Electrochemical SARS-CoV-2 IgG immunosensor with a high-surface-area PThi/MXene/SPE

This study reports on the development and comprehensive characterization of a novel, highly sensitive electrochemical biosensor for detecting SARS-CoV-2 IgG antibodies. This biosensor utilizes a screen-printed electrode (SPE) modified with a multi-layered MXene (Ti3C2Tx) film and a polymerized thionine (PThi) layer. Integrating three MXene layers increased the electrode's electroactive surface area from 2.90 mm2 (bare SPE) to 11.59 mm2, and further to 19.18 mm2 with the PThi coating. This synergistic platform provides superior conductivity and increased anchoring sites for the anti-IgG capture probe. Rigorous optimization of immunosensing parameters identified an optimal concentration of 0.5 µg/mL SARS-CoV-2 IgG, pH 7.0, at room temperature (RT), and a 30-minute incubation time. The finished biosensor demonstrated excellent selectivity against common interfering substances and moderate storage stability under the tested conditions (91% stability over 20 days, retaining 46.46% of its initial signal after 50 days at + 4 °C). Crucially, the biosensor's performance was evaluated using commercial serum samples. Analysis showed that a 1/10 dilution of the serum was necessary to mitigate matrix effects and maximize signal. Results from the biosensor across various serum dilutions showed trend-level consistency with ELISA. This supports its potential as a fast, sensitive, and point-of-care (PoC) platform for SARS-CoV-2 IgG detection.