the base to hold the permanent magnets. A substrate (205), such as silicon (Si), silicon dioxide (SiCh), plastic, sapphire, or other suitable material, is affixed to a block using double-sided tape to hold it in place. The block is placed between the two permanent magnets. The substrate (205) is positioned to be at the center of the magnetic field (207) to ensure uniform alignment of the magneticnanoparticles (201). One embodiment of the invention uses a 3D-printed well or a sapphire crucible attached to the block. This allows for casting the nanocomposite materials into desired shapes. In this setup, the substrate (205) acts as a mold for the solid-state nanocomposite.

[0121] The solution (214) containing the magnetic nanoparticles (201) and the polystyrene dissolved in toluene is carefully deposited onto the substrate (205) using a micropipette. In alternative embodiments, a syringe pump or other automated dispensing system is implemented for more precise control over the deposition process. The solution (214) forms a high surface tension droplet on the substrate (205), facilitating chain formation in the magnetic field. The block is then placed between the two permanent magnets. The entire setup is maintained in a stable position until the toluene evaporates, resulting in the formation of close-packed nanoparticle chains (203) within a rigid polystyrene matrix.

[0122] This method of using a setup with two permanent magnets provides uniformity with simple components that are readily available, easy to use, and at an affordable cost. The tunability of the magnetic field strength, the controlled deposition of the solution, and the use of a substrate help ensure reliable and consistent alignment of magnetic nanoparticles (201) in the nanocomposite. The setup shown is useful as a benchtop fabrication technique with minimal infrastructure or training requirements. It enables rapid experimentation with different materials and configurations for optimization of the magnetic nanoparticle solid-state composite (206). This offers advantages in terms of cost, time, and complexity compared to more sophisticated fabrication methods such as lithography or sputtering. The resulting aligned magnetic nanoparticle solid-state composites (206) exhibit superior performance in MPI applications due to the enhanced magnetic anisotropy arising from the non-random configuration of nanoparticles. Furthermore, this fabrication technique is scalable for larger- volume production by adapting the size and configuration of the magnets and substrate.

[0123] Example 2.

[0124] FIG. 3 presents a comparison of the magnetic particle imaging (MPI) signal response of aligned magnetic nanoparticles in a polystyrene nanocomposite versus the same nanoparticles dispersed in toluene, highlighting the impact of the solid matrix (200) on MPI performance. The figure shows liquid versus solid magnetic nanoparticle environments. Certain graphs compare magnetic particle spectroscopy (MPS) signal intensity versus harmonic number. Other graphs compare magnetic response (normalized harmonics or magnetic response) versus AC drive field amplitude. Some of the plots in FIG. 3 show the harmonic spectra of the MPI signal for nanoparticles (201) in polystyrene and toluene at different field amplitudes. At lower field amplitudes, the aligned polystyrene nanocompositeexhibits a stronger MPI signal compared to the nanoparticles in toluene. The signal from the nanoparticles in toluene increases with applied field amplitude and becomes similar to that of the aligned polystyrene composite at higher field amplitudes. Specifically, the aligned polystyrene nanocomposite shows a greater response at low fields (5.2 mT and 8.6 mT) but a similar response at high fields (21 mT and 27 mT). The nearly identical response at high fields demonstrates that the solid-state composite (206) with non-random configuration (202) can achieve comparable performance to nanoparticles in liquid suspension. This shows that a solid- state composite combined with methods to arrange the magnetic particles can produce high- quality MPI signals. This is important for applications where Brownian motion of nanoparticles is not feasible, particularly for medical imaging where the particles are not moving.

[0125] Certain plots in FIG. 3 provide insight into the magnetic behavior by comparing the magnetic responses versus AC drive field amplitude. The bottom left plots show data of harmonics. The response of nanoparticles (201) in toluene exhibits a Langevin-like behavior, as expected for a liquid suspension, with a non-linear response observed. On the contrary, the aligned polystyrene nanocomposite exhibits a more complex behavior, deviating from the Langevin model. This deviation arises from the non-random configuration of the nanoparticles (201) in polystyrene, leading to alterations in the magnetic anisotropy and interparticle interactions. This is useful for understanding and controlling the response of nanoparticles (201) in solid media, and the plots show how effective nanocomposites can be used to perform these types of tests.

[0126] The data in FIG. 3 demonstrates the non-obvious technical advantage of using a solid-state composite (206) with a non-random configuration (202) for MPI applications. The enhanced signal at low fields and the comparable signal at high fields, combined with the deviation from Langevin behavior, demonstrates that there is a novel functionality and use to the solid-state nanocomposite (206). The ability to tailor the magnetic response through structural control (208) opens up new possibilities for designing MPI tracers (206) and sensors with enhanced sensitivity and resolution. The use of polystyrene nanocomposites also enhances the material’s reliability and reproducibility for sensor applications. Furthermore, the solid-state nature of the composite (206) offers advantages in terms of stability, handling, and integration with other devices.

[0127] FIG. 4 presents a comparative analysis of MPI signal responses and DC magnetometry data for aligned and randomly oriented nanoparticles, emphasizing the effect of the non-random configuration (202) on the magnetic behavior of the solid-state composite (206). The figure is comprised of three plots comparing the signal from aligned versusrandomly oriented magnetic nanoparticles. The left plot shows time versus amplitude for MPI response of the two samples at 25 kHz. The middle plot shows harmonic number versus amplitude for the two samples. The right plot shows applied DC field versus normalized magnetization M / Mmax. Data shown in the left two plots is from MPI measurements. Data shown in the right plot is from DC magnetometry measurements.

[0128] The leftmost plot in FIG. 4 displays the time-domain MPI signal response for aligned and randomly oriented nanoparticles at 25 kHz and a field of 14 mT. The aligned sample exhibits a significantly larger signal amplitude compared to the randomly oriented sample. This difference in signal strength is due to the enhanced magnetic anisotropy arising from the alignment of the magnetic nanoparticles (201) in a chain-like structure (203). The data from the aligned sample is nearly an order of magnitude larger than that from the randomly oriented sample. This shows the non-obvious technical advantage of a non-random configuration (202) of magnetic nanoparticles (201) in a solid matrix (200). The randomly oriented sample has a sinusoidal signal with two peaks per a drive cycle while the aligned sample has a more complex signal with four peaks per a drive cycle.

[0129] The middle plot in FIG. 4 presents the harmonic spectra of the MPI signal for the two samples. The aligned sample again shows an enhanced MPI signal, particularly in the lower harmonic frequencies, and the signal is about an order of magnitude larger. The enhanced signal observed in the aligned sample is attributed to the increased magnetic anisotropy resulting from the non-random configuration (202) of nanoparticles (201). This enhancement in signal strength is particularly relevant for MPI applications, where a stronger signal translates to improved image quality and sensitivity. Both samples exhibit MPI response curves that monotonically decrease with increasing harmonic number.

[0130] The rightmost plot in FIG. 4 shows DC magnetometry data (M vs. H) for aligned and randomly oriented samples, providing insights into their static magnetic properties. While there are some differences observed in the hysteresis loops of the two samples, these differences are subtle and do not fully explain the significant enhancement in MPI signal observed for the aligned sample. This suggests that the dynamic magnetic behavior, rather than static magnetic properties, plays a dominant role in determining the MPI signal strength. In the plot, the randomly oriented sample has nearly zero coercivity while the aligned sample shows a larger coercivity. Also, the magnetization of the aligned sample saturates at a higher applied field.

[0131] FIG. 4 demonstrates the significant technical advantages achieved by aligning the magnetic nanoparticles (201) in a non-random configuration (202). The enhancedMPI signal observed in both time-domain and frequency-domain measurements, combined with the subtle differences in DC magnetometry data, underscores the role of magnetic anisotropy and dynamic magnetic behavior in influencing MPI signal strength. This alignment enhances sensitivity and improves image quality for MPI applications. The use of a solid matrix (200) enables the fabrication of stable and reproducible tracers (206), making this approach suitable for various sensing and imaging applications. The data presented in FIG. 4 demonstrates the novelty and non-obviousness of the magnetic nanoparticle solid-state composite with a non-random configuration (202) of magnetic nanoparticles (201). This composite (206), by leveraging the principles of magnetic anisotropy, offers a unique solution for enhancing MPI signal strength and resolution.

[0132] FIG. 5 presents a comparative analysis of MPI signal responses for magnetic nanoparticles embedded in different polymer matrices, further demonstrating the influence of the solid matrix (200) and the non-random configuration (202) on MPI performance. Three different fabrication methods are compared, each using a different matrix material. The figure is comprised of three plots comparing the signal from nanoparticles in three different polymer matrix configurations. The left plot shows time versus normalized MPI signal intensity at 25 kHz. The middle plot shows harmonic number versus normalized MPS intensity at 25 kHz. The right plot shows applied field versus normalized magnetization M / Mmax. Data shown in the left two plots is from MPI measurements. Data shown in the right plot is from DC magnetometry measurements.

[0133] The leftmost plot in FIG. 5 displays the time-domain MPI signal response for nanoparticles aligned in polystyrene, layered or laminated in PDMS, and mixed and aligned or randomly oriented in PDMS. The polystyrene and layered PDMS samples exhibit a substantially enhanced signal compared to the mixed PDMS samples, regardless of alignment. This highlights the importance of the fabrication process and the resulting non-random configuration (202) of nanoparticles in achieving enhanced MPI signal. The polystyrene and layered PDMS samples show a complex time-varying signal with four peaks per a drive cycle. The mixed PDMS samples, both aligned and random, show a sinusoidal signal with two peaks per a drive cycle. The frequency for this data is 25 Hz.

[0134] The middle plot in FIG. 5 shows the harmonic spectra of the MPI signal for the three samples. The polystyrene and layered PDMS samples again exhibit a significantly stronger signal across all harmonics compared to the mixed PDMS samples. This difference in signal strength, consistent with the time-domain data, further emphasizes the role of the solid matrix (200) and the non-random configuration (202) in enhancing the MPI signal. All samplesexhibit MPI response curves that monotonically decrease with increasing harmonic number. The signal from the polystyrene and layered PDMS are nearly identical and more than an order of magnitude larger than that from the mixed PDMS samples.

[0135] The rightmost plot in FIG. 5 presents DC magnetometry (M vs. H) data for the three samples, providing information about their static magnetic properties. The mixed and aligned sample has the lowest coercivity. The other samples have similar coercivities. The normalized magnetization of the mixed PDMS sample, both aligned and randomly oriented, saturates at a lower applied field compared to the polystyrene and layered PMDS samples.

[0136] FIG. 5 underscores the importance of selecting the appropriate materials and fabrication methods for the solid matrix (200). The choice of the materials allows for a large range of parameters and properties to be selected. There are clear advantages to the different fabrication methods with respect to how the final signals are received. This is particularly relevant for achieving desired magnetic properties and enhanced MPI signals. The polystyrene and layered PDMS approaches provide high signal, while the mixed PDMS approach results in a lower signal. This difference allows the user to tailor the resulting nanocomposite (206) based on its composition, structure, and magnetic properties to the performance of the device in its use. The data clearly demonstrates that there is a new and novel approach to using this nanocomposite (206) to enhance its magnetic properties, increasing its utility in MPI applications. Furthermore, this approach has reproducibility and better control over the manufacturing process, resulting in a better outcome.

[0137] Example 3.

[0138] FIG. 6 presents scanning electron microscopy (SEM) images of aligned polystyrene nanocomposites, providing detailed visualization of the chain-like structures (203) formed by the magnetic nanoparticles (201). The figure is comprised of seven SEM images, (a)-(g). Images (a)-(d) are at lower magnification. Images (e)-(g) are at higher magnification. Images (a), (b), (c), and (d) show aligned nanoparticles. FIG. 6(a) shows an SEM image of 21 nm magnetic nanoparticles aligned in polystyrene on a silicon dioxide substrate. The alignment direction is from left to right as shown by the arrow. The chain-like structures (203) are clearly visible and appear to be well-aligned along the direction of the applied magnetic field (207) during fabrication. The length of these chain structures is hundreds of micrometers and about 10 pm thick. FIG. 6(b) shows an SEM image of 21 nm nanoparticles aligned in polystyrene on a plastic substrate that has a carbon coating for better imaging in the SEM. The alignment direction is from left to right as shown by the arrow. The image in FIG. 6(b) is similar to that of FIG. 6(a). This demonstrates that the alignment process is reproducible on differentsubstrates (205). FIG. 6(c) shows an SEM image of slightly larger, 23 nm magnetic nanoparticles aligned in polystyrene on a silicon dioxide substrate. The alignment direction is vertical as shown by the arrow. Again, long chain structures are clearly visible. This shows that the chain formation (203) is reproducible for different sizes of magnetic nanoparticles (201). FIG. 6(d) shows an SEM image of 23 nm magnetic nanoparticles that are similar to those used in FIG. 6(c) but without the application of the magnetic field during fabrication. These SEM images show structures that have formed into clusters or clumps. This shows the importance of applying the magnetic field during fabrication in achieving a non-random configuration (202) of magnetic nanoparticles (201) within the nanocomposite.

[0139] FIG. 6(e) is a higher resolution SEM image of a portion of the sample shown in FIG. 6(a). The inset in the lower left shows an image at even higher magnification. Individual 21 nm nanoparticles (201) are clearly visible and arranged closely together in a chain-like structure (203). This image confirms the size and shape of the nanoparticles (201) and also their configuration and assembly within the polystyrene. FIG. 6(f) is a higher resolution SEM image of a portion of the sample shown in FIG. 6(c). Individual 23 nm nanoparticles (201) are visible in a chain-like structure (203). This provides a clearer image of the non-random configuration (202) at the nanoscale. FIG. 6(g) is a higher resolution SEM image of the sample shown in FIG. 6(d). Nanoparticles (201) in this image appear to be clustered together, forming a film-like structure.

[0140] The SEM images in FIG. 6 visually confirm the successful fabrication of magnetic nanoparticle solid-state composites (206) with aligned chain-like structures (203). The images provide detailed information about the size, shape, and arrangement of individual nanoparticles and demonstrate the importance of magnetic field alignment during fabrication to achieve a non-random configuration (202). The high-resolution images further reveal the close packing and order within the chain structures, highlighting the potential for enhanced magnetic properties. These techniques and results are important for improving magnetic particle imaging, drug delivery, and to create new types of sensor applications. There is greater stability, reliability, and sensitivity of the material, giving it novel uses not found with prior art.

[0141] FIG. 7 further explores the magnetic properties and signal responses of various nanocomposites, providing a comprehensive comparison of different nanoparticle arrangements and their impact on MPI signal intensity. The figure is comprised of three plots, (h)-(j). Plot (h) compares the MPI signals from different nanocomposite samples. Plot (i) shows MPI signal at different field orientations. Plot (j) demonstrates MPFs sensitivity by showingdetection of low quantities of magnetic nanoparticles. FIG. 7(h) shows normalized MPI signal intensities versus harmonic number for various samples, including aligned and non-aligned polystyrene-wrapped samples, a PDMS-mixed sample, and different nanoparticle sizes. The 21 nm and 23 nm aligned polystyrene samples exhibit a significantly enhanced MPI signal compared to the non-aligned and mixed PDMS samples. The signal from the aligned samples is nearly two orders of magnitude larger than the mixed sample and approximately one order of magnitude larger than the non-aligned sample. This data reinforces the findings from FIGS. 3 and 4, demonstrating that aligning nanoparticles in a non-random configuration (202), such as chains (203), within a suitable solid matrix (200), such as polystyrene, leads to a substantial enhancement in MPI signal strength. This enhancement translates to improved image quality and increased sensitivity for MPI applications. Furthermore, the data suggests that the alignment process is robust across different nanoparticle sizes (21 nm and 23 nm).

[0142] FIG. 7(i) shows normalized MPI signal amplitude versus harmonic number for the 23 nm aligned and randomly oriented polystyrene samples at different field orientations. The data in FIG. 7(i) shows the effect of changing the magnetic field direction relative to the alignment of the sample. When the field is applied parallel to the alignment direction of the polystyrene sample, the signal is strongest. Conversely, minimal MPI signal is detected from the randomly oriented sample regardless of the field direction. This anisotropy in signal response arises from the non-random configuration (202) of the nanoparticles (201) within the nanocomposite. The aligned nanoparticles, forming chain-like structures (203), exhibit a directional magnetic anisotropy, leading to an enhanced MPI signal when the applied field is parallel to the chain axis. This directional sensitivity can be exploited in applications where directional magnetic sensing or imaging is needed, offering a unique advantage over randomly oriented samples.

[0143] FIG. 7(j) shows the same normalized MPI signal amplitude versus harmonic number as in FIG. 7(i) for aligned 21 nm nanoparticles at low quantities and compares them to the background signal. Even at low quantities of nanoparticles, the composite still produces a signal larger than the background signal. The signal-to-noise ratio (SNR) for the sample is around 20. This high SNR, even with minimal amounts of magnetic material, demonstrates the exceptional sensitivity of the MPI technique when used with the novel magnetic nanoparticle solid-state composite (206) and highlights its potential for detecting small quantities or low concentrations of magnetic tracers in various settings.

[0144] The results presented in FIG. 7 have several technical advantages for enhancing the performance of MPI. The significant increase in MPI signal observed for alignedsamples, combined with directional sensitivity and high SNR at low particle concentrations, make the magnetic nanoparticle solid-state composite (206) attractive for various applications, especially in biological systems where using very small quantities of a material is preferable. The use of a solid matrix such as polystyrene offers further advantages in terms of material stability, reproducibility, and ease of integration with other devices, which leads to improved functionality and more reliable performance in MPI systems. It also enables a new solution to material and thermal sensing.

[0145] Example 4.

[0146] FIG. 8 explores modulating MPI signals by utilizing the swelling properties of the solid matrix (200), specifically focusing on polydimethylsiloxane (PDMS) layered nanocomposites. Panel (a) shows swelling to a swollen state via exposure to a solvent in the dried state. Plots (b) and (c) provide experimental data illustrating changes in MPI signal due to swelling using different solvents. FIG. 8(a) illustrates the mechanism behind signal modulation through swelling of the solid matrix (200). In the dried state, the magnetic nanoparticles (201) are closely packed, resulting in a stronger MPI signal due to enhanced interparticle interactions. Upon swelling, the matrix expands, increasing the separation distance (210) between the nanoparticles (201). This decrease in particle density weakens the interparticle interactions, which can result in a measurable decrease in MPI signal strength. Thus, by modulating the degree of swelling, one can effectively control the MPI signal, enabling the development of sensors that respond to environmental stimuli that induce swelling or contraction of the matrix. FIG. 8(b) presents experimental data demonstrating the change in the time-domain MPI signal of polystyrene and PDMS nanocomposites. The polystyrene sample shows a minimal change in signal between the dried and swollen states, indicating that the polystyrene matrix does not swell significantly. In contrast, the PDMS sample exhibits a substantial decrease in signal amplitude upon swelling, which is consistent with FIG. 8(a). This difference in behavior highlights selecting a matrix material (200) with appropriate swelling properties to enable signal modulation. The frequency used for this measurement is 25 kHz, and the field is 28 mT. FIG. 8(c) further explores the signal modulation capabilities of PDMS nanocomposites by exposing them to different solvents (211) and measuring the resulting signal change between the dried and swollen states. Hexanes, a good solvent for PDMS, induce a larger degree of swelling and a correspondingly greater change in MPI signal compared to acetone, which swells PDMS to a lesser extent. This demonstrates the potential for using the magnetic nanoparticle solid-state composite (206) as a sensor for detecting specific solvents or other analytes that induce swelling of the matrix. Swelling and drying cycles between statesalso show repeatable behavior of the system. This novel sensing modality has not been previously demonstrated with prior art and has high performance, reliability, and utility. Also, it may lead to new types of diagnostic and therapeutic treatments.

[0147] FIG. 9 shows experimental evidence of the MPI signal modulation achieved by swelling a PDMS-based magnetic nanoparticle solid-state composite (206) using different solvents (211), showcasing the sensor’s selectivity and demonstrating its potential for detecting specific analytes. The data shown in FIG. 9 complements the time-domain measurements presented in FIG. 8 by providing frequency-domain analysis of the MPI signal (209). Specifically, FIG. 9 shows harmonic spectra of the nanocomposite during swelling / drying cycles. Two plots are shown, (d) and (e), that show measured amplitude as a function of harmonic number. Plot (d) shows data for the nanocomposite subjected to swelling and drying cycles using hexanes. Plot (e) shows data for the nanocomposite subjected to swelling and drying cycles using acetone. FIG. 9(d) presents the harmonic spectra of the MPI signal (209) for the PDMS nanocomposite during three cycles of swelling with hexanes and subsequent drying. The initial dry state, before the introduction of any solvent (211), serves as a baseline for comparison. Upon exposure to hexanes, the solid matrix (200) swells, increasing the separation distance (210) between the magnetic nanoparticles (201). This structural change (208) results in a decrease in MPI signal amplitude across a broad range of harmonics. After the hexanes evaporate, the matrix returns to its original, non-swollen, state, and the MPI signal amplitude recovers to its pre-swelling value. The signal recovery upon drying of the solvent (211) is important for reuse. This cycle of signal decrease upon swelling and recovery upon drying is consistently observed over three cycles, demonstrating the reproducibility and stability of the modulation process. This reversible and tunable signal modulation forms the basis for the sensing functionality of the nanocomposite. The peak drive field for this measurement is 28 mT and the drive frequency is 25 kHz. FIG. 9(e) shows harmonic spectra similar to FIG. 9(d), but using acetone as the solvent (211). Acetone, known to induce less swelling in PDMS compared to hexanes, results in a smaller decrease in the MPI signal amplitude upon swelling. This difference in signal modulation highlights the nanocomposite’s selectivity to different solvents, allowing for differentiation between various analytes based on their specific interactions with the polymer matrix. The reversible nature of the signal change is also observed with acetone, further confirming the stability and robustness of the modulation process.

[0148] The data presented in FIG. 9 demonstrates the technical advantages of using the magnetic nanoparticle solid-state composite (206) as an environmentally sensitive sensor.The observed signal modulation, its reversibility, and dependence on the specific solvent (211) highlight the unique capabilities of this sensing modality. The ability to tailor the response by selecting an appropriate matrix material (200) and solvent, combined with the non-random configuration (202) of magnetic nanoparticles (201), provides a high degree of control over the signal (209). This results in improved sensitivity and accuracy. It allows for the detection of small changes in environmental conditions. This is a novel approach not easily derived from existing knowledge, with applications in diverse fields such as environmental monitoring, material science, and biomedicine. The repeatability of the signal modulation through multiple swelling and drying cycles further enhances the utility of the nanocomposite (206) as a reusable sensor, providing a cost-effective and sustainable solution for long-term monitoring applications.

[0149] Example 5.

[0150] FIG. 10 presents transmission electron microscopy (TEM) images of nanocomposites fabricated using different methods, providing insights into the physical structure and arrangement of magnetic nanoparticles within the solid matrix. Two distinct nanocomposites are examined: FesCh nanoparticles (201) in PDMS and FesCh nanoparticles (201) in polystyrene. Images (a)-(d) show nanoparticles in PDMS, fabricated by mixing and aligning. Images (e)-(h) show nanoparticles in polystyrene, deposited on a plastic weighing boat. FIG. 10(a) is a TEM image showing iron oxide (FesCh) nanoparticles (201) in a PDMS matrix. This sample was fabricated by mixing the nanoparticles (201) into the PDMS precursor solution and then applying a magnetic field during curing. The darker regions correspond to the FesCh nanoparticles (201), and the lighter region is the PDMS matrix (200). The nanoparticles (201) appear to be clustered together. FIG. 10(b) shows a higher magnification TEM image of the sample from FIG. 10(a). At this magnification, no crystallographic texture is visible in the arrangement of the nanoparticles (201). FIG. 10(c) is a higher magnification TEM image of another region of the sample in FIG. 10(a). The inset diffraction pattern confirms the presence of FesCh.

[0151] FIG. 10(d) presents a selected area electron diffraction pattern from the sample shown in FIG. 10(a). The diffraction spots are arranged with six-fold symmetry, wherein Zone Axis:

[0110] and the spots are indexed. The spot pattern confirms the crystalline nature of the FesCh nanoparticles and provides information about the crystallographic orientation of the nanoparticles within the PDMS matrix (200). The diffraction pattern indicates some degree of crystallographic texturing, suggesting preferential alignment of certaincrystallographic planes along the magnetic field during fabrication. This texturing can contribute to the enhanced magnetic response observed in the mixed PDMS sample.

[0152] FIG. 10(e) shows a low magnification TEM image of FesCh nanoparticles (201) in polystyrene, deposited on a plastic weighing boat substrate. This sample was fabricated by first aligning the nanoparticles in polystyrene and then depositing the solution onto the substrate. The darker regions are the nanoparticles (201), and the lighter region is polystyrene (200). At this magnification, the aligned structure is visible. FIG. 10(f) shows a higher magnification TEM image of a portion of the sample in FIG. 10(e). The nanoparticles are arranged closely together, forming an ordered structure in the polystyrene matrix. FIG. 10(g) is a higher magnification TEM image of another region of the polystyrene nanocomposite sample in FIG. 10(e). Individual nanoparticles (201) are clearly visible. The inset diffraction pattern confirms the presence of FesCh. FIG. 10(h) shows an electron diffraction pattern from the polystyrene sample, which again confirms the crystalline structure of the FesCh nanoparticles. The ring pattern, unlike the spot pattern in FIG. 10(d), indicates a more random orientation of the nanoparticles (201) within the polystyrene matrix (200) compared to the mixed PDMS sample.

[0153] Example 6.

[0154] FIG. 11 presents a TEM image of a PDMS nanocomposite with aligned, layered magnetic nanoparticles. The image shows a thin section of the nanocomposite, highlighting the layered structure and the arrangement of magnetic nanoparticles within the PDMS matrix. This method involves laminating the magnetic nanoparticles between PDMS layers. Portions of the TEM grid used to support the sample are also visible. The darker regions in the image correspond to the magnetic nanoparticles (201), which appear to be arranged in layers or clusters within the lighter PDMS matrix (200). The layered structure is clearly visible, with distinct bands of nanoparticles separated by the PDMS material. This layered configuration, achieved by laminating the nanoparticles (201) between two layers of PDMS, results in a non-random configuration (202) that contributes to enhanced magnetic anisotropy. This method provides for a high degree of utility, allowing the user to create nanocomposites without needing to be well versed in sophisticated techniques, thereby simplifying the process and producing useful results. The physical interconnectivity between the nanoparticles (201) and the PDMS layers and using known materials for the magnetic nanoparticles (201) and the polymer allow for an enhanced and predictable MPI signal output based on the non-random configuration of the nanoparticles (201). This allows for higher spatial resolution of the output signals. Furthermore, the process of making the layers is relatively simple to implement, withreadily available tools and materials, enabling researchers to easily create nanocomposites with enhanced magnetic properties. The scale bar in the image indicates a length of 2 pm, providing a sense of scale for the structures observed. The arrangement of the magnetic nanoparticles(201) shown is different from the chains (203) observed in polystyrene samples, highlighting the influence of the matrix material (200) on the resultant structure and the physical dimensional characteristics achievable. The layered structure in PDMS, achieved through the lamination process, yields comparable MPI signal enhancement to the chain-like structures in polystyrene, demonstrating the feasibility of alternative fabrication methods and allowing for the adaptation of the process to the unique characteristics of different matrix materials (200). The use of standard techniques ensures reliability and repeatability of the results.

[0155] FIG. 12 presents magnified TEM views of the PDMS nanocomposite shown in FIG. 11, offering a closer look at the layered structure and the arrangement of magnetic nanoparticles (201) within the PDMS matrix (200). The figure shows three higher magnification TEM images of the layered PDMS nanocomposite shown in FIG. 11. The images reveal details about the nanoparticle arrangement and morphology within the layered structure. The darker regions correspond to the magnetic nanoparticles, and the lighter regions represent the PDMS matrix. The nanoparticles (201) appear to be closely packed within the layers, but with some variations in interparticle spacing. This close packing and the layered configuration(202) contribute to the enhanced magnetic properties observed in these nanocomposites. The physical structure is also more clearly shown. The scale bars in the images vary from 200 nm to 2 mm. The magnification is useful to understand what is occurring at the nano-scale. The higher magnification in FIG. 12 allows for a more detailed analysis of the nanoparticle arrangement (202) within the PDMS matrix (200). The nanoparticles appear to form clusters or aggregates within each layer, with some degree of ordering or alignment within these clusters. This arrangement, different from the chain-like structures (203) observed in polystyrene samples, highlights the role of the matrix material (200) in influencing nanoparticle organization. The layered structure (formed by the lamination process) in PDMS offers a distinct morphology compared to the chain structures (formed by alignment in a magnetic field) in polystyrene. Despite these structural differences, both nanocomposites exhibit enhanced MPI signal, demonstrating the feasibility of achieving comparable performance with different fabrication methods. This non-obvious approach is enabled by the careful selection of materials, their relative concentrations, and precise control over processing parameters during fabrication. By varying the fabrication technique to use lamination rather than alignment in a magnetic field, an alternative embodiment of the nanocomposite exhibits high performancewith better stability and processability. The use of different sizes of the plurality of magnetic nanoparticles (201) and the non-magnetic elements will have a measurable effect on the signal readings.

[0156] FIG. 13 provides further magnified TEM views of the PDMS nanocomposite, similar to FIG. 12. This closer examination reveals additional details about the nanoparticle arrangement and morphology. Two images of the layered PDMS nanocomposite are at higher magnification. The images highlight the arrangement and morphology of the magnetic nanoparticles. The lamination technique used to fabricate the PDMS nanocomposite yields a layered structure with closely packed nanoparticles, similar to the polystyrene nanocomposites. This structural similarity is consistent with the comparable MPI signal enhancement observed for both types of nanocomposites. FIG. 13 reveals details about the arrangement (202) and morphology of the nanoparticles (201) within each layer. The nanoparticles (201) are not uniformly distributed within the layers but appear to form clusters or aggregates, with some variations in interparticle spacing (210). This clustering behavior and variation in interparticle spacing are similar to observations made in polystyrene nanocomposites, suggesting a degree of commonality in the nanoparticle organization despite differences in matrix material (200) and fabrication method. The morphology of the nanoparticles (201) in the PDMS matrix (200) appears to be predominantly spherical, similar to observations made in other samples. The nanoparticles (201) are closely packed within each layer, indicating a high concentration of magnetic material within the composite. This dense packing, combined with the layered structure, contributes to the enhanced magnetic anisotropy. The varying degrees of darkness within the nanoparticle regions suggest variations in thickness or density of the nanoparticle clusters within the PDMS matrix. The physical structure and connectivity allows the layers to form chains and improve the signal strength. It gives a reliable response, and the predictable nature has significant utility.

[0157] Example 7.

[0158] FIG. 14 shows an optical image of the layered PDMS nanocomposite providing a macroscopic view of the sample and highlighting the layered structure formed by the magnetic nanoparticles. The darker lines or bands within the transparent PDMS matrix correspond to the layers of magnetic nanoparticles, which are visibly distinct due to their higher refractive index. The width or thickness of these nanoparticle layers appears to be uniform across the sample, suggesting a controlled and reproducible fabrication process. The scale and resolution of the optical image provide a macroscopic perspective on the layered structure, complementing the nanoscale details revealed by the TEM images in previous figures. Thetransparency of the PDMS matrix (200) allows for easy observation of the embedded nanoparticle layers (201). The close packing of the nanoparticles in the layers (202) explains the light scattering. This structure results in enhanced magnetic anisotropy for achieving signal modulation in the nanocomposite. Furthermore, the uniformity and consistency of the layered structure across the sample demonstrate the robustness of the lamination technique in producing large-scale nanocomposites with tailored magnetic properties.

[0159] FIG. 15 provides both optical and SEM images of the layered PDMS nanocomposite, offering complementary perspectives on the material’s structure and the arrangement of magnetic nanoparticles. The figure includes two images, an optical microscopy image on the left, and a scanning electron microscopy image on the right, of the same sample. The optical image shows a cross-section of the nanocomposite, revealing the distinct layers formed by the magnetic nanoparticles within the PDMS matrix. The combination of these two imaging modalities helps bridge the gap between macroscopic and microscopic structural details. The scale bar in the SEM image shows 500 pm. The sample is coated with 15 nm of gold / palladium (Au / Pd) for better imaging. The optical image on the left side of FIG. 15 provides a macroscopic view of the layered PDMS nanocomposite. The alternating dark and light bands correspond to the layers of magnetic nanoparticles (201) and the PDMS matrix (200), respectively. The layers appear to be uniform in thickness and run parallel to each other across the entire width of the sample. The arrows point to the layered structure that is visible. The visibility of these layers in the optical image is due to differences in refractive index between the nanoparticles and the PDMS matrix. The SEM image on the right side of FIG. 15 is a view of the cross-section of the nanocomposite. The layered structure is again evident, with the brighter regions corresponding to the layers of magnetic nanoparticles and the darker regions representing the PDMS matrix. The arrows highlight the areas of closely packed nanoparticles in the layered structure. The higher resolution of the SEM image reveals the morphology and arrangement of the individual nanoparticles within the layers. The nanoparticles appear to form close-packed clusters, with variations in their interparticle spacing. This arrangement, influenced by the PDMS matrix and the fabrication process, contributes to the magnetic properties of the nanocomposite. The combined optical and SEM images in FIG. 15 provide a comprehensive understanding of the structural characteristics of the layered PDMS nanocomposite. The optical image offers a macroscopic perspective of the layered structure, confirming its uniformity and extent across the sample. The SEM image, by providing a closer look at the nanoparticle arrangement, surface morphology, and their connectivity, enhances our understanding of the nanocomposite’s magnetic behavior. Thismulti-scale imaging approach is crucial for characterizing the material’s structure and correlating it with its performance in MPI applications. The images demonstrate the non- obvious advantage of using a layered structure in a solid matrix (200) to achieve enhanced MPI signal, a configuration not typically found in conventional MPI tracers. The technique shown is easy to perform and has high reproducibility and reliability. The choice of materials also increases its utility for a wider range of users and has a practical application to material science.

[0160] Example. 8

[0161] The left panel of FIG. 16 shows an MPS response versus drive field amplitude for chaining particles in solution (circles) and in solid nanocomposite (squares). The top right panel shows data for MPS response versus harmonic number at low fields, wherein the nanocomposite sample exhibits superior response at all harmonics. The bottom right panel shows data for MPS response versus harmonic number at high magnetic fields, wherein the fully chained nanoparticles in solution and in nanocomposite exhibit almost identical response at all harmonics.

[0162] While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.

[0163] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like.

[0164] As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.

[0165] All references are incorporated herein by reference.

[0166] The use of the terms “a,” “an,” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such.

[0167] The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances. / / PARTS LIST / / solid matrix 200 plurality of magnetic nanoparticles 201 non-random configuration 202 chain-like structure 203 thin film 204 substrate 205 magnetic nanoparticle solid-state composite 206 alternating magnetic field 207 structural characteristic 208 magnetic particle imaging (MPI) signal 209 separation distance 210 solvent 211 magnetic particle imaging (MPI) scanner 212 environmental condition 213 solution 214 matrix precursor 215

Claims

What is claimed is:

1. A magnetic nanoparticle solid-state composite comprising: a solid matrix (200); and a plurality of magnetic nanoparticles (201) arranged within the solid matrix (200) in a non-random configuration (202), wherein the non-random configuration (202) of the plurality of magnetic nanoparticles (201) enhances a magnetic property of the composite.

2. The magnetic nanoparticle solid-state composite of claim 1, wherein the solid matrix (200) comprises a polymer.

3. The magnetic nanoparticle solid-state composite of claim 2, wherein the polymer comprises polydimethylsiloxane (PDMS) or polystyrene.

4. The magnetic nanoparticle solid-state composite of claim 1, wherein the plurality of magnetic nanoparticles (201) are arranged in a chain-like structure (203) within the solid matrix(200).

5. The magnetic nanoparticle solid-state composite of claim 1, wherein the plurality of magnetic nanoparticles (201) are arranged as a thin film (204) within the solid matrix (200).

6. The magnetic nanoparticle solid-state composite of claim 1, wherein the plurality of magnetic nanoparticles (201) comprise iron oxide.

7. The magnetic nanoparticle solid-state composite of claim 6, wherein the iron oxide comprises magnetite or maghemite.

8. The magnetic nanoparticle solid-state composite of claim 1, further comprising a substrate (205), wherein the solid matrix (200) with the plurality of magnetic nanoparticles(201) is disposed on the substrate (205).

9. The magnetic nanoparticle solid-state composite of claim 8, wherein the substrate (205) comprises a non-magnetic material.

10. The magnetic nanoparticle solid-state composite of claim 1, wherein the nonrandom configuration (202) is selected to modulate a magnetic particle imaging (MPI) signal of the composite.

11. A process for modulating a magnetic particle imaging (MPI) signal using a magnetic nanoparticle solid-state composite, the process comprising: subjecting a magnetic nanoparticle solid-state composite (206) to an alternating magnetic field (207), the magnetic nanoparticle solid-state composite (206) including: a solid matrix (200); and a plurality of magnetic nanoparticles (201) arranged within the solid matrix (200) in a non-random configuration (202); and modulating a structural characteristic (208) of the magnetic nanoparticle solid-state composite (206) to modify a magnetic particle imaging (MPI) signal (209) emanating from the magnetic nanoparticle solid-state composite (206) in response to the alternating magnetic field (207).

12. The process of claim 11, wherein modulating the structural characteristic (208) comprises changing a separation distance (210) between the plurality of magnetic nanoparticles (201).

13. The process of claim 12, wherein changing the separation distance (210) comprises swelling or contracting the solid matrix (200).

14. The process of claim 13, wherein the solid matrix (200) comprises a shape-changing or stretchable polymer.

15. The process of claim 14, wherein the shape-changing or stretchable polymer comprises polydimethylsiloxane (PDMS).

16. The process of claim 13, further comprising exposing the magnetic nanoparticle solid-state composite (206) to a solvent (211) to induce swelling or contraction of the solid matrix (200).

17. The process of claim 16, wherein the solvent (211) comprises hexanes or acetone.

18. The process of claim 11, further comprising: detecting the modulated magnetic particle imaging (MPI) signal (209) with a magnetic particle imaging (MPI) scanner (212); and correlating the modulated magnetic particle imaging (MPI) signal (209) to an environmental condition (213).

19. The process of claim 18, wherein the environmental condition (213) comprises solvent concentration, pH, presence of a biomolecule, and temperature.

20. The process of claim 11, wherein the non-random configuration (202) comprises chain-like structures (203) and thin films (204).

21. A process for making a magnetic nanoparticle solid-state composite (206), the process comprising: dispersing a plurality of magnetic nanoparticles (201) in a solution (214), the solution (214) including a solvent (211) and a matrix precursor (215); applying a magnetic field (207) to the solution (214) to induce a non-random configuration (202) of the plurality of magnetic nanoparticles (201); and solidifying the matrix precursor (215) to form a solid matrix (200), thereby fixing the non-random configuration (202) of the plurality of magnetic nanoparticles (201) within the solid matrix (200) to form the magnetic nanoparticle solid-state composite (206).

22. The process of claim 21, wherein the matrix precursor (215) comprises a polymer precursor.

23. The process of claim 22, wherein the polymer precursor is cured to form a polymer.

24. The process of claim 22, wherein the solvent (211) is selected such that a viscosity of the solution (214) allows for the formation of ordered chains or bundles of the plurality of magnetic nanoparticles (201) during application of the magnetic field (207).

25. The process of claim 21, wherein the magnetic field (207) has an amplitude equal to or greater than approximately 10 mT.

26. The process of claim 21, further comprising depositing the solution (214) onto a substrate (205) prior to applying the magnetic field (207).

27. The process of claim 21, wherein the non-random configuration (202) comprises arranging the plurality of magnetic nanoparticles (201) in a chain-like structure (203).

28. The process of claim 21, wherein the non-random configuration (202) comprises arranging the plurality of magnetic nanoparticles (201) as a thin film (204).

29. The process of claim 21, wherein the plurality of magnetic nanoparticles (201) comprise iron oxide.

30. The process of claim 21, further comprising laminating the plurality of magnetic nanoparticles (201) between layers of a matrix material to form the solid matrix (200).

Images