Construction Of Highly Sensitive Photoelectrochemical Bioanalysis Systems

Photoelectrochemical（PEC）is a new science branch developed on the basis of electrochemical（EC）,mainly involving the conversion process between photo and electrical and electrical and chemical.The PEC bioanalysis combines the PEC and biorecognition to analyze the target which directly or indirectly changes the nature of the photoactive material or electrolyte environment,triggering the signal change and achieving quantitative analysis.In this paper,the chemically stable,non-toxic petal-like BiVO₄,tremella-like Bi₂WO₆,and hydrangea Bi₂WO₆ are used as photo anodes.The detection of miRNA-21,carcinoembryonic antigen（CEA）and chloramphenicol（CAP）were sequentially achieved using different signal generation and amplification mechanisms.The main research work consists of the following three parts:（1）miRNA-21 mediated rolling circle amplification（RCA）reaction and Nt.Bst NBⅠendonuclease hydrolysis process to produce many single-stranded DNA fragments（cDNA）,which could hybridize with probe DNA fixed on the surface of BiVO₄ photoanode to form double-strand DNA（ds DNA）.After methylene blue（MB）specifically embeding in ds DNA,ds DNA has hole conduction characteristics.Under photo excitation,photo-generated electrons and holes were generated in BiVO₄.The helix structure of ds DNA mediated holes transfer to MB,the efficiency of charge carrier separation was improved,including anode photocurrent increased.Based on this,we designed an ultra-sensitive PEC platform for miRNA-21 detection.In the concentration range of 5.0×10^-3 to 1.0×10⁴ pmol/m L,the photocurrent is linearly related to the concentration of miRNA-21,and the detection limit is 0.3 fmol/m L（S/N=3）.（2）The free MB diffused easily to the surface of the Bi₂WO₆ photoanode and acted as signal molecules to increase the photocurrent.In contrast,MB embedded by the G-quadruplex couldn’t approach the electrode surface due to the steric hindrance effect,resulting in a small signal.Based on this,CEA aptamer was treated as a primer which participated in the RCA to produce G bases-rich single-stranded DNA.Then,single-stranded DNA folded into a G-quadruplex with the assist of K⁺,which can capture mostly MB in solution.In the presence of CEA,the RCA reaction did not proceed,most of the MB in solution existed in a free state,and the photocurrent increased.The content of CEA affected the content of free MB in the solution,which in turn affected photocurrent.When the concentration of CEA is in the range of 10 fg/m L to 10 ng/m L,the photocurrent is linearly correlated with the concentration of CEA,and the detection limit is 2.6fg/m L（S/N=3）.（3）K₄Fe（CN）₆ could combine with Bi³⁺on the surface of Bi₂WO₆ to generate ferrocyanide（BiHCF）in situ.BiHCF（Ⅱ）and Bi₂WO₆ interated to form a heterostructure,under photo excitation,the photogenerated holes of Bi₂WO₆ were transported to BiHCF,the efficiency of electron-hole separation increased,resulting anode photocurrent increased.Mesoporous silica nanoparticles were used as carriers to encapsulate K₄Fe（CN）₆,the CAP aptamer was served as biological gate,CAP mediated capture/release K₄Fe（CN）₆.Based on this,a homogeneous PEC biosensor was constructed for CAP detection.The photocurrent increases with the increase of CAP content,which is linearly related in the concentration range of 0.05 n M to 100 nmol/m L,and the detection limit is 12 pmol/m L（S/N=3）.