Rotational diffusometry with integrated LAMP method for rapid and highly sensitive pathogenic nucleic acid detection*

Nucleic acid amplification tests (NAATs), based on polymerase chain reaction (PCR) have gained massive popularity in molecular diagnostics, due to their high sensitivity and accuracy. However, the operational complexity and requirement of expensive thermocyclers hinder the use of PCR for rapid onsite screening. Loop-mediated isothermal amplification (LAMP) is an alternative and attractive nucleic acid amplification technique that is accurate with high sensitivity and specificity. Therefore, to carry out a rapid, sensitive, and accurate NAAT, we combine LAMP with rotational diffusometry enabled by functionalized Janus particles. Here we use the SARS-CoV-2 cDNA targeting nsp-2 gene in a recombinant plasmid as a proof of concept for COVID-19 diagnostics. According to the Stokes-Einstein-Debye equation, the rotational diffusivity is inversely proportional to the liquid viscosity. Therefore, a positive LAMP will rapidly increase the sample viscosity, resulting a slower rotational diffusion of the Janus particles. A limit of detection of 70 ag/µL was achieved in just 10 min with a sample volume as low as 2 µL. Furthermore, the LAMP assay was successfully developed on an open-well microfluidic platform.