Dual-modal biosensor for mercuric ion detection based on CuO@CuS/D-TA COF heterojunction with excellent catalase-like, electrochemical and photoelectrochemical properties.

In this study, a dual-mode biosensor based on the heterojunction of CuO@CuS/D-TA COF was constructed for ultra-sensitive detection of Hg using both photoelectrochemical and electrochemical approaches. Briefly, a 2D ultra-thin covalent organic framework film (D-TA COF film) with excellent photoelectrochemical signals was prepared on ITO surfaces through an in situ growth method. Subsequently, the probe H1 was immobilized onto the biosensor via Au-S bonds. In the presence of Hg, the formation of T-Hg-T complexes triggered hybridization chain reactions (HCR), leading to the attachment of abundant CuO@CuS probes onto the biosensor. As a p-type semiconductor, CuO@CuS could form a heterojunction with the underlying D-TA COF films. Meanwhile, it exhibited catalase-like activity, and the O produced by its catalytic decomposition of HO can interact with the D-TA COF films, thus achieving double amplification of the photocurrent signal. Benefiting from the excellent and inherent Cu/Cu redox pairs of CuO@CuS, satisfactory differential pulse voltammetry (DPV) signals were obtained. As expected, the dual-mode biosensor was realized with wider linear ranges and low detection limits. Additionally, the analytical performance for Hg in real water samples was excellent. Briefly, this suggested approach offers a facile and highly efficient modality for monitoring heavy metal ions in aquatic environments.