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 (∼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.
Emerging artificial enzymes with reprogrammed and augmented catalytic activity and substrate selectivity have long been pursued with sustained efforts. The majority of current candidates have rather poor catalytic activity compared with natural molecules. To tackle this limitation, we design artificial enzymes based on a structurally well-defined Au 25 cluster, namely clusterzymes, which are endowed with intrinsic high catalytic activity and selectivity driven by single-atom substitutions with modulated bond lengths. Au 24 Cu 1 and Au 24 Cd 1 clusterzymes exhibit 137 and 160 times higher antioxidant capacities than natural trolox, respectively. Meanwhile, the clusterzymes demonstrate preferential enzyme-mimicking catalytic activities, with Au 25 , Au 24 Cu 1 and Au 24 Cd 1 displaying compelling selectivity in glutathione peroxidase-like (GPx-like), catalase-like (CAT-like) and superoxide dismutase-like (SOD-like) activities, respectively. Au 24 Cu 1 decreases peroxide in injured brain via catalytic reactions, while Au 24 Cd 1 preferentially uses superoxide and nitrogenous signal molecules as substrates, and significantly decreases inflammation factors, indicative of an important role in mitigating neuroinflammation.
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