Setting up the cut-off level of a sensitive barcode lateral flow assay with magnetic nanoparticles.

A barcode lateral flow immunoassay (LFIA) based on magnetic nanoparticles with a controllable cut-off level was developed for the first time. The regulation of the cut-off levels was based on the changes in the position and concentration of three antibodies (two monoclonal and polyclonal) with different affinities (KD=4.22×10(-9), 9.67×10(-9), 1.05×10(-8) M), respectively. To obtain specific conjugates, monoclonal antibodies were covalently immobilized on the magnetic nanoparticles' surface. Potato virus X causing a reduction in the potato yield was used as a model polyvalent antigen. To detect potato virus X in the leaf extracts, a barcode LFIA with cut-off levels of 3, 30, and 150ng/mL was used for the analysis. The application of magnetic concentration leads to a six-fold reduction in the first cut-off level (0.5ng/mL) in comparison with magnetic LFIA without the concentration stage.