Design and Evaluation of Three Immuno-based Assays for Rapid Detection of Human Norovirus Virus-like Particles

This study designed and evaluated three versatile immuno-based assays for the rapid detection of GI.1 norovirus virus-like particles at low (0-3.0 μg/mL) levels: 1) enzymatic absorbance-based ELISAs, 2) a fluorescentbased immunoassay, and 3) a “signal-down” capture ELISA. Variables including controllable variations in assay format (indirect or sandwich), assay time, binding sequence, and reporter molecule (fluorophore or enzyme) were thoroughly investigated and optimized in all three assays. Selectivity tests in the three-hour absorbance-based ELISA using VLPs representing two GI and two GII strains indicated the assays were selective to GI strains over GII strains. The three-hour enzymatic absorbance-based assay turned out to be a robust and rapid method capable of detecting GI.I VLPs in the range of 0.037 to 0.555 μg/mL, and the three-hour fluorescent immunoassay was capable of detecting VLPs in a high concentration range of 0.5-2.0 μg/mL under optimized conditions. The “signal-down” capture ELISA was conceptually demonstrated for the detection of VLPs at concentrations in excess of 1.0 μg/ mL, but did not appear to be suitable for quantifying VLPs under its current conditions. The methods reported here provide proof-of-concept that various ELISA-type approaches could be further developed to provide robust norovirus detection assays having various detection ranges, limits, and linearity.