Surface plasmon-enhanced aptamer-based fluorescence detection of cocaine using hybrid nanostructure of cadmium-free ZnSe/In2S3 core/shell quantum dots and gold nanoparticles

Cocaine abuse remains a global public health problem and a contributing factor to various social problems. In this work, we report on the development of a novel amphiphilic polymer (A-polym)-functionalized cadmium-free ZnSe/In2S3 core/shell quantum dots (QDs)-cationic cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticle (AuNP) fluorescence nanoprobe for cocaine. ZnSe/In2S3 QDs were synthesized using the classic organometallic synthetic route for group II – VI semiconductor QDs and was surface-capped with organophosphorous-based ligands and organic-based stabilizers. A-polym, synthesized using an anhydride-capped polymer backbone and a nucleophilic agent, was used as a capping agent to coat and stabilize the QDs surface. The A-polym-coated QDs was electrostatically linked to cationic cetyltrimethylammonium bromide (CTAB)-capped gold nanoparticles (AuNPs) to form an A-polym-QDs-AuNP nanohybrid. The electrostatic interaction between the A-polym-coated QDs and CTAB-AuNPs quenched the fluorescence emission of the bound QDs. An MNS 4.1 anticocaine thiolated DNA aptamer (Aptm) was adsorbed on the A-polym-QDs-AuNP surface to form an Aptm-A-polym-QDs-AuNP nanoprobe. Upon interaction of cocaine with the Aptm-A-polym-QDs-AuNP nanoprobe, the fluorescence of the bound QDs was remarkably enhanced based on localized surface plasmon resonance-induced fluorescence emission signal. In general, the QDs functioned as the fluorophore reporter, CTAB-AuNP as a plasmon amplifier and the Aptm as the receptor. Under optimum reaction conditions, cocaine was selectively and quantitatively detected with a detection limit of 0.8 nM. Selectivity was achieved against other drugs and cocaine metabolites. The efficacy of the Aptm-A-polym-QDs-AuNP nanoprobe to detect cocaine in adulterated cocaine samples was successfully achieved.