Amplification-Free, Ultrasensitive, and Quantitative Detection of SARS-CoV-2 RNA Using Plasmonic Fiber Optic Absorbance Biosensor

COVID-19 has significantly emphasized the importance of reliable nucleic acid-based tools that can effectively detect and control the spread of infectious diseases. Herein, we report a plasmonic fiber optic absorbance biosensor (P-FAB) strategy for amplification-free detection of viral ribonucleic acid (RNA) at ultralow concentrations. The sensing strategy involves a plasmonic sandwich nucleic acid assay on a U-bent fiber optic sensor (U-FOS) with thiolated oligonucleotide-capped gold nanoparticles as labels. The sensor output is perceived in the form of absorption of the light passing through U-FOS coupled between an LED light source and a portable fiber optic spectrometer. The sensor exhibited a high sensitivity toward SARS-CoV-2 viral RNA, targeted using complementary oligonucleotides, with a detection limit down to 100 copies/µL within 30 min and a sample volume as low as 25 µL. These promising results on rapid and sensitive P-FAB-based nucleic acid detection and quantification reveal the potential of the biosensor for affordable and easy-to-use point-of-care diagnostic devices.