Multifocal Particle Detection System and Method Based on Metalens Array

Abstract

This invention discloses a multifocal particle detection system and method based on a metalens array, comprising an illumination module, an imaging module, an image acquisition module, an analysis and calculation module, and a microfluidic device. The illumination module includes a laser, a collimating lens, a beam expander, and a metalens array arranged sequentially along the beam propagation direction. First, a parallel beam is generated by the laser, collimating lens, and beam expander, covering the entire aperture of the metalens array. Then, a set of focal points is generated by the metalens array. The microfluidic device is placed between the illumination module and the imaging module to hold the solution sample containing the particles to be measured. The image acquisition module is located behind the focal plane of the metalens array. The analysis and calculation module is used to obtain the relevant physical quantities of the particles to be measured in the solution. This invention utilizes a metalens array to generate a focal point array within an extremely short working distance, simplifying the optical path and facilitating integration with microfluidic devices.

Description

Technical Field

[0001] This invention belongs to the field of particle velocity and density measurement technology in flow fields, specifically relating to a multifocal particle detection system and method based on metalens array. Background Technology

[0002] Correlation spectroscopy is a powerful quantitative technique for particle dynamics, widely used in biomedicine, biophysics, and chemistry. By recording the light intensity fluctuations caused by the free diffusion or directional flow of particles in a focused beam, correlation analysis of these fluctuations over time allows for the quantitative calculation of particle concentration, diffusion coefficients, and other physical parameters. Fluorescence correlation spectroscopy (FCS) uses fluorescent dyes or proteins to label biological particles. By recording the fluctuations in fluorescence intensity of the sample under focused light excitation, the relevant physical parameters of the particles can be obtained. Fluorescent labeling allows for the specific analysis of biomolecules of interest in biological samples. Furthermore, by labeling different particles with different colors of fluorescence, two-color fluorescence correlation spectroscopy can be used to study the interactions between different biomolecules. However, due to the phototoxicity and photobleaching properties of fluorescent substances, fluorescence correlation spectroscopy is difficult to use for long-term measurements of biological samples, and many particulate matter in daily life cannot be fluorescently labeled. Therefore, people are eager to explore a fluorescent label-free correlation spectroscopy method that uses the reflection or scattering signals of light by target particles to perform intensity correlation analysis, and obtain the flow rate of particles in freely diffused or directionally flowing liquids, as well as related physical quantities such as particle concentration and diffusion coefficient.

[0003] Furthermore, traditional correlation spectroscopy techniques obtain the intensity information of particles in motion over time by generating a single focal point. This technique requires knowledge of the spatial volume of the generated focal point to quantitatively calculate the particle's physical parameters. In fluorescence correlation spectroscopy, a dual-focal fluorescence correlation spectroscopy technique has been proposed: a differential interference prism is added to a confocal microscope to separate two orthogonally polarized laser beams into two focal points. Simultaneously, the intensity fluctuations of particles in the observation regions of the two focal points, which are separated by a certain lateral distance, are recorded. The relevant information of the measured physical parameters in the two focal regions is calculated using autocorrelation and cross-correlation functions. Compared to traditional single-focal correlation spectroscopy, this technique only requires prior knowledge of the lateral distance between the two focal points to quantitatively obtain the particle's physical parameters and dynamic information. Nevertheless, under the conditions of traditional correlation spectroscopy, the size and distribution of the observation region corresponding to the particle information within the sample are very limited, making it impossible to perform higher-throughput and more comprehensive measurements of the particles under test. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a multi-focus particle detection system and method based on a metalens array. The technical problem to be solved by this invention is achieved through the following technical solution:

[0005] This invention provides a multifocal particle detection system based on a metalens array, comprising an illumination module, an imaging module, an image acquisition module, an analysis and calculation module, and microfluidic devices, wherein...

[0006] The illumination module, the imaging module, and the image acquisition module are sequentially coupled together along the beam transmission direction;

[0007] The illumination module includes a laser, a beam expander, a collimating lens, and a dielectric metalens array arranged sequentially along the beam transmission direction. First, a parallel beam is generated by the laser, the collimating lens, and the beam expander, and the parallel beam covers the entire aperture of the dielectric metalens array. The polarizer and the quarter-wave plate are used to control the polarization state of the beam. Then, a set of focal arrays is generated by the dielectric metalens array.

[0008] The microfluidic device is placed between the illumination module and the imaging module to hold the solution sample containing the particles to be tested;

[0009] The imaging module includes an imaging objective lens;

[0010] The image acquisition module is located at the rear end of the focal plane of the medium metalens array. It is used to image the particle to be tested or to perform secondary imaging on the focal array on the rear focal plane of the medium metalens array, and then use the obtained focal array to observe the particle to be tested.

[0011] The analysis and calculation module is used to statistically analyze the light intensity values ​​of the particles under test observed in real time, and to perform autocorrelation and cross-correlation analysis to obtain the relevant physical quantities of the particles under test in the solution.

[0012] In one embodiment of the present invention, the dielectric metalens array comprises a substrate and a periodic uniform array of structural units located above the substrate, wherein,

[0013] The substrate is made of silicon dioxide, resin, or aluminum oxide. The size and period of the structural units in the periodic uniform array of structural units are smaller than the wavelength of electromagnetic waves in a vacuum. The shape of the structural units includes cubic waveguides, cylindrical waveguides, and elliptical cylindrical waveguides. The material of the structural units is silicon, gallium nitride, or titanium dioxide.

[0014] In one embodiment of the present invention, the illumination module includes a laser, a beam expander, a collimating lens, a polarizer, a quarter-wave plate, and a dielectric metalens array arranged sequentially along the beam propagation direction. The microfluidic device is located at the common focal plane of the dielectric metalens array and the imaging objective lens, and the plane of the microfluidic device is perpendicular to the beam propagation direction. The image acquisition module is a CCD camera.

[0015] In one embodiment of the present invention, a converging lens is provided between the dielectric metalens array and the microfluidic device for secondary imaging of the focal array generated by the dielectric metalens array, and the beam after secondary imaging is converged into the sample region of the microfluidic device.

[0016] In one embodiment of the present invention, the image acquisition module is further configured to acquire multiple consecutive images of the particle under test in a flowing state, and adjust the relevant parameters of the image sequence acquired by the multiple consecutive acquisitions to ensure that the particles and the background in the sampling area can be distinguished.

[0017] In one embodiment of the present invention, the analysis and calculation module is specifically used for:

[0018] Intensity information is extracted from one or more focal regions generated in each frame of the image sequence. The signal intensity values ​​in the regions containing particle swarm flow information are integrated and summed to obtain a set of light intensity data curves that change over time.

[0019] Numerical compensation is performed on the obtained light intensity data curve to eliminate the impact of the decrease in signal-to-background ratio.

[0020] Image correlation calculations are performed on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information of each focal region and the cross-correlation results of the intensity information between focal regions;

[0021] The particle flow velocity is obtained by fitting the data curves of the obtained autocorrelation and cross-correlation results.

[0022] Another aspect of the present invention provides a multifocal particle detection method based on a metalens array, comprising:

[0023] S1: Obtain a multi-frame continuous image sequence of the particle under test in a flowing state using the multi-focus particle detection system based on metalens array according to any one of the above embodiments;

[0024] S2: Perform image correlation spectroscopy on the image sequence to obtain the autocorrelation curve of a single focus and the cross-correlation curve of a multifocus. Obtain the values ​​of the flow rate and concentration parameters of the particles to be measured by function fitting.

[0025] In one embodiment of the present invention, S1 includes:

[0026] S1.1: Turn on the power of the illumination module, adjust the light source intensity, and ensure that the image formed by the meta-lens array by the CCD camera is clearly visible and the exposure is appropriate;

[0027] S1.2: Adjust the positional relationship between the medium metalens array, the imaging objective lens, and the CCD camera so that the focal point generated by the medium metalens array can be clearly imaged onto the CCD camera;

[0028] S1.3: Fix the microfluidic device between the dielectric metalens array and the imaging objective lens, and make the observation area in the microfluidic device clearly imaged by axially moving the position of the microfluidic device, and inject a solution containing the test particles into the microfluidic device at a constant speed;

[0029] S1.4: When the solution flow is in a stable state, acquire multiple frames of continuous images of the particles to be tested in the sample, and adjust the relevant parameters of the image sequence acquired by the multiple frames of continuous acquisition to ensure that the particles to be tested and the background information can be clearly distinguished in the images captured by the CCD camera.

[0030] In one embodiment of the present invention, step S2 includes:

[0031] S2.1: Extract the intensity information inside any one or more focal regions generated in each frame of the image sequence, integrate and sum the signal intensity values ​​in the region containing particle swarm flow information to obtain a set of intensity curves that change with time, with each focal region's intensity information data corresponding to one curve;

[0032] S2.2: Numerical compensation is performed on the obtained intensity curve to eliminate the impact of the decrease in signal-to-background ratio;

[0033] S2.3: Perform image correlation calculation on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information of each focal region and the cross-correlation results of the intensity information between focal regions;

[0034] S2.4: Fit the obtained autocorrelation and cross-correlation data curves to obtain the particle flow velocity.

[0035] In one embodiment of the present invention, S2.4 includes:

[0036] The obtained autocorrelation and cross-correlation data curves are fitted to calculate the particle flow velocity and concentration. The physical model used for fitting is as follows:

[0037]

[0038]

[0039] in, This is the result of autocorrelation calculation of intensity information within a focal region. The results are from cross-correlation calculations of the intensity information within the two focal regions. N This represents the average number of particles flowing through the observation area. The diffusion time parameter is caused by the Brownian motion of the particle itself. For time parameters related to particle flow caused by external forces, This represents the actual distance between any two chosen foci. This represents the radius value of the current focus.

[0040] Using formula v f = The particle flow velocity is obtained by... N The particle concentration is obtained by dividing by the volume of the observation area.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] 1. This invention does not require fluorescent labeling. It utilizes the reflection or scattering characteristics of light by target particles to perform correlation analysis of image intensity values, and can measure the physical quantities of particles in their natural state. The medium metalens array used in this invention makes the traditional multifocal correlation spectroscopy measurement system more compact, and the number of focal points generated behind can be flexibly changed by controlling the polarization state of the electromagnetic waves illuminating the metalens array.

[0043] 2. This invention utilizes a metalens array with a thickness only on the subwavelength scale to generate single or multiple focal points within a very short working distance for illuminating and observing analyte particles in a solution. It is also easily integrated with microfluidic devices, resulting in a compact optical system. Furthermore, the number of focal points generated by this metalens array is flexibly adjustable, allowing for simultaneous measurement of multiple regions within the sample. By recording image sequences and performing subsequent computational processing, information such as particle velocity and concentration can be obtained. Compared to traditional correlation spectroscopy measurement systems, this method utilizes a metalens array to generate multiple focal points within an extremely short working distance, enabling simultaneous measurement of multiple points within the sample, simplifying the optical path, and facilitating integration with microfluidic devices. Moreover, the number of focal points is flexibly adjustable.

[0044] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of a multifocal particle detection system based on a metalens array provided in an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the optical path of a multifocal particle detection system based on a metalens array provided in an embodiment of the present invention;

[0047] Figure 3 These are actual images of the metalens array designed in a multifocal particle detection system based on a metalens array provided in this embodiment of the invention, obtained under illumination conditions of left-hand circularly polarized light, right-hand circularly polarized light, and elliptical polarized light, respectively, in 4-focal mode, 9-focal mode, and 13-focal mode.

[0048] Figure 4 These are the 1500th, 3000th, 4500th, and 6000th frames of a 6000-frame image sequence captured by a CCD camera in a multifocal particle detection system based on a metalens array provided in this embodiment of the invention.

[0049] Figure 5 This is a curve showing the change of light intensity values ​​at different focal points over time, obtained by a multifocal particle detection system based on a metalens array provided in this embodiment of the invention.

[0050] Figure 6 These are two sets of experimental data and fitted curves obtained by performing autocorrelation calculations on a single focal data point at different speeds. V sta This represents the actual sample flow rate value obtained from experimental measurements. V fit This represents the sample flow rate value obtained through fitting calculation;

[0051] Figure 7 These are two sets of experimental data and fitted curves obtained by cross-correlation calculations on multiple focal data points at different speeds. V sta This represents the actual sample flow rate value obtained from experimental measurements. V fit This represents the sample flow rate value obtained through fitting calculation;

[0052] Figure 8 These are three sets of experimental data and fitted curves obtained by autocorrelation calculations on multiple focal data points at different concentrations. C sta This represents the actual sample concentration value obtained from the experiment. C fit This represents the sample concentration value obtained through fitting calculation.

[0053] Explanation of reference numerals in the attached figures:

[0054] 1-Laser; 2-Beam expander lens; 3-Collimating lens; 4-Polarizer; 5-Quarter-wave plate; 6-Dielectric metalens array; 7-Microfluidic device; 8-Imaging objective lens; 9-CCD camera. Detailed Implementation

[0055] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of the multifocal particle detection system and method based on metalens array proposed in accordance with the present invention is provided in conjunction with the accompanying drawings and specific embodiments.

[0056] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0057] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes said element.

[0058] Example 1

[0059] Please see Figure 1 , Figure 1 This is a schematic diagram of a multifocal particle detection system based on a metalens array provided in an embodiment of the present invention. The multifocal particle detection system includes an illumination module, an imaging module, an image acquisition module, an analysis and calculation module, and a microfluidic device 7, wherein the illumination module, imaging module, and image acquisition module are sequentially coupled along the beam transmission direction.

[0060] The illumination module includes a laser 1, a beam expander 2, a collimating lens 3, a polarizer 4, a quarter-wave plate 5, and a dielectric metalens array 6 arranged sequentially along the beam transmission direction. First, a parallel beam is generated by the laser 1, collimating lens 2, and beam expander 3. The polarizer 4 and quarter-wave plate 5 convert the incident linearly polarized light into circularly or elliptically polarized light, and the parallel beam covers the entire aperture of the dielectric metalens array 6, generating a focal array. A microfluidic device 7 is placed between the illumination module and the imaging module to hold the solution sample containing the test particles. The imaging module includes an imaging objective lens 8. An image acquisition module is located behind the focal plane of the dielectric metalens array and is used to image the test particles or perform secondary imaging of the focal array on the rear focal plane of the dielectric metalens array, and then use the obtained focal array to observe the test particles. The analysis and calculation module is used to statistically analyze the light intensity values ​​of the test particles observed in real time, and perform autocorrelation and cross-correlation analyses to obtain the relevant physical quantities of the test particles in the solution.

[0061] Specifically, in this embodiment, the design wavelength of the dielectric metalens array is 635nm. Therefore, a continuous laser with a wavelength of 635nm is used in the illumination module, which is shaped into a parallel beam with a diameter sufficient to cover the entire effective structure of the metalens array after being collimated and expanded by a lens. The dielectric metalens array is located after the illumination module and modulates the incident parallel beam to form multiple converging beams to generate multiple focal points. A microfluidic device is used as a container to hold the solution containing the particles to be tested. It is placed in the optical path of the imaging system. The state of the particles to be tested flowing through the channel of the microfluidic device can be observed in real time and recorded by the analysis and calculation module. In other embodiments of the present invention, the microfluidic device can also be replaced by a live biological sample. The image acquisition module is located at the rear end of the back focal plane of the dielectric metalens array. This image acquisition module performs secondary imaging of the focal array on the back focal plane of the metasurface while directly imaging the particles to be tested.

[0062] The dielectric metalens array used in this embodiment is a metasurface capable of generating multiple focal points, and each sub-metalens in the array functions as a convex lens. Please refer to [link to relevant documentation]. Figure 2 , Figure 2This is a schematic diagram of the optical path of a multifocal particle detection system based on a metalens array according to an embodiment of the present invention. The dielectric metalens array comprises 13 sub-metalenses, each with a focal length of 10 micrometers, and the overall dimensions of the sub-metalenses are 30 × 30 micrometers. Each sub-metalense consists of a substrate of low dielectric constant material and a periodically uniform array of structural units of high dielectric constant. In this example, the substrate of the sub-metalense is made of silicon dioxide, while the structural units on the substrate surface are made of silicon. The thickness of the substrate is a non-characteristic parameter and has no significant impact on the performance of the sub-metalense device; a suitable thickness ensures the stability of the fabricated sub-metalense device. The size and period of the structural units in the periodically uniform array are both smaller than the wavelength of electromagnetic waves in a vacuum, and the selected structural units are cubic waveguides with a rectangular cross-section. The phase of the beam is controlled by the PB phase modulation method on the metasurface of the entire dielectric metalens array. That is, the phase delay can be nearly linearly controlled by rotating around the vertical axis of the structural unit and controlling the rotation angle. The specific relationship can be expressed as follows: ,in This represents the amount of phase delay required at different locations on the metasurface. Let be the angle through which the structural unit at any position is rotated relative to the reference position. The relationship between the required phase retardation at each position within each sub-mesh lens and the coordinates of that position must satisfy:

[0063]

[0064] in, Indicates the operating wavelength of the sub-meta-lens. This indicates the focal length of the sub-meta-lens. This represents the radial coordinate of a single sub-metalens in the metalens array. Sub-metalens designed based on the above relationship can achieve the effect of converging parallel light into a point. By integrating multiple sub-metalens on the entire metalens array, the function of shaping a single laser beam into multiple converged beams can be realized, thereby enabling multi-point sampling.

[0065] like Figure 2 As shown, the illumination module of this embodiment includes a laser 1, a beam expander lens 2, a collimating lens 3, a polarizer 4, a quarter-wave plate 5, and a dielectric metalens array 6 arranged sequentially along the beam propagation direction. The laser emitted by the laser 1 has a wavelength of 635 nm, which is the working wavelength designed for the metasurface of the dielectric metalens array. The imaging module is an imaging objective lens 8; the image acquisition module is a CCD camera 9. A microfluidic device 7 is placed between the imaging objective lens 8 and the CCD camera 9. The microfluidic device 7 serves as a container for holding the solution containing the particles to be measured, thereby imaging the particles.

[0066] Specifically, the polarizer 4 and quarter-wave plate 5 convert the polarization state of the laser emitted by the laser 1 into circular or elliptical polarization, thereby ensuring the normal operation of the metasurface based on PB phase modulation. Optionally, a second set of polarizers and quarter-wave plates (not shown in the figures) is provided behind the microfluidic device 7 to control the polarization state of the emitted light, so as to more flexibly control the working mode of the dielectric metalens array in the system. In this embodiment, only one set is used.

[0067] In this embodiment, the collimating lens 3 is located before the dielectric metalens array 6, ensuring that the collimated beam it generates can completely illuminate the metasurface of the dielectric metalens array 6. The transmitted light forms a focal array and directly illuminates the microfluidic device 7. At the rear end, the imaging objective 8 and CCD camera 9 collect the light modulated by the metalens array 6 and the sample for imaging. It should be noted that in another embodiment of the invention, in... Figure 2 Adding a converging lens to the optical path and placing it after the medium meta-lens array 6 allows for secondary imaging of the focal array generated on the meta-surface. The beam after secondary imaging is then focused on the sample area of ​​the microfluidic device 7. The imaging objective 8 is still placed behind the microfluidic device 7 and coaxial with it, so that the beam emitted from the converging lens is transmitted to the entrance pupil of the imaging objective 8.

[0068] On the other hand, the dielectric metalens array 6 in this embodiment combines propagation phase and PB phase phase modulation methods with the imaging system to achieve polarization multiplexing, enabling more flexible focus generation schemes. Specifically, the metasurface can control the polarization state of the incident light by rotating the polarizer 4, thereby achieving different operating modes: see details. Figure 3 When the incident light is right-handedly polarized, it can generate 4 focal points arranged in a 2×2 pattern. When the incident light is left-handedly polarized, it can generate 9 focal points arranged in a 3×3 pattern. When the incident light is specifically elliptically polarized, both of the above modes can be excited simultaneously.

[0069] Furthermore, the multi-focus particle detection in this embodiment can measure the properties of particles in a flowing solution, and the analysis and calculation module can measure the flow velocity information of the particles to be measured in the solution. Specifically, the analysis and calculation module in this embodiment is used for:

[0070] Intensity information is extracted from any one or more focal regions generated in each frame of the image sequence. The signal intensity values ​​in the region containing particle swarm flow information are integrated and summed to obtain a set of intensity curves that change over time.

[0071] Numerical compensation is performed on the obtained intensity curve to eliminate the impact of the decrease in signal-to-background ratio;

[0072] Image correlation calculations are performed on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information of each focal region and the cross-correlation results of the intensity information between focal regions;

[0073] The particle flow velocity is obtained by fitting the data curves of the obtained autocorrelation and cross-correlation results.

[0074] In practice, the operation of this multifocal particle detection includes the following steps:

[0075] Step 1: Turn on the power of laser 1 and adjust the intensity of the emitted laser to ensure that CCD camera 9 can clearly image the medium metalens array 6 and that the exposure is appropriate. Overexposure will cause the loss of effective information of the particles to be measured in the observation area.

[0076] Step 2: Fix the microfluidic device or living biological sample at the common focal point of the converging lens and the imaging objective lens, ensuring that the plane containing the microfluidic device or biological sample is perpendicular to the optical axis of the optical system, and that the light beam can completely pass through the effective detection area of ​​the microfluidic device or biological sample. In this embodiment, an aqueous solution of PMMA microsphere powder is used as the sample to be tested. To reduce the aggregation effect of particles and ensure that there are always uniform PMMA microspheres flowing through the observation area, it is necessary to ensure an appropriate concentration ratio of PMMA microsphere solution. The solution used contains 0.025g of PMMA microsphere powder and approximately 1ml of water solvent.

[0077] Step 3: The microfluidic device 7 is axially moved to focus, ensuring a clear image of its observation area. The solution to be tested is then injected into the inlet of the microfluidic device 7 at a constant speed, while the solution flowing through the channel exits from the outlet. In this embodiment, the sample solution is injected into a syringe, and a microfluidic pump is used to push the syringe. Once the flow of the solution within the microfluidic device reaches a steady state, the observed particle swarm in the solution can be used as valid image data for calculation.

[0078] Step 4: Using image acquisition software associated with the CCD camera on a computer, adjust the frame rate to approximately 200 frames per second to continuously acquire and store multiple frames of the particle sample in its flowing state. Adjust the exposure time, gain, and γ value of the images acquired by the CCD camera in the software to ensure high contrast and appropriate brightness between the particles and the background in the observation area. In this embodiment, a total of 6000 frames were captured continuously for approximately 30 seconds, yielding the following results: Figure 4 The actual images shown here are from frames 1500, 3000, 4500, and 6000, selected for demonstration when the meta-lens array is in 4-focal mode. In all of them, the passing PMMA spheres can be clearly seen within the detection area formed by the four focal points.

[0079] Step 5: Sum the signal intensities in each observation area of ​​the image sequence obtained in Step 4 to obtain a set of intensity-time relationship curves with a duration of 30s. Numerical compensation is then performed to eliminate the influence of signal-to-background ratio fluctuations. Next, based on one or more sets of intensity integral-time curves, the image correlation spectrum is calculated to further obtain the autocorrelation curve of a single focus and the cross-correlation curve of multiple focuses. Finally, the specific value of particle velocity is obtained by fitting a physical function.

[0080] Step 5 includes the following specific steps:

[0081] S5.1: Extract the intensity information within any one or more focal regions generated in each frame of the image sequence, integrate and sum the signal intensity values ​​within the observation area containing particle swarm flow information, thereby obtaining a set of time-varying intensity integral curves with a total duration of 30 seconds, such as... Figure 5 As shown, image focus 1 and image focus 2 correspond to the intensity integral versus time curves of the two observation areas through which the PMMA ball flows.

[0082] S5.2: Numerical compensation is performed on the obtained intensity curve to eliminate the influence of signal-to-background ratio fluctuations. In this embodiment, the 6000 intensity integral data obtained in step S5.1 are first scaled down to 100 data points using the method of averaging at equal intervals, and then fitted using the following function:

[0083]

[0084] in, a , b , c These are the three coefficients to be fitted. Represents the independent variable, time. This represents the dependent variable, light intensity, as it changes over time. i This indicates the first polynomial in the fitted polynomial. i The independent variable data of the scaled data is then expanded into an array of length 6000 using nearest neighbor interpolation. The fitted strength value is then obtained using the fitted function. The resulting strength integral curve after compensation is shown below. Figure 6 As shown.

[0085] S5.3: Introducing Delay τ Then, perform image spectral correlation calculations on the intensity value array obtained through fitting correction:

[0086]

[0087]

[0088] in, G a This is the result of autocorrelation calculation of intensity information within a specific focal region. G C The results of cross-correlation calculations on intensity information within two focal regions are all functions related to time delay. For a certain focus at any point in time t The image intensity value below, In order to be in t + The corresponding image intensity value at time t. and The intensity values ​​of the two relevant focal points in the image are respectively selected. The two focal areas must be regions through which the same particle group flows sequentially in a specific direction.

[0089] In this embodiment, the dielectric metalens array is configured to operate in four-focal mode, with the two left foci selected as the observation area. First, the autocorrelation of the two areas is calculated using the integral intensity curves obtained in step 5.2. Simultaneously, the flow rate of the solution sample is changed by adjusting the propulsion speed of the microfluidic pump to obtain statistical results under different speed conditions. The experimental results are as follows: Figure 6 As indicated by the dotted markers, the left and right images correspond to the flow rates of 4 μL / min and 5 μL / min set in the microfluidic pump, respectively. Furthermore, based on the integral intensity curves obtained in step 5.2, cross-correlation calculations were performed on the two regions, yielding the following experimental results: Figure 7 The dots are shown in the diagram. It should be noted that, to demonstrate that the measurable velocity range of this method is sufficiently large, Figure 7 When calculating the cross-correlation results, the microfluidic pump speed was specifically adjusted to 40 μL / min and 45 μL / min for the experiment.

[0090] S5.4: Fit the obtained autocorrelation and cross-correlation data curves according to the following physical model or a deformation based on it:

[0091]

[0092]

[0093] in, N This represents the average number of particles flowing through the observation area. This is the diffusion time parameter caused by the Brownian motion of the particle itself. For the time parameter related to particle flow caused by external forces, This represents the actual distance between any two observed regions containing the focal points. This represents the radius value at a given focus. Then, the formula is used... The particle flow velocity is obtained by... N The particle concentration is obtained by dividing by the volume of the observation area.

[0094] In this embodiment, the autocorrelation results obtained from the two different slower-speed experiments are first analyzed according to the above formula. The corresponding physical function was fitted, and the measurement and fitting results are shown below. Figure 6 The parameters obtained by fitting under two speed conditions The times are 0.044s and 0.027s, respectively. The radius of each circular observation area formed by the focal point is 11.2 μm. Using the formula... The fitting speeds under the two slow conditions can be calculated to be 252 μm / s and 417 μm / s, respectively. On the other hand, the cross-correlation results obtained from the experiments at the two different faster speeds are based on the above formula... The corresponding physical function was fitted, and the measurement and fitting results are shown below. Figure 7 The parameters obtained by fitting under two speed conditions The values ​​are 0.004s and 0.003s, respectively. Similarly, the fitted velocities under the two rapid conditions can be calculated to be 2909 μm / s and 4267 μm / s, respectively. The average error between the fitted results and the actual velocities is approximately 8.07%. Therefore, the method of this embodiment can measure particle velocity relatively accurately.

[0095] This invention eliminates the need for fluorescent labeling, utilizing the reflection or scattering characteristics of light by target particles for intensity correlation analysis, enabling measurements of particles in their natural state. The metalens array employed in this invention makes traditional multifocal correlation spectroscopy systems more compact, and the number of focal points generated can be flexibly altered by controlling the polarization state of the electromagnetic waves illuminating the metalens array. This invention utilizes a metalens array with a thickness only on the subwavelength scale to generate single or multiple focal points within a very short working distance for illuminating and observing analyte particles in solution. It is also easily integrated with microfluidic devices, resulting in a compact optical system. Furthermore, the number of focal points generated by this metalens array is flexibly adjustable, allowing simultaneous measurement of multiple regions within the sample. By recording image sequences and performing subsequent computational processing, information such as particle velocity and concentration can be obtained. Compared to traditional correlation spectroscopy systems, this method utilizes a metalens array to generate focal points within an extremely short working distance, simplifying the optical path and facilitating integration with microfluidic devices. Moreover, the number of focal points is flexibly adjustable, allowing for simultaneous measurement of multiple points within the sample.

[0096] Example 2

[0097] Based on Example 1, this example provides a multifocal particle detection method based on a metalens array, which specifically includes:

[0098] S1: Use the multifocal particle detection system based on metalens array described in Example 1 to obtain a multi-frame continuous image sequence of the particle under test in a flowing state.

[0099] Specifically, S1 in this embodiment includes:

[0100] S1.1: Turn on the power of the illumination module, adjust the light source intensity, and ensure that the image formed by the meta-lens array by the CCD camera is clearly visible and the exposure is appropriate;

[0101] S1.2: Fix the microfluidic device at the common focal point of the dielectric metalens array and the imaging objective lens, ensuring that the plane where the microfluidic device is located is perpendicular to the beam propagation direction, and at the same time ensuring that the beam can completely pass through the effective detection area of ​​the microfluidic device;

[0102] S1.3: Move the position of the microfluidic device axially to make the observation area in the microfluidic device clearly imaged, and inject the solution containing the test particles into the microfluidic device at a constant speed to make the flow state of the solution stable.

[0103] S1.4: Perform multi-frame continuous image acquisition on the particles under test in the flowing state, and adjust the relevant parameters of the image sequence obtained by multi-frame continuous acquisition to ensure that there is high contrast and appropriate brightness between the particles and the background in the sampling area.

[0104] S2: Perform image correlation spectroscopy on the image sequence to obtain the autocorrelation curve of a single focus and the cross-correlation curve of a multifocus. Obtain the values ​​of the flow rate and concentration parameters of the particles to be measured by function fitting.

[0105] In this embodiment, S2 includes:

[0106] S2.1: Extract the intensity information inside any one or more focal regions generated in each frame of the image sequence, integrate and sum the signal intensity values ​​in the region containing particle swarm flow information to obtain a set of intensity curves that change with time, with each focal region's intensity information data corresponding to one curve;

[0107] S2.2: Numerical compensation is performed on the obtained intensity curve to eliminate the impact of the decrease in signal-to-background ratio;

[0108] S2.3: Introducing delay τImage correlation calculations are performed on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information in each focal region and the cross-correlation results of the intensity information between focal regions. The expressions for the autocorrelation results and the cross-correlation results are as follows:

[0109]

[0110]

[0111] in, This is the result of autocorrelation calculation of intensity information within a focal region. The results are from cross-correlation calculations of the intensity information within the two focal regions. The image intensity value at any given time point t, where a focal point is located. For time point t+ The corresponding image intensity value, and The intensity values ​​of the two relevant focal points in the image are respectively selected. The two focal regions are the areas through which the same particle group flows in a specific direction.

[0112] S2.4: Fit the obtained autocorrelation and cross-correlation data curves to obtain the particle flow velocity.

[0113] In this embodiment, the above experimental steps were performed on three groups of samples with different concentrations, and the obtained autocorrelation results were based on the above formula. The corresponding physical function was fitted, and the specific results are shown in [link to results]. Figure 8 The three subplots in the figure, from left to right, correspond to the measurement and fitting results under three concentration conditions, respectively. The average particle number obtained from the fitting under the three concentration conditions is shown. N The focal lengths are 0.82, 0.55, and 0.34, respectively, and the area of ​​each circular focal spot formed by the focal length appears as 201 μm on the camera screen. 2 If the thickness of the microfluidic device is 100 μm, then the observation volume is 201 μm. 2 ×100 μm=0.201×10 -4 μL. Using c=N / V The fitted concentrations under the two slow-speed conditions can be calculated to be 4.10 × 10⁻⁶. 4 / μL, 2.76×10 4 / μL, 1.67×10 4 / μL, while the actual statistical concentrations of these three samples were 4.17×10 4 / μL, 2.64×10 4 / μL, 1.83×10 4 / μL, with an average measurement error of 4.93%, the calculation results can accurately reflect the actual fluid concentration.

[0114] This invention designs a multifocal particle detection method based on a metalens array. Multiple focal points generated by the metalens array are used to sample analyte particles in solution, followed by data processing and related calculations. Compared to fluorescence correlation spectroscopy, this method eliminates the need for fluorescent labeling, avoids photobleaching during observation, and allows measurement of particles in their natural state. Compared to traditional dual-focal correlation spectroscopy imaging systems, the introduction of a metalens array makes the optical system more compact and facilitates multi-point detection with more than two focal points. In this embodiment, a correlation spectroscopy system with at least four and up to thirteen focal points is achieved using a single metasurface, effectively enriching the information content of a single experimental data set, and the number of focal points is flexibly adjustable.

[0115] In the several embodiments provided by this invention, it should be understood that the apparatus and methods disclosed in this invention can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For example, the division of modules is merely a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0116] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated module can be implemented in hardware or in the form of hardware plus software functional modules.

[0117] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A multifocal particle detection system based on a metalens array, characterized in that, It includes an illumination module, an imaging module, an image acquisition module, an analysis and calculation module, and microfluidic devices (7), among which, The illumination module, the imaging module, and the image acquisition module are sequentially coupled together along the beam transmission direction; The illumination module includes a laser (1), a beam expander (2), a collimating lens (3), a polarizer (4), a quarter-wave plate (5), and a dielectric meta-lens array (6) arranged sequentially along the beam transmission direction. First, a parallel beam is generated by the laser (1), the collimating lens (2), and the beam expander (3), and the parallel beam covers the entire aperture of the dielectric meta-lens array (6). Then, a set of focal points is generated by the dielectric meta-lens array (6). The microfluidic device (7) is placed between the illumination module and the imaging module to carry the solution sample containing the particles to be tested; The imaging module includes an imaging objective lens (8); The image acquisition module is located at the rear end of the focal plane of the imaging objective (8), and is used to image the particle to be tested or to perform secondary imaging on the focal array on the rear focal plane of the medium metalens array, and then use the obtained focal array to observe the particle to be tested; the image acquisition module is a CCD camera (9), the microfluidic device (7) is located at the common focal plane of the medium metalens array (6) and the imaging objective (8), and the plane where the microfluidic device (7) is located is perpendicular to the beam propagation direction; The analysis and calculation module is used to statistically analyze the light intensity values ​​of the particles under test observed in real time, and to perform autocorrelation and cross-correlation analysis to obtain the relevant physical quantities of the particles under test in the solution.

2. The multifocal particle detection system based on a metalens array according to claim 1, characterized in that, The dielectric metalens array consists of a substrate and a periodic, uniform array of structural units located above the substrate, wherein... The substrate is made of silicon dioxide, resin, or aluminum oxide. The characteristic size and period of the structural units in the periodic uniform array of structural units are smaller than the wavelength of electromagnetic waves in a vacuum. The shape of the structural units includes cubic waveguides, cylindrical waveguides, and elliptical cylindrical waveguides. The material of the structural units is silicon, gallium nitride, or titanium dioxide.

3. The multifocal particle detection system based on a metalens array according to claim 1, characterized in that, In addition to using the medium meta-lens array (6) to directly image the sample, a converging lens is set between the medium meta-lens array (6) and the microfluidic device (7) to perform secondary imaging of the focal array generated by the medium meta-lens array (6), and then the beam after secondary imaging is converged into the sample area of ​​the microfluidic device (7).

4. The multifocal particle detection system based on a metalens array according to claim 1, characterized in that, The image acquisition module is also used to acquire multiple frames of continuous images of the particles under test in a flowing state, and to adjust the relevant parameters of the image sequence obtained by the multiple frames of continuous acquisition to ensure that the particles and background information in the sampling area can be clearly distinguished.

5. The multifocal particle detection system based on a metalens array according to claim 4, characterized in that, The analysis and calculation module is specifically used for: Intensity information is extracted from one or more focal regions generated in each frame of the image sequence. The signal intensity values ​​in the regions containing particle swarm flow information are integrated and summed to obtain a set of light intensity data curves that change over time. Numerical compensation is performed on the obtained light intensity data curve to eliminate the impact of the decrease in signal-to-background ratio. Image correlation calculations are performed on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information of each focal region and the cross-correlation results of the intensity information between focal regions; The particle flow velocity is obtained by fitting the data curves of the obtained autocorrelation and cross-correlation results.

6. A multifocal particle detection method based on a metalens array, characterized in that, include: S1: The multi-focus particle detection system based on metalens array according to any one of claims 1 to 5 obtains a multi-frame continuous image sequence of the particle under test in a flowing state; S2: Perform image correlation spectroscopy on the image sequence to obtain the autocorrelation curve of a single focus and the cross-correlation curve of a multifocus. Obtain the values ​​of the flow rate and concentration parameters of the particles to be measured by function fitting.

7. The multifocal particle detection method based on metalens array according to claim 6, characterized in that, S1 includes: S1.1: Turn on the power of the illumination module, adjust the light source intensity, and ensure that the image formed by the meta-lens array by the CCD camera is clearly visible and the exposure is appropriate; S1.2: Adjust the positional relationship between the medium metalens array, the imaging objective lens, and the CCD camera so that the focal point generated by the medium metalens array can be clearly imaged onto the CCD camera; S1.3: Fix the microfluidic device between the dielectric metalens array and the imaging objective lens, and make the observation area in the microfluidic device clearly imaged by axially moving the position of the microfluidic device, and inject a solution containing the test particles into the microfluidic device at a constant speed; S1.4: When the solution flow is in a stable state, acquire multiple frames of continuous images of the particles to be tested in the sample, and adjust the relevant parameters of the image sequence acquired by the multiple frames of continuous acquisition to ensure that the particles to be tested and the background information can be clearly distinguished in the images captured by the CCD camera.

8. The multifocal particle detection method based on metalens array according to claim 6, characterized in that, Step S2 includes: S2.1: Extract the intensity information inside any one or more focal regions generated in each frame of the image sequence, integrate and sum the signal intensity values ​​in the region containing particle swarm flow information to obtain a set of intensity curves that change with time, with each focal region's intensity information data corresponding to one curve; S2.2: Numerical compensation is performed on the obtained intensity curve to eliminate the impact of the decrease in signal-to-background ratio; S2.3: Perform image correlation calculation on the numerically compensated intensity information to obtain the autocorrelation results of the intensity information of each focal region and the cross-correlation results of the intensity information between focal regions; S2.4: Fit the obtained autocorrelation and cross-correlation data curves to obtain the particle flow velocity.

9. The multifocal particle detection method based on metalens array according to claim 8, characterized in that, S2.4 includes: The obtained autocorrelation and cross-correlation data curves are fitted to calculate the particle flow velocity and concentration. The physical model used for fitting is as follows: in, This is the result of autocorrelation calculation of intensity information within a focal region. The results are from cross-correlation calculations of the intensity information within the two focal regions. N This represents the average number of particles flowing through the observation area. The diffusion time parameter is caused by the Brownian motion of the particle itself. The time parameter is related to the particle flow caused by external forces. This represents the actual distance between any two chosen foci. This represents the radius value of the current focus. Using formula v f = The particle flow velocity is obtained by... N The particle concentration is obtained by dividing by the volume of the observation area.

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