A Highly Sensitive pNIPAM Microgel-Based Electrochemical Biosensor for the Detection of SARS-CoV-2 Proteins

The late 2019 witnessed the outbreak and widespread transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a new highly contagious disease. This disease became a global pandemic in March 2020 due to a lack of effective treatment and diagnosis systems. Existing methods for the detection of SARS-CoV-2 have several obvious drawbacks. Therefore, special attention has been paid to develop new diagnostic tools for the early detection of SARS-CoV-2. In this study, a new pNIPAM (poly-N-isopropylacrylamide) microgel based electrochemical sensor was explored to detect the SARS-CoV-2 spike protein (S protein) in human saliva, allowing a non-invasive detection manner. The microgel was composed of copolymer of N-isopropylacrylamide and acrylic acid, and the gold nanoparticles were encapsulated within the microgel through a facile and economical fabrication method. The gold particle containing microgel,, was applied to electrode surfaces forming a film with porous network structure and high conductivity. The porous network structure provided a highly biocompatible and contamination-resistant microenvironment, similar to aqueous biological tissues, which ensured a good reaction environment for S protein capture, thus improving the specificity and sensitivity of the sensing platform for S proteins detection. The antibodies to S protein were bound to conductive membranes via amide bonds, and the electrochemical performance of the sensor was evaluated through differential pulse voltammetry. Under the optimal experimental conditions, the linear range of the sensor was 10 -13 - 10-9 mg/mL, while the detection limit was 9.55 fg/mL. Furthermore, the S protein was instilled in artificial saliva as the infected human saliva model for the evaluation of the sensing platform. The sensing platform exhibited excellent specificity and sensitivity in detecting spike protein, indicating its potential application for the time-saving and inexpensive detection of SARS-CoV-2.