Study Of Photoelectrochemical Biosensor Based On Functional CdS Nanorods And DNA Assembly

Photoelectrochemical(PEC)analysis is a novel detection technique developed rapidly recently,which has the advantages of high sensitivity,low background signal and desirable selectivity,obtaining the great progress in sensing applications.However,compared with the traditional fluorescence analysis and electrochemistry,PEC analysis technology has some limitations,such as poor stability of photoactive materials,high requirements of photoelectric conversion efficiency and dependence on external light sources.In order to solve these existing problems,this work were mainly carried out from the following three aspects:1.Beta-cyclodextrin-functionalized CdS nanorods(β-CD@CdS NRs)with high stability and desirable photo-electricity activity were first synthesized,and designed a novel PEC biosensor for human immune deficiency virus(HIV)DNA detection by coupling with catalytic hairpin assembly(CHA)-mediated biocatalytic precipitation(BCP)and the host-guest interaction between adamantine(ADA)and β-CD.In the presence of HIV DNA,CHA process was triggered with the aid of hairpin DNA1 and ADA-labelled hairpin DNA2,and then generated large amounts of G-quadruplex,which could be formed hemin/G-quadruplex DNAzyme to catalyze 4-chloro-l-naphthol to generate insoluble precipitation on photoelectrode surface,followed by the decreased photocurrent response due to the corresponding stereo-hindrance effect.Under optimized conditions,this biosensor exhibited wide linear dynamic range(10 fM-1 nM)and low detection limit of 1.16 fM,as well as high sensitivity,excellent stability,and satisfactory feasibility in human-serum samples.Moreover,the prepared β-CD@CdS NRs could be applied to the construction of other advanced sensing platform,showing great prospect in clinical diagnostics.2.β-CD@CdS NRs/WS2 NSs heterostructures were introduced as dual-functional building blocks for designing an ultrasensitive PEC bioassay of microRNA-21(miR-21)based on cyclic strand displacement reaction(SDR)-mediated Cu2+ quenching and host-guest interaction between β-CD and ADA,in which β-CD@CdS NRs/WS2 NSs heterojunction serves as a signaling and linking unit,and avidin-labeled CuO nanoparticle(Avidin-CuO NPs)as a quenching unit.In the presence of miR-21,ADA-labeled hairpin DNA1 was unfolded by DNA hybridization and triggered SDR cycling with the aid of biotin-labeled hairpin DNA2(Bio-H2),which generated plenty of double-stranded DNA structures with biotin molecules at the outer terminal point of dsDNA.When Avidin-CuO was immobilized onto the electrode surface via biotin-avidin affinity binding and then dissolved by hydrochloric acid,the released Cu2+could react with the CdS NRs to generate Cu,S,leading to a decreased photocurrent response.Under the optimized conditions,this biosensor displayed desirable linearity in the range from 0.1 fM to 10 pM,a low detection limit of 25.1 aM and satisfactory selectivity,and was applied to miR-21 analysis in serum samples,holding great potential for early diagnosis of some cancers.3.By solvothermal synthesis of MoS2@CdS NRs,combined with magnetic beads Fe3O4@SiO2@β-CD and Pb2+ shear enzyme,a self-luminescent PEC biosensor was designed to detect thrombin.The DNA strand with one end modified PbS QDs(PbS-S1)was fixed on the surface of the magnetic bead through host-guest recognition.Then,the thrombin aptamer(S2)was added to form a double chain with the complementary chain PbS-S1.When the target thrombin was present,S2 combined with thrombin,making the naked PbS-S1 and Pb2+ dependent DNase(S3)sheared under the effect of Pb2+,so that the D.NA fragments modified PbS QDs at the broken end were dropped onto the surface of MoS2@CdS NRs.Then,the electrode was put into the luminol-H2O2 mixed solution.Luminol would produce light source because MoS2 NSs on the surface of the NRs could catalyze H2O2.While PbS QDs attached to the surface of MoS2@CdS NRs could not only hinder the catalytic effect of MoS2 NSs,also could play a role of photoelectric inhibition on MoS2@CdS.Under the double effects,the photoelectric current decreases significantly,so as to quantitatively detect the concentration of thrombin.Under the optimal conditions,the linear range of the sensor was 1 fM-100 pM,and it had a detection limit of 0.3 fM,showing good selectivity and practical sample analysis ability.This method had a high signal-to-noise ratio,which was conducive to the development of photoelectric biosensor miniaturization.