A split photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material

Abstract

The present invention discloses a split-type photoelectrochemical biosensing analysis method based on a Bi2S3 / Ag3PO4 heterojunction composite material. First, a Bi2S3 / Ag3PO4 heterojunction is prepared by multi-step hydrothermal method, and then modified on the surface of a fluorine-doped tin oxide electrode to form a Bi2S3 / Ag3PO4 photoelectrode; when a target is present, the capture aptamer on the surface of the magnetic bead can capture the triggering aptamer chain, thereby triggering the HCR reaction. With the help of the specific recognition effect between streptavidin and biotin, alkaline phosphatase is introduced on the surface of the magnetic bead to catalyze the substrate to form ascorbic acid as an electron donor, thereby enhancing the current. Carcinoembryonic antigen is quantitatively analyzed by photocurrent signal. This analysis method combines hybridization chain reaction and enzymatic signal amplification strategy, and has the advantages of simple preparation, high sensitivity, and reusability.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrochemical biosensing, and specifically relates to a split photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction. Background Art

[0002] Cancer is a malignant disease caused by gene misalignment and mutation, posing a threat to human health and a major cause of death worldwide. According to a 2022 report released by the National Cancer Center, cancer incidence is expected to continue to increase in the coming decades. Tumor markers are active substances that reflect the presence of cancer. Their presence and changes in state are typically associated with specific tumor types. Carcinoembryonic antigen (CEA) is a broad-spectrum tumor marker. When CEA concentrations in human serum exceed 20 μg / L, it indicates the presence of tumor cells. In recent years, commonly used CEA detection methods include enzyme-linked immunosorbent assay (ELISA), immunofluorescence, immunoblotting, and colorimetric immunoassay. However, these methods remain challenging due to high operating costs, relatively complex detection processes, and the potential for false positive or negative results. Therefore, the development of more sensitive, rapid, and specific biosensors is urgently needed.

[0003] Compared to traditional detection methods, photoelectrochemical (PEC) biosensors, which combine photoelectrochemical (PEC) technology with biosensors, exhibit a variety of excellent properties. In PEC bioanalysis, light excitation is used to generate electrical signals. Light and electricity are two completely separate and distinct energy forms, making this method more sensitive. Furthermore, expensive optical instruments (such as fluorescence spectrophotometers and UV-visible spectrophotometers) are not required, making the process relatively low-cost. Traditional PEC sensors require the gradual modification of photoelectrodes, a relatively cumbersome process. In the split-type sensing mode, the process of fixing the recognition element is separated from the PEC signal transduction, which is beneficial for maintaining the activity of biomolecules. At the same time, it avoids the contradiction between the maintenance of activity and the need for material fixation, light irradiation, cleaning, and repetition, significantly improving the convenience of operation.

[0004] In PEC biosensing, the photoelectric activity of the photosensitive material directly affects the sensor's analytical performance. Therefore, to enhance sensor sensitivity, it is necessary to prepare composite materials with matching band gaps to improve the material's photoelectric activity 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 split photoelectrochemical biosensing method based on Bi2S3 / Ag3PO4 heterojunction and enzymatic signal amplification.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A split-type photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material: first, Ag3PO4 is loaded on the surface of Bi2S3 to form a heterojunction composite material, and the composite material is dispersed on the surface of a fluorine-doped tin oxide electrode to prepare a Bi2S3 / Ag3PO4 photoelectrode; then, a capture aptamer chain is modified on the surface of magnetic beads to capture 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, carcinoembryonic antigen is quantitatively analyzed through the photocurrent signal.

[0008] Furthermore, the above-mentioned split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material specifically includes the following steps:

[0009] (1) Preparation of Bi2S3 / Ag3PO4 heterojunction composite materials;

[0010] (2) Preparation of Bi2S3 / Ag3PO4 photoelectrode;

[0011] (3) Modifying the surface of magnetic beads to capture the aptamer to obtain a magnetic complex;

[0012] (4) The magnetic complex obtained in step (3), T-apt and carcinoembryonic antigen sample are incubated together, and then incubated with DNA hybridization solution and streptavidin-labeled alkaline phosphatase in sequence, and then ascorbic acid phosphate is added for reaction;

[0013] (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.

[0014] Furthermore, the preparation steps of the Bi2S3 / Ag3PO4 heterojunction composite material in step (1) are as follows:

[0015] 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, and 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;

[0016] 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. 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. The product was washed with ethanol to obtain a Bi2S3 / Ag3PO4 composite material.

[0017] Furthermore, the preparation steps of the Bi2S3 / Ag3PO4 photoelectrode in step (2) are as follows:

[0018] S1: The Bi2S3 / Ag3PO4 composite material was ultrasonically dissolved in water for 5 min to form a 1 mg / mL dispersion;

[0019] S2: The fluorine-doped tin oxide electrode was cleaned with ethanol and deionized water in sequence and then dried at 60°C. The dispersion obtained in step S1 was added dropwise to the FTO electrode and dried to obtain the Bi2S3 / Ag3PO4 photoelectrode.

[0020] Furthermore, the surface modification of magnetic beads to capture aptamers in step (3) includes the following specific steps:

[0021] S1: The magnetic beads were rinsed several times with 2-(N-morpholino)ethanesulfonic acid buffer and then dispersed in the above buffer to a final concentration of 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 the magnetic beads. The mixture was incubated at room temperature with shaking for 15 min, and then the C-apt chain was added. The mixture was incubated at room temperature overnight to obtain a magnetic complex.

[0022] S2: The magnetic complex obtained in step S1 was dispersed in 500 μL of PBS containing 1.0 wt% BSA and incubated for 2 h. The complex was then redispersed in 100 μL of PBS to prepare C-apt / MB, which was stored at 4 °C.

[0023] 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.

[0024] Furthermore, step (4) includes the following specific steps:

[0025] 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 with shaking at 37°C for 60 min to obtain magnetic material;

[0026] 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;

[0027] 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 a shaking environment for 30 min;

[0028] 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.

[0029] Furthermore, the nucleotide sequence of T-apt in step S1 is shown as SEQ ID NO.2.

[0030] Furthermore, 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.

[0031] The above-mentioned split photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material is applied in the detection of carcinoembryonic antigen.

[0032] The principle of the analytical method of the present invention is as follows:

[0033] A Bi2S3 / Ag3PO4 heterojunction was prepared by multi-step hydrothermal reaction to form a Bi2S3 / Ag3PO4 photoelectrode. The capture aptamer chain was then modified on the surface of the magnetic beads to obtain a magnetic bead complex. When the target was present, the magnetic bead complex could capture the triggering aptamer chain, further triggering the HCR reaction. With the help of the specific binding of streptavidin and biotin, a large amount of alkaline phosphatase (ALP) was introduced on the magnetic beads. ALP catalyzed the substrate to produce ascorbic acid (AA). The reaction-completed solution was transferred to the detection pool, and the Bi2S3 / Ag3PO4 photoelectrode was used as the working electrode. The photocurrent signal was 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, thereby achieving the quantification of CEA in the sample to be tested ( Figure 1 ).

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] (1) The present invention prepares Bi2S3 / Ag3PO4 photoelectrode by a simple hydrothermal method to form the transducer layer of the biosensor, which is simple to operate and low in cost.

[0036] (2) Ag3PO4 has high photocatalytic activity, but its charge separation efficiency is low, and electron-hole pairs are easily recombined. Bi2S3, on the other hand, has high light absorption and photoelectron transfer efficiency in the visible spectrum. The different Fermi levels of the two materials can promote the transfer of photogenerated electrons and the effective separation of carriers between them. Compared with single materials Bi2S3 and Ag3PO4, the composite material Bi2S3 / Ag3PO4 heterojunction synthesized by the present invention can reduce the recombination of electron-hole pairs in the photoelectrode material, promote the separation of photogenerated carriers, and improve the photoelectric performance.

[0037] (3) The present invention adopts a split sensing strategy, which simplifies the experimental operation process and improves the convenience of detection.

[0038] (4) The present invention uses aptamers and HCR to amplify signals, which has good universality.

[0039] (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, thereby improving the detection performance of the sensor. The constructed PEC aptamer sensor has a low detection limit, high specificity for CEA, and good analytical performance.

[0040] In summary, the present invention constructs an efficient and sensitive photoelectrochemical biosensor, using the composite material Bi2S3 / Ag3PO4 as the transducer and HCR as the signal amplification method, which effectively improves the ease of operation, sensitivity and specificity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the principle of the split photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction and enzymatic signal amplification.

[0042] Figure 2 SEM images of photosensitive materials Bi2S3 (A), Ag3PO4 (B) and Bi2S3 / Ag3PO4 (C).

[0043] Figure 3 is the photocurrent response; Figure 3 A is the photocurrent response of Ag3PO4 (a, b) and Bi2S3 / Ag3PO4 (c, d) modified electrodes to ascorbic acid (a, c: no AA in the electrolyte; b, d: AA in the electrolyte); Figure 3 B is the current response of the Bi2S3 / Ag3PO4 modified electrode in the presence or absence of the target (a: without CEA, b: with CEA).

[0044] Figure 4Polyacrylamide gel electrophoresis diagram (M: DNA marker, 1: H1, 2: H2, 3: H1+H2, 4: H1+H2+C-apt, 5: H1+H 2: +T-apt).

[0045] Figure 5 The photocurrent response (A) and the corresponding linear curve (B) of the photoelectrochemical biosensor at different CEA concentrations.

[0046] Figure 6 Tests of the sensor's selectivity (A) and stability (B). DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and drawings. Obviously, the described embodiments and drawings are only part of the embodiments of the present invention, not all of them.

[0048] In an embodiment of the present invention, a split photoelectrochemical biosensor for detecting carcinoembryonic antigen (CEA) is provided based on a Bi2S3 / Ag3PO4 composite material, combined with HCR and enzymatic signal amplification strategies. This is an advanced detection tool that combines photosensitive materials and biorecognition elements, and achieves high-sensitivity detection of the target 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 ultimately recording and outputting the signal through an electrochemical workstation. The present invention achieves effective detection of CEA, and the method is highly sensitive, rapid, simple, and has a low background signal.

[0049] Example 1

[0050] 1. Preparation of Bi2S3 / Ag3PO4 Photoelectrode

[0051] S1: Disperse 1.83 g of bismuth nitrate pentahydrate in 25 mL of ethylene glycol and stir magnetically for 20 min to obtain solution A; add 1.35 g of sodium sulfide nonahydrate to 30 mL of water and stir magnetically for 15 min to obtain solution B; ultrasonically disperse 1.92 g of urea in 20 mL of water to obtain solution C; quickly add solution B to solution A to obtain a large amount of black suspension with a pungent odor, then add solution C and ultrasonically disperse for 20 min to obtain a mixed solution. The obtained mixed solution is heated in a 100 mL polytetrafluoroethylene-lined reactor and maintained at 180 °C for 24 h. After the reaction is completed, the product is naturally cooled to room temperature and centrifuged. The precipitate is washed three times with ultrapure water and ethanol respectively, and vacuum dried at 60 °C for 6 h to obtain the product Bi2S3.

[0052] S2: Disperse 0.1 g of Bi2S3 obtained in S1 in 40 mL of water and sonicate for 20 minutes to obtain a Bi2S3 suspension. Add 6 mL of 0.1 M silver nitrate aqueous solution and stir for 4 hours. Then, add potassium dihydrogen phosphate (KH2PO4) at an equal mass ratio (silver nitrate: KH2PO4 = 1:1) dropwise and stir for 3 hours. Transfer the solution to a reactor and heat at 140°C for 12 hours. After the reaction is complete, centrifuge the solution, and wash the precipitate three times with ethanol to obtain the Bi2S3 / Ag3PO4 composite. Ag3PO4 was prepared using the same process but without the addition of Bi2S3.

[0053] S3: The Bi2S3 / Ag3PO4 composite material obtained in S2 was ultrasonicated in water for 5 min to form a 1 mg / mL dispersion;

[0054] S4: The fluorine-doped tin oxide electrode (FTO) was cleaned with ethanol and deionized water in sequence. 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 photoelectrode was prepared by depositing the Ag2S3 / Ag3PO4 on the FTO electrode and drying it at room temperature.

[0055] 2. Modification of magnetic bead surface to capture aptamer chains

[0056] S1: Carboxylated magnetic beads (MB, Aladdin, particle size 100 nm) were rinsed several times with 2-(N-morpholino)ethanesulfonic acid (MES) buffer (0.1 M, pH 6.0) and then redispersed in MES to a final MB concentration of 1.0 mg / mL. 200 μL of MB was placed in a centrifuge tube. Then, 200 μL of N-hydroxysuccinimide (NHS) solution (10 mM) and 200 μL of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) solution (40 mM) were added. The mixture was incubated at room temperature with shaking for 15 min. Then, C-apt chain (100 μL, 20 µM) was added to the centrifuge tube, incubated at room temperature overnight, and the magnetic beads and solution were separated using a magnet to obtain a magnetic complex; the base sequence of C-apt was: 5′-TTAACTTATTCGACCATATTTTTTTTTT-NH2-3′ (SEQ ID NO.1).

[0057] S2: The magnetic complex obtained in S1 was washed several times with PBS (10 mM, pH 7.4), redispersed in 500 μL of PBS (10 mM, pH 7.4) containing 1.0 wt% BSA, and incubated for 2 h. Finally, it was redispersed in 100 μL of PBS (10 mM, pH 7.4) to obtain the magnetic complex C-apt / MB, which was stored at 4°C.

[0058] S3: C-apt / MB (25 μL), T-apt (25 μL, 1.0 μM), and a test sample (50 μL) containing different concentrations (0.05, 0.1, 0.2, 1, 4, and 20 ng / mL) of CEA were mixed and incubated with shaking at 37°C for 60 min. The magnetic beads and solution were separated using a magnet to obtain magnetic material. The base sequence of T-apt was: 5′-AGTCTAGGATTCGGCGTGGGTTAATTTTTTCCCATAGGGAAGTGGGGGA-3′ (SEQ ID NO. 2).

[0059] 3. Triggering HCR reaction and introducing ALP

[0060] S1: After washing the magnetic material obtained from S3 several times with PBS, it was mixed with DNA hybridization solution (100 μL, containing 5.0 μM H1 and 5.0 μM H2) and reacted at 37°C for 50 min;

[0061] The base sequence of H1 is: 5′-biotin-TTAACCCACGCCGAATCCTAGACTCAAAGTAGTCTAGGATTCGGCGTG-3′ (SEQ ID NO. 3);

[0062] The base sequence of H2 is 5′-AGTCTAGGATTCGGCGTGGGTTAACACGCCGAATCCTAGACTACTTTG-biotin-3′ (SEQ ID NO. 4);

[0063] S2: After separating the magnetic beads and the solution using 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 Bioengineering, B110054) was added to the centrifuge tube. The mixture was incubated in an oscillating environment at 37°C for 30 min. The magnetic beads and the solution were separated using a magnet to obtain a magnetic complex.

[0064] S3: After separating the magnetic beads and the solution using a magnet, the beads were washed with PBS (10 mM, pH 7.4) to remove excess SA-ALP in S2. The magnetic complex obtained in S2 was then mixed with AAP solution (400 μL, 10 mM) and reacted at 37°C for 25 min.

[0065] 4. Quantitative Analysis of Tumor Markers Using Photocurrent Signals

[0066] The solution after the S6 reaction was collected and added to the detection cell. The Bi2S3 / Ag3PO4 photoelectrode was used as the working electrode. The photocurrent signal was tested using a classic three-electrode system (reference electrode: calomel electrode; counter electrode: platinum electrode) (electrochemical workstation: CHI760E; xenon lamp: PLS-SXE300). Tumor markers were quantitatively analyzed based on the photocurrent signal.

[0067] Figure 2 SEM images of the photosensitive materials Bi2S3 (A), Ag3PO4 (B) and Bi2S3 / Ag3PO4 (C) prepared in Example 1; Figure 2 In A, we can see that Bi2S3 presents a rod-like structure. Figure 2 B shows that Ag3PO4 is a polyhedral structure with a particle size of about 5 μm. Figure 2 In C, Ag3PO4 can be seen covering the Bi2S3 rods.

[0068] Figure 3 A is the photocurrent response of the Ag3PO4 electrode (modification steps are the same as those of the Bi2S3 / Ag3PO4 photoelectrode) and the Bi2S3 / Ag3PO4 photoelectrode to ascorbic acid. The photocurrent is significantly enhanced after the formation of the complex, indicating that the efficiency of electron-hole transfer has been improved. In addition, the addition of AA (as an electron donor) further enhances the photocurrent. Figure 3 B is the current response of the Bi2S3 / Ag3PO4 modified electrode in the presence or absence of the target. Comparing the two curves, the photocurrent is significantly enhanced when CEA is present.

[0069] Figure 4 Figure 3 is a polyacrylamide gel electrophoresis diagram, and the results show that T-apt is a key factor in triggering HCR.

[0070] 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, log C. [CEA] There was a good linear relationship between the concentrations of ethanol and ethanol (ng / mL), and the linear equation was 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 .

[0071] Figure 6To test the selectivity (A) and stability (B) of this split-type photoelectrochemical biosensor, thrombin, human immunoglobulin G (HIgG), prostate-specific antigen (PSA), and alpha-fetoprotein (AFP) were selected as interfering substances at concentrations 10 times that of CEA. The results demonstrated good selectivity and strong anti-interference properties of the PEC biosensor. The photocurrent signal intensity exhibited good stability over multiple cycles, demonstrating the excellent stability of the prepared sensor.

[0072] 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-type photoelectrochemical biosensing analysis method based on Bi2S3 / Ag3PO4 heterojunction composite material, characterized by: First, Ag3PO4 is loaded on the surface of Bi2S3 to form a heterojunction composite material, and the composite material is dispersed on the surface of a fluorine-doped tin oxide electrode to prepare a Bi2S3 / Ag3PO4 photoelectrode. Then, a capture aptamer chain is modified on the surface of magnetic beads to capture carcinoembryonic antigen and trigger a hybridization chain reaction. Alkaline phosphatase is then introduced on the surface of the magnetic beads to catalyze ascorbic acid phosphate to form ascorbic acid. Finally, carcinoembryonic antigen is quantitatively analyzed using the photocurrent signal. 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) The magnetic complex obtained in step (3), T-apt and carcinoembryonic antigen sample are incubated together, and then incubated with DNA hybridization solution and streptavidin-labeled alkaline phosphatase in sequence, and then ascorbic acid phosphate is added for reaction; (5) Using Bi2S3 / Ag3PO4 photoelectrode as the working electrode, a three-electrode system was used on an electrochemical workstation to detect the photocurrent signal; 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, and 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. Then, potassium dihydrogen phosphate of equal mass ratio was added dropwise and stirred for 3 h. The reactor was heated at 140 °C for 12 h. The product was washed with ethanol to obtain a Bi2S3 / Ag3PO4 composite material. The DNA hybridization solution in step (4) includes 5.0 μM H1 and 5.0 μM H2; the nucleotide sequence of H1 is 5′-biotin-TTAACCCACGCCGAATCCTAGACTCAAAGTAGTCTAGGATTCGGCGTG-3′, and the nucleotide sequence of H2 is 5′-AGTCTAGGATTCGGCGTGGGTTAACACGCCGAATCCTAGACTACTTTG-biotin-3′.

2. 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 dissolved in water for 5 min to form a 1 mg / mL dispersion; S2: The fluorine-doped tin oxide electrode was cleaned with ethanol and deionized water in sequence and then dried at 60°C. The dispersion obtained in step S1 was added dropwise to the FTO electrode and dried to obtain the Bi2S3 / Ag3PO4 photoelectrode.

3. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 1, characterized in that: The magnetic bead surface modification and capture of the aptamer in step (3) includes 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 a final concentration of 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 the magnetic beads. The mixture was incubated at room temperature with shaking for 15 min, and then the 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 in 500 μL of PBS containing 1.0 wt% BSA and incubated for 2 h. The complex was then redispersed in 100 μL of PBS to prepare C-apt / MB, which was stored at 4 °C.

4. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 3, 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 5′-TTAACTTATTCGACCATATTTTTTTTTT-NH2-3′.

5. 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 with shaking at 37°C for 60 min to obtain magnetic material; 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 a shaking 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.

6. The split-type photoelectrochemical biosensing analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material according to claim 5 is characterized in that: The nucleotide sequence of T-apt in step S1 is 5′-AGTCTAGGATTCGGCGTGGGTTAATTTTTTCCCATAGGGAAGTGGGGGA-3′.

7. Use of the split-type photoelectrochemical biosensor analysis method based on the Bi2S3 / Ag3PO4 heterojunction composite material as described in any one of claims 1 to 6 in detecting carcinoembryonic antigen.

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