Visual test paper based on Au/δ-MnO2 hollow nanosphere oxidase-like activity regulation using hexavalent chromium as a smart switch

Paper-based sensing platform is a point of need analytical toolkit for safety testing. However, the sensitivity, specificity, and simplicity are still challenging. Herein, we report a novel strategy (Au/S-MnO2 hollow nanosphere and 3,30,5,50-tetramethylbenzidine (TMB) induced test strips for signal-on detection) that can be utilized for hexavalent chromium (Cr6+) detection. Interestingly, Cr6+ (CrO42-) as a smart switch can remarkably enhance the oxidase-like activity of Au/S-MnO2 hollow nanosphere. The presence of Cr6+ can regulate the surface electronic redistribution of Au/S-MnO2 and adjust the geometric configuration, which leads to the improvement in oxidase-like activity of Au/S-MnO2. As a proof-of concept application, a visual paper-based sensing platform of Cr6+ along with quantitative analysis by the test strips was successfully constructed. This paper-based sensing platform exhibits a linear range with excellent selectivity for other interfering substances and lower limit of detection of 0.09 pmol center dot L-1, providing a promising toolkit at-home Cr6+ measurement and environmental monitoring.