Dual-mode electrochemical and colorimetric sensing of catechol enabled by a spatially engineered indium single-atom...

Catechol, a common aromatic diol pollutant, poses significant ecological risks due to its persistence and toxicity. However, precise monitoring is challenged by complex sample matrices when relying on a single analytical mode. To address this, a dual-mode sensing platform for catechol was developed using a spatially engineered indium (In) single-atom nanozyme. Highly dispersed In single atoms were anchored on a S,N-codoped porous carbon matrix (InSAs@S-NC) via a NaCl template-assisted ion-imprinting strategy, effectively preventing active site aggregation and enhancing catalytic performance. The InSAs@S-NC nanozyme exhibited outstanding oxidase-like activities, enabling the colorimetric detection of catechol through two distinct chromogenic pathways. When coupled with its inherent electrochemical activity, the nanozyme also facilitated highly sensitive electrochemical analysis for catechol. Consequently, the dual-mode sensing system based on InSAs@S-NC achieved wide linear ranges (colorimetric modes: 10-500 μM for reduction system and 5-200 μM for oxidation system, electrochemical mode: 2-443 μM) with low detection limits (0.11, 0.16, and 0.38 μM, respectively). Practical utility was demonstrated by analyzing catechol in environmental and beverage samples (water, sewage, and red wine), showing high recoveries (98.9-110.2%), good reproducibility, and consistent cross-verification between modes (deviation <5.6%). This study revealed that the spatial confinement of In atom sites promoted reactant affinity and electron transfer, underpinning enhanced multi-enzyme and electrocatalytic activities. This work highlighted spatial engineering as an effective strategy for designing robust multi-functional nanozymes and presented a reliable dual-mode sensing approach for environmental pollutant monitoring.