Fig. 2

Schematic scenario for a sandwich-like FP screening assay principle. This first reported sandwich-like FP screening assay is based on the FP technique combining with BAS. Incubation of FP tracer (FITC-S-Biotin, purple dashed line) with Mpro (scissor) and subsequent addition of avidin (red crescent) produced a FP signal that was proportional to the relative amount of cleaved and uncleaved FP tracer. The uncleaved FP tracer produced a high mP value upon binding to avidin because of the exciting of bioactive compounds (blue hexagon), whereas the cleaved, a small FITC-AVLQ fragment that cannot bind to avidin produced a low mP value because of the exciting of inactive compounds (yellow hexagon). This newly developed screening protocol is mainly divided into three separate steps for laboratory use, and the appearance of this screening system looks like a sandwich