Applicability of the Dendrimer-quantum Dot (Den-QD) Bioconjugate as a Novel Nanocomposite for Signal Amplification in the Fabrication of Cocaine Aptasensor

A selective aptasensor was developed using the electrochemical transduction method for the ultrasensitive detection of cocaine. In this method, dendrimer-quantum dot (Den-QD) bioconjugate was utilized as a specific nanocomposite to efficiently fabricate the aptasensor. CdTe QD, which carries highly significant properties, was immobilized on the surface of a glassy carbon electrode (GCE), and polyamidoamine (PAMAM) dendrimer (Den) was covalently attached to the carboxyl-terminated surface of the CdTe QDs. This clever combination of QD and Den provides a highly stable matrix for the increased loading of aptamer (Apt) as a cocaine molecular receptor via covalent attachment. The Apt was functionalized with AuNPs leading to the amplification of the electrochemical signal. In this study, upon the incubation of cocaine on the aptasensor surface, the peak current of the redox probe decreased due to the hindered electron transfer reaction on the sensing surface. This study shows that the proposed aptasensor can detect cocaine by electrochemical impedance spectroscopy (EIS) technique at a linear range (5.00  10-3-6.00 nM) and a capability of detection down to 1.60 pM. The excellent specificity of this sensing system is demonstrated using some common analgesic drugs, and finally, the proposed aptasensor was successfully used to measure cocaine in the human serum sample. The proposed methodology may hold great promise for the design of other aptasensors and immunosensors based on the use of the Den-QD bioconjugate as a nanocomposite with high performance.