Signal-on Type Nucleic Acid Photoelectrochemical Biosensor Constructed By N-type Semiconductor

Photoelectrochemistry（PEC）is a novel analytical method developed on the basis of electrochemistry and optics.PEC biosensing technology is an important manifestation of the great progress made by PEC technology in the field of analytical detection.PEC detection device utilize two forms of energy,light and electricity,as the excitation source and detection signal,respectively,effectively reducing the background signal of the sensing platform and making the sensitivity of the detection greatly improved.So far,PEC technology has made important achievements in the field of analytical detection and has proposed a variety of sensing strategies for the detection of biological analytes,such as cells,nucleic acids,biomolecules and ions,proteins and enzymes.Combining stable and highly active photoelectric materials with suitable signal amplification strategies is the key to enhance the detection capability of PEC biosensors.In this paper,n-type semiconductor materials with good initial photoelectric signals were synthesized and used as substrate materials by hydrothermal method.A photoelectrochemistry biosensing platform for sensitive analysis of nucleic acids based on different signal amplification strategies was successfully constructed,and the structure and properties of the materials,detection mechanism,and analytical application capability of the biosensors were thoroughly investigated.The main research contents and related conclusions are as follows:（1）A photoelectrochemical biosensor for miRNA-21 detection based on Bi2S3@Cd In2S4MicroRNA（miRNA）is an ideal biomarker,and the sensitive monitoring of low-abundance miRNA is of great significance for the treatment of cancer at the onset stage.Herein,a novel Y-shaped DNA-mediated PEC sensing platform based on the Bi₂S₃@CdIn₂S₄ photoanode is proposed for the sensitive detection of miRNA-21.First,an n-n type Bi₂S₃@CdIn₂S₄ heterojunction with tight interface is formed for the first time through a layer-by-layer assembly strategy due to the matched band structures brtween Bi₂S₃ and CdIn₂S₄.The photocurrent intensity of Bi₂S₃@CdIn₂S₄/GCE electrode is 1.7-fold higher than that of Bi₂S₃/GCE electrode and 2.5-fold higher than that of CdIn₂S₄/GCE electrode under visible light irradiation.Additionally,miRNA-21-triggered catalytic hairpin assembly facilitates the formation of Y-shaped DNA structure with CdS quantum dots.As the photosensitizer of Bi₂S₃@CdIn₂S₄heterojunction,CdS quantum dots accelerate the separation of electron-hole pairs in the sensing system and realizes photocurrent signal enhancement,thus realizing the“signal on”detection of the miRNA-21.The proposed PEC biosensor exhibits a superior sensitivity of 0.18 fmol/L and the recoveries of human serum range from 98.0 to 104%with a relative standard deviation of 5.8%–8.9%.Therefore,the constructed PEC biosensor has potential application value in the early diagnosis and treatment of miRNA-related diseases.（2）A photoelectrochemical biosensor based on BiVO4/CdS/AuNPs for detection of miRNA-21As a promising biomarker,the sensitive detection of miRNA is important for the monitoring and treatment of various cancers.In this paper,a photoelectrochemical sensing platform based on BiVO₄/CdS/AuNPs photoanodes combined with a hand-in-hand DNA structure is constructed for“signal on”detection of miRNA-21.First,BiVO₄/CdS/AuNPs complex with a tight interface is prepared by a layer-by-layer assembly strategy,and the obtained complex has a good initial photocurrent due to the matching band structure between the BiVO₄ and CdS,and the Surface plasmon resonance effect of AuNPs on the optoelectronic material.In addition,the miRNA-21triggered the hybrid reaction and promoted the formation of the hand-in-hand structure with Fc.Next,the 3’end of probe A and the 5’end of probe B acted as DNAzyme and assembled with the 3’end of probe B in the adjacent Y-shaped structure to form a large number of hand-in-hand structures.With the addition of cofactor Mg²⁺,the short strand modified with Fc is sheared and released to the surface of electrode.Afterwards,the photocurrent signal continues to be amplified due to the cycle of target,enabling sensitive detection of miRNA-21 in the range of 100 fmol/L to 100 nmol/L,and with detection limits as low as 0.35 fmol/L.Therefore,this PEC biosensor has potential applications in the early monitoring and prevention of miRNA-related diseases.（3）A photoelectrochemical biosensor based on Zn In2S4@AuNPs coupled with circular DNA walker for detection of circulating tumor DNAThe circulating tumor DNA（ctDNA）is a crucial cancer marker,its sensitive monitoring is useful for early diagnose and therapy of tumor-related diseases.Herein,a bipedal DNA walker with multiple recognition sites is designed through the transition of dumbbell-shaped DNA nanostructure to realize the dual amplification of the signal and achieve ultrasensitive detection of ctDNA.Initially,the ZnIn₂S₄@AuNPs is obtained by combining the drop coating method with electrodeposition method.When the target is present,the dumbbell-shaped DNA structure transforms into an annular bipedal DNA walker that can walk unrestrictedly on the modified electrode.After the cleavage endonuclease（Nb.BbvCI）was added to the sensing system,the ferrocene on the substrate is released from the electrode surface,and the transfer efficiency of photogenerated electron-hole pairs is extremely improved,enabling the“signal on”testing of ctDNA.The detection limit of the prepared PEC biosensor is 0.31 fmol/L,and the recovery of actual samples varied between 96.8 and 103.6%with an average relative standard deviation of about 8%,the PEC biosensor with bipedal DNA walker shown sensitive analytical performance in the detection of actual samples.