Universal Ratiometric Photoelectrochemical Bioassay with Target-Nucleotide Transduction-Amplification and Electron-Transfer Tunneling Distance Regulation Strategies for Ultrasensitive Determination of microRNA in Cells.

A universal ratiometric photoelectrochemical (PEC) bioassay, which could be readily expanded for ultrasensitive determination of various targets in complex biological matrixes, was established by coupling a target-nucleotide transduction-amplification with DNA nanomachine mediated electron-transfer tunneling distance regulation strategies. With the help of target-nucleotide transduction-amplification strategy, the one input target signal could be transducted to corresponding multiple output DNA signals by nucleotide specific recognition technology, simultaneously leading to an efficient signal amplification for target. Then the output DNA could initiate the formation of four-way junction DNA nanomachine through binding-induced combination, by which the electron-transfer tunneling distance between photoactive materials and sensing interface could be regulated, simultaneously resulting an enhanced photocurrent signal from SiO2@methylene blue (SiO2@MB) as wavelength-selective photoactive material in close proximity to sensing interface and a reduced photocurrent signal from another wavelength-selective photoactive material CdS quantum dots (CdS QDs) away from sensing interface for photocurrent signal ratio calculation. Using microRNA-141 (miRNA-141) as target model, the constructed biosensor demonstrated favorable accuracy and excellent sensitivity down to the femtomolar level. Impressively, the proposed assay overcame the heavy dependence of target on photoactive materials in current ratiometric PEC assay and demonstrated admirably universal applicability for determination of various targets such as metal ions, miRNAs, DNAs, and proteins by merely two different photoactive materials (SiO2@MB and CdS QDs), paving the way to application of universal ratiometric PEC assay in environmental tests, clinical diagnosis, and other related subjects.