Brownian Motion in Biological Sensing

Back Matter

“…Rods have hydrodynamic properties that, when implemented in a Brownian motion sensing scheme, can be used to provide better resolution of different targets, and possibly greater sensitivity, due to the higher peak frequencies as compared to spheres of similar dimensions. In addition, the size monodispersity of biologically self-assembled sensor rods should yield narrower frequency peaks than those observed from traditional coated magnetite particles of wider size distributions (Hoffmann et al, 2007;Nutting et al, 2006).…”

“…The peak amplitude of χ″(ω) is shifted to a lower frequency when magnetic particles in solution bind target molecules, increasing the effective hydrodynamic radius and, thus, the Brownian rotational diffusion time ( Figure A-1). For particle radii of approximately 25-350 nm, a change in susceptibility can be directly measured using relatively simple equipment via changes in the inductance and/or resistance detected by an antenna coil in the presence of a small external variable frequency AC magnetic field (Hoffmann et al, 2007). At larger radii, peaks in χ″(ω) may disappear altogether, providing the opportunity for indirect detection of even larger analytes such as viruses, spores and bacteria.…”