Temperature-compensated spr glucose sensor based on fitting centroid method

Abstract

The application discloses a temperature compensation SPR glucose sensor based on a fitting centroid method, a tapered single-mode optical fiber is formed by fusing a multimode optical fiber and a single-mode optical fiber and corroding the single-mode optical fiber by hydrofluoric acid, a silver film is coated on the single-mode optical fiber corroded by the hydrofluoric acid, and reduced graphite oxide and PDDA / PBA are attached to the silver film as a sensing layer. The designed sensor has both SPR and MZI effects, can detect the concentration of a glucose solution and monitor the temperature at the same time, so that the interference caused by the temperature can be reduced, the SPR transmission spectrum is fitted into a Gaussian function, and the centroid coordinates of a figure surrounded by the function and a set baseline are taken as reference points. Compared with the sensor related to a traditional structure, the application has higher accuracy and linearity.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, specifically relating to a temperature-compensated SPR glucose sensor based on the centroid fitting method. Background Technology

[0002] Surface plasmon resonance (SPR) spectroscopy, a label-free detection technique, has developed rapidly over the past few decades and has been applied in various sensing fields. Its principle is that when light propagates through the interface between a medium and a metal, the evanescent wave generated by the light matches the vibrational frequency of the metal electrons, causing the free electrons to resonate and generate surface plasmon waves (SPWs), which propagate along the interface between the metal and the dielectric layer. Light of a certain wavelength is absorbed due to resonance, producing absorption peaks. When the refractive index of the external analyte changes, the vibrational frequency matching condition changes, and the position of the absorption peak generated by SPR shifts accordingly. This is the basic principle of SPR sensors. Because SPR sensors have a good affinity for biological and chemical analytes, they are very suitable for detecting the concentration and content of various biological and chemical analytes, playing a crucial role in label-free biosensors.

[0003] Compared to traditional prism-based SPR sensors, fiber optic sensors offer advantages such as high sensitivity, flexibility, and ease of operation. Based on their sensing structures, fiber optic SPR sensors can be categorized into cladding-etched light sensors, terminal-reflective multimode fiber optic SPR sensors, side-polished multimode fiber optic SPR sensors, photonic crystal fiber structures, and heterogeneous core structures. However, multiple modes propagate within optical fibers, each with different incident angles. Therefore, the performance of fiber optic SPR sensors differs slightly from prism-based sensors: prism structures allow for selective incident angles, while the multiple modes within an optical fiber exhibit multiple incident angles. Since the incident angles are finite, each angle has its own resonant wavelength. This broadens the resonance valley of the transmission spectrum introduced by the fiber optic sensing probe, leading to some adverse effects and a decrease in sensor performance, including sensitivity, gain coefficient, and detection resolution.

[0004] Currently, glucose solution concentration sensors exhibit temperature-induced interference due to changes in the refractive index of the glucose solution during operation. Furthermore, simply reducing temperature interference is insufficient; real-time temperature detection is required without compromising sensor performance. For glucose solution concentration detection, a sensor with a simple structure, stable performance, and the ability to avoid temperature interference, even for real-time temperature measurement, is essential. However, SPR-based multi-parameter sensors suffer from limited detection ranges due to multiple resonance troughs and crosstalk between different detection troughs, significantly restricting their application in the sensor technology field.

[0005] A multimode interferometric fiber optic glucose concentration sensor and its fabrication method are disclosed in patent CN108982417A. The sensor includes an SMS-type fiber, the structure of which is single-mode fiber-multimode fiber-single-mode fiber. The multimode fiber has its cladding removed, and glucose oxidase is immobilized on its surface using a crosslinking agent. This sensor overcomes the limitation of fiber optic sensors requiring fiber gratings. Without the influence of fiber gratings, the sensor is unaffected by strain and temperature, resulting in lower environmental requirements and reduced costs. However, this patent cannot simultaneously detect temperature and fails to address the technical problem of crosstalk between different detection troughs. Summary of the Invention

[0006] Technical problem solved: This invention discloses a temperature-compensated SPR glucose sensor based on the fitting centroid method, which can solve the problems of low detection accuracy, low resolution and susceptibility to temperature crosstalk of current fiber optic SPR sensors.

[0007] Technical solution:

[0008] A temperature-compensated SPR glucose sensor based on the centroid fitting method, the glucose fiber SPR sensor comprising an input multimode fiber, a tapered single-mode fiber, an output multimode fiber, a spectrometer, and a computer;

[0009] The input multimode fiber, the tapered single-mode fiber, and the output multimode fiber are coaxially arranged. One end of the tapered single-mode fiber is fused to the input multimode fiber, and the other end is fused to the output multimode fiber. The end of the output multimode fiber that is not connected to the tapered single-mode fiber is connected to a computer via a spectrometer. The end of the input multimode fiber that is not connected to the tapered single-mode fiber is connected to a light source.

[0010] The outer wall of the tapered single-mode fiber is coated with a metal film, and a reduced graphene oxide film is attached to the metal film. The reduced graphene oxide film is modified with PDDA solution and has a positive potential. PBA boric acid is adsorbed onto the reduced graphene oxide by electrostatic adsorption. The glucose fiber SPR sensor uses the SPR effect on the surface of the tapered single-mode fiber to detect the concentration of the glucose solution. At the same time, it uses the MZI effect caused by a part of the light leaking from the splice to the cladding and then back to the fiber core to detect the temperature of the glucose solution.

[0011] The computer performs Gaussian fitting on the SPR transmission spectrum measured by the spectrometer, first fitting it to a Gaussian function and then differentiating the fitted Gaussian function. The ordinate at the maximum absolute value of the derivative is set as the baseline, and the centroid abscissa of the graph enclosed by the baseline and the Gaussian function is calculated. The centroid abscissa is used as the reference point for SPR troughs for data analysis.

[0012] Furthermore, the core diameters of the input multimode fiber and the output multimode fiber are the same, both being 62.5 μm; the cladding diameters of the input multimode fiber and the output multimode fiber are the same, both being 125 μm; the core diameter of the tapered single-mode fiber is 8.2 μm; the maximum and minimum cladding diameters of the tapered single-mode fiber are 125 μm and 60 μm, respectively; the central region of the tapered single-mode fiber is the narrowest and its length is 3 cm.

[0013] Furthermore, the outer wall of the tapered single-mode optical fiber is coated with a silver film with a thickness of 50 nm.

[0014] Furthermore, the thickness of the reduced graphene oxide film ranges from 4 nm to 8 nm.

[0015] This invention also discloses a method for preparing a temperature-compensated SPR glucose sensor based on the fitting centroid method, characterized in that the glucose fiber SPR sensor is the temperature-compensated SPR glucose sensor based on the fitting centroid method as described above.

[0016] The preparation method includes the following steps:

[0017] Step 1: Welding;

[0018] The coating layer of the single-mode fiber is removed to obtain the single-mode fiber cladding and core. The fiber is cut according to the length of the sensing part, and one end of the fiber is fused to one end of the input multimode fiber, and the other end is fused to one end of the output multimode fiber.

[0019] Step 2: Corrosion;

[0020] Hydrofluoric acid is drop-coated onto the surface of a single-mode fiber, leaving a section of the single-mode fiber at each end uncovered by hydrofluoric acid. The single-mode fiber is then etched to obtain a tapered single-mode fiber.

[0021] Step 3: Coating;

[0022] On the cladding surface of a tapered single-mode fiber corroded by hydrofluoric acid, a thin metal film is deposited on the surface of the tapered single-mode fiber using a magnetic sputtering method.

[0023] Step 4: Deposit the sensing membrane;

[0024] On the surface of a tapered single-mode optical fiber coated with an outer metal film, a reduced graphene oxide film and a PDDA / PBA sensing layer are sequentially fixed by a pulling method to obtain a glucose solution concentration optical fiber sensor based on the fitting centroid method and temperature compensation.

[0025] Furthermore, in step 2, a portion of the single-mode fiber is immersed in 40% hydrofluoric acid using a drop-coating method, leaving 1 cm of single-mode fiber at each end unimmersed in the hydrofluoric acid. Different etching times are set for different parts of the single-mode fiber to form a conical structure, with the finest part being etched for 50 minutes.

[0026] Furthermore, in step 3, the coating process includes the following sub-steps:

[0027] Use a clamp to place the tapered single-mode fiber with the matching layer already coated into the vacuum cavity, fix it, and position the tapered single-mode fiber directly above the target material;

[0028] Close the vacuum chamber and evacuate to a vacuum level of 8×10⁻⁶. -4 Argon gas is introduced at a flow rate of 5-6 sccm, and the gate valve of the vacuum chamber is adjusted to stabilize the argon gas pressure in the vacuum chamber at 0.5 Pa-0.6 Pa.

[0029] Turn on the substrate rotation, adjust the DC source current to 43mA and the power to 12W, use a metal film as the sputtering material, sputter on one side of the tapered single-mode fiber for 150s, then flip the tapered single-mode fiber and sputter on the other side of the tapered single-mode fiber for the same time.

[0030] Furthermore, in step 4, the process of depositing the sensing film includes the following sub-steps:

[0031] Reduced graphene oxide was deposited on a metal film on the surface of a tapered single-mode optical fiber, and the reduced graphene oxide dispersion was subjected to ultrasonic treatment at a frequency of 20-25 kHz for 0.5 h.

[0032] Repeat the following operation five times: Immerse the tapered single-mode optical fiber in a reduced graphene oxide dispersion with a concentration of 0.5 mg / ml for 20 seconds using the pull-up method, repeat the pull-up twelve times, and then dry it on an 80℃ drying table for 20 minutes to fix it.

[0033] A tapered single-mode optical fiber coated with a silver film and a reduced graphene oxide film was immersed in a 1 mg / ml PDDA solution for 1 hour to make the fiber surface positively charged.

[0034] An optical fiber is immersed in a PBA solution, allowing the PBA boric acid to adsorb onto the positively charged PDDA and interact with the large aromatic rings of the reduced graphene oxide to form a π-π covalent bond, thus fixing it onto the reduced graphene oxide film, thereby obtaining a glucose solution concentration sensing unit.

[0035] This invention also discloses a signal processing method for a temperature-compensated SPR glucose sensor based on the centroid fitting method, the signal processing method comprising the following steps:

[0036] The single-mode fiber portion of the temperature-compensated SPR glucose sensor based on the fitting centroid method, as described above, is placed in the detection container of the glucose solution to be tested, and the detection container is sealed.

[0037] The broadband optical source is turned on, and the light signal emitted by the source is transmitted through the input multimode fiber to the tapered single-mode fiber. The light signal propagates in the tapered single-mode fiber, and the resulting output spectrum enters the output multimode fiber. The output multimode fiber then guides the light signal to a spectrometer. The spectrometer transmits real-time data to a computer via a data interface. The computer performs Gaussian function fitting on the real-time data to derive the function expression T. gauss :

[0038]

[0039] Where T is the spectral transmittance, λ is the wavelength of light, and λ c It is the center wavelength of light, and FWHM is the free spectral range of the SPR signal;

[0040] For function T gauss The process involves setting the ordinate of the inflection point of the derivative function as the baseline coordinate:

[0041]

[0042] Y base =T gauss (a);

[0043] Where 'a' is the x-coordinate of the absolute value of the derivative of the fitted Gaussian function, and Y... base It is the ordinate of the baseline;

[0044] Determine the centroid coordinates of the region D bounded by the baseline and the fitted Gaussian function, and analyze the sensitivity of the measured glucose solution by analyzing the centroid coordinates.

[0045]

[0046] In the formula, in the formula, Let λ be the wavelength represented by the calculated centroid coordinates, D be the region enclosed by the baseline and the fitted Gaussian function, x be the wavelength of the incident light, F be the function expression formed by Gaussian fitting of the SPR curve, and σ be the subdomain corresponding to region D.

[0047] Beneficial effects:

[0048] First, the temperature-compensated SPR glucose sensor based on the centroid fitting method of this invention utilizes the fusion splicing of single-mode and multimode optical fibers, and then uses hydrofluoric acid etching to corrode the single-mode fiber into a tapered shape, thus fabricating a simple and highly stable fiber SPR sensor. Simultaneously, this invention utilizes the SPR effect on the surface of the single-mode fiber to detect glucose solution concentration and the MZI effect formed by the fusion of multimode and tapered single-mode fibers to detect temperature, respectively. These two detection methods enable dual-parameter detection, and the impact of detection methods on each other's performance is minimal across different wavelength bands. Furthermore, triggering the MZI effect using HF etching has a lower cost compared to the tapering method.

[0049] Secondly, the temperature-compensated SPR glucose sensor based on the fitting centroid method of this invention uses the fitting centroid method instead of the traditional lowest point of the trough as the detection reference point. This method processes all points that meet the vibration frequency matching conditions, optimizing the adverse effects of low sensor resolution caused by the widening of the transmission resonance valley due to multiple incident angles in the optical fiber and the widening of the transmission resonance valley after the sensitization of the attached two-dimensional material. It also improves the linearity and sensitivity of the sensor. Compared with the traditional centroid method, this invention uses a simpler mathematical integration method to calculate the centroid coordinates by integrating the specified region after Gaussian fitting the spectral signal into a function expression, simplifying the process by eliminating the need for image processing and other steps. This method also reduces the adverse effects of the widening of the transmission spectrum resonance valley introduced by the optical fiber sensing probe. The glucose optical fiber SPR sensor of this invention is simple to manufacture, low in cost, has strong anti-electromagnetic interference, and high mechanical strength, making it suitable for detection in complex environments.

[0050] Third, the temperature-compensated SPR glucose sensor based on the centroid fitting method of this invention, with the addition of reduced graphene oxide, combines the advantages of both graphene and graphene oxide. It possesses excellent optical properties and an enhanced electron transfer rate, increasing the sensor's surface electric field and improving detection sensitivity, while also exhibiting good biocompatibility. The reduced graphene oxide surface has carboxyl and amino functional groups, enabling it to adsorb more glucose molecules and improve the sensor's detection limit. Compared to traditional GOD glucose oxidase, the PBA used in this invention has less of a temperature-dependent absorption capacity for glucose, and the reduced graphene oxide can isolate the silver film from air, preventing silver film oxidation and increasing sensor lifespan.

[0051] Fourth, the temperature-compensated SPR glucose sensor based on the fitting centroid method of the present invention can increase the light leakage by forming a tapered single-mode fiber through hydrofluoric acid etching. While enhancing the SPR effect, it can also effectively reduce the influence of multimode interference and enhance the depth of the MZI effect interference fringes. Attached Figure Description

[0052] Figure 1This is a schematic diagram of the sensing unit structure of a temperature-compensated SPR glucose sensor based on the fitting centroid method according to an embodiment of the present invention.

[0053] Figure 2 This is a schematic diagram of the temperature-compensated SPR glucose sensor structure based on the fitting centroid method according to an embodiment of the present invention.

[0054] Figure 3 These are transmission spectra of the sensor in solutions with different refractive indices in this embodiment of the invention;

[0055] Figure 4 The present invention processes spectral data using an optimized centroid method, as shown in the schematic diagram.

[0056] Figure 5a This is a linear fitting graph of the sensor using the traditional SPR sensor sensitivity detection method in an embodiment of the present invention. Figure 5b This is a linear fitting graph of the SPR sensor sensitivity detection using the centroid optimization method in an embodiment of the present invention.

[0057] Figure 6a This embodiment of the invention utilizes the transmission spectra of an MZI sensor at different temperatures. Figure 6b This is a linear fit graph of the temperature sensitivity detection of the MZI sensor;

[0058] Figure 7a These are transmission spectra obtained using an SPR sensor in glucose solutions of different concentrations in this embodiment of the invention. Figure 7b This is a linear fit graph of glucose detection by the SPR sensor.

[0059] The reference numerals in the attached figures are as follows: 1. Incident multimode fiber, 2. Outgoing multimode fiber, 3. Tapered single-mode fiber, 4. Silver layer, 5. Reduced graphene oxide layer, 6. PDDA-PBA sensing layer, 7. Glucose molecule, 8. Broadband light source, 9. Outlet, 10. Inlet, 11. Sensor sensing unit, 12. Glass tube, 13. Spectrometer, 14. Computer. Detailed Implementation

[0060] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0061] See Figure 2 This invention discloses a temperature-compensated SPR glucose sensor based on the centroid fitting method. The glucose fiber SPR sensor includes an input multimode fiber, a tapered single-mode fiber, an output multimode fiber, a spectrometer, and a computer.

[0062] The input multimode fiber, the tapered single-mode fiber, and the output multimode fiber are coaxially arranged. One end of the tapered single-mode fiber is fused to the input multimode fiber, and the other end is fused to the output multimode fiber. The end of the output multimode fiber that is not connected to the tapered single-mode fiber is connected to the computer via a spectrometer. The end of the input multimode fiber that is not connected to the tapered single-mode fiber is connected to the light source.

[0063] The outer wall of the tapered single-mode fiber is coated with a metal thin film, and a reduced graphene oxide film is attached to the metal thin film. The reduced graphene oxide film is modified with PDDA solution and has a positive potential. PBA boric acid is adsorbed onto the reduced graphene oxide by electrostatic adsorption. The glucose fiber SPR sensor uses the SPR effect on the surface of the tapered single-mode fiber to detect the concentration of the glucose solution. At the same time, it uses the MZI effect caused by a portion of the light leaking from the splice to the cladding and then returning to the fiber core to detect the temperature of the glucose solution.

[0064] The computer performs Gaussian fitting on the SPR transmission spectrum measured by the spectrometer, first fitting it to a Gaussian function and then differentiating the fitted Gaussian function. The ordinate at the maximum absolute value of the derivative is set as the baseline, and the centroid abscissa of the graph enclosed by the baseline and the Gaussian function is calculated. The centroid abscissa is used as the reference point for SPR troughs for data analysis.

[0065] See Figure 1 The sensing unit includes a tapered single-mode fiber 3 and a multimode fiber. The multimode fiber is divided into a first multimode fiber 1 and a second multimode fiber 2. One end of the first multimode fiber 1 is connected to one end of the tapered single-mode fiber 3, and the other end of the single-mode fiber core 3 is connected to one end of the second multimode fiber 2. A silver layer 4, a reduced graphene oxide layer 5, and a PDDA-PBA sensing layer 6 are sequentially disposed on the outer wall of the tapered single-mode fiber from the inside to the outside. The light source 8 is connected to the first multimode fiber 1 at the incident end through the incident light path and the sensor sensing unit 11. The second multimode fiber 2 at the other end of the sensor sensing unit 11 is connected to the spectrometer 13 through the output light path and processed by the computer 14.

[0066] Regarding the dimensional parameters of each optical fiber, as long as they can simultaneously generate SPR and MZI effects, the glucose fiber SPR sensor can detect glucose solution concentration using the SPR effect on the surface of the single-mode fiber and detect temperature using the MZI effect formed by the fusion of multimode fiber and tapered single-mode fiber. These two detection methods achieve dual-parameter detection, and the impact of detection methods on each other's performance is minimal across different wavelength bands. Specifically, this embodiment uses fiber fusion splicing technology, where a portion of the light leaks from the fusion point of the multimode fiber and single-mode fiber into the cladding and finally returns to the fiber core, generating an MZI effect for temperature detection. This reduces crosstalk caused by temperature in glucose solution concentration detection, and the glucose solution and temperature detection locations are the same, improving the accuracy of temperature measurement.

[0067] Below is an example of the structural parameters and fabrication method of one type of glucose fiber optic SPR sensor:

[0068] Step 1: Remove the coating from single-mode fibers with cladding and core diameters of 125μm and 8.2μm respectively to obtain single-mode fiber cladding and core. For multimode fibers with cladding and core diameters of 125μm and 62.5μm respectively, use a fiber cleaver to smoothly cut the end faces of both single-mode and multimode fibers according to the length of the sensing section, leaving a 3cm length of single-mode fiber. Clean the surfaces of both single-mode and multimode fibers with alcohol. Then, use a fiber optic fusion splicer to perform splicing with the following parameters: cleaning discharge 150ms, discharge power 3000bit, discharge time 2500ms, and advance distance 10μm. Fusion splice one end of the single-mode fiber to one end of the input multimode fiber, and the other end to one end of the output multimode fiber.

[0069] Step 2: When etching the single-mode fiber, a 40% concentration of hydrofluoric acid is used to immerse the single-mode fiber portion through a drop-coating method, leaving 1 cm of fiber unimmersed at both ends. The hydrofluoric acid diffuses towards both ends over time, forming a tapered structure depending on the etching time at different locations. Etching for 50 minutes yields a tapered single-mode fiber with a minimum diameter of 60 μm.

[0070] Step 3: A 50nm thick silver film is deposited on the fiber surface using magnetron sputtering. The magnetron sputtering process parameters are as follows: The fiber with the matching layer already deposited is placed in the vacuum chamber using a clamp, and fixed so that the fiber is directly above the target. The vacuum chamber is closed and evacuated to 8×10⁻⁴ Pa. Argon gas is then introduced at a flow rate of 5–6 sccm. The gate valve of the vacuum chamber is adjusted to stabilize the argon gas pressure in the vacuum chamber at 0.5–0.6 Pa. The substrate rotation is turned on, and the DC source current is adjusted to 43mA with a power of 12W. A metal film is used as the sputtering material. After sputtering for 2 min 30 s, the fiber is flipped, and sputtering is performed on the other side of the fiber for the same amount of time. A 50nm thick silver film is obtained.

[0071] Step 4: On the surface with the outer metal film coated on the outer wall, the reduced graphene oxide film and the PDDA / PBA sensing layer are sequentially fixed by the Czochralski method to obtain a high-sensitivity fiber optic sensor for glucose solution concentration based on the centroid fitting method optimization and temperature compensation. Specifically, this includes the following sub-steps:

[0072] (1) Deposit reduced graphene oxide on a metal film on the surface of the optical fiber. Sonicate the reduced graphene oxide dispersion at a frequency of 20-25 kHz for 0.5 h. Soak the single-mode optical fiber in a reduced graphene oxide dispersion with a concentration of 0.5 mg / ml for 20 seconds using the pull-up method. Repeat the pull-up process 12 times. Then dry the fiber on a drying table at 80 ℃ for 20 minutes to fix it. Repeat this step five times.

[0073] (2) A glucose solution sensing film was attached to an optical fiber. The glucose sensing film was obtained by immersing a single-mode optical fiber coated with a silver film and a reduced graphene oxide film in a 1 mg / ml PDDA solution for 1 hour, making the fiber surface positively charged. The optical fiber was then immersed in a PBA solution. Since the PBA solution is negatively charged in water, it adsorbs onto the positively charged PDDA and forms π-π interactions between the large aromatic rings of the reduced graphene oxide, thus fixing the PDDA onto the reduced graphene oxide film, resulting in a highly sensitive glucose solution concentration sensing unit. The structural parameters of the final glucose fiber SPR sensor are as follows:

[0074] The multimode fiber has a core and cladding diameter of 62.5 μm and 125 μm, respectively. The tapered single-mode fiber, etched with hydrofluoric acid, has a core and cladding diameter of 8.2 μm and 125 μm, respectively. The minimum diameter of the etched single-mode fiber is 60 μm, and its length is 3 cm. Its outer wall is coated with a silver film with a thickness of 50 nm. The thickness of the reduced graphene oxide film is approximately 4 nm-8 nm. The broadband light source wavelength range is 350–1590 nm. The spectrometer wavelength range is 400 nm–1000 nm. The near-infrared spectrometer wavelength range is 1510 nm–1590 nm. This fiber optic sensor for glucose solution concentration has a temperature sensitivity of 138 pm / ℃, a refractive index sensitivity of 5157 nm / RIU, and can detect biomolecule concentrations from 1 mmol / L to 10 mmol / L. Test examples are as follows:

[0075] The glucose fiber optic SPR sensor is placed in a glass tube 12 with an inlet 10 and an outlet 9. The broadband light source 8 is turned on, and the light signal emitted by the broadband light source is transmitted through the input optical fiber 1 to the single-mode optical fiber 3. The light signal is transmitted in the single-mode optical fiber, and the output spectrum formed after passing through the single-mode optical fiber enters the output optical fiber 1. The light signal is then guided to the spectrometer and near-infrared spectrometer 13 through the output optical fiber. The spectrometer transmits the real-time data to the computer 14 for data processing through the data interface.

[0076] First, solutions with different refractive indices are added to glass tube 12. The sensor is then placed in these solutions, resulting in the following: Figure 3 The transmission spectrum is shown. As the solution refractive index increases, the resonance wavelength shifts to the right. Figure 5aBased on the fitting curve of refractive index and resonant wavelength, the slope of the corresponding straight line can be obtained, and the sensitivity of the sensor can be further calculated to be 4896 RIU / nm. The liquid inside the glass tube is heated using a heating stage to obtain the following... Figure 5a The MZI interference spectrum is shown. As temperature increases, the troughs of the spectrum shift to the right, according to... Figure 5b Based on the fitting curve of refractive index and resonant wavelength, the slope of the corresponding straight line can be obtained, and then the sensitivity of the sensor can be further calculated to be 138 pm / ℃.

[0077] The signal transmitted to the computer is fitted with a Gaussian function to obtain a function expression, and then the function is processed.

[0078]

[0079] Set the ordinate of the inflection point of the fitted function as the baseline coordinate:

[0080]

[0081] Y base =T gauss (a);

[0082] The centroid coordinates of the region D bounded by the baseline and the fitted Gaussian function were determined, and the sensitivity of the measured glucose solution was analyzed by analyzing the centroid coordinates.

[0083]

[0084] The algorithm schematic diagram is attached. Figure 4 As shown.

[0085] By optimizing the centroid method Figure 5a Based on the fitting curve of refractive index and resonant wavelength, the slope of the corresponding straight line can be obtained, and the sensitivity of the sensor can be further calculated to be 5157 RIU / nm. Compared with the traditional detection method, the linearity increases from 0.97036 to 0.99852. Experimental results show that the temperature-compensated SPR glucose sensor based on the centroid fitting method can achieve dual-parameter measurement and improve the linearity of the sensor.

[0086] This embodiment further includes experiments to detect the concentration of glucose solutions, using solutions with concentrations of 0 mmol / L, 1 mmol / L, 2.5 mmol / L, 5 mmol / L, and 10 mmol / L. Because glucose molecules specifically bind to boric acid (PBA), this binding causes a change in the refractive index of the silver film on the outer side of the single-mode membrane, resulting in a shift of the absorption peak at a specific wavelength. The shift of the absorption peak increases with increasing concentration. Simultaneously, the real-time temperature can be obtained by referencing the peak position using an MZI interferometer, thus achieving temperature and glucose solution concentration detection (see details). Figure 6a and Figure 6b Then, by using the centroid fitting optimization method, the following can be obtained: Figure 7a and Figure 7b The image shows accurate information about the concentration of the glucose solution. The sensor's sensitivity to glucose is 2.7625 nm / mmol, and its linearity of 0.991 indicates that the sensor has good linearity in the detection of glucose solutions.

[0087] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A temperature-compensated SPR glucose sensor based on the fitted centroid method, characterized in that, The glucose fiber optic SPR sensor includes an input multimode fiber, a tapered single-mode fiber, an output multimode fiber, a spectrometer, and a computer; The input multimode fiber, the tapered single-mode fiber, and the output multimode fiber are coaxially arranged. One end of the tapered single-mode fiber is fused to the input multimode fiber, and the other end is fused to the output multimode fiber. The end of the output multimode fiber that is not connected to the tapered single-mode fiber is connected to a computer via a spectrometer. The end of the input multimode fiber that is not connected to the tapered single-mode fiber is connected to a light source. The outer wall of the tapered single-mode fiber is coated with a metal film, and a reduced graphene oxide film is attached to the metal film. The reduced graphene oxide film is modified with PDDA solution and has a positive potential. PBA boric acid is adsorbed onto the reduced graphene oxide by electrostatic adsorption. The glucose fiber SPR sensor uses the SPR effect on the surface of the tapered single-mode fiber to detect the concentration of the glucose solution. At the same time, it uses the MZI effect caused by a part of the light leaking from the splice to the cladding and then back to the fiber core to detect the temperature of the glucose solution. The computer performs Gaussian fitting on the SPR transmission spectrum measured by the spectrometer, first fitting it to a Gaussian function and then differentiating the fitted Gaussian function. The ordinate at the maximum absolute value of the derivative is set as the baseline, and the centroid abscissa of the graph enclosed by the baseline and the Gaussian function is calculated. The centroid abscissa is used as the reference point for SPR troughs for data analysis.

2. The temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 1, characterized in that, The input and output multimode fibers have the same core diameter of 62.5 μm; the cladding diameters of the input and output multimode fibers are the same of 125 μm; the core diameter of the tapered single-mode fiber is 8.2 μm; the maximum and minimum cladding diameters of the tapered single-mode fiber are 125 μm and 60 μm, respectively; the central region of the tapered single-mode fiber is the narrowest and its length is 3 cm.

3. The temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 1, characterized in that, The outer wall of the tapered single-mode optical fiber is coated with a silver film with a thickness of 50 nm.

4. The temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 1, characterized in that, The thickness of the reduced graphene oxide film ranges from 4 nm to 8 nm.

5. A method for fabricating a temperature-compensated SPR glucose sensor based on the centroid fitting method, characterized in that, The glucose fiber optic SPR sensor is the temperature-compensated SPR glucose sensor based on the fitting centroid method as described in any one of claims 1-4; The preparation method includes the following steps: Step 1: Welding; The coating layer of the single-mode fiber is removed to obtain the single-mode fiber cladding and core. The fiber is cut according to the length of the sensing part, and one end of the fiber is fused to one end of the input multimode fiber, and the other end is fused to one end of the output multimode fiber. Step 2: Corrosion; Hydrofluoric acid is drop-coated onto the surface of a single-mode fiber, leaving a section of the single-mode fiber at each end uncovered by hydrofluoric acid. The single-mode fiber is then etched to obtain a tapered single-mode fiber. Step 3: Coating; On the cladding surface of a tapered single-mode fiber corroded by hydrofluoric acid, a thin metal film is deposited on the surface of the tapered single-mode fiber using a magnetic sputtering method. Step 4: Deposit the sensing membrane; On the surface of a tapered single-mode optical fiber coated with an outer metal film, a reduced graphene oxide film and a PDDA / PBA sensing layer are sequentially fixed by a pulling method to obtain a glucose solution concentration optical fiber sensor based on the fitting centroid method and temperature compensation.

6. The method for preparing a temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 5, characterized in that, In step 2, a portion of the single-mode fiber is immersed in 40% hydrofluoric acid using a drop-coating method, leaving 1 cm of single-mode fiber at each end unimmersed in the hydrofluoric acid. Different etching times are set for different parts of the single-mode fiber to form a conical structure, with the finest part being etched for 50 minutes.

7. The method for preparing a temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 5, characterized in that, Step 3, the coating process includes the following sub-steps: Use a clamp to place the tapered single-mode fiber with the matching layer already coated into the vacuum cavity, fix it, and position the tapered single-mode fiber directly above the target material; Close the vacuum chamber and evacuate to a vacuum level of 8×10⁻⁶. -4 Argon gas is introduced at a flow rate of 5-6 sccm, and the gate valve of the vacuum chamber is adjusted to stabilize the argon gas pressure in the vacuum chamber at 0.5 Pa - 0.6 Pa. Turn on the substrate rotation, adjust the DC source current to 43mA and the power to 12W, use a metal film as the sputtering material, sputter on one side of the tapered single-mode fiber for 150s, then flip the tapered single-mode fiber and sputter on the other side of the tapered single-mode fiber for the same time.

8. The method for preparing a temperature-compensated SPR glucose sensor based on the fitting centroid method according to claim 5, characterized in that, Step 4, the process of depositing the sensing film includes the following sub-steps: Reduced graphene oxide was deposited on a metal film on the surface of a tapered single-mode optical fiber, and the reduced graphene oxide dispersion was subjected to ultrasonic treatment at a frequency of 20-25 kHz for 0.5 h. Repeat the following operation five times: Immerse the tapered single-mode optical fiber in a reduced graphene oxide dispersion with a concentration of 0.5 mg / ml for 20 seconds using the pull-up method, repeat the pull-up twelve times, and then dry it on an 80℃ drying table for 20 minutes to fix it. A tapered single-mode optical fiber coated with a silver film and a reduced graphene oxide film was immersed in a 1 mg / ml PDDA solution for 1 hour to make the surface of the optical fiber positively charged. An optical fiber is immersed in a PBA solution, allowing the PBA boric acid to adsorb onto the positively charged PDDA and interact with the large aromatic rings of the reduced graphene oxide to form a π-π covalent bond, thus fixing it onto the reduced graphene oxide film, thereby obtaining a glucose solution concentration sensing unit.

9. A signal processing method for a temperature-compensated SPR glucose sensor based on the centroid fitting method, characterized in that, The signal processing method includes the following steps: The single-mode fiber portion of the temperature-compensated SPR glucose sensor based on the fitting centroid method as described in any one of claims 1-4 is placed in the detection container of the glucose solution to be tested, and the detection container is sealed. The broadband optical source is turned on, and the light signal emitted by the source is transmitted through the input multimode fiber to the tapered single-mode fiber. The light signal propagates in the tapered single-mode fiber, and the resulting output spectrum enters the output multimode fiber. The output multimode fiber then guides the light signal to the spectrometer. The spectrometer transmits real-time data to the computer via a data interface, where the computer performs Gaussian function fitting to derive the function expression. : ； in It is spectral transmittance. It is the wavelength of light. It is the central wavelength of light. It is the free spectral range of the SPR signal; For functions The process involves setting the ordinate of the inflection point of the derivative function as the baseline coordinate: ； ； in It is the x-coordinate of the absolute value of the derivative of the fitted Gaussian function. It is the ordinate of the baseline; Determine the centroid coordinates of the region D bounded by the baseline and the fitted Gaussian function, and analyze the sensitivity of the measured glucose solution by analyzing the centroid coordinates. ； In the formula, The wavelength represented by the calculated centroid coordinates, It is the region enclosed by the baseline and the fitted Gaussian function. It is the wavelength of the incident light. It is the function expression formed by Gaussian fitting of the SPR curve. It is a region The corresponding subdomain.

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