A rapid near-patient detection system for SARS-CoV-2 using saliva

Abstract

The highly infectious nature of SARS-CoV-2 necessitates the use of widespread testing to control the spread of the virus. Presently, the standard molecular testing method (reverse transcriptase-polymerase chain reaction, RT-PCR) is restricted to the laboratory, time-consuming, and costly. This increases the turnaround time for getting test results. This study sought to develop a rapid, near-patient saliva-based test for COVID-19 (Saliva-Dry LAMP) with similar accuracy to that of standard RT-PCR tests. A lyophilized dual-target reverse transcription-loop-mediated isothermal amplification (RT-LAMP) test with fluorometric detection by the naked eye was developed. The assay relies on dry reagents that are room temperature stable. A device containing a centrifuge, heat block, and blue LED light system was manufactured to reduce the cost of performing the assay. This test has a limit of detection of 1 copy/µL and achieved a positive percent agreement of 100% [95% CI 88.43% to 100.0%] and a negative percent agreement of 96.7% [95% CI 82.78-99.92%] relative to a reference standard test. Saliva-Dry LAMP can be completed in 105 min. Precision, cross-reactivity, and interfering substances analysis met international regulatory standards. The combination of ease of sample collection, dry reagents, visual detection, low capital equipment cost, and excellent analytical sensitivity make Saliva-Dry LAMP particularly useful for resource-limited settings.

Figure 1

Visual results of Saliva-Dry LAMP reactions as viewed under a blue light transilluminator. The two reactions on the left are negative (orange) and the two reactions on the right (bright green) are positive read outs.

Figure 2

The Biobox was Biobox manufactured to perform the Saliva-Dry LAMP experiments. (A) Computer-aided design drawing with exploded view of the Biobox. The device is comprised of a heat block, centrifuge, and blue LED transilluminator which met specifications to perform the Saliva-Dry LAMP reaction. Photographs of the side (B) and top (C) view of the Biobox are shown for reference.

Figure 3

Saliva-Dry LAMP workflow diagram and equipment requirements. The workflow for conducting Saliva-Dry LAMP on (A) commercially-available instruments and (B) the Biobox.