Regensburg 2010 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 43: Colloids and Complex Liquids II
CPP 43.9: Talk
Thursday, March 25, 2010, 16:15–16:30, H39
Total internal reflection microscopy: From scattering intensity to absolute position — •Thomas Brettschneider1, Giovanni Volpe1,2, Laurent Helden1, and Clemens Bechinger1,2 — 12. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany — 2Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany
Total Internal Reflection Microscopy (TIRM) is a sensitive and non-intrusive technique to measure the interaction potentials between a colloidal particle immersed in a liquid and a wall. The equilibrium distribution of the particle-wall separation distance z is sampled monitoring the intensity I scattered by the Brownian particle under evanescent illumination. From this one can determine the distance resolved interaction potential and corresponding forces with femtonewton resolution. The central point of the data analysis is the a priori knowledge of the relation between the measured scattering intensity I and the corresponding particle distance z. For short penetration depths of the evanescent field, it has been demonstrated that I(z)∝ exp(−z/δ). This, however, poses considerable constraints to the experimental conditions and the range of forces where TIRM can be applied. Here, we introduce a method to experimentally determine I(z) by making solely use of the distance-dependent hydrodynamic interactions between the particle and the wall. We demonstrate, that our method largely extends the range of conditions accessible with TIRM, and even allows measurements on highly reflecting gold surfaces where multiple reflections lead to large deviations from an exponential I(z) relationship.