PD-LAMP Smartphone Detection of SARS-CoV-2 on Chip
Posted by Adam Awdish on
Pooled Human Saliva from Innovative Research was used in the following study:
PD-LAMP Smartphone Detection of SARS-CoV-2 on Chip
Ashlee J. Colbert, Dong Hoon Lee, Katherine N. Clayton, Steven T. Wereley, Jacqueline C. Linnes, Tamara L. Kinzer-Ursem
Analytica Chimica Acta
March 7, 2022
Part of why SARS-CoV-2 (COVID-19) has been able to reach pandemic levels is because it can have a long incubation period prior to the normal onset of symptoms, and further, it doesn’t always cause symptoms in infected individuals. On top of this, symptoms can range in severity between patients, and milder symptoms caused by COVID-19 can easily be mistaken for those caused by less severe illnesses like the flu, pneumonia, etc. When these factors are compounded, it shows that the virus is capable of easily transmitting between unknowing carriers and demonstrates the need for fast, reliable screening to be available to the public to slow its spread.
The first tests developed for SARS-CoV-2 detection were Nucleic acid amplification tests (NAATs) and serological tests. RT-PCR tests, a highly sensitive form of NAAT, were originally the gold standard for detecting COVID-19, however, they rely on RNA extraction and thermocycler equipment to function. This greatly limited their use when the necessary lab resources were not readily available. Later, isothermal nucleic acid amplification (INAAT) tests were developed as an alternative to RT-PCR tests. INAAT-based tests amplify DNA without thermal cycling, eliminating the need for costly and complex resources equipment and trained personnel.
As the technology surrounding COVID-19 detection continued to advance, it became clear that samples collected from a patient’s saliva provided more sensitive results for COVID-19 diagnosis than results provided from nasal swabs. This observation was confirmed by later studies that found that complications like chronic nose bleeds may result from repeated nasal swabs, making saliva swabbing a safer and more comfortable option. The FDA has approved saliva-based diagnostic tests; however, the tests being used still rely on RNA extraction combined with PCR methods.
One method of detection, reverse transcriptase loop-mediated isothermal amplification (RT-LAMP), can detect nucleic acids in under an hour with high sensitivity and easy-to-read fluorescent, colorimetric, or electrochemical results. RT-LAMP amplifies and copies the target RNA, and these copies offer more resistance to inhibitors than PCR. Due to this inhibitor resistance, LAMP assays can be performed on crude samples, cutting out the costs associated with RNA extraction.
In this study, researchers combined the use of RT-LAMP with particle diffusometry (PD), an imaging technique on smartphones, to detect COVID-19 in crude saliva samples. The assay met target profiles set by the World Health Organization and was able to detect as little as 30 viral particles per μL of saliva and produce results in under 35 minutes. Further, it’s not limited to SARS-CoV-2 detection and doesn’t require specialized storage, making it a viable option for future viral resting of saliva samples at the point of care.
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