Visible-light induced photoelectrochemical biosensor for the detection of microRNA based on Bi sub(2)S sub(3) nanorods and streptavidin on an ITO electrode

We demonstrate a photo-electrochemical biosensor for the sensitive and specific detection of microRNA using Bi sub(2)S sub(3) nanorods as a photoactive material and streptavidin as the unit that inhibits photocurrent. Bi sub(2)S sub(3) nanorods were synthesized hydrothermally in organic phase and displayed excellent light-to-current conversion efficiency. The Bi sub(2)S sub(3) was deposited on an indium tin oxide (ITO) slice and then modified with gold nanoparticles onto which biotinylated hairpin probe DNA was deposited as a monolayer. Following hybridization between the biotinylated probe DNA and the target microRNA, the stem-loop structure of the probe DNA was unfolded and the biotin directed outwards into the solution. Streptavidin was then added to bind to biotin via the strong streptavidin-biotin interactions. This causes the photocurrent of the modified ITO to decrease due to steric hindrance that blocks the transfer of electrons from added ascorbic acid to the surface of the electrode. The method has a detection limit as low as 3.5 fM of microRNA and can excellently discriminate even singly mismatched microRNA. The method was successfully applied to investigate the effect of abscisic acid on the expression level of microRNA-159a in seeds of Arabidopsis thaliana. We conclude that the assay presented here has a large potential as a method for quantification of microRNA and for studying the epigenetic regulation of flowering plants. Figure The photocurrent generation and decrease mechanism of the PEC biosensor.