Channel Effect Enhancing Hg2+ Adsorption to Modulate d-Orbitals of the Active Centers for Regulating Enzymatic Activity.

Nanozymes have shown great promise in detecting heavy metal pollution (specifically Hg2+), while their development and application are usually hindered by vague catalytic mechanism. Herein, NiCo2O4 nanosheets supported Pd nano (Pd@NiCo2O4) with controllable morphologies were constructed by a surfactant-oriented strategy. Taking advantage of the anionic property of sodium dodecyl sulfonate (SDS), the surface of SDS-NiCO2O4 nanosheets (S-NiCo2O4) exhibits channel features. Compared with the CTAB-directed Pd@NiCo2O4 (C-Pd@NiCo2O4), the channel effect of S-Pd@NiCo2O4 can more easily adsorb catalysed substrates (TMB), resulting in a red shift of the absorbance. This can switch the enzymatic activity from bifunctional performance (OXD and POD) to monofunctional activity (OXD). Significantly, the channel effect of S-Pd@NiCo2O4 enhances the adsorption of Hg2+, which suppresses the formation of Pd-Hg alloy and promotes the formation of HgO. The formation of Pd-Hg alloy in C-Pd@NiCo2O4, enhances enzymatic activity by facilitating electron transfer through d-d orbital interactions. In contrast, the Hg-O interaction can modulate the d-band structure of S-Pd@NiCo2O4 to reduce its enzymatic activity. Therefore, the S-Pd@NiCo2O4 can overcome negative effects (high endogenous H2O2 disturbing the fluorescence signal of C-Pd@NiCo2O4 for Hg2+ detection) of complex TME to visually detect Hg2+ in cancer cells.