Chapter 16 - Fluorescence-based biosensors for SARS-CoV-2 viral infection diagnostics

Abstract

Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infected around 181,424,444 people as of June 29, 2021, across 194 counties, and cause 3,929,667 deaths as per the statistics of the WHO. In the present scenario, the global pandemic reassures the significance of science, technology development, and its immediate response during urgency. Most of the world nations adopt isolation, testing, and tracing strategies to control the spreading of coronavirus 2019 (COVID-19) as per the guidelines of WHO. The need for extensive COVID-19 testing persists in the current scenario since there is a dilemma in the asymptomatic spread of the pandemic. Early and prompt diagnosis of SARS-CoV-2 (the virus responsible for COVID-19) becomes a major challenge in the biomedical field and the scientific world anticipates cost-effective, easy-to-use biosensors for SARS-CoV-2 detection. Generally, biosensors derive an electrochemical, piezoelectric, or optical response from a biochemical process involving target-analyte recognition. Among different modalities, the fluorescence-based technique has received great attention due to its high sensitivity and specificity and is achieved by the suitable design of various fluorescent probes. Significant changes in the fluorescence during target recognition can be modulated to a sensor response which can be employed for signal transduction in both nucleic acid and protein-based detection of viruses. Incorporation of different techniques such as Förster resonance energy transfer, total internal reflection fluorescence, surface plasmon resonance fluorescence (SPRF), etc. considerably improves the signal responses. Apart from the high selectivity and sensitivity of FRET-based biosensors, it also offers quantitative detection through ratiometric fluorescence measurements. Each technique selectively uses different fluorescent reporters like SYBR green, acridine orange, hydroxynaphthol blue, calcein, etc. The selection of fluorophores typically relies on certain emission characteristics such as intensity, quantum yield, lifetime, and energy transfer. Fluorophores having a high quantum yield offer a high signal-to-noise ratio which subsequently solves the issue of background fluorescence up to an extent. Thus fluorescence-based biosensors provide greater opportunities in diagnostic applications through the intelligent design of fluorophores and fluorophore-based probes. In this chapter, we focus on fluorescence-based biosensors for SARS-CoV-2 detection with a general introduction on prevalent fluorescence-based virus diagnostic techniques.