Multi-phase SERS detection of SARS-CoV-2 from liquids to aerosols and pseudovirus

Rapid, ultrasensitive, and specific detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains challenging, particularly for micro-volume samples. This study presents a capillary-based three-dimensional Ag/ZnO nanorod surface-enhanced Raman spectroscopy (SERS) biosensing platform that enables dual-mode (liquid and aerosol) viral detection within the same device. The capillary configuration inherently provides a large surface-to-volume ratio and acts as a confined reaction chamber, eliminating the need for external liquid or gas cells while minimizing sample consumption. Vertically aligned Ag/ZnO nanorod arrays grown on the inner wall further increase the density of electromagnetic hotspots, achieving an enhancement factor of 1.07 × 10 ¹ ¹ with excellent signal uniformity (RSD = 4.65%). After ACE2 functionalization, the biosensor enables label-free, direct detection of the 2019-nCoV antigen S protein in phosphate-buffered saline (PBS) and pharyngeal swabs solution (PSS), with a limit of detection (LOD) of 1 fg/mL. In addition, a sandwich-structured sensing configuration was designed to further amplify the Raman response. Importantly, without additional instrumentation, the same capillary SERS platform also enables direct detection of the 2019-nCoV antigen S protein aerosol with a LOD of 10 fg/mL and the SARS-CoV-2 Spike Pseudovirus at 100 fg/mL. This biosensor integrates sampling, enrichment, and readout in a low-volume device, reduces the risk of cross-contamination, and maintains high analytical performance.