Yolanda Fintschenko

Profiling of impurities in heroin by capillary electrochromatography and laser-induced fluorescence detection

Capillary electrochromatography (CEC) with laser-induced fluorescence (LIF) detection was investigated for the analysis of acidic and neutral impurities in heroin. The phenanthrene-like heroin impurities exhibit high native fluorescence when excited with a doubled argon ion laser (operating at 257 nm). The limit of detection for acetylthebaol is 66 pg ml(-1). CEC-LIF analysis of heroin samples of different geographical origin gave distinguishable peak-enriched chromatograms. A sulfonic acid C12 polymer monolith column provided similar resolving power to a 1.5 mm non-porous ODS column for the isocratic analysis of a refined heroin sample. Analysis of a crude heroin sample via a multi-step gradient CEC resolved a significantly higher number of peaks than gradient high-performance liquid chromatography or micellar electrokinetic capillary chromatography.

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.

Engineered Improvement of the Generation-2 μChemlab™ Biotoxin Detector

The μChemLab™ program is developing hand-portable systems for detecting a broad range of chemical, biological, and viral agents in both gas and liquid samples. The μChem Lab liquid sample analyzer employs electrokinetic sample injection, chip-based electrophoretic microseparations and laser-induced florescence detection to analyze liquid samples. A second-generation liquid phase prototype is described. The device incorporates improvements from technological advances and applied research experience. New features include a modular design that readily accommodates on-chip preconcentration and additional separation techniques. The redesign reduces hardware failures, minimizes downtime during component replacement, improves usability, and provides increased sensitivity. Improvements have been made without compromising previous system performance.

On-Chip Packed Channel Separations

We describe the first use of a UV-initiated porous polymer monolith (PPM) in a microfabricated electrochromatographic separation device. Porous polymer monoliths have several characteristics that make them particularly attractive as a stationary phase for chip electrochromatography (ChEC). The PPM requires no frits, is easily introduced into the system prior to polymerization, and is photopatternable. Relevant ChEC properties such as charge polarity, charge density, hydrophobicity, and porosity are controlled by adjusting the composition of the polymer precursor solution.

Characterization of porous polymer monoliths as flow restrictors for capillary electrophoresis on a chip

Capillary electrophoresis (CE) lends itself to miniaturization, because it uses electroosmotic flow rather than moving parts for flow generation. Its analytical figures of merit improve as channel dimensions decrease. However, solution flow in the small planar channels used in CE-on-a-chip is very sensitive to reservoir solution height. This adds a pressure driven flow components, which decreases resolution, sensitivity, and separation efficiency of the EOF-driven technique. We have observed that this contribution to parabolic flow from uneven solution heights can be minimized by using a porous polymer monolith (PPM) as a flow restriction plug in the reservoirs of a 75 micrometers wide X 15 micrometers deep microchannel etched in glass. Our results indicate an average PPM pore size of 1 micrometers is sufficient for flow restriction. Pore sizes below this result in charge trapping of even small dye molecules. Images of the flow profile on and off the monolith show the inverse-parabolic effect on the electroosmotic flow profile due to mismatched zeta potentials between the polymer and the fused silica wall surfaces depending on PPM surface charge and plug length.