Development of a dual-label time-resolved fluoroimmunoassay for the detection of α-fetoprotein and hepatitis B virus surface antigen.

Time-resolved fluorometry of lanthanide chelates is one of the most useful non-isotopic detection techniques and has been used in numerous applications in biomedical science. We developed a time-resolved fluoroimmunoassay (TRFIA) to quantify α-fetoprotein (AFP) and hepatitis B virus surface antigen (HBsAg) in human serum. Based on a two-site sandwich protocol, monoclonal antibodies (McAbs) against AFP and HBsAg were co-coated in 96 microtitration wells and tracer McAbs against HBsAg and AFP were labeled with europium (Eu) and samarium (Sm) chelates, respectively. After application of diluted serum samples, Eu(3+)- and Sm(3+)-McAbs were added and fluorescence signals of Sm(3+) and Eu(3+) tracers were collected. Detection limits of AFP and HBsAg were 0.09 mIU/L and 0.01 µg/L, respectively. Measurement ranges of AFP-TRFIA and HBsAg-TRFIA were 1-1000 mIU/L and 0.2-150 µg/L, respectively. Intra- and inter-assay coefficients of variation of AFP-TRFIA were 3.3-4.1% and 5.7-7.2% and for HBsAg-TRFIA were 2.9-3.9% and 4.9-6.8%, respectively. Linear correlation of TRFIA and chemiluminescence immunoassay measurements resulted in a correlation coefficient of 0.9949 for AFP and 0.9940 for HBsAg. For the endurance test, Eu-labeled McAbs were stable for at least one year at -20°C and the results of the TRFIA with the same reagents were also reproducible after one year. The availability of a highly sensitive, reliable and convenient AFP/HBsAg TRFIA will allow the quantification of both AFP and HBsAg, thereby providing diagnostic value in various clinical conditions and could be applied for clinical use.