Fluorescence Turn‐Off‐On Sensing Strategy for the Detection of Pb2+ and Metalaxyl Fungicide Using Yellow Fluorescent Carbon Dots From Cordia dichotoma Fruits

ABSTRACT In this work, a facile and rapid fluorescence turn‐off‐on sensing method was developed for the detection of Pb 2+ and metalaxyl fungicide in environmental samples using yellow carbon dots (CDs) from Cordia dichotoma fruits. The prepared C. dichotoma ‐CDs showed the emission band (𝜆 Em ) at 535 nm under 448 nm of excitation wavelength. The fluorescence intensity of C. dichotoma ‐CDs quenches by Pb 2+ ion and then restores by metalaxyl fungicide, favoring to develop a fluorescence turn‐off‐on sensing strategy. The intensity ratios ( I 0 / I and I / I 0 ) are linear against Pb 2+ (0.01–50 μM) and metalaxyl fungicide (0.025–10 μM) concentrations, offering the detection limits of 0.0054 and 0.0087 μM for Pb 2+ and metalaxyl fungicide, respectively. Additionally, the potential application of C. dichotoma ‐CD‐based fluorescence turn‐off‐on sensing approach was effectively demonstrated for Pb 2+ and metalaxyl fungicide assays in real samples, which confirms that C. dichotoma ‐CDs act as “turn‐off‐on” fluorescent probe for assaying of Pb 2+ and metalaxyl fungicide, respectively.