A photoacoustic microfluidic detection system based on planar waveguide

Abstract

The present invention is applicable to the field of photoacoustic microfluidic detection, and provides a photoacoustic microfluidic detection system based on a planar waveguide, including: a microfluidic chip module, a laser excitation module, a laser detection module block and a signal processing module; wherein the microfluidic chip module includes a microfluidic channel and a planar waveguide arranged above the microfluidic channel; the laser excitation module is used to excite the target sample in the microfluidic channel below the planar waveguide to emit ultrasonic waves; the laser detection module is used to receive the photoacoustic signal generated by the target sample after being excited, and convert it into a voltage signal; the signal processing module is used to receive the voltage signal of the laser detection module and process it to obtain the optical signal of the target sample. The present invention has a simple structure, low cost, high integration, and a wide detection range. It can realize large-area rapid scanning detection of biological or chemical samples, obtain photoacoustic signals of multiple points of the sample, and then quickly image the sample.

Description

Technical Field

[0001] The invention belongs to the technical field of photoacoustic microfluidic detection, and in particular relates to a photoacoustic microfluidic detection system based on planar waveguide. Background Art

[0002] As a system-on-chip, microfluidics can conduct biological or chemical experiments in micrometer-scale space. Therefore, it is of great significance to achieve real-time detection of samples on microfluidics. However, current microfluidic detection technologies, such as laser-induced fluorescence and electrochemical detection, have the defects of contaminating samples and insufficient detection sensitivity. Therefore, a highly sensitive, fast-response, label-free real-time detection method is needed to detect samples in microfluidic chips. Photoacoustic detection is a detection method based on the photoacoustic effect. Due to its high sensitivity, good contrast, fast response, simple structure and label-free characteristics, people have begun to apply photoacoustic detection to the field of microfluidic detection.

[0003] The existing photoacoustic microfluidic systems use ultrasonic transducers as probes to detect photoacoustic waves. For example, some studies have achieved real-time detection of tumor cells (“Capture of circulating tumor cells using photoacoustic flowmetry and two phase flow”, Biomedical Optics 17(6), 061221 (June 2012)). Flow droplet imaging technology has also been developed (“Opto-acousto-fluidic microscopy for three-dimensional label-free detection of droplets and cells in microchannels”, Lab Chip, 2018, 18, 1292). Further research has achieved real-time counting of red blood cells (“Real-time red blood cell counting and osmolarity analysis using a photoacoustic-based microfluidic system”, Lab Chip, 2021, 21, 2586). However, these studies are inevitably affected by the defects of ultrasonic transducers based on piezoelectric materials and the complex process of microfluidic chip manufacturing. In view of the shortcomings of the current photoacoustic microfluidic system, such as limited detection range, difficulty in miniaturization, poor compatibility, and high cost, some researchers have developed a purely optical detection method based on polarized light and combined with a microfluidic chip, which has realized the detection of the photoacoustic signal of the sample. However, the microfluidic chip currently used is a combination of a microchannel and a prism, which only uses a single reflection of the prism. The detection light and the excitation light overlap at one point, realizing the single-point photoacoustic signal measurement of the sample, with a small detection area and a narrow range. In order to better study biological or chemical samples and image the samples, we need to scan and detect the samples to obtain more photoacoustic signals from the samples. Therefore, the development of a simple, economical, practical, large detection area, fast and high-performance photoacoustic microfluidic system is of great significance for the application and promotion of photoacoustic detection in microfluidic detection. Summary of the invention

[0004] The purpose of the present invention is to provide a photoacoustic microfluidic detection system based on planar waveguide which is simple, economical, practical, has a large detection area, and is fast and high-performance.

[0005] The present invention is implemented as follows: a planar waveguide-based photoacoustic microfluidic detection system, characterized in that the system comprises: a microfluidic chip module, a laser excitation module, a laser detection module block and a signal processing module; wherein,

[0006] The microfluidic chip module includes a microchannel and a planar waveguide arranged above the microchannel;

[0007] The laser excitation module is used to excite the target sample in the microchannel below the planar waveguide to emit ultrasonic waves;

[0008] The laser detection module is used to receive the photoacoustic signal generated by the target sample after being excited, and convert it into a voltage signal;

[0009] The signal processing module is used to receive and process the voltage signal of the laser detection module to obtain the optical signal of the target sample.

[0010] A further technical solution of the present invention is: the laser excitation module includes a two-dimensional galvanometer, and the two-dimensional galvanometer is used to control the excitation light to perform rapid scanning on the target sample in two vertical directions of x and y.

[0011] A further technical solution of the present invention is that the planar waveguide is a one-dimensional planar waveguide or a two-dimensional planar waveguide.

[0012] A further technical solution of the present invention is: the reflector structures on both sides of the two-dimensional planar waveguide are coated with metal films on both sides of the waveguide, and the mirror surfaces are placed vertically.

[0013] A further technical solution of the present invention is that the upper cladding of the one-dimensional planar waveguide and the two-dimensional planar waveguide is the same as the liquid medium in the microchannel in the microfluidic chip.

[0014] A further technical solution of the present invention is: the laser detection module introduces a phase-type photoacoustic sensor and uses a phase-type detection method to perform photoacoustic imaging.

[0015] The beneficial effects of the planar waveguide-based photoacoustic microfluidic detection system of the present invention are:

[0016] The invention has the advantages of simple structure, low cost, high integration and wide detection range, and can realize large-area rapid scanning detection of biological or chemical samples, obtain photoacoustic signals of multiple points of the samples, and then rapidly image the samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of Example 1 and Example 2 of the photoacoustic microfluidic detection system based on planar waveguide of the present invention;

[0018] Figure 2 Schematic diagram of the structure of the microfluidic chip in Example 1 of the planar waveguide-based photoacoustic microfluidic detection system of the present invention;

[0019] Figure 3Schematic diagram of the three-dimensional structure of the microfluidic chip in Example 2 of the photoacoustic microfluidic detection system based on planar waveguide of the present invention;

[0020] Figure 4 It is a front view of the three-dimensional structure of the microfluidic chip in Example 2 of the photoacoustic microfluidic detection system based on planar waveguide of the present invention;

[0021] Figure 5 It is a top view of the three-dimensional structure of the microfluidic chip in Example 2 of the photoacoustic microfluidic detection system based on planar waveguide of the present invention;

[0022] Figure 6 It is a simulation schematic diagram of a specific embodiment of the planar waveguide-based photoacoustic microfluidic detection system of the present invention;

[0023] Figure 7 It is a schematic diagram of theoretical calculation and simulation results of a specific embodiment of the planar waveguide-based photoacoustic microfluidic detection system of the present invention;

[0024] Figure 8 It is a schematic diagram of the structure of Example 3 of the photoacoustic microfluidic detection system based on planar waveguide of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a planar waveguide-based photoacoustic microfluidic detection system, which comprises a microfluidic chip module, a laser excitation module, a laser detection module block and a signal processing module.

[0026] Among them, the microfluidic chip module includes a microchannel and a planar waveguide arranged above the microchannel; the laser excitation module is used to excite the target sample in the microchannel below the planar waveguide to emit ultrasonic waves; the laser detection module is used to receive the photoacoustic signal generated by the target sample after being excited and convert it into a voltage signal; the signal processing module is used to receive and process the voltage signal of the laser detection module to obtain the optical signal of the target sample and display it.

[0027] The simple planar waveguide is composed of three layers of uniform medium. The middle medium layer is called the waveguide layer or core layer, and the medium layers on the upper and lower sides of the core layer are called cladding layers. By using the principle of multiple total internal reflections of light in the waveguide, each reflection point is used as a detection point to expand the detection area. In addition, it is simple to make and low in cost. Combining it with microfluidics technology is a simple and easy method to quickly scan and image samples.

[0028] The planar waveguide-based photoacoustic microfluidic detection system of the present invention has a simple structure, low cost, high integration, and a wide detection range. It can realize large-area rapid scanning detection of biological or chemical samples, obtain photoacoustic signals at multiple points of the samples, and then quickly image the samples.

[0029] Furthermore, in the planar waveguide-based photoacoustic microfluidic detection system of the present invention, the laser excitation module includes a two-dimensional galvanometer, which is used to control the excitation light to quickly scan the target sample in two perpendicular directions of x and y.

[0030] Furthermore, the planar waveguide is a one-dimensional planar waveguide or a two-dimensional planar waveguide.

[0031] Furthermore, the reflector structures on both sides of the two-dimensional planar waveguide are coated with metal films on both sides of the waveguide, and the mirrors are placed vertically.

[0032] Furthermore, the upper cladding of the one-dimensional planar waveguide and the two-dimensional planar waveguide is the same as the liquid medium in the microchannel in the microfluidic chip.

[0033] Furthermore, the laser detection module introduces a phase-type photoacoustic sensor and uses a phase-type detection method to perform photoacoustic imaging.

[0034] The following combination Figures 1 to 8 The structure and working principle of the planar waveguide-based photoacoustic microfluidic detection system of the present invention are further explained.

[0035] Example 1

[0036] like Figure 1 , 2 As shown, the laser excitation module includes a pulse excitation light source 5, a beam expander 6, an adjustable attenuation plate 7, a beam splitter 8, a two-dimensional galvanometer G, an objective lens 10, and a photoelectric probe. A pulse laser is emitted from the pulse excitation light source 5, collimated and amplified by the beam expander 6, filtered by the adjustable attenuation plate 7, and then split by the beam splitter 8. One beam of light enters the photoelectric probe 9 as a trigger signal for the subsequent signal processing module. The other beam of light 532 is reflected by the two-dimensional galvanometer G and focused by the objective lens 10 onto the sample 300 in the microchannel 200 of the microfluidic chip, exciting the target sample to emit ultrasonic waves.

[0037] The laser detection module includes a continuous laser light source 1, a polarizer 2, a quarter wave plate 3, a reflector M, a polarization beam splitter PBS and an optical probe 11. The continuous laser light source emits a continuous laser beam, which is converted into linear polarized light by the polarizer 2 and then converted into circular polarized light by the quarter wave plate 3. After the circular polarized light passes through the reflector M, it is incident from the side of the planar waveguide into the planar waveguide at a certain angle and undergoes multiple total internal reflections. Figure 2As shown, the one-dimensional planar waveguide includes a core layer 100 and an upper cladding layer 110. The microfluidic chip is encapsulated by the microchannel 200 of the lower layer and the one-dimensional planar waveguide above the microchannel. There is a liquid medium in the microchannel. When there is an ultrasonic wave in the microchannel on the lower surface of the planar waveguide, the refractive index of the liquid around the corresponding reflection point changes, and the energy of the P polarized light and the S polarized light in the reflected light of the corresponding point undergoes nonlinear changes with different responses, while the P polarized light and the S polarized light at other points have the same reflectivity. In the range where the incident angle is close to the total reflection angle, the P polarized light and the S polarized light are most sensitive to the change of the refractive index of water, and the signal difference between the two is also the largest. Therefore, by fine-tuning the reflector of the incident plane waveguide, the incident angle is reduced to just not causing total reflection, and this angle close to the total reflection angle is used as the incident angle. The reflected light 633 after multiple reflections in the planar waveguide is reflected by the reflector M again, and the S polarized light and the P polarized light in the reflected light are separated into two beams by the polarization beam splitter 9, which are respectively received by two probes of the high-bandwidth balanced light detector 11.

[0038] Each reflection point on the lower surface of the core layer in the planar waveguide is a detection point, which expands the detection area. The two-dimensional galvanometer G can control the two coordinate systems of the vertical coordinates of the excitation laser. The galvanometer G controls the excitation light 532 to perform rapid scanning in the x direction (horizontal direction) to excite photoacoustic signals at multiple points in the x direction on the sample. Each excitation can generate a photoacoustic signal. The optical probe can receive each photoacoustic signal and obtain photoacoustic signals at multiple points in the x direction of the sample.

[0039] The signal processing module 12 includes a filter, an amplifier and an oscilloscope. The change in the intensity difference between the detected P-polarized light and the S-polarized light is converted into a voltage signal by the balanced light detector in the laser detection module, and the interference signal is first filtered out by the filter, and then the signal is amplified by the amplifier, and finally the signal is collected by the high-bandwidth oscilloscope. Among them, the oscilloscope uses the photoelectric signal received by the photoelectric probe in the above-mentioned excitation module as a trigger, and the final display is the photoacoustic signal. The oscilloscope can quickly collect each photoacoustic signal, thereby realizing rapid imaging of the sample.

[0040] Embodiment 2:

[0041] like Figure 1 , 3 As shown, the laser excitation module includes a pulse excitation light source 5, a beam expander 6, an adjustable attenuation plate 7, a beam splitter 8, a two-dimensional galvanometer G, an objective lens 10, and a photoelectric probe. A pulsed laser is emitted from the pulse excitation light source 5, collimated and amplified by the beam expander 6, filtered by the adjustable attenuation plate 7, and then split by the beam splitter 8. One beam of light enters the photoelectric probe 9 as a trigger signal for the subsequent signal processing module. The other beam of light 532 is reflected by the two-dimensional galvanometer G and focused by the objective lens 10 onto the sample 300 in the microchannel 400 of the microfluidic chip, exciting the sample to emit ultrasonic waves.

[0042] The laser detection module includes a continuous laser light source 1, a polarizer 2, a quarter wave plate 3, a reflector M, a polarization beam splitter PBS and an optical probe 11. The continuous laser light source emits a continuous laser beam, which is converted into linear polarized light by the polarizer 2 and then converted into circular polarized light by the quarter wave plate 3. After the circular polarized light passes through the reflector M, it is incident from the side of the planar waveguide into the planar waveguide at a certain angle and undergoes multiple total internal reflections back and forth, forming a detection point at each reflection point on the lower surface. Figure 3 As shown in Figures 4 and 5, the two-dimensional plane waveguide includes a core layer 500, an upper cladding layer 510, and a reflector M placed on both sides. The microfluidic chip is encapsulated by the microchannel 200 in the lower layer and the two-dimensional plane waveguide above the microchannel. When there is ultrasound in the microchannel on the lower surface of the plane waveguide, the refractive index of the liquid around the corresponding reflection point changes, and the energy of the P polarized light and the S polarized light in the reflected light of the corresponding point undergoes nonlinear changes with different responses, while the reflectivity of the P polarized light and the S polarized light at other reflection points remains unchanged. In the range where the incident angle is close to the total reflection angle, the P polarized light and the S polarized light are most sensitive to the change of the refractive index of water, and the signal difference between the two is also the largest. Therefore, by fine-tuning the reflector of the incident plane waveguide, the incident angle is reduced to just not causing total reflection, and this angle close to the total reflection angle is used as the incident angle. After multiple reflections in the planar waveguide, the reflected light 634 is reflected by the reflector M again, and the S polarized light and P polarized light in the reflected light are separated into two beams by the polarization beam splitter 9, which are respectively received by two probes of the high-bandwidth balanced light detector 11.

[0043] like Figure 4 , 5 As shown, represents the reflection point on the upper surface of the core layer of a two-dimensional planar waveguide, It represents the reflection point on the lower surface of the core layer of the two-dimensional planar waveguide. Each reflection point on the lower surface of the core layer in the two-dimensional planar waveguide is a detection point, which further expands the detection area. The two-dimensional galvanometer G can control the two coordinate systems of the vertical coordinates of the excitation laser. The galvanometer G controls the excitation light 532 to perform rapid scanning in the two vertical directions of x and y, and excites photoacoustic signals of multiple points in the two vertical directions of x and y of the sample. Each excitation can generate a photoacoustic signal. The optical probe can receive each photoacoustic signal and obtain photoacoustic signals of multiple points in the two vertical directions of x and y of the sample.

[0044] The signal processing module includes a filter, an amplifier and an oscilloscope. The balanced light detector in the laser detection module converts the intensity difference between the detected P-polarized light and the S-polarized light into a voltage signal, which is first filtered out by a filter to remove interference signals, then amplified by an amplifier, and finally acquired by a high-bandwidth oscilloscope. The oscilloscope uses the photoelectric signal received by the photoelectric probe in the above-mentioned excitation module as a trigger, and the photoacoustic signal is finally displayed. The oscilloscope can quickly acquire each photoacoustic signal, thereby realizing rapid imaging of the sample.

[0045] Embodiment three:

[0046] like Figure 2 , 3 As shown in Figure 7, the laser excitation module includes a pulse excitation light source 3, a beam expander 4, an adjustable attenuation plate 5, a beam splitter 6, a two-dimensional galvanometer G, an objective lens 8 and a photoelectric probe 7. A pulse laser is emitted from the pulse excitation light source 3, collimated and amplified by the beam expander 4, filtered by the adjustable attenuation plate 5, and then split by the beam splitter 6, one of which enters the photoelectric probe 7 as a trigger signal for the subsequent signal processing module 10. The other beam of light 532 is reflected by the two-dimensional galvanometer G and focused by the objective lens 8 onto the sample 300 in the microchannel of the microfluidic chip, exciting the sample to emit ultrasonic waves.

[0047] The laser detection module includes a continuous laser light source 1, a polarizer P, a 1 / 2 wave plate HWP, a 1 / 4 wave plate QWP, a reflector M and a phase-type photodetector 9. The continuous laser light source emits a continuous laser beam, the linear polarization ratio of the beam is increased by the linear polarizer P, and the ratio between the P polarization component and the S polarization component is adjusted by the 1 / 2 wave plate and the 1 / 4 wave plate. After the detection light passes through the reflector M, it is incident from the side of the planar waveguide into the planar waveguide at a certain angle and undergoes multiple total internal reflections back and forth, and a detection point is formed at each reflection point on the lower surface. When there is an ultrasonic wave in the microchannel on the lower surface of the planar waveguide, the refractive index of the liquid around the corresponding reflection point changes, and the phase of the P polarized light and the S polarized light in the reflected light of the corresponding point undergoes nonlinear changes with different responses, and the phase difference between the P polarized light and the S polarized light at other reflection points remains unchanged. With an angle greater than the total reflection angle (arcsin (1.33 / 1.457)) as the incident angle, the reflected light of the detection light after multiple reflections in the planar waveguide is reflected by the reflector M and enters the phase-type photodetector through the linear polarizer.

[0048] like Figure 2 , 3 , combined with microfluidic chips based on one-dimensional and two-dimensional planar waveguide structures, large-area detection of samples can be achieved. The galvanometer scans the samples quickly, which can realize rapid scanning photoacoustic detection of samples.

[0049] The signal processing module includes a filter, an amplifier and an oscilloscope. The phase difference between the detected P-polarized light and S-polarized light is converted into a voltage signal by a phase-type photodetector. The interference signal is first filtered out by a filter, then the signal is amplified by an amplifier, and finally the signal is collected by a high-bandwidth oscilloscope. The oscilloscope uses the photoelectric signal received by the photoelectric probe in the above-mentioned excitation module as a trigger, and the final display is the photoacoustic signal, thereby realizing rapid photoacoustic imaging of the sample.

[0050] The present invention has carried out theoretical calculation and simulation on the situation of one-dimensional waveguide, as follows:

[0051] The refractive index of the core layer of the planar waveguide is 1.457, the refractive index of the upper cladding water is 1.333, and the refractive index of the lower cladding water is 1.33301. The total reflection angle is calculated to be arcsin(1.333 / 1.457) when the refractive index of water is 1.333. The detection light enters the planar waveguide at an angle of (π / 2-arcsin(1.333 / 1.457))rad. The reflectivity of the S-polarized light and the P-polarized light when the refractive index of water is 1.33301 is calculated to be Rs=0.9654 and Rp=0.9589 respectively. Then the total reflection angle after n reflections (Rs n -Rp n ) and (Rs n +Rp n ) ratio. Then we take a three-layer planar waveguide as a model, that is, the refractive index of the waveguide core is 1.457, the waveguide core width is set to 350um, the upper boundary is set as an impedance boundary, the refractive index is set to 1.333, representing the cladding above water, and the lower boundary is also an impedance boundary condition, the refractive index is set to 1.33301 to represent the effect of the photoacoustic effect on the refractive index of water, the waveguide core width is set to 350um, the length changes with the increase of reflection times, and the incident light is a Gaussian beam. Comsol software was used to simulate and calculate the detection light incident on the planar waveguide at an angle of (π / 2-arcsin(1.333 / 1.457))rad. After n reflections in the waveguide (Rs n -Rp n ) and (Rs n +Rp n ), the theoretical and simulation results are as follows Figure 6 , the figure shows (Rs n -Rp n ) and (Rs n +Rp n ) increases linearly with the increase of the number of reflections. It can be seen that the theoretical results are highly consistent with the simulation results, proving that the present invention is feasible.

[0052] The working principle of the planar waveguide-based photoacoustic microfluidic detection system of the present invention is described below.

[0053] Let the incident light intensity of the detection light be I, the intensities of the S polarized light and the P polarized light in the incident light be Is, Ip, Is=Ip, the reflectivity of the S polarized light and the P polarized light at each reflection point be Rs1, Rs2, Rs3...Rsn, Rp1, Rp2, Rp3...Rpn, and the intensities of the S polarized light and the P polarized light in the reflected light after n reflections be Isn, Ipn, that is

[0054] (1) Reflectivity of the S-polarized light at the i-th reflection point of the probe light in the waveguide

[0055] (2) The reflectivity of the P-polarized light at the i-th reflection point in the waveguide

[0056]

[0057] Right now

[0058] remember Then there is Right now

[0059] Take the logarithm of X, that is

[0060]

[0061] When the reflectances Rs and Rp of all points are the same, equation (3) becomes

[0062]

[0063] but

[0064] When only the reflectivity Rsx, Rpx of one of the reflection points changes, and the reflectivity of other points remains unchanged Rs, Rp, equation (3) becomes

[0065]

[0066] but

[0067] That is, the change in the reflectivity of S-polarized light and P-polarized light at each reflection point will cause the change in the reflected light Isn and Ipn.

[0068] The beneficial effects of the planar waveguide-based photoacoustic microfluidic detection system of the present invention are:

[0069] The invention has the advantages of simple structure, low cost, high integration and wide detection range, and can realize large-area rapid scanning detection of biological or chemical samples, obtain photoacoustic signals of multiple points of the samples, and then rapidly image the samples.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A photoacoustic microfluidic detection system based on planar waveguide, characterized in that: The system includes: a microfluidic chip module, a laser excitation module, a laser detection module and a signal processing module; wherein, The microfluidic chip module includes a microchannel and a planar waveguide arranged above the microchannel; The laser excitation module is used to excite the target sample in the microchannel below the planar waveguide to emit ultrasonic waves; The laser detection module is used to receive the photoacoustic signal generated by the target sample after being excited, and convert it into a voltage signal; The signal processing module is used to receive and process the voltage signal of the laser detection module to obtain the optical signal of the target sample; The laser excitation module includes a two-dimensional galvanometer, which is used to control the excitation light to quickly scan the target sample in two vertical directions of x and y; The planar waveguide is a one-dimensional planar waveguide or a two-dimensional planar waveguide; the one-dimensional planar waveguide comprises a two-part structure of a core layer and an upper cladding layer, and the two-dimensional planar waveguide comprises a four-part structure of a core layer, an upper cladding layer and reflectors placed on both sides; There is liquid medium in the microchannel. When there is ultrasound in the microchannel on the lower surface of the planar waveguide, the refractive index of the liquid around the corresponding reflection point changes, and the energy of the P-polarized light and the S-polarized light in the reflected light at the corresponding point undergoes nonlinear changes with different responses, while the reflectivity of the P-polarized light and the S-polarized light at other points is the same. The laser undergoes multiple total internal reflections in the planar waveguide, and each reflection point on the lower surface of the core layer in the planar waveguide serves as a detection point.

2. The planar waveguide-based photoacoustic microfluidic detection system according to claim 1, characterized in that: For the reflector structures on both sides of the two-dimensional planar waveguide, the surfaces of both sides of the waveguide are coated with metal films, and the mirror surfaces are placed vertically.

3. The planar waveguide-based photoacoustic microfluidic detection system according to claim 1, characterized in that: The laser detection module introduces a phase-type photoacoustic sensor and uses a phase-type detection method to perform photoacoustic imaging.

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