Research On The Application Of Transition Metal Materials In Photoelectrochemical Biosensor

Photoelectrochemical（PEC）sensor is a promising low-cost analytical tool.The basic principle is that the photoelectric active material generates and transmits electric charge under the excitation of visible light,and analyzes the content of the object to be measured by the change of electric signal before and after the photoelectric recognition reaction.Compared with other optical detection techniques,the PEC method can simplify the equipment and reduce the cost;compared with traditional electrochemical sensors,the PEC sensor shows a wider application prospect due to its sensitive detection capability.This paper proposes a novel photoelectrochemical immunosensor based on a transition metal composite with a tunable band gap and novel signal amplification strategy.The photoactive composite containing transition metals was formed into a type II heterojunction with staggered energy levels.A multi-component heterojunction with high photoelectric conversion performance was further developed.The double electrode system is introduced to improve the photoelectric response of the sensor,and the problem of charge recombination at the heterojunction interface is solved fundamentally.The main work is as follows:（1）A label-free immunosensor for detecting pancreatic cancer markers（CA242）was constructed using type II heterojunction with staggered energy levels as photoactive substrate material.A label-free immunosensor for detecting pancreatic cancer markers（CA242）was constructed using SnS₂/Cd-ZnIn_2.2S_y as a photoactive substrate material.The hexagonal nanoflake SnS₂ was used as the substrate to successfully compound three-dimensional（3D）Cd-ZnIn_2.2S_y with a flower-like structure by calcination.Due to the type II heterojunctio formation between SnS₂ and Cd-ZnIn_2.2S_y,the stepped energy levels formed facilitate electron transport and reduce the recombination of e^-/h⁺pairs,enhancing photoelectron unidirectional transmission capability.In addition,the 3D flower-like structure of Cd-ZnIn_2.2S_y produces light refraction inside the material,resulting in an obvious photocurrent response.By efficiently immobilizing captured antibodies on the SnS₂/Cd-ZnIn_2.2S_y photoelectrode,a sensitive PEC immunosensor is established to detect CA242 with the detection range of 10^-4 U/mL～10² U/mL and the lowest detection limit of 3.06×10^-5 U/mL.The PEC immunosensor constructed in this work has good repeatability,specificity and stability,indicating great application potential in improving the sensitivity of tumor marker detection.（2）A heterojunction with high visible light absorption,fast separation of electron-hole pairs and sufficient chemical stability was developed to construct a more efficient label-free PEC sensing system.Based on the hydrophilicity of the bimetallic sulfide ZnCdS solid solution,the PEC biosensor for detecting programmed death ligand 1（PD-L1）was designed with ZnCdS/NiS/ZnCdS intercalated double heterojunction.Compared with the single heterojunction system designed in the previous work,the double heterojunction structure significantly promotes the effective spatial separation of photo-generated carriers and exhibits a higher photoelectric conversion capacity.The constructed double heterojunction sensing platform has high sensitivity and selectivity for PD-L1 detection,which has an excellent linear range of 10 fg/mL～10 ng/mL with a detection limit of 4.02 fg/mL.It shows the great potential of ZnCdS/NiS/ZnCdS in improving the sensitivity of PEC clinical diagnosis.The dual heterojunction design opens the possibility of constructing a multifunctional PEC sensing platform.The method of the dual heterojunction opens a new way to build a multifunctional PEC sensing platform.（3）A double-electrode sensing platform was designed to accelerate the separation of carriers at the heterojunction interface and make the label-free immunosensor achieve more sensitive detection performance.Here,a double-photoelectrode PEC sensing platform was fabricated based on antenna-like strategy by integrating MIL-68（In）-NH₂,a p-type metal-organic framework（MOF）photocatalyst,as a photocathode with the type-II heterojunction of CdSe/MgIn₂S₄ as a photoanode synchronously.According to ligand-to-metal charge transition（LMCT）,the photo-generated carriers of MIL-68（In）-NH₂ transferred from the organic ligand to the metal cluster,which provides an efficient antenna-like transfer path for the charge at the heterojunction interface.In addition,the sufficient Fermi energy difference between the double-photoelectrode provides a continuous internal driving force for the fast separation of photo-generated carriers at the anode detection interface,significantly improving the photoelectric conversion efficiency.Therefore,compared with the traditional optical electrode,the double optical electrode PEC sensing platform developed by the antennae-like strategy has a higher photocurrent response,2.5 times higher than that of the single optical anode detection platform.Based on this strategy,we constructed a PEC biosensor for the detection of programmed death-ligand 1（PD-L1）,a biomarker for cancer diagnosis,prognosis and treatment efficacy.The elaborated PD-L1 biosensor exhibited sensitive and precise detection capability with a detection range of 1×10^-5 to 1×10³ ng/mL and a lower detection limit of 3.26×10^-6 ng/mL,and demonstrated the feasibility of serum sample detection,providing a novel and viable approach for the unmet clinical need of PD-L1 quantification.More importantly,the heterojunction interface charge separation mechanism proposed in this study provides a new research direction for the design of sensors with high-sensitivity PEC performance.