Interface ligand engineering of Au nanoclusters with near-infrared boosted peroxidase-like activity for total antioxidant capacity analysis

Total antioxidant capacity (TAC) is a significant indicator for evaluating nutritional value of fruit and beverage industries, in the aspects of their reactive oxygen species (ROS) scavenging activity. The sensitivity and selectivity of the TAC assay based on the peroxidase (POD) assay is restricted by their poor catalytic activity. Herein, a simple and sensitive strategy for assessing TAC in fruits based on light (808 nm) boosted POD like activity of Au-25 nanoclusters (NCs) have been reported. The absorption bands of mercaptohexanoic acid (MHA)-protected Au-25 NCs could be extended into the near-infrared region (similar to 770 nm) by introducing neutrally charged ligands or 2,2'(ethylene dioxy) diethyl thiol (EDT)) as bi-thiol ligands, which may contribute to more obvious light enhanced POD activity. The most intense absorption at 770 nm can be obtained by the ratio of MHA/EDT=1.7:0.3 (denoted as MEA-17). Since we have confirmed that ROS is involved in the light enhanced POD like activity, the concentration of various antioxidants AA, GSH and L-Cys, can be analyzed by their inhibitory effect to the oxidation of TMB. More importantly, light enhanced POD like activity of MEA-17 have been successfully utilized to analysis TAC value in various fresh fruits. This work not only provide novel direction for the rational development of near-infrared light-enhanced POD-like nanozyme, but also further expands the prospect of the application of Au-25 NCs protected with thiols for TAC analysis.