Rapid and low-cost diagnosis of COVID-19 is essential to identify the infected subjects, particularly the asymptomatic cases, primarily to arrest the spread of the disease through local transmission. Antibody-based chromatographic serological tests, as an alternative to RT-PCR, offer only limited help due to high false positives. We propose to exploit our field-deployable/portable plasmonic fiber-optic absorbance biosensor (P-FAB) platform for one-step, wash-free detection of SARS-CoV-2 virus particles directly in saliva sample with minimal sample pre-processing.

Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 μL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10⁻¹⁸ M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented.