Nano- and microfluidics using optical tweezers with fast single particle tracking

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Optical tweezers with fast single particle tracking are microscopic rheometric tools with nanometer resolution in space and subpico -newton resolution in force. The proposed project has two intentions to contribute to basic questions in colloid- and polymer-research and to address technological problems of micro- and nanofluidics. In detail the following experiments are planned: 1.) Measurements of the force-distance dependence between two isolated single colloids of which one is hold by a micro-pipette and the other by optical tweezers. The separation between the colloids can be varied in nanometer steps. 2.) Measurement of the force-distance-dependence between a single colloid and a wall in the steady state and in fluid flow for coated and uncoated surfaces. 3.) Measurement of depletion forces between single colloids in the steady state and in flow for polymer solutions of varying concentration and for polymers of different topology. 4.) A fluctuation analysis of the Brownian motion of a colloid in an optical trap enables one to deduce the local tensor of viscosity. By that inhomogeneous microscopic structures like microchannels or living biological systems can be explored. 5.) Measurement of the flow profile of homogeneous and hetereogeneous liquids in small confining geometries like plates with micrometer separation, microchannels, etc. with - and without surface modifications (e.g. hydrophobization).