Rapid screening method for halofuginone residues in poultry eggs and liver using time-resolved fluorometry combined with the all-in-one dry chemistry assay concept

The present study describes the development and validation of an immunoassay for the screening of coccidiostat halofuginone in poultry eggs and liver. The power of time-resolved fluorometry is utilised with a novel all-in-one dry chemistry assay concept, in which all the reagents needed for the competitive immunoassay are built into a single microtiter well in a dry, stable form. The entire immunoassay is performed by an automated immunoanalyser and the total assay time is only 18 min. The assay protocol is simple: the extracted sample is added to the well and after the 15 min sample incubation and wash steps are completed, the fluorescence signal is measured directly from the surface of the dry well in a time-resolved manner. The analytical limit of detection has been calculated as 0.02 ng ml−1 (n = 12) and the functional limit of detection as 1.7 and 1.0 ng g−1 for egg (n = 6) and liver (n = 6) samples, respectively. If needed, the assay sensitivity can be further improved simply by adjusting the dilution factor of the samples. The mean recovery has been determined as 90.5% for egg at concentration levels of 15 and 60 ng g−1, and as 106.0% for liver at concentrations of 7.5 and 30 ng g−1. The intra-assay variations have typically been below 10% and interassay variations have ranged between 7.7 and 11.6%. The halofuginone immunoassay has also been validated according to Commission Decision 2002/657/EC.