Highly active silver-based laccase-like nanozyme for colorimetric distinction and detection of phenylenediamine isomers

Abstract

Laccase-like nanozymes can efficiently simulate the catalytic performance of laccase while demonstrating superior cost-effectiveness and stability, and are considered as promising substances in the environmental protection field. Given the copper-containing structure of natural laccase, various copper-centered laccase mimics have been reported. However, certain laccase-like nanozymes with non-copper metal centers also exhibit excellent performance, even surpassing many copper-based laccase mimics. Despite this, they have not received sufficient attention, and therefore the field of non-copper-based laccase-like nanozymes requires further exploration and development urgently. To explore new avenues for non-copper laccase-like nanozymes, a silver-based laccase-like nanozyme (AgMal) with enhanced catalytic activity was successfully synthesized by utilizing silver ions as the active center coordinated with sodium malate in this study. AgMal exhibited superior activity and stability compared to natural laccase and efficiently catalyzed the oxidation of a series of laccase substrates. In light of the different colors and absorption spectra of environmental pollutants phenylenediamine isomers (o-phenylenediamine: OPD, m-phenylenediamine: MPD, and p-phenylenediamine: PPD) catalyzed by AgMal, an easy, sensitive, and rapid colorimetric approach was established for their identification and detection. The limits of detection (LOD) were 0.47 μM, 0.16 μM and 0.55 μM for OPD, MPD and PPD, respectively. Furthermore, a portable colorimetric-sensing platform based on the combination of a makeup cotton pad test strip and a smartphone has been designed to facilitate the rapid detection of OPD, MPD, and PPD without the need for additional instruments. This work provided valuable insights into the design and application of Ag nanozymes that mimic laccase while highlighting the substantial potential for developing non-copper laccase-like nanozymes.