Photoelectrochemical Aptamer Biosensor Of Antibiotic Based On Metal Sulfide

Photoelectroehemical（PEC）biosensors are based on the combination of photoactive materials and biological recognition elements,and monitor the corresponding biological recognition reactions through the changes of the current signal of the electrodes to achieve quantitative analysis of the measured objects.The PEC conversion efficiency of photoactive materials directly determines the analytical performance of sensors.Therefore,the selection of photoactive materials with excellent performance is of great significance for the construction of highly sensitive PEC biosensors.Metal sulfide composite materials have strong visible light absorption,simple and efficient synthesis methods,and excellent photoelectric catalytic performance,and have broad application prospect in biosensors.In order to improve the analytical performance of PEC biosensors,three new PEC aptasensing methods were constructed using metal sulfide semiconductors and their complexes as substrate materials,combined with terminal deoxynucleotidyl transferase（TdT）assisted signal amplification strategies,and applied in the detection of antibiotic in food and environment.The main work contents are as follows:1.Signal-off photoelectrochemical aptasensor for kanamycin:Strand displacement reaction combines p-n competitionIn this work,a "signal-off" PEC aptasensor for the determination of kanamycin was constructed based on the competitive quenching effect of p-n type semiconductors and strand displacement reaction（SDR）.The n-type semiconductor composite material AuNPs@MgIn₂S₄-graphene was used as photoelectric substrate material,and the capture DNA（S1）was immobilized on the electrode through Au-S.In the presence of kanamycin,SDR was triggered to obtain messenger DNA（S2）labeled by p-type CuInS₂ quantum dots,which was introduced into the electrode surface by the principle complementary base pairing.CuInS2 quantum dots can compete to consume electron donor（AA）and light energy in the PEC system,thereby quenching the anodic photocurrent of AuNPs@MgIn₂S₄-graphene.Under the optimized experimental conditions,the sensor was used for the quantitative analysis of kanamycin,with a linear range of 1 pM-10 μM,a detection limit of 1.70 pM,and good stability and selectivity.2.An ultrasensitive label-free photoelectrochemical aptasensor based on TdT amplification and catalytic reaction of G4/heminIn this work,an ultrasensitive PEC assay based on TdT and G-quadruplex/hemin（G4/hemin）catalyzed reaction-assisted signal amplification was established for the determination of ampicillin.A novel AuNPs@SnIn4S8-graphene composite material was used as photoactive material and obtained strong basic photocurrent signal.In the presence of the target,P1 obtained by SDR was introduced into the electrode surface,and a large amount of G4/hemin was formed after the addition of TdT and hemin.Subsequently,G4/hemin with simulated horseradish peroxidase activity was able to catalyze the oxidation of 4-chloro-1-naphthol by H₂O₂,forming benzo-4-chlorohexadienone precipitate on the surface of the modified electrode,which severely hindered electron transfer,effectively suppressing the photocurrent output.The PEC aptasensor had good stability and high sensitivity,and could be used for the quantitative analysis of ampicillin with a linear range of 10 fM-30 nM and a detection limit of 4.97 fM.3.An ampicillin photoelectrochemical aptasensor based on hemin-induced photocurrent polarity switchingIn this work,n-type semiconductor SnS was used as photoelectric substrate material to generate anodic photocurrent,AuNPs were used as carriers to synthesize SO-AuNPs-S1 complex and immobilized on the electrode surface to obtain more G4/hemin formed by the terminal polymerization of TdT.In the SnS/SO-AuNPs-G4/hemin system,due to the matched energy level between SnS and hemin,the photocurrent direction of the ITO/SnS electrode was changed from anodic photocurrent to cathodic photocurrent,and produced a relatively large cathodic photocurrent.This PEC aptasensor had good analytical performance for the target ampicillin,with a wide linear range（100 fM-500 nM）and good selectivity.