Microcystins are a major group of cyanobacterial heptapeptide toxins found in freshwater and brackish environments. There is currently an urgent requirement for highly-sensitive, rapid and in-expensive detection methodologies for these toxins. A novel single chain fragment variable (scFv) fragment was generated and is the first known report of a recombinant anti-microcystin avian antibody. In a surface plasmon resonance-based immunoassay, the antibody fragment displayed cross-reactivity with seven microcystin congeners (microcystin-leucine-arginine (MC-LR) 100%, microcystin-tyrosine-arginine (MC-YR) 79.7%, microcystin-leucine-alanine (MC-LA) 74.8%, microcystin-leucine-phenylalanine (MC-LF) 67.5%, microcystin-leucine-tryptophan (MC-LW) 63.7%, microcystin-arginine-arginine (MC-RR) 60.1% and nodularin (Nod) 69.3%, % cross reactivity). Following directed molecular evolution of the parental clone the resultant affinity-enhanced antibody fragment was applied in an optimized fluorescence immunoassay on a planar waveguide detection system. This novel immuno-sensing format can detect free microcystin-LR with a functional limit of detection of 0.19 ng mL(-1)and a detection range of 0.21-5.9 ng mL(-1). The assay is highly reproducible (displaying percentage coefficients of variance below 8% for intra-day assays and below 11% for inter-day assays), utilizes an inexpensive cartridge system with low reagent volumes and can be completed in less than twenty minutes.
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