Liquid phase immunoassays utilizing magnetic markers and SQUID magnetometer.
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.
Kuma
Hiroyuki
H
Department of Clinical Chemistry and Laboratory Medicine, Faculty of Pharmaceutical Sciences, Nagasaki International University, Sasebo, Japan. kuma@niu.ac.jp
Oyamada
Hiroko
H
Tsukamoto
Akira
A
Mizoguchi
Takako
T
Kandori
Akihiko
A
Sugiura
Yoshinori
Y
Yoshinaga
Kohji
K
Enpuku
Keiji
K
Hamasaki
Naotaka
N
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
D016209:Interleukin-8; D058726:Nanoconjugates; D010710:Phosphates; D001360:Avidin; D007073:Immunoglobulin E