A new Aptasensor to detect Salmonella Typhi Hemolysin E protein utilising a graphene oxide-chitosan modified printed circuit board gold electrode.

This study presents the first report of HlyE protein (HlyE) detection utilising an electrochemical aptasensor platform. HlyE is a virulent protein produced by Salmonella enterica serotype Typhi (S. Typhi), responsible for typhoid fever. The aptasensor was developed using the in-house-designed printed circuit board gold electrode, modified with graphene oxide-chitosan nanocomposite via the drop cast technique. This platform was immobilised with a specific HlyE aptamer sequence utilising the carbodiimide crosslinking chemistry. The electrochemical characteristics of the developed aptasensor were analysed using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy techniques using a benchtop potentiostat. The aptasensor successfully detects the HlyE protein ranging from 1.25 to 20 ng/μL, with a detection limit of 0.137 ng/μL within 30 min under optimal detection conditions. The aptasensor demonstrates excellent specificity, reproducibility and stability up to 14 days at room temperature. A preliminary clinical study indicates that the aptasensor was able to discriminate direct serum samples containing HlyE protein from S. Typhi-infected patients among healthy individuals and patients with other diseases using a portable potentiostat reader. Their detection was comparable with the commercially available Typhidot assay, demonstrating its practicality for early diagnosis of S. Typhi infection. Thus, the aptasensor device developed in this study works efficiently as a portable and rapid diagnostic tool for S. Typhi point-of-care detection.