Ultrasensitive, Real-Time Detection of Viral Antigens and RNA Enabled by Scalable Graphene-Based FET Sensors for Pathogen Detection: A Case Study on COVID-19.

Herein, a novel and simple electrospray (ES) printing technique was developed for the fabrication of ultrathin graphene layers with precisely controlled nanometer-scale thickness, where graphene oxide (GO) was electrosprayed on wafers and subsequently chemically reduced into reduced GO (rGO). Utilizing that technique, we prepared ultrathin rGO in-plane graphene field-effect transistor (GFET)-based biosensors coupled with a portable prototype measuring system for point-of-care detection of pathogens. We illustrate the use of such prepared GFETs to detect COVID-19, using the SARS-CoV-2 nucleocapsid protein antigen (N-protein) and genomic viral RNA as detection targets. The electrosprayed and chemically reduced rGO films enhance the molecular detection in GFET sensors through significant local gating effects. The device detects the N-protein from the SARS-CoV-2 Omicron variant in a culture medium with an LOD of 1.44 PFU/mL and in clinical oropharyngeal samples with an LOD of 45 genome copies/mL in 5 min. It also successfully detects viral RNA in oropharyngeal swabs within 10 min. The GFET sensor responses were further analyzed using our proprietary wireless, miniaturized, and portable FET analyzer, coupled with a smartphone detecting app. Altogether, we present low-cost and mass-producible GFETs with high-quality graphene channels, enabling a portable, efficient, and accurate solution for point-of-care pathogen detection and in clinical testing. This technology has the potential to become a crucial tool in preventing future global epidemic outbreaks.