Particle sorting by a structured microfluidic ratchet device with tunable selectivity: Theory and Experiment

We theoretically predict and experimentally demonstrate that several different particle species can be separated from each other by means of a ratchet device, consisting of periodically arranged triangular (ratchet) shaped obstacles. We propose an explicit algorithm for suitably tailoring the externally applied, time-dependent voltage protocol so that one or several, arbitrarily selected particle species are forced to migrate oppositely to all the remaining species. As an example we present numerical simulations for a mixture of five species, labelled according to their increasing size, so that species 2 and 4 simultaneously move in one direction and species 1, 3, and 5 in the other. The selection of species to be separated from the others can be changed at any time by simply adapting the voltage protocol. This general theoretical concept to utilize one device for many different sorting tasks is experimentally confirmed for a mixture of three colloidal particle species

Chiral particle separation by a non-chiral micro-lattice

We conceived a model experiment for a continuous separation strategy of chiral molecules (enantiomers) without the need of any chiral selector structure or derivatization agents: Micro-particles that only differ by their chirality are shown to migrate along different directions when driven by a steady fluid flow through a square lattice of cylindrical posts. In accordance with our numerical predictions, the transport directions of the enantiomers depend very sensitively on the orientation of the lattice relatively to the fluid flow

Non-equilibrium migration mechanisms for microfluidic bioanalysis

Regtmeier J. Non-equilibrium migration mechanisms for microfluidic bioanalysis. Bielefeld (Germany): Bielefeld University; 2007.The leitmotif of this work is to exploit Brownian motion for bioanalysis in the context of migration and separation in microfluidic systems operating far from thermal equilibrium. The increasing importance of bioanalysis is based on the fast growing fields of biotechnology and pharmaceutics. They have a great demand of fast, cheap and robust bioanalytical systems. On the one hand, these systems have to provide pure samples, and on the other hand, have to assure the quality of the product. In order to contribute to these demands, fundamental physical phenomena are studied, such as Absolute Negative Mobility, ratchets and diffusion control and their relevance to bioanalytical applications is illustrated. Two possible approaches are pursued: either the phenomena are directly studied with biological samples or with microparticles as models for cells in order to provide a proof of principle

On-Chip Continuous Flow Interaction Studies Of DNA and Protein Complexed DNA

Everwand M, Anselmetti D, Regtmeier J. On-Chip Continuous Flow Interaction Studies Of DNA and Protein Complexed DNA. In: Proceedings of Fourteenth International Conference on Miniaturized Systems for Chemistry and Life Sciences (µTAS 2010). Groningen, The Netherlands: The Chemical and Biological Microsystems Society (CBMS); 2010: 19-21

Nanofluidic devices for dielectrophoretic mobility shift assays by soft lithography

Viefhues M, Regtmeier J, Anselmetti D. Nanofluidic devices for dielectrophoretic mobility shift assays by soft lithography. Journal Of Micromechanics And Microengineering. 2012;22(11): 115024.We report development and application of 3D structured nano-microfluidic devices that were produced via soft lithography with poly(dimethylsiloxane). The procedure does not rely on hazardous or time-consuming production steps. Here, the nanochannels were created by channel-spanning ridges that reduce the flow height of the microchannel. Several realizations of the ridge layout and nanochannel height are demonstrated, depicting the high potential of this technique. The nanochannels proved to be stable even for width-to-height aspect ratios of 873:1. Additionally, an application of these submicrometer structures is presented with a new technique of a dielectrophoretic mobility shift assay (DEMSA). The DEMSA was used to detect different DNA variants, e.g. protein-DNA-complexes, via a shift in (dielectrophoretically retarded) migration velocities within an array of nanoslits

Fast and continuous-flow separation of DNA-complexes and topological DNA variants in microfluidic chip format

Viefhues M, Regtmeier J, Anselmetti D. Fast and continuous-flow separation of DNA-complexes and topological DNA variants in microfluidic chip format. The Analyst. 2013;138(1):186-196.The efficient detection, separation and purification of topological and (protein-) complexed DNA variants is mandatory for many state-of-the-art molecular medicine technologies, like medical diagnostics, gene- and cancer-therapy as well as plasmid vaccination. Here, we present the proof-of-concept of a novel micro-nanofluidic device for a fast and efficient, continuous-flow, and virtually label-free detection/purification protocol that goes beyond the standard methods of electrophoretic mobility shift assays, capillary electrophoresis and affinity chromatography. Based on dielectrophoretic trapping, analyte mixtures of small linear DNA-fragments (2.868 kbp and 6.0 kbp), topological DNA variants like plasmids (6.766 kbp) and minicircle-DNA (2.257 kbp), or cytostatic- and protein-DNA complexes were separated in the vicinity of a channel-spanning bowed ridge (creating a nanoslit). One analyte is continuously deflected due to dielectrophoretic trapping at the ridge whereas other species pass the nanoslit unhindered, resulting in two molecule specific pathways with baseline separated resolution. This offers one-step real-time separation of low analyte volumes on a one-minute timescale at low-costs. The underlying dielectrophoretic mechanism was quantified by determining the electrical polarizabilities of the molecules. Additionally, we compared the continuous-flow detection of DNA-complexes with well-established electrophoretic mobility shift assays. Future analytical and preparative applications, such as for plasmid pharmaceuticals as well as continuous sample harvesting in parallel microchip format, are discussed

Brownian motion - Absolute negative particle mobility

Ros A, Eichhorn R, Regtmeier J, Duong TT, Reimann P, Anselmetti D. Brownian motion - Absolute negative particle mobility. Nature. 2005;436(7053):928

High Resolution Imaging of Dried and Living Single Bacterial Cell Surfaces: Artefact or not?

Greif D, Wesner D, Anselmetti D, Regtmeier J. High Resolution Imaging of Dried and Living Single Bacterial Cell Surfaces: Artefact or not? Microscopy Today. 2011;19(05):22-25