The heavy-chain and kappa light-chain variable region genes of an antizearalenone hybridoma cell line (2G3-6E3-2E2) were isolated by PCR and joined by a DNA linker encoding peptide (Gly 4 Ser) 3 as a single-chain Fv (scFv) DNA fragment. The scFv DNA fragment was cloned into a phagemid (pCANTAB5E) and expressed as a fusion protein with E tag and phage M13 p3 in Escherichia coli TG1. In the presence of helper phage M13K07, the scFv fusion protein was displayed on the surfaces of recombinant phages. High-affinity scFv phages were enriched through affinity selection in microtiter wells coated with zearalenone-ovalbumin conjugate. The selected recombinant phages were used to infect E. coli HB2151 for the production of soluble scFv antibodies. One selected clone (pQY1.5) in HB2151 secreted a soluble scFv antibody (QY1.5) with a high zearalenone-binding affinity (concentration required for 50% inhibition of binding, 14 ng/ml), similar to that of parent monoclonal antibody in a competitive indirect enzyme-linked immunosorbent assay. However, scFv QY1.5 exhibited higher cross-reactivity with zearalenone analogs and had greater sensitivity to methanol destabilization than the parent monoclonal antibody did. Nucleotide sequence analyses revealed that the light-chain portion of scFv QY1.5 had a nucleotide sequence identity of 97% to a mouse germ line gene V K 23.32 in mouse kappa light-chain variable region subgroup V, whereas the heavy-chain nucleotide sequence was classified as mouse heavy-chain subgroup III (D) but without any closely related members having highly homologous complementarity-determining region sequences. The potential of soluble scFv QY1.5 for routine screening of zearalenone and its analogs was demonstrated with zearalenone-spiked corn extracts. Zearalenone [6-(10-hydroxy-6-oxo-trans-1-undecenyl)-resorcylic acid lactone] is a mycotoxin produced by members of the genus Fusarium after infection of corn and small grains (8, 19, 21). When fed to animals, the compound causes hyperestrogenism with symptoms such as enlargement of the uterus and nipples, vulvar swelling, vaginal prolapse, and infertility (10, 20). As a consequence of these estrogenic effects, there is a need for routine screening of agricultural commodities used for human and animal consumption. Methods for the analysis of zearalenone in food and feeds include thin-layer chromatography (5, 30, 31), gas-liquid chromatography (30, 34), high-pressure liquid chromatography (11, 30, 36), and, more recently, immunoassays (2, 4, 15, 32, 35, 37). Compared with other methods, immunoassays have several advantages for rapid field tests, including high specificity, sensitivity, facile sample preparation, and ease of use (27). However, the development of antibodies requires the use of animals, specialized cell culturing facilities, and an extensive commitment of time and labor. Production of monoclonal antibodies from hybridoma cell lines also requires specialized cell culture facilities and usually is time-consuming. Advances in the field of recombinant ant...