Amino-functionalized bimetallic MOF nanozyme via solvent-assisted ligand exchange for interference-free phenolic detection

Abstract

Natural laccase is promising for the detection of phenolic pollutants but suffers from inherent instability and high cost. To address these limitations, we proposed an amino-functionalization strategy to enhance the catalytic behavior of a bimetallic MOF nanozyme (Cu–Mn NMOF) via solvent-assisted ligand exchange (SALE). Mechanistic studies revealed that the introduced amino groups intrinsically modulated the electronic structure of the Cu centers (XPS shift: +0.7 eV) and facilitated enhanced synergistic electron transfer. Consequently, the amino-modified Cu–Mn NMOF not only exhibited superior laccase-like efficiency (V_max = 3.98 µM min⁻¹, K_m = 0.42 mM) compared to its precursor, but also obtained additional intrinsic oxidase-like functionality via electronic structure regulation. Importantly, while the modified electronic structure also endowed the nanozyme with an additional oxidase-like functionality, it effectively avoided the autoxidation of the chromogenic agent 4-aminoantipyrine (4-AP), thus ensuring an interference-free colorimetric signal during phenolic oxidation. Leveraging this robust laccase-driven pathway, Cu–Mn NMOF achieved a detection limit of 0.91 µM for phenolic pollutants within a broad linear range (0–150 µM). The nanozyme also exhibited excellent stability under harsh conditions and remarkable activity enhancement under high ionic strength. Furthermore, it demonstrated high reliability for practical environmental monitoring, achieving excellent recoveries (92.02–113.75%) in actual lake and tap water samples. By integrating amino-driven bimetallic synergy with an interference-free sensing pathway, this work establishes Cu–Mn NMOF as a practical and robust sensing platform for the detection of phenolic pollutants.