Manganese dioxide nanosheet-mediated etching of gold nanorods for a multicolor colorimetric assay of total antioxidant capacity

A simple and efficient strategy based on the manganese dioxide (MnO2) nanosheet-mediated etching of gold nanorods (AuNRs) has been demonstrated, affording an effective and convenient way to develop a high-resolution multicolor colorimetric method for the visual detection of antioxidants. The UV-visible absorption spectroscopy and transmission electron microscopy results revealed that the MnO2 nanosheets etched the AuNRs quickly in weakly acidic solutions at room temperature, resulting in a significant blue shift in the AuNR longitudinal local surface plasmon resonance peak and vivid color changes. The feasibility of the etching process was theoretically evaluated by comparing the standard electron potentials of Au(I)/Au(0) and Mn(IV)/Mn(II). Changes in the chemical valencies of Au and Mn during the etching process were analyzed via X-ray photoelectron spectroscopy, which further confirmed that the etching process occurred. Key factors, including the concentrations of the MnO2 nanosheets, cetyltrimethylammonium bromide, and H+, and incubation time, were then investigated. The application of MnO2 nanosheet-mediated AuNR etching for antioxidant analysis was based on the antioxidant-induced decomposition of MnO2 nanosheets. With the merits of simplicity and user friendliness, this method provides a promising platform for the visual detection of total antioxidant capacity in real beverages.