Advancements in Testing Strategies for COVID-19

Abstract

The SARS-CoV-2 coronavirus, also known as the disease-causing agent for COVID-19, is a virulent pathogen that may infect people and certain animals. The global spread of COVID-19 and its emerging variation necessitates the development of rapid, reliable, simple, and low-cost diagnostic tools. Many methodologies and devices have been developed for the highly sensitive, selective, cost-effective, and rapid diagnosis of COVID-19. This review organizes the diagnosis platforms into four groups: imaging, molecular-based detection, serological testing, and biosensors. Each platform's principle, advancement, utilization, and challenges for monitoring SARS-CoV-2 are discussed in detail. In addition, an overview of the impact of variants on detection, commercially available kits, and readout signal analysis has been presented. This review will expand our understanding of developing advanced diagnostic approaches to evolve into susceptible, precise, and reproducible technologies to combat any future outbreak.

Keywords: SARS-CoV-2; coronavirus; diagnosis; immunoassays; variants.

Figure 1

SARS-CoV-2 structure diagram. The majority of building proteins include spike (S), membrane (M), envelope (E), and nucleocapsid (N). The viral envelope and a lipid bilayer derived from the host cell membrane contain the proteins S, M, and E. The N protein binds to the viral RNA at the virion’s core.

Figure 2

(a) NISDA assay (non-enzymatic RT-LAMP); components of reaction mixture include DNA duplex and two DNA probes (M1 and M2). Template displacement is triggered by toehold upon detecting the target, followed by a cascade of sequential amplification of the signal. Quenched 6-FAM fluorophore (bhq-1) restores fluorescence upon detecting target (viral RNA/DNA) after 30 min at 42 °C. Letters labels represent domains, while prime labeled domains donated complementary sequences Readapted with permission [93]. Copyright © 2021, The Authors. (b) Colorimetric sensor based on iLACO system. I: LAMP in Master Mix II: Combining different dyes. Reproduced with permission [94]. © 2021 The Authors. Published by Elsevier Ltd.

Figure 3

(a) A schematic representation of CRISPR Csm complex type III (Thermus thermophilus) consisting of a CRISPR-RNA (red) and a set of 5 stoichiometrically unequal proteins [Cas 101 (pink), Csm41 (blue), Csm36 (gray), Csm24 (green), Csm51 (white)]. Enzymatic cascade (Cas10-polymerase, Cas DNAase and Csm3 RNAase) activates due to the binding of CRISPR-RNA. Csm3 subunits cleave target RNA and the inactivation of Cas10. The complex RNase-dead is generated due to mutant TtCsm^Csm-D34A. (b) SARS-CoV-2 genome and N1 region of CRISPR RNA (crRNA_N1). (c) Fluorometric detection, a transcribed SARS-CoV-2, and N-gene of SARS-CoV-1. A non-sequence-specific ancillary nuclease, cyclic tetra-adenylate (cA₄), activates the TtCsm6.RNA tether furnish link between a fluorophore () to a quencher (). Mutant in the right graph showed a lower LOD (3-folds) than the wild in the left graph. (d) Colorimetric detection of SARS-CoV-2 by mutant N1 complex by a dye phenol red (a pH-sensitive dye) incubated at 60 °C for 30 min. (e) Visible fluorometric detection by the mutant N1 complex using calcein, incubated for 60 min at 60 °C [102].

Figure 4

Near-Infrared Lanthanide—Doped Nanoparticles (NIR-RENPs), lateral flow immunoassay test format for the viral antigen detection. Reproduced with permission [124]. Copyright © 2020 American Chemical Society.

Figure 5

Antisense oligonucleotide for the direct detection of the viral genome from the gold nanoparticles, ASO labeled with Raman active compound for the high specificity. Reproduced with permission [198]. Copyright © 2012 American Chemical Society.

Figure 6

FDA-approved commercial kits: (A) The number of testing kits (molecular and Immunoassay based) produced by the Global manufacturers (B) Status of molecular-assay based kits, (C) Status of serological assay based.