Identifying the active site of ultrathin NiCo LDH as an efficient peroxidase mimic with superior substrate affinity for sensitive detection of hydrogen peroxide

Nanozymes have been extensively investigated to imitate protein enzymes in biomimetic chemistry and the identification of the active site is believed to be the pre-requisite before one can effectively regulate their activity. Herein, ultrathin NiCo LDH nanosheets are synthesized via a fast co-precipitation at room temperature and can be stably dispersed in water without any additives of surfactants or organic solvents. By tuning the ratio between Ni and Co in LDH nanosheets, the activity is tuned and their peroxidase-like activity is determined by Co sites that show higher affinity to both 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide (H₂O₂) due to the strong Lewis acidity of Co³⁺ and the low redox potential of Co³⁺/Co²⁺. Together with their small crystallite size, ultra-thin thickness and tunable composition, NiCo LDH is used as a nanozyme for highly sensitive colorimetric detection of H₂O₂ and the limit of detection (LOD) reaches 0.48 μM.