Loop-Mediated Isothermal Amplification Detection of SARS-CoV-2 and Myriad Other Applications.

As the second year of the COVID-19 pandemic begins, it remains clear that a massive increase in the ability to test for SARS-CoV-2 infections in a myriad of settings is critical to controlling the pandemic and to preparing for future outbreaks. The current gold standard for molecular diagnostics is the polymerase chain reaction (PCR), but the extraordinary and unmet demand for testing in a variety of environments means that both complementary and supplementary testing solutions are still needed. This review highlights the role that loop-mediated isothermal amplification (LAMP) has had in filling this global testing need, providing a faster and easier means of testing, and what it can do for future applications, pathogens, and the preparation for future outbreaks. This review describes the current state of the art for research of LAMP-based SARS-CoV-2 testing, as well as its implications for other pathogens and testing. The authors represent the global LAMP (gLAMP) Consortium, an international research collective, which has regularly met to share their experiences on LAMP deployment and best practices; sections are devoted to all aspects of LAMP testing, including preanalytic sample processing, target amplification, and amplicon detection, then the hardware and software required for deployment are discussed, and finally, a summary of the current regulatory landscape is provided. Included as well are a series of first-person accounts of LAMP method development and deployment. The final discussion section provides the reader with a distillation of the most validated testing methods and their paths to implementation. This review also aims to provide practical information and insight for a range of audiences: for a research audience, to help accelerate research through sharing of best practices; for an implementation audience, to help get testing up and running quickly; and for a public health, clinical, and policy audience, to help convey the breadth of the effect that LAMP methods have to offer.

Saliva "Treat-and-Heat" Triplex Reverse Transcription Loop-Mediated Isothermal Amplification Assay for SARS-CoV-2.

The demand for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) molecular diagnostics that are faster, cheaper, and simpler to run than nasopharyngeal-based reverse transcription quantitative PCR (RT-qPCR) tests remains unmet in many parts of the world. In the Philippines, geographical and economic access to quality diagnostic testing remains out of reach for many communities. We describe the preclinical development of a fluorescence-based reverse transcription loop-mediated isothermal amplification test that uses drooled saliva as the biospecimen. Six treat-and-heat ("direct") procedures that inactivate the virus and release the target RNA were compared. Using duplexed As1e and E1 primers, protocols derived from Ben-Assa et al. (2020) using proteinase K or from Rabe and Cepko (2020) using TCEP (Tris(2-carboxyethyl)phosphine hydrochloride)/EDTA provided reliable RNA amplification. The TCEP/EDTA-based method in particular showed improvement in robustness in duplex vs. singleplex format. Inclusion of human ß-actin primers provided a triplex test with an internal amplification control that could be distinguished from SARS-CoV-2 amplicons based on melt curve analysis. After including the dUTP/uracil-DNA glycosylase system and implementing laboratory procedures to avoid cross-contamination, false positive amplification was acceptably rare. The duplex or triplex tests are predicted to reliably detect patient salivary viral loads >100 copies/µL and to yield equivocal results between 10 and 100 copies/µL. These viral loads, corresponding to RT-qPCR C t ∼29-32, are expected to identify the majority of infected and, particularly, of infectious patients. If clinically validated, the test would provide additional testing capacity requiring only a fraction of the time, cost, and infrastructure of the current nasopharyngeal swab-based RT-qPCR test, thereby improving access to testing for more Filipinos.

Single-molecule detection technologies in miniaturized high-throughput screening: fluorescence intensity distribution analysis.

Single-molecule detection technologies are becoming a powerful readout format to support ultra-high-throughput screening. These methods are based on the analysis of fluorescence intensity fluctuations detected from a small confocal volume element. The fluctuating signal contains information about the mass and brightness of the different species in a mixture. The authors demonstrate a number of applications of fluorescence intensity distribution analysis (FIDA), which discriminates molecules by their specific brightness. Examples for assays based on brightness changes induced by quenching/dequenching of fluorescence, fluorescence energy transfer, and multiple-binding stoichiometry are given for important drug targets such as kinases and proteases. FIDA also provides a powerful method to extract correct biological data in the presence of compound fluorescence.