Table 4.

Categories of challenges for the detection of COVID-19 techniques.

Challenges, Detection of COVID-19 Virus Techniques According to Critical Review Research
Virus Detection Categories	Techniques	Limitation
Indirect detection: DNA, RNA	Electronic sensors	Signal transduction process found is not always apparent. Heterogeneous interface structures. Long time result.
Indirect detection: DNA, RNA	Magnetic sensors	These require several washing steps, and a well-trained technician is necessary. Sensitivity medium and time-consuming.
Indirect detection: Spike protein	Electrochemical sensors	Immobilization method of the concerned nanomaterial to minimize the chance of error. Needs a long time.
Indirect detection: IgM antibody, DNA, RNA	Optical sensors: LSPR, P-FAB, EWA, QCM, SPR and LSPCF	Requirement for point of care remains difficult. High cost.
Direct detection: CT image	CT scan	The opacity of ground-glasses. Irregular linear patterns in the scan. Lacking in a sample dataset.
Direct detection: X-ray image	CXR	Abnormalities of the radiograph. Foggy opacity. A sensitivity of 59%. Lacking in a sample dataset.
All Detection Techniques of COVID-19 Viruses Based On
Viral RNA, DNA Identification	Long time result; can take 4 h to 3 days. Errors in sampling. Sample preparation, isolation, washing and analysis.
Antibody or Antigen Identification	Low concentration and homogeneous protein. Lacking sensitivity.