Development of electrochemical detection for cortisol and hepatitis C virus core antigen

Abstract

This dissertation focused on the development of electrochemical biosensors for the determination of essential biomarkers by using a label-free assay. This dissertation can be divided into two parts. In the first part, a non-invasive aptamer-based electrochemical biosensor using disposable screen-printed graphene electrodes (SPGEs) was developed for simple, rapid, and sensitive determination of cortisol. The specific recognition of the cortisol DNA aptamer (CApt) was modified with streptavidin magnetic beads (MBs) before simple immobilization onto the electrode surface using a neodymium magnet. The electrochemical behavior of the aptamer-based biosensor was assessed by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Furthermore, EIS was also employed to perform the quantitative analysis of the target analyte. Under optimal conditions, a linear range from 0.10 to 100 ng mL-1 with a low detection limit of 2.1 pg mL-1 was obtained. The proposed biosensing system exhibited a satisfactory recovery in the range 97.4-109.2% with 5.7-6.6% RSD in spiked artificial human sweat. For the second part, a paper-based electrochemical immunosensor was prepared based on Pt nanoparticles deposited on single-walled carbon nanotubes (PtSWCNTs) modified SPGE for hepatitis C virus (HCV) infection diagnosis. PtSWCNTs, synthesized via deposition precipitation (DP) method, were first introduced as a substrate for immobilizing antibodies on the electrode surface and then enhancing the electrochemical sensitivity. The hepatitis C virus core antigen (HCV-cAg) level was determined by differential pulse voltammetry (DPV) using [Fe(CN)6]3-/4- as a redox solution. The proposed biosensor offers a linear range from 0.05 to 1,000 pg mL-1, a low limit of detection (LOD) of 0.015 pg mL-1, excellent response precision, and high selectivity. Furthermore, the proposed immunosensor has been utilized to quantify HCV-cAg in human serum samples with reliable results compared to standard immunoassays. Therefore, these electrochemical biosensors have the potential to be versatile and feasible for simple, sensitive, selective, disposable, and low-cost clinical diagnosis.