The RBD Ab and IgG secondary Ab were coated on the nitrocellulose membrane as test and control, respectively to test the presence of antigen (Ag) in the sample. Further, the excess antibody bonded with the control line coated with secondary IgG antibody validating the functionality of the test strip. An absorbent pad was placed at the end of the strip to prevent backflow across the strip.
The presence of band colour at test and control line indicates a positive result whereas a single line in control indicates a negative result. Depending on the target analyte, various parameters such as blocking buffer, antibody conjugation concentration, and antibody coating concentration on the membrane have been optimized to obtain band color with maximum binding efficiency. The band intensity of the test line was analysed using a simple smartphone-based application for image acquisition and analysis of the test line color, which can split any color data into its three primary color components — red, green, and blue (RGB data). The specific color component shows the trend of increasing or decreasing intensity of color. This study was published in the Journal of Medical Virology recently.
The developed LFIA strips can be useful as a portable, point of care device (PoC) for on-site detection of SARS-CoV-2 particularly at home or even in rural areas. Moreover, the cost of LFIA strips is much less as compared to standard RT-PCR test making it a more economical option for people who cannot afford the RT-PCR test.