Translation and Rotation Dynamics in a Magnetic-Label Biosensor

Abstract

Magnetic particles are used in magnetic-label biosensors to accelerate molecular binding to the sensor surface as well as to apply stringency by magnetic forces [1]. The biochemical and physical interactions of the particles with the biosensor surface play a key role in the molecular association and dissociation processes. In this paper we quantify the translation and rotation dynamics of particles at a sensor surface, interacting with the surface by nucleic-acids or protein molecules. We apply magnetic fields to actuate the particles and investigate their dynamics with single-particle resolution. We will present measurements on the 3-dimensional mobility of 500 nm particles that are biologically bound to a biosensor surface, recorded using evanescent field microscopy with millisecond time resolution [2]. Our data show that the position and intensity histograms scale systematically with the length of the captured nucleic-acid analyte molecules and with the magnitude of the applied magnetic field. We also present measurements on the rotation dynamics of protein-coated particles in a rotating magnetic field [3]. We demonstrate that a controlled torque is generated by the magnetic particles, which is used to quantify the rotation behavior and torsion stiffness of proteins captured onto the sensor surface by the magnetic particles. The data show that different protein pairs have distinctly different torsion moduli. [1] D. M. Bruls et al., Lab Chip 9 (2009) 3504. [2] K. van Ommering et al., J. Phys. D: Appl. Phys. 43 (2010) 155501 & 385501. [3] X.J.A. Janssen et al., submitted to the Biophysical Journal (2010).