Fabrication of an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure

Abstract

This invention belongs to the fields of immunoassay and biosensing technology, and provides a method for preparing an "on-off-on" type PEC sensor regulated by a Ferris wheel-shaped DNA structure. First, a CoS / CoCdS heterojunction with a "self-sensitization" effect is generated in situ as a photoelectric substrate to provide an initial "on" signal. Subsequently, triggered by the target analyte MC-LR, a Ferris wheel-shaped DNA structure with steric hindrance effect is formed through a DNA cascade reaction. This structure acts as a steric hindrance layer covering the electrode surface, hindering electron transfer and causing the signal to briefly switch to an "off" state. By specifically modifying AgInS2 QDs at the ends of the DNA Ferris wheel-shaped structure and constructing a ternary heterojunction using the band-matching principle, a clear signal switching from "off" to "on" is achieved, thus enabling highly sensitive detection of MC-LR. Detection of MC-LR is achieved based on the different photoelectrochemical signal intensities for different concentrations of the analyte.

Description

Technical Field

[0001] This invention relates to a novel construction of an "on-off-on" sensing strategy that modulates the "self-sensitization" effect using a Ferris wheel-shaped DNA nanostructure, and a method for preparing a novel CoS / CoCdS in-situ heterojunction optoelectronic substrate material. First, a CoS / CoCdS heterojunction with a "self-sensitization" effect is generated in situ to provide an initial "on" signal as the optoelectronic substrate. Subsequently, triggered by the target compound MC-LR, a Ferris wheel-shaped DNA structure with steric hindrance is formed through a DNA cascade reaction. This structure acts as a steric hindrance layer covering the electrode surface, hindering electron transfer and causing the signal to briefly switch to an "off" state. By specifically modifying AgInS2 QDs at the ends of the DNA Ferris wheel-shaped structure and constructing a ternary heterojunction using the band-matching principle, a clear signal switching from "off" to "on" is achieved, thereby enabling highly sensitive detection of MC-LR. This invention belongs to the field of novel functional materials and biosensing detection technology. Background Technology

[0002] Microcystin-LR (MC-LR), a highly toxic cyclic heptapeptide released by cyanobacteria, poses a serious threat to human health. It primarily targets the liver, causing acute liver injury and even liver failure by inhibiting protein phosphatase. Long-term low-dose exposure can lead to liver fibrosis and liver cancer. In addition, it also has nephrotoxicity, neurotoxicity, and immunosuppressive effects, and has been listed as a potential human carcinogen. Therefore, the development of highly sensitive detection methods is crucial for public health protection.

[0003] While combining nucleic acid aptamers with photoelectrochemical (PEC) sensing platforms can significantly improve detection performance, their application in the analysis of trace toxins (such as MC-LR) in the environment and food remains limited by low signal amplification efficiency and weak electrical signal response. This study constructed a DNA cascade reaction-driven photoelectrochemical sensing platform based on MC-LR triggering of the target analyte. During signal amplification, a DNA nanoassembly with a "Ferris wheel" shaped topology was successfully constructed using a CHA-HCR cascade reaction triggered by MC-LR. This nanostructure acts as a steric hindrance layer on the surface of the photoactive material at the sensing interface, hindering the transfer of electrons and holes, thereby significantly suppressing the photocurrent signal. This process transitions the sensing system from an initial signal "on" state to a signal "off" mode. Subsequently, the generated "Ferris wheel" shaped DNA nanostructure exposes specific base recognition sites at its ends, enabling efficient and specific anchoring of DNA single strands modified with AgInS2 QDs. AgInS2 QDs, acting as photosensitizers, can achieve band matching with the substrate material CoS / CoCdS to construct a stable ternary heterojunction structure. This heterojunction effectively promotes the separation and migration of photogenerated carriers, significantly recovering the previously quenched photocurrent signal and allowing the sensing system to re-enter the signal "on" state, thereby achieving highly sensitive and specific detection of MC-LR.

[0004] This approach significantly enhances detection selectivity through the highly specific design of nucleic acid sequences and effectively overcomes the technical bottleneck of inaccurate detection of low-concentration target substances due to weak signals by utilizing a cascade amplification mechanism. The generated "Ferris wheel-shaped" DNA nanostructure exposes specific base recognition sites at its ends, enabling efficient and specific anchoring of DNA single strands modified with AgInS2 QDs. AgInS2 QDs, acting as a photosensitizer, achieve band matching with the substrate material CoS / CoCdS, constructing a stable ternary heterojunction structure. This heterojunction effectively promotes the separation and migration of photogenerated carriers, significantly restoring the previously quenched photocurrent signal, allowing the sensing system to re-enter the signal "on" state, ultimately achieving highly sensitive and selective dual-signal response detection of the target substance MC-LR. This dual detection strategy effectively reduces background interference through an "on-off-on" signal conversion mechanism, significantly improving the signal-to-noise ratio and detection reliability. Simultaneously, this strategy achieves two signal amplifications and verifications in a single detection, providing a reliable analytical platform for the accurate detection of trace target substances in complex matrices. Summary of the Invention

[0005] One of the objectives of this invention is to achieve "self-sensitization" of the CoS / CoCdS heterojunction by generating the hydroxyl layer in situ, thereby constructing a stable and efficient photoelectric conversion substrate, providing an initial "on" signal, and laying a good foundation for subsequent signal switching.

[0006] The second objective of this invention is to form a "Ferris wheel"-shaped DNA structure with steric hindrance effect through a DNA cascade reaction in the presence of the target MC-LR. This structure can partially hinder electron transfer, causing the signal to switch to a temporary "off" state.

[0007] The third objective of this invention is to use this DNA structure as a signal amplification platform, modify its periphery with AgInS2 QDs, and use its photosensitization effect to efficiently recover the signal, realize the switch from "off" to "on", and thus complete the detection of MC-LR with high specificity and high sensitivity.

[0008] The technical solution of the present invention is as follows: 1. A method for fabricating an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure, characterized by comprising the following steps: (1) Cut the ITO glass into 2 × 0.8 cm pieces. 2 The strips were ultrasonically cleaned in sequence with detergent, acetone, ethanol and deionized water for 30 min and then dried at 60 ℃ for 24 h. (2) Take 8.0 µL of CoS / CoCdS in-situ heterojunction material dispersion with a concentration of 2.0 ~ 10.0 mg / mL and drop it onto the electrode surface; (3) Add 6.0 µL of citrate-stabilized gold nanoparticle solution to the electrode surface to introduce high-density thiol reactive binding sites, air dry at room temperature, rinse the electrode surface with deionized water, and air dry at room temperature. (5) Take 10.0 µL of the pre-prepared DNA Ferris wheel structure solution with a concentration of 1.0 ~ 5.0 nmol / L and add it to the electrode surface. Incubate at 4°C for 14 hours to fix the DNA to the electrode surface through Au-S bonds. Rinse the electrode surface with deionized water and air dry at room temperature. (6) Continue to add 5.0 µL of 2.0 ~ 10.0 mmol / L 6-mercapto-1-hexanol (HT) aqueous solution to the modified electrode to block the non-specific active sites on the electrode surface. Rinse the electrode surface with deionized water and air dry at room temperature. (7) Finally, 5.0 µL of DNA strands with AgInS2 QDs linked to them and 0.2 ~ 1.0 μmol / L were added to the surface of the above HT blocking electrode as photosensitizers and incubated at 37°C for 1 h to allow them to specifically bind to the electrode interface through DNA hybridization reaction. A PEC sensor that can be used to detect MC-LR was successfully constructed and stored in a 4°C refrigerator for later use.

[0009] 2. The method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure as described in claim 1, wherein the preparation of the CoS / CoCdS heterojunction material is characterized by the following steps: (1) Preparation of CoS First, 7.8 mmol of dimethylimidazole was dissolved in 80 mL of anhydrous methanol to prepare solution A. Then, 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in 80 mL of anhydrous methanol to prepare solution B. Solution A was slowly poured into solution B, and the mixture was stirred continuously until homogeneous. The mixture was then allowed to stand overnight for aging. The resulting product was washed several times with anhydrous methanol and dried to obtain the ZIF-67 precursor. 40 mg of the ZIF-67 precursor was dispersed in 20 mL of ethanol to form a homogeneous dispersion (solution C). Separately, 180 mg of thioacetamide was dissolved in 40 mL of ethanol to prepare solution D. Under continuous vigorous stirring, solution D was slowly added to solution C, and the reaction was allowed to proceed for 45 min. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180 °C for 1–5 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The resulting solid product was washed with methanol multiple times and dried at 60°C and atmospheric pressure for 26 hours to finally obtain a black solid CoS material. (2) Preparation of CoS / CoCdS heterojunction materials 24 mg of CoS and 20 mg of CdCl2 were weighed and dissolved sequentially in 40 ml of anhydrous ethanol. After vigorous stirring at room temperature for 1.5 h, the mixture was transferred to a polytetrafluoroethylene reactor and reacted at 150 °C for 2–8 h. Subsequently, the mixture was washed several times with anhydrous methanol and dried non-vacuum for 12 h to obtain a black CoS / CoCdS in-situ heterojunction material.

[0010] 3. The method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure as described in claim 1, wherein the preparation of the AgInS2QDs material is characterized by the following steps: First, 0.1 mmol AgNO3 and 0.4 mmol In(NO3)3 were weighed and dissolved in 50 mL of deionized water, respectively. After vigorous stirring, the solutions were transferred to a flask. Then, 8.3 μL MPA and 3 mL 0.6 mmol Na2S·9H2O were added to the solution under vigorous stirring. The reaction mixture was then heated under reflux at 100 °C for 1–5 h. After the reaction was complete, the system was cooled to room temperature, and the resulting precipitate was washed repeatedly with anhydrous ethanol to remove impurities. The resulting orange precipitate was then redispersed in 50 mL of deionized water to form a homogeneous dispersion. Finally, the dispersion was stored at 4 °C in the dark for subsequent experiments.

[0011] 4. The method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure as described in claim 1, for the detection of MC-LR, characterized in that the steps are as follows: (1) The photoelectrochemical workstation was used to test the three-electrode system. The Ag / AgCl electrode was used as the reference electrode, the Pt electrode was used as the counter electrode, and the prepared BiOI homojunction photoelectrochemical sensor based on DNA orbital pre-enhancement and signal inversion was used as the working electrode. A 100 W LED lamp was used as the irradiation source, and the lamp was switched on and off every 20 seconds. The bias voltage was set to 0 V. (2) In 10 mL of PBS buffer solution containing 0 to 0.2 mol / L ascorbic acid at pH = 6.81 to 8.04, the photoelectric signals generated in the antigens of different concentrations were detected, and the working curve was plotted; (3) Replace the MC-LR solution with the sample solution to be tested for detection.

[0012] Beneficial results of the present invention (1) This invention successfully prepared an in-situ heterojunction CoS / CoCdS composite material using ZIF-67 as a precursor through a controllable derivatization strategy, and further optimized the construction of a hydroxyl layer on its surface. Due to its wide specific surface area, the hydroxyl layer effectively promoted the oxidation process of surface hydroxyl groups by holes, realizing the efficient separation of electron-hole pairs, thereby constructing a high-performance signal "on" type photoelectric sensing substrate.

[0013] (2) The present invention triggers a cascade reaction by the target MC-LR to drive the formation of a “Ferris wheel” shaped DNA nanostructure. This structure causes the photoelectric signal to enter the “off” state through the steric hindrance effect.

[0014] (3) This invention utilizes the DNA nanostructure end to bind AgInS2 QDs to form a ternary heterojunction, and reconstructs and enhances the electron transfer pathway through energy level matching to realize the signal re-"turning on".

[0015] (4) The photoelectrochemical sensor prepared by the present invention realizes reliable detection of MC-LR. The “on-off-on” signal switching strategy significantly improves the detection sensitivity and specificity, providing a high-precision analytical method for the detection of trace toxins in complex matrices. Detailed Implementation

[0016] (The present invention will now be further described through specific embodiments, but is not limited thereto.) Example 1. A method for fabricating an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure, characterized by comprising the following steps: (1) Cut the ITO glass into 2 × 0.8 cm pieces. 2 The strips were ultrasonically cleaned in sequence with detergent, acetone, ethanol and deionized water for 30 min and then dried at 60 ℃ for 24 h. (2) Take 8.0 µL of 2.0 mg / mL CoS / CoCdS in-situ heterojunction material dispersion and drop it onto the electrode surface; (3) Add 6.0 µL of citrate-stabilized gold nanoparticle solution to the electrode surface to introduce high-density thiol reactive binding sites, air dry at room temperature, rinse the electrode surface with deionized water, and air dry at room temperature. (5) Take 10.0 µL of the pre-prepared DNA Ferris wheel structure solution with 1.0 nmol / L and add it to the electrode surface. Incubate at 4℃ for 14 hours to fix the DNA to the electrode surface through Au-S bonds. Rinse the electrode surface with deionized water and air dry at room temperature. (6) Continue to add 5.0 µL of 2.0 mmol / L 6-mercapto-1-hexanol (HT) aqueous solution to the modified electrode to seal the non-specific active sites on the electrode surface. Rinse the electrode surface with deionized water and air dry at room temperature. (7) Finally, 5.0 µL of DNA strands with AgInS2 QDs linked to AgInS2 were added to the surface of the above-mentioned HT blocking electrode as photosensitizers and incubated at 37°C for 1 h to allow it to specifically bind to the electrode interface through DNA hybridization reaction. A PEC sensor that can be used to detect MC-LR was successfully constructed and stored in a 4°C refrigerator for later use.

[0017] Example 2. A method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure, characterized by comprising the following steps: (1) Cut the ITO glass into 2 × 0.8 cm pieces. 2 The strips were ultrasonically cleaned in sequence with detergent, acetone, ethanol and deionized water for 30 min and then dried at 60 ℃ for 24 h. (2) Take 8.0 µL of CoS / CoCdS in-situ heterojunction material dispersion with a concentration of 4.0 mg / mL and drop it onto the electrode surface; (3) Add 6.0 µL of citrate-stabilized gold nanoparticle solution to the electrode surface to introduce high-density thiol reactive binding sites, air dry at room temperature, rinse the electrode surface with deionized water, and air dry at room temperature. (5) Take 10.0 µL of the pre-prepared DNA Ferris wheel structure solution with 2.0 nmol / L and add it to the electrode surface. Incubate at 4℃ for 14 hours to fix the DNA to the electrode surface through Au-S bonds. Rinse the electrode surface with deionized water and air dry at room temperature. (6) Continue to add 5.0 µL of 4.0 mmol / L 6-mercapto-1-hexanol (HT) aqueous solution to the modified electrode to block the non-specific active sites on the electrode surface. Rinse the electrode surface with deionized water and air dry at room temperature. (7) Finally, 5.0 µL of DNA strands with AgInS2 QDs linked to AgInS2 were dropped onto the surface of the above-mentioned HT blocking electrode as photosensitizers and incubated at 37°C for 1 h to allow it to specifically bind to the electrode interface through DNA hybridization reaction. A PEC sensor that can be used to detect MC-LR was successfully constructed and stored in a 4°C refrigerator for later use.

[0018] Example 3. A method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure, characterized by comprising the following steps: (1) Cut the ITO glass into 2 × 0.8 cm pieces. 2 The strips were ultrasonically cleaned in sequence with detergent, acetone, ethanol and deionized water for 30 min and then dried at 60 ℃ for 24 h. (2) Take 8.0 µL of CoS / CoCdS in-situ heterojunction material dispersion with a concentration of 6.0 mg / mL and drop it onto the electrode surface; (3) Add 6.0 µL of citrate-stabilized gold nanoparticle solution to the electrode surface to introduce high-density thiol reactive binding sites, air dry at room temperature, rinse the electrode surface with deionized water, and air dry at room temperature. (5) Take 10.0 µL of the pre-prepared DNA Ferris wheel structure solution with 3.0 nmol / L and add it to the electrode surface. Incubate at 4℃ for 14 hours to fix the DNA to the electrode surface through Au-S bonds. Rinse the electrode surface with deionized water and air dry at room temperature. (6) Continue to add 5.0 µL of 6-mercapto-1-hexanol (HT) aqueous solution to the modified electrode to seal the non-specific active sites on the electrode surface. Rinse the electrode surface with deionized water and air dry at room temperature. (7) Finally, 5.0 µL of DNA strands with AgInS2 QDs linked to AgInS2 were added to the surface of the above-mentioned HT blocking electrode as photosensitizers and incubated at 37°C for 1 h to allow it to specifically bind to the electrode interface through DNA hybridization reaction. A PEC sensor that can be used to detect MC-LR was successfully constructed and stored in a 4°C refrigerator for later use.

[0019] Example 4. The preparation of the CoS / CoCdS heterojunction material is characterized by comprising the following steps: (1) Preparation of CoS First, 7.8 mmol of dimethylimidazole was dissolved in 80 mL of anhydrous methanol to prepare solution A. Then, 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in 80 mL of anhydrous methanol to prepare solution B. Solution A was slowly poured into solution B, and the mixture was stirred continuously until homogeneous. The mixture was then allowed to stand overnight. The resulting product was washed several times with anhydrous methanol and dried to obtain the ZIF-67 precursor. 40 mg of the ZIF-67 precursor was dispersed in 20 mL of ethanol to form a homogeneous dispersion (solution C). Separately, 180 mg of thioacetamide was dissolved in 40 mL of ethanol to prepare solution D. Under continuous vigorous stirring, solution D was slowly added to solution C, and the reaction was allowed to proceed for 45 min. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180 °C for 2 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The resulting solid product was washed with methanol multiple times and dried at 60°C and atmospheric pressure for 26 hours to finally obtain a black solid CoS material. (2) Preparation of CoS / CoCdS heterojunction materials 24 mg of CoS and 20 mg of CdCl2 were weighed and dissolved sequentially in 40 ml of anhydrous ethanol. After vigorous stirring at room temperature for 1.5 h, the mixture was transferred to a polytetrafluoroethylene reactor and reacted at 150 °C for 3 h. Subsequently, the mixture was washed several times with anhydrous methanol and dried in a non-vacuum environment for 12 h to obtain a black CoS / CoCdS in-situ heterojunction material.

[0020] Example 5. The preparation of the AgInS2QDs material, characterized by the following steps: First, 0.1 mmol AgNO3 and 0.4 mmol In(NO3)3 were weighed and dissolved in 50 mL of deionized water, respectively. After vigorous stirring, the solutions were transferred to a flask. Then, 8.3 μL MPA and 3 mL 0.6 mmol Na2S·9H2O were added to the solution under vigorous stirring. The reaction mixture was then heated under reflux at 100 °C for 2 h. After the reaction was complete, the system was cooled to room temperature, and the resulting precipitate was washed repeatedly with anhydrous ethanol to remove impurities. The resulting orange precipitate was then redispersed in 50 mL of deionized water to form a homogeneous dispersion. Finally, the dispersion was stored at 4 °C in the dark for subsequent experiments.

[0021] Example 6. Detection for MC-LR, characterized by the following steps: (1) The photoelectrochemical workstation was used to test the three-electrode system. The Ag / AgCl electrode was used as the reference electrode, the Pt electrode was used as the counter electrode, and the prepared BiOI homojunction photoelectrochemical sensor based on DNA orbital pre-enhancement and signal inversion was used as the working electrode. A 100 W LED lamp was used as the irradiation source, and the lamp was switched on and off every 20 seconds. The bias voltage was set to 0 V. (2) In 10 mL of PBS buffer solution containing 0.1 mol / L ascorbic acid at pH = 7.38, the photoelectric signals generated in the analyte antigen at different concentrations were detected, and the working curve was plotted; (3) Replace the MC-LR solution with the sample solution to be tested for detection.

Claims

1. A method for preparing a "on-off-on" PEC sensor based on the regulation of the ferris wheel-like DNA structure, characterized in that, Includes the following steps: (1) ITO glass was cut into 2 x 0.8 cm 2 strips, sequentially cleaned with detergent powder, acetone, ethanol, and deionized water for 30 min under ultrasonication and dried at 60 °C for 24 h; (2) Take 8.0 µL of CoS / CoCdS in-situ heterojunction material dispersion with a concentration of 2.0 ~ 10.0 mg / mL and drop it onto the electrode surface; (3) Add 6.0 µL of citrate-stabilized gold nanoparticle solution to the electrode surface to introduce high-density thiol reactive binding sites, air dry at room temperature, rinse the electrode surface with deionized water, and air dry at room temperature. (5) Take 10.0 µL of the pre-prepared DNA Ferris wheel structure solution with a concentration of 1.0 ~ 5.0 nmol / L and add it to the electrode surface. Incubate at 4°C for 14 hours to fix the DNA to the electrode surface through Au-S bonds. Rinse the electrode surface with deionized water and air dry at room temperature. (6) Continue to add 5.0 µL of 2.0 ~ 10.0 mmol / L 6-mercapto-1-hexanol (HT) aqueous solution to the modified electrode to block the non-specific active sites on the electrode surface. Rinse the electrode surface with deionized water and air dry at room temperature. (7) Finally, 5.0 µL of DNA strands with AgInS2 QDs linked to them and 0.2 ~ 1.0 μmol / L were added to the surface of the above HT blocking electrode as photosensitizers and incubated at 37°C for 1 h to allow them to specifically bind to the electrode interface through DNA hybridization reaction. A PEC sensor that can be used to detect MC-LR was successfully constructed and stored in a 4°C refrigerator for later use.

2. The method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure as described in claim 1, wherein the preparation of the CoS / CoCdS heterojunction material is characterized in that, The steps are as follows: (1) Preparation of CoS First, 7.8 mmol of dimethylimidazole was dissolved in 80 mL of anhydrous methanol to prepare solution A. Then, 1.2 mmol of cobalt nitrate hexahydrate (Co(NO3)2·6H2O) was dissolved in 80 mL of anhydrous methanol to prepare solution B. Solution A was slowly poured into solution B, and the mixture was stirred continuously until homogeneous. The mixture was then allowed to stand overnight for aging. The resulting product was washed several times with anhydrous methanol and dried to obtain the ZIF-67 precursor. 40 mg of the ZIF-67 precursor was dispersed in 20 mL of ethanol to form a homogeneous dispersion (solution C). Separately, 180 mg of thioacetamide was dissolved in 40 mL of ethanol to prepare solution D. Under continuous vigorous stirring, solution D was slowly added to solution C, and the reaction was allowed to proceed for 45 min. The mixture was then transferred to a polytetrafluoroethylene-lined high-pressure reactor and reacted at 180 °C for 1–5 h. After the reaction was completed, the reactor was allowed to cool naturally to room temperature. The resulting solid product was washed with methanol multiple times and dried at 60°C and atmospheric pressure for 26 hours to finally obtain a black solid CoS material. (2) Preparation of CoS / CoCdS heterojunction materials 24 mg of CoS and 20 mg of CdCl2 were weighed and dissolved sequentially in 40 ml of anhydrous ethanol. After vigorous stirring at room temperature for 1.5 h, the mixture was transferred to a polytetrafluoroethylene reactor and reacted at 150 °C for 2–8 h. Subsequently, the mixture was washed several times with anhydrous methanol and dried non-vacuum for 12 h to obtain a black CoS / CoCdS in-situ heterojunction material.

3. A method for preparing a "on-off-on" PEC sensor based on the regulation of the DNA tower structure according to claim 1, wherein the preparation of the AgInS2 QDs material is characterized by, The steps are as follows: First, 0.1 mmol AgNO3 and 0.4 mmol In(NO3)3 were weighed and dissolved in 50 mL of deionized water, respectively. After vigorous stirring, the solutions were transferred to a flask. Then, 8.3 μL MPA and 3 mL 0.6 mmol Na2S·9H2O were added to the solution under vigorous stirring. The reaction mixture was then heated under reflux at 100 °C for 1–5 h. After the reaction was complete, the system was cooled to room temperature, and the resulting precipitate was washed repeatedly with anhydrous ethanol to remove impurities. The resulting orange precipitate was then redispersed in 50 mL of deionized water to form a homogeneous dispersion. Finally, the dispersion was stored at 4 °C in the dark for subsequent experiments.

4. The method for preparing an "on-off-on" type PEC sensor based on a Ferris wheel-shaped DNA structure as described in claim 1, for the detection of MC-LR, characterized in that, The steps are as follows: (1) The photoelectrochemical workstation was used to test the three-electrode system. The Ag / AgCl electrode was used as the reference electrode, the Pt electrode was used as the counter electrode, and the prepared BiOI homojunction photoelectrochemical sensor based on DNA orbital pre-enhancement and signal inversion was used as the working electrode. A 100 W LED lamp was used as the irradiation source, and the lamp was switched on and off every 20 seconds. The bias voltage was set to 0 V. (2) In 10 mL of PBS buffer solution containing 0 to 0.2 mol / L ascorbic acid at pH = 6.81 to 8.04, the photoelectric signals generated in the antigens of different concentrations were detected, and the working curve was plotted; (3) Replace the MC-LR solution with the sample solution to be tested for detection.