Method for measuring a magnetic property of magnetic nanoparticles

Abstract

Method for measuring a magnetic property of magnetic nanoparticles, comprising the following steps: (a) Passing a liquid (29) containing the nanoparticles (31) through an alternating magnetic field (B), (b) Measuring a magnetization parameter that describes a dependence of a magnetization of the nanoparticles (31) on the alternating field (B), and (c) Guiding the liquid (29) through a coiled capillary (30) through the alternating magnetic field (B) characterized by the step: (d) before passing the liquid (29) through the coiled capillary (30) fractionating the magnetic nanoparticles (31) in the liquid (29) so that a fractionated liquid stream is produced, (e) wherein measuring the magnetization parameter is a time-resolved measurement of the magnetization parameter on the fractionated fluid flow.

Description

[0001] The invention relates to a method for measuring a magnetic property of magnetic nanoparticles, comprising the features of claim 1.

[0002] According to a second aspect, the invention relates to a nanomagnetic particle analysis device for determining a magnetic property of magnetic nanoparticles with the features of claim 5.

[0003] Nanoscale particles are used, for example, in medicine and pharmaceuticals. They usually consist of a magnetic core with a magnetic moment that has a preferred direction and a shell. Depending on the material and the size of the nanoparticle, the magnetic moment is either stationary or can change direction due to thermal fluctuations. The shell serves to stabilize the magnetic properties of the core material. For example, the shell protects against oxidation and / or agglomeration of the nanoparticles.

[0004] Depending on the desired functionality, the nanoparticles must exhibit specific magnetic properties. Furthermore, there are requirements regarding their size, shape, chemical composition, and / or crystallographic structure. Since both physiological and physical nanoparticle properties show a significant dependence on the size of the nanoparticles, the precise determination of the size distribution and the distribution of the magnetic properties of the nanoparticles is an important metrological task.

[0005] Dynamic light scattering (DLS) is a well-established method for analyzing nanoparticles, as it provides a representative picture of the sample as an integrated measurement technique. Furthermore, if the nanoparticles consist of only a single domain, their magnetic moment can be deduced from their hydrodynamic properties, taking into account the hull thickness and assuming a spherical geometry.

[0006] A detection method is known from US patent 2009 / 0085557A1 in which a liquid stream is passed through a capillary and exposed to an alternating magnetic field. The Brownian relaxation time is then measured using the dynamic magnetic susceptibility and the magnetic relaxation. Such a method is only partially suitable for the complete characterization of the magnetic particles.

[0007] A method for measuring agglutination parameters is known from US patent 2010 / 0033158A1, in which the magnetic particles are processed in an assay. A disadvantage of this method is the comparatively long measurement time.

[0008] US Patent 2010 / 0243574A1 describes a fractionation device for fractionating fluids with magnetic particles. Discrete portions of individual fractions obtained in this way can then be analyzed. However, particularly high measurement accuracies cannot be achieved with this device.

[0009] The invention is based on the objective of improving the measurement of magnetic properties of magnetic nanoparticles.

[0010] The invention solves the problem by means of a method having the features of claim 1.

[0011] The invention also solves the problem by means of a nanomagnetic particle analysis device with the features of claim 5.

[0012] An advantage of the invention is that a sample containing magnetic nanoparticles can be characterized with high accuracy. First, a fractionated liquid stream is generated, which can be achieved by field-flow fractionation. In this process, the nanoparticles are fractionated based on a specific property, such as their size. The resulting liquid stream is then passed through the coiled capillary. Due to the small inner diameter of the capillary, the liquid flow is laminar, without turbulence. This ensures that the magnetization parameter is always determined only by the particles belonging to the fraction currently flowing through the capillary. Measurement errors caused by sedimented magnetic particles or particles trapped in a dead zone can be largely eliminated.The method according to the invention thus enables a time-saving and precise characterization of dispersed magnetic nanoparticles.

[0013] Since it is known at any given time which fraction is currently flowing through the capillary, the magnetic property of this fraction can be correlated with the property according to which the fractionation was performed. In other words, the invention allows the magnetic particles to be characterized based on two independent parameters simultaneously.

[0014] Another advantage is that the use of a coiled capillary ensures that a sufficiently large quantity of magnetic particles is always present in the sample holder, so that a favorable signal-to-noise ratio can be achieved.

[0015] Another advantage is that the measurement can be performed quickly. Measurement times of less than one minute, and in particular less than 10 seconds, are achievable for characterizing a sample.

[0016] In the context of this description, the liquid containing the nanoparticles is understood to be, in particular, an elution. The elution is preferably designed such that the nanoparticles do not agglomerate, or only to a negligible extent, during the execution of the process according to the invention.

[0017] Magnetic nanoparticles are understood to be, in particular, ferromagnetic and / or superparamagnetic nanoparticles.

[0018] The term magnetization parameter refers in particular to a number, a quantity, a vector of numbers and / or quantities, or any other set of individual parameters by which the magnetic properties of nanoparticles can be characterized. For example, the magnetization parameter is the spectrum of the signal recorded by a receiving coil or magnetic field sensors. The receiving coil detects the magnetic field in the immediate vicinity of the nanoparticles in the sample holder under the influence of an alternating magnetic field. In addition to the first harmonic, which corresponds to the excitation frequency (i.e., the frequency of the alternating magnetic field), the spectrum contains prominent odd harmonics from which the magnetization of the nanoparticles can be determined.

[0019] A coiled capillary is understood to be, in particular, a liquid channel whose clear cross-section is at most 4 mm, and more specifically, at most 2 mm. Preferably, the coiled capillary is spirally wound. Such a capillary can be manufactured particularly easily and reliably.

[0020] Nanoparticles are understood to be, in particular, particles whose equivalent diameter is less than 1000 nanometers, less than 500 nanometers, and especially not more than 300 nanometers. Preferably, the equivalent diameter is greater than 1 nanometer, and particularly greater than 10 nanometers. It should be noted that a magnetic nanoparticle always contains magnetic material, but need not consist entirely of it.

[0021] The capillary is preferably made of quartz glass or plastic. A plastic tube has the advantage of being disposable after use, thus ensuring that no contamination between two samples is possible. The use of a glass capillary also offers the advantage of multiple uses due to its resistance to chemical cleaners such as hydrochloric acid.

[0022] Fractionation is understood to mean, in particular, that a liquid stream is produced from the sample containing nanoparticles, wherein one, and in particular exactly one, property of the nanoparticles changes monotonically, and in particular strictly monotonically, over time. If, for example, fractionation is performed according to the equivalent diameter, which is a preferred embodiment, the equivalent diameter at a predetermined location where the fractionated liquid stream flows past decreases or increases strictly monotonically over time.

[0023] Preferably, the fractionation process is continuous, meaning that the individual fractions blend smoothly into one another. For example, fractionation can be carried out using field-flow fractionation, particularly asymmetric-flow field-flow fractionation. The property used for fractionation can be, for example, size, shape, anisotropy, density, and / or electrical conductivity.

[0024] According to a preferred embodiment, the liquid is guided through the capillary at a flow rate selected to ensure laminar flow within the capillary. This has the advantage of avoiding sedimentation effects and separation processes that could alter the properties of the fractionated liquid stream. Furthermore, a coiled capillary eliminates the need for additional connections between the supply line and the liquid sample holder in the measurement area, since the supply line itself also serves as the liquid sample holder. One of the main causes of band broadening, and thus a loss of temporal resolution, is the connections between tubing and flow cells, as well as the flow cells themselves, because their geometry (sharp-edged transitions) often leads to mixing of the liquid stream.

[0025] According to a preferred embodiment, the liquid is guided through the capillary in such a way that the Reynolds number, calculated as the quotient of the product of the density of the liquid with the nanoparticles, a flow rate, a capillary diameter (as the numerator), and the dynamic viscosity of the liquid with the nanoparticles, is at most 3000. This condition must always be met if one or more of the aforementioned parameters change over time.

[0026] According to a preferred embodiment, the method comprises the step of time-resolved measurement of the size distribution of the nanoparticles in the fractionated liquid stream. The size whose distribution is measured is understood to be, in particular, the equivalent diameter in the Stokes region or the diameter measured by DLS (dynamic light scattering) or MALLS (multiangle laser light scattering). Preferably, at least the Guinier radius of the nanoparticles is also measured.

[0027] A nanoparticle measuring device according to the invention preferably comprises a size distribution measuring device for measuring the size distribution of the nanoparticles in the fractionated liquid stream. For example, the size distribution measuring device is a device for performing dynamic light scattering and / or multi-angle light scattering.

[0028] The magnetization parameter is preferably measured by DC and / or AC susceptometry, magnetic particle spectroscopy, magnetorelaxometry, nuclear magnetic resonance, electron spin resonance, and magneto-optical relaxation measurement. From the measurement curves obtained using these methods, the effective magnetic moment of the particles can be determined using known physical relationships. Additionally, under certain assumptions, the effective magnetic and hydrodynamic size and size distribution of the particles, the saturation magnetization, and the directional dependence of the magnetization can also be derived. These quantities are magnetization parameters as described herein.

[0029] Particularly preferably, the magnetization parameter is measured at least in part by nonlinear AC susceptibility measurement, as described, for example, in B. Gleich, J. Weizenecker, Nature 435 (2005) 1214-1217 or in N. Loewa, F. Wiekhorst, et al., IEEE Trans Magn. 49 (2013) 275-278. For this purpose, the nonlinear magnetization response MNP is measured under periodic—preferably sinusoidally oscillating—excitation. The time-dependent measurement signal is acquired broadband via a receiving coil and is generally represented in the frequency domain by Fourier transform. In addition to the first harmonic (excitation frequency), it also contains pronounced odd harmonics (spectral moments).

[0030] Preferably, a fixed excitation frequency of, for example, f ~25 kHz and variable excitation amplitudes of 0–30 millitesla are used. Applying Langevin theory, the measured signal spectrum allows the reconstruction of the size distribution of the magnetic nanoparticles contained in the sample. The advantage of MPS lies primarily in its high measurement speed (at 25 kHz, half a period t corresponds to ). messThe method offers a short pulse duration (=20 µs) and high sensitivity. The nonlinear magnetic particle signal is measured specifically without the influence of the linear diamagnetic background. Depending on the particle properties, detection limits for nanoparticulate iron down to the picogram range are possible. Compared to conventional batch measurements, the detection limit is significantly reduced (by a factor of 2) when using a capillary, as it does not need to be changed. Furthermore, due to the moderate excitation amplitude <50 mT (compared to NMR, ESR, and TLC susceptometry), the dipolar interaction is not dominant for typical particle sizes, thus preventing significant sample alteration during the measurement.

[0031] An inventive nanomagnetic particle analysis device preferably has a liquid supply device which is configured to supply the liquid in such a way that it flows laminarly in the capillary.

[0032] Preferably, the nanomagnetic particle analysis device comprises a size distribution measuring device for measuring the size distribution of the nanoparticles in the fractionated liquid stream and / or a measuring device for determining the concentration in the form of a UV or refractive index (RI) detector. The size distribution measuring device is preferably a DLS or multi-angle light scattering (MALLS) measuring device.

[0033] According to a preferred embodiment, the nanomagnetic particle analysis device comprises a fraction collector for volume-resolved enrichment of the eluting liquid stream.

[0034] The invention will now be explained in more detail with reference to the accompanying drawings. These drawings show Fig. 1 a schematic view of a nanomagnetic particle analysis device according to the invention, Fig. 2 a capillary of the analysis device according to Fig. 1 and Fig. 3 a measurement curve obtained within the framework of a method according to the invention.

[0035] Fig. Figure 1 shows a nanomagnetic particle analysis device 10 according to the invention, comprising a liquid sample holder 12 and an alternating field generator 14. The alternating field generator 14 includes a coil 16 which can be supplied with an alternating current I by a control unit 20 (shown schematically). The alternating current I has a frequency f of, for example, f = 25 kHz. The coil 16 generates an alternating magnetic field B with an amplitude B in a sample holder 22. 22 for example B 22 =30 millitesla.

[0036] It can be seen that the nanomagnetic particle analysis device 10 has a liquid feed device 24, which is shown schematically. When the sample 26 is fed into the liquid feed device, it generates a liquid flow of liquid 29 by means of a particle fractionation device 28 (see figure). Fig. 2), which is directed into the liquid sample carrier 12.

[0037] The nanomagnetic particle analysis device 10 also includes a measuring coil 18, by means of which the magnetic field B is measured. This field is generated by the alternating field generator 14 and the magnetization of the material in the sample holder 22. The view at the bottom left shows the structure of the measuring coil 18 and its position relative to the capillary 30 in detail.

[0038] The liquid sample holder 12 has a capillary 30, which in this case is made of quartz glass and is spirally wound. The liquid supply device 24 comprises a pump 32, shown schematically, which is configured to supply a liquid containing the sample 26 at a flow rate v that is at least substantially constant over time. The flow rate v is selected such that the Reynolds number R=ρvDinnenη at most 3000. In this formula, D innen the inner diameter of the capillary (cf. Fig. 2).

[0039] With respect to a flow direction S upstream of the alternating field generator 14, a size distribution measuring device 34 is arranged, which in this case comprises a MALLS detector 42 and a DLS detector 43 and by means of which a measurement can be carried out by means of light scattering. In addition, a further concentration measuring device in the form of a UV detector and / or an RI detector is arranged upstream of the alternating field generator. The size distribution measuring device 34 provides the distribution function F, which is determined for each equivalent diameter d. äqui The nanoparticle specifies the proportion of nanoparticles, which can be expressed, for example, in mass percent or volume percent, that have a maximum equivalent diameter d. äqui The equivalent diameter refers in particular to the hydrodynamic equivalent diameter.

[0040] Fig. Figure 2 shows a partial view of capillary 30. It can be seen that it has a measuring section 36. In this measuring section 36, capillary 30 is spirally wound, as can be seen in the lower part of the image. In the operating state, measuring section 36 is located in the measuring coil 18.

[0041] In the present case, the measuring section 36 is designed such that an outer cuboid has a side length of less than 12 mm, in particular less than 10 mm. In the present case, the outer cuboid has a side length of 8 mm. The outer cuboid is the imaginary cuboid of minimum side length that completely surrounds the measuring section. The volume of liquid present in the capillary within the measuring section is preferably less than 100 microliters, more preferably less than 20 microliters. In the present case, the corresponding volume Vf = 8.9 microliters.

[0042] The choice of the appropriate measurement volume depends on the required resolution for a given flow rate. The smaller the volume for a constant flow rate, the higher the temporal resolution. Furthermore, the required measurement volume is determined by the detection limit (minimum detectable particle concentration). The larger the volume, the lower the concentrations that can be detected.

[0043] The capillary diameter D of capillary 30 is 0.5 ± 0.15 millimeters in this case. The outer diameter D außen is approximately 2±0.5 millimeters.

[0044] To carry out a method according to the invention, liquid is first drawn from the liquid supply device 24 ( Fig. 1) into the liquid sample carrier. The amount of liquid dispensed, V(t), is determined and stored as a function of time. The control unit 20 energizes the outer coil 16, causing it to generate the alternating magnetic field B.

[0045] The measuring coil 18 comprises a receiving coil 17, in which the measuring section 36 of the liquid sample carrier 12 is arranged, and a reference coil 19, which together form a gradiometer arrangement. This suppresses the excitation frequency and increases the measurement accuracy. It is possible, and represents a preferred embodiment, for the measuring coil 18 to be spatially arranged within the coil 16.

[0046] An induced voltage U is generated using the measuring coil 18. ind (t) measured as a function of time t.

[0047] Before passing through the sample intake 22, the liquid flows into the size distribution measuring device 34, which also measures the size distribution as a function of time t. Since the time difference for each liquid fraction of the fractionated liquid flow between the two measuring devices is known, it is possible to determine at what time this liquid fraction flowed through the sample intake 22 and when it flowed through the size distribution measuring device 34. This time difference is determined, for example, in a preliminary test by bolus injection. The aforementioned measurement results are supplied to an evaluation unit 38, which can be part of the control unit 20 and liquid supply device 24, but this is not necessary.

[0048] Fig. Figure 3 shows a measurement result obtained with the nanomagnetic particle analysis device 10 according to the invention. The abscissa shows the elution volume V. elutionin milliliters. The DLS curve indicates the particle diameter d of the particles as measured with DLS. It can be seen that the particle diameter is approximately linear with the elution volume V. elution increases because in this case asymmetric flow-field-flow fractionation was used, which causes a separation of the applied sample according to hydrodynamic size.

[0049] The curve labeled MPS shows the amplitude of the third harmonic µ3 in ammeter squared normalized to the iron content c. Fe in moles of iron. It can be seen that this curve passes through a maximum for particles with a diameter between 50 and 60 nanometers and is not linearly correlated with the hydrodynamic size of the particles, thus demonstrating the added value of the magnetic measuring device.

[0050] In addition to or as an alternative to the size distribution measuring device, the nanomagnetic particle analysis device 10 can have a concentration measuring device configured to measure a concentration c Fe on nanoparticles in the fractionated liquid stream. Such a measurement result is found in the study with C FeUV The curve is shown. It can be seen that the measured sample contains a large proportion of very small nanoparticles, which, however, possess a very small magnetic moment. Reference symbol list 10 Nanomagnetic particle analysis device 12 liquid sample carriers 14 alternating field generators 16 coil 17 Receiving coil 18 Measuring coil 20 Control unit 22 Sample recording 24 Liquid supply device 26 Sample 28 Particle fractionating device 29 Liquid 30 capillaries 31 nanoparticles 32 Pump 34 Size distribution measuring device 36 Measurement section 38 evaluation units 41 Faction Collectors 42 MALLS detector 43 DLS detector C Fe concentration d particle diameter D capillary diameter D innen capillary inner diameter F distribution function R S Flow direction Alternating current t time U ind induced voltage v Flow rate V(t) amount of liquid

Claims

[1] Method for measuring a magnetic property of magnetic nanoparticles, comprising the steps: (a) Passing a liquid (29) containing the nanoparticles (31) through an alternating magnetic field (B), (b) Measuring a magnetization parameter that describes a dependence of a magnetization of the nanoparticles (31) on the alternating field (B), and (c) Guiding the liquid (29) through a coiled capillary (30) through the alternating magnetic field (B) characterized by the step: (d) before passing the liquid (29) through the coiled capillary (30) fractionating the magnetic nanoparticles (31) in the liquid (29) so that a fractionated liquid stream is produced, (e) wherein measuring the magnetization parameter is a time-resolved measurement of the magnetization parameter on the fractionated fluid flow. [2] Method according to any of the foregoing claims, characterized by, that the liquid (29) is passed through the capillary (30) at a flow rate (v) which is chosen such that there is a laminar flow in the capillary (30). [3] Method according to any of the preceding claims, characterized by , that the liquid (29) is guided through the capillary (30) in such a way that the Reynolds number (R=ρvDη), which is calculated as the quotient of the product of the density (p) of the liquid, a flow rate (v) and a capillary diameter (D) of the capillary as the numerator and the dynamic viscosity (η) as the denominator, which is at most 3000. [4] Method according to any of the preceding claims, characterized by the step: time-resolved measurement of a size distribution (F) of the nanoparticles (31) in the fractionated liquid stream. [5] Nanomagnetic particle analysis device for determining a magnetic property of magnetic nanoparticles (31), with (a) a liquid sample holder (12) for receiving a liquid (29) containing the magnetic nanoparticles (31), and (b) an alternating field generator (14) for generating an alternating magnetic field (B) in a sample holder (22) designed to receive the liquid sample carrier (12), (c) wherein the liquid sample holder (12) comprises a coiled capillary (30) for guiding the liquid (29), characterized by (d) a liquid supply device (24), - which is connected to the capillary (30) for supplying the liquid (29) at a flow rate (v) and - a particle fractionation device (28) for fractionating nanoparticles (31) in the liquid (29) so that a fractionated liquid stream is produced. [6] Nanomagnetic particle analysis device according to claim 5, characterized by, that the liquid supply device (24) is configured to supply the liquid (29) such that a Reynolds number (R=ρvDinnenη), which is calculated as the quotient of the product of the density (p) of the liquid, a flow velocity (v) and a capillary inner diameter (D) innen ) of the capillary (30) as numerator and of the dynamic viscosity (η) as denominator is at most 3000. [7] Nanomagnetic particle analysis device according to one of claims 5 to 6, characterized by a size distribution measuring device (34) for measuring the size distribution (F) of the nanoparticles (31) in the fractionated liquid stream. [8] Nanomagnetic particle analysis device according to any one of claims 5 to 7, characterized by a concentration measuring device for measuring the concentration (c Fe ) the nanoparticles (31) in the fractionated liquid stream.

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