Hierarchical hematite/TiO2 nanorod arrays coupled with responsive mesoporous silica nanomaterial for highly sensitive photoelectrochemical sensing.

The photoelectrochemical (PEC) technique has resulted in substantial progress in chemical sensing applications. However the complicated photoelectrode modification procedures would enable undesired background noise and decreasing sensitivity. Hence, it is important to explore a new approach alternative to inconvenient substrate modification. Herein, inspired by the stimuli-responsive drug delivery systems, an innovative PEC system is developed for efficiently microRNA-21 (miRNA-21) tracing. Hierarchical nanocomposites based on hematite (α-Fe2O3) coated self-ordered titanium dioxide nanorod arrays (TiO2 NRAs) exhibited enhanced response to solar light, promoted charge carrier separation and transfer efficiency was adopted as photoelectrode directly. Functional mesoporous silica nanomaterial (MSN) is prepared as nanocarriers for efficient loading of Cu2+, further capped with miRNA-21 responsive capture RNA probe. Thereafter, the capture RNA probe endows the functional MSN with responsiveness to miRNA-21. With the presence of miRNA-21, this system is thus triggered and a quickly release of capped Cu2+ occurs due to the dissociation of capture RNA probe presented on the MSN surface via base-pair hybridization. The released Cu2+ was then served as electron acceptor reduced to Cu° at the counter electrode to enhance electron-hole pair separation efficiency, leading to a promoted photocurrent response. Consequently, the miRNA-21 can be accurately quantified. Taking advantage of its sensitivity and specificity, this versatile strategy demonstrates a new route for the design PEC sensing approach without any photoelectrode modification procedure, and holds great potential for biosensing and clinical diagnosis.