1. Fluidics and Simulation, Institut für Mikrotechnik Mainz GmbH, Carl Zeiss Strasse 18-20, 55129 Mainz, Germany, Nanobiotechnology and Bioanalysis Group, Department of Chemical Engineering, University of Rovira i Virgili, Av. Paisos Catalan, 26, 43007, Tarragona, Spain, and Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain