Magnetics Research

Research Project

Biosensors based on time-dependent properties of magnetic fluids

This project aims to develop new methods of detection of biomolecules in aqueous solution. The methods are based on the detection of shifts in the frequency dependent magnetic susceptibility of magnetic colloids due to increases in hydrodynamic radius on specific binding with biomolecules [1].

Magnetic fluids comprise suspensions of magnetic particles in either aqueous or organic fluids. In order to obtain a stable dispersion of magnetic particles in an aqueous medium, the characteristics of the particle surface have to be tailored to the medium. Particle-solvent interactions and interparticle repulsions must become strong enough to overcome Van der Waals attraction between the particles [2] and magnetic attraction in the case of particles with a permanent magnetic moment.

One method of stabilisation is coating of the magnetic particles with organic polymers [3-5]. This has been shown to stabilise the magnetic particles against aggregation and can produce a biocompatible fluid. Enzymes and other biomolecular recognition elements and receptors can be covalently bound to the organic polymers [6,7] thus creating composite structure particles that can act as magnetic labels in aqueous media.


The project involves developing a novel methodology for the detection of binding of biomolecules to colloidal magnetic particles in suspension. The methodology exploits the time-dependent magnetic properties of magnetic colloidal suspensions and could form the basis for new types of biosensor. The methodology could be applied to the general class of assays based on the streptavidin - biotin interaction, for example.

The time-dependent magnetic properties of aqueous media containing magnetic particles are altered when biomolecules such as proteins bind to the nanoscale particles in suspension [8,9]. The cause of the change in magnetic relaxation times is the larger hydrodynamic radius of the biomolecule-magnetic particle composite compared with the magnetic particle alone.

Theory shows that the relaxation time is proportional to the hydrodynamic volume of the particle in suspension. Time sensitive magnetic measurement devices such as AC magnetic susceptometers are able to measure a spectrum of relaxation times within a suspension of magnetic particles thus enabling particle sizes to be measured.

References:

  1. Connolly, J. and St. Pierre, T.G. (2001) J. Magn. Magn. Mat., 225, 156-160.
  2. E. Tronc, J. P. Jolivet, Nanophase Materials, G.C. Hadjipanayis, R.W. Siegel eds (Kluwer Academic Publishers, 1994).
  3. L. Shen P.E. Labinis, T.A. Hatton, J Magn. Magn. Mater. 194 (1999) 37.
  4. C. Del Gratta, S. Della Penna, P. Battista, et.al. Phys. Med. Biol. 40 (1995) 671.
  5. R.S. Molday, D. MacKenzie, Immunology 52 (1982) 353.
  6. M Meza, Scientific and Clinical Applications of Magnetic Carriers, ed U. Häfeli, W. Schütt, J. Teller, M. Zborowski (Plenum Press, NewYork, 1997).
  7. I. Safarik, M. Safariková, Scientific and Clinical Applications of Magnetic Carriers, ed U. Häfeli, W. Schütt, J. Teller, M. Zborowski (Plenum Press, NewYork, 1997).
  8. C. B. Kriz, K. Rådevik, D. Kriz, Anal. Chem. 68 (1996) 1966.
  9. R Kötitz, W. Weitschies, L. Trahms, et.al., J Magn. Magn. Mater. 194 (1999) 62.