Multi-shaped cationic gold nanoparticle-L-cysteine-ZnSeS quantum dots hybrid nanozyme as an intrinsic peroxidase mimic for the rapid colorimetric detection of cocaine

Current presumptive tests for illicit drugs can suffer from false positive results and poor selectivity, and consequentially there is a need to develop new colour spot tests specifically designed to circumvent these existing challenges. In this work, we report on a new fluorescent hybrid nanozyme peroxidase-like catalytic colorimetric sensor and demonstrate proof of concept of this novel colorimetric-specific presumptive test for cocaine. A novel peroxidase-mimic hybrid nanozyme was developed based on the localized surface plasmon resonance-enhanced fluorescence interaction between multi-shaped cationic cetyltrimethylammonium bromide (CTAB)-functionalized gold nanoparticles (AuNPs) and anionic non-cadmium fluorescent-emitting _L -cysteine-capped ZnSeS alloyed quantum dots (QDs). The affinity-based interaction of cocaine with the QDs-CTAB-AuNP surface was induced by its distinct structural conformation and this forms the basis for the selective recognition. Thus, the hybrid nanozyme could function both as a catalytic affinity-based receptor and as an optical signal transducer based on the catalysed oxidation of 3,5,5-tetramethylbenzidine by H ₂ O ₂ . A positive bluish-green colour, specific to cocaine recognition, was colorimetrically obtained under optimum catalytic conditions. The optimized assay system detected cocaine within two minutes with unique specificity and distinct colour reaction. Under the optimum cocaine reaction conditions, the analysis of other substances and drugs on the colorimetric response of the QDs-CTAB-AuNP hybrid nanozyme revealed no colour interference, thus demonstrating that the developed probe could be utilized as a presumptive colour spot test for cocaine.