1. A preparation method of a non-immobilized aptamer photoelectric sensor for detecting atrazine is characterized by comprising the steps of preparing an APT-GN compound and preparing an MCT/Ag NPs/BiOBr/ITO electrode;

the preparation method of the APT-GN compound comprises the following steps: mixing the graphene dispersion liquid with the atrazine aptamer, and obtaining an APT-GN compound after ultrasonic treatment and separation;

the preparation method of the MCT/Ag NPs/BiOBr/ITO electrode comprises the following steps:

1) dropwise coating the BiOBr dispersion liquid on the surface of the pretreated ITO electrode, and drying to obtain a BiOBr/ITO electrode;

2) depositing Ag NPs on the surface of the BiOBr/ITO electrode to obtain an Ag NPs/BiOBr/ITO electrode;

3) soaking the Ag NPs/BiOBr/ITO electrode in MCT solution to obtain an MCT/Ag NPs/BiOBr/ITO electrode;

the MCT is n-octyl mercaptan.

2. The method for preparing a non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein the graphene dispersion is prepared by the following steps: ultrasonically dispersing graphene in water to prepare a dispersion liquid with the concentration of 0.10-0.20mg/mL, namely the graphene dispersion liquid; the mixing process is as follows: centrifuging 1OD atrazine aptamer at 10000r/min of 5000-.

3. The method for preparing the non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein the ultrasonic process comprises the following steps: performing ultrasonic treatment in ice bath for 2-3 h; the separation process is as follows: centrifuging at 2000-4000r/min for 3-5min, and then discarding the lower bulk graphene.

4. The method for preparing a non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein in the step 1), the BiOBr dispersion solution is prepared by the following steps: adding Bi (NO)₃)₃Adding the ethylene glycol solution into an ethylene glycol solution of KBr, stirring for 30-40min, then carrying out ultrasonic treatment for 10-15min, then reacting for 5-7h at the temperature of 175-185 ℃, separating to obtain BiOBr, and preparing the BiOBr into a dispersion liquid of 30-40mg/mL, namely the BiOBr dispersion liquid.

5. The method for preparing a non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein in the step 1), the pretreatment process of the ITO electrode comprises the following steps: and sequentially placing the ITO electrode in NaOH solution, acetone, ethanol and deionized water, respectively ultrasonically cleaning for 10-15min, and then drying in the air atmosphere.

6. The method for preparing a non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein in the step 2), the deposition process of Ag NPs comprises: immersing the BiOBr/ITO electrode into 1-3mmol/L AgNO₃In the solution, the solution is then irradiated for 1-1.5h with a Xe lamp of 250-350W.

7. The method for preparing a non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 1, wherein in the step 3), the MCT solution is an ethanol solution of MCT, and the concentration is 30-50 mmol/L; the soaking time is 20-25 h.

8. A non-immobilized aptamer-based photosensor for detecting atrazine, prepared by the method of any one of claims 1 to 7, comprising APT-GN complex and MCT/Ag NPs/BiOBr/ITO electrodes.

9. Use of the non-immobilized aptamer-based photosensor for detecting atrazine according to claim 8, wherein the sensor is used for detecting atrazine in an aqueous environment.

10. The use of the non-immobilized aptamer photoelectric sensor for detecting atrazine according to claim 9, wherein the detection process comprises: dropwise adding an incubation system on the surface of an MCT/Ag NPs/BiOBr/ITO electrode, incubating for 1-2h, cleaning and drying, establishing a three-electrode system by taking the incubated MCT/Ag NPs/BiOBr/ITO electrode as a working electrode, a platinum sheet as a counter electrode, a saturated calomel electrode as a reference electrode and a PBS (phosphate buffer solution) buffer solution as a supporting electrolyte, measuring the increment of the photocurrent density under visible light, and obtaining the concentration of atrazine in the water environment according to the corresponding relation between the increment of the photocurrent density and the concentration of atrazine; the incubation system comprises a Tris-HCl buffer solution, an APT-GN compound, a water solution to be detected and a DNase I enzyme solution.

Background

Atrazine (ATZ) is a common triazine herbicide, and Atrazine residues can be detected in various places such as soil, surface water, underground water and the like due to large using amount, strong stability and difficult degradation. In addition, the compound is also one of typical environmental endocrine disruptors, can disturb the endocrine system of a human body after being contacted for a long time, can cause serious damage to the reproductive system, the central nervous system, cardiovascular and cerebrovascular systems and the like, and has potential carcinogenicity. In 2007, the Ministry of health in China clearly stipulates that the concentration of atrazine in drinking water body needs to be lower than 3 mu g L-¹. Therefore, a simple, convenient and efficient analysis method is established, and the method has very important significance for realizing efficient and sensitive detection of the atrazine in the water body.

The existing detection methods of atrazine mainly comprise an instrument analysis method and a sensing analysis method, and although good detection effects are obtained to a certain extent by the detection methods, various problems exist. For example, the instrumental analysis method often depends on large-scale instruments such as high performance liquid chromatography, mass spectrometry, gas chromatograph-mass spectrometer and the like, the instruments are expensive, and various limitations such as complex operation process, tedious sample pretreatment, long detection process time consumption, difficulty in rapid monitoring and the like exist. The sensing analysis method mainly comprises an immunoadsorption sensing method, a molecular imprinting sensing method, an aptamer sensing method and the like, identification elements such as antibodies, enzymes, molecular imprinting polymers or aptamers and the like are generally required to be fixed on the surface of an electrode by the sensing analysis technology, and the sensing analysis technology has the defects of small area of the electrode, limited loading capacity of the identification elements, easiness in reaching a saturated state, easiness in falling off of the identification elements in the detection process, poor stability and the like, so that the development of a sensing system is greatly limited.

Disclosure of Invention

The invention aims to provide a non-immobilized aptamer photoelectric sensor for detecting atrazine. The method utilizes the pi-pi stacking effect between graphene and an aptamer to prepare an APT-GN compound as an identification element, and utilizes the Ag-S bond self-assembly effect to carry out sulfydryl functionalization on the surface of an Ag NPs/BiOBr/ITO electrode to obtain an MCT/Ag NPs/BiOBr/ITO electrode serving as a sensing electrode, so that the non-immobilized nucleic acid aptamer photoelectric sensor based on graphene-thiol signal regulation is obtained. The invention adopts a non-fixed sensing strategy, can realize the high-efficiency analysis and detection of the ATZ in a homogeneous solution without fixing an identification element on an electrode, avoids the direct modification process of an aptamer on the electrode, effectively improves the stability and the sensitivity of the sensor, and has the detection limit as low as 1.2 pM. In addition, the aptamer is used as an identification element, so that the selectivity of the sensor is greatly improved, and the method is simple to operate, is rapid and efficient, and can be used for detection and analysis of trace pollutants.

The purpose of the invention can be realized by the following technical scheme:

a preparation method of a non-fixed nucleic acid aptamer photoelectric sensor for detecting atrazine comprises the steps of preparing an APT-GN compound and preparing an MCT/Ag NPs/BiOBr/ITO electrode;

the preparation method of the APT-GN compound comprises the following steps: mixing the graphene dispersion liquid with the atrazine aptamer, and obtaining an APT-GN compound after ultrasonic treatment and separation;

the preparation method of the MCT/Ag NPs/BiOBr/ITO electrode comprises the following steps:

1) dropwise coating the BiOBr dispersion liquid on the surface of the pretreated ITO electrode, and drying to obtain a BiOBr/ITO electrode;

2) depositing Ag NPs on the surface of the BiOBr/ITO electrode to obtain an Ag NPs/BiOBr/ITO electrode;

3) soaking the Ag NPs/BiOBr/ITO electrode in MCT solution to obtain an MCT/Ag NPs/BiOBr/ITO electrode;

the MCT is n-octyl mercaptan.

Further, the preparation process of the graphene dispersion liquid comprises the following steps: ultrasonically dispersing graphene in water to prepare a dispersion liquid with the concentration of 0.10-0.20mg/mL, namely the graphene dispersion liquid; the mixing process is as follows: centrifuging 1OD atrazine aptamer at 10000r/min of 5000-.

Further, the ultrasound process is: performing ultrasonic treatment in ice bath for 2-3 h; the separation process is as follows: centrifuging at 2000-4000r/min for 3-5min, and then discarding the lower bulk graphene.

Further, in step 1), the preparation process of the BiOBr dispersion liquid is as follows: adding Bi (NO)₃)₃Adding the ethylene glycol solution into an ethylene glycol solution of KBr, stirring for 30-40min, performing ultrasonic treatment for 10-15min, reacting for 5-7h at the temperature of 175-185 ℃, separating (centrifuging, respectively cleaning with water and ethanol for 2-3 times, and drying in an oven at the temperature of 55-65 ℃ for 6-8h) to obtain BiOBr, and preparing the BiOBr into a dispersion liquid of 30-40mg/mL, namely the BiOBr dispersion liquid. BiOBr is prepared by a hydrothermal method.

Further, in step 1), the pretreatment process of the ITO electrode is: and sequentially placing the ITO electrode in NaOH solution, acetone, ethanol and deionized water, respectively ultrasonically cleaning for 10-15min, and then drying in the air atmosphere.

Preferably, the ITO electrode is 1.0 × 5.0cm of indium tin oxide transparent conductive glass.

Further, in step 2), the deposition process of the Ag NPs is as follows: immersing the BiOBr/ITO electrode into 1-3mmol/L AgNO₃In the solution, the solution is then irradiated for 1-1.5h with a Xe lamp of 250-350W. And depositing Ag NPs by adopting a photo-reduction method.

Further, in the step 3), the MCT solution is an ethanol solution of MCT, and the concentration is 30-50 mmol/L; the soaking time is 20-25 h.

The non-immobilized aptamer photoelectric sensor for detecting atrazine is prepared by the method, and comprises an APT-GN compound and an MCT/Ag NPs/BiOBr/ITO electrode.

The application of the non-immobilized aptamer photoelectric sensor for detecting atrazine is used for detecting atrazine in a water environment. And the analysis and detection of atrazine are realized through the signal sensitization effect generated by the dissociated graphene counter electrode in the aptamer recognition process.

Further, the detection process is as follows: dropwise adding an incubation system on the surface of an MCT/Ag NPs/BiOBr/ITO electrode, incubating for 1-2h, cleaning and airing (soaking the electrode in high-purity water for light dipping and washing, and airing in an air atmosphere), and establishing a three-electrode system by taking the incubated MCT/Ag NPs/BiOBr/ITO electrode as a working electrode, a platinum sheet as a counter electrode, a saturated calomel electrode as a reference electrode and PBS (0.1mol/L) as supporting electrolyte, measuring the increment of photocurrent density under visible light, and obtaining the concentration of atrazine in the water environment according to the corresponding relation between the increment of the photocurrent density and the concentration of atrazine; the incubation system comprises Tris-HCl buffer solution (10-20 mu L), APT-GN complex (5-10 mu L), aqueous solution to be detected (3-6 mu L) and DNase I enzyme solution (2-4 mu L). The method comprises the steps of firstly, changing an aqueous solution to be detected in an incubation system into atrazine solutions with different concentrations for incubation, measuring I-t curves of the atrazine incubated with different concentrations in a PBS buffer solution, and drawing a working curve according to the logarithmic relation between photocurrent density increment caused by assembling dissociated graphene on an electrode and the atrazine concentration; when the aqueous solution to be detected is detected, the concentration of the atrazine is obtained by utilizing the working curve and the increment of the photocurrent density.

The sensor can perform selective determination: adding different interfering substances into the incubation system, measuring the change of photocurrent by using an I-t curve, calculating the relative ratio of the photocurrent to the photocurrent under the condition without the interfering substances, and investigating the selectivity of the sensor.

Specifically, the method for selectively measuring the non-immobilized aptamer photoelectric sensor comprises the following steps: adding a solution containing other interfering substances with the concentration of 100 times into an incubation system, performing an I-t curve under the same condition by adopting the same method, researching the change condition of photocurrent density increment, and investigating the selection performance of the sensor. The interfering substance is glyphosate, monosultap, omethoate, acetamiprid, trichlorfon or clofentezine.

The non-fixed sensing process does not need to fix the recognition element on the surface of the electrode, namely, the capture and combination process of the recognition element on the target is carried out in a homogeneous solution, and the quantitative detection of the target is realized through the change of a photoelectrochemical signal generated in the process. Compared with the traditional fixed sensing method, the method greatly avoids the complex and fussy immobilization process, is simple and convenient to operate, can realize the recycling of the electrodes, greatly improves the stability of sensing detection, and reduces the detection cost. In addition, the aptamer recognition element in the solution can fully recognize and combine with atrazine, so that the detection sensitivity is improved, and the signal change under pM concentration can be detected.

Photoelectrochemical (PEC) analysis methods combine the advantages of both photocatalysis and electrochemical catalysis, with higher catalytic activity and detection sensitivity than single technologies. In the photoelectrochemical process, two energy forms of excitation of the photoelectric material and detection of a current signal are separately carried out, so that a background signal is greatly reduced, and ultrahigh sensitivity and stability can be obtained. The invention takes BiOBr/Ag NPs as photoelectric substrate materials, the narrow band gap of the BiOBr/Ag NPs enables the photoelectric substrate materials to have good visible light absorption performance, the deposition of the Ag NPs with surface plasma effect further promotes the absorption of the composite materials to light and the transmission performance to carriers, and simultaneously, a large number of load sites are provided for the assembly of mercaptan. Therefore, the invention provides a good technical basis for the detection of the trace target by adopting a photoelectrochemical means, and has important significance for realizing the high-efficiency detection of the atrazine.

Aptamer (aptamer), also known as an "artificial antibody", is a single-stranded DNA or RNA fragment obtained by in vitro screening by exponential enrichment ligand phylogenetic evolution (SELEX) technology, and can be specifically and tightly bound to a corresponding target, thereby realizing specific detection of a target molecule. The aptamer is used as an identification unit, and has the advantages of small size, good affinity, easy artificial synthesis and modification, strong stability, low detection limit when being used for detecting small molecules and the like. Therefore, the invention uses the aptamer as a recognition element to construct the non-immobilized aptamer photoelectric sensor for detecting atrazine, so as to obtain good selectivity.

Graphene (Graphene) is a monolayer of carbon atoms through sp²The two-dimensional structure zero band gap material formed by hybridization and close packing has the advantages of large specific surface area, excellent conductivity and light absorption performance, high chemical stability and mechanical stability, high charge migration rate, good biocompatibility and the like. Particularly, the graphene has a unique two-dimensional plane conjugated structure and strong hydrophobic effect on the surface, and can generate pi-pi interaction with biomolecules such as DNA (deoxyribonucleic acid) and the like, so that stable combination and load are realized, and the DNA is effectively protected from being cracked by the shear enzyme, so that an excellent carrier is provided for constructing an aptamer sensing platform, the charge transmission rate is greatly promoted, and an important basis is provided for realizing high-sensitivity detection of a sensing system.

The existing atrazine sensing technology needs to fix chemical recognition elements such as enzymes, antibodies, aptamers, molecular imprinting and the like on the surface of an electrode, and often has the problems of small geometric area of the electrode, limited load capacity of the recognition elements, easiness in reaching a saturated adsorption state, difficulty in recycling the electrode, time-consuming and complex fixing process, high cost, instable assembly of recognition molecules, easiness in falling and the like. Aiming at the problems, the invention constructs a non-fixed nucleic acid aptamer photoelectric sensor for realizing efficient analysis and detection of atrazine.

Specifically, an aptamer-graphene compound (APT-GN) is formed by utilizing a pi-pi stacking effect between an aptamer and graphene, wherein the aptamer is used as a recognition element, the graphene is used as a signal regulation switch, meanwhile, a sulfydryl functionalized BiOBr/Ag NPs electrode is used as a photoelectric signal blocking substrate electrode, a BiOBr photoelectric material with good visible light response is synthesized by a hydrothermal method, Ag NPs are deposited by utilizing a photoreduction process, the light absorption capacity of the electrode is remarkably enhanced, meanwhile, a large number of load sites are provided for assembly of mercaptan, and therefore the sulfydryl functionalized BiOBr/Ag NPs electrode with signal blocking is obtained. When ATZ exists in the system, due to the fact that the ATZ and the aptamer are specifically combined into a new compound, graphene is separated and combined to the surface of the mercapto-functionalized BiOBr/Ag NPs electrode, and a photocurrent response signal is turned on. Meanwhile, DNase I added into the system can also cut the aptamer chain at a specific site to release ATZ, so that the cyclic recovery and signal amplification of the target are realized. And establishing a quantitative analysis sensing platform through the corresponding relation between the photocurrent increment and the ATZ concentration. The linear range of the sensing system for ATZ detection is 5.0pM-10.0nM, and the detection limit is as low as 1.2 pM. Meanwhile, due to the specific action of the aptamer, the sensing system still shows excellent selectivity in the presence of 100-time concentration interferents, and has a good application prospect in actual water sample analysis.

Compared with the prior art, the invention has the following characteristics:

1) the analytical detection process of the sensor on the ATZ is carried out in a homogeneous solution instead of on the surface of a sensing electrode. The construction of the non-fixed homogeneous solution detection system effectively avoids the complex and tedious fixing process of the recognition element on the surface of the sensing electrode, simultaneously can also lead the target object and the aptamer in the system to have sufficient recognition and combination effects, avoids the limitation that the saturated adsorption state is easily reached because the load capacity of the recognition element on the electrode is limited, and in addition, effectively prevents the problems of denaturation and inactivation of the recognition element on the surface of the electrode and the like caused by overhigh temperature of the electrode under continuous illumination, thereby greatly improving the detection effect of the atrazine.

2) BiOBr/Ag NPs with good visible light absorption performance are used as photoelectric substrate materials, the BiOBr materials have good visible light absorption performance due to the narrow band gaps of the BiOBr materials, the deposition of the Ag NPs with the surface plasma effect further promotes the absorption of the composite materials to light and the transmission performance of carriers, meanwhile, a large number of attachment sites are provided for assembly of thiol, and a foundation is provided for high-sensitivity detection.

3) According to the invention, effective amplification of signals is realized by using DNase I endonuclease to assist in recycling of target objects, digestion of the DNase I endonuclease on an aptamer promotes release of more free graphene, assembly of the free graphene on the surface of a thiolated electrode is used as a signal switch, a blocked photo-generated carrier transfer channel is effectively opened, amplification of photocurrent response signals is realized, and detection sensitivity of ATZ is greatly improved.

4) The method utilizes the aptamer as a recognition element, is combined with the graphene through pi-pi stacking effect, has the advantages of simple steps, easiness in implementation, no need of modification and fixation on an electrode and the like, can realize specific recognition on target molecules ATZ in the detection process, and effectively improves the selectivity of the sensor.

5) The non-immobilized aptamer sensor disclosed by the invention is based on the advantages of a non-immobilized sensing analysis strategy, combines a high-sensitivity photoelectrochemical analysis means, further utilizes the signal sensitization effect of graphene by virtue of the characteristics of high selectivity, high affinity and the like of an aptamer, and realizes high-sensitivity and high-selectivity detection on trace atrazine in a water sample, wherein the linear detection range of the non-immobilized aptamer sensor is 5.0pM-10.0nM, and the detection limit is as low as 1.2 pM. The method is simple, convenient, efficient, rapid and sensitive, and is expected to be used for on-site monitoring in the environment.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) atlas of the Ag NPs/BiOBr/ITO electrode prepared in example 1.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

The invention provides a preparation method of a non-immobilized nucleic acid aptamer photoelectric sensor for detecting atrazine, which comprises the steps of preparing an APT-GN compound and preparing an MCT/Ag NPs/BiOBr/ITO electrode;

the preparation method of the APT-GN compound comprises the following steps: and mixing the graphene dispersion liquid with the atrazine aptamer, and performing ultrasonic treatment and separation to obtain the APT-GN compound.

The preparation process of the graphene dispersion liquid comprises the following steps: ultrasonically dispersing graphene in water to prepare a dispersion liquid with the concentration of 0.10-0.20mg/mL, namely the graphene dispersion liquid; the mixing process is as follows: centrifuging 1OD atrazine aptamer at 10000r/min of 5000-. The ultrasonic process comprises the following steps: performing ultrasonic treatment in ice bath for 2-3 h; the separation process is as follows: centrifuging at 2000-4000r/min for 3-5min, and then discarding the lower bulk graphene.

The preparation method of the MCT/Ag NPs/BiOBr/ITO electrode comprises the following steps:

1) dropwise coating the BiOBr dispersion liquid on the surface of the pretreated ITO electrode, and drying to obtain a BiOBr/ITO electrode;

2) depositing Ag NPs on the surface of the BiOBr/ITO electrode to obtain an Ag NPs/BiOBr/ITO electrode;

3) soaking the Ag NPs/BiOBr/ITO electrode in MCT solution to obtain an MCT/Ag NPs/BiOBr/ITO electrode;

MCT is n-octyl mercaptan.

In the step 1), the preparation process of the BiOBr dispersion liquid comprises the following steps: adding Bi (NO)₃)₃Adding the ethylene glycol solution into an ethylene glycol solution of KBr, stirring for 30-40min, then carrying out ultrasonic treatment for 10-15min, reacting for 5-7h at the temperature of 175-185 ℃, separating to obtain BiOBr, and preparing the BiOBr into a dispersion liquid of 30-40mg/mL, namely the BiOBr dispersion liquid. The pretreatment process of the ITO electrode comprises the following steps: and sequentially placing the ITO electrode in NaOH solution, acetone, ethanol and deionized water, respectively ultrasonically cleaning for 10-15min, and then drying in the air atmosphere.

In the step 2), the deposition process of the Ag NPs is as follows: immersing the BiOBr/ITO electrode into 1-3mmol/L AgNO₃In the solution, the solution is then irradiated for 1-1.5h with a Xe lamp of 250-350W.

In the step 3), the MCT solution is an ethanol solution of MCT, and the concentration is 30-50 mmol/L; the soaking time is 20-25 h.

The invention also provides a non-fixed nucleic acid aptamer photoelectric sensor for detecting atrazine, which is prepared by adopting the method and comprises an APT-GN compound and an MCT/Ag NPs/BiOBr/ITO electrode.

The invention also provides application of the non-immobilized aptamer photoelectric sensor for detecting atrazine, and the sensor is used for detecting atrazine in a water environment.

The detection process comprises the following steps: dropwise adding an incubation system on the surface of an MCT/Ag NPs/BiOBr/ITO electrode, incubating for 1-2h, cleaning and drying, establishing a three-electrode system by taking the incubated MCT/Ag NPs/BiOBr/ITO electrode as a working electrode, a platinum sheet as a counter electrode, a saturated calomel electrode as a reference electrode and a PBS (phosphate buffer solution) buffer solution as a supporting electrolyte, measuring the increment of the photocurrent density under visible light, and obtaining the concentration of atrazine in the water environment according to the corresponding relation between the increment of the photocurrent density and the concentration of atrazine; the incubation system comprises a Tris-HCl buffer solution, an APT-GN compound, a water solution to be detected and a DNase I enzyme solution.

Example 1:

the preparation method of the non-immobilized aptamer photoelectric sensor for detecting atrazine comprises the following steps:

(1) APT-GN complexes were prepared. Graphene is ultrasonically dispersed in high-purity water to prepare the material with the concentration of 0.15 mg-mL-¹The 1OD atrazine aptamer was further centrifuged at 8000rpm for 3min, and then the graphene dispersion was added to give an aptamer concentration of 10. mu.M. And (3) covering a pipe cover tightly, placing the pipe cover in an ice bath, performing ultrasonic treatment for 3h, finally centrifuging the obtained suspension for 5min at 3000rpm, and removing the lower bulk graphene to obtain the APT-GN compound.

(2) And (4) pretreating the ITO electrode. Before the ITO conductive glass is used for preparing an electrode, strict surface treatment is required to ensure that the surface is clean. And sequentially putting the ITO into a 1M NaOH solution, acetone, ethanol and deionized water, ultrasonically cleaning for 15min respectively, taking out, and then placing in an air atmosphere for drying.

(3) Preparing BiOBr powder by a hydrothermal method. 1mmol of Bi (NO)₃)₃·5H₂O and 1mmol KBr were dissolved in 14mL of ethylene glycol, respectively, and stirred for 30 min. Adding Bi (NO)₃)₃The solution is added into KBr solution drop by drop, stirred for 30-40min and treated with ultrasound for 10-15 min. And transferring the mixed solution into an autoclave with a polytetrafluoroethylene lining, reacting for 6 hours at 180 ℃, centrifuging the reaction product, respectively washing for 3 times by using high-purity water and ethanol, and drying for 6 hours in an oven at 60 ℃.

(4) And (4) dropping BiOBr on the surface of the ITO electrode. 30 mg/mL-¹The BiOBr dispersion liquid is dripped on clean ITO glass, the dripping area is controlled to be 1.0 multiplied by 1.0cm, and the BiOBr/ITO electrode is obtained after being dried in a 60 ℃ drying oven。

(5) And modifying Ag NPs on the surface of the BiOBr/ITO electrode in situ by a photoreduction method. The BiOBr/ITO electrode was immersed in 2.0mM AgNO₃In the solution, a 300W Xe lamp is used for irradiating for 1h, and then the Ag NPs/BiOBr/ITO electrode is prepared.

(6) MCT is assembled on the surface of the Ag NPs/BiOBr/ITO electrode. And soaking the Ag NPs/BiOBr/ITO electrode in 40mM MCT ethanol solution for 24h, wherein MCT can be assembled on the surface of the electrode through Ag-S bond action, and obtaining the MCT/Ag NPs/BiOBr/ITO electrode.

FIG. 1 is a scanning electron microscope atlas of the prepared Ag NPs/BiOBr/ITO electrode. As can be seen from fig. 1, the BiOBr material synthesized by the hydrothermal method is a large spherical structure formed by stacking a plurality of sheets, and the sizes of the spherical structures are different due to different stacking degrees of the sheets. The vertically grown lamellar structure of the electrode greatly increases the specific surface area of the electrode material, provides a large number of loading sites for further deposition of Ag NPs, and also can see that Ag nanoparticles are attached to the surface of the BiOBr, so that the successful preparation of the Ag NPs/BiOBr/ITO electrode is proved, and meanwhile, a connecting bridge is provided for further assembly of MCT.

The electrochemical properties of the MCT/Ag NPs/BiOBr/ITO electrode were characterized using the CHI 660c workstation. And (3) adding an incubation system (20 mu L of Tris-HCl buffer solution, 10 mu L of APT-GN compound, 6 mu L of ATZ solution with different concentrations and 4 mu L of DNase I enzyme solution) dropwise on the surface of the prepared MCT/Ag NPs/BiOBr/ITO electrode in sequence, and incubating for 1 h. Taking the prepared MCT/Ag NPs/BiOBr/ITO electrode as a working electrode, a platinum sheet electrode as a counter electrode, a saturated calomel electrode as a reference electrode, 0.1M PBS buffer solution as supporting electrolyte, measuring an I-t curve under visible light, and simultaneously using 5mM of [ Fe (CN)₆]⁴-/[Fe(CN)₆]³(containing 0.1mol/L KCl) as a supporting electrolyte, and an EIS curve was measured. The result shows that the photoelectric property is greatly improved by the deposition of Ag NPs, the photocurrent response is reduced by further modification of MCT, the obvious signal blocking effect is achieved, graphene is dissociated and combined on the surface of an electrode by adding the incubation system solution, and the photocurrent response signal is recovered.

Example 2:

photoelectrochemical detection of atrazine was carried out using the non-immobilized aptamer photoelectric sensor prepared in example 1.

And (3) adding an incubation system (20 mu L of Tris-HCl buffer solution, 10 mu L of APT-GN compound, 6 mu L of ATZ solution with different concentrations and 4 mu L of DNase I enzyme solution) dropwise on the surface of the prepared MCT/Ag NPs/BiOBr/ITO electrode in sequence, and incubating for 1 h. The prepared MCT/Ag NPs/BiOBr/ITO electrode is used as a working electrode, a platinum sheet electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, 0.1M PBS buffer solution is used as supporting electrolyte, a series of I-t curves incubated by atrazine with different concentrations are measured under visible light, and the photocurrent is converted into photocurrent density (j) according to the area of the electrode. The result shows that the photocurrent density is gradually increased along with the increase of the atrazine concentration within a certain atrazine concentration range, because the atrazine is specifically combined into a new compound by an aptamer in the incubation process, the graphene in the APT-GN compound is dissociated and combined onto the surface of an MCT/Ag NPs/BiOBr/ITO electrode, a photo-generated carrier transfer channel is opened, and the photocurrent response blocked by the MCT is recovered. And drawing a working curve by using the relation between the increment (delta j) of the photocurrent density and the logarithm of the atrazine concentration, thereby realizing the detection of atrazine. The detection limit of the non-immobilized aptamer photoelectric sensor on the ATZ based on graphene-thiol signal regulation is as low as 1.2pM, and the linear detection range is 5.0pM-10.0 nM.

Example 3:

selective detection was performed using the non-immobilized aptamer photoelectric sensor prepared in example 1.

A series of atrazine solutions of different concentrations in the incubation system of example 2 was changed to atrazine of 1nM concentration and a mixture of different interferents of 100-fold concentration. After 1h incubation, the I-t curves in the presence of different interferents were determined under visible light using the same three-electrode system as in example 2. The result shows that the measured photocurrent has no obvious change even in the presence of 100 times concentration of interferents such as glyphosate, monosultap, omethoate, acetamiprid, trichlorfon, clofentezine and the like, interference factors are less than 15 percent, and the good selectivity of the sensor is reflected.

Example 4:

the non-immobilized aptamer photoelectric sensor prepared in example 1 is used for detecting atrazine in an actual water sample.

The water of the Sanhaogong pond of the university of Tongji is selected as an actual water sample to confirm the detection capability in practical application, and a series of atrazine solutions with different concentrations in the incubation system in the embodiment 2 are respectively replaced by the actual water sample of the Sanhaogong pond or the standard samples with different concentrations prepared by the actual water sample. After incubation for 1h, the three-electrode system same as that in example 2 was used to measure the variation of photocurrent density under visible light, and the atrazine concentration and spiking recovery rate in the actual water sample were calculated according to the plotted working curve.

Example 5:

in the embodiment, a hydrothermal method and photoreduction are adopted to prepare the photoelectric signal enhanced Ag NPs/BiOBr/ITO electrode, and then the Ag-S bond function is utilized to self-assemble MCT, so that the sulfydryl functionalized signal blocked MCT/Ag NPs/BiOBr/ITO electrode is prepared. The preparation method of the MCT/Ag NPs/BiOBr/ITO electrode comprises the following steps:

step (1): pretreating an ITO electrode: and (3) putting the cut ITO electrode of 1.0 multiplied by 5.0cm into 1M NaOH solution, acetone, ethanol and deionized water in sequence, ultrasonically cleaning for 15min respectively, taking out, and then placing in an air atmosphere for airing.

Step (2): preparing BiOBr powder by a hydrothermal method:

step (2-1): preparing Bi (NO)₃)₃Solutions and KBr solutions;

step (2-2): adding Bi (NO)₃)₃Mixing the solution and the KBr solution, stirring and performing ultrasonic treatment;

step (2-3): transferring the mixed solution into an autoclave with a polytetrafluoroethylene lining, reacting for 6h at 180 ℃, centrifuging, respectively washing for 3 times by using high-purity water and ethanol, and drying in an oven.

And (3): and (3) dropping BiOBr on the surface of the ITO electrode: 30 mg/mL-¹The BiOBr dispersion liquid is dripped on clean ITO glass, the dripping area is controlled to be 1.0 multiplied by 1.0cm, and the mixture is placed in an oven for drying;

and (4): depositing Ag NPs by a photoreduction method: BiOBr/ITO electrodeImmersion in 2.0mM AgNO₃In the solution, irradiating for 1h by using a 300W Xe lamp, taking out, cleaning by using deionized water, and drying in an oven;

and (5): MCT self-assembly: and (3) soaking the Ag NPs/BiOBr/ITO electrode in 40mM MCT ethanol solution for 24h, taking out, washing with deionized water, and drying in an oven to obtain the MCT/Ag NPs/BiOBr/ITO electrode.

The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.