Single-Chain Variable Fragment (scFv) Antibodies Optimized for Environmental Analysis of Uranium

Recombinant single-chain variable fragment antibodies (scFv) were specifically generated and selected for the measurement of environmental uranium with an antibody-based sensor. These sFvs, which recognized UO2 2+ complexed to 2,9-dicarboxyl-1,10-phenanthroline-acid (DCP), were produced using genetic material obtained from the spleen cells of rabbits immunized with UO2 2+–DCP conjugated to keyhole limpet hemocyanin. Immunoglobulin light chain and heavy chain genes were amplified and cloned into the phagemid pSD3 for generation of a recombinant antibody library and phage-displayed antibodies. The screening process was designed to isolate antibodies that bound to a “loaded” noncovalent complex with high affinity, while selecting against binding to an “unloaded” complex. After five rounds of panning, individual positive scFv clones were used to infect E. coli TG1 and soluble scFv antibodies were purified and characterized. Binding studies showed that the best scFv bound tightly to the UO2 2+–DCP complex (K d, 19.6 nM). However, because of the depletion experiments performed on this library during the panning process, this scFv bound 1200-fold less tightly (K d, 23.5 μM) to metal-free DCP. This scFv (clone 3A) was subsequently used to accurately determine the UO2 2+ concentrations in environmental water samples using a sensor based on kinetic exclusion analysis. The present studies demonstrate that recombinant scFvs with properties engineered for specific applications (i.e., biosensor-based measurement of metals in groundwater) can be prepared if the correct genetic material and techniques are employed. The phage display system permitted the generation of proteins with very specific binding properties (in this case, high affinity for a metal-chelate complex and low affinity for metal-free chelator). The recombinant scFvs isolated in these studies will be the basis for rapid and affordable assays for the detection of residual uranium in environmental water samples.