An indirect enzyme-linked immunosorbent assay (ELISA) for the detection of antibody to duck hepatitis virus (DHV) is described. The results of ELISA were compared with those of an agar gel diffusion precipitin (AGDP) test and a serum-neutralization (SN) test. The specificity of the ELISA was in accordance with the specificity of the AGDP and SN tests, but there was a difference in sensitivity. The positive detection rates of ELISA, SN test, and AGDP test for 93 clinical samples were 68.8%, 68.8%, and 18.8%, respectively. A positive/negative (P/N) value larger than or equal to 2.1 plus an absorbance value larger than or equal to 0.4 was used as a comprehensive positive standard for the ELISA. This eliminated false-positive reactions. The results showed that the ELISA was a rapid, sensitive, and accurate method for detecting antibody to DHV.
Novel tracers were designed and then used to develop a rapid, specific and sensitive fluorescence polarisation immunoassay (FPIA) method to detect nifursol in feed. The 3-((2-(2-hydroxy-3,5-dinitrobenzoyl)hydrazono)methyl)benzoic acid was used for the production of immunogen and 3,5-dinitrosalicylic acid was used for synthesis of fluorescein-labelled tracer. Based on monoclonal antibody and tracer, an optimised FPIA method was established with IC 50 of 5.0 ng mL (1 , and low cross-reactivity with other nitrofurans ( B0.05%). FPIA provides a suitable means for screening of a large number of samples. The limits of detection calculated from the analysis of 20 known negative feed samples (pig feed, chicken feed and fish feed) were 0.4Á0.8 ng g (1 (mean'3 SD). Recoveries of nifursol fortified ranged from 85.0 to 95.0%. The coefficients of variation were less than 10%.
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