Fabrication of a near-infrared fluorescence-emitting SiO2-AuZnFeSeS quantum dots-molecularly imprinted polymer nanocomposite for the ultrasensitive fluorescence detection of levamisole

Levamisole is an anthelminthic drug that is usually used as a cutting agent to lace illicit cocaine samples and has been classified as a dangerous substance. In this work, we report on the fabrication of a novel fluorescence sensor for levamisole using AuZnFeSeS alloyed quantum dots (QDs)-molecularly imprinted polymer (MIP) nanocomposite. Firstly, organic-phased AuZnFeSeS QDs were synthesized via the organometallic hot-injection pyrolysis of metal precursors, surfactants, and organic ligands. Silica (SiO2) was then encapsulated on the QDs surface to render it compact, stable, and biocompatible. Via a free radical polymerization approach, a robust MIP shell templated with levamisole was coated around the SiO2-AuZnFeSeS QDs surface to form a AuZnFeSeS QDs@MIP core/shell nanocomposite. Passivation of the SiO2-AuZnFeSeS QDs core surface with the MIP shell led to radiative exciton recombination process, whereby the QDs fluorescence was enhanced. Interestingly, the SiO2-AuZnFeSeS QDs was characterized by rod-shaped and spherical-shaped particle morphology. Under optimum conditions, the fluorescence of the AuZnFeSeS QDs@MIP nanocomposite was quenched in the presence of levamisole and was selective against other tested drugs. Quantitative detection was achieved in the concentration range of 0.5 – 100 μM with a limit of detection of 0.05 μM (47.4 nM). Validation of the MIP-levamisole affinity was demonstrated by the superior sensitivity of the AuZnFeSeS QDs@MIP over the AuZnFeSeS QDs@NIP (non-templated material). Levamisole was successfully detected in a mixed drug sample containing cocaine with satisfactory analytical recoveries. This work is the first reported use of a cadmium-free quintenary alloyed QDs@MIP nanocomposite fluorescence detection system for levamisole.