Electrochemical microsensor and its preparation method and application

Abstract

The present invention discloses an electrochemical microsensor, comprising: a device substrate; a bottom layer of polyimide formed on the device substrate; a top layer of polyimide formed on the top surface of the bottom layer of polyimide and designed to match the pattern of a working electrode lead, a reference electrode and its lead, and a counter electrode and its lead; a silver mirror film formed on the top surface of the top layer of polyimide, respectively constituting the working electrode lead, the reference electrode and its lead, and the counter electrode and its lead; and a working electrode, which is nitrogen-oxygen co-doped laser-induced graphene formed on the bottom layer of polyimide and conductively connected to the working electrode lead. A method for preparing an electrochemical microsensor and its application for detecting nitrous acid are disclosed. The present invention has the beneficial effects of good conductivity, low detection limit, stable performance, high reusability, and a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrite detection, and more particularly to an electrochemical microsensor and a preparation method and application thereof. Background Art

[0002] Currently, there are not many electrochemical microdevices on the market, mainly because the device detection effect of spray-printed graphite electrodes is generally poor and the stability is poor. This makes it difficult for ordinary families with testing needs to use these microdevices in real life. On the other hand, nitrite is a common harmful substance widely present in food. Common pickles, pickled meat products, overnight dishes, and vegetables with excessive nitrogen fertilizer application all have high concentrations of nitrite. High doses of nitrite are highly toxic. Nitrite accumulation in the body can lead to nitrite food poisoning, and long-term consumption of nitrite can even lead to esophageal and gastric cancer.

[0003] Therefore, how to design and prepare an electrochemical microsensor that is sensitive in detection, stable in use, compact and convenient, and can be used in various ordinary households is an invention of great significance. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0005] In order to achieve these objects and other advantages according to the present invention, there is provided an electrochemical microsensor comprising:

[0006] device substrate;

[0007] a bottom layer of polyimide formed on the device substrate;

[0008] a top layer of polyimide formed on the surface of the bottom layer of polyimide and designed to match the pattern of the working electrode lead, the reference electrode and its lead, and the counter electrode and its lead;

[0009] Silver mirror film, formed on the surface of the top polyimide layer, respectively constituting the working electrode lead, the reference electrode and its lead, and the counter electrode and its lead;

[0010] The working electrode is nitrogen-oxygen co-doped laser-induced graphene formed on the bottom polyimide and conductively connected to the working electrode lead.

[0011] Preferably, the top polyimide layer and the bottom polyimide layer are both polyimide tapes.

[0012] Preferably, the electrochemical microsensor further comprises an epoxy resin layer for encapsulating the electrochemical microsensor.

[0013] The preparation method of the electrochemical microsensor comprises the following steps:

[0014] cutting the outline of the electrochemical microsensor on the supporting substrate to obtain a device substrate;

[0015] Two layers of polyimide tape are sequentially attached to the surface of the supporting substrate and are denoted as bottom polyimide and top polyimide;

[0016] The top polyimide surface is pretreated to obtain a silver mirror film;

[0017] Carving on the surface of the silver mirror film to obtain electrode silver wires and removing the top layer of polyimide and the silver mirror film except for the portion covered by the electrode silver wires, wherein the motor silver wires include a working electrode lead, a reference electrode and its lead, and a counter electrode and its lead;

[0018] A nitrogen-oxygen co-doped laser-induced graphene conductively connected to a working electrode lead is prepared on a bottom polyimide layer as a working electrode;

[0019] The whole device is obtained by cutting according to the shape of the device substrate.

[0020] Preferably, the supporting substrate is a transparent plastic glass plate made of PVC.

[0021] Preferably, the top polyimide surface is pretreated to obtain a silver mirror film, specifically:

[0022] The top polyimide surface is modified with potassium hydroxide to form potassium polycarbamate through an imide ring-opening reaction;

[0023] After cleaning, add 0.1M AgNO3 solution and soak for 3-3.2h;

[0024] After cleaning, add a glucose solution with a pH value of 12 and a concentration of 0.5 M and soak for 15-17 minutes.

[0025] Preferably, nitrogen and oxygen co-doped laser-induced graphene is prepared by:

[0026] Using an ultraviolet laser marking machine, marking was performed in a filling manner to obtain nitrogen-oxygen co-doped laser-induced graphene with a resistance value of 40-60Ω.

[0027] Preferably, the method for preparing the electrochemical microsensor further comprises: connecting the working electrode and the working electrode lead at adjacent locations with conductive silver paste to achieve conductive connection between the working electrode and the working electrode lead.

[0028] Preferably, the method for preparing the electrochemical microsensor further comprises encapsulating the entire device with epoxy resin.

[0029] The electrochemical microsensor is used for detecting nitrite.

[0030] The present invention has at least the following beneficial effects:

[0031] ①. Better conductive effect: The surface silver film is generated by the silver mirror reaction of the PI surface, and the shape of the electrode wire is cut by laser, so that the conductive effect of the electrode is better than that of the conventional spray-printed graphite electrode;

[0032] ② Lower detection limit: Compared with conventional spray-printed graphite electrodes, the working electrode of the electrochemical microsensor is a nitrogen-oxygen co-doped modified graphene prepared from a PI film, which has better electrode detection capabilities and is more capable of detecting nitrite than conventional spray-printed graphene electrodes;

[0033] ③. More stable performance: The working electrode of conventional spray-printed graphite electrodes may have problems such as loose contact with the substrate, which may lead to stability issues such as electrode shedding during the detection process and uneven detection curves. The electrochemical microsensor uses nitrogen-oxygen co-doped modified graphene as the working electrode, which is carved on the surface of the PI film. This allows for a stronger bond with the substrate during the detection process, resulting in a smoother detection curve.

[0034] ④. High reusability: In multiple actual tests, the electrochemical microsensor can repeat the test 20-30 times with a relative deviation of less than 10% in potential.

[0035] ⑤. Wider application range: Electrochemical microsensors are portable and small, and do not require large amounts of solution immersion. Compared with traditional large sensors, they save reagents, and the working electrode, reference electrode, and counter electrode are integrated to shorten the distance between electrodes and reduce resistance. In addition to meeting the outdoor rapid testing requirements of testing agencies, they can also be used in ordinary households to test pickled foods. They are easy to operate and test results can be obtained quickly.

[0036] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a laser cutting diagram of the outer contour shape of the electrochemical microsensor according to one of the technical solutions of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of a polyimide tape attached to the surface of a supporting substrate according to one of the technical solutions of the present invention;

[0039] Figure 3This is a schematic structural diagram of forming a silver mirror on the surface of a polyimide tape according to one of the technical solutions of the present invention;

[0040] Figure 4 This is a schematic structural diagram of the electrode silver wire according to one of the technical solutions of the present invention;

[0041] Figure 5 This is the overall design diagram of the electrochemical microsensor described in one of the technical solutions of the present invention;

[0042] Figure 6 This is a picture of an actual product of the electrochemical microsensor described in one of the technical solutions of the present invention;

[0043] Figure 7 This is a DPV curve diagram of the electrochemical microsensor detecting standard nitrite according to one of the technical solutions of the present invention;

[0044] Figure 8 A linear relationship diagram of the electrochemical microsensor according to one of the technical solutions of the present invention;

[0045] Figure 9 This is an anti-interference curve diagram of the electrochemical microsensor according to one of the technical solutions of the present invention;

[0046] Figure 10 This is a DPV curve diagram of the electrochemical microsensor for detecting nitrite in drinking water according to one of the technical solutions of the present invention;

[0047] Figure 11 This is a DPV curve diagram of the electrochemical microsensor detecting nitrite in milk water according to one of the technical solutions of the present invention;

[0048] Figure 12 This is a DPV curve diagram of the electrochemical microsensor detecting nitrite in kimchi water according to one of the technical solutions of the present invention.

[0049] The specific reference numerals are: 1-support substrate, 2-polyimide tape, 3-device substrate, 4-silver mirror film, 5-electrode silver wire, 6-working electrode, 7-reference electrode, 8-counter electrode, 9-conductive silver paste, 10-epoxy resin. DETAILED DESCRIPTION

[0050] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0051] <Scheme 1>

[0052] Electrochemical microsensors, including:

[0053] The device substrate 3 may be a transparent plastic glass plate made of PVC with a thickness of 0.4-0.6 mm, preferably 0.5 mm;

[0054] A bottom layer of polyimide, formed on the device substrate 3, wherein the bottom layer of polyimide can be a polyimide tape 2 with a thickness of 50 μm;

[0055] A top layer of polyimide formed on the surface of the bottom layer of polyimide and designed to match the pattern of the working electrode lead, the reference electrode 7 and its lead, and the counter electrode 8 and its lead, wherein the top layer of polyimide can be specifically a polyimide tape 2 with a thickness of 50 μm;

[0056] Silver mirror film 4, formed on the surface of the top polyimide layer, respectively constituting the working electrode lead, reference electrode 7 and its lead, counter electrode 8 and its lead;

[0057] The working electrode 6 is a nitrogen-oxygen co-doped laser-induced graphene formed on the underlying polyimide and conductively connected to the working electrode lead. The working electrode 6, the reference electrode 7, and the counter electrode 8 are integrated at one end of the device substrate 3. One end of the working electrode lead is electrically connected to the working electrode 6. The reference electrode lead and the reference electrode 7 are both composed of a silver mirror film 4, so their opposite ends are butted together. The counter electrode lead and the counter electrode 8 are both composed of a silver mirror film 4, so their opposite ends are butted together. The other ends of the working electrode lead, the reference electrode lead, and the counter electrode lead are integrated at the other end of the device substrate 3.

[0058] 10 layers of epoxy resin for encapsulating electrochemical microsensors.

[0059] <Scheme 2>

[0060] The preparation method of the electrochemical microsensor comprises the following steps:

[0061] (1) The supporting substrate 1 is made of insulating material, specifically a transparent plastic glass plate made of PVC with a thickness of 0.4-0.6 mm, preferably 0.5 mm.

[0062] (2) Design the shape and size of the electrochemical microsensor, as follows: Figure 1 As shown;

[0063] According to the design, a UV laser marker is used to pre-cut the support substrate 1 to cut out the outline of the electrochemical microsensor to obtain the device substrate 3. The cutting parameters of the UV laser marker are set as follows: wavelength 355nm, frequency 70kHz, focal length 9.1cm, cutting rate 1ms, and power 90%;

[0064] (3) The pre-cut device substrate 3 is not removed from the supporting substrate 1 first, and two layers of polyimide (PI) tape are directly pasted on the surface of the entire supporting substrate 1. Specifically:

[0065] A polyimide tape 2 (single layer thickness 50 μm) was pasted on the plastic glass plate to form a bottom polyimide layer;

[0066] Paste polyimide tape 2 on the bottom polyimide to form a top polyimide layer;

[0067] (4) The top polyimide surface is pretreated to make it conductive. The main methods are:

[0068] In the first step, the top polyimide surface is modified into potassium polycarbamate by an imide ring-opening reaction using potassium hydroxide (KOH). Specifically, a 4M KOH solution is dripped onto the top polyimide surface and soaked for 3.8-4.2 hours to achieve a ring-opening reaction of the top polyimide.

[0069] In the second step, the top polyimide surface of the first step is cleaned with deionized water, and then a 0.1M AgNO3 solution is prepared and dropped on the surface of the top polyimide after ring opening, and immersed for 3-3.2 hours to achieve the replacement of silver ions with potassium ions in potassium polyurethane on the surface of the top polyimide;

[0070] The third step is to prepare a 0.5 M glucose solution and adjust the pH value of the glucose solution to 12 with a 1 M KOH solution to obtain an alkaline glucose solution;

[0071] The top polyimide surface of the second step is cleaned with deionized water, and then alkaline glucose solution is dropped onto its surface and immersed for 15-17 minutes to obtain a dense and highly conductive silver mirror film 4 on the top polyimide surface, such as Figure 3 As shown;

[0072] (5) After the prepared silver mirror film 4 is dried, Figure 4 The surface of the pattern shown is engraved to obtain the three-electrode silver wire 5 of the electrochemical microsensor, and the three-electrode silver wire 5 includes a working electrode lead, a reference electrode 7, a reference electrode lead, a counter electrode 8, and a counter electrode lead;

[0073] After engraving, the top polyimide and silver mirror film 4 are completely removed except for the portion covered by the electrode silver wires 5 of the three electrodes, that is, only the silver film portion related to the electrode silver wires 5 of the three electrodes is left, such as Figure 4 As shown;

[0074] (6) Prepare the working electrode 6 on the bottom polyimide exposed at the bottom end of the working electrode lead, specifically:

[0075] Use UV laser marking machine, according to Figure 5 The pattern is marked in a filling manner. The marking parameters are: wavelength 300-400 mm, frequency 60-80 kHz, focal length 9.1 cm, rate range 10-30 ms, power 20-30%. In each experiment, due to sample differences, the rate and power are adjusted according to the actual situation. The ultimate goal is to obtain nitrogen and oxygen co-doped laser-induced graphene with a resistance value of 40-60 Ω (preferably 50 Ω) as the working electrode 6;

[0076] (7) According to the size and shape of the device substrate 3, use an ultraviolet laser marking machine to cut the bottom layer of polyimide outside the device substrate 3 to obtain the entire device, such as Figure 5 As shown, the cutting parameters of the UV laser marking machine are: wavelength 355nm, frequency 70kHz, focal length 9.1cm, cutting rate 1ms, power 90%;

[0077] (8) Connect the working electrode 6 and the working electrode lead with conductive silver paste 9;

[0078] The silver wires (including the connection points of the conductive silver paste 9) are completely encapsulated with epoxy resin 10 to prevent corrosion or physical damage of the silver wires that may cause electrode instability.

[0079] experiment

[0080] 1. Electrochemical detection

[0081] The electrochemical sensor micro-device prepared in Example 1 was connected to the gold fingers of the three-electrode system using flat crocodile copper clips, with the working electrode 6 corresponding to the working electrode end of the electrochemical workstation, the counter electrode corresponding to the counter electrode end of the electrochemical workstation, and the reference electrode 7 corresponding to the reference electrode 7 end of the electrochemical workstation;

[0082] The electrolyte was 0.1 mol / L phosphate buffer (PBS, pH = 5.6). During the test, NaNO2 solution was added starting from the blank solution (0 ppm) and the NaNO2 concentration in the test solution was controlled to 0.1 ppm, 0.2 ppm, 0.3 ppm, 0.4 ppm, 0.5 ppm, 0.6 ppm, 0.7 ppm, and 0.8 ppm in sequence. NO2 was recorded by differential pulse voltammetry (DPV). - Electrochemical signal of oxidation to detect the reaction behavior of nitrite;

[0083] DPV parameter settings: initial potential: 0.5 V, end potential: 1.0 V, potential increment: 0.004 V, amplitude: 0.05 V. Pulse width: 0.2 s, pulse period: 0.5 s;

[0084] The results are as follows Figure 7 As shown, the relationship between each curve and the concentration of NaNO2 in the test solution is a (0ppm), b (0.1ppm), c (0.2ppm), d (0.3ppm), e (0.4ppm), f (0.5ppm), g (0.6ppm), h (0.7ppm), i (0.8ppm), Figure 7 It can be seen that when there is no sodium nitrite in the electrolyte, there is no oxidation peak in the DPV curve. When there is nitrite in the electrolyte, an obvious oxidation peak appears in the DPV curve at a potential of 0.62V.

[0085] Furthermore, a linear relationship diagram of the detection current and the drop concentration was fitted based on the relationship between the oxidation peak current value and the drop concentration, as shown in FIG. Figure 8 As shown by Figure 8 It can be seen that a good linear relationship of R = 0.9997 is obtained;

[0086] Furthermore, according to the calculation formula of the limit of detection (LOD): LOD = 3S / N, where S represents the standard deviation of the blank solution and N represents the slope of the fitted line, it was calculated that the detection limit of the electrochemical microsensor prepared in <Example 1> for nitrite was 0.01 ppm. The results showed that the sensor had good current response and sensitivity to nitrite in the solution.

[0087] 2. Anti-interference test

[0088] Selectivity or anti-interference is a key parameter of electrochemical microsensors. In order to explore the anti-interference ability of the electrochemical microsensor prepared in <Example 1> to several common ions in the water environment, different salt solutions (acid radical solutions) were added to the measuring solution (10μM nitrite solution) to investigate the effect of external interfering species on the detection of 10μM nitrite solution.

[0089] The electrochemical response is recorded by IA curve, such as Figure 9 As shown, 1 represents a 10 μM nitrite solution, and the sensor has an obvious amperometric response to each 10 μM nitrite solution; when other salt solutions are added, from 2 to 7, respectively, Na2SO4, NaCl, Na2CO3, NaPO4, sodium acetate and glucose, and the concentration of each substance is controlled to 50 μM (the concentration in the test solution), no obvious current response is observed for the other added salt solutions, indicating that the electrochemical microsensor prepared in <Example 1> can resist high concentrations of interfering ions when detecting nitrite, that is, it can be used as a highly selective nitrite detection sensor.

[0090] 3. Blind Sample Testing

[0091] The electrochemical microsensor prepared in Example 1 was connected to the gold fingers of the three-electrode system using flat crocodile copper clips, with the working electrode 6 corresponding to the working electrode end of the electrochemical workstation, the counter electrode 8 corresponding to the counter electrode end of the electrochemical workstation, and the reference electrode 7 corresponding to the reference electrode end of the electrochemical workstation;

[0092] Drinking water, milk, and kimchi water were taken as blind samples to be tested, and the blind samples were filtered with a 0.22 μm cellulose membrane to remove particles and sediments, and then diluted with 0.1 M PBS buffer (pH 5.6) to obtain blind sample solutions, including drinking water blind sample solution, milk blind sample solution, and kimchi water blind sample solution;

[0093] Use 0.1M PBS buffer as a blank control, add 5 μL of drinking water blind sample solution to the test solution and mix well to prepare the drinking water test solution;

[0094] Use 0.1M PBS buffer as blank control, add 5μL of milk blind sample solution to the test solution and mix well to prepare the milk test solution;

[0095] Use 0.1M PBS buffer as a blank control, add 5 μL of kimchi water blind sample solution to the test solution and mix well to prepare the kimchi water test solution;

[0096] The test process starts with a blank control and then adds the corresponding amount of blind sample solution. The electrochemical signal is recorded by differential pulse voltammetry (DPV) to obtain the detection current of the drinking water test solution, milk test solution, and kimchi water test solution respectively.

[0097] Based on the linear relationship between the detection current and the dripping concentration obtained in <Experiment 1, Electrochemical Detection>, as well as the detection currents of the drinking water test solution, milk test solution, and kimchi water test solution, the concentration values ​​of drinking water, milk, and kimchi water were obtained, which were 0 ppm, 0.3 ppm, and 1.5 ppm, respectively.

[0098] like Figure 10 As shown, it represents the DPV curve of the drinking water test solution. Figure 10 It can be seen that the NO2 in the test solution of drinking water - The concentration is below the minimum detection concentration of the electrochemical microsensor;

[0099] like Figure 11 As shown, it represents the DPV curve of the milk test solution. Figure 11 It can be seen that the milk test solution shows an oxidation peak, that is, the electrochemical microsensor can detect NO2 in the actual milk sample. - ;

[0100] like Figure 12 As shown, it represents the DPV curve of the kimchi water test solution. Figure 12 It can be seen that the kimchi water test solution shows an oxidation peak, that is, the electrochemical microsensor can detect NO2 in the actual kimchi water sample. - ;

[0101] These results demonstrate the practicality and reliability of the developed electrochemical microsensor, and also prove that the electrochemical microsensor is feasible for detecting nitrite and can be effectively used for the rapid detection of nitrite in real life.

[0102] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing an electrochemical microsensor, characterized in that: The following steps are involved: cutting the outline of the electrochemical microsensor on the supporting substrate to obtain a device substrate; Two layers of polyimide tape are sequentially attached to the surface of the supporting substrate and are denoted as bottom polyimide and top polyimide; The top polyimide surface is pretreated to obtain a silver mirror film; Carving on the surface of the silver mirror film to obtain electrode silver wires and removing the top layer of polyimide and the silver mirror film except for the portion covered by the electrode silver wires, wherein the electrode silver wires include a working electrode lead, a reference electrode and its lead, and a counter electrode and its lead; A nitrogen-oxygen co-doped laser-induced graphene conductively connected to a working electrode lead is prepared on a bottom polyimide layer as a working electrode; Cutting according to the shape of the device substrate to obtain the entire device; The top polyimide surface is pretreated to obtain a silver mirror film, specifically: The top polyimide surface is modified with potassium hydroxide to form potassium polycarbamate through an imide ring-opening reaction; After cleaning, add 0.1 M AgNO3 solution and soak for 3-3.2 h; After cleaning, add a 0.5 M glucose solution with a pH of 12 and soak for 15-17 min.

2. The method for preparing an electrochemical microsensor according to claim 1, wherein: The supporting base is a transparent plastic glass plate made of PVC material.

3. The method for preparing an electrochemical microsensor according to claim 1, wherein: Preparation of nitrogen and oxygen co-doped laser-induced graphene, specifically: Using a UV laser marking machine, marking was performed in a filling mode to obtain nitrogen-oxygen co-doped laser-induced graphene with a resistance value of 40-60 Ω.

4. The method for preparing an electrochemical microsensor according to claim 1, wherein: Also includes: Conductive silver paste is used to connect the working electrode and the working electrode lead at adjacent locations to ensure conductive connection between the working electrode and the working electrode lead.

5. The method for preparing an electrochemical microsensor according to claim 1, wherein: The entire device is encapsulated with epoxy resin.

6. An electrochemical microsensor prepared by the preparation method according to claim 1, characterized in that: include: device substrate; a bottom layer of polyimide formed on the device substrate; a top layer of polyimide formed on the surface of the bottom layer of polyimide and designed to match the pattern of the working electrode lead, the reference electrode and its lead, and the counter electrode and its lead; Silver mirror film, formed on the surface of the top polyimide layer, respectively constituting the working electrode lead, the reference electrode and its lead, and the counter electrode and its lead; The working electrode is nitrogen-oxygen co-doped laser-induced graphene formed on the bottom polyimide and conductively connected to the working electrode lead.

7. The electrochemical microsensor according to claim 6, wherein The top polyimide layer and the bottom polyimide layer are both polyimide tapes.

8. The electrochemical microsensor according to claim 6, wherein Also included is an epoxy resin layer for encapsulating the electrochemical microsensor.

9. Use of the electrochemical microsensor as claimed in claim 6 to detect nitrite.

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