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/δ-MnO 2 hollow nanosphere and 3,3′,5,5′-tetramethylbenzidine (TMB) induced test strips for signal-on detection) that can be utilized for hexavalent chromium (Cr 6+ ) detection. Interestingly, Cr 6+ (CrO 4 2− ) as a smart switch can remarkably enhance the oxidase-like activity of Au/δ-MnO 2 hollow nanosphere. The presence of Cr 6+ can regulate the surface electronic redistribution of Au/δ-MnO 2 and adjust the geometric configuration, which leads to the improvement in oxidase-like activity of Au/δ-MnO 2 . As a proof-of-concept application, a visual paper-based sensing platform of Cr 6+ 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 μmol·L −1 , providing a promising toolkit at-home Cr 6+ measurement and environmental monitoring. Graphical abstract