title: Liquid phase immunoassays utilizing magnetic markers and SQUID magnetometer.
abstract: 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.
authors.affiliation: Department of Clinical Chemistry and Laboratory Medicine, Faculty of Pharmaceutical Sciences, Nagasaki International University, Sasebo, Japan. kuma@niu.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kuma
authors.forename: Hiroko
authors.initials: H
authors.lastname: Oyamada
authors.forename: Akira
authors.initials: A
authors.lastname: Tsukamoto
authors.forename: Takako
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kandori
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Sugiura
authors.forename: Kohji
authors.initials: K
authors.lastname: Yoshinaga
authors.forename: Keiji
authors.initials: K
authors.lastname: Enpuku
authors.forename: Naotaka
authors.initials: N
authors.lastname: Hamasaki
mesh_terms: D000818:Animals; D001360:Avidin / Q000737:chemistry; D002176:Candida albicans / Q000302:isolation & purification; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation / Q000379:methods* / Q000592:standards*; D007073:Immunoglobulin E / Q000032:analysis / Q000097:blood / Q000276:immunology; D016209:Interleukin-8 / Q000032:analysis / Q000097:blood / Q000276:immunology; D008280:Magnetics; D058726:Nanoconjugates / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D012015:Reference Standards; D012441:Saccharomyces cerevisiae / Q000302:isolation & purification; D013696:Temperature
chemical_list: D016209:Interleukin-8; D058726:Nanoconjugates; D010710:Phosphates; D001360:Avidin; D007073:Immunoglobulin E