Optimized aptamer-based next generation biosensor for the ultra-sensitive determination of SARS-CoV-2 S1 protein in saliva samples

Abstract

COVID-19 is an infectious disease caused by the SARS-CoV-2 virus, which rapidly spread worldwide and resulted in a pandemic. Efficient and sensitive detection techniques have been devised since the onset of the epidemic and continue to be improved at present. Due to the crucial role of the SARS-CoV-2 S1 protein in facilitating the virus's entry into cells, efforts in detection and treatment have primarily centered upon this protein. In this study, a rapid, ultrasensitive, disposable, easy-to-use, cost-effective next generation biosensor based on optimized aptamer (Optimer, OPT) was developed by using a disposable pencil graphite electrode (PGE) and applied for the impedimetric determination of SARS-CoV-2 S1 protein. The S1 protein interacted with the OPT in the solution phase and then immobilized onto the PGE surface. Subsequently, measurements using electrochemical impedance spectroscopy (EIS) were conducted in a solution containing a redox probe of 1 mM [Fe(CN)₆]^3-/4-. Under optimum conditions, the limit of detection (LOD) for the S1 protein in buffer medium at concentrations ranging from 10¹ to 10⁶ ag/mL was calculated as 8.80 ag/mL (0.11 aM). The selectivity of the developed biosensor was studied against MERS-CoV-S1 protein (MERS) and Influenza Hemagglutinin antigen (HA). Furthermore, the application of the biosensor in artificial saliva medium is demonstrated. The LOD was also calculated in artificial saliva medium in the concentration range of 10¹-10⁵ ag/mL and calculated as 2.01 ag/mL (0.025 aM). This medium was also used to assess the selectivity of optimized-aptamer based biosensor.

Keywords: COVID-19; Electrochemical aptasensor; Electrochemical impedance spectroscopy; Infectious disease; Optimer; Optimized aptamer; SARS-CoV-2 S1 protein.