Simultaneous Determination of α-Fetoprotein and Free β-Human Chorionic Gonadotropin by Element-Tagged Immunoassay with Detection by Inductively Coupled Plasma Mass Spectrometry

BACKGROUND: An inductively coupled plasma mass spectrometry (ICP-MS)-based immunoassay has been proposed independently by Baranov et al. (Anal Chem 2002;74:1629-36) and our group, but the applicability of this method for multianalyte analysis in clinical samples has not been fully illustrated. We developed a dual-label immunoassay method for the simultaneous determination of alpha-fetoprotein (AFP) and free beta-human chorionic gonadotropin (hCGbeta) in human serum. METHODS: Monoclonal antibodies immobilized on microtiter plates captured AFP and hCGbeta, which were detected by use of Eu(3+)-labeled anti-AFP and Sm(3+)-labeled anti-hCGbeta monoclonal antibodies. Eu(3+) and Sm(3+) were dissociated from the immunocomplex with HNO(3) solution (10 mL/L) and delivered by peristaltic pump to the ICP mass spectrometer. RESULTS: The measurable ranges of AFP and hCGbeta were 4.6-500 and 5.0-170 microg/L, respectively, with detection limits of 1.2 and 1.7 microg/L (3 SD above mean of zero calibrator), respectively. The intraassay imprecision (CV) for AFP was 8.3%, 4.0%, and 2.7% at 16.3, 86, and 354 microg/L, respectively, and the interassay CV was 10%, 5.7%, and 3.5%. For hCGbeta, the intraassay CV was 5.4%, 6.4%, and 3.1%, respectively, at 10.5, 45.2, and 105 microg/L, and the interassay CV was 7.2%, 8.0%, and 3.7%. Comparison with IRMAs for AFP and hCGbeta yielded correlation coefficients (r(2)) of 0.97 and 0.95. CONCLUSIONS: Two proteins can be measured simultaneously by immunoassays using two rare earth elemental tags (Eu(3+) and Sm(3+)) and ICP-MS detection. The multielement capability and the multiple potential elemental labels make ICP-MS attractive for multianalyte immunoassays. Implementation of ICP-MS-linked immunoassays may be relatively straightforward because the labeling and immunoreaction procedures have been well developed for clinical time-resolved immunofluorometric assays.