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

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.