Abstract: The invention discloses a biosensor device (100) to detect the presence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection in a biological sample. The device includes an optical fiber probe (104) having a curved portion (104a) with a probe region (105) immobilized with bioreceptor molecules (201) configured to bind to the target molecule V indicative of the presence of the SARS-CoV-2. The probe has a light source (102) and a detector (106) on either end. The device works on the principle of plasmonic fiberoptic absorbance biosensing. Plasmonic gold nanoparticles (120) are used as either sensor substrate over the fiber or labels conjugated with a biorecognition molecule (211). The probe is exposed to a biological sample either directly for label-free detection, or after mixing with labels to realize a sandwich assay. The target biomolecules are detected by a proportional drop in the light intensity passing through the probe.