Exciton–Plasmon Interactions between CdS@g-C₃N₄ Heterojunction and Au@Ag Nanoparticles Coupled with DNAase-Triggered Signal Amplification: Toward Highly Sensitive Photoelectrochemical Bioanalysis of MicroRNA

Novel exciton–plasmon interactions (EPI) between CdS@g-C3N4 heterojunction and Au@Ag nanoparticles (NPs) was introduced for the first time into the photoelectrochemical (PEC) biosensing system for highly sensitive microRNA-21 detection using duplex-specific nuclease-assisted cycle amplification for sensitivity enhancement. The photoelectrode of CdS@g-C3N4 nanowires could generate a great photocurrent because of the formation of the p–n heterojunction. Due to the natural absorption overlap, the exciton of CdS@g-C3N4 and the plasmon of Au@Ag NPs could be induced simultaneously to form EPI. Specifically, the perfect overlap of the wide absorption spectrum of Au@Ag NPs with the photoluminescence spectrum of CdS@g-C3N4 allows the resonance energy transfer and EPI between CdS@g-C3N4 nanowire and Au@Ag NPs simultaneously. The effective EPI renders the signal change modulated by the interparticle distance significantly. Such a signaling mechanism was then used to construct the PEC biosensor for microRNA-21 detection, within which the duplex-specific nuclease (DSN) was further introduced to enhance the sensitivity. The constructed PEC biosensor exhibits the sub-fM level (0.05 fM) detection of microRNA-21 with a wide range from 0.1 fM to 1.0 nM. In complex biological samples, the proposed method also possesses good specificity, reproducibility, and stability.