Gregory J. Fiechtner

Separation and concentration of water-borne contaminants utilizing insulator-based dielectrophoresis.

This report focuses on and presents the capabilities of insulator-based dielectrophoresis (iDEP) microdevices for the concentration and removal of water-borne bacteria, spores and inert particles. The dielectrophoretic behavior exhibited by the different particles of interest (both biological and inert) in each of these systems was observed to be a function of both the applied electric field and the characteristics of the particle, such as size, shape, and conductivity. The results obtained illustrate the potential of glass and polymer-based iDEP devices to act as a concentrator for a front-end device with significant homeland security and industrial applications for the threat analysis of bacteria, spores, and viruses. We observed that the polymeric devices exhibit the same iDEP behavior and efficacy in the field of use as their glass counterparts, but with the added benefit of being easily mass fabricated and developed in a variety of multi-scale formats that will allow for the realization of a truly high-throughput device. These results also demonstrate that the operating characteristics of the device can be tailored through the device fabrication technique utilized and the magnitude of the electric field gradient created within the insulating structures. We have developed systems capable of handling numerous flow rates and sample volume requirements, and have produced a deployable system suitable for use in any laboratory, industrial, or clinical setting.

Polymeric microfluidic devices for the monitoring and separation of water-borne pathogens utilizing insulative dielectrophoresis

We have successfully demonstrated selective trapping, concentration, and release of various biological organisms and inert beads by insulator-based dielectrophoresis within a polymeric microfluidic device. The microfluidic channels and internal features, in this case arrays of insulating posts, were initially created through standard wet-etch techniques in glass. This glass chip was then transformed into a nickel stamp through the process of electroplating. The resultant nickel stamp was then used as the replication tool to produce the polymeric devices through injection molding. The polymeric devices were made of Zeonor 1060R, a polyolefin copolymer resin selected for its superior chemical resistance and optical properties. These devices were then optically aligned with another polymeric substrate that had been machined to form fluidic vias. These two polymeric substrates were then bonded together through thermal diffusion bonding. The sealed devices were utilized to selectively separate and concentrate a variety of biological pathogen simulants and organisms. These organisms include bacteria and spores that were selectively concentrated and released by simply applying D.C. voltages across the plastic replicates via platinum electrodes in inlet and outlet reservoirs. The dielectrophoretic response of the organisms is observed to be a function of the applied electric field and post size, geometry and spacing. Cells were selectively trapped against a background of labeled polystyrene beads and spores to demonstrate that samples of interest can be separated from a diverse background. We have implemented a methodology to determine the concentration factors obtained in these devices.

Particle mixing and concentration through competing electrokinetic and hydrodynamic flows

We have developed a novel, low voltage particle concentration and separation paradigm that exploits the interplay between electrokinetic, dielectrophoretic, and pressure-driven flows. The devices presented utilize weak DC fields (5-25 V/cm) and patterned, insulating microfluidic channels. This approach has been applied to species varying in size by two orders of magnitude on the same chip (2 /spl mu/m-20 nm), can be applied to both biological and synthetic particles, and permits the channel geometry to be optimized to a specific size range.

Insulating dielectrophoresis for the continuous separation and concentration of Bacillus subtilis

This paper presents a novel microdevice for the dielectrophoretic manipulation of particles and cells for sample preparation and analysis. A two level isotropic etch of a glass substrate was used to create insulating ridges in micron sized channels. These ridges created a non-uniform field when a direct current field was applied across the channel and the dielectrophoretic force that resulted from the ridge was used to manipulate particles. We show the continuous concentration and separation of Bacillus subtilis from a two component sample mixture. When the applied voltage is at or above 30V/mm the flow of Bacillus subtilis was restricted to the central channel as a result of negative DEP away from the field concentration produced by the insulating ridges. Under the same applied electric fields the 200-nm polystyrene particles DEP away from the insulating ridges was negligible for the 200-nm particles, which flowed uninhibited down the three exit channels.

A general methodology and applications for conduction-like flow-channel design.

A novel design methodology is developed for creating conduction devices in which fields are piecewise uniform. This methodology allows the normally analytically intractable problem of Lagrangian transport to be solved using algebraic and trigonometric equations. Low-dispersion turns, manifolds, and expansions are developed. In this methodology, regions of piece-wise constant specific permeability (permeability per unit width) border each other with straight, generally tilted interfaces. The fields within each region are made uniform by satisfying a simple compatibility relation between the tilt angle and ratio of specific permeability of adjacent regions. This methodology has particular promise in the rational design of quasi-planar devices, in which the specific permeability is proportional to the depth of the channel. For such devices, the methodology can be implemented by connecting channel facets having two or more depths, fabricated, e.g., using a simple two-etch process.

Continuous Particle Filtration and Concentration by Multigradient Dielectrophoresis

A novel methodology for designing selective particle concentrators in electrokinetic flows is presented. The technique is based on two-level etching of channels to produce ridges along which field gradients are patterned. The field gradients are then used to deflect particles using dielectrophoresis. Using uniform-field designs as a basis, fields in the vicinity of a single ridge are examined both experimentally and numerically. Although isotropic etching causes local deviations from piecewise continuous fields, ridges are found to serve as selective particle deflectors in experiments with both polystyrene beads and Bacillus subtilis. Sequences of parallel ridges are also tested, illustrating the efficacy of corrugated ridge structures for selective particle concentration.Copyright

Faceted Design of Microscale Channels for Electrokinetic Flows

A novel methodology for designing microfluidic channels for low-dispersion, electrokinetic flows is presented. The technique relies on trigonometric relations that apply for ideal electrokinetic flows, allowing faceted channels to be designed using common drafting software and a hand calculator. Flows are rotated and stretched along the abrupt interface between adjacent regions having differing specific permeability. Two-interface systems are used to eliminate hydrodynamic rotation of bands injected into channels. Regions bounded by interfaces form faceted flow “prisms” with uniform velocity fields that can be combined with other prisms to obtain a wide range of turning angles and expansion ratios. Lengths of faceted prisms can be varied arbitrarily, simplifying chip layout and allowing the ability to select time-of-flight for a given faceted prism. The method is tested using combined experimental and computational demonstrations of flow displacers. Designs are demonstrated using two-dimensional numerical solutions of the Laplace equation. Experimental flow visualization is performed using standard epi-fluorescence microscopy techniques.Copyright