ZnIn2S4 QDs@TiO2 nanosphere-BiOI double heterojunction combined with unique tripod DNA walker amplification for photoelectrochemical biosensing of microRNA-21

In this study, a new amplified signal probe of ZnIn2S4 quantum dot@TiO2 nanosphere was used to sensitize the BiOI substrate, which was combined with a unique tripod DNA walker to develop a new photoelectrochemical (PEC) biosensor for microRNA-21 (miRNA-21) assay. TiO2 has good PEC activity for its narrow band gap, and a large number of ZnIn2S4 quantum dots (QDs) were attached to the TiO2 to form a good heterojunction, realizing double enhancement of PEC performance. Moreover, a tripod DNA walker for target-cycling amplification was synthesized using a simple catalytic hairpin assembly (CHA). After DNA hairpin 5 (HP5) was linked to the BiOI-modified electrode, the prepared three-legged DNA walker opened HP5 DNA, and formed a single-stranded DNA (ssDNA). Then the ZnIn2S4 QDs@TiO2 signal probe was linked to the electrode by specific hybridization of ssDNA with the tripod walker, realizing noticeable amplification of PEC signal for sensitive detection of miRNA-21. This work combined the excellent PEC characteristic, the amplified signal of ZnIn2S4 QDs@TiO2 heterojunction, and an enzyme-free tripod walker amplification technique to achieve sensitive detection of target, which opens a new PEC analysis method for clinical application.

Automated summary

In this study, a new photoelectrochemical (PEC) biosensor was developed for the sensitive detection of miRNA-21 using a ZnIn2S4 quantum dot@TiO2 nanosphere as an amplified signal probe. The PEC activity of TiO2 and the enhanced performance of the ZnIn2S4 QDs@TiO2 heterojunction were combined with a tripod DNA walker for target-cycling amplification. This work opens up a new PEC analysis method for clinical application by utilizing the excellent PEC characteristic, amplified signal of ZnIn2S4 QDs@TiO2 heterojunction, and an enzyme-free tripod walker amplification technique.