Preparation And Analysis Of Perovskite-based Photoelectrochemical Biosensors

The health of the human body is closely related to the activity of many substances in the body.For example,the abnormality of alkaline phosphatase activity usually indicates that the bones and liver and other organs are diseased,and the abnormality of dopamine is usually inextricably linked with neurological diseases.Therefore,it is of great significance to realize the quantitative sensing of these substances.Photoelectrochemical biosensor,as an analysis method of light source and signal separation,has the advantages of low cost,simple equipment and strong ability to resist background signal interference.In recent years,it has been widely used in the construction of various sensors.However,the choice of photoelectric active materials plays a significant role in the performance of photoelectrochemical biosensors.As one of the fastest growing and most promising photoelectrochemical active materials so far,perovskite has attracted widespread attention.In the past few years of research,their photoelectric conversion efficiency has been increased to 25.5%.In addition to the long diffusion length,low synthesis cost and diversified composition,perovskites are widely used in many fields due to their long carrier life,large light absorption coefficient and high photocatalytic activity,such as photodetectors,diodes,solar cells,et al.However,they are rarely used in biosensing.The main reason is that most perovskites are lead-based materials,which are highly toxic to living organisms,and the structure of perovskites is not stable while exposed to the outer environment they have poor stability in the external environment,which greatly limits their performance.More importantly,their water solubility and biocompatibility are very poor,which is very unfavorable for the construction of biosensors.Therefore,the development of perovskite materials with high stability and high biocompatibility is essential to improve the performance of photoelectrochemical biosensors.In this paper,we mainly developed the perovskite and its composite materials with high stability,biocompatibility and low toxicity,and made full use of their characteristics to construct high-performance photoelectrochemical biosensors,mainly including the following two parts:1.Normally,polarization of photo-active materials in current photoelectric（PE）systems cannot be adjusted,and thus electron transfer route of these systems are unchangeable,which greatly limits their performance in various fields.Herein,we attempted to modulate the polarization of perovskite-based heterostructures by both in situ semiconductor generation and enzymatic catalysis.Owing to the band alignment,Cs₃Bi₂Br₉quantum dots（QDs）and Bi OBr are confirmed to construct a Z-scheme structure,leading to a large anodic photocurrent.In the presence of ascorbic acid2-phosphate（AAP）,Bi PO₄is in situ generated on the surface of Cs₃Bi₂Br₉QDs/Bi OBr heterostructure,reassigning energy bands of Bi OBr.As a result,polarization of photo-active materials is converted,and a new Z-scheme structure with reversed electron transfer route is constructed,which lead to an evident cathodic photocurrent.Furthermore,abundant electron donors（ascorbic acid）can be obtained by catalyzing AAP with alkaline phosphatase（ALP）.In this case,photogenerated holes in Bi OBr are preferentially annihilated by electron donors,thereby blocking transfer of photogenerated electrons in Cs₃Bi₂Br₉QDs/Bi OBr/Bi PO₄heterostructure.Consequently,a second polarization conversion is triggered by enzymatic catalysis,resulting in the recovery of an anodic photocurrent.Benefited from the polarization conversion,a PEC biosensor with a feature of two-wing signal switch is designed,and ALP in small volume of human serum can be quantified with this method.In this work,polarization of perovskite-based photo-active materials is tuned and employed in biosensing,proposing an alternative perspective on design of advanced PE systems.2.Although in-situ generation of heterostructures on perovskites can significantly enhance their biosensing performance,but this method only limits in certain perovskites containing special ions such as Bi³⁺,in order to find a more general method in improving the biosensing performance of perovskites,in the work of this chapter,an all-inorganic perovskite Cs₃Bi₂I₉was in situ generated in Ui O-66 to form a Cs₃Bi₂I₉QDs@Ui O-66 composite material.The holes in Ui O-66 happened to be the excellent growth position of Cs₃Bi₂I₉QDs.Due to the encapsulation of MOF,Cs₃Bi₂I₉QDs were isolated from the outside world,which ensured the good stability of these two materials.At the same time,the energy band matching of Cs₃Bi₂I₉and Ui O-66 further improved its photoelectrochemical properties.The carboxyl group in Ui O-66 makes Cs₃Bi₂I₉QDs@Ui O-66 have good water affinity and biocompatibility,and the encapsulation of Ui O-66 further reduces the toxicity of Cs₃Bi₂I₉QDs,which solves the general problem of toxicity and low stability and biocompatibility in perovskites.And we used the self-polymerization of dopamine to form polydopamine with abundant benzoquinone electron acceptor groups,and then took the advantage of the improve of charge transfer efficiency to use them in photoelectrochemical biosensors.Finally,the detection range of dopamine was increased and the whole detection system was with a lower detection limit.It was obtained a new general idea for the application of perovskite materials in biosensing.