Luminescent determination of propineb fungicide by using a carbon quantum dots-europium ions system

We propose a modification of lanthanide-sensitized luminescence (LSL) to increase the selectivity and sensitivity of analytical methods based on this detection. LSL consists in the formation of complexes of lanthanide ions and organic compounds. Then, an intramolecular energy transfer occurs from the excited state of the ligand (organic analyte) to the emitting level of the lanthanide. The utilization of luminescent nanoparticles (carbon quantum dots, CQDs) in LSL systems can enhance their sensitivity and selectivity. CQDs can react with lanthanide ions through their carboxylic groups. These systems can thus be used as time-resolved luminescent probes. Propineb (PPN), a well-known dithiocarbamate fungicide, has been selected as the target analyte to show the advantages of using CQDs in LSL systems. The method proposed is based on the quenching produced by PPN in europium-CQDs luminescence, obtaining a detection limit of 0.03 μg mL^-1 PPN and a method detection limit of 3 mg kg^-1 in capers (bud and fruit), fulfilling the maximum residue limit in these samples (25 mg kg^-1). The results showed that the use of nanoparticles in LSL systems may provide novel and simple analytical methods for the screening of contaminants in the agri-food sector.