Cadmium-free silica-encapsulated molecularly imprinted AuZnCeSeS quantum dots nanocomposite as an ultrasensitive fluorescence nanosensor for methamphetamine detection

One of the major challenges facing forensic drug analysis is the difficulty in detecting ultralow concentration of illicit drugs in biological matrices without the need for an extraction or a pre-treatment step. This work report on the development of a novel AuZnCeSeS quantum dots (QDs)-molecular imprinted polymer (MIP) nanocomposite fluorescent probe for methamphetamine (METH) recognition. Silica-coated AuZnCeSeS QDs were synthesized and characterized using spectrophotometric, spectroscopic and electron microscopy techniques. Via a free radical polymerization reaction, a thin layer of MIP shell with METH as the template was coated around the QDs surface leading to the formation of a QDs-MIP nanocomposite probe. The MIP coating passivated the QDs surface leading to radiative fluorescence enhancement of the bound QDs. Under optimum reaction conditions, METH was selectively and quantitatively detected via a fluorescence quenching reaction process. The unique selectivity of the nanoprobe for METH recognition showed clearly that METH was able to precisely re-bind to the MIP surface with size and shape reorganization. While the MIP shell functioned to provide the required selectivity, the AuZnCeSeS QDs functioned to fluorescently report the surface binding interaction. The use of a AuZnCeSeS QDs-non-imprinted polymer as probe to detect METH resulted in poor sensitivity and selectivity; hence, demonstrating the suitability of the AuZnCeSeS QDs-MIP nanoprobe to accurately detect METH. METH was detected within a wide concentration range from 0.05 to 50,000 nM with a detection limit of ∼0.02 nM (0.0036 ng/mL). The developed AuZnCeSeS QDs-MIP nanoprobe was efficiently used to detect METH in untreated urine sample with recovery efficiency from ∼100 to 110%