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. 2022 Mar 10;249:123375. doi: 10.1016/j.talanta.2022.123375

Fig. 1.

Fig. 1

Diagnostic principle of the combined colorimetric COVID-19 RT-LAMP-XO and IC-RT-LAMP-LG assay with AI-assisted automated result analysis (RT-LAMP-DETR). A RNA extracted from commercial RNA extraction kits can be eluted in water, and directly supplied to the COVID-19-RT-LAMP-XO and IC-RT-LAMP-LG reactions. The two tests were designed to complement each other to ensure the accuracy of test results. During the incubation at 65 °C, in the presence of target RNAs (Nsp 9 for COVID-19-RT-LAMP-XO, and human 18 S rRNA for IC-RT-LAMP-LG), the buildup of excess protons (H+) in the reactions will cause a dramatic pH drop, and change the hues of pH-sensitive dyes that can be further analyzed with the naked-eye or an AI model for automated, high-volume testing. With the exception of RNA extraction, the entire operation takes less than 2 hours to finish with very limited hands-on time. B The colorimetric results of the combined COVID-19-RT-LAMP-XO and IC-RT-LAMP-LG assay could be cross-compared according to the graphical guideline to accurately interpret the test results. For the COVID-19-RT-LAMP-XO assay, the presence of SARS-CoV-2 in the test samples will trigger the change of reaction hue from purple to yellow. On the contrary, for the IC-RT-LAMP-LG assay, the presence of human 18 S rRNA in the test samples will trigger the change of reaction hue from purple to green. In both tests, a lack of detection targets will preserve the original purple hue of the reaction. In the context of point-of-care testing, the outcomes of IC-RT-LAMP-LG assay provide a qualitative assessment of the RNA extraction process, and can be used as an alternative method to the standard spectrophotometry for nucleic acid quality determination. C Images of multiple reaction tubes can be taken via a smartphone camera for AI-assisted automated result analysis by the RT-LAMP-DETR mode. Details of the RT-LAMP-DETR analysis pipeline are in Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)