An enzyme-free glucose photoelectrochemical sensing electrode, sensor and preparation method thereof

Abstract

The present invention belongs to the field of photoelectrochemical sensing. In order to solve the problem of poor fluidity of the solution to be tested on the surface of the sensing electrode, an enzyme-free glucose photoelectrochemical sensing electrode, a sensor and a preparation method thereof are disclosed, comprising an n-type silicon layer / conductive layer / waterproof insulating layer; the upper surface of the n-type silicon layer is convex upwardly to form a nanowire array; the surface of the nanowire array is coated with a p-type metal oxide semiconductor thin film layer; the heterojunction energy band structure formed by the p-type metal oxide semiconductor thin film layer and the n-type silicon layer is a staggered type, and the n-type silicon layer forms an ohmic contact with the conductive layer. Under the irradiation of incident light, the photogenerated electron-hole pairs generated by the p-type metal oxide semiconductor thin film layer and the nanowire array are effectively separated under the combined action of the built-in electric field of the heterojunction and the external bias voltage. It is possible to achieve high sensitivity, high selectivity and low background noise detection of glucose without enzyme modification and with a certain external bias voltage.

Description

Technical Field

[0001] The invention belongs to the field of photoelectrochemical sensing and relates to a photoelectrochemical sensing electrode, a sensor and a preparation method thereof. Background Art

[0002] Diabetes is a metabolic disease characterized by high blood sugar and a global public health problem. In order to effectively control the blood sugar levels of diabetic patients and prevent the occurrence of complications, it is of great significance to design a convenient, efficient and stable glucose sensor to monitor the blood sugar levels of patients in real time.

[0003] Glucose sensors can be divided into enzymatic glucose sensors and non-enzymatic glucose sensors according to whether they are modified by glucose enzymes. Non-enzymatic glucose sensors can be divided into optical sensors, electrochemical sensors, and photoelectrochemical sensors based on different sensing principles. Currently, most blood glucose meters on the market use enzymatic glucose sensors, but glucose enzymes are easily inactivated by drastic changes in the environment such as temperature and pH value, which greatly limits their application range (Lee H, et al. Advanced Healthcare Materials, 2018, 7(8): 1701150). In enzyme-free glucose sensors, optical sensors use the effect of changes in the concentration of the analyte on the refractive index of the environment to infer the specific concentration of the analyte. The advantage is high sensing sensitivity, but the disadvantage is that it does not have sensing specificity for glucose, and the preparation cost is usually high, which is not conducive to large-scale promotion (Yuan Y, et al. Photonic Sensors, 2019, 9(4): 309-316); electrochemical sensors usually use the current response changes of metal or metal oxide micro-nano structures to changes in glucose concentration to detect glucose concentration. The advantages are that they are not easily affected by environmental interference and have good stability. The disadvantage is that they use electrical signals as both excitation signals and detection signals, resulting in large background noise (Teymourian H, et al. Chemical Society Reviews, 2020, 49(21): 7671-7709); photoelectrochemical sensors are based on the photoelectric properties of semiconductor materials, using optical signals as excitation signals. Due to changes in glucose concentration, photocurrent response changes are generated, and electrical signals are used as detection signals. This can significantly reduce background noise while ensuring high sensitivity, high stability, and high selectivity of the sensor (Cao L, et al. RSC Advances, 2019, 9(27): 15307-15313). In addition, most of the photoelectrochemical sensors currently studied use disordered structures or semi-enclosed structures (such as porous titanium oxide), and the flowability of the substance to be measured on the surface of the sensor electrode is poor, which restricts the further improvement of the sensor sensitivity (Lin X, et al. Chinese Chemical Letters, 2019, 30(6): 1157-1160). Summary of the invention

[0004] The present invention is to solve the problems of the existing glucose sensor technology that requires glucose enzyme modification, low sensitivity, low selectivity, large background noise and poor fluidity of the solution to be tested on the surface of the sensing electrode, and proposes the following technical solutions:

[0005] An enzyme-free glucose photoelectrochemical sensing electrode comprises an n-type silicon layer and a conductive layer arranged on the lower surface of the n-type silicon layer; the upper surface of the n-type silicon layer protrudes upward to form a nanowire array; the upper surface of the n-type silicon layer is uniformly coated with a p-type metal oxide semiconductor film layer; the p-type metal oxide semiconductor film layer and the n-type silicon layer form a heterojunction, and the heterojunction energy band structure is a staggered second-type heterojunction; the n-type silicon layer and the conductive layer form an ohmic contact; the lower surface of the conductive layer, the side wall of the conductive layer, and the side wall of the n-type silicon layer are all coated with a waterproof insulating layer.

[0006] Under the irradiation of incident light, the p-type metal oxide semiconductor thin film layer and the nanowire array produce photogenerated electron-hole pairs, which are effectively separated under the combined action of the built-in electric field of the heterojunction and the external bias voltage to form a photocurrent proportional to the glucose concentration.

[0007] The upper surface of the n-type silicon layer is uniformly coated with a p-type metal oxide semiconductor thin film layer, which covers the top and side walls of the nanowire array and the gap between the bottom of the nanowire array. The p-type metal oxide semiconductor thin film layer forms a conformal structure with the upper surface of the n-type silicon layer.

[0008] Preferably, the material of the p-type metal oxide semiconductor thin film layer includes: copper oxide (CuO x ), nickel oxide (NiO x ), cobalt oxide (CoO x ), iron oxide (FeO x ), manganese oxide (MnO x ), cerium oxide (CeO x ) or a mixture consisting of more than one of them.

[0009] Preferably, the p-type metal oxide semiconductor thin film layer is formed by continuous accumulation of nanoparticles and has a thickness of 20 to 300 nm.

[0010] Preferably, the resistivity of the n-type silicon layer is 1-10Ωcm.

[0011] Preferably, the nanowire array disposed on the upper surface of the n-type silicon layer is arranged in a hexagonal or tetragonal pattern, the center spacing between adjacent nanowires is 1 to 5 μm, the length of a single nanowire is 2 to 10 μm, and the diameter is 300 to 4000 nm.

[0012] Preferably, the nanowire array is manufactured by chemically wet etching or reactive ion etching the upper surface of the n-type silicon layer.

[0013] Preferably, the conductive layer material is a metal with a work function lower than 4.3 eV.

[0014] Preferably, the counter electrode is made of metal platinum.

[0015] A non-enzyme glucose photoelectrochemical sensor, wherein the conductive layer of the non-enzyme glucose photoelectrochemical sensing electrode is provided with a lead end, and the lead end is sequentially connected to an ammeter, an applied voltage, and a counter electrode; the non-enzyme glucose photoelectrochemical sensing electrode and the counter electrode are placed in a light-transmitting container; and the light-transmitting container is filled with a glucose electrolyte to be tested.

[0016] When incident light irradiates the surface of the enzyme-free glucose photoelectrochemical sensing electrode, both the p-type metal oxide semiconductor thin film layer and the n-type silicon layer absorb light to generate photogenerated electron-hole pairs; under the combined action of the built-in electric field of the heterojunction and the external bias voltage, the photogenerated electron-hole pairs are separated, and the photogenerated electron holes are transmitted to the interface between the p-type metal oxide semiconductor thin film layer and the glucose electrolyte to be measured, and selectively undergo oxidation reaction with the glucose molecules in the glucose electrolyte to be measured; the photogenerated electrons are transmitted to the conductive layer through the n-type silicon layer, and then transmitted to the counter electrode to undergo corresponding reduction reaction; a photogenerated current is formed between the enzyme-free glucose photoelectrochemical sensing electrode and the counter electrode; the ammeter is used to monitor the size of the photogenerated current, and the glucose concentration to be measured is measured according to the correlation between the photogenerated current and the concentration of the glucose electrolyte to be measured.

[0017] Preferably, the incident light is white light, sunlight or simulated sunlight.

[0018] In the scheme of the present invention, the heterojunction constructed by the n-type silicon layer and the p-type metal oxide semiconductor thin film layer can efficiently absorb the incident light to generate photogenerated electron-hole pairs, and effectively separate the photogenerated electron-hole pairs under the combined action of the built-in electric field and the external bias voltage of the heterojunction. The photogenerated electron-holes are transmitted to the interface between the p-type metal oxide semiconductor thin film layer and the electrolyte, and selectively undergo oxidation reaction with the glucose molecules in the electrolyte. The photogenerated electrons are transmitted to the counter electrode through the conductive layer to undergo reduction reaction. With the generation of photogenerated electron-holes inside the sensing electrode and the transfer at the interface between the sensing electrode and the electrolyte, the valence state of the metal element in the p-type metal oxide semiconductor thin film layer is increased and then combined with the electrons in the glucose molecule as an electron acceptor, thereby being reduced again. This cyclic process of the valence state of the metal element first rising and then falling makes the enzyme-free glucose photoelectrochemical sensing electrode have recognition characteristics for glucose molecules. As the glucose concentration increases, the more intense the oxidation reaction on the surface of the sensing electrode, the larger the photogenerated current formed, and finally the enzyme-free glucose photoelectrochemical sensing electrode has sensing characteristics for glucose molecules.

[0019] In addition, the nanowire array on the upper surface of the n-type silicon layer has a large specific surface area, which can provide growth sites and photoelectrochemical active sites for the subsequently introduced p-type metal oxide semiconductor thin film layer; the nanowire array on the upper surface of the n-type silicon layer and the p-type metal oxide semiconductor thin film layer constitute a nanowire core / shell structure heterojunction, which has excellent optical anti-reflection performance and can efficiently absorb and utilize incident light of a wide spectrum. Due to its semiconductor electrical properties, the n-type silicon layer shows a small dark current of the enzyme-free glucose photoelectrochemical sensor electrode, which is much lower than the electrochemical sensor based on a conductive substrate. Since the enzyme-free glucose photoelectrochemical sensor electrode does not use glucose enzyme, it has better temperature and pH stability than the enzymatic glucose sensor. Due to its open and controllable columnar morphology, the nanowire array is more conducive to the circulation of the solution to be tested compared to the disordered nanostructure and porous structure, making its sensing sensitivity higher.

[0020] The present application also discloses a method for preparing an enzyme-free glucose photoelectrochemical sensing electrode, comprising the following steps:

[0021] Step 1: Select an n-type planar silicon substrate as the n-type silicon layer, perform template-assisted chemical wet etching or reactive ion etching on the upper surface of the n-type planar silicon substrate, and prepare a size-controllable nanowire array on the upper surface of the n-type silicon layer;

[0022] Step 2: depositing a p-type metal oxide semiconductor thin film layer on the surface of the nanowire array;

[0023] Step 3: Making a conductive layer on the back of the n-type silicon layer and leading out a wire on the conductive layer;

[0024] Step 4: Use waterproof insulating glue to coat a waterproof insulating layer on the lower surface of the conductive layer, the side wall of the conductive layer, and the side wall of the n-type silicon layer.

[0025] Preferably, depositing a p-type metal oxide semiconductor thin film layer on the surface of the nanowire array in step 2 is further divided into the following steps:

[0026] (a) First, a 20-100 nm thick p-type metal oxide semiconductor thin film seed layer is pre-sputtered or pre-evaporated on the upper surface of the n-type silicon layer;

[0027] (b) Then, the n-type silicon layer deposited with the p-type metal oxide thin film seed layer is placed in a reaction vessel, and a 100-300 nm thick p-type metal oxide thin film layer is grown on the upper surface of the p-type metal oxide semiconductor thin film seed layer through a hydrothermal reaction.

[0028] Further: In step (b), a p-type metal oxide hydrothermal reaction precursor solution is added to the reaction kettle and reacted at 100 to 300° C. for 1 to 12 hours.

[0029] The p-type metal oxide semiconductor thin film layer is obtained by annealing the 20-100nm thick p-type metal oxide semiconductor thin film seed layer and the 100-300nm thick p-type metal oxide semiconductor thin film layer obtained by different preparation methods in steps (a) and (b).

[0030] Technical Effects

[0031] By adopting the scheme of the present invention, the glucose concentration can be detected with high sensitivity, high selectivity and high stability under the condition of white light or sunlight irradiation, no enzyme modification and external bias voltage. Because under the condition of external bias voltage, both the n-type silicon layer and the p-type metal oxide semiconductor thin film layer can absorb the incident light and form a heterojunction with a staggered energy band structure (i.e., the conduction band bottom and valence band top of the n-type silicon are lower than the conduction band bottom and valence band top of the p-type metal oxide semiconductor thin film layer, and the conduction band bottom of the n-type silicon is higher than the valence band bottom of the p-type metal oxide semiconductor thin film), and at the same time, after the heterojunction contacts with the glucose electrolyte to be tested, the energy band of the p-type metal oxide semiconductor thin film near the solid-liquid interface bends upward, and this energy band distribution is conducive to the separation of photogenerated electrons and holes to the solid-liquid interface. Since the length, diameter and period of the nanowire array can be controlled by controlling the geometric parameters of the template, chemical corrosion or reactive ion etching process parameters, the p-type metal oxide semiconductor thin film layer introduced subsequently can continuously cover the top, sidewall and gap area of ​​the nanowire array at the bottom of the nanowire while ensuring a large specific surface area, providing high-efficiency light absorption and high-density active sites for the enzyme-free glucose photoelectrochemical sensing electrode, and finally making the enzyme-free glucose photoelectrochemical sensing electrode highly sensitive to changes in glucose concentration. Due to the cyclic change of the valence state of the metal element in the p-type metal oxide semiconductor thin film layer in the glucose detection process, the enzyme-free glucose photoelectrochemical sensing electrode has sensing selectivity for glucose molecules. Due to the ordered, open columnar morphology of the nanowire array, (compared to the semi-enclosed nanopore structured sensing electrode) it can provide convenience for the flow of the solution to be tested on the surface of the sensing electrode, thereby facilitating the improvement of sensing sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 :Schematic diagram of the structure of the enzyme-free glucose photoelectrochemical sensing electrode;

[0033] Wherein: 11 is a waterproof insulating layer, 12 is a conductive layer, 13 is an n-type silicon layer with a nanowire array protruding on the top, and 14 is a p-type metal oxide semiconductor thin film layer.

[0034] Figure 2 :Schematic diagram of the working of an enzyme-free glucose photoelectrochemical sensor;

[0035] Wherein: 21 is an ammeter, 22 is a light-transmitting container, and 23 is a counter electrode;

[0036] Figure 3 :Schematic diagram of carrier transport principle of enzyme-free glucose photoelectrochemical sensing electrode;

[0037] Wherein: 31 is the process of the p-type metal oxide semiconductor thin film layer absorbing light to generate photogenerated electron-hole pairs, 32 is the process of the n-type silicon layer absorbing light to generate photogenerated electron-hole pairs, 33 is the photogenerated electron hole, 34 is the photogenerated electron, and 35 is the glucose electrolyte to be tested.

[0038] Figure 4 : Scanning electron micrographs of samples obtained at different stages of the preparation process of the enzyme-free glucose photoelectrochemical sensing electrode;

[0039] Among them: 41 is a side view image of the prepared nanowire array, 42 is a side view image of the nanowire array after magnetron sputtering a thin copper oxide film layer, 43 is a side view image of a nanowire array coated with a thicker copper oxide film layer after hydrothermal growth, 44 is a top view image of the sample corresponding to 41, 45 is a top view image of the sample corresponding to 42, and 46 is a top view image of the sample corresponding to 43.

[0040] Figure 5 : The current density variation curves of the four types of sensor electrodes prepared under 0.5V bias, different glucose concentrations, with or without cyclic light;

[0041] Among them: 51 is an enzyme-free glucose photoelectrochemical sensing electrode based on an n-type silicon layer with a nanowire array on the upper surface, 52 is an enzyme-free glucose photoelectrochemical sensing electrode based on an n-type planar silicon layer / copper oxide thin film layer, 53 is an enzyme-free glucose photoelectrochemical sensing electrode based on FTO / p-type copper oxide thin film layer, and 54 is an enzyme-free glucose photoelectrochemical sensing electrode based on an n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the upper surface.

[0042] Figure 6 : The sensing sensitivity fitting curve of the enzyme-free glucose photoelectrochemical sensing electrode based on the n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the upper surface.

[0043] Figure 7 : Sensing selectivity test curve of the enzyme-free glucose photoelectrochemical sensing electrode based on an n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the upper surface.

[0044] Figure 8 : A bar graph showing the photocurrent response percentage of an enzyme-free glucose photoelectrochemical sensing electrode based on an n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the upper surface to typical interfering substances. DETAILED DESCRIPTION

[0045] In order to more clearly illustrate the present technical solution, further description is given below in conjunction with the accompanying drawings and embodiments.

[0046] Embodiment 1

[0047] like Figure 1 As shown, an enzyme-free glucose photoelectrochemical sensing electrode comprises an n-type silicon layer 13 and a conductive layer 12 arranged on the lower surface of the n-type silicon layer; the upper surface of the n-type silicon layer protrudes upward to form a nanowire array; the upper surface of the n-type silicon layer is uniformly coated with a p-type metal oxide semiconductor thin film layer 14; the p-type metal oxide semiconductor thin film layer and the n-type silicon layer form a heterojunction, and the heterojunction energy band structure is a staggered second-type heterojunction; the n-type silicon layer and the conductive layer form an ohmic contact; the lower surface of the conductive layer, the side wall of the conductive layer, and the side wall of the n-type silicon layer are all coated with a waterproof insulating layer 11.

[0048] The nanowire array is prepared by chemical wet etching or reactive ion etching on the upper surface of the n-type silicon layer. The p-type metal oxide semiconductor thin film layer forms a pn-type heterojunction with the n-type silicon layer, and the energy band structure type of the heterojunction is a staggered second-type heterojunction (i.e., the conduction band bottom and valence band top of the p-type metal oxide semiconductor thin film layer are respectively higher than the conduction band bottom and valence band top of the n-type silicon layer, and the conduction band bottom of the n-type silicon layer is higher than the valence band top of the p-type metal oxide semiconductor thin film layer). Under the combined action of the built-in electric field of the heterojunction and the external bias, the photogenerated electron-hole pairs generated by the n-type silicon layer and the p-type metal oxide semiconductor thin film layer absorbing incident light can be effectively separated. The n-type silicon layer forms an ohmic contact with the conductive layer. The p-type metal oxide semiconductor thin film layer forms a solid-liquid junction with the electrolyte, and under the external bias, the energy band of the p-type metal oxide semiconductor thin film layer bends upward near the solid-liquid junction interface.

[0049] Embodiment 2

[0050] An enzyme-free glucose photoelectrochemical sensor, such as Figure 2 As shown, a lead terminal is provided on the conductive layer 12 of the non-enzyme glucose photoelectrochemical sensing electrode, which is connected to a voltage source, an ammeter 21, and a counter electrode 23 in sequence; the non-enzyme glucose photoelectrochemical sensing electrode and the counter electrode are placed in a light-transmitting container 22; the light-transmitting container is filled with a glucose electrolyte 35 to be tested; a waterproof insulating layer separates the conductive layer from the electrolyte; when incident light irradiates the surface of the photoelectrochemical sensing electrode, a certain bias voltage (such as 0.5V) is applied between the photoelectrochemical sensing electrode and the counter electrode, and the corresponding energy band structure is as follows Figure 3As shown, both the n-type silicon layer and the p-type metal oxide semiconductor thin film layer can absorb incident light to generate photogenerated electron-hole pairs, 31 is the process of the p-type metal oxide semiconductor thin film layer absorbing light to generate photogenerated electron-hole pairs, and 32 is the process of the n-type silicon layer absorbing light to generate photogenerated electron-hole pairs; the generated photogenerated electron-hole pairs are separated under the combined action of the built-in electric field of the heterojunction and the external bias voltage, wherein the photogenerated electron holes 33 are transported to the interface between the p-type metal oxide semiconductor thin film layer and the glucose electrolyte to be tested, and selectively undergo oxidation reaction with glucose molecules, wherein the photogenerated electrons 34 flow into the conductive layer, and finally are transported to the counter electrode through an external wire to undergo reduction reaction, thereby generating a photocurrent response between the enzyme-free glucose photoelectrochemical sensing electrode and the counter electrode 23; the ammeter can monitor the change in current size, and the displayed photocurrent value is positively correlated with the glucose concentration in the electrolyte, thereby realizing the detection of glucose concentration.

[0051] The nanowire array presents an orderly arrangement and an open columnar morphology, which can provide convenience and a large contact area for the flow of the solution to be tested on the surface of the sensing electrode on the one hand, and provide a high-density growth site for the subsequent growth of the p-type metal oxide semiconductor thin film layer on the other hand, thereby facilitating the improvement of the sensing sensitivity. During the sensing process, the valence state of the metal element in the p-type metal oxide semiconductor thin film layer will increase first and then decrease in a cyclic change with the oxidation process of the glucose molecules, which makes the enzyme-free glucose photoelectrochemical sensing electrode selectively sensitive to glucose molecules.

[0052] The n-type silicon layer and the p-type metal oxide semiconductor thin film layer have extremely high resistance in a dark environment due to their semiconductor electrical properties, so that the dark current of the enzyme-free glucose photoelectrochemical sensor electrode is small, and the resistance is significantly reduced when there is light, so that the enzyme-free glucose photoelectrochemical sensor electrode has a large photocurrent. This current difference with and without light can significantly reduce background noise. At the same time, due to the lack of glucose enzyme modification, the glucose photoelectrochemical sensor electrode has good adaptability and performance stability to changes in temperature and pH.

[0053] In view of the above characteristics, the enzyme-free glucose photoelectrochemical sensing electrode can achieve high-sensitivity, high-selectivity and low-background-noise detection of glucose without enzyme modification and with a certain bias voltage.

[0054] Embodiment 3

[0055] A method for preparing an enzyme-free glucose photoelectrochemical sensing electrode, the preparation process comprising:

[0056] 1) A 0.5 mm thick, n-type doping, and resistivity 1-10 Ωcm planar silicon layer is used as an n-type silicon layer, and a nanowire array is prepared on its upper surface. The nanowire array is arranged in a hexagonal pattern, and its microscopic morphology is as follows: Figure 4 As shown in 41 and 44;

[0057] 2) Using radio frequency magnetron sputtering technology, a 10-50 nm thick copper oxide seed layer is pre-sputtered on the surface of the sample prepared in step 1), and its microscopic morphology is as follows: Figure 4 As shown in 42 and 45;

[0058] 3) The sample prepared in step 2) was placed in a reaction kettle, and 80 mL of a mixture of 20 mM copper nitrate and 20 mM hexamethylenetetramine was added. After reacting at 80°C for 3 to 5 hours, the sample was taken out and washed with deionized water. After natural drying, the microscopic morphology thereof was as follows: Figure 4 As shown in 43 and 46;

[0059] 4) annealing the sample prepared in step 3) at 200-500° C. in an air atmosphere for 1-3 hours to obtain a heterojunction of an n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the upper surface;

[0060] 5) A conductive layer is made at the bottom of the sample obtained in step 4), and after the lead end is led out, the side wall of the conductive layer and the heterojunction of the n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the top is sealed with a waterproof insulating material, leaving only the front side of the heterojunction of the n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the top exposed, thereby obtaining the enzyme-free glucose photoelectrochemical sensing electrode.

[0061] from Figure 4 It can be seen that after the preparation steps, the top, sidewalls and bottom gap of the n-type silicon layer with an ordered nanowire array on the top are covered with a p-type copper oxide thin film layer. This significant change in micromorphology proves that the p-type copper oxide thin film layer is successfully grown on the surface of the n-type silicon layer with a nanowire array on the top. In order to test its sensing properties of glucose concentration, simulated sunlight is used as the light source, an electrochemical workstation is used as the measuring instrument, a quartz electrolytic cell is used as the phototransmitting electrolytic cell, a platinum mesh electrode is used as the counter electrode, and a 0.1M NaOH solution containing different concentrations of glucose is used as the electrolyte. Ag / AgCl electrode is also introduced as the reference electrode in the test system to control the working potential of the enzyme-free glucose photoelectrochemical sensor electrode.

[0062] In order to prove the superior performance of the heterojunction photoelectrochemical sensing electrode of n-type silicon layer / p-type copper oxide thin film layer with nanowire array on top, three types of samples were introduced as control groups: one is the n-type silicon layer with nanowire array on top (no other material layer is modified), the second is the p-type copper oxide thin film layer grown on the n-type silicon layer, and the third is the p-type copper oxide thin film layer grown on the FTO substrate. The above three types of control sensing electrodes and the target sensing electrode were placed in the same test system, and a 0.5V potential was applied to the working electrode. In the absence of light, the same volume and concentration of glucose solution were added to the 0.1M NaOH electrolyte solution. Light was introduced after each addition to conduct current density-time tests with / without light. Figure 5 As shown in Figure 2, although the unmodified nanowire array exhibited a photocurrent response, it did not produce a significant increase in photoresponse current in response to an increase in glucose concentration (e.g. Figure 5 51 curve in the figure); the sensor electrode with a p-type copper oxide thin film layer grown on an n-type silicon layer produces a photocurrent response with a small increase in glucose concentration (such as Figure 5 52 curve in the figure); the p-type copper oxide sensing electrode directly grown on FTO has no obvious photocurrent response, and its dark current and photocurrent are almost equal at the same glucose concentration, and increase to a certain extent with the increase of concentration, that is, it shows electrochemical sensing characteristics (non-photoelectrochemical sensing characteristics) (such as Figure 5 53 curve in the figure); the sensing electrode constructed of n-type ordered silicon nanowire array / p-type copper oxide thin film layer produced a significantly increased photocurrent response to the increase in glucose concentration, while the dark current was very small (such as Figure 5 54 curve in the figure).

[0063] Furthermore, the sensitivity and selectivity of the heterojunction photoelectrochemical sensing electrode of the n-type silicon layer / p-type copper oxide thin film layer with a nanowire array on the top were tested in the range of glucose concentration from 0 to 1000 μM. Figure 6 As shown in Figure 2, the prepared photoelectrochemical sensing electrode exhibits a good linear relationship in the glucose concentration range of 0 to 1000 μM, and the sensing sensitivity is 755.259 μA mM -1 cm -2 In NaOH electrolyte, to simulate the real human body fluid environment, 1mM glucose, 0.1mM ascorbic acid, 0.1mM sucrose, 0.1mM uric acid, 145mM sodium chloride, and 7mM glucose were added successively. The photocurrent density changes under incident light conditions are as follows: Figure 7 As shown. After normalization calculation of the response photocurrent, Figure 8 As shown, the photocurrent responses of the prepared photoelectrochemical sensing electrode to ascorbic acid, uric acid, and sodium chloride are all less than 2% of the response to glucose, and the photocurrent response to sucrose is only 0.2% of the response to glucose.

[0064] The above test results fully demonstrate that the enzyme-free glucose photoelectrochemical sensor electrode prepared by this scheme can realize high-sensitivity, high-selectivity and low-background-noise sensing testing of glucose in the concentration range of 0 to 1000 μM under the condition of applying a certain bias voltage and without enzyme modification.

[0065] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An enzyme-free glucose photoelectrochemical sensor, comprising: The enzyme-free glucose photoelectrochemical sensing electrode, the ammeter, and the counter electrode are characterized in that: the enzyme-free glucose photoelectrochemical sensing electrode comprises an n-type silicon layer and a conductive layer arranged on the lower surface of the n-type silicon layer; the upper surface of the n-type silicon layer protrudes upward to form a nanowire array; the upper surface of the n-type silicon layer is uniformly coated with a p-type metal oxide semiconductor thin film layer; the p-type metal oxide semiconductor thin film layer and the n-type silicon layer form a heterojunction, and the heterojunction energy band structure is a staggered second-type heterojunction; the n-type silicon layer and the conductive layer form an ohmic contact; the lower surface of the conductive layer, the side wall of the conductive layer, and the side wall of the n-type silicon layer are all coated with a waterproof insulating layer; Under incident light, the p-type metal oxide semiconductor thin film layer and the nanowire array generate photogenerated electron-hole pairs, which are effectively separated under the combined action of the built-in electric field of the heterojunction and the external bias voltage to form a photocurrent proportional to the glucose concentration. The material of the p-type metal oxide semiconductor thin film layer includes: any one of copper oxide, nickel oxide, cobalt oxide, iron oxide, manganese oxide, cerium oxide or a mixture of multiple thereof; The nanowire array is obtained by chemically wet etching or reactive ion etching the upper surface of the n-type silicon layer; The nanowire array is orderly arranged and has an open columnar morphology; The conductive layer is provided with lead terminals, which are sequentially connected to an ammeter, an applied voltage, and a counter electrode; the enzyme-free glucose photoelectrochemical sensing electrode and the counter electrode are placed in a light-transmitting container; the light-transmitting container is filled with a glucose electrolyte to be tested.

2. The enzyme-free glucose photoelectrochemical sensor according to claim 1, characterized in that: When incident light irradiates the surface of the enzyme-free glucose photoelectrochemical sensing electrode, both the p-type metal oxide semiconductor thin film layer and the n-type silicon layer absorb light to generate photogenerated electron-hole pairs; under the combined action of the built-in electric field of the heterojunction and the external bias voltage, the photogenerated electron-hole pairs are separated, and the photogenerated electron holes are transmitted to the interface between the p-type metal oxide semiconductor thin film layer and the glucose electrolyte to be measured, and selectively undergo oxidation reaction with the glucose molecules in the glucose electrolyte to be measured; the photogenerated electrons are transmitted to the conductive layer through the n-type silicon layer, and then transmitted to the counter electrode to undergo corresponding reduction reaction; a photogenerated current is formed between the enzyme-free glucose photoelectrochemical sensing electrode and the counter electrode; the ammeter is used to monitor the size of the photogenerated current, and the glucose concentration to be measured is measured according to the correlation between the photogenerated current and the concentration of the glucose electrolyte to be measured.

3. The enzyme-free glucose photoelectrochemical sensor according to claim 1, characterized in that: The p-type metal oxide semiconductor thin film layer is formed by continuous accumulation of nanoparticles and has a thickness of 20 to 300 nm.

4. The enzyme-free glucose photoelectrochemical sensor according to claim 1, characterized in that: The resistivity of the n-type silicon layer is 1-10Ωcm, and the conductive layer is made of a metal with a work function lower than 4.3eV.

5. The enzyme-free glucose photoelectrochemical sensor according to claim 1, characterized in that: The nanowire array arranged on the upper surface of the n-type silicon layer is arranged in a hexagonal or tetragonal manner, the center spacing between adjacent nanowires is 1-5 μm, the length of a single nanowire is 2-10 μm, and the diameter is 300-4000 nm.

Images