Jpn. J. Appl. Phys. 46 (2007) pp. 7524-7529 |Previous Article| |Next Article| |Table of Contents|
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Liquid Phase Immunoassay Using Magnetic Markers and Superconducting Quantum Interference Device
Research Institute of Superconductor Science and Systems, Kyushu University, Fukuoka 819-0395, Japan
1Faculty of Pharmaceutical Sciences, Nagasaki International University, Nagasaki 859-3298, Japan
2Department of Applied Chemistry, Kyushu University, Fukuoka 819-0395, Japan
3Department of Applied Chemistry, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan
4Institute of Electrical Measurement and Fundamental Electrical Engineering, TU Braunschweig, Hans-Sommer-Str. 66, D-38106 Braunschweig, Germany
(Received July 4, 2007; revised July 23, 2007; accepted July 24, 2007; published online November 6, 2007)
A liquid phase immunoassay utilizing magnetic markers and a high-Tc 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.
KEYWORDS:liquid phase immunoassay, biosensor, SQUID, magnetic marker, Brownian rotation
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