AVS 51st International Symposium
    Biomaterial Interfaces Thursday Sessions
       Session BI-ThA

Paper BI-ThA5
Biological Sensors Based on Brownian Relaxation of Magnetic Nanoparticles

Thursday, November 18, 2004, 3:20 pm, Room 210D

Session: Biosensors and Bio-Diagnostics
Presenter: S.D. Bader, Argonne National Laboratory
Authors: S.-H. Chung, Argonne National Laboratory
A. Hoffmann, Argonne National Laboratory
S.D. Bader, Argonne National Laboratory
L. Chen, Argonne National Laboratory
C. Liu, Argonne National Laboratory
B. Kay, Argonne National Laboratory
L. Makowski, Argonne National Laboratory
Correspondent: Click to Email
We present a biological sensing platform that is based on a modification of the dynamic magnetic properties of ferromagnetic nanoparticles suspended in a liquid. For a narrow size range the ac magnetic susceptibility of the ferromagnetic nanoparticles is dominated by Brownian relaxation. By coating the nanoparticles with a suitable ligand the Brownian relaxation and thus the ac magnetic susceptibility can be modified through the binding to the corresponding bio-receptor. The size of the particles has to be large enough to avoid superparamagnetism and at the same time small enough to have a homogeneous single domain magnetization. We demonstrate a proof-of-principle of this concept by using avidin-coated Fe@sub 3@O@sub 4@ particles that are ~10 nm in diameter, which were investigated before and after binding to biotinylated S-protein and bacteriophage particles. The ac susceptibility measurements show that the magnetic relaxation occurs via a Brownian mechanism; the frequency shift for the peak in the imaginary part of the susceptibility after binding to the target indicates the increase of the hydrodynamic radius. We are currently developing magnetic phage viruses in order to further improve this bio-sensing platform. @FootnoteText@ * Supported by DOE, BES under contract W-31-109-ENG-38, and DARPA under contract 8C67400.