A biosensor based on TiO2/Sb2S3 nanorod array for visible-light induced photoelectrochemical detection of miRNA-155

• A biosensor based on TiO 2 /Sb 2 S 3 nanorod arrays (NRAs) is constructed. • It is the first report of photoelectrochemical sensor based on Sb 2 S 3 NRAs. • Sb 2 S 3 NRAs offer good light-harvesting and efficient charge transport. • TiO 2 /Sb 2 S 3 heterojunction promotes efficient charge separation. • The biosensor achieves the low LOD (0.42 fM) and wide linear region (1 fM–0.1 µM). The aberrant expression of microRNAs (miRNAs) has a close association with the onset and progression of various diseases. MiRNAs have become potential biomarkers for diagnostic applications. Photoelectrochemical (PEC) detection of miRNAs is a highly promising analytical technique. Its performance primarily depends on the following characteristics of semiconductor materials deposited on photoelectrodes: i good light-harvesting capability, ii effective charge separation and transport, and iii large specific surface area. Semiconductor heterojunction based on zero-dimensional nanoparticles and/or two-dimensional nanosheets can ensure efficient charge separation and large active area for PEC assay, but its charge transport path is not well established due to the nanoparticle and/or nanosheet interface. Heterojunction based on one-dimensional semiconductor nanorod arrays (NRAs) can improve the performance of charge transport, but common TiO 2 or ZnO NRAs have poor photoresponse to visible light, and biotoxic narrow band-gap semiconductors (e.g., CdTe and CdS) may be used cooperatively. Therefore, to construct PEC biosensors with low toxic materials, which satisfy all the above characteristics, is still severely challenged. Herein, the heterojunction of TiO 2 /Sb 2 S 3 NRAs is fabricated as the core components of the PEC biosensor for miRNA detection, following the structure of FTO/TiO 2 /Sb 2 S 3 NRAs/Au/thiol-modified RNA probes. Using miRNA-155 as a detection target, the detection can be achieved by photoelectric signal enhancement when the probe RNAs hybridizing with the miRNAs. The appropriate band gap (i.e., 1.64 eV) and large extinction coefficient of Sb 2 S 3 offer favorable photoresponse to visible light; the TiO 2 /Sb 2 S 3 heterojuction promotes charge separation at the interface; the Sb 2 S 3 NRAs with dominant [hk1] orientation ensures effective charge transport and large specific surface area. Excellent performance of the biosensor is achieved, including the wide linear region (i.e., from 1 fM to 0.1 µM), the low limit of detection (i.e., 0.42 fM), the good photocurrent stability with a relative standard deviation of 0.76 %, the outstanding detection selectivity, and the good repeatability. To our knowledge, it is the first report of a PEC sensor based on Sb 2 S 3 NRAs, offering a promising approach for evaluating miRNA expression.