Liquid phase immunoassay using magnetic markers and superconducting quantum interference device

Keiji Enpuku, Tsuyoshi Tanaka, Takashi Matsuda, Hiroyuki Kuma, Naotaka Hamasaki, Feng Dang, Naoya Enomoto, Junichi Hojo, Kohji Yoshinaga, Frank Ludwig, Fatemeh Ghaffari, Erik Heim, Meinhard Schilling

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


A liquid phase immunoassay utilizing magnetic markers and a high-T c superconducting quantum interference device (SQUID) was studied. In this method, the biological target is detected using magnetic markers, i.e., the magnetic signal from the markers that bound to the target is detected with the SQUID. The detection was performed in a solution containing both the bound and unbound (free) markers without using the so-called bound/free (BF) separation process. The bound markers were distinguished from the free markers by utilizing the Brownian rotation of the free markers. First, the properties of the free markers in the solution, such as the M-H curve and magnetic relaxation, were measured to study the background signal from the free markers. Markers that exhibit remanence were used for the experiment. Using the obtained results, we discuss the effects of the residual earth field and aggregation of the markers on the background signal. Next, we detected a fungus, Candida albicans, with the described liquid phase immunoassay. Good relationship was obtained between the detected signal and the number of fungi. The minimum detectable number of fungi was as small as 30.

Original languageEnglish
Pages (from-to)7524-7529
Number of pages6
JournalJapanese Journal of Applied Physics
Issue number11
Publication statusPublished - Nov 6 2007

All Science Journal Classification (ASJC) codes

  • General Engineering
  • General Physics and Astronomy


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