Liquid phase immunoassays utilizing magnetic markers and SQUID magnetometer

Hiroyuki Kuma, Hiroko Oyamada, Akira Tsukamoto, Takako Mizoguchi, Akihiko Kandori, Yoshinori Sugiura, Kohji Yoshinaga, Keiji Enpuku, Naotaka Hamasaki

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


Background: Immunoassays are one main detection system used in the field of clinical chemistry. Recent developments of a new detection method utilizing a magnetic marker and magnetic sensor have enabled rapid and sensitive immunoassay without the need for bound/free (BF) separation. Methods: Newly-synthesized conjugated avidin was used as the magnetic marker for quantitative analysis of human interleukin-8 (hIL-8) and immunoglobulin E (hIgE) in several media. A superconducting quantum interference device sensor detected the magnetic fields from markers fixed to antigens by the sandwich method. Magnetic signals from unbound markers were nearly zero due to Brownian rotation. Results: Our magnetic immunoassay could detect four attomoles of model proteins (hIL-8, hIgE) in phosphate buffer without BF separation. Using our standard curve, the range of protein detected ranged from 40 femtomoles to 4 attomoles, and we observed a strong association between protein amounts and magnetic signals from the bound markers. The homogeneous immunoassay could also quantify three hundred cells from the fungus Candida albicans in phosphate buffer. Conclusions: The present study demonstrates the ability of magnetic markers for measuring biological targets without BF separation. This detection system has great potential for use as the next generation's analytical system.

Original languageEnglish
Pages (from-to)1263-1269
Number of pages7
JournalClinical Chemistry and Laboratory Medicine
Issue number9
Publication statusPublished - Sept 1 2010

All Science Journal Classification (ASJC) codes

  • Clinical Biochemistry
  • Biochemistry, medical


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