title: Simultaneous determination of alpha-fetoprotein and free beta-human chorionic gonadotropin by element-tagged immunoassay with detection by inductively coupled plasma mass spectrometry.
abstract: 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.
authors.affiliation: Department of Chemistry, Key Laboratory for Atomic and Molecular Nanosciences of Education Ministry, Tsinghua University, 100084 Beijing, People's Republic of China.
authors.forename: Sichun
authors.initials: S
authors.lastname: Zhang
authors.forename: Chao
authors.initials: C
authors.lastname: Zhang
authors.forename: Zhi
authors.initials: Z
authors.lastname: Xing
authors.forename: Xinrong
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor / Q000097:blood* / Q000737:chemistry; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood* / Q000737:chemistry / Q000276:immunology; D023381:Endpoint Determination; D005063:Europium / Q000032:analysis*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D013058:Mass Spectrometry; D012493:Samarium / Q000032:analysis*; D000509:alpha-Fetoproteins / Q000032:analysis* / Q000737:chemistry / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D014408:Biomarkers, Tumor; D018997:Chorionic Gonadotropin, beta Subunit, Human; D000509:alpha-Fetoproteins; D012493:Samarium; D005063:Europium