Assays for selection of single-chain fragment variable recombinant antibodies to metal nanoclusters

The protocols herein describe colony-lift and fluorescent immunoassays that were used to identify bacterial colonies that produced single-chain fragment variable (ScFv) recombinant antibodies reactive with zero-state silver. A large (approx 2.9-billion member) phage-displayed antibody library was panned against zero valent silver. Bacterial colonies obtained after two rounds of selection were either lifted onto nitrocellulose filters or picked to individual wells of 384-well microtiter culture plates. Colonies lifted onto filters were placed onto zero valent silver-coated filters and induced to produce soluble ScFv antibodies. ScFv antibodies, expressed by individual colonies, that bound to silver nanocluster-coated filters were detected using an anti-ScFv antibody conjugated to horseradish peroxidase and a chemiluminescent substrate. Colonies picked to 384-well micotiter culture plates were induced to express soluble ScFv antibodies. ScFv antibodies in bacterial periplasmic extract were transferred from 384-well culture plates to 384-well assay plates containing zero-state silver particles and an anti-ScFv antibody conjugated to a fluorescent dye. ScFv antibodies, expressed by individual bacterial clones, that bound to zero valent silver nanoparticles in 384-well assay plates were detected using an FMAT 8100 fluorescent plate reader. The colony-lift and fluorescent immunoassays detected ScFv antibodies reactive with zero valent silver. Similar assay formats should also be useful to detect bacterially expressed recombinant antibodies or proteins to other nanoclusters.