Signal-off photoelectrochemical determination of miRNA-21 using aptamer-modified In2O3@Cu2MoS4 nanocomposite.

In2O3@Cu2MoS4 nanocomposite with superior photoelectrochemical (PEC) performance is used for the first time as a photoactivity material, and a signal-off PEC biosensing platform for miRNA detection has been successfully constructed. Firstly, the Cu2MoS4 nanosheets are synthesized by a hydrothermal method, and then, the homogeneous In2O3 nanoparticles (In2O3 NPs) are synthesized by calcination in the air. The In2O3@Cu2MoS4 nanocomposite is constructed with the Cu2MoS4 nanosheets as matrix and In2O3 NPs as sensitizer through a layer-by-layer assembly strategy. The nanocomposite with a tight interface and the matched band structure restrains the electron-hole pair recombination. Under visible light (400-700 nm), the nanocomposite exhibits a strong initial signal. With the catalyzed hairpin assembly, dozens of PbS quantum dots (QDs) are introduced on the surface of an electrode, significantly reducing the photocurrent of n-type In2O3@Cu2MoS4. Since PbS QDs can compete with the nanocomposite for light energy and electron donors, the signal decreased. Under optimal conditions, the biosensor manifests a broad linear range (1 fM-1 nM) and a low detection limit of about 0.57 fM, at a working potential of 0 V (vs. Ag/AgCl). The recovery of spiked human serum is between 94.0 and 102%, and the relative standard deviation (RSD) is between 1.3 and 2.7%. Therefore, the as-fabricated biosensor exhibits a potential for the determination of miRNA-21 in practical applications.Graphical abstract The In2O3@Cu2MoS4 nanocomposite owns a strong anode photocurrent signal, which can be used as a photoactive material to construct a "signal-off" biosensor for the detection of miRNA in non-enzymatically catalyzed hairpin assembly (CHA) reaction.