Behzad Rezaei, Hamid Reza Jamei, Ali Asghar Ensafi

A B S T R A C T
An aptamer-based method is described for the electrochemical determination of lysozyme. A glassy carbon electrode was modified with a nanocomposite composed of reduced graphene oxide (rGO), multi-walled carbon nanotubes (MWCNTs), chitosan (CS), and a synthesized carbon quantum dot (CQD) from CS. The composition of the nanocomposite (rGO-MWCNT/CS/CQD) warrants a high surface-to-volume ratio, high conductivity, high stability, and great electrocatalytic activity. This nanocomposite provides 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 immobilized on the nanocomposite through covalent coupling between the amino groups of the aptamer and the amino groups of the nanocomposite using glutaraldehyde (GLA) linker. The modified electrode was characterized by electrochemical methods including differential pulse voltammetry (DPV), cyclic voltammetry (CV), and
electrochemical impedance spectroscopy (EIS). In the presence of lysozyme, the immobilized aptamer selectively caught the target lysozyme on the electrode interface that leads to a decrease in the DPV peak current and an increase in Charge Transfer Resistance (Rct) in EIS as an analytical signal. Using the obtained data from DPV and EIS techniques, two calibration curves were drawn. The anti-lysozyme aptasensor proposed has two very low LODs. These measures are 3.7 and 1.9 fmol L−1 within the wide detection ranges of 20 fmol L−1 to 10 nmol L−1, and 10 fmol L−1 to 100 nmol L−1 for DPV and EIS calibration curves, respectively. The GCE/rGO-MWCNT/CS/ CQD showed sensitivity, high eproducibility, specificity and rapid response for lysozyme which can be used in biomedical fields.

Keywords:
Aptamer, Lysozyme, Electrochemical aptasensor, Reduced graphene oxide, Multi-walled carbon, nanotubes, Chitosan, Carbon quantum dot