A smartphone-read ultrasensitive and quantitative saliva test for COVID-19

Point-of-care COVID-19 assays that are more sensitive than the current RT-PCR (reverse transcription polymerase chain reaction) gold standard assay are needed to improve disease control efforts. We describe the development of a portable, ultrasensitive saliva-based COVID-19 assay with a 15-min sample-to-answer time that does not require RNA isolation or laboratory equipment. This assay uses CRISPR-Cas12a activity to enhance viral amplicon signal, which is stimulated by the laser diode of a smartphone-based fluorescence microscope device. This device robustly quantified viral load over a broad linear range (1 to 10(5)copies/mu l) and exhibited a limit of detection (0.38 copies/mu l) below that of the RT-PCR reference assay. CRISPR-read SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) RNA levels were similar in patient saliva and nasal swabs, and viral loads measured by RT-PCR and the smartphone-read CRISPR assay demonstrated good correlation, supporting the potential use of this portable assay for saliva-based point-of-care COVID-19 diagnosis.

Automated summary

A portable and ultrasensitive saliva-based COVID-19 assay with a 15-minute sample-to-answer time has been developed, utilizing CRISPR-Cas12a activity to enhance viral amplicon signal without requiring RNA isolation or laboratory equipment. The device can quantify viral load over a broad linear range and has a lower limit of detection compared to the RT-PCR reference assay, showing potential for saliva-based point-of-care COVID-19 diagnosis.