Enzyme-free carbon dots@MgO nanocomposite as an efficient sensor for on-site detection and degradation of paraoxon toxins

Serial nanocomposites consisting of blue fluorescent carbon dots (B-CDs) and MgO nanoparticles were facilely prepared. Then on-site detection and degradation of ethyl-paraoxon were achieved and evaluated. It was revealed that ethyl-paraoxon was firstly decomposed into p-nitrophenol by MgO. Then, p-nitrophenol could significantly quench the fluorescence of decorated B-CDs due to an inner filter effect (IFE). The 0.05B-CDs@MgO showed excellent comprehensive performance among the serial xB-CDs@MgO samples due to its relatively high degradation ability towards ethyl-paraoxon and potent initial fluorescence emission intensity at an excitation wavelength of 360 nm between pH 4 and 10. Finally, based on the IFE, on-site paper sensors via color recognition app on a smartphone were explored compared with a conventional fluorescence spectrometer. Both the quantitative fluorescence intensities and G/B values showed the multi-piecewise linear correlations to ethyl-paraoxon concentration up to 3000 μg/mL in river water with a limit of detection to 0.06 μg/mL and 3.48 μg/mL as well as high recovery rates between 99%-102% and 95%–116%, respectively. The in vitro cytotoxicity and phytotoxicity assessment of the 0.05B-CDs@MgO revealed dose-dependent effects. Such portable and integrated fluorescent B-CDs@MgO nanocomposites on paper arrays show excellent potential in shortening the detection time and reducing the detection cost as a new strategy for the on-site quantitative detection and degradation of ethyl-paraoxon in actual river water.