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

¹ Department of Chemistry, Key Laboratory for Atomic and Molecular Nanosciences of Education Ministry, Tsinghua University, 100084 Beijing, People’s Republic of China.

^aAuthor for correspondence. Fax 86-10-6277-0327; e-mail xrzhang{at}chem.tsinghua.edu.cn.

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 -fetoprotein (AFP) and free ß-human chorionic gonadotropin (hCGß) in human serum.

Methods: Monoclonal antibodies immobilized on microtiter plates captured AFP and hCGß, which were detected by use of Eu³⁺-labeled anti-AFP and Sm³⁺-labeled anti-hCGß monoclonal antibodies. Eu³⁺ and Sm³⁺ were dissociated from the immunocomplex with HNO₃ solution (10 mL/L) and delivered by peristaltic pump to the ICP mass spectrometer.

Results: The measurable ranges of AFP and hCGß were 4.6–500 and 5.0–170 µg/L, respectively, with detection limits of 1.2 and 1.7 µg/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 µg/L, respectively, and the interassay CV was 10%, 5.7%, and 3.5%. For hCGß, the intraassay CV was 5.4%, 6.4%, and 3.1%, respectively, at 10.5, 45.2, and 105 µg/L, and the interassay CV was 7.2%, 8.0%, and 3.7%. Comparison with IRMAs for AFP and hCGß yielded correlation coefficients (r²) of 0.97 and 0.95.

Conclusions: Two proteins can be measured simultaneously by immunoassays using two rare earth elemental tags (Eu³⁺ and Sm³⁺) 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.

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