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Abstract: Total Internal Reflection Microscopy TIRM is a sensitive non-invasivetechnique to measure the interaction potentials between a colloidal particleand a wall with femtonewton resolution. The equilibrium distribution of theparticle-wall separation distance z is sampled monitoring the intensity Iscattered by the Brownian particle under evanescent illumination. Central tothe data analysis is the knowledge of the relation between I and thecorresponding z, which typically must be known a priori. This posesconsiderable constraints to the experimental conditions where TIRM can beapplied short penetration depth of the evanescent wave, transparent surfaces.Here, we introduce a method to experimentally determine Iz by relying only onthe distance-dependent particle-wall hydrodynamic interactions. We demonstratethat this method largely extends the range of conditions accessible with TIRM,and even allows measurements on highly reflecting gold surfaces where multiplereflections lead to a complex Iz.



Author: Giovanni Volpe, Thomas Brettschneider, Laurent Helden, Clemens Bechinger

Source: https://arxiv.org/







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