TIRM-Method

Total Internal Reflection Microscopy (TIRM) is a relatively new powerful technique to optically measure the interaction forces between a colloidal particle and a surface using single particle evanescent light scattering. The distribution of separation distances sampled by Brownian motion of a particle is used to obtain the potential energy profile of interactions between a particle and a plane surface with femto Newton resolution. In our labs the technique has been employed to measure electrostatic interactions, depletion forces, magnetic interactions, critical Casimir forces and non-equilibrium dynamics of colloids near a wall. Besides the development of a new light scattering model that can take into account the exact geometry and parameters of TIRM experiments, the latest technical improvement of the TIRM-method was the development of a new technique to measure in situ the intensity-distance-relation which is central to TIRM data evaluation and had to be assumed a priori until now. This new method largely extends the range where TIRM can be applied and even allows measurements on highly reflecting gold surfaces and particles. Furthermore, this technique was paving the way to new high precision measurements of Brownian dynamics of particles close to a wall which offered the possibility to investigate the influence of noise on force measurements, i.e. effects of spurious drift and force.

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