DISCO-LAMP: A Novel discontinuous LAMP assay for isothermal antigen detection

Proximity ligation assay (PLA), in which the ligation of two DNA probes is greatly accelerated by the associating target molecules, has emerged as a highly sensitive technique for protein detection. The detection of the ligated DNA typically relies on PCR, which requires temperature cycling. In this study, we report on a novel discontinuous (DISCO)-LAMP assay that enables the wash-free detection of PLA products via loop-mediated isothermal amplification (LAMP). Due to the exponential amplification nature of LAMP, a careful balance between efficient amplification of the ligated full-length DNA and minimal background amplification from the individual constituent probes is essential but often challenging to achieve. After extensive template/primer design and assay optimization, DISCO-LAMP assay achieved a detection limit of 1 fM for the ligated DNA probe while maintaining undetectable background amplification at 1 nM of each individual probe. DISCO-LAMP detected Shiga toxin 2 (Stx2) with a limit of detection (LoD) of 100 fM when functionalized with Stx2-binders, as well as both Wuhan-1 and Omicron spike protein when functionalized with DS16, a newly engineered DARPin targeting a conserved epitope on the SARS-CoV-2 Spike protein. We believe DISCO-LAMP represents a versatile and efficient LAMP-based PLA technology that is readily adaptable for sensing diverse targets.