Dear Colleagues,

Early and rapid diagnosis of COVID-19 (SARS-CoV-2) followed by strict confinement is still the best way to control infection and viral mutation. Although the vaccines and treatment available for this disease are promising, more contagious COVID-19 variants stemming from viral mutation widen the spread of the disease and cause continued infection.

This Special Issue calls for rapid diagnostic approaches for SARS-CoV-2, including RT-PCR and biosensing systems, and immunoassays toward the development of point-of-care (POC) devices. Research papers are invited to highlight cutting-edge diagnostic technologies for the early and rapid detection of COVID-19 to contain the disease. The Special Issue includes three review papers to cover (i) the pathophysiology and structural aspects of SARS-CoV-2, (ii) the technology behind commercial systems for detection of viral antigens, and (iii) the detection of patient antibodies.

Unlike PCR, which looks for genetic material (ribonucleic acid or RNA) of SARS-CoV-2, the viral spike (S) protein is considered the main target, which contains two subunits, S1 and S2. The former subunit contains the RBD (RNA-binding domain) that mediates the binding of the virus to susceptible cells. The nucleocapsid (N) protein is another abundant RNA-binding protein, which plays an important role in viral genome packaging. Two antibodies, IgM and IgG against the S protein and its subunits, arise almost simultaneously and can be detected in serum within 1–3 weeks after infection. However, IgM and another antibody, IgA, decay more rapidly than IgG, and the clinical significance of IgA in SARS-CoV-2 infection is still unclear.

The currently available antibody tests for SARS-CoV-2 assess IgM and/or IgG to one of two viral proteins: spike (S) or N. As SARS-CoV-2 vaccines are constructed to encode the S protein or its portion, a positive test for S IgM and/or IgG could indicate prior infection and/or vaccination. Briefly, the absence of both anti-S and anti-N antibodies is interpreted to mean that the subject is not vaccinated or infected. By contrast, the presence of these two antibodies is considered to mean that the subject was previously infected but may or may not be vaccinated. Vaccinated people only exhibit anti-S antibodies but not anti-N antibodies. Some people do not develop detectable IgG antibodies following infection; therefore, of importance is the detection of the above three antibodies simultaneously. 

This Special Issue is also devoted to the use of nanomaterials (graphene, carbon nanotubes, gold nanoparticles, etc.) and their potential applications in various diagnosis methods of COVID-19. This Special Issue also covers potential specific sensors (electrochemical detection including impedance spectroscopy)/immunoassay kits for the aforementioned targets.

Prof. Dr. John H. T. Luong
Prof. Dr. Bansi Dhar Malhotra
Guest Editors

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• COVID-19 detection
• biosensing schemes
• point of care devices
• spike (S) protein
• nucleocapsid (N) protein
• IgG, IgM, and IgA detection