D-type dual-core PCF-spr refractive index sensor and detection system

Abstract

The application discloses a D-type double-core PCF-SPR refractive index sensor and a detection system, belongs to the technical field of optical fiber sensing, and is characterized in that a core single hole is arranged in the center of a PCF cladding, a hexagonal outer air hole is arranged outside the core single hole, two symmetrical polishing surfaces are polished on both sides of the PCF cladding area and a micro channel is formed in the center, and an Au layer and a TiO2 layer are sequentially arranged at both ends outside the polishing surfaces. The polishing surfaces are coated with a sensitizing material, the SPR effect of the sensor can be enhanced, the design that the polishing surfaces are polished on both sides and a micro channel is formed in the middle and the existence of the core single hole make the evanescent wave generated by the fiber core and the Au-TiO2 coated on the polishing surface form a double-core coupling effect, and the SPR effect is more remarkable. It is verified that the RI identification range of the sensor is 1.26-1.41, the refractive index sensitivity is as high as 24,600 nm / RIU, and therefore the sensor has a good application prospect in the fields of environmental detection, medical diagnosis and biochemical sensing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber sensing, and particularly relates to a D-type double-core PCF-SPR refractive index sensor and a hemoglobin concentration detection system based on the same. BACKGROUND

[0002] Abnormal increase or decrease of hemoglobin concentration and other abnormal conditions of hemoglobin concentration will seriously threaten people's health. Decrease of hemoglobin concentration indicates that the human body has anemia symptoms, which may be caused by various diseases including iron deficiency anemia, aplastic anemia, megaloblastic anemia, myelodysplastic syndrome, and the like. Increase of hemoglobin concentration is commonly seen in myeloproliferative diseases, such as polycythemia vera, essential thrombocythemia, and the like. Hemoglobin detection is an important link for diagnosing and treating diseases related to abnormal hemoglobin concentration in clinical practice. However, some existing methods for detecting hemoglobin concentration cannot achieve real-time feedback and rapid detection, and therefore, it is of great practical significance to develop a hemoglobin concentration detection system and method that is effective, sensitive in feedback, and reliable in results.

[0003] In recent years, optical sensing methods are commonly used to detect the concentration of proteins in a solution, and surface plasmon resonance (SPR) sensing technology is a kind of optical sensing technology that has developed rapidly. SPR occurs when the propagating light hits the metal film at the surface interface at the matching frequency of the incident photons and the surface electrons. SPR detects the collective oscillation of free electrons, in which the light propagates into the metal film called plasmonic metal, and these free electrons are called surface plasmons. Any slight change in the refractive index (RI) near the plasmonic metal will cause a significant change in the effective mode refractive index of the core. The effective RI of the surface plasmon polariton (SPP) mode is also changed, and then the shift of the resonance wavelength can be detected. The outer surface of the optical fiber can be directly placed with the plasmonic metal / liquid to be detected. During the detection process, the wavelength sensitivity (WS) is obtained by measuring the optical signal of the measured substance, so as to infer the refractive index and concentration of the measured substance attached to the surface of the sensor metal film. SPR technology has been widely used in the fields of life science, medical diagnosis, food safety, and the like due to its high sensitivity, small size, real-time detection, and other outstanding advantages, and has become one of the most promising sensing technologies.

[0004] The emergence of photonic crystal fiber (PCF) further promotes the development of the field of optical sensing. PCF is composed of periodically arranged air holes, and different designs of air holes make it contain corresponding transmission modes. Compared with traditional sensors, PCF sensors have special advantages such as flexible and variable structure layout, high sensitivity, and low transmission loss. In recent years, SPR has been introduced into PCF, and PCF-SPR based on surface plasmon resonance has become a new type of efficient detection technology for detecting biochemical substances. And because the continuous blood hemoglobin detection based on optical method does not consume the measured substance blood hemoglobin, and this method is not affected by the electrical signal of bioelectricity, the refractive index and concentration of the measured substance can be measured in real time, so the miniaturized PCF-SPR sensor is widely used in biological detection.

[0005] However, the previously proposed PCF-SPR sensors generally have the problems of narrow refractive index detection range and low sensitivity. For example, G. An et al. conceived a gold-coated D-shaped PCF-SPR sensor, the detection range of which is 1.33-1.38, and the maximum wavelength sensitivity (WS) is 10,493 nm / RIU, reaching the highest at 1.38. In 2018, Chen et al. proposed a D-shaped PCF sensor with a WS of 11,055 nm / RIU. In 2020, Li et al. designed an Ag-graphene layer coated PCF-SPR sensor with a U-shaped groove, which showed a WS of 12,600 nm / RIU when the RI of the analyte changed from 1.33 to 1.41. The highest WS of these sensors is generally in the range of 6000-13000 nm / RIU, so its sensitivity still needs to be improved.

[0006] In order to further improve the performance of the PCF-SPR sensor, the person skilled in the art proposes a scheme of coating silver (Ag), gold (Au), indium tin oxide (ITO), zirconium nitride (ZrN), titanium nitride (TiN), titanium dioxide (TiO2), graphene and other materials on the polished surface of the D-shaped structure optical fiber to excite surface plasmon resonance. As disclosed in Chinese patent CN 112858186 A, a birefringent PCF refractive index sensor based on a D-shaped double-metal coating is composed of a D-shaped PCF formed by polishing part of the cladding region, titanium dioxide and a gold film. The D-shaped design of the PCF structure and the asymmetric arrangement of the air holes make the evanescent wave generated by the core leak more to the cladding, and the PCF-SPR effect is stronger. A certain thickness of TiO2 material is deposited between the gold film and the substrate material, which not only helps to firmly attach the gold film to the quartz fiber, but also plays a sensitizing role. The sensor can achieve high sensitivity detection in the effective refractive range of 1.37-1.42, with an average wavelength sensitivity of 7920 nm / RIU, and a maximum wavelength sensitivity of up to 16000 nm / RIU. The WS has been significantly improved, but the above-mentioned sensor structures can only identify analytes with RI greater than 1.33, and the refractive index detection range is obviously limited.

[0007] Therefore, further research is needed on the sensor structure, and a PCF-SPR biosensor with high sensitivity and capable of identifying analytes with RI less than 1.33 for detecting hemoglobin concentration in blood will have very important practical significance and will have extremely high application prospects in the field of optoelectronic sensing. SUMMARY

[0008] The purpose of the present application is to solve the problems of low sensitivity and narrow detection range of existing PCF-SPR biosensors, and to propose a D-shaped double-core PCF-SPR refractive index sensor that can be efficiently used for hemoglobin concentration detection.

[0009] The present application is realized as follows: a D-shaped double-core PCF-SPR refractive index sensor is provided, which has a core single hole in the center of the cladding of the photonic crystal optical fiber, a hexagonally distributed outer layer air hole in the cladding outside the core single hole, two symmetrical polished surfaces formed by polishing a certain depth on both sides of the PCF cladding region and a microchannel structure formed in the center, and a fixed Au layer and a TiO2 layer are sequentially arranged at the outer sides of the two ends of the polished surface.

[0010] Further, the diameter of the microchannel is 2.2-2.4 μm.

[0011] Further, the thickness of the Au layer is 28-30 nm, and the thickness of the TiO2 layer is 8-10 nm.

[0012] Further, the outer layer air holes include four symmetrically distributed outer layer small air holes and six symmetrically distributed outer layer large air holes, the outer layer small air holes are close to the core single-hole design, and the outer layer large air holes are arranged outside the outer layer small air holes; the core single-hole has a hole diameter of 0.12-0.22 μm, the outer layer small air holes have a diameter of 0.62-0.72 μm, and the outer layer large air holes have a diameter of 1.4-1.5 μm.

[0013] Further, the polishing depth H is 3.55-3.65 μm.

[0014] Further, the RI identification range of the sensor is 1.26-1.41, the maximum wavelength sensitivity obtained by the sensor is 24,600 nm / RIU, and the RI resolution is 4.07*10 -6 RIU.

[0015] Preferably, the core single-hole has a hole diameter of 0.22 μm.

[0016] Preferably, the micro-channel has a diameter of 2.2 μm.

[0017] The D-type double-core PCF-SPR refractive index sensor can be used to establish a hemoglobin concentration detection system, which includes an optical tunable source OTS, an input optical fiber, the D-type double-core PCF-SPR refractive index sensor, an output optical fiber, an optical spectrum analyzer OSA, and a computer, which are connected in sequence through a single-mode optical fiber SMF, the outer surface of the TiO2 layer of the D-type double-core PCF-SPR refractive index sensor is coated with a layer of silane coupling agent, the analyte or sensing layer is located outside the PCF, and the input and output of the hemoglobin solution to be measured are controlled by a pump; when the analyte and the thin film on the surface of the optical fiber interact, the blue shift or red shift of the loss peak can be observed, and then the spectrum diagram is obtained by monitoring the OSA, and finally the spectrum obtained by the optical spectrum analyzer is analyzed, and the accurate concentration of the protein in the blood can be calculated by combining the spectrum diagram with the wavelength shift and the refractive index curve.

[0018] Further, the silane coupling agent coated on the outer surface of the TiO2 layer of the D-type double-core PCF-SPR refractive index sensor is a silane coupling agent KH560 with a cycloalkyl group, and the thickness of the silane coupling agent layer is 1.94-1.96 μm.

[0019] Advantages:

[0020] 1. The D-type double-core PCF-SPR refractive index sensor disclosed in the application is subjected to double-side polishing treatment in the cladding region, and the structure design of the upper and lower double-side polishing and the micro-channel formed in the center can effectively improve the absorption of the core to the reflected and scattered energy and improve the coupling strength between the core mode and the SPP mode.

[0021] 2. The Au-TiO2 coating on both sides of the microchannel in the application can enhance the interaction between the evanescent wave and the analyte, so the combination can better constrain the energy dissipation of the core and the SPP mode when the strong coupling occurs under the condition of meeting the phase matching condition; compared with pure Au coating, coating a small amount of TiO2 can significantly enhance the adsorption effect of Au on the quartz fiber, and a large number of electrons on the surface will attract the field from the core, improving the coupling result between the core mode and the SPP mode;

[0022] 3. The single-hole core design in the PCF helps to adjust the effective RI of the core mode and thus affect the mode coupling, the hexagonal arrangement of the outer air holes can control the propagation direction of light, limit the scattering of light and thus reduce the loss, and the geometric arrangement mode of the outer air holes is simple, which is also helpful for production and manufacturing;

[0023] 4. The refractive index sensor based on the photonic crystal fiber surface plasmon resonance disclosed in the application has a detection range of 1.26-1.41 RIU, and can identify analytes with an RI less than 1.33, which is a major breakthrough compared with existing sensing materials, and the refractive index sensitivity is as high as 24,600 nm / RIU, and the resolution is 4.07x10 -6 ;

[0024] 5. The PCF-SPR refractive index sensor disclosed in the application not only coats TiO2 on the polished surface to help tune the wavelength of the resonance peak, but also further coats epoxy-based silane coupling agent KH560 on the outer surface of TiO2 when the sensor is applied to a hemoglobin concentration detection system, KH560 has specific adsorption properties for protein molecules, and the TiO2 surface has abundant active hydroxyl groups, which are easy to be surface functionalized with KH560, the use of KH560 for surface modification of the sensor forms a biological membrane that specifically adsorbs protein molecules and does not interact with other substances in the solution, and the structure can enhance the adsorption of the sensor to hemoglobin molecules;

[0025] 6. The D-shaped double-core PCF-SPR sensor disclosed in the application solves the problems of low sensitivity and low biological molecule adsorption of traditional sensors, and is very suitable for use in the fields of biological sensing and medical diagnosis. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1is the system structure schematic diagram of the hemoglobin concentration detection system based on the D-type double-core PCF-SPR refractive index sensor, wherein, 1-optical tunable source (OTS), 2-single-mode optical fiber (SMF), 3-D-type double-core PCF-SPR refractive index sensor, 4-hemoglobin molecules, 5-optical spectrum analyzer (OSA), 6-computer, 7-silicon dioxide, 8-Au layer, 9-TiO2 layer, 10-core single hole, 11-outer small air hole, 12-outer large air hole, 13-silane coupling agent, 14-analyte, 15-microchannel;

[0027] Figure 2 is the dispersion relationship diagram between the core mode and the SPP mode when the D-type double-core PCF-SPR refractive index sensor prepared in example one is coupled;

[0028] Figure 3 is the relationship diagram between the core single hole diameter size change and the loss spectrum in the D-type double-core PCF-SPR refractive index sensor prepared in example one;

[0029] Figure 4 is the relationship diagram between the microchannel diameter size change and the loss spectrum in the D-type double-core PCF-SPR refractive index sensor prepared in example one;

[0030] Figure 5 is the relationship curve simulation diagram between the wavelength and the normalized resonance loss peak intensity under different refractive indexes of the D-type double-core PCF-SPR refractive index sensor prepared in example one;

[0031] Figure 6 is the relationship diagram between the external refractive index and the resonance peak wavelength when the D-type double-core PCF-SPR refractive index sensor prepared in example one is used for detection. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present application are described in detail below, so that the advantages and features of the present application can be more easily understood by those skilled in the art, and the protection scope of the present application is more clearly and definitely defined.

[0033] Example one, a D-type double-core PCF-SPR refractive index sensor

[0034] Figure 1The structure diagram of the D-type double-core PCF-SPR refractive index sensor and the system structure diagram of the hemoglobin concentration detection system based on the same are provided, the material of the photonic crystal fiber is silica 7, a core single hole 10 is arranged at the center of the cladding of the photonic crystal fiber, a plurality of outer air holes in a hexagonal distribution are arranged in the cladding outside the core single hole 10, and the outer air holes include four symmetrically distributed outer small air holes 11 and six symmetrically distributed outer large air holes 12, the air holes can be manufactured by using capillaries with different diameters to scale the air holes to different sizes, the outer small air holes 11 are designed close to the core single hole 10, the outer large air holes 12 are arranged outside the outer small air holes 11, the diameter d2 of the outer small air holes 11 is 0.72 μm, the hole center distance d of the outer small air holes 11 and the core single hole 10 is 1.96 μm, and the diameter d3 of the outer large air holes 12 is 1.4 μm. The hexagonal hole structure design can not only shorten the electron transport distance, thereby improving the electron transport capacity of the electrons, but also tune the wavelength of the resonance peak.

[0035] Two symmetric polishing surfaces are formed on both sides of the PCF cladding area by polishing to a certain depth, the polishing depth H is preferably 3.65 μm, and a fixed Au layer 8 and a TiO2 layer 9 are uniformly coated on the polishing surfaces in sequence by using a chemical vapor deposition (CVD) technique, the thickness of the Au layer 8 is 30 nm, the thickness of the TiO2 layer 9 is 10 nm, the TiO2 layer 9 can not only enhance the sensitivity of the sensor but also enhance the adsorption of the nanometer gold particles to the quartz fiber, in addition, the nanometer TiO2 has good biocompatibility as a biologically inert material.

[0036] In the embodiment, the polishing surfaces are coated with a sensitizing material at both ends, the design can tune the effect of strong coupling between the central core mode and the surface plasmon mode, and the wavelength sensitivity of the sensor can be obtained by measuring the shift of the resonance wavelength of the loss peak of the measured substance. When detecting the hemoglobin concentration of blood, TiO2 is used as the outer sensing layer of the sensor, which can promote the selection of hemoglobin molecules 4 and ensure the smoothness of the transportation of the hemoglobin molecules 4.

[0037] In order to further improve the absorption of the core to the reflected and scattered energy and improve the coupling strength between the core mode and the SPP mode, in addition to the polishing treatment on both sides of the cladding of the photonic crystal fiber, an arc-shaped microchannel is integrally polished at the middle position of the polishing surface, and the diameter dy of the microchannel is 2.2-2.4 μm. The double-sided polishing microchannel design of the PCF and the existence of the central single small air hole (core single hole) make the evanescent wave generated by the core and the Au-TiO2 coated on the polishing surface form a double-core coupling effect, and the SPR effect is more significant.

[0038] Figure 2The dispersion relation between the core mode and the SPP mode in the coupled mode is shown when the phase matching condition is met. A limiting loss peak can be observed in a narrow band, which shows a wavelength shift corresponding to any change in the RI of the dielectric medium adjacent to the metal layer. Under resonant conditions, since the real part of the effective RI of the core mode matches the effective RI of the surface plasmon mode, the maximum energy is exchanged from the core mode to the surface plasmon mode, that is, when the incident wavelength meets a certain value, most of the energy of the incident light is converted into the energy of the plasma wave (SPW), causing the energy of the reflected light to drop sharply, and a resonant absorption peak appears in the reflection spectrum. The incident wavelength at this time is called the resonant wavelength of the SPR. In the core mode (such as Figure 2 As shown in the illustration (a), the sensor collects most of the energy. Figure 2 As can be clearly seen from the inset (b) of Figure 2, in the SPP mode, the energy at the interface between the metal surface and the analyte is fully penetrated. However, at a wavelength of 0.899 μm, strong coupling occurs when the phase matching condition is met ( Figure 2 In the illustration (c), the loss reaches a peak of 60.23dB / cm.

[0039] Figure 3 The curve of the loss spectrum changing with wavelength when the diameter d1 of the core single hole 10 varies in the range of 0.12μm-0.22μm. It can be observed from the figure that as the diameter increases, the loss peak moves to a higher wavelength, and the width of the locally occurring SPR phenomenon gradually narrows, resulting in the aggregation of more electrons, enhanced resonance intensity, and red shift of the resonance wavelength. The sensor obtained maximum loss peaks of 29.45dB / cm and 60.23dB / cm at 837nm and 899nm, respectively. When d1 = 0.22μm, the maximum resonance wavelength shift of 64nm is reached, that is, the sensitivity is maximum, which indicates that higher confinement loss means strong coupling between the core and SPP mode. Therefore, the diameter d1 of the core single hole is preferably 0.22μm.

[0040] Figure 4 The figure shows the loss spectrum curve when the diameter dy of microchannel 15 is varied. This figure shows that changing the diameter dy of microchannel 15 causes changes in the resonance wavelength and intensity. As the diameter of microchannel 15 increases, the resonance wavelength exhibits a significant blue shift, and the loss peak gradually decreases. This is due to the difference between the sensing surface and the center of the PCF. This phenomenon occurs at longer distances, which reduces the mode coupling strength. To achieve maximum wavelength sensitivity, the diameter dy of microchannel 15 is preferably 2.2 μm.

[0041] Figure 5The wavelength and normalized resonance loss peak relationship simulation diagram of the D-type double-core PCF-SPR refractive index sensor prepared in the embodiment for different refractive index solutions, and the simulation structure is the performance of the Au / TiO2-coated PCF-SPR fiber sensor. The surrounding environment is set to be a liquid with different refractive indexes, which can be used to simulate different concentrations of hemoglobin, and the refractive indexes are set to be 1.26, 1.27, 1.28, 1.29, 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, respectively. The abscissa is the wavelength of the transmitted light, and the ordinate is the resonance loss peak. The RI resolution is 4.07 x 10 -6 RIU, as shown in the figure, with the increase of the refractive index, the SPR spectrum will produce red shift.

[0042] Figure 6 The D-type double-core PCF-SPR refractive index sensor prepared in the embodiment is used for detecting the relationship between the external refractive index and the resonance peak wavelength. The abscissa is the external refractive index, and the ordinate is the resonance peak wavelength. As shown in the figure, the numerical relationship between the external refractive index and the resonance peak wavelength. Due to the existence of the TiO2 layer, the change of the SPR resonance wavelength is larger than that of the Au only, and the sensitivity is higher. Figure 6 is the relationship curve between the refractive index and the resonance wavelength when the Au thickness is 30 nm and the TiO2 thickness is 10 nm, the fitting curve is Y = -401879 + 1521072x - 2302260x 2 + 1741891x 3 - 658798x 4 + 99641x 5 , the linear fitting degree is R 2 = 0.99574, and the sensitivity reaches 24,600 nm / RIU, while the sensitivity of the traditional Au film-coated fiber SPR sensor is 11,750 nm / RIU, so compared with the photonic crystal fiber SPR sensor without TiO2 modification, the structure sensitivity of the sensor prepared in the application is higher, and the effect of detecting the hemoglobin concentration is better.

[0043] Embodiment two, a hemoglobin concentration detection system

[0044] The detection system is based on the D-shaped double-core PCF-SPR refractive index sensor prepared in Example 1, which comprises an optical tunable source OTS (1), an inlet optical fiber (inlet), a D-shaped double-core PCF-SPR refractive index sensor (3), an outlet optical fiber (outlet), an optical spectrum analyzer OSA (5) and a computer (6), which are connected by a single-mode optical fiber SMF (2); the analyte or sensing layer is located outside the PCF, and the inlet (inlet) and outlet (inlet) of the pump control (to be tested hemoglobin solution) can be controlled.

[0045] However, considering that the system is mainly used for hemoglobin concentration detection, and the TiO2 surface has a large number of active hydroxyl groups, the surface functionalization of the TiO2 surface is further considered by surface chemical modification reaction. Specifically, in this embodiment, a layer of silane coupling agent 13 (preferably silane coupling agent KH560) with epoxy group with a thickness of 1.94-1.96 μm is coated on the outer surface of TiO2 to modify the surface of TiO2 nanoparticles. Since the epoxy-based silane coupling agent KH560 has specific adsorption properties for protein molecules, it can be used as a biological recognition film to detect hemoglobin concentration, and the bonding of the functional groups on the surface of TiO2 can enhance the adsorption of the sensor to the hemoglobin molecules, making the refractive index sensor more suitable for application in the blood protein concentration detection system.

[0046] When the analyte (sensed by RI) and the film on the surface of the optical fiber interact, a blue shift (shift to a shorter wavelength) or a red shift (shift to a longer wavelength) of the loss peak can be observed, which can be easily monitored by OSA. Since the wavelength position of the surface plasmon resonance peak is related to the external refractive index, and the hemoglobin concentration determines the external refractive index. Therefore, by combining the spectrum with the wavelength shift and the refractive index curve, the concentration of the protein can be calculated.

[0047] The above is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A D-type dual-core PCF-SPR refractive index sensor, characterized in that: A core single hole is provided in the center of the cladding of the photonic crystal fiber. An outer layer of air holes with a hexagonal distribution is provided in the cladding outside the core single hole. Two symmetrical polished surfaces are polished to a certain depth on both sides of the PCF cladding area, and a microchannel structure is formed in the center. Fixed Au layers and TiO2 layers are provided at the outer ends of the polished surfaces in sequence. The outer layer air pores include four symmetrically distributed outer layer small air pores and six symmetrically distributed outer layer large air pores. The outer layer small air pores are designed close to the core single pore, and the outer layer large air pores are located outside the outer layer small air pores; the pore diameter of the core single pore is 0.12-0.22 μm, the diameter of the outer layer small air pores is 0.62-0.72 μm, and the diameter of the outer layer large air pores is 1.4-1.5 μm.

2. A D-type dual-core PCF-SPR refractive index sensor according to claim 1, characterized in that: The diameter of the microchannel is 2.2-2.4 μm.

3. A D-type dual-core PCF-SPR refractive index sensor according to claim 1, characterized in that: The thickness of the Au layer is 28-30 nm, and the thickness of the TiO2 layer is 8-10 nm.

4. A D-type dual-core PCF-SPR refractive index sensor according to claim 1, characterized in that: The polishing depth H is 3.55-3.65 μm.

5. A D-type dual-core PCF-SPR refractive index sensor according to claim 2, characterized in that: The diameter of the microchannel is 2.2 μm.

6. A D-type dual-core PCF-SPR refractive index sensor according to claim 4, characterized in that: The pore size of the core single pore is 0.22 μm.

7. A hemoglobin concentration detection system, characterized in that: It is established according to a D-type dual-core PCF-SPR refractive index sensor according to any one of claims 1-6. The system includes an optical tunable source OTS, an input optical fiber, a D-type dual-core PCF-SPR refractive index sensor, an output optical fiber, an optical spectrum analyzer OSA and a computer. The components are connected in sequence through a single-mode optical fiber SMF. The outer surface of the TiO2 layer of the D-type dual-core PCF-SPR refractive index sensor is coated with a layer of silane coupling agent. The analyte or sensing layer is located outside the PCF, and the input and output of the hemoglobin solution to be tested is controlled by a pump; when the analyte interacts with the thin film on the surface of the optical fiber, a blue shift or red shift of the loss peak can be observed.

8. A hemoglobin concentration detection system according to claim 7, characterized in that: The silane coupling agent coated on the outer surface of the TiO2 layer of the D-type dual-core PCF-SPR refractive index sensor is the silane coupling agent KH560 with a cycloalkyl group, and the thickness of the silane coupling agent layer is 1.94-1.96 μm.

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