Two colorimetric LAMP systems for nucleic acid-based diagnostics

This study introduces an advanced 8-well loop-mediated isothermal amplification (LAMP) system specifically designed for the automated colorimetric detection of SARS-CoV-2. Incorporating two distinct configurations having either three light-emitting diodes (LEDs) with varying emission wavelengths per well, paired with a photodiode detector, or utilizing white LED illumination with a red, green, and blue (RGB) sensor. The colorimetric LAMP aims to provide a more accessible and rapid diagnostic tool than traditional fluorescence methods due to the system's simplicity.

We designed, assembled, and compared two colorimetric home-assembled LAMP systems, the first one based on three LEDs, each with a different color with a photodiode, and the second one having RGB and a white LED, with traditional fluorescence-based LAMP method performed on a commercial qPCR instrument. Results demonstrated that the colorimetric RT-LAMP assays achieved critical threshold time (C_T), closely matching the C_T value of fluorescence-based detection accomplished by the qPCR instrument. We performed the fundamental experiment employing an identical RNA copy number of 1,570copies·μL^-1, getting the C_T value of (16.70 ± 0.43) min (mean ± standard deviation from 23 measurements). Then, we also performed different RNA numbers of copies between the highest and lowest RNA contents of ≈ 157,000 copies·μL^-1 and ≈ 1570 copies·μL^-1, respectively, getting C_T values from (13.30 ± 0.04) min to (13.75 ± 0.30) min and (17.04 ± 0.02) min to (17.26 ± 0.02) min, all (mean ± standard deviation from three measurements). The colorimetric systems demonstrated rapid response and precision across varied viral loads while keeping the system simple due to the colorimetric detection method.

The LAMP system's rapid and precise detection capabilities underscore its potential as an effective tool for point-of-need diagnostics. It is crucial for timely responses in ongoing and future pandemic scenarios. This system enhances testing accessibility and provides a robust platform for potential adaptation to other pathogenic threats, making it a valuable asset in global health diagnostics.