Noninvasive saliva glucose sensor based on Au-CeO2 / CNT ternary interface compound and preparation method thereof

Abstract

The invention relates to the technical field of biosensors, in particular to a noninvasive saliva glucose sensor based on an Au-CeO2 / CNT ternary interface compound and a preparation method of the noninvasive saliva glucose sensor. An Au-CeO2 / CNT ternary interface compound is loaded on the surface of the working electrode; the ternary interface compound comprises oxidized multi-walled carbon nanotubes, cerium oxide nanoparticles loaded on the surfaces of the oxidized multi-walled carbon nanotubes, and gold nanoparticles deposited on the interfaces of the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles. A ternary interface compound is loaded on the surface of a working electrode, precious metal gold on the compound serves as a catalytic active site to adsorb glucose, active hydroxyl is generated in combination with rich oxygen vacancies of CeO2, H atoms on glucose-CHO are removed, the catalytic oxidation reaction rate of glucose is increased, and the catalytic oxidation efficiency of glucose is improved. The electron transfer efficiency of the compound is improved by compounding and oxidizing the multi-walled carbon nanotube carrier.

Description

Technical Field

[0001] The present invention relates to the technical field of biosensors, and in particular to a non-invasive saliva glucose sensor based on an Au-CeO2 / CNT ternary interface composite and a preparation method thereof. Background Art

[0002] Currently, several research efforts have focused on developing noninvasive glucose sensors for diabetes monitoring. Among the various biofluids that can be collected noninvasively (saliva, sweat, or tears), saliva is the easiest to extract. Furthermore, many biomarkers in saliva efflux directly from the blood via extracellular or paracellular pathways, reflecting the body's physiological state and providing a noninvasive method for glucose analysis. Consequently, research on saliva as a diagnostic fluid has rapidly advanced. However, the glucose concentration in human saliva (30-80 μM) is only 1% of that in blood (3.6-7.5 mM), making saliva diagnostics extremely challenging. Therefore, there is an urgent need to develop ultrasensitive glucose sensing devices to detect low-concentration glucose in saliva samples.

[0003] However, existing non-enzymatic glucose sensing materials for saliva fail to effectively balance the requirements of utility, cost, and convenience in terms of stability, sensitivity, and selectivity. Furthermore, non-enzymatic glucose electrochemical sensors typically operate under alkaline or weakly alkaline conditions, making it difficult to achieve detection performance under neutral conditions, which correspond to human pH.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a non-invasive saliva glucose sensor based on Au-CeO2 / CNT ternary interface composite and a preparation method thereof, aiming to solve the problem of poor electron transport performance of existing glucose sensors under neutral conditions.

[0006] The technical solutions of the present invention are as follows: A non-invasive salivary glucose sensor based on an Au-CeO2 / CNT ternary interface complex comprises a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode; the surface of the working electrode is loaded with the Au-CeO2 / CNT ternary interface complex; the Au-CeO2 / CNT ternary interface complex comprises oxidized multi-walled carbon nanotubes (O-MWCNTs, abbreviated as CNTs), cerium oxide nanoparticles loaded on the surface of the oxidized multi-walled carbon nanotubes, and gold nanoparticles loaded at the interface between the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles.

[0007] The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises the following components: a mass ratio of the oxidized multi-walled carbon nanotubes, the cerium oxide nanoparticles, and the gold nanoparticles is (1-2):(1-2):(0.5-1).

[0008] In the non-invasive saliva glucose sensor based on the Au-CeO2 / CNT ternary interface complex, the particle size of the gold nanoparticles is 5.6 nm-9.6 nm.

[0009] The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises: a working electrode comprising a glassy carbon electrode, a gold electrode, and a platinum electrode; a counter electrode comprising a glass wire electrode, a platinum electrode, and a graphite electrode; and a reference electrode comprising an Ag / AgCl electrode and a saturated calomel electrode.

[0010] A method for preparing a non-invasive salivary glucose sensor based on an Au-CeO2 / CNT ternary interface composite comprises the following steps: The Au-CeO2 / CNT ternary interface composite is mixed with a solvent to obtain a suspension; The suspension is added dropwise to the surface of the working electrode, and after drying, a working electrode loaded with the Au-CeO2 / CNT ternary interface composite is obtained; The working electrode loaded with the Au-CeO2 / CNT ternary interface complex, a reference electrode, and a counter electrode form a three-electrode system to obtain a non-invasive saliva glucose sensor based on the Au-CeO2 / CNT ternary interface complex.

[0011] The method for preparing the non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises the following steps: Ce(OH)3 was deposited on oxidized multi-walled carbon nanotubes using ammonia precipitation method and then calcined to obtain CeO2 / CNT composites. Gold nanoparticles are loaded on the surface of the CeO2 / CNT composite by an in-situ reduction method using sodium borohydride to obtain an Au-CeO2 / CNT ternary interface composite.

[0012] The method for preparing the non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises the following steps: depositing Ce(OH)3 on oxidized multi-walled carbon nanotubes using an ammonia precipitation method and calcining the resulting CeO2 / CNT composite. The multi-walled carbon nanotubes are subjected to a reflux oxidation treatment in nitric acid, and then washed and dried to obtain oxidized multi-walled carbon nanotubes; Mixing the oxidized multi-walled carbon nanotubes with cerium nitrate hexahydrate and ammonia water to obtain oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface; The oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface are calcined to obtain a CeO2 / CNT composite.

[0013] The method for preparing the non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite, wherein the mass ratio of the oxidized multi-walled carbon nanotubes to the cerium nitrate hexahydrate is (0.2-0.5):1.

[0014] The method for preparing the non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises the following steps: the calcination temperature is 380°C-420°C, the calcination time is 3h-4h, and the heating rate of the calcination is 3°C / min-5°C / min.

[0015] The method for preparing the non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite comprises the following steps: loading gold nanoparticles on the surface of the CeO2 / CNT composite using an in-situ sodium borohydride reduction method to obtain the Au-CeO2 / CNT ternary interface composite; Mixing the CeO2 / CNT composite with an organic solvent to obtain a carrier suspension; The surfactant is dissolved in water, and an organic solvent and HAuCl4·4H2O solution are added, and the pH is adjusted to obtain a mixed solution; The carrier suspension is mixed with the mixed solution, and a NaBH4 solution is added to obtain an Au-CeO2 / CNT ternary interface composite after a reduction reaction.

[0016] Beneficial effects: The present invention provides a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface complex and a preparation method thereof. The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface complex comprises a three-electrode system consisting of a working electrode, a counter electrode and a reference electrode; the surface of the working electrode is loaded with the Au-CeO2 / CNT ternary interface complex; the Au-CeO2 / CNT ternary interface complex comprises oxidized multi-walled carbon nanotubes, cerium oxide nanoparticles loaded on the surface of the oxidized multi-walled carbon nanotubes, and gold nanoparticles deposited at the interface between the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles. The non-invasive saliva glucose sensor of the present invention loads an Au-CeO2 / CNT ternary interface complex on the working electrode surface. The precious metal gold nanoparticles on the complex serve as catalytic active sites to adsorb glucose. Combined with the abundant oxygen vacancies of CeO2, active hydroxyl groups are generated, which remove H atoms from the glucose-CHO, thereby accelerating the rate of glucose catalytic oxidation reaction. Furthermore, the electron transfer efficiency of the complex is increased by composite oxidation of multi-walled carbon nanotube carriers. Furthermore, the non-invasive saliva glucose sensor, based on the construction of the ternary interface, has a low detection limit, a wide linear range, a fast response, and high stability. It exhibits excellent electron transfer performance under neutral conditions (close to the pH range of saliva), demonstrating excellent detection performance. This means that direct testing of low-concentration glucose is possible without pretreatment of the saliva sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of Au-CeO2 / CNT ternary interface composite; Figure 2 Schematic diagram of the preparation process of the Au-CeO2 / CNT ternary interface composite in Example 1; Figure 3 TEM images of Au-CeO2 / CNT ternary interface composite, Au / CeO2 and Au / CNT, where (a) and (b) are TEM images of Au / CNT, (c) and (d) are TEM images of Au / CeO2, and (e) and (f) are TEM images of Au-CeO2 / CNT; Figure 4 XRD patterns of Au-CeO2 / CNT ternary interface composite and Au / CNT; Figure 5 XPS characterization of the surface chemical composition and valence state of the Au-CeO2 / CNT ternary interface composite and Au / CNT, where (a) is Au 4f and (b) is Ce 3d; Figure 6CV curves of Au / CNT and Au-CeO2 / CNT noninvasive salivary glucose sensors in 0.1M PBS and 0.5M glucose; Figure 7 CV curves of Au-CeO2 / CNT with different CeO2:CNT mass ratios in 0.1M PBS and 0.1M PBS and 0.01M glucose; Figure 8 This is the chronoamperometric curve of the Au-CeO2 / CNT non-invasive saliva glucose sensor when different concentrations of glucose are continuously added; Figure 9 is a calibration curve diagram between current and glucose concentration; Figure 10 It response diagram of Au-CeO2 / CNT electrode after adding saliva samples with different concentrations of glucose (0.05mM, 0.10mM and 0.15mM); Figure 11 Figure 3 is a graph showing the relationship between current density and glucose concentration for saliva samples with 0.05 mM, 0.10 mM, and 0.15 mM glucose added. DETAILED DESCRIPTION

[0018] The present invention provides a noninvasive salivary glucose sensor based on an Au-CeO2 / CNT ternary interface composite and a method for preparing the same. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0019] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0020] Early diagnosis, timely prevention, and continuous monitoring of blood glucose levels, keeping them within an ideal range, are crucial for preventing, managing, or delaying the progression of diabetes complications, thereby improving overall treatment outcomes. Therefore, to meet the growing demand for diabetes diagnosis and monitoring in both the home and clinic setting, developing simple and effective blood glucose testing methods has become a research trend. Currently, while some commercially available handheld blood glucose meters can measure glucose, they require collecting blood samples from patients via venipuncture or finger puncture. Repeating this procedure multiple times daily can be painful and can lead to cross-infection, significantly reducing patient compliance with blood glucose monitoring. Therefore, there is a need to develop low-cost, rapid, painless, and convenient blood glucose measurement technologies to serve clinical diagnosis and home monitoring, helping millions of patients worldwide better manage their health. While non-enzymatic glucose sensing materials for saliva exist, they generally operate under alkaline or weakly alkaline conditions, making it difficult to achieve detection performance under neutral conditions, which correspond to human pH. Therefore, the ability to fabricate nanostructured electrodes with high electrocatalytic activity and electron transfer capacity under neutral conditions is crucial for the development of non-enzymatic glucose sensors.

[0021] Based on this, the present invention provides a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite, comprising a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode; the surface of the working electrode is loaded with the Au-CeO2 / CNT ternary interface composite; Figure 1 As shown, the Au-CeO2 / CNT ternary interface composite includes oxidized multi-walled carbon nanotubes, cerium oxide nanoparticles supported on the surface of the oxidized multi-walled carbon nanotubes, and gold nanoparticles supported at the interface between the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles.

[0022] In this embodiment, the non-invasive saliva glucose sensor loads an Au-CeO2 / CNT ternary interface complex on the surface of the working electrode, utilizes the precious metal gold nanoparticles on the complex as catalytic active sites to adsorb glucose, combines with the abundant oxygen vacancies of CeO2 to generate active hydroxyl groups, removes H atoms from glucose-CHO, thereby accelerating the rate of glucose catalytic oxidation reaction, and increases the electron transfer efficiency of the complex by composite oxidation of multi-walled carbon nanotube carriers. Moreover, the non-invasive saliva glucose sensor is based on the construction of the ternary interface, which makes it have a low detection limit, a wide linear range, a fast response characteristic, and high stability. It can directly test low-concentration glucose under neutral conditions (close to the pH range of saliva) without pretreatment of saliva samples.

[0023] In some embodiments, the mass ratio of the oxidized multi-walled carbon nanotubes, the cerium oxide nanoparticles, and the gold nanoparticles is (1-2):(1-2):1. Controlling the mass ratio of the oxidized multi-walled carbon nanotubes, the cerium oxide nanoparticles, and the gold nanoparticles within the aforementioned range reduces the amount of precious metals used in the ternary interface composite, significantly reducing detection costs. Furthermore, within the aforementioned mass ratio range, the cerium oxide nanoparticles provide a large number of oxygen vacancies in the composite, which promotes electron transport and thus provides an electrocatalytically active interface. Simultaneously, controlling the mass ratio within the aforementioned range allows the ternary interface composite in the sensor to have a larger electrochemically active area and a larger glucose oxidation current.

[0024] In some embodiments, the mass ratio of the oxidized multi-walled carbon nanotubes, the cerium oxide nanoparticles and the gold nanoparticles is 1:1:0.5. At this time, the mass ratio of the oxidized multi-walled carbon nanotubes to the cerium oxide nanoparticles is 1:1. The working electrode at this mass ratio has the largest electrochemical active area and the largest glucose oxidation current. At this time, a certain amount of gold nanoparticles loaded can serve as catalytic active sites to adsorb glucose, reduce the amount of precious metals used, and reduce detection costs.

[0025] In some embodiments, the gold nanoparticles have a particle size of 5.6 nm to 9.6 nm. Gold nanoparticles in this particle size range can adapt to the ternary interface structure and improve the stability of the gold nanoparticles.

[0026] In some embodiments, the working electrode comprises one of a glassy carbon electrode, a gold electrode, and a platinum electrode; the counter electrode comprises one of a glass wire electrode, a platinum electrode, and a graphite electrode; and the reference electrode comprises one of an Ag / AgCl electrode and a saturated calomel electrode. Working, counter, and reference electrodes made of the aforementioned materials have high electrical conductivity, can withstand high current densities, and exhibit a certain degree of chemical stability.

[0027] In a preferred embodiment, the working electrode is a glassy carbon electrode; the counter electrode is a glass wire electrode; and the reference electrode is an Ag / AgCl electrode.

[0028] In addition, the present invention also provides a method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite, comprising the steps of: Step S10: mixing the Au-CeO2 / CNT ternary interface complex with a solvent to obtain a suspension; Step S20: adding the suspension dropwise to the surface of the working electrode, and after drying, obtaining a working electrode loaded with the Au-CeO2 / CNT ternary interface composite; Step S30: The working electrode loaded with the Au-CeO2 / CNT ternary interface complex, the reference electrode, and the counter electrode are combined into a three-electrode system to obtain a non-invasive saliva glucose sensor based on the Au-CeO2 / CNT ternary interface complex.

[0029] In this embodiment, the preparation process is simple and does not require special conditions. The non-invasive saliva glucose sensor prepared by this method loads the Au-CeO2 / CNT ternary interface complex on the working electrode surface, uses the precious metal gold nanoparticles on the complex as catalytic active sites to adsorb glucose, combines with the abundant oxygen vacancies of CeO2 to generate active hydroxyl groups, removes H atoms from glucose-CHO, thereby accelerating the rate of glucose catalytic oxidation reaction, and increases the electron transfer efficiency of the complex by composite oxidation of multi-walled carbon nanotube carriers. In addition, the non-invasive saliva glucose sensor is based on the construction of the ternary interface, which makes it have a low detection limit, a wide linear range, a fast response characteristic, and high stability. It can be used under neutral conditions (close to the pH range of saliva) without the need for pretreatment of saliva samples, thereby achieving direct testing of low-concentration glucose.

[0030] In some embodiments, in step S10, the solvent consists of ethanol, deionized water, and Nafion reagent; the volume ratio is (7-10):(8-12):1.

[0031] In some embodiments, in step S10, the step of preparing the Au-CeO2 / CNT ternary interface composite comprises: Step S11: depositing Ce(OH)3 on the oxidized multi-walled carbon nanotubes using an ammonia precipitation method, and calcining the resultant CeO2 / CNT composite. Step S12: loading gold nanoparticles on the surface of the CeO2 / CNT composite by an in-situ reduction method using sodium borohydride to obtain an Au-CeO2 / CNT ternary interface composite.

[0032] In this embodiment, Ce(OH)3 is first deposited on the oxidized multi-walled carbon nanotubes by utilizing an ammonia precipitation method, and then after calcination, Ce(OH)3 can be decomposed into CeO2, and the calcination treatment can promote the combination between CeO2 and the oxidized multi-walled carbon nanotubes to form a CeO2 / CNT composite; finally, gold nanoparticles are loaded on the interface of the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles by utilizing a sodium borohydride in situ reduction method to obtain an Au-CeO2 / CNT ternary interface composite.

[0033] In some embodiments, in step S11, the step of depositing Ce(OH)3 on oxidized multi-walled carbon nanotubes using an ammonia precipitation method and calcining the resulting CeO2 / CNT composite comprises: Step S111: subjecting the multi-walled carbon nanotubes to a reflux oxidation treatment in nitric acid, followed by washing and drying to obtain oxidized multi-walled carbon nanotubes; Step S112: mixing the oxidized multi-walled carbon nanotubes with cerium nitrate hexahydrate and ammonia water to obtain oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface; Step S113: calcining the oxidized multi-walled carbon nanotubes with Ce(OH) 3 precipitated on the surface to obtain a CeO 2 / CNT composite.

[0034] In some embodiments, step S111 specifically comprises: oxidizing multi-walled carbon nanotubes (MWCNTs) in concentrated nitric acid at 75°C under reflux for 12 hours, then washing the acid-treated MWCNTs with deionized water until neutral, and drying to obtain oxidized multi-walled carbon nanotubes, referred to as CNTs. To increase the contact area between the support and CeO2, the MWCNTs are first pretreated to increase the carboxyl and hydroxyl functional groups on their surfaces, thereby increasing their adsorption sites.

[0035] In some embodiments, step S112 is specifically as follows: first, CNTs (oxidized multi-walled carbon nanotubes) and Ce(NO3)3·6H2O are ultrasonically dispersed in deionized water in a certain proportion; then, an appropriate amount of NH3·H2O solution is added and stirred for a certain period of time to fully precipitate cerium ions to generate Ce(OH)3 precipitates, which are attached to the surface of the CNTs; then, the precipitates are separated by centrifugation and washed three times with deionized water and ethanol respectively to remove interfering ions, thereby obtaining oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface.

[0036] In some embodiments, the step S113 is specifically as follows: drying the precipitate obtained in the step S112 at 60°C for 12 hours, and then calcining it under a nitrogen inert atmosphere, during which Ce(OH)3 decomposes into CeO2 at high temperature. At the same time, the inert atmosphere can prevent CNTs from being oxidized at high temperature, and high-temperature calcination promotes the bonding between CeO2 and CNTs to form a CeO2 / CNT composite.

[0037] In some embodiments, the mass ratio of the oxidized multi-walled carbon nanotubes to the cerium nitrate hexahydrate is (0.2-0.5):1. By controlling the mass ratio of the oxidized multi-walled carbon nanotubes to the cerium nitrate hexahydrate within the above range, a CeO2 / CNT composite with a mass ratio of (1-2):(1-2) can be obtained after the reaction.

[0038] In some embodiments, the calcination temperature is 380°C to 420°C, the calcination time is 3 hours to 4 hours, and the heating rate is 3°C / min to 5°C / min. The calcination decomposes the cerium hydroxide supported on the surface of the oxidized multi-walled carbon nanotubes to produce CeO2. The high-temperature calcination promotes the bonding between CeO2 and CNTs to form a CeO2 / CNT composite.

[0039] In a preferred embodiment, the temperature of the calcination treatment is 400° C., the time of the calcination treatment is 4 hours, and the heating rate of the calcination treatment is 5° C. / min.

[0040] In some embodiments, in step S12, the step of loading gold nanoparticles on the surface of the CeO2 / CNT composite using a sodium borohydride in-situ reduction method to obtain an Au-CeO2 / CNT ternary interface composite comprises: Step S121: mixing the CeO2 / CNT composite with an organic solvent to obtain a carrier suspension; Step S122: dissolving the surfactant in water, adding an organic solvent and HAuCl4·4H2O solution, and adjusting the pH to obtain a mixed solution; Step S123: mixing the carrier suspension with the mixed solution, adding NaBH4 solution, and performing a reduction reaction to obtain an Au-CeO2 / CNT ternary interface composite.

[0041] Specifically, the CeO2 / CNT composite was added to an ethanol solution and ultrasonically treated to fully disperse the support, producing a uniform support suspension. Polyvinyl alcohol (PVA) was added to deionized water and heated to fully dissolve the PVA. Ethanol was then added, followed by a HAuCl4·4H2O solution. The pH of the solution was adjusted with H2SO4 to facilitate the subsequent adsorption of Au onto the CNT composite support. Finally, the solution was added dropwise to the support suspension under stirring. NaBH4 solution was quickly added to fully reduce the HAuCl4. After continued stirring, the mixture was centrifuged, the precipitate washed with deionized water and ethanol, and then dried overnight to obtain the Au-CeO2 / CNT ternary interface composite. The use of polyvinyl alcohol (PVA) as a surfactant helped control the size and dispersibility of the subsequent Au nanoparticles.

[0042] In some embodiments, in step S122, the pH is 2-4, which is conducive to the subsequent adsorption of Au on the carbon nanotube composite support.

[0043] The present invention will be described in detail with reference to the following examples. It should also be understood that the following examples are only intended to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above disclosure of the present invention fall within the scope of protection of the present invention.

[0044] Example 1 This embodiment provides an Au-CeO2 / CNT ternary interface composite, specifically comprising the following: 1) The Au-CeO2 / CNT ternary interface composite was prepared by a two-step deposition process. The preparation process is shown in the figure. Figure 2 As shown, the details are as follows: The MWCNTs were reflux-oxidized in concentrated nitric acid at 75°C for 12 h, and then the acid-treated MWCNTs were washed with deionized water until neutral. The oxidized MWCNTs obtained after drying were recorded as CNTs.

[0045] 0.396 g of CNTs were ultrasonically dispersed in 100 mL of water, and 1.0 g of Ce(NO₃)₃·6H₂O powder was added and stirred to dissolve. Then, 12.9 mL of NH₃·H₂O solution was added and stirred for 4 hours. The precipitate was separated by centrifugation and washed three times with deionized water and ethanol, respectively. The precipitate was dried at 60°C for 12 hours and finally heated to 400°C under a nitrogen atmosphere for 4 hours to obtain a CeO₂ / CNT composite with a CeO₂:CNT mass ratio of 1:1.

[0046] 40 mg of CeO2 / CNT was added to 5 mL of ethanol solution and ultrasonically dispersed for 30 minutes to prepare a uniform support suspension. Then, 10 mg of polyvinyl alcohol (PVA) was weighed and added to 20 mL of deionized water. After heating to dissolve, the solution was adjusted to 20 mL. 20 mL of ethanol was then added, along with 2.1 mL of a 10 mg / mL HAuCl4·4H2O solution. The pH of the solution was adjusted to 2 with 0.5 mol / L H2SO4. Finally, this solution was added dropwise to the support suspension with stirring, followed by 5 mL of a 15 mg NaBH4 solution. After stirring for 5 hours, the mixture was centrifuged, and the precipitate was washed three times with deionized water and ethanol, respectively, before being dried at 60°C overnight to obtain the Au-CeO2 / CNT ternary interface composite.

[0047] 2) Using a method similar to 1), the same amount of Au nanoparticles were loaded on CeO2 and CNT to obtain Au / CeO2 and Au / CNT, respectively.

[0048] The Au-CeO2 / CNT ternary interface composites, Au / CeO2 and Au / CNT prepared in 1) and 2) were characterized by transmission electron microscopy. The TEM (transmission electron microscopy) images are shown in Figure 2. Figure 3 As shown, Figure 3 (a) and (b) are TEM images of Au / CNT, (c) and (d) are TEM images of Au / CeO2, and (e) and (f) are TEM images of Au-CeO2 / CNT. (B), (D), and (F) are high-resolution transmission electron micrographs. It can be seen from the figures that Au nanoparticles tend to deposit at the interface between CeO2 and CNT (circled), forming an Au-CeO2 / CNT ternary interface. Compared with Au / CeO2 and Au / CNT catalysts, this ternary interface structure stabilizes the Au nanoparticles and reduces their size (7.6±2.0nm).

[0049] The Au-CeO2 / CNT ternary interface composite and Au / CNT were characterized by X-ray diffractometer, and the XRD patterns were as follows: Figure 4 As shown, the characteristic diffraction peaks of CNT, Au and CeO2 are displayed, confirming the formation of the ternary composite material.

[0050] XPS characterization was used to study the surface chemical composition and valence state of Au-CeO2 / CNT ternary interface composite and Au / CNT, such as Figure 5 As shown in the figure (where (a) is Au 4f and (b) is Ce 3d), it can be seen that the XPS peaks near 84.14 and 87.85 eV in the Au-CeO2 / CNT ternary interface composite correspond to Au 0 The 4f7 / 2 and 4f5 / 2 states of the α-Hydroxy-Au-Pb ... + The Au in Au-CeO2 / CNT (92.4%) and Au / CNT (91.4%) catalysts 0 At the same time, the Au in the Au-CeO2 / CNT ternary interface composite 0 The peak shifted negatively by only 0.06 eV, which means that the electronic structure of Au is not the main factor affecting the catalytic activity. 3+ The content is 25.1%, indicating that there are a large number of oxygen vacancies in the Au-CeO2 / CNT catalyst, which promotes the transport of electrons and thus provides an electrocatalytic active interface.

[0051] Example 2 This embodiment provides a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite. The preparation process is as follows: 5 mg of the Au-CeO2 / CNT ternary interface complex prepared in Example 1 was weighed and added to a 2 ml sample tube. 1.5 ml of a mixed solution consisting of ethanol, deionized water, and Nafion reagent (volume ratio of 45:50:5) was added thereto, and ultrasonicated for more than 1 hour to form a uniform suspension. A 3 mm glassy carbon electrode was polished in an electrode polisher, rinsed with deionized water, and dried in an infrared drying oven to ensure that the electrode surface was free of contamination. 5 μL of the above sample suspension was taken with a microliter syringe and added dropwise to the surface of the glassy carbon electrode. The working electrode was naturally dried. An Ag / AgCl electrode was used as a reference electrode and a glass wire electrode was used as a counter electrode. After assembly, a non-invasive salivary glucose sensor was obtained.

[0052] In comparison, a non-invasive salivary glucose sensor was prepared using Au / CNT using the same method.

[0053] The performance of the noninvasive salivary glucose sensor was characterized using a three-electrode system in phosphate buffer solution (PBS = 7.4) under neutral conditions. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) were performed to characterize the electrocatalytic performance of the sensor electrode itself and its glucose electrocatalytic performance. Prior to electrochemical testing, the PBS solution (phosphate buffer solution) was purged with nitrogen for 30 minutes to remove dissolved oxygen from the electrolyte. Performance testing examined the effects of the assembly of Au, CeO2, and CNTs, as well as the CeO2 doping level, on the catalytic performance, and explored the electrocatalytic reaction mechanism of the Au-CeO2 / CNT ternary interface composite.

[0054] Specifically, the non-invasive salivary glucose sensors prepared using Au / CNT and Au-CeO2 / CNT were subjected to cyclic voltammetry (CV) measurements in 0.1M PBS and 0.5M glucose solutions. The CV curves of the sensors in 0.1M PBS and 0.5M glucose are shown in Figure 2. Figure 6 As shown, the scan rate is 100 mV s -1 The largest redox peak was observed in the Au-CeO2 / CNT system. The results show that Au-CeO2 / CNT has the highest electrochemical performance and can accelerate the electron transfer rate.

[0055] The electron transport properties and glucose oxidation properties of Au-CeO2 / CNT with different CeO2:CNT mass ratios (1:0.7, 1:1, 1:1.5, 1:2) are compared. The CV curves of Au-CeO2 / CNT with different CeO2:CNT mass ratios in 0.1M PBS (left) and 0.1M PBS and 0.01M glucose (right) are shown in Figure 2. Figure 7As shown, it can be seen that when CeO2:CNT=1:1, the obtained Au-CeO2 / CNT non-invasive saliva glucose sensor has the largest electrochemical active area and the largest glucose oxidation current.

[0056] The electrochemical sensing performance of the prepared Au-CeO2 / CNT non-invasive saliva glucose sensor was further evaluated by amperometry. At a constant potential of 0.40 V (vs Ag / AgCl), the chronoamperometric curve of the Au-CeO2 / CNT non-invasive saliva glucose sensor was measured by continuously adding different concentrations of glucose (0.05 mM-9 mM). The results are shown in Figure 2. Figure 8 As shown; during the glucose titration process, even at low concentrations, it shows a typical step-like current response as the concentration increases ( Figure 8 The inset in Figure 2 shows the chronoamperometric curves at glucose concentrations of 0.05 mM–1 mM), demonstrating the excellent current response characteristics of the electrode to glucose. Figure 9 The calibration curve between current and glucose concentration is shown in the figure. The corresponding linear fitting curve shows that the linear fitting equation has good linearity in the entire concentration range (R 2 =0.998), the linear fitting equation is y=2.053×10 -2 x+3.651×10 -4 Taking into account the surface area of ​​the working electrode, the sensitivity of the sensor was calculated to be 9.124 μA / mM / cm 2 The sensor's limit of detection (LOD) was calculated using a signal-to-noise ratio of 3, yielding a LOD of 1.79 μM. Compared to previously reported glucose detection performance of Au-based electrodes under neutral conditions, this sensor exhibits a lower LOD and exhibits a significantly larger linear range.

[0057] Finally, to evaluate the potential application of this glucose sensor in real-world samples, glucose sensing experiments were conducted using human saliva samples. Specifically, saliva samples were collected from volunteers and used for glucose sensing measurements. On the day of collection, participants should avoid consuming licorice-based foods and lip balm-based lip care products. Smoking, brushing teeth, eating, drinking, or drinking coffee should be avoided 30 minutes prior to collection. Before collection, the participants should rinse their mouths with water to remove food debris. Saliva samples were collected using a Salivette saliva collection tube. Participants were instructed to place a cotton swab in the tube and hold it sublingually for 1-3 minutes, or chew the swab for 1 minute. The saliva was then spitted back into the tube. Saliva was then collected after centrifugation. After collection, depending on the nature of the test substance, the saliva sample was either temporarily refrigerated at 4°C or directly frozen at -20°C or -80°C until testing.

[0058] Since the concentration of glucose in healthy human saliva is very low (20µM-400µM), in order to obtain saliva samples of different concentrations for use in the calibration curve, different concentrations of glucose (0.05mM, 0.10mM, and 0.15mM) were added to 100 μL of saliva. Sensing tests were carried out in 0.1M PBS medium. The current response of the Au-CeO2 / CNT electrode after adding saliva samples of different concentrations of glucose (0.05mM, 0.10mM, and 0.15mM) is shown in Figure 2. Figure 10 As shown in the figure, it shows the current response of the sensor electrode after adding the original saliva sample and the saliva sample added with glucose. The current response value increases proportionally with the glucose concentration, confirming the effectiveness of the sensor in actual sample analysis. The relationship between the current and glucose concentration of the saliva samples with 0.05mM, 0.10mM and 0.15mM glucose is shown in the figure. Figure 11 As shown in the figure, the calibration curve of glucose detection in human saliva is given. The calculation results show that the sensitivity of the Au-CeO2 / CNT electrode for detecting glucose in saliva is 2.4μA·mM -1 cm -2 .

[0059] In summary, the present invention provides a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface complex and a preparation method thereof. The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface complex includes a three-electrode system consisting of a working electrode, a counter electrode, and a reference electrode; the surface of the working electrode is loaded with the Au-CeO2 / CNT ternary interface complex; the Au-CeO2 / CNT ternary interface complex includes oxidized multi-walled carbon nanotubes, cerium oxide nanoparticles loaded on the surface of the oxidized multi-walled carbon nanotubes, and gold nanoparticles deposited at the interface between the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles. The non-invasive saliva glucose sensor of the present invention loads an Au-CeO2 / CNT ternary interface complex on the surface of the working electrode, utilizes the precious metal gold nanoparticles on the complex as catalytic active sites to adsorb glucose, combines with the abundant oxygen vacancies of CeO2 to generate active hydroxyl groups, and removes H atoms from the glucose-CHO, thereby accelerating the glucose catalytic oxidation reaction rate. The electron transfer efficiency of the complex is increased by composite oxidation of multi-walled carbon nanotube carriers. Furthermore, the non-invasive saliva glucose sensor, based on the construction of the ternary interface, has a low detection limit, a wide linear range, a fast response characteristic, and high stability. It can directly test low-concentration glucose under neutral conditions (close to the pH range of saliva) without pretreatment of the saliva sample.

[0060] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A non-invasive salivary glucose sensor based on Au-CeO2 / CNT ternary interface composite, characterized in that: The invention comprises a three-electrode system consisting of a working electrode, a counter electrode and a reference electrode; the surface of the working electrode is loaded with an Au-CeO2 / CNT ternary interface complex; the Au-CeO2 / CNT ternary interface complex comprises oxidized multi-walled carbon nanotubes, cerium oxide nanoparticles loaded on the surface of the oxidized multi-walled carbon nanotubes, and gold nanoparticles loaded at the interface between the oxidized multi-walled carbon nanotubes and the cerium oxide nanoparticles.

2. The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 1, characterized in that: The mass ratio of the oxidized multi-walled carbon nanotubes, the cerium oxide nanoparticles and the gold nanoparticles is (1-2):(1-2):(0.5-1).

3. The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 1, characterized in that: The particle size of the gold nanoparticles is 5.6nm-9.6nm.

4. The non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 1, characterized in that: The working electrode includes one of a glassy carbon electrode, a gold electrode, and a platinum electrode; the counter electrode includes one of a glass wire electrode, a platinum electrode, and a graphite electrode; and the reference electrode includes one of an Ag / AgCl electrode and a saturated calomel electrode.

5. A method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to any one of claims 1 to 4, characterized in that: Including steps: The Au-CeO2 / CNT ternary interface composite is mixed with a solvent to obtain a suspension; The suspension is added dropwise to the surface of the working electrode, and after drying, a working electrode loaded with the Au-CeO2 / CNT ternary interface composite is obtained; The working electrode loaded with the Au-CeO2 / CNT ternary interface complex, a reference electrode, and a counter electrode form a three-electrode system to obtain a non-invasive saliva glucose sensor based on the Au-CeO2 / CNT ternary interface complex.

6. The method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 5, characterized in that: The steps for preparing the Au-CeO2 / CNT ternary interface composite include: Ce(OH)3 was deposited on oxidized multi-walled carbon nanotubes using ammonia precipitation method and then calcined to obtain CeO2 / CNT composites. Gold nanoparticles are loaded on the surface of the CeO2 / CNT composite by an in-situ reduction method using sodium borohydride to obtain an Au-CeO2 / CNT ternary interface composite.

7. The method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 6, characterized in that: The step of depositing Ce(OH)3 on oxidized multi-walled carbon nanotubes by ammonia precipitation method and calcining to obtain a CeO2 / CNT composite comprises: The multi-walled carbon nanotubes are subjected to a reflux oxidation treatment in nitric acid, and then washed and dried to obtain oxidized multi-walled carbon nanotubes; Mixing the oxidized multi-walled carbon nanotubes with cerium nitrate hexahydrate and ammonia water to obtain oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface; The oxidized multi-walled carbon nanotubes with Ce(OH)3 precipitated on the surface are calcined to obtain a CeO2 / CNT composite.

8. The method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 7, characterized in that: The mass ratio of the oxidized multi-walled carbon nanotubes to the cerium nitrate hexahydrate is (0.2-0.5):

1.

9. The method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 6 or 7, characterized in that: The temperature of the calcination treatment is 380° C.-420° C., the time of the calcination treatment is 3 h-4 h, and the heating rate of the calcination treatment is 3° C. / min-5° C. / min.

10. The method for preparing a non-invasive salivary glucose sensor based on the Au-CeO2 / CNT ternary interface composite according to claim 6, characterized in that: The step of loading gold nanoparticles on the surface of the CeO2 / CNT composite by using a sodium borohydride in-situ reduction method to obtain an Au-CeO2 / CNT ternary interface composite comprises: Mixing the CeO2 / CNT composite with an organic solvent to obtain a carrier suspension; The surfactant is dissolved in water, and an organic solvent and HAuCl4·4H2O solution are added, and the pH is adjusted to obtain a mixed solution; The carrier suspension is mixed with the mixed solution, and a NaBH4 solution is added to obtain an Au-CeO2 / CNT ternary interface composite after a reduction reaction.

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