Study On Novel Photoelectrochemical Biosensors Based On Heterojunction Composite Materials

Photoelectrochemical(PEC)biosensor is an emerging research field based on photoelectrochemical technology and biosensor analysis.Because of its simple operation,high sensitivity,low background signal and good bio-affinity,it has been rapidly developed into an important analytical technique for different bio-recognition elements.The analytical performance of PEC biosensor depends on photoelectric active materials.Photoelectic active materials can convert biological or chemical information into observable PEC signal.Therefore,the development of photoelectric active materials with high photoelectric conversion efficiency is one of the key steps in designing a PEC biosensor with high performance to achieve a high sensitivity.Heterojunction refers to the interf ace between two different kinds of semiconductors.Composites with heterojunction structure and characteristics are usually called heterojunction composites.Constructing heterojunctions of two or more semiconductors is considered to be one of the most pop ular schemes for designing photoelectrodes with the desired performance,and has been applied to PEC biosensors.Because of energy band matching,heterojunction composites with excellent properties are produced by combining different types of semiconductor s.In this work,three photochemical sensors for detecting carbohydrate antigen 125(CA125)and the activity of alkaline phosphatase(ALP)were constructed based on the preparation of new heterostructure composites and the corresponding analysis was carried out:(1)A new photoelectric material of CuO-ZnO heterojunction was prepared by direct calcination of Cu²⁺-doped ZIF-8 in oxygen atmosphere.The morphology and structure of the composite were characterized by scanning electron microscopy,transmission electron microscopy,nitrogen adsorption-desorption method and X-ray diffraction.Under visible light irradiation,CuO-ZnO heterojunction exhibits excellent PEC behavior in aqueous media with the presence of ascorbic acid(AA)and dissolved oxygen.Taking the CA125-antibody functionalized CuO-ZnO heterojunction(CuO-ZnO-Ab₂)as a signal source,a novel PEC immunosensing platform was constructed for ultrasensitive assay of CA125.Because of the target-induced introduction of photoelectric material to the sensing platform,the proposed PEC immunosensor has excellent performance for CA125 assay:near-zero background noise,wide linear response range(1×10^-5-100 U/mL)and low detection limit(3.2×10^-6 U/mL).The developed CuO-ZnO heterojunction and the related PEC sensing platform may have promising applications in ultrasensitive and highly accurate monitoring of various proteins in bioanalysis and disease diagnosis.(2)The p-p heterojunction composite material NiO-CuO was synthesized using Ni/Cu-BTC polyhedron as precursor.The morphology and structure of the composite were characterized by scanning electron microscopy,nitrogen adsorption-desorption method,X-ray diffraction and X-ray photoelectron spectroscopy.When NiO-CuO was modified on the surface of indium tin oxide(ITO)electrode,a simple and highly sensitive PEC enzyme sensor was developed to detect the activity of ALP.ALP can catalyze the sodium SodiumL-ascorbyl-2-phosphate(AAP)to AA in solution.The NiO-CuO heterojunction has excellent PEC properties because of its porous structure,homogeneous dispersion and high sensitivity to AA in solution.The PEC enzyme sensor exhibits wide linear response range(1-1000 U/L)and low detection limit(0.04 U/L)for detecting ALP activity.This method opens up a new way for the preparation of new photoelectric materials and PEC biological analysis.(3)A“signal off”type PEC immunosensor with NiO-CuO as the initial electrode has been successfully developed based on the catalysis of 5-bromo-4-chloro-3-indole phosphate(BCIP)by ALP.And it is used to realize high sensitivity detection of CA125.First,the CA125 antibody Ab₁ was introduced to the electrode surface by glutaraldehyde crosslinking.Then Ab₂-AuNPs-ALP was introduced by antigen-antibody specific recognition in the presence of CA125.Because BCIP hydrolyzed by ALP produces insoluble blue precipitation(BCIP dimer)to accumulate on the photoelectrode,the photocurrent signal of the initial electrode is greatly reduced.The linear range of CA125 detection is from 5×10^-6 U/mL to 1 U/mL,and the detection limit is as low as 6.3×10^-7 U/mL.With the advantages of simple structure,high selectivity,good reproducibility and stability,the developed PEC sensor has potential application values in the detection and prevention of tumor diseases.