Detection method for high-sensitivity detection of chlorpyrifos based on OPECT (Optical Photon Emission Computed Tomography) and application

Abstract

The invention discloses a detection method for high-sensitivity detection of chlorpyrifos based on OPECT and application, a prepared TiO2 / CdS / CPF gate electrode, an OECT transistor, a reaction chamber and a PBS buffer solution are assembled into a biosensor, an object to be detected is dropped on the surface of the gate electrode and irradiated by an LED light source, OPECT detection is carried out, and high-sensitivity and high-specificity detection of chlorpyrifos (CPF) is successfully realized. According to the detection method, a traditional gate electrode is replaced with a TiO2 / CdS heterojunction, the TiO2 / CdS heterojunction serves as a photosensitive gate to be introduced into an organic photoelectrochemical transistor (OPECT) system, the light absorption capacity and the charge separation efficiency are remarkably improved through the narrow-band gap synergistic effect of the heterojunction, and the bottleneck that traditional TiO2 is low in photoelectric conversion efficiency is solved.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical detection, and in particular relates to a detection method and application of chlorpyrifos based on OPECT high-sensitivity detection. Background Art

[0002] Chlorpyrifos is toxic to humans, animals and the environment. Its residues may affect human health through the food chain, especially for children, pregnant women and sensitive groups. Therefore, it is of great significance to develop a method for accurate analysis of trace amounts of chlorpyrifos, especially in food safety and environmental protection.

[0003] At present, there are many methods for detecting chlorpyrifos residues, mainly including high performance liquid chromatography, chromatograph, enzyme-linked immunosorbent assay, electrochemical method, etc. However, the above detection methods all have disadvantages in practical applications. For example, the chromatography equipment is expensive, the operation is complicated, and it requires professional personnel to operate. The environment requirements are high and the analysis process is complicated. The electrochemical method is mainly based on photoelectrochemical (PEC) sensors. Photoelectrochemical (PEC) sensors are a type of biosensor that uses light as an excitation source and analyzes the target substance through the electrochemical signal generated between the photosensitive electrode and the substance to be tested under light irradiation. PEC sensing is simple to operate and has low background noise, but its ability to amplify the detection signal is poor, and the detection sensitivity is insufficient. When detecting low-concentration substances, the output electrical signal does not change significantly. Although organic electrochemical transistors (OECTs) have unique signal amplification capabilities, strong stability, and low cost, they are widely used in biochemical sensing, but the gate bias voltage (V G ) may cause damage to biological molecules. Therefore, a detection method for chlorpyrifos with high sensitivity, low cost, easy operation and low requirements on the operating environment is urgently needed. Summary of the invention

[0004] In order to solve the above problems, the present invention designs a detection method and application of chlorpyrifos based on OPECT with high sensitivity. The present invention introduces TiO2 / CdS heterojunction as a photosensitive gate into the organic photoelectrochemical transistor (OPECT) system, and significantly improves the light absorption capacity and charge separation efficiency through the narrow band gap synergistic effect of the heterojunction, thereby solving the bottleneck of low photoelectric conversion efficiency of traditional TiO2. 2+ This technology was applied to the detection of organophosphorus pesticide residues through chelation with CPF, and high-sensitivity and high-specificity detection of chlorpyrifos (CPF) was successfully achieved.

[0005] To achieve the above object, the present invention designs a detection method for chlorpyrifos based on OPECT with high sensitivity, comprising the following steps:

[0006] Step 1), gate electrode preparation:

[0007] a. Immerse the FTO electrode in a TiO2 liquid precursor containing TNBT and 6M HCl, perform a hydrothermal reaction and anneal for 1h to obtain a TiO2 nanorod array film, wherein the TiO2 nanorods have a length of 2-3 μm and a diameter of 100-200 nm;

[0008] b. Immerse the prepared TiO2 nanorod array film in a CdS precursor solution containing CdCl2·2H2O, thiourea and ammonia water, react in a water bath at 80°C for 4 min, wash and dry to obtain a TiO2 / CdS heterojunction film, wherein the CdS deposition particle size is 8-10 nm and the CdS deposition layer thickness is 30-60 nm;

[0009] Step 2), OECT transistor preparation:

[0010] Cr and Au layers were deposited as source (S) and drain (D) layers on a glass substrate by vacuum thermal evaporation, and 5% dimethyl sulfoxide was spin-coated in the formed channel area;

[0011] Step 3) Construction and use of biosensor:

[0012] The test substance was dropped on the surface of the gate electrode and incubated at 37°C for 10 minutes. The C=N and P=S groups in the chlorpyrifos molecules contained in the test substance reacted with Cd 2+ After chelation and fixation, a TiO2 / CdS / CPF modified electrode was formed. The modified gate electrode and OECT transistor were then placed in PBS buffer and irradiated with a 3w white light LED as the light source for OPECT detection.

[0013] OPECT detection: TiO2 / CdS / CPF is used as the gate electrode (G) to form an OECT with the source electrode (S) and the drain electrode (D). VG=0 V and VDS=0.1 V are applied, and the channel current IDS is recorded by on-off periodic light source modulation.

[0014] As a further improvement of the detection method of chlorpyrifos based on OPECT with high sensitivity of the present invention: the TiO2 liquid precursor contains 0.25g TNBT and 15mL HCl; during the hydrothermal reaction, the conductive surface of the FTO electrode is downward, and the hydrothermal reaction is carried out at 150°C for 24 hours, followed by annealing at 500°C for 1 hour. After annealing, the surface crystal form of the nanorods is rutile phase, and the main peak of the XRD spectrum is located at 35.9° (101 crystal plane).

[0015] As a further improvement of the detection method of chlorpyrifos based on OPECT with high sensitivity of the present invention: 0.01 mM CdCl2·2H2O and 0.01 mM thiourea were added to 150 mL of deionized water and stirred for 15 minutes, and 10.8 mL of ammonia water was added to the mixed solution to obtain a CdS precursor solution.

[0016] As a further improvement of the detection method of chlorpyrifos based on OPECT with high sensitivity of the present invention: in the preparation of OECT transistor, a 10*12mm Na / Ca glass substrate is taken, and it is acoustically cleaned in acetone, ethanol, and deionized water in sequence and quickly blown dry with nitrogen; the designed mask is fixed on the glass substrate, and 10nm Cr and 100nm Au are deposited in sequence by a vacuum evaporator to form a 0.2mm*6.0mm channel; the obtained substrate is cleaned in plasma water for 10 min, and spin-coated with 5% dimethyl sulfoxide at 3500 rpm for 30s in a glove box, and the coated film is annealed at 180°C in an argon atmosphere for 1h.

[0017] As a further improvement of the detection method of chlorpyrifos based on OPECT high sensitivity detection of the present invention: during OPECT detection, an LED light source with a light power density of ≥20 mW / cm² and a wavelength of 420-650 nm is used as an excitation source; the on-off cycle light source frequency is 0.5-2 Hz, and the duty cycle is 50%-70%.

[0018] To achieve the above objectives, the present invention designs a high-sensitivity OPECT biosensor for detecting chlorpyrifos, comprising: a reaction chamber; a gate electrode; an OECT transistor; a PBS buffer contained in the reaction chamber; wherein the PBS buffer has a pH of 7.2-7.4 and contains 0.1 M AA.

[0019] To achieve the above objectives, the detection method for chlorpyrifos based on OPECT with high sensitivity of the present invention is applied to the detection of organophosphorus pesticide residues to achieve high sensitivity and high specificity detection of chlorpyrifos (CPF).

[0020] Beneficial Effects

[0021] Compared with the prior art, the detection method and application of chlorpyrifos based on OPECT high sensitivity detection has the following beneficial effects:

[0022] First, the detection method and application described in the present invention utilize TiO2 / CdS heterojunction to replace the traditional gate electrode, and introduce the TiO2 / CdS heterojunction as a photosensitive gate into the organic photoelectrochemical transistor (OPECT) system, which significantly improves the light absorption capacity and charge separation efficiency through the narrow band gap synergistic effect of the heterojunction, thus solving the bottleneck of low photoelectric conversion efficiency of traditional TiO2.

[0023] Second, the detection method and application described in the present invention apply organic photoelectrochemical transistor (OPECT) technology to the detection of organophosphorus pesticide residues, successfully achieving high-sensitivity and high-specificity detection of chlorpyrifos (CPF), filling the application gap of OPECT technology in the field of pesticide residue detection.

[0024] Third, the detection method and application of the present invention drives the directional migration of electrolyte ions by photovoltage (Vp), and combines the signal amplification effect of transistors to achieve the goal of eliminating the need for external gate bias (V G )-supported self-powered sensing. This approach avoids the risk of electrochemical damage in traditional OECTs for biomolecule detection.

[0025] Fourth, the detection method and application of the present invention utilizes the C=N and P=S groups in chlorpyrifos (CPF) and Cd 2+ The chelation of ions was used to construct a specific electron transfer blocking model. This method does not require complex biological probe modification and significantly improves the selectivity and anti-interference ability of detection. The C=N and P=S groups in chlorpyrifos (CPF) are used to bind to Cd 2+ The chelation of ions constructs a specific electron transfer blocking model. This method does not require complex biological probe modification and significantly improves the selectivity and anti-interference ability of the detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the preparation process and electron transfer mechanism of the biosensor of the present invention;

[0027] Figure 2 It is the comparison of photocurrent of CdS with different particle sizes deposited on TiO2;

[0028] Figure 3 It is the photocurrent reduction rate when 100 ng / mL of CPF is added when CdS with different particle sizes is deposited on TiO2;

[0029] Figure 4 The biosensor of the present invention is used to measure CPF with different concentrations and interferences. DS Comparison chart of test data;

[0030] Figure 5 It is the XRD and morphology characterization diagram of the gate electrode (TiO2 / CdS) in the present invention;

[0031] Figure 6 The XPS analysis of CPF and Cd 2+ The complexation between them is characterized in the figure;

[0032] Figure 7It is a test of the photoelectric properties of TiO2, TiO2 / CdS, and TiO2 / CdS / CPF in the present invention;

[0033] Figure 8 The transfer curves of the TiO2 / CdS gate OPECT device before and after illumination were obtained before and after the addition of chlorpyrifos;

[0034] Fig. 9 The I of OPECT with TiO2 / CdS as gate DS and I GS response;

[0035] Fig.10 is the OPECT current gain with TiO2 / CdS as gate. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. This embodiment is based on the technical solution of the present invention and provides a detailed implementation method.

[0037] Example 1

[0038] The method for constructing the high-sensitivity OPECT biosensor described in this embodiment comprises the following steps:

[0039] Preparation of gate electrode (step 1): TiO2 nanorod arrays were directly grown on FTO substrates by a one-step hydrothermal method. First, the FTO electrode was ultrasonically cleaned in acetone, ethanol and deionized water for 30 min, and then dried in a drying oven at 60°C; then, TNBT (0.25 g) was added to 6M HCl (15 mL) to obtain a TiO2 liquid precursor; the cleaned FTO electrode was placed in the TiO2 liquid precursor with the conductive surface facing down and hydrothermally treated at 150°C for 24 h; finally, a TiO2 nanorod array film was obtained, which was then annealed at 500°C for 1 h. The TiO2 nanorods in the prepared TiO2 nanorod array film were 2-3 μm in length and 100-200 nm in diameter.

[0040] TiO2 / CdS heterojunction film was prepared by chemical bath deposition. CdCl2·2H2O (0.01 mM) and thiourea (0.01 mM) were added to 150 mL of deionized water and stirred for 15 minutes. Then, 10.8 mL of ammonia water was added to the solution and the prepared TiO2 nanorod array film was immersed in the CdS precursor solution and heated in a water bath at 80°C for 4 minutes. The TiO2 / CdS heterojunction film was taken out, washed with deionized water and ethanol, and finally dried in vacuum at 60°C to obtain a TiO2 / CdS heterojunction film on a FTO substrate, wherein the CdS deposition particle size was 8-10 nm and the CdS deposition layer thickness was 30-60 nm.

[0041] Preparation of OECT transistor (step 2): Cut the sodium / lime glass substrate into small pieces of 10×12 mm, clean them with acetone, ethanol and deionized water ultrasonically in sequence, and then blow dry them quickly with nitrogen. Fix the pre-designed mask on the glass substrate, and spray Cr (10 nm) and Au (100 nm) in sequence through a vacuum thermal evaporator, where the channel length is 0.2 mm and the width is 6.0 nm. Clean the obtained substrate in plasma for ten minutes. Spin-coat 5% dimethyl sulfoxide on the substrate at 3500 rpm for 30 s in a glove box. Anneal the coated film at 180°C in an argon atmosphere for 1h.

[0042] The biosensor described in the patent of the present invention refers to a detection unit composed of a PBS buffer solution contained in a reaction chamber, a gate electrode prepared in the above steps, and an OECT transistor. The PBS buffer solution has a pH of 7.2-7.4 and contains 0.1 M AA.

[0043] like Figure 1 As shown, the preparation of TiO2 / CdS heterojunction gate material is as follows Figure 1 As shown in (a), this method is simple and low-cost. Specifically, a rutile TiO2 nanorod array film was synthesized by a one-pot hydrothermal method, and then a TiO2 / CdS heterojunction film was obtained by a chemical bath deposition method. The OPECT built on PEC and OECT retains some of the components of the traditional OECT, such as Figure 1 As shown in (b), the source (S) and drain (D) electrodes are connected through a channel covered by an organic semiconductor and connected to the photosensitive gate (TiO2 / CdS, TiO2 / CdS / CPF) through an electrolyte to form the main body of the device. 2+ It will produce chelation with CPF, which will be beneficial to the selective detection of CPF. 2+ The chelation between them will form a shielding effect on the gate, resulting in I G Reduce, I DS Increase as Figure 1 As shown in (c), CPF can be effectively detected.

[0044] The above method was used to prepare a biosensor for the detection of chlorpyrifos (CPF): the liquid to be detected was dropped on the surface of the TiO2 / CdS heterojunction electrode and incubated at 37°C for 10 min. The electrode was washed with deionized water 3 times after each modification. In this process, the C=N and P=S groups in CPF interacted with the Cd in CdS. 2+The chelation effect of CPF was used to fix CPF on the electrode surface, and the prepared electrode was marked as TiO2 / CdS / CPF. TiO2 / CdS / CPF and OECT transistor were inserted into the reaction chamber, PBS buffer was set in the reaction chamber, OPECT detection was performed with 3 W white light LED (light power density ≥ 20 mW / cm², wavelength 420-650 nm) as the light source, TiO2 / CdS / CPF was used as the gate electrode (G) and the source electrode (S) and drain electrode (D) formed OECT, and V was applied G =0 V, V DS = 0.1 V, modulated by an on-off cycle light source (frequency 0.5-2 Hz, duty cycle 50%-70%), and the channel current I was recorded DS . Channel current I DS It is proportional to the concentration of chlorpyrifos, so chlorpyrifos can be detected sensitively.

[0045] In order to verify the feasibility of TiO2 / CdS / CPF in the detection system described in the present invention, TiO2 / CdS films with different appearances were prepared with different CdS deposition times for comparative testing. The CdS deposition time was set to 2 min, 4 min, and 6 min, respectively. As the deposition time increased, the deposition particle size increased. At 2 min, the CdS particle size was 5-7nm, the CdS was not obvious, and the TiO2 film did not change color. At 4 min, the TiO2 film turned slightly yellow, and the CdS particle size was 8-10nm. At 6 min, the yellow color of the TiO2 film deepened, and the CdS particle size was 10-15nm. The photocurrent test of TiO2 / CdS deposited at different particle sizes showed that the photocurrent reached the maximum at 4 min, that is, when the CdS particle size was 8-10 nm, and was relatively stable in the five-cycle cyclic test, with the highest efficiency of photogenerated electron-hole pair separation. When 100 ng / mL CPF was added, the photocurrent decreased the most, reaching 68.75%. The gate electrode current decreased by 37.14% when deposited for 2 min, and by 6.83% when deposited for 6 min, as shown below: Figure 3 shown.

[0046] The biosensor described in the present invention is a detection platform based on PEC and OECT. The OPECT retains the components of the traditional OECT. In addition to the semiconductor polymer film contacted by S, D, E and the photosensitive gate, a light source is used as the excitation source, which can eliminate an external power supply and easily achieve zero V G For OPECT, the essence of converting the tiny voltage signal change on the gate into the amplified signal of the channel current is the change in the conductivity of the polymer. DS When the organic semiconductor film is in the state of being oriented, the carriers will move in a directional manner, generating a stable IDS When a positive V is applied to the gate G This drives the cations in the solution to be injected into the channel, making the PEDOT in the conductive oxidation state + Transformed into reduced PEDOT 0 , which leads to I DS The specific process is as follows:

[0047] n(PEDOT + :PSS - )+M n+ +ne - → nPEDOT 0 +M n+ :nPSS -

[0048] Where n is the charge number of the cation, and M n+ is the cation in the electrolyte. Essentially, The device's ionic circuit consists of two capacitors connected in series, one capacitor Corresponds to The double electrical layer at the interface ( ), and another capacitor Corresponds to Interface. In the absence of light, for the initial Devices, The potential drop at the interface is:

[0049]

[0050] because The gate of the device is decorated with photosensitive materials. Under light conditions, the material undergoes electronic transition accompanied by charge transfer, resulting in The interface potential drop decreases. Assuming that the light-induced The change in interface potential drop is , at a fixed gate voltage Down, The interface potential drop increases to , corresponding to the effective gate voltage The increase can be calculated by the following formula:

[0051]

[0052] Therefore, the V generated by light p Will cause In OPECT-based biosensors, as long as the analyte can cause the OPECT device to generate V under light conditions, the transfer curve of the OPECT device will shift. p changes have occurred, will change, resulting in I DS changes, and finally realize the detection of the object to be tested.

[0053] Specifically, if Figure 4 As shown, the biosensor and detection method of the present invention are used to verify the feasibility of introducing the TiO2 / CdS heterojunction as a photosensitive gate into an organic photoelectrochemical transistor (OPECT) system to detect chlorpyrifos (CPF). DS The value is closely related to the CPF concentration dropped on the TiO2 / CdS gate, so the proposed OPECT system can be used to detect CPF. Figure 4 (a) The I corresponding to different CPF concentrations was recorded. DS The response over time. An increase in CPF concentration leads to an increase in I DS It gradually increases, indicating that the degree to which CPF participates in the ion exchange reaction on the gate is enhanced. Figure 4 (b) The dynamic relationship is further illustrated by the fitting curve. △I / I0 shows a good linear increasing relationship with the logarithm of CPF concentration, ranging from 0.1 pg / mL to 100 ng / mL. The sensor shows good selectivity for the target analyte. Figure 4 As shown in (c), when other interfering pesticides (trichlorfon, phoxim, norfloxacin) including organophosphorus-sulfur pesticides were added at concentrations ten times higher than the target, there was no significant change in the channel current, and the effects of other high concentrations (100 times that of the target analyte) of anions and cations were negligible.

[0054] method Material Linear range Detection limit PEC Sensors <![CDATA[ZnS / Co9S8]]> 0.05-40 ppb 0.0166 ppb PEC Sensors <![CDATA[CoS2 / CdS]]> 0.03-100 ppb 0.01 ppb PEC Sensors <![CDATA[Bi2S3@g-C3N4]]> <![CDATA[50-10 5 ppb]]> 0.03 ppb PEC Sensors <![CDATA[Bi / Bi3O4Br]]> 0.01-200 ppb 0.0017 ppb Fluorescent probes FD@ALB 40-200 μM 0.57 μM Surface enhanced Raman spectroscopy AuNPs 0.001-1 ppm 0.009 ppb OPECT This work <![CDATA[TiO2 / CdS]]> <![CDATA[10 2 -10 -4 ppb]]> 2.2 fg / mL

[0055] Table 1: Linear range and detection limit of chlorpyrifos by different detection methods

[0056] Comparison with the performance of other reported chlorpyrifos detection methods, as shown in Table 1 , intuitively demonstrates that the present method has obvious advantages in terms of sensing materials, LOD (2.2 fg / mL), and wide response range.

[0057] The present invention uses a hydrothermal method to obtain TiO2 nanorods with a length of 2-3 μm and a diameter of 100-200 nm, and deposits a particle size of 8-10 nm, and deposits 30-60 nm CdS to obtain a TiO2 / CdS heterojunction film. In order to verify the feasibility of using the TiO2 / CdS heterojunction film as a gate electrode (light absorption characteristics) when using an OPECT system to detect CPF, TiO2, TiO2 / CdS, and TiO2 / CdS / CPF are characterized.

[0058] Figure 5(a) is the XRD spectra of FTO, TiO2 and TiO2 / CdS. For TiO2NRAs film, the diffraction peaks at 35.9° and 62.6° can be attributed to the (101), (002) and (301) crystal planes of rutile TiO2 (JCPDS 75-1748). The characteristic diffraction peaks at 26.4° and 43.9° are attributed to the (111) and (220) crystal planes of cubic CdS (JCPDS 75-581). In all spectra, the remaining diffraction peaks are from the FTO bottom layer (JCPDS 41-1445), and no impurity diffraction peaks are detected. Figure 5 (b) SEM of TiO2 / CdS heterojunction film. The SEM image clearly shows that the TiO2 film is composed of multiple nanorods, and the thickness of a single nanorod is about 50~100 nm. These nanorods are neatly arranged to form a TiO2 nanorod array. The inset is an enlarged SEM image of the TiO2 / CdS heterojunction film, and it can be clearly seen that the surface of the TiO2 nanorod array is coated with CdS nanoparticles. Figure 5 (c) TEM of TiO2 / CdS heterojunction reveals more microstructural information of the TiO2 / CdS heterojunction. Due to the small size of CdS nanoparticles, the morphology of the TiO2 nanorod array does not change after treatment. Figure 5 (d) is the HRTEM image of the TiO2 / CdS heterojunction. The lattice fringes can be clearly seen in the image, and the measured interplanar spacings of 3.3575 Å and 3.2615 Å correspond to the (111) and (110) planes of CdS and TiO2, respectively.

[0059] Figure 6 The high-resolution XPS spectra of TiO2 / CdS and TiO2 / CdS / CPF. The position of Cd 3d orbital in the X-ray electron spectrum is 5 / 2 (405.4 eV) and Cd 3d 3 / 2 (412.2 eV), after adding CPF, the orbital binding energy peak obviously shifted to the low binding energy direction (405.1 eV and 411.8 eV), and the electron cloud density increased, proving that the chemical coordination environment of Cd changed, confirming the chelation effect of Cd and CPF. Figure 6 (a) SO X The presence of indicates that sulfur is in a higher oxidation state (such as SO2, SO3, etc.). The addition of CPF may change the oxidation state of the 2p orbital by changing the electronic environment of sulfur, thereby causing SO X The XPS signal intensity weakened. Figure 6 (b) Further verification of CPF and Cd 2+ coordination effect.

[0060] Figure 7 (a) is the UV-visible diffuse reflectance absorption spectra of TiO2, TiO2 / CdS, and TiO2 / CdS / CPF; Figure 7 (b) is a schematic diagram of the charge transfer mechanism of TiO2 / CdS heterojunction under light. Figure 7 (c) EIS spectra of TiO2, TiO2 / CdS, TiO2 / CdS / CPF, Figure 7 (d) Transient PEC responses of TiO2, TiO2 / CdS, and TiO2 / CdS / CPF in 10 mM phosphate-buffered saline (PBS) electrolyte containing 0.1 M AA when the concentration of CPF was fixed at 100 ng / mL.

[0061] This verification test uses the EIS method to study the interfacial charge transfer resistance. As we all know, the diameter of the semicircle in the Nyquist plot is related to the charge transfer resistance (Ret), which reflects the charge transfer efficiency at the interface between the electrode and the electrolyte. Figure 7 As shown in (c), a relatively small electron transfer resistance (Ret) was observed on the bare TiO2 nanorod array (black curve), while the Ret value of the TiO2 / CdS nanohybrid film increased (red curve). After adding 100 ng / mL CPF, Ret decreased to about 249 Ω. The increase in Ret of TiO2 / CdS may be due to the formation of CdS that hinders the Fe (CN)6 3- / 4- Charge transfer to the electrode. CPF combines with TiO2 / CdS electrode, consumes some metal ions, and Fe (CN)6 3- / 4- It is easier to transfer electrons to the electrode. The formation of TiO2 / CdS heterojunction was confirmed, and the chelation effect of TiO2 / CdS and CPF was further confirmed. Figure 7 As shown in (d), the transient PEC responses of TiO2, TiO2 / CdS and TiO2 / CdS / CPF electrodes were studied under the optimal experimental parameters. The TiO2 / CdS heterojunction electrode exhibited a very high anodic photocurrent response of about 1.7 μA, which is about 8 times higher than that of pure TiO2 (~ 0.27 μA). The interface between the TiO2 nanoparticles and the CdS nanoparticles is the excited e - The transferred channel, the excited e - It can be seen from the conduction band of CdS (C B ) quickly moved to TiO2 and produced a strong photocurrent response. After adding 100 ng / mL chlorpyrifos, the photocurrent response decreased significantly, indicating that an effective detection method for chlorpyrifos based on TiO2 / CdS heterojunction was successfully established.

[0062] Figure 8The transfer curves of the TiO2 / CdS gate OPECT device before and after illumination are obtained by using the biosensor of the present invention before and after adding chlorpyrifos. In the scanning voltage range of 0 ~ 0.5 V, the device shows obvious transfer characteristics in the absence of illumination (solid line) and with illumination (dashed line). After the addition of chlorpyrifos, the interface charge transfer resistance increases, thereby reducing the photoelectric conversion efficiency. Fig. 9 The I of OPECT with TiO2 / CdS as gate DS and I GS Response, when the light is on for 50 seconds, I GS Rapidly increasing, I DS It dropped rapidly and stabilized at 0.83 mA. This is because the doping state of PEDOT:PSS was changed during the illumination process, making the oxidized PEDOT + PEDOT in reduced form 0 , the conductivity decreases, resulting in I DS It is noteworthy that a small change in gate current of about 0.5 μA will result in a large change in channel current of about 0.46 mA. Fig.10 This is the OPECT current gain with TiO2 / CdS as the gate. As shown in the test graph, the corresponding current gain is as high as 800 times.

[0063] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for detecting chlorpyrifos based on high sensitivity of OPECT, characterized in that: The steps include: Step 1), gate electrode preparation: The FTO electrode was immersed in a TiO2 liquid precursor containing TNBT and 6M HCl, and annealed for 1h after hydrothermal reaction to obtain a TiO2 nanorod array film, wherein the TiO2 nanorods were 2-3 μm in length and 100-200 nm in diameter; b. Immerse the prepared TiO2 nanorod array film in a CdS precursor solution containing CdCl2·2H2O, thiourea and ammonia water, react in a water bath at 80°C for 4 min, wash and dry to obtain a TiO2 / CdS heterojunction film, wherein the CdS deposition particle size is 8-10 nm and the CdS deposition layer thickness is 30-60 nm; Step 2), OECT transistor preparation: Cr and Au layers were deposited as source (S) and drain (D) layers on a glass substrate by vacuum thermal evaporation, and 5% dimethyl sulfoxide was spin-coated in the formed channel area; Step 3) Construction and use of biosensor: The test substance was dropped on the surface of the gate electrode and incubated at 37°C for 10 minutes. The C=N and P=S groups in the chlorpyrifos molecules contained in the test substance reacted with Cd 2+ After chelation and fixation, a TiO2 / CdS / CPF modified electrode was formed. The modified gate electrode and OECT transistor were then placed in PBS buffer and irradiated with a 3w white light LED as the light source for OPECT detection. OPECT detection: TiO2 / CdS / CPF is used as the gate electrode (G) to form an OECT with the source electrode (S) and the drain electrode (D). V is applied G =0 V, V DS = 0.1 V, and the channel current I is recorded by switching on and off the light source. DS .

2. The method for detecting chlorpyrifos based on high sensitivity of OPECT as claimed in claim 1, characterized in that: The TiO2 liquid precursor contains 0.25g TNBT and 15mL HCl. During the hydrothermal reaction, the conductive surface of the FTO electrode is downward, and the hydrothermal reaction is carried out at 150°C for 24 hours, followed by annealing at 500°C for 1 hour. After annealing, the surface crystal of the nanorods is rutile phase, and the main peak of the XRD spectrum is located at 35.9° (101 crystal plane).

3. The method for detecting chlorpyrifos based on OPECT with high sensitivity as claimed in claim 2 is characterized in that: 0.01 mM CdCl2·2H2O and 0.01 mM thiourea were added to 150 mL of deionized water and stirred for 15 minutes. 10.8 mL of ammonia water was added to the mixed solution to obtain a CdS precursor solution.

4. The method for detecting chlorpyrifos based on high sensitivity of OPECT as claimed in claim 3, characterized in that: In the preparation of OECT transistors, a 10*12mm Na / Ca glass substrate was taken, and acoustically cleaned in acetone, ethanol, and deionized water in sequence, and then quickly blown dry with nitrogen. The designed mask was fixed on the glass substrate, and 10nm Cr and 100nm Au were deposited in sequence using a vacuum evaporator to form a 0.2mm*6.0mm channel. The obtained substrate was cleaned in plasma water for 10 min, and spin-coated with 5% dimethyl sulfoxide at 3500 rpm for 30 s in a glove box. The coated film was annealed at 180° C. in an argon atmosphere for 1 h.

5. The method for detecting chlorpyrifos based on high sensitivity of OPECT as claimed in claim 4, characterized in that: During OPECT detection, an LED light source with a light power density of ≥20 mW / cm² and a wavelength of 420-650 nm is used as the excitation source; the on-off cycle frequency of the light source is 0.5-2 Hz, and the duty cycle is 50%-70%.

6. A biosensor for use in the detection method according to any one of claims 1 to 5, characterized in that: include: Reaction chamber; Gate electrode; OECT transistor; PBS buffer placed in the reaction chamber; The PBS buffer has a pH of 7.2-7.4 and contains 0.1 M AA.

7. A use of the biosensor as claimed in claim 6, characterized in that: The application of the biosensor lies in the high sensitivity and high specificity detection of the chlorpyrifos content in the object to be detected.

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