Journal
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS
Volume 320, Issue 18, Pages 2279-2283Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jmmm.2008.04.132
Keywords
field-induced magnetic birefringence; magnetic nanoparticles; ferrofluid; brownian relaxation; immunoassay
Funding
- NIEHS NIH HHS [P42 ES004699, P42 ES004699-170005] Funding Source: Medline
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Optical detection of the frequency-dependent magnetic relaxation signal is used to monitor the binding of biological molecules to magnetic nanoparticles in a ferrofluid. Biological binding reactions cause changes in the magnetic relaxation signal due to an increase in the average hydrodynamic diameter of the nanoparticles. To allow the relaxation signal to be detected in dilute ferrofluids, measurements are made using a balanced photodetector, resulting in a 25 mu V/root Hz noise floor, within 50% of the theoretical limit imposed by photon shot noise. Measurements of a ferrofluid composed of magnetite nanoparticles coated with anti-IgG antibodies show that the average hydrodynamic diameter increases from 115.2 to 125.4 nm after reaction with IgG. (C) 2008 Elsevier B.V. All rights reserved.
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