During measurements, antigenCantibody complex is formed to which complementary enzyme-linked antigen is bound, followed by the addition of color changing substrate that generates a signal proportional to antigen/antibody concentration. diagnosis. In addition to existing devices, we have also discussed diagnostic devices in the research phase showing high potential for clinical use. Our approach would be of enormous benefit in selecting a diagnostic device under a given scenario, which would ultimately help in controlling the current pandemic caused by the coronavirus, which is still far from over with new variants emerging. fluorescein amidites, 6-carboxy-X-rhodamine reference, Ministry of Food and Drug Safety, Emergency Use authorization, European CE marking for In-vitro diagnostic, National Medicines Regulatory Authority, Food and drug administration, Central Drug Standard Control Organisation, Research use only, South African Health Products Regulatory Authority, Limit of Detection, Indian Council of Medical Research, Hexchloro-Fluroscein United States (US) developed a one-step RT-PCR that uses gene-specific and region-specific probes. Many other countries have also developed gene-specific COVID-19 testing kits. Some of them are Altona Diagnostics (Germany) [20], CerTest biotech (Spain) [25], and Seegene (Korea) [23]. Corman et al. [26] generated a novel in vitro transcribed RNA standard that accurately matches the sequence of SARS-CoV-2, thereby increasing the?sensitivity. Tang et al. [27] used stool specimens to detect COVID-19 by RT-PCR with 59% accuracy. COROSURE (IIT Delhi, India) RT-PCR Kit [16] detected COVID-19 using a probe-free method, considerably reducing the cost to USD 9 without compromising the accuracy. COVIRAP [17], RT-PCR kit developed by IIT Kharagpur, India uses a paper strip to detect DNA of the SARS-CoV-2 which can be interpreted by a mobile application. It shows 94% sensitivity and 96% specificity. GeneXpert system which was earlier used to detect other diseases like tuberculosis and HIV has now been approved by the US Food and Drug Administration for emergency use in COVID-19 OTSSP167 detection, which can detect with OTSSP167 a sensitivity of 100% and specificity of 80% [24]. Some limitations of RT-PCR are long-term nucleic acid extraction, requirement of trained staff, errors during sample preparation, and high cost for large volumes. A few RT-PCR kits can also fail to differentiate between influenza virus OTSSP167 and SARS-CoV-2. Computed tomography scan (CT-scan) For COVD-19-infected patients, a CT-scan of lungs shows infiltrates, ground-glass opacities, and sub-segmental consolidations (Fig.?2). CT-scan has higher sensitivity (86C98%) and fewer false-negative results than RT-PCR [28]. CT-scan imaging supported decision-making, provided immediate isolation and appropriate patient treatment [29]. CT-scan combined with other diagnostic techniques provides better diagnosis during the early stages of infection [30]. CT-scan is limited as the lungs are not always the infected organ. COVID-19 can cause multi-organ dysfunctions [31]. Parameters associated with COVID-19 infection observed in CT-scan are also not specific to COVID. The imaging time for a CT-scan is longer, is expensive, and requires a radiologist to analyze the results. In addition to this, CT-scan uses ionizing radiation for detection and the harmful effects of radiation can prove a big deterrent in using CT-scan imaging for diagnosing COVID-19. Open in a separate window Fig. 2 a CT-scan of lungs for a healthy patient [32]. b CT-scan image of COVID infected patient with arrows showing ground-glass opacities [32] Serological techniques: RASGRP immunoassay (antibody and antigen detection) Antigen or antibodies in liquid (generally serum) samples are measured using antigenCantibody interaction. The immune system produces antibodies?in response to antigens, such as?pathogenic bacteria?and?viruses. The presence of antibodies (Immunoglobins A, G, and M [IgA, IgG, and IgM]) in body fluid are an indication of the corresponding infection. IgM antibodies corresponding to SARS-CoV-2 are first to be detected since IgM are the first to respond to infection. IgG are detectable 7C10?days after?the infection [33]. Antigen-detection diagnostics directly detect SARS-CoV-2 proteins (antigens) present in the human body post-infections. SARS-CoV-2 antigens are replicated in respiratory secretions and nucleocapsid (N) proteins are released in large amounts in serum, fecal matter, urine, and throat wash samples [34]. Diao et al. [35] measured antigen in the infected patients’ urine samples, indicating that antigen can also be detected non-invasively. Antigen detection is inexpensive and does not require instrumentation, and its kits can be mass-produced easily. However, it suffers from low sensitivity because of the absence of amplification. Major serological diagnostic kits are compared in Table ?Table22. Table 2 Comparison of kits based on serological tests (ELISA, CLIA, and LFIA) for COVID-19 detection emergency use listing procedure Enzyme-linked immunosorbent assay (ELISA) ELISA is a plate-based assay in which a known antigen or antibody,.