An ultrasensitive and selective electrochemical aptasensor based on rGO- MWCNTs/Chitosan/carbon quantum dot for the detection of lysozyme

Using a nanocomposite of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS on glassy carbon electrode (GCE) surface, an ultrasensitive and selective electrochemical aptasensor was prepared for lysozyme detection. The proposed nanocomposite (rGO-MWCNTs/CS/CQD) can provide a high surface-to-volume ratio, high conductivity, high stability, great electrocatalytic activity, and a suitable site for better immobilization of aptamers (due to the existence of many amino and carboxyl functional groups, and remaining oxygen-related defects properties in rGO). In addition, this nanocomposite allows considerable enhancement of the electrochemical signal and contributes to improving sensitivity. The amino-linked lysozyme aptamers were easily immobilized onto the nanocomposite through covalent coupling between the amino groups of aptamer and amino groups of the nanocomposite using glutaraldehyde (GLA) linker. For the aptasensor characterization, electrochemical methods including differential pulse voltammetry (DPV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used. In this electrochemical aptasensor, in the presence of lysozyme, the immobilized aptamer selectively catches the target lysozyme on the electrode interface that leads to a decrease in the DPV peak current and an increase Rct in EIS as an analytical signal. Using the obtained data from DPV and EIS techniques, two calibration curves were drawn. The proposed anti-lysozyme aptasensor has two very low LODs 3.7and 1.85 fmol L-1 within the wide detection ranges of 10 fmol L-1 to 50 nmol L-1, and 20 fmol L-1 to 50 nmol L-1 for EIS and DPV calibration curves, respectively. The aptasensor also shows high reproducibility, sensitivity, rapidity, and specificity for lysozyme that could be used in biomedical fields.