CN105388201A - Three-electrode integrated electrochemical sensor based on microelectrode array - Google Patents

Abstract

The invention discloses a three-electrode integrated electrochemical sensor based on a microelectrode array. The sensor includes a bismuth film modified microelectrode array (gold working electrode), a silver/silver chloride electrode (reference electrode), and a platinum electrode (counter electrode). ). The three electrodes are prepared by a standard MEMS process, and multiple equidistant disks are uniformly distributed on the gold electrode as a microelectrode array. During the electrochemical detection process, heavy metal enrichment and stripping reactions occur on the microelectrode array, and the surface is modified with a bismuth film in order to expand the detection types and scope of heavy metals. The surface of the silver electrode is plated with silver chloride to form the Ag|AgCl reference electrode. The platinum electrode acts as a counter electrode and forms a path with the working electrode. The concentration of heavy metals was determined by differential pulse stripping voltammetry. The results showed that the sensor has high detection sensitivity, low detection limit, and high signal-to-noise ratio. The sensor is easy to operate and requires less sample volume. It can be used for on-site rapid detection of heavy metals. Detection can realize real-time and efficient monitoring of environmental pollution.

Description

A three-electrode integrated electrochemical sensor based on microelectrode array

technical field

The invention relates to the technical field of electrochemical sensors and heavy metal detection, in particular to a three-electrode integrated electrochemical sensor based on a microelectrode array.

Background technique

The safety of food, drinking water and oceans is a widespread and growing concern. Among them, due to the cumulative effect of heavy metals in the food chain, heavy metal pollution is particularly harmful to human health and the balance of the ecological environment. Therefore, real-time rapid on-site detection of heavy metals is very important.

At present, heavy metal detection methods include atomic spectroscopy, inductively coupled plasma mass spectrometry, electrochemical analysis and other methods. Atomic spectroscopy and inductively coupled plasma mass spectrometry have high sensitivity, low detection limit, and good repeatability, but they have high requirements for the experimental environment, expensive instruments and reagents, and require professional operation, so they are suitable for laboratory analysis.

The electrochemical method is easy to operate, has high sensitivity and good repeatability, and is suitable for on-site rapid detection and real-time monitoring. Among them, the differential pulse stripping voltammetry method first reduces and enriches the heavy metal ions on the surface of the working electrode; then combines the differential pulse technology to scan the working electrode, and the deposited metal is oxidized and stripped; according to the measured stripping voltammetry curve, the heavy metal ions can be analyzed. Qualitative and quantitative analysis. The method can simultaneously detect various heavy metal ions in the solution, and has high sensitivity and resolution.

Microelectrode has the advantages of fast mass transfer rate, small electric double layer capacitance, and small iR drop, but the total current intensity on the microelectrode is small, usually 10 ^-9 ~ 10 ^-12 A, which increases the difficulty of detection. In addition to retaining the characteristics of a single microelectrode, the microelectrode array does not change the RC constant and iR drop, and the current intensity is the sum of the microelectrodes, which greatly improves the Faraday current. To sum up, the microelectrode array has the advantages of high mass transfer rate, high sensitivity, low detection limit, and anti-interference, and has been widely studied and applied.

Electrochemical detection is mainly done in a three-electrode system. The three-electrode system consists of a working electrode, a counter electrode and a reference electrode. The current research is mainly on the miniaturization of the working electrode, while the reference electrode and the counter electrode often use external traditional electrodes. The traditional three-electrode detection requires a large test sample, and a series of operations such as installation and fixing are cumbersome, and the change of the relative position of the working electrode and the counter electrode will introduce interference, which reduces the repeatability and accuracy of the detection.

Contents of the invention

In order to improve the sensitivity, accuracy, repeatability and detection efficiency of heavy metal detection and reduce the external interference introduced by the traditional three-electrode system to heavy metal detection, the present invention designs a three-electrode integrated electrochemical sensor based on a microelectrode array, in which the working electrode Micro-electrode array is used, which is integrated with counter electrode and reference electrode on one chip. The sensor can be used not only for on-site rapid detection of trace heavy metals, but also for electrochemical analysis at the cell molecular level.

The present invention is achieved through the following technical solutions: a three-electrode integrated electrochemical sensor based on a microelectrode array, the sensor includes: a quartz substrate, a metal layer, an insulating layer, a first wire, a second wire and a third wire; The metal layer includes platinum electrodes, gold electrodes, silver electrodes, platinum leads, silver leads, gold leads, platinum pads, silver pads and gold pads; wherein the metal layer is attached to the quartz substrate; the silver electrodes are Cylindrical, the diameter of the silver electrode is 600-1000 μm; the gold electrode is circular, with the same central axis as the silver electrode, the inner diameter of the gold electrode is 1200-1600 μm, the wall thickness is 100-200 μm, the upper surface of the gold electrode is along the A number of disks of the same size are evenly distributed on the circumference as a microelectrode array. The diameter of the microelectrodes is 10-100 μm, and the distance between the microelectrodes is greater than 5 times the diameter; the platinum electrode is circular and has the same central axis as the silver electrode. The inner diameter of the platinum electrode is 1800-3000 μm, and the wall thickness is 100-500 μm; the insulating layer covers the quartz substrate and the metal layer, and the thickness of the insulating layer is higher than the metal layer, and makes platinum electrodes, silver electrodes, platinum pads, silver soldering The microelectrode array on the upper surface of the disk and the gold pad is exposed; the gold electrode, the gold lead, the gold pad and the third wire are connected and conducted in sequence, and the platinum electrode, the platinum lead, the platinum pad and the first wire are connected and conducted in sequence , the silver electrode, the silver lead, the silver pad and the second wire are sequentially connected and conducted.

Further, a bismuth film is electroplated on the microelectrode array, silver chloride is plated on the surface of the silver electrode; the bismuth plated microelectrode array is used as the working electrode, the silver electrode is plated with silver chloride as the Ag|AgCl reference electrode, and the platinum electrode is used as the counter electrode.

A method for preparing a three-electrode integrated electrochemical sensor based on a microelectrode array, the method comprising the following steps:

(1) Preparation of gold electrodes: After cleaning and drying the quartz substrate, magnetron sputtering Cr adhesion layer (30-50nm) and Au layer (200-400nm), spin-coating positive photoresist, and exposing under ultraviolet light Development, dry etching of gold electrodes after curing;

(2) Preparation of platinum electrodes: magnetron sputtering Ti adhesion layer (30-50nm) and Pt layer (200-400nm), spin-coating positive photoresist, after exposure and development, dry-etch platinum counter electrode;

(3) Preparation of silver electrodes: first coat a layer of 0.5 μm positive photoresist on the chip, after full exposure and development, remove the photoresist on the silver electrode pattern, and use plasma in a high vacuum environment The positively charged argon ions bombard the silver target (cathode), and the ejected silver atoms are deposited on the quartz substrate chip (anode), forming a 100-200nm silver layer, and finally the silver is removed by lift-off process. The silver metal layer and photoresist other than the electrodes are removed together;

(4) Preparation of insulating layer: Deposit a layer of insulating layer Si ₃ N ₄ on the front of the quartz substrate chip by plasma enhanced chemical vapor deposition (PECVD), then spin-coat photoresist, expose and develop with ultraviolet light, and etch the microelectrode array , Platinum electrodes, silver electrodes, gold pads, platinum pads, and insulating layers on the surface of silver pads, and the insulating layers in other areas are retained;

(5) Make a reference electrode: use the silver electrode as the anode and the platinum electrode as the cathode, immerse in 0.1mM HCl solution, and electroplate with a constant current of 0.4mA/ ^cm2 for 300-600s, so that the surface of the silver electrode AgCl plating;

(6) Bismuth film modified by the working electrode: the platinum electrode is used as the counter electrode, the first wire is used as the signal lead-out line of the counter electrode, the silver electrode and electroplated silver chloride are used as the reference electrode, and the second wire is used as the signal lead-out of the reference electrode line, the microelectrode array is used as the working electrode, and the third wire is used as the signal lead-out line of the working electrode, thus forming a three-electrode system, which is respectively connected to the counter electrode port, reference electrode interface and working electrode interface of the electrochemical workstation; the electrode All parts are immersed in the solution of the test box for electrochemical modification and measurement: in 1MH ₂ SO ₄ solution, perform cyclic voltammetry scanning, the scanning voltage range is -0.2V～+1.5V, and the scanning rate is 0.05V/s , repeat multiple scans to clean and activate the electrode; change to Bi(NO ₃ ) ₃ solution (1mol/L KNO ₃ and 1% HNO ₃ as the bottom solution), the Bi ³⁺ concentration is 0.005-0.03mol/L, and constant Potentiometric scanning, the potential range is -0.45～-0.3V, the electroplating time is 100～300s, bismuth ions are reduced on the surface of the working electrode, and a bismuth film is formed on the microelectrode array 11 with a thickness less than 100nm. Rinse with deionized water and dry with nitrogen to obtain a three-electrode integrated electrochemical sensor based on microelectrode array.

The beneficial effects of the present invention are:

1. The present invention uses quartz glass as the substrate, gold, silver, and platinum as electrode materials, and adopts traditional standard MEMS technology. The size is small, the materials are common, and it is easy to produce in batches;

2. The present invention integrates the three-electrode system on one chip, which is easy to operate and has a simple interface, and can be placed in a portable electrochemical instrument for rapid on-site detection;

3. The present invention adopts a microelectrode array, which has high sensitivity, low detection limit, and strong anti-interference; the spacing of the microelectrodes is greater than 5 times the diameter, which can reduce the shielding effect caused by the too small distance between the electrodes; the microelectrodes are pre-coated with bismuth film , can increase the detection types and range of heavy metal ions, and improve the accuracy and repeatability of detection;

4. silver electrode of the present invention, gold electrode and platinum electrode concentric axis, make the distance of each microelectrode distance reference electrode and counter electrode equate, make the potential difference between working electrode and reference electrode caused by solution impedance all Same, reduce the interference introduced by external reference electrode and counter electrode.

Description of drawings

Figure 1 is a schematic diagram of the structural assembly of a three-electrode integrated electrochemical sensor based on a microelectrode array, (a) is the overall diagram, (b) is a schematic diagram of electrochemical detection, and (c) is a schematic diagram of the sensor structure decomposition;

In the figure, quartz substrate 1, platinum electrode 2, gold electrode 3, silver electrode 4, platinum lead 5, silver lead 6, gold lead 7, platinum pad 8, silver pad 9, gold pad 10, microelectrode array 11 , metal layer 12, bismuth film 13, silver chloride 14, insulating layer 15, first wire 16, second wire 17, third wire 18;

Figure 2 is a flow chart of the preparation method of the three-electrode integrated electrochemical sensor; (a) quartz substrate, (b) deposition of adhesion layer and gold, (c) spin-coated photoresist, (d) exposure and development, (e) Dry etching of gold electrodes, (f) dry etching of platinum electrodes, (g) spin-coating photoresist, (h) exposure and development, (i) evaporation and sputtering of silver layer, (j) lift-off process to make silver Electrode, (k) PECVD deposition insulating layer, (l) etching insulating layer;

Fig. 3 is the heavy metal detection DPSV curve of the present invention;

Fig. 4 (a) is the standard calibration curve of the stripping peak current and the Cd concentration of the heavy metal detection of the present invention; (b) is the standard calibration curve of the stripping peak current and the Pb concentration.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific examples.

1. In Figure 1(a), the surface of the microelectrode array is pre-coated with bismuth film to form the working electrode, the surface of the silver electrode is electroplated with silver chloride to form the reference electrode, and the platinum electrode is used as the counter electrode; the three electrodes are fabricated in the MEMS process. On a quartz substrate, it can be connected with an external heavy metal electrochemical detector through relevant auxiliary wires. Figure 1(c) shows the internal structure and association of the sensor, wherein the gold electrode 3, the gold lead 7, the gold pad 10 and the third wire 18 are sequentially connected and conducted, and the platinum electrode 2, the platinum lead 5, the platinum pad 8 and the The first wires 16 are sequentially connected and conducted, and the silver electrodes 4 , silver leads 6 , silver pads 9 and the second wires 17 are sequentially connected and conducted.

Two, the present invention is based on the preparation method of the three-electrode integrated electrochemical sensor of microelectrode array, comprises the following steps (see Fig. 2):

1. Preparation of gold electrodes: After cleaning and drying the quartz substrate (Fig. 2a), magnetron sputtering Cr adhesion layer (30-50nm) and Au layer (200-400nm) (Fig. 2b). Positive photoresist was spin-coated (Fig. 2c), exposed and developed under ultraviolet light (Fig. 2d), and after curing, gold electrodes were dry-etched (Fig. 2e).

2. Preparation of platinum electrodes: magnetron sputtering Ti adhesion layer (30-50nm) and Pt layer (200-400nm). The positive photoresist was spin-coated, and after exposure and development, the platinum counter electrode was dry-etched (Figure 2f).

3. Preparation of silver electrodes: First, coat a layer of 0.5 μm positive photoresist on the chip (Fig. 2g). After sufficient exposure and development, remove the photoresist on the silver electrode pattern (Fig. 2h). In a high vacuum environment, positively charged argon ions in the plasma are used to bombard the silver target (cathode), and the ejected silver atoms are deposited on the quartz substrate chip (anode), forming a 100-200nm silver layer (Figure 2i ), and finally use the lift-off process to remove the silver metal layer and photoresist except the silver electrode (Figure 2j).

4. Preparation of insulating layer A layer of insulating layer Si ₃ N ₄ was deposited on the front of the quartz substrate chip by plasma enhanced chemical vapor deposition (PECVD) (Fig. 2k), then spin-coated photoresist, exposed and developed by ultraviolet light, and etched gold The insulating layer on the surface of the microelectrode array, platinum electrode, silver electrode, gold pad, platinum pad, and silver pad, and the insulating layer in other areas are retained, as shown in Figure 2l.

5. Welding wires: use welding gold wire to connect the first wire to the platinum pad, connect the second wire to the gold pad, and connect the third wire to the silver pad.

3. Reference electrode preparation method

First soak the silver surface with 3MHNO ₃ , then use the silver electrode as the anode and the platinum electrode as the cathode, and conduct anodic polarization with a constant current of 0.4mA/cm ² in 0.1M HCl for 300-600s.

4. Pre-plated bismuth film

The gold microelectrode array is used as the working electrode, the platinum electrode is used as the counter electrode, and the Ag|AgCl is used as the reference electrode to form a three-electrode system, which is connected to the corresponding electrode interface of the analytical instrument.

a Electrode activation

In 1M H ₂ SO ₄ solution, a cyclic voltammetry scan was performed, and the parameters are shown in Table 1. Repeat multiple sweeps until a stable waveform appears.

Table 1 Gold microelectrode activation

parameter name parameter value initial potential 0.05V high potential +1.5V low potential -0.2V scan rate 0.05V/s

b pre-coated bismuth film

Replace with Bi(NO ₃ ) ₃ solution (1mol/L KNO ₃ and 1% HNO ₃ as bottom solution), in which the concentration of Bi ³⁺ is 0.005～0.03mol/L, scan by constant potential method, and the potential is -0.45～-0.3 Between V, the electroplating time is 100-300s, and the parameters are shown in Table 2.

Table 2 Pre-coated bismuth film

parameter name parameter value initial potential -0.45～-0.3V time 100～300s

5. Heavy metal detection

The bismuth film microelectrode array prepared above is used as the working electrode, the silver-silver chloride electrode is used as the reference electrode, and the platinum electrode is used as the counter electrode, which together constitute a three-electrode integrated electrochemical sensor. The three leads are respectively connected to the working electrode interface, reference electrode interface and counter electrode interface of the electrochemical analyzer. After configuring the buffer solution and setting the stripping voltammetry parameters, the heavy metal detection of lead, cadmium or nickel is completed.

1. PH buffer solution configuration:

Ka=[H ⁺ ][Ac ^- ]/[HAc]; pH=pKa+lg([Ac ^- ]/[HAc]); pKa=4.76 (25°C)

Take 2.72g of sodium acetate crystals, and dissolve 2.62mL of glacial acetic acid (0.0458mol) in 200mL of deionized water to prepare an acetic acid-sodium acetate buffer solution with a pH of 4.4.

2. The parameters of stripping voltammetry are set as shown in Table 3

Table 3 Differential pulse stripping voltammetry detection of heavy metals

parameter name parameter value parameter name parameter value enrichment potential -1.35V scanning speed 0.05V/s enrichment time 60s Pulse period 0.2s resting potential -1.2V Pulse amplitude 50mV resting time 10s Pulse Width 0.06s Scan voltage range -1.2V～-0.01V The sampling period 0.02s

3. The measurement results are shown in Figure 4. The experimental results show that the three-electrode sensor can be used for rapid detection and analysis of heavy metals, and has good linearity and sensitivity, and low detection limit.

Claims (3)

1. A three-electrode integrated electrochemical sensor based on a microelectrode array is characterized in that the sensor comprises: a quartz substrate (1), a metal layer (12), an insulating layer (15), a first wire (16), the first Two wires (17) and a third wire (18); the metal layer (12) includes platinum electrodes (2), gold electrodes (3), silver electrodes (4), platinum leads (5), silver leads (6) , gold lead wire (7), platinum pad (8), silver pad (9) and gold pad (10); Wherein, metal layer (12) is attached on the quartz substrate (1); Said silver electrode (4 ) is cylindrical, and the diameter of the silver electrode (4) is 600-1000 μm; the gold electrode (3) is circular, and has the same central axis as the silver electrode (4), and the inner diameter of the gold electrode (3) is 1200-1600 μm , the wall thickness is 100-200 μm, the upper surface of the gold electrode (3) is uniformly distributed along the circumference of several discs of the same size as the micro-electrode array (11), the diameter of the micro-electrodes is 10-100 μm, and the distance between the micro-electrodes is greater than that 5 times the diameter; the platinum electrode (2) is circular and has a central axis with the silver electrode (4), the inner diameter of the platinum electrode (2) is 1800-3000 μm, and the wall thickness is 100-500 μm; the insulating layer (15) Covered on the quartz substrate (1) and the metal layer (12), the thickness of the insulating layer (15) is higher than the metal layer (12), and makes the platinum electrode (2), silver electrode (4), platinum pad (8) , the silver pad (9) and the microelectrode array (11) on the upper surface of the gold pad (10) are exposed; the gold electrode (3), the gold lead (7), the gold pad (10) and the third wire (18) The platinum electrode (2), the platinum lead wire (5), the platinum pad (8) and the first wire (16) are sequentially connected and conductive, the silver electrode (4), the silver lead wire (6), the silver The welding pad (9) and the second wire (17) are sequentially connected and conducted. 2. a kind of three-electrode integrated electrochemical sensor based on microelectrode array according to claim 1, is characterized in that, on microelectrode array (11), is coated with bismuth film (13), on described silver electrode (4) The surface is plated with silver chloride (14); the microelectrode array (11) is coated with bismuth film (13) as the working electrode, the silver electrode (4) is plated with silver chloride (14) as the Ag|AgCl reference electrode, and the platinum electrode (2 ) as the counter electrode. 3. a preparation method of the three-electrode integrated electrochemical sensor claimed in claim 1, is characterized in that, the method comprises the following steps: (1) Preparation of gold electrodes: After cleaning and drying the quartz substrate, magnetron sputtering Cr adhesion layer (30-50nm) and Au layer (200-400nm), spin-coating positive photoresist, and exposing under ultraviolet light Development, dry etching of gold electrodes after curing; (2) Preparation of platinum electrodes: magnetron sputtering Ti adhesion layer (30-50nm) and Pt layer (200-400nm), spin-coating positive photoresist, after exposure and development, dry-etch platinum counter electrode; (3) Preparation of silver electrodes: first coat a layer of 0.5 μm positive photoresist on the chip, after full exposure and development, remove the photoresist on the silver electrode pattern, and use plasma in a high vacuum environment The positively charged argon ions bombard the silver target (cathode), and the ejected silver atoms are deposited on the quartz substrate chip (anode), forming a 100-200nm silver layer, and finally the silver is removed by lift-off process. The silver metal layer and photoresist other than the electrode and the attached wire pad are removed together; (4) Preparation of insulating layer: Deposit a layer of insulating layer Si ₃ N ₄ on the front of the quartz substrate chip by plasma enhanced chemical vapor deposition (PECVD), then spin-coat photoresist, expose and develop with ultraviolet light, and etch the microelectrode array , Platinum electrodes, silver electrodes, gold pads, platinum pads, and insulating layers on the surface of silver pads, and the insulating layers in other areas are retained; (5) Make a reference electrode: use the silver electrode (4) as the anode, and the platinum electrode (2) as the cathode, immerse in the 0.1mM HCl solution, and perform electroplating with a constant current of 0.4mA/ ^cm2 for 300-600s , so as to plate AgCl on the surface of the silver electrode; (6) Working electrode modified bismuth film: the platinum electrode (2) is used as the counter electrode, the first wire (16) is used as the signal lead-out line of the counter electrode, and the silver electrode (4) and electroplated silver chloride (14) are used as reference electrode, the second wire (17) is used as the signal lead-out wire of the reference electrode, the microelectrode array (11) is used as the working electrode, and the third wire (18) is used as the signal lead-out wire of the working electrode, thereby forming a three-electrode system, respectively Connect to the counter electrode port, reference electrode interface and working electrode interface of the electrochemical workstation; immerse the electrode part in the solution of the test box for electrochemical modification and measurement: in 1MH ₂ SO ₄ solution, perform cyclic voltammetry Scanning, the scanning voltage range is -0.2V～+1.5V, the scanning rate is 0.05V/s, and the scanning is repeated several times to complete the electrode cleaning and activation; replace it with Bi(NO ₃ ) ₃ solution (1mol/LKNO ₃ and 1 %HNO ₃ as the bottom solution), the concentration of Bi ³⁺ is 0.005～0.03mol/L, and the constant potential method is scanned, the potential range is -0.45～-0.3V, the electroplating time is 100～300s, bismuth ions are generated on the working electrode After reduction, a bismuth film is formed on the microelectrode array (11), with a thickness less than 100 nm. Rinse with deionized water and dry with nitrogen to obtain a three-electrode integrated electrochemical sensor based on microelectrode array.