Microfluidic refractive index sensor based on concave reflection grating

Abstract

The utility model discloses a micro-fluidic refractive index sensor based on a concave reflection grating, which comprises a multilayer structure, the multilayer structure comprises a silicon dioxide top cover and a substrate, the substrate is provided with a trapezoidal grating structure layer, the trapezoidal grating structure layer comprises a thin film layer and a plurality of trapezoidal gratings arranged on the thin film layer, and the trapezoidal gratings are arranged on the thin film layer. The top of each trapezoidal grating is provided with a groove, the depth of the groove is 20-100 nm, and the width of the groove is 100-500 nm. The surface plasma resonance is excited on a metal-medium interface, and the micro-fluidic groove cavity is arranged between the silicon dioxide top cover and the grating structure, so that the space overlapping between a strong electric field and an object to be analyzed is obviously increased, and the sensitivity of refractive index sensing is improved; a concave microstructure is introduced into a common periodic grating structure, so that the binding capacity of the grating to a light field is enhanced, the light field is concentrated in a high-refractive-index area, and the quality factor of refractive index sensing is improved.

Description

Technical Field

[0001] The utility model relates to a microfluidic refractive index sensor based on a concave reflection grating, belonging to the technical field of micro-nano optoelectronics. Background Art

[0002] In recent years, with the growing demand for medical diagnosis, environmental testing, and forensic identification, the research and development of sensors has become increasingly important. Compared with traditional detection methods, surface plasmon resonance sensors have outstanding advantages such as label-free, real-time dynamic detection, and high sensitivity. They have broad application prospects in environmental monitoring, food safety, and early disease detection.

[0003] Surface plasmon resonance is very sensitive to changes in the surrounding environment. A small change in the refractive index of the interface medium will cause a shift in the resonance peak, which shows that surface plasmon resonance has great potential applications in sensor design. The grating structure can provide wave vector matching for the excitation of surface plasmon resonance, and greatly simplifies the optical device through structure-assisted coupling. Therefore, optical sensing technology using grating structure to realize surface plasmon resonance has received more and more attention and application.

[0004] However, existing technologies for optical sensors that use grating structures to achieve surface plasmon resonance mostly focus on improving the sensitivity of sensor devices, with less attention paid to the peak half width of the spectrum. The quality factors of these sensors are generally low. For example, Chinese patent application No. 2018106519091 discloses a refractive index sensor with a metal-dielectric-metal-dielectric (MDMD) grating structure, with a sensitivity of 1084nm / RIU, and its quality factor FoM value is given in the corresponding literature, which is only 23. The corresponding literature of this patent is Wang L, et al. Applied Optics, 2018. 57(25): 7338-7343; Chinese patent application No. 202021931132.3 discloses a nano-gold grating transmission microfluidic sensor based on surface plasmon resonance, with a sensitivity of 1063nm / RIU, and its quality factor FoM value is given in the corresponding literature, which is only 29.7. The corresponding literature of this patent is Wang M, et al. AOPC 2020, Beijing,Proc.of SPIE Vol. 11569: 115690U. Some studies have focused on the peak half width of the spectrum and the quality factor of the sensor, but have not yet focused on improving the quality factor. For example, Chinese patent application No. 2018103147896 discloses a refractive index sensor based on a metal-dielectric-metal (MIM) grating with a sensitivity of 1500 RIU / nm and a quality factor FoM value of 75; a gold-silicon nanowire array plasma grating sensor has a sensitivity of 1348 RIU / nm and a quality factor FoM value of 190, which is relatively high, but still has room for improvement. The corresponding literature is Wen L, et al. ACS Nano, 2019. 13(6): 6963-6972.

[0005] In actual sensing applications, the peak half width of the spectrum is directly related to the sensor's detection accuracy of the resonant wavelength. The narrower the peak half width of the spectrum, the higher the detection accuracy. The quality factor comprehensively considers the influence of sensitivity and peak half width on sensing performance. When the sensitivity of the sensor is basically the same, the larger the quality factor, the higher the detection accuracy, that is, the stronger the comprehensive sensing performance of the sensor. Therefore, it is obviously necessary to provide a new type of optical sensor device that uses a grating structure to realize surface plasmon resonance, so that it has a high quality factor while maintaining high sensitivity. Utility Model Content

[0006] The utility model aims to provide a novel microfluidic refractive index sensor based on a concave reflection grating, aiming to solve the technical problem that the quality factor of high-sensitivity sensor devices in the prior art is generally low.

[0007] To achieve the above-mentioned invention object, the technical solution adopted by the utility model is: a microfluidic refractive index sensor based on a concave reflection grating, comprising a multilayer structure, the multilayer structure comprising a silicon dioxide top cover and a substrate, a trapezoidal grating structure layer is provided on the substrate, the trapezoidal grating structure layer comprises a thin film layer and a plurality of trapezoidal gratings arranged on the thin film layer, the trapezoidal grating period is 1210-1290nm, the trapezoidal grating height is 95-155nm, the lower bottom width of the trapezoidal grating is 625-1250nm, and the upper bottom width is 600-1000nm, each trapezoidal grating is provided with a groove at the top, the groove depth is 20-100nm, and the width is 100-500nm;

[0008] There is a slit layer between the silicon dioxide top cover and the trapezoidal grating structure layer as a microfluidic cavity, and the height of the microfluidic cavity is 1100-1900nm. The microfluidic cavity is provided with a test material inlet on one side and a test material outlet on the other side, and the test material passes through the microfluidic cavity for sensing test.

[0009] In a preferred technical solution, the period of the trapezoidal grating is 1210-1260nm, the height of the trapezoidal grating is 110-140nm, the width of the lower base is 900-1100nm, and the width of the upper base is 700-800nm.

[0010] In a preferred technical solution, the groove depth is 60-90 nm, the groove width is 200-400 nm, and the microfluidic groove cavity height is 1300-1700 nm.

[0011] In a preferred technical solution, the refractive index of the object to be measured is 1.33-1.37.

[0012] In a preferred technical solution, the thin film layer is a gold thin film layer.

[0013] In a preferred technical solution, the substrate is a silicon substrate.

[0014] In a preferred technical solution, the incident angle of the incident light is 0-10°.

[0015] In a preferred technical solution, the wavelength of the incident light is 1500nm-1660nm.

[0016] A detection method based on the sensor described in the above scheme comprises the following steps:

[0017] (1) setting the incident light to be incident on the sensor surface;

[0018] (2) performing wavelength scanning calculation to obtain a reflection spectrum of the incident light passing through the refractive index sensor;

[0019] (3) When the refractive index of the object to be tested changes, different reflection spectrum curves corresponding to different refractive indices of the object to be tested in the microfluidic cavity are recorded;

[0020] (4) The change in the refractive index of the object to be measured in the microfluidic cavity is measured by the change in the wavelength corresponding to the minimum value of the reflection spectrum.

[0021] In a preferred technical solution, the incident angle of the incident light onto the sensor surface is 0-10 degrees.

[0022] In a preferred technical solution, the wavelength of the incident light is 1500nm-1600nm.

[0023] Due to the application of the above technical solution, the utility model has the following advantages compared with the prior art:

[0024] The utility model application utilizes a grating to provide wave vector matching, excites surface plasma resonance at a metal-medium interface, and combines plasma resonance with guided mode resonance; a microfluidic cavity is formed between a silicon dioxide top cover and a gold grating structure, and the strongest part of the electric field intensity is almost concentrated in the microfluidic cavity, so that more light fields leak into an object to be measured with a low refractive index, thereby ensuring high sensitivity of refractive index sensing; a concave microstructure is introduced into a periodic trapezoidal grating structure, so that the design of the grating structure is more flexible, and the grating's ability to bind the light field is enhanced, resulting in the light field being concentrated in a high refractive index region, thereby improving the quality factor of the refractive index sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a three-dimensional structural schematic diagram of the microfluidic refractive index sensor device based on the concave reflection grating of the utility model (the front part is removed to show the internal structure).

[0026] Figure 2 This is a relationship diagram of the reflection, transmission and absorption conditions corresponding to different wavelengths under the conditions of vertical incidence and the refractive index of the object to be measured being 1.33 for the sensor in Example 1 of the utility model.

[0027] Figure 3 This is a simulated electric field intensity distribution diagram of the sensor in Example 1 of the utility model under the condition of vertical incidence and incident light wavelength of 1547.8nm.

[0028] Figure 4 It is a schematic diagram of reflection spectrum curves corresponding to different refractive indices of the object to be measured under vertical incidence conditions of the sensor in Example 1 of the utility model.

[0029] Figure 5 This is a graph showing the relationship between the different refractive indices of the object to be measured and the corresponding resonance wavelengths under vertical incidence conditions in the sensor of the first embodiment of the present invention.

[0030] Figure 6 Schematic diagram of reflection spectrum curves corresponding to different refractive indices of the object to be measured under vertical incidence conditions of the sensor in Example 2 of the utility model.

[0031] Figure 7 This is a graph showing the relationship between the different refractive indices of the object to be measured and the corresponding resonance wavelengths under vertical incidence conditions in the second embodiment of the present invention.

[0032] Figure 8 Schematic diagram of reflection spectrum curves corresponding to different refractive indices of the object to be measured under vertical incidence conditions of the sensor in Example 3 of the utility model.

[0033] Fig. 9 This is a graph showing the relationship between the different refractive indices of the object to be measured and the corresponding resonance wavelengths under vertical incidence conditions in the sensor of Example 3 of the utility model.

[0034] Fig.10 It is a cross-sectional view of the microfluidic refractive index sensor device based on the concave reflection grating of the present utility model.

[0035] Among them: 1. substrate; 2. thin film layer; 3. trapezoidal grating; 4. microfluidic cavity; 5. silicon dioxide top cover; 6. groove. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0037] Embodiment 1

[0038] See also Figure 1 or Fig.10 As shown, the utility model discloses a microfluidic refractive index sensor based on a concave reflection grating, comprising a multilayer structure, wherein the multilayer structure comprises a silicon dioxide top cover 5 and a substrate 1, wherein a trapezoidal grating structure layer is provided on the substrate 1, wherein the trapezoidal grating structure layer comprises a thin film layer 2 and a plurality of trapezoidal gratings 3 arranged at equal intervals on the thin film layer, wherein the trapezoidal grating period is 1210-1290nm, the trapezoidal grating height is 95-155nm, the lower bottom width of the trapezoidal grating is 625-1250nm, and the upper bottom width is 600-1000nm, and a groove 6 is provided on the top of each trapezoidal grating 3, wherein the groove 6 has a depth of 20-100nm and a width of 100-500nm;

[0039] A slit layer is provided between the silicon dioxide top cover and the trapezoidal grating structure layer as a microfluidic cavity 4 . The height of the microfluidic cavity 4 is 1100-1900 nm. The object to be tested passes through the microfluidic cavity 4 for sensing test.

[0040] See also Figure 1In this embodiment, a fluid channel inlet is opened on the left side of the substrate, and a fluid channel outlet is opened on the right side of the substrate. The object to be tested enters the microfluidic cavity through the fluid channel inlet and flows out of the microfluidic cavity through the fluid channel outlet. Figure 1 , Fig.10 The downward arrow represents incident light, and the upward arrow represents reflected light.

[0041] The substrate 1 in this embodiment can be a silicon substrate, which can be made into a U-shaped structure in cross section to form a cavity with the top cover, the thin film layer 2 can be a gold thin film layer, and the trapezoidal grating 3 can be a gold trapezoidal grating.

[0042] In the first embodiment, the preferred trapezoidal grating period is 1250nm, the designed trapezoidal grating height is 125nm, the designed trapezoidal grating bottom width is 1000nm, the designed trapezoidal grating top width is 750nm, the designed groove depth is 80nm, the designed groove width is 400nm, and the designed microfluidic slot cavity height is 1500nm. The object to be tested is sensed through the microfluidic slot cavity. Microfluidic technology is used to accurately control the fluid to be analyzed in the microfluidic slot cavity to meet the sensing requirements.

[0043] First, the light source is set to emit incident light vertically incident on the sensor surface, and the refractive index of the analyte is set to 1.33; a wavelength scanning calculation is performed to solve the 1500nm-1600nm band, and the spectral response within the band is obtained, including the transmission spectrum, reflection spectrum and absorption spectrum.

[0044] like Figure 2 As shown, the horizontal axis is the wavelength, the vertical axis is the spectral response corresponding to the refractive index of the object to be measured when n=1.33, the solid line represents the reflection spectrum, the dashed line represents the transmission spectrum, and the dotted line represents the absorption spectrum. The transmittance of the gold grating to the incident light in the 1500nm-1600nm band is always zero, so this application will discuss the reflection spectrum.

[0045] like Figure 3 The figure shows the simulated electric field intensity distribution when the incident light wavelength is 1547.8nm. The light field energy is highly concentrated in the microfluidic cavity, which triggers the enhanced resonance absorption, resulting in a sharp decrease in the reflected light energy and the formation of an obvious reflection valley in the reflection spectrum. At this time, a slight change in the background refractive index will cause the position of the reflection valley to shift.

[0046] Sensitivity (S) is usually defined as the change in wavelength per unit refractive index of the analyte, which can be expressed by the following formula. It represents the change in the resonant wavelength, that is, the wavelength shift corresponding to the reflection valley we are discussing. Indicates the change in the refractive index of the analyte.

[0047]

[0048] The peak half width (FWHM) refers to the peak width corresponding to half of the peak value on the spectrum line. The narrower the output spectrum peak half width, the higher the detection accuracy. The quality factor FoM value is defined as the ratio of sensitivity to peak half width, which can be expressed by the following formula. This performance index can comprehensively reflect the sensitivity and peak half width of the sensor. The larger the quality factor, the stronger the sensor's sensing performance.

[0049]

[0050] This embodiment also discloses a detection method for a microfluidic refractive index sensor based on a concave reflection grating, comprising the following steps: (1) setting the incident light to be incident on the sensor surface; (2) performing wavelength scanning calculation to obtain a reflection spectrum of the incident light passing through the refractive index sensor; (3) when the refractive index of the object to be tested changes, recording different reflection spectrum curves corresponding to different refractive indices of the object to be tested in the microfluidic groove cavity; (4) measuring the change in the refractive index of the object to be tested in the microfluidic groove cavity by the change in the wavelength corresponding to the minimum value of the reflection spectrum line.

[0051] Figure 4 This is a schematic diagram of the reflection spectrum curve corresponding to different refractive indices of the object to be tested in the microfluidic slot cavity when using the microfluidic refractive index sensor based on the concave reflection grating to detect vertical incidence. Set different refractive indices of the object to be tested in the microfluidic slot cavity, and the refractive index parameter gradually increases from 1.33 to 1.37 in steps of 0.01. Scan the wavelength of the 1520nm-1620nm band to obtain Figure 4 By observing these five reflection spectrum curves, it can be found that the reflection spectrum curves appear red shifted as the refractive index of the object to be measured in the microfluidic cavity increases. Figure 4 It can be seen that when the refractive index of the object to be measured increases from 1.33 to 1.37, the wavelength corresponding to the minimum value of its reflection spectrum curve increases from 1547.8nm to 1588.4nm.

[0052] Figure 5 The figure is a relationship diagram between different refractive indices of the object to be measured in the microfluidic cavity and the corresponding resonance wavelength when the microfluidic refractive index sensor based on the concave reflection grating described in the present application is used to detect the vertical incidence.

[0053] Depend on Figure 4 and Figure 5It can be obtained that the refractive index sensitivity is 1015nm / RIU, the peak half width of the reflection spectrum is 1.3nm, and finally the quality factor FoM value can be obtained to be 780.88. Compared with the existing optical sensor using grating structure to realize surface plasmon resonance as shown in the background technology part, the sensitivity of the sensor described in this solution remains basically unchanged, and the quality factor is significantly increased, that is, the sensor described in this solution has both high sensitivity and high quality factor.

[0054] Table 1 shows the calculation results of the sensitivity, peak half width and quality factor FoM value of the microfluidic refractive index sensor based on the concave reflection grating of the present invention when the incident angle changes from 0° to 10° in steps of 2°. As shown in Table 1, when the incident angle is 10°, the refractive index sensitivity is 836nm / RIU, the reflection spectrum peak half width is 3nm, and the quality factor FoM value is 278.67, which still has good sensing performance.

[0055] Table 1 Calculation results of sensitivity (S), peak half width (FWHM) and quality factor FoM value when the incident angle changes from 0° to 10° in steps of 2°

[0056] θ (°) S (nm / RIU) FWHM (nm) FoM 0 1015 1.3 780.77 2 1010 1.3 776.92 4 1080 3.1 348.387 6 840 1.7 494.118 8 990 3.4 247.5 10 836 3 278.67 Embodiment 2

[0057] The trapezoidal grating period is 1210nm, the trapezoidal grating height is 125nm, the lower bottom width of the trapezoidal grating is 1000nm, the upper bottom width of the trapezoidal grating is 750nm, the groove depth is 80nm, the groove width is 400nm, the microfluidic slot cavity height is 1500nm, and the object to be tested is sensed through the microfluidic slot cavity, see Figure 6 , Figure 7 The wavelength of 1560nm-1660nm band was scanned, and the sensitivity was calculated by the formula to be 1100nm / RIU, the peak half width was 3nm, and the quality factor FoM value was 366.67. Embodiment 3

[0058] The period of the trapezoidal grating is 1250nm, the height of the trapezoidal grating is 125nm, the bottom width of the trapezoidal grating is 1000nm, the top width of the trapezoidal grating is 750nm, the groove depth is 80nm, the groove width is 300nm, the height of the microfluidic slot is 1500nm, and the object to be tested is sensed through the microfluidic slot, see Figure 8 , Fig. 9 The wavelength of 1520nm-1610nm band was scanned, and the sensitivity was calculated by the formula to be 1010nm / RIU, the peak half width was 1.75nm, and the quality factor FoM value was 577.14.

[0059] In summary, this technical solution is a microfluidic refractive index sensing technology based on a concave reflection grating, which has outstanding characteristics such as high sensitivity, high quality factor, label-free, and real-time dynamic detection. It has broad application prospects in the fields of environmental monitoring, food safety, and early disease detection.

[0060] There are many implementation methods for this technical solution. All technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of this technical solution.

Claims

1. A microfluidic refractive index sensor based on a concave reflection grating, comprising a multilayer structure, characterized in that: The multilayer structure includes a silicon dioxide top cover and a substrate, a trapezoidal grating structure layer is provided on the substrate, the trapezoidal grating structure layer includes a thin film layer and a plurality of trapezoidal gratings arranged on the thin film layer at equal intervals, the trapezoidal grating period is 1210-1290nm, the trapezoidal grating height is 95-155nm, the lower bottom width of the trapezoidal grating is 625-1250nm, the upper bottom width is 600-1000nm, each trapezoidal grating is provided with a groove at the top, the groove depth is 20-100nm, and the width is 100-500nm; A slit layer is provided between the silicon dioxide top cover and the trapezoidal grating structure layer as a microfluidic cavity, the height of the microfluidic cavity is 1100-1900nm, and the object to be tested is subjected to sensing test through the microfluidic cavity.

2. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The period of the trapezoidal grating is 1210-1260nm, the height of the trapezoidal grating is 110-140nm, the width of the lower base is 900-1100nm, and the width of the upper base is 700-800nm.

3. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The groove has a depth of 60-90 nm and a width of 200-400 nm.

4. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The microfluidic groove cavity height is 1300-1700nm.

5. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The refractive index of the object to be measured is 1.33-1.

37.

6. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The incident angle of the incident light is 0-10°.

7. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The wavelength of the incident light is 1500nm-1660nm.

8. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The thin film layer is a gold thin film layer.

9. The microfluidic refractive index sensor based on concave reflection grating according to claim 1, characterized in that: The substrate is a silicon substrate.

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