Rapid and Quantitative Screening of Bacteria-Virus Co-Infection in Saliva Based on Ready-to-Use Portable Resonant Sensors

Seasonal outbreaks of respiratory infections place a significant burden on hospital-centered diagnostic and treatment systems. Co-infections involving both bacterial and viral pathogens further complicate infection assessment, highlighting the need for rapid and accurate diagnostic tools. In this work, we present a ready-to-use, portable resonant sensing system capable of rapidly and quantitatively detecting key coinfection biomarkers in saliva, specifically C-reactive protein (CRP) and respiratory syncytial virus (RSV) fusion protein. The sensor operates via competitive immune binding within a hydrogel-based resonant structure, where biomarker binding induces shifts in resonant frequency that are wirelessly detected. To preserve antibody activity and hydrogel mechanical integrity, we developed an integrated, ready-to-use sensor system optimized for ultrasensitive detection. This platform enables analysis of unprocessed saliva samples within 5 min, achieving low limits of detection of 24 fg/mL for CRP and 31 fg/mL for RSV fusion protein. Quantitative analysis of patient samples demonstrated strong concordance with both enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) results. This portable sensing platform offers a promising solution for point-of-care coinfection diagnostics, supporting real-time infection monitoring and potentially easing the burden on healthcare systems.