Label-free immunosensor for detection of hepatitis C (HCV) core antigen using ternary polypyrrole-Ag doped ZnO-exfoliated graphene nanocomposite

A label-free immunosensor for detection of hepatitis C (HCV) core antigen was fabricated using a ternary nanocomposite based on polypyrrole (PPy), silver doped zinc oxide (Ag-ZnO) and exfoliated graphene (Ex-Gr). The negatively charged anticore mAbs 19D9D6 (1 NLB monoclonal antibodies) were immobilized at the PPy/Ag-ZnO/Ex-Gr 9 % nanocomposite surface as it is suitable for non-covalent (electrostatic) immobilization for fabricating the label-free immunosensor. The isoelectric point (IEP) achieved at around pH 7 for PPy shifts to the lower value of pH 5.75 for PPy/Ag-ZnO/Ex-Gr 9 % nanocomposite. The linear sweep voltammetric (LSV) analysis of the as-prepared samples indicate high electrochemical activity. Similarly, electrochemical impedance spec-troscopy (EIS) and cyclic voltammetry confirmed the hindrance in the faradaic processes due to the presence of the interfacial biomolecules layer, after surface modification confirming the fabrication of the immunosensor. The LSV current signal response decrement for the concentration range of antigen [HCV core nucleocapsid polypeptide (residues 13-40) (RNTNRRPQ DVKFPGGGQI VGGVYLLPRR)] ranging from 0.001 ng mL-1 to 200 ng mL-1 was performed depicting the hindrance to electron transfer increases with increase in the antigen concentration as antigen antibody interaction takes place thickening the insulative layer of biomolecules at the interface leading to gradual decrease in the current response. The limit of detection was measured to be approximately 0.41 pg mL-1, respectively (S/N = 3). The single interfering protein doesn't decrease the LSV current response for HCV (50 ng mL-1) depicting the immunospecificity i-e selectivity of the fabricated immu-nosensor. The as prepared label-free immunosensor displayed lower limit of detection, high selectivity and stability.