Split type photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material

Abstract

The invention discloses a split type photoelectrochemical biosensing analysis method based on a Bi2S3 / Ag3PO4 heterojunction composite material. The preparation method comprises the following steps: firstly, preparing a Bi2S3 / Ag3PO4 heterojunction through a multi-step hydrothermal method, and modifying the Bi2S3 / Ag3PO4 heterojunction on the surface of a fluorine-doped tin oxide electrode to form a Bi2S3 / Ag3PO4 photoelectrode; when a target object exists, the capture aptamer on the surface of the magnetic bead can capture and trigger the aptamer chain, and then the HCR reaction is triggered. By means of the specific recognition effect between streptavidin and biotin, alkaline phosphatase is introduced to the surfaces of the magnetic beads, a substrate is catalyzed to form ascorbic acid serving as an electron donor, and the current is enhanced. And carrying out quantitative analysis on the carcino-embryonic antigen through a photocurrent signal. The analysis method combines a hybridization chain reaction and an enzymatic signal amplification strategy, and has the advantages of simplicity in preparation, high sensitivity, reusability and the like.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectrochemical biosensor technology and specifically relates to a Bi 2 S 3 / Ag 3 PO 4 Heterojunction split photoelectrochemical biosensing analysis method. Background Art

[0002] Cancer is a malignant disease caused by gene mislocation and mutation, which poses a threat to human health and is one of the major causes of death in the global population. According to a report released by the National Cancer Center in 2022, the incidence of cancer is expected to continue to increase in the next few decades. Tumor markers are a class of active substances that reflect the presence of cancer. The changes in their presence and state are usually associated with specific types of tumors. Carcinoembryonic antigen (CEA) is a broad-spectrum tumor marker. When the CEA concentration in human serum exceeds 20 μg / L, it indicates the presence of tumor cells. In recent years, commonly used CEA detection methods include enzyme-linked immunosorbent assay, immunofluorescence, immunoblotting, and colorimetric immunoassay, etc., but the high operating cost, relatively complex detection process, and the possibility of false positive or false negative results still need to be solved. Therefore, there is an urgent need to develop more sensitive, rapid, and specific biosensors.

[0003] Compared with traditional detection methods, photoelectrochemical biosensing, which combines photoelectrochemical (PEC) technology with biosensing, exhibits many excellent properties. In PEC bioanalysis, light excitation is used to generate electrical signals, and light and electricity are two completely separate and different energy forms, which makes this method more sensitive. In addition, it does not require the participation of expensive optical instruments (such as fluorescence spectrophotometers, UV-visible spectrophotometers, etc.), and the cost is low. Traditional PEC sensors require gradual modification of photoelectrodes, and the process is relatively cumbersome; in the split sensing mode, the process of fixing the recognition element is separated from the PEC signal transduction, which is conducive to maintaining the activity of biological molecules, while avoiding the contradiction between its activity maintenance conditions and material fixation, light irradiation, cleaning and repetition, etc., which can significantly improve the convenience of operation.

[0004] In PEC biosensing, the photoelectric activity of photosensitive materials directly affects the analytical performance of the sensor. Therefore, in order to improve the sensitivity of the sensor, it is necessary to prepare a bandgap-matched composite material to improve the photoelectric activity of the material and enhance its response to changes in the surrounding microenvironment. Summary of the invention

[0005] Based on the above background, the present invention aims to provide a 2 S 3 / Ag 3 PO4 A split photoelectrochemical biosensing method constructed by heterojunction and enzymatic signal amplification.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A Bi-based 2 S 3 / Ag 3 PO 4 Split photoelectrochemical biosensing analysis method based on heterojunction composite materials: Firstly, in Bi 2 S 3 Surface loading Ag 3 PO 4 A heterojunction composite material is formed, and the composite material is dispersed on the surface of a fluorine-doped tin oxide electrode to obtain Bi 2 S 3 / Ag 3 PO 4 photoelectrode; then the capture aptamer chain is modified on the surface of the magnetic beads to capture the carcinoembryonic antigen and trigger a hybridization chain reaction; then alkaline phosphatase is introduced on the surface of the magnetic beads to catalyze ascorbic acid phosphate to form ascorbic acid, and finally the carcinoembryonic antigen is quantitatively analyzed by the photocurrent signal.

[0007] Furthermore, the above-mentioned Bi 2 S 3 / Ag 3 PO 4 The split photoelectrochemical biosensing analysis method of the heterojunction composite material specifically comprises the following steps: (1) Bi 2 S 3 / Ag 3 PO 4 Preparation of heterojunction composite materials; (2) Bi 2 S 3 / Ag 3 PO 4 Preparation of photoelectrodes; (3) Modifying the surface of magnetic beads to capture the aptamer to obtain a magnetic complex; (4) incubating the magnetic complex obtained in step (3), T-apt and carcinoembryonic antigen sample together, and then incubating with DNA hybridization solution and streptavidin-labeled alkaline phosphatase in sequence, and then adding ascorbic acid phosphate for reaction; (5) With Bi 2 S 3 / Ag 3 PO 4 The photoelectrode was the working electrode, and the photocurrent signal was detected using a three-electrode system on an electrochemical workstation.

[0008] Furthermore, in step (1), Bi 2 S 3 / Ag 3 PO 4 The preparation steps of heterojunction composite materials are as follows: S1: 1.83 g of bismuth nitrate pentahydrate was dispersed in 25 mL of ethylene glycol and stirred for 20 min to obtain solution A, 1.35 g of sodium sulfide nonahydrate was added to 30 mL of water and stirred for 15 min to obtain solution B, 1.92 g of urea was ultrasonically dispersed in 20 mL of water to obtain solution C; solution B was quickly added to solution A to obtain a black suspension with a pungent odor, and then solution C was added and ultrasonically dispersed for 20 min to obtain a mixed solution, and the obtained mixed solution was heated at 180 ° C for 24 h in a polytetrafluoroethylene-lined reactor, the product was naturally cooled to room temperature, the precipitate was centrifuged and washed with ultrapure water and ethanol respectively, and then vacuum dried at 60 ° C for 6 h to obtain Bi 2 S 3 ; S2: Bi obtained in step S1 2 S 3 Disperse in water and ultrasonicate for 20 min, add 6 mL of 0.1 M silver nitrate aqueous solution and stir for 4 h, then add potassium dihydrogen phosphate in equal mass ratio dropwise and stir for 3 h, heat the reactor at 140 °C for 12 h, and the product is washed with ethanol to obtain Bi 2 S 3 / Ag 3 PO 4 Composite materials.

[0009] Furthermore, in step (2), Bi 2 S 3 / Ag 3 PO 4 The preparation steps of the photoelectrode are as follows: S1: Bi 2 S 3 / Ag 3 PO 4 The composite material was sonicated in water for 5 min to form a 1 mg / mL dispersion; S2: Clean the fluorine-doped tin oxide electrode with ethanol and deionized water in turn, place the electrode at 60 °C for drying, drop the dispersion obtained in step S1 onto the FTO electrode, and obtain Bi after drying. 2 S 3 / Ag 3 PO 4 Photoelectrode.

[0010] Furthermore, the magnetic bead surface modification to capture the aptamer in step (3) comprises the following specific steps: S1: The magnetic beads were rinsed several times with 2-(N-morpholino)ethanesulfonic acid buffer and then dispersed in the above buffer to make the final concentration of the magnetic beads 1.0 mg / mL. 200 μL of N-hydroxysuccinimide solution and 200 μL of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride solution were added to 200 μL of the buffer containing magnetic beads. The mixture was incubated at room temperature for 15 min under shaking, and then C-apt chain was added. The mixture was incubated at room temperature overnight to obtain a magnetic complex. S2: The magnetic complex obtained in step S1 was dispersed into 500 μL PBS containing 1.0 wt% BSA and incubated for 2 h, and then redispersed into 100 μL PBS to prepare C-apt / MB, which was stored at 4 °C.

[0011] The concentration of the N-hydroxysuccinimide solution is 10 mM, and the concentration of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride solution is 40 mM; the nucleotide sequence of the C-apt chain is shown in SEQ ID NO.1.

[0012] Furthermore, step (4) includes the following specific steps: S1: 25 μL of C-apt / MB, 25 μL of 1.0 μM T-apt, and 50 μL of samples containing different concentrations of CEA were mixed and incubated at 37 °C for 60 min with shaking to obtain magnetic substances; S2: After washing the magnetic material obtained in step S1 several times with PBS, add 100 μL of DNA hybridization solution and react at 37 °C for 50 min; S3: After washing the mixture obtained in step S2 with PBS, 50 μL of 2 μg / mL streptavidin-labeled alkaline phosphatase was added and incubated at 37°C in an oscillating environment for 30 min; S4: After washing with PBS to remove excess streptavidin-labeled alkaline phosphatase, add 400 μL of 10 mM ascorbic acid phosphate solution and react at 37°C for 25 min.

[0013] Furthermore, the nucleotide sequence of T-apt in step S1 is shown in SEQ ID NO.2.

[0014] Furthermore, the DNA hybridization solution in step S2 includes 5.0 μM H 1 and 5.0 μM H 2 ;H 1 The nucleotide sequence of H is shown in SEQ ID NO.3. 2 The nucleotide sequence is shown in SEQ ID NO.4.

[0015] The above-mentioned Bi-based2 S 3 / Ag 3 PO 4 Application of heterojunction composite split photoelectrochemical biosensor analysis method in the detection of carcinoembryonic antigen.

[0016] The principle of the analytical method of the present invention is as follows: Bi was prepared by multi-step hydrothermal 2 S 3 / Ag 3 PO 4 Heterojunction, thus forming Bi 2 S 3 / Ag 3 PO 4 Photoelectrode. Then, the capture aptamer chain is modified on the surface of the magnetic bead to obtain a magnetic bead complex. When the target is present, the magnetic bead complex can capture the trigger aptamer chain, further triggering the HCR reaction, and with the help of the specific binding of streptavidin and biotin, a large amount of alkaline phosphatase (ALP) is introduced on the magnetic bead. ALP catalyzes the substrate to produce ascorbic acid (AA). The reaction-completed solution is transferred to the detection pool to be detected by Bi 2 S 3 / Ag 3 PO 4 The photoelectrode is the working electrode, and the photocurrent signal is tested using a classic three-electrode system on an electrochemical workstation. AA, as an electron donor, can enhance the photocurrent and establish a connection between the photocurrent signal and the concentration of the target substance, thereby achieving the quantification of CEA in the sample to be tested ( Figure 1 ).

[0017] Compared with the prior art, the advantages of the present invention are: (1) The present invention prepares Bi by a simple hydrothermal method 2 S 3 / Ag 3 PO 4 The photoelectrode forms the transducer layer of the biosensor and is simple to operate and low in cost.

[0018] (2) Ag 3 PO 4 It has high photocatalytic activity, but its charge separation efficiency is low, and electron-hole pairs are easy to recombine. 2 S 3 It has high light absorption and photoelectron transfer efficiency in the visible spectrum, and the different Fermi levels of the two can promote the transfer of photogenerated electrons and the effective separation of carriers between the two. 2 S 3 / Ag 3 PO 4 Heterojunction, compared with single material Bi2 S 3 、Ag 3 PO 4 , which can reduce the electron-hole pair recombination of the photoelectrode material, promote the separation of photogenerated carriers, and improve the photoelectric performance.

[0019] (3) The present invention adopts a split sensing strategy, which simplifies the experimental operation process and improves the convenience of detection.

[0020] (4) The present invention uses aptamers and HCR to amplify signals, which has good universality.

[0021] (5) The enzymatic reaction product can enhance the photocurrent of the material. The introduction of HCR can amplify the amplitude change of the signal increase and improve the detection performance of the sensor. The constructed PEC aptamer sensor has a low detection limit, high specificity for CEA, and good analytical performance.

[0022] In summary, the present invention constructs an efficient and sensitive photoelectrochemical biosensor using the composite material Bi 2 S 3 / Ag 3 PO 4 The sensor is used as a transducer and HCR is used as a signal amplification method, which effectively improves the ease of operation, sensitivity and specificity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Based on Bi 2 S 3 / Ag 3 PO 4 Schematic diagram of the principle of the split photoelectrochemical biosensing analysis method constructed by heterojunction and enzymatic signal amplification.

[0024] Figure 2 Bi is a photosensitive material 2 S 3 (A), Ag 3 PO 4 (B) and Bi 2 S 3 / Ag 3 PO 4 (C) SEM image.

[0025] Figure 3 is the photocurrent response; Figure 3 A is Ag 3 PO 4 (a, b) and Bi 2 S 3 / Ag 3 PO 4(c, d) Photocurrent response of the modified electrode to ascorbic acid (a, c: no AA in the electrolyte; b, d: AA in the electrolyte); Figure 3 B is Bi 2 S 3 / Ag 3 PO 4 Current responses of the modified electrode in the presence and absence of the target (a: without CEA, b: with CEA).

[0026] Figure 4 This is the polyacrylamide gel electrophoresis diagram (M: DNA marker, 1: H 1 , 2:H 2 , 3:H 1 +H 2 , 4:H 1 +H 2 +C-apt,5:H 1 +H 2: +T-apt).

[0027] Figure 5 The photocurrent response (A) and the corresponding linear curve (B) of the photoelectrochemical biosensor at different CEA concentrations.

[0028] Figure 6 Tests of the sensor's selectivity (A) and stability (B). DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. Obviously, the described embodiments and drawings are only part of the embodiments of the present invention, rather than all the embodiments.

[0030] In the embodiment of the present invention, a method based on Bi 2 S 3 / Ag 3 PO 4 Composite material, combined with HCR and enzymatic signal amplification strategy, is a split photoelectrochemical biosensor for detecting carcinoembryonic antigen CEA. This is an advanced detection tool that combines photosensitive materials and biorecognition elements, and achieves high-sensitivity detection of targets by monitoring changes in photocurrent. Under light, the photoelectrically active material undergoes charge separation and transfer, thereby generating an electrical signal between the working electrode and the counter electrode in an electrolyte solution containing a specific electron donor or acceptor, and finally the signal is recorded and output by an electrochemical workstation. The present invention realizes the effective detection of CEA, and the method is highly sensitive, fast and simple, and has a low background signal.

[0031] Example 1 1.Bi 2 S 3 / Ag3 PO 4 Preparation of photoelectrodes S1: 1.83 g of bismuth nitrate pentahydrate was dispersed in 25 mL of ethylene glycol and magnetically stirred for 20 min to obtain solution A; 1.35 g of sodium sulfide nonahydrate was added to 30 mL of water and magnetically stirred for 15 min to obtain solution B; 1.92 g of urea was ultrasonically dispersed in 20 mL of water to obtain solution C; solution B was quickly added to solution A to obtain a large amount of black suspension with a pungent odor, and then solution C was added and ultrasonically dispersed for 20 min to obtain a mixed solution. The obtained mixed solution was heated in a 100 mL polytetrafluoroethylene-lined reactor and maintained at 180 °C for 24 h. After the reaction was completed, the product was naturally cooled to room temperature and centrifuged. The precipitate was washed three times with ultrapure water and ethanol respectively, and vacuum dried at 60 °C for 6 h to obtain the product Bi 2 S 3 .

[0032] S2: Bi obtained in S1 2 S 3 Take 0.1 g and disperse it in 40 mL water and ultrasonicate for 20 min to obtain Bi 2 S 3 The suspension was then added with 6 mL of 0.1 M silver nitrate aqueous solution and stirred for 4 h. Then potassium dihydrogen phosphate with the same mass ratio (silver nitrate: potassium dihydrogen phosphate = 1:1) was added dropwise and stirred for 3 h. The above solution was transferred to a reactor and heated at 140 °C for 12 h. After the reaction was completed, centrifugation was performed and the precipitate was washed with ethanol three times to obtain Bi 2 S 3 / Ag 3 PO 4 Composite material; same process but without Bi addition 2 S 3 That is, prepare Ag 3 PO 4 .

[0033] S3: Bi obtained in S2 2 S 3 / Ag 3 PO 4 The composite material was sonicated in water for 5 min to form a 1 mg / mL dispersion; S4: The fluorine-doped tin oxide electrode (FTO) was cleaned with ethanol and deionized water in turn. After cleaning, the electrode was dried in a 60 °C oven. 30 μL of the dispersion of S3 was dropped onto a fixed area of ​​0.28 cm 2 The Bi 2 S 3 / Ag 3PO 4 Photoelectrode.

[0034] 2. Modification of magnetic bead surface to capture aptamer chains S1: Carboxylated magnetic beads (MB, Aladdin, particle size 100 nm) were rinsed several times with 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution (0.1 M, pH 6.0), and then redispersed in MES to a final concentration of 1.0 mg / mL of MB. 200 μL of MB was placed in a centrifuge tube, followed by addition of N-hydroxysuccinimide (NHS) solution (200 μL, 10 mM) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) solution (200 μL, 40 mM), and incubated at room temperature for 15 min under shaking. C-apt chain (100 μL, 20 µM) was then added to the centrifuge tube, incubated overnight at room temperature, and the magnetic beads and solution were separated by a magnet to obtain a magnetic complex; the base sequence of C-apt is: 5′-TTAACTTATTCGACCATATTTTTTTTT-NH 2 -3′ (SEQ ID NO. 1).

[0035] S2: The magnetic complex obtained in S1 was washed several times with PBS (10 mM, pH 7.4), and then dispersed in 500 μL PBS (10 mM, pH 7.4) containing 1.0 wt% BSA and incubated for 2 h. Finally, it was redispersed in 100 μL PBS (10 mM, pH 7.4) to obtain the magnetic complex C-apt / MB, which was stored at 4 °C.

[0036] S3: C-apt / MB (25 μL), T-apt (25 μL, 1.0 μM) and test samples (50 μL) containing different concentrations (0.05, 0.1, 0.2, 1, 4, 20 ng / mL) of CEA were mixed and incubated with shaking at 37 °C for 60 min; the magnetic beads and the solution were separated by a magnet to obtain the magnetic substance, wherein the base sequence of T-apt was: 5′-AGTCTAGGATTCGGCGTGGGTTAATTTTTTCCCATAGGGAAGTGGGGGA-3′ (SEQ ID NO.2).

[0037] 3. Triggering HCR reaction and introducing ALP S1: After washing the magnetic material obtained from S3 several times with PBS, mix it with DNA hybridization solution (100 μL, containing 5.0 μM H 1 and 5.0 μM H 2 ) and react at 37 °C for 50 min; Among them, H 1The base sequence is: 5′-biotin-TTAACCCACGCCGAATCCTAGACTCAAAGTAGTCTAGGATTCGGCGTG-3′ (SEQ ID NO. 3); H 2 The base sequence is 5′-AGTCTAGGATTCGGCGTGGGTTAACACGCCGAATCCTAGACTACTTTG-biotin-3′ (SEQ ID NO. 4); S2: After the magnetic beads and the solution were separated by a magnet, the mixture obtained in S1 was washed with PBS (10 mM, pH 7.4), and streptavidin-labeled alkaline phosphatase (SA-ALP, 50 μL, 2 μg / mL, Shanghai Biotechnology, B110054) was added to the centrifuge tube. The mixture was incubated at 37 °C in an oscillating environment for 30 min. The magnetic beads and the solution were separated by a magnet to obtain a magnetic complex.

[0038] S3: After the magnetic beads and solution were separated by a magnet, they were washed with PBS (10 mM, pH 7.4) to remove excess SA-ALP in S2, and then the magnetic complex obtained from S2 was mixed with AAP solution (400 μL, 10 mM) and reacted at 37 °C for 25 min.

[0039] 4. Quantitative analysis of tumor markers using photocurrent signals Collect the solution after S6 reaction and add it to the detection cell to detect Bi 2 S 3 / Ag 3 PO 4 The photoelectrode was used as the working electrode, and the photocurrent signal was tested using a classic three-electrode (reference electrode: calomel electrode; counter electrode: platinum electrode) system (electrochemical workstation: CHI760E; xenon lamp: PLS-SXE300), and tumor markers were quantitatively analyzed based on the photocurrent signal.

[0040] Figure 2 The photosensitive material Bi prepared in Example 1 2 S 3 (A), Ag 3 PO 4 (B) and Bi 2 S 3 / Ag 3 PO 4 (C) SEM image; Figure 2 It can be seen from A that Bi 2 S 3 It has a rod-like structure. Figure 2 B shows Ag 3 PO 4The particle size is about 5 μm. Figure 2 Ag can be seen in C 3 PO 4 Covered in Bi 2 S 3 On the stick.

[0041] Figure 3 A is Ag 3 PO 4 Electrode (modification steps are the same as Bi 2 S 3 / Ag 3 PO 4 Photoelectrode) and Bi 2 S 3 / Ag 3 PO 4 The photocurrent response of the photoelectrode to ascorbic acid shows that the photocurrent is significantly enhanced after the formation of the complex, indicating that the efficiency of electron-hole transfer is improved, and the addition of AA (as an electron donor) further enhances the photocurrent; Figure 3 B is Bi 2 S 3 / Ag 3 PO 4 The current response of the modified electrode in the presence and absence of the target. Comparing the two curves, the photocurrent is significantly enhanced when CEA is present.

[0042] Figure 4 This is a polyacrylamide gel electrophoresis diagram. The results show that T-apt is a key factor in triggering HCR.

[0043] Figure 5 Photocurrent response (A) and corresponding linear curve (B) of the photoelectrochemical biosensor at different CEA concentrations. As shown in the figure, as the CEA concentration gradually increases, the photocurrent intensity increases accordingly. In the CEA concentration range of 0.05~20 ng / mL, the photocurrent intensity I (μA) is proportional to the logarithm of the CEA concentration lg C [CEA] There is a good linear relationship between the concentrations of 1% and 2% (ng / mL), and the linear equation is I = 0.321 × lg C [CEA] + 0.844 (R 2 = 0.9936, n = 6), with a limit of detection (LOD) of 11.3 pg mL -1 .

[0044] Figure 6To test the selectivity (A) and stability (B) of the split photoelectrochemical biosensor method, thrombin, human immunoglobulin G (HIgG), prostate-specific antigen (PSA) and alpha-fetoprotein (AFP) were selected as interfering substances, and the concentration of the interfering substances was 10 times that of CEA. The results showed that the PEC biosensor had good selectivity and strong anti-interference ability. Through multiple cycles of detection, the obtained photocurrent signal intensity showed good stability, indicating that the prepared sensor has excellent stability.

[0045] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A split photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material, characterized in that: Firstly, Ag3PO4 was loaded on the surface of Bi2S3 to form a heterojunction composite material, and the composite material was dispersed on the surface of fluorine-doped tin oxide electrode to obtain Bi2S3 / Ag3PO4 photoelectrode. Secondly, the capture aptamer chain was modified on the surface of magnetic beads to capture carcinoembryonic antigen and trigger a hybridization chain reaction. Alkaline phosphatase was then introduced on the surface of magnetic beads to catalyze ascorbic acid phosphate to form ascorbic acid. Finally, carcinoembryonic antigen was quantitatively analyzed by photocurrent signal.

2. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1 is characterized in that: The specific steps include: (1) Preparation of Bi2S3 / Ag3PO4 heterojunction composite materials; (2) Preparation of Bi2S3 / Ag3PO4 photoelectrode; (3) Modifying the surface of magnetic beads to capture the aptamer to obtain a magnetic complex; (4) incubating the magnetic complex obtained in step (3), T-apt and carcinoembryonic antigen sample together, and then incubating with DNA hybridization solution and streptavidin-labeled alkaline phosphatase in sequence, and then adding ascorbic acid phosphate for reaction; (5) The Bi2S3 / Ag3PO4 photoelectrode was used as the working electrode, and the photocurrent signal was detected using a three-electrode system on an electrochemical workstation.

3. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1, characterized in that: The preparation steps of the Bi2S3 / Ag3PO4 heterojunction composite material in step (1) are as follows: S1: 1.83 g of bismuth nitrate pentahydrate was dispersed in 25 mL of ethylene glycol and stirred for 20 min to obtain solution A, 1.35 g of sodium sulfide nonahydrate was added to 30 mL of water and stirred for 15 min to obtain solution B, 1.92 g of urea was ultrasonically dispersed in 20 mL of water to obtain solution C; solution B was quickly added to solution A to obtain a black suspension with a pungent odor, and then solution C was added and ultrasonically dispersed for 20 min to obtain a mixed solution, and the obtained mixed solution was heated at 180 ° C for 24 h in a polytetrafluoroethylene-lined reactor, the product was naturally cooled to room temperature, the precipitate was centrifuged and washed with ultrapure water and ethanol respectively, and then vacuum dried at 60 ° C for 6 h to obtain Bi2S3; S2: The Bi2S3 obtained in step S1 was dispersed in water and ultrasonicated for 20 min, 6 mL of 0.1 M silver nitrate aqueous solution was added and stirred for 4 h, and then potassium dihydrogen phosphate in an equal mass ratio was added dropwise and stirred for 3 h. The reactor was heated at 140 °C for 12 h, and the product was washed with ethanol to obtain a Bi2S3 / Ag3PO4 composite material.

4. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1, characterized in that: The preparation steps of the Bi2S3 / Ag3PO4 photoelectrode in step (2) are as follows: S1: The Bi2S3 / Ag3PO4 composite material was ultrasonically treated in water for 5 min to form a 1 mg / mL dispersion; S2: After cleaning the fluorine-doped tin oxide electrode with ethanol and deionized water in turn, the electrode is placed at 60°C for drying, and the dispersion obtained in step S1 is dropped onto the FTO electrode. After drying, the Bi2S3 / Ag3PO4 photoelectrode is obtained.

5. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1, characterized in that: The step (3) of modifying the surface of magnetic beads to capture the aptamer comprises the following specific steps: S1: The magnetic beads were rinsed several times with 2-(N-morpholino)ethanesulfonic acid buffer and then dispersed in the above buffer to make the final concentration of the magnetic beads 1.0 mg / mL. 200 μL of N-hydroxysuccinimide solution and 200 μL of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride solution were added to 200 μL of the buffer containing magnetic beads. The mixture was incubated at room temperature for 15 min under shaking, and then C-apt chain was added. The mixture was incubated at room temperature overnight to obtain a magnetic complex. S2: The magnetic complex obtained in step S1 was dispersed into 500 μL PBS containing 1.0 wt% BSA and incubated for 2 h, and then redispersed into 100 μL PBS to prepare C-apt / MB, which was stored at 4 °C.

6. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 5, characterized in that: The concentration of the N-hydroxysuccinimide solution is 10 mM, and the concentration of the 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride solution is 40 mM; the nucleotide sequence of the C-apt chain is shown in SEQ ID NO.

1.

7. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1, characterized in that: Step (4) includes the following specific steps: S1: 25 μL of C-apt / MB, 25 μL of 1.0 μM T-apt, and 50 μL of samples containing different concentrations of CEA were mixed and incubated at 37 °C for 60 min with shaking to obtain magnetic substances; S2: After washing the magnetic material obtained in step S1 with PBS for several times, 100 μL of DNA hybridization solution was added and reacted at 37 °C for 50 min; S3: After washing the mixture obtained in step S2 with PBS, 50 μL of 2 μg / mL streptavidin-labeled alkaline phosphatase was added and incubated at 37°C in an oscillating environment for 30 min; S4: After washing with PBS to remove excess streptavidin-labeled alkaline phosphatase, add 400 μL of 10 mM ascorbic acid phosphate solution and react at 37°C for 25 min.

8. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 7 is characterized in that: The nucleotide sequence of T-apt in step S1 is shown in SEQ ID NO.

2.

9. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 7, characterized in that: The DNA hybridization solution in step S2 includes 5.0 μM H1 and 5.0 μM H2; the nucleotide sequence of H1 is shown in SEQ ID NO.3, and the nucleotide sequence of H2 is shown in SEQ ID NO.

4.

10. Application of the split photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material as described in any one of claims 1 to 9 in detecting carcinoembryonic antigen.

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