Pico-force optical exchange (pico-FOX): utilizing optical forces applied to an orthogonal electroosmotic flow for particulate enrichment from mixed sample streams.

Results are reported from a combined optical force and electrokinetic microfluidic device that separates individual particulates from molecular components in a mixed sample stream. A pico-Newton optical force was applied to an orthogonal electroosmotic flow carrying a hydrodynamically pinched, mixed sample, resulting in the separation of the various particles from the sample stream. Different combinations of polystyrene, PMMA, and silica particles with a commercially available dye were utilized to test the different separation modes available, from purely optical force to combined optical and electrophoretic forces. The impact of various particle properties on particle separation and separation efficiency were explored, including size (2, 6, 10 µm), refractive index, and electrophoretic mobility. Particle addressability was achieved by moving particles to different outlets on the basis of particle size, refractive index, and electrophoretic differences. Separations of 6 and 10 µm polystyrene particles led to only 3% particle contamination in the original sample stream and interparticle type enrichment levels >80%. The unique addressability of three different particle materials (polystyrene, PMMA, and silica) of the same size (2 µm) led to each being separated into a unique outlet without measurable contamination of the other particle types using optical force and electrophoretic mobility. In addition to particle separation, the device was able to minimize dye diffusion, leading to >95% dye recovery. This combined platform would have applications for noninvasive sample preparation of mixed molecular/particulate systems for mating with traditional analytics as well as efficient removal of harmful, degrading components from complex mixtures.

Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation.

Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high-throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods.

Identifying indoor environmental patterns from bioaerosol material using HPLC.

A substantial portion of the atmospheric particle budget is of biological origin (human and animal dander, plant and insect debris, etc.). These bioaerosols can be considered information-rich packets of biochemical data specific to the organism of origin. In this study, bioaerosol samples from various indoor environments were analyzed to create identifiable patterns attributable to a source level of occupation. Air samples were collected from environments representative of human high-traffic- and low-traffic indoor spaces along with direct human skin sampling. In all settings, total suspended particulate matter was collected and the total aerosol protein concentration ranged from 0.03 to 1.2 µg/m(3). High performance liquid chromatography was chosen as a standard analysis technique for the examination of aqueous aerosol extracts to distinguish signatures of occupation compared to environmental background. The results of this study suggest that bioaerosol "fingerprinting" is possible with the two test environments being distinguishable at a 97% confidence interval.

Manipulation and capture of Aß amyloid fibrils and monomers by DC insulator gradient dielectrophoresis (DC-iGDEP).

Here we report a novel method for the manipulation and concentration of Aß amyloid fibrils, implicated in Alzheimer's disease, using DC insulating gradient dielectrophoresis (DC-iGDEP). Fibril enrichment was found to be ∼400%. Simulations suggest that capture of the full range of amyloid protein aggregates is possible with optimized device design.

Exploring the feasibility of bioaerosol analysis as a novel fingerprinting technique.

The purpose of this review is to investigate the feasibility of bioaerosol fingerprinting based on current understanding of cellular debris (with emphasis on human-emitted particulates) in aerosols and arguments regarding sampling, sensitivity, separations, and detection schemes. Target aerosol particles include cellular material and proteins emitted by humans, animals, and plants and can be regarded as information-rich packets that carry biochemical information specific to the living organisms present where the sample is collected. In this work we discuss sampling and analysis techniques that can be integrated with molecular (e.g. protein)-detection procedures to properly assess the aerosolized cellular material of interest. Developing a detailed understanding of bioaerosol molecular profiles in different environments suggests exciting possibilities of bioaerosol analysis with applications ranging from military defense to medical diagnosis and wildlife identification.

Blood cell capture in a sawtooth dielectrophoretic microchannel.

Biological fluids can be considered to contain information-rich mixtures of biochemicals and particles that enable clinicians to accurately diagnose a wide range of pathologies. Rapid and inexpensive analysis of blood and other bodily fluids is a topic gaining substantial attention in both science and medicine. One line of development involves microfluidic approaches that provide unique advantages over entrenched technologies, including rapid analysis times, microliter sample and reagent volumes, potentially low cost, and practical portability. The present study focuses on the isolation and concentration of human blood cells from small-volume samples of diluted whole blood. Separation of cells from the matrix of whole blood was accomplished using constant potential insulator-based gradient dielectrophoresis in a converging, sawtooth-patterned microchannel. The channel design enabled the isolation and concentration of specific cell types by exploiting variations in their characteristic physical properties. The technique can operate with isotonic buffers, allowing capture of whole cells, and reproducible capture occurred at specific locales within the channel over a global applied voltage range of 200-700 V.

Characterization of particle capture in a sawtooth patterned insulating electrokinetic microfluidic device.

Here we present a scheme to separate particles according to their characteristic physical properties, including size, charge, polarizability, deformability, surface charge mobility, dielectric features, and local capacitance. Separation is accomplished using a microdevice based on direct current insulator gradient dielectrophoresis that can isolate and concentrate multiple analytes simultaneously at different positions. The device is dependent upon dielectrophoretic and electrokinetic forces incorporating a global longitudinal direct current field as well as using shaped insulating features within the channel to induce local gradients. This design allows for the production of strong local field gradients along a global field causing particles to enter, initially transported through the channel by electrophoresis and electroosmosis (electrokinetics), and to be isolated via repulsive dielectrophoretic forces that are proportional to an exponent of the field gradient. Sulfate-capped polystyrene nano and microparticles (20, 200 nm, and 1 µm) were used as probes to demonstrate the influence of channel geometry and applied longitudinal field on separation behavior. These results are consistent with models using similar channel geometry and indicate that specific particulate species can be isolated within a distinct portion of the device, whereas concentrating particles by factors from 10(3) to 10(6).

Insulator-based dielectrophoretic separation of small particles in a sawtooth channel.

Insulator-based dielectrophoretic separation of small particles in a sawtooth channel is studied in the limit of dilute concentration. Pathlines for the movements of infinitesimal particles are constructed and the geometric changes of these pathlines are used to establish the criterion for blocking and trapping particles with different physical properties. The sharp corners of the sawtooth channel create much stronger dielectrophoretic force than channels with smooth corners for blocking particle movements. Particle blocking and trapping depend on particle properties and the geometry of the device. It is shown that once the channel geometric aspect ratios are specified, the blocking criterion depends on only a single dimensionless parameter C defined in terms of the particle mobility ratio (dielectrophoretic versus electrokinetic), the applied voltage and the spacing between the teeth. Selective blocking and trapping of particles can be realized by varying the geometry of the channel progressively. High-resolution separation can be achieved by tuning the differential in the parameter C to a desired level.

Bioanalytical separations using electric field gradient techniques.

The field of separations science will be strongly impacted by new electric-field-gradient-based strategies. Many new capabilities are being developed with analytical targets ranging from particles to small molecules, and soot to living cells. Here we review the emerging area of electric field gradient techniques, dividing the large variety of techniques by the target of separation. In doing so, we have contributions using dielectrophoresis, electric field gradient focusing (including dynamic, true moving bed, and pulsed field), electrocapture and electrophoretic focusing, temperature gradient focusing, and focusing with centrifugal force. We cover the literature from the start of 2007 to June 2008, along with some introductory discussions. Even with the relatively short time frame, this young and dynamic field of inquiry produced some 100 contributions describing new and unique techniques and several new applications.

Uptake and dissolution of gaseous ethanol in sulfuric acid.

The solubility of gas-phase ethanol (ethyl alcohol, CH3CH2OH, EtOH) in aqueous sulfuric acid solutions was measured in a Knudsen cell reactor over ranges of temperature (209-237 K) and acid composition (39-76 wt % H2SO4). Ethanol is very soluble under these conditions: effective Henry's law coefficients, H, range from 4 x 10(4) M atm(-1) in the 227 K, 39 wt % acid to greater than 10(7) M atm(-1) in the 76 wt % acid. In 76 wt % sulfuric acid, ethanol solubility exceeds that which can be precisely determined using the Knudsen cell technique but falls in the range of 10(7)-10(10) M atm(-1). The equilibrium concentration of ethanol in upper tropospheric/lower stratospheric (UT/LS) sulfate particles is calculated from these measurements and compared to other small oxygenated organic compounds. Even if ethanol is a minor component in the gas phase, it may be a major constituent of the organic fraction in the particle phase. No evidence for the formation of ethyl hydrogen sulfate was found under our experimental conditions. While the protonation of ethanol does augment solubility at higher acidity, the primary reason H increases with acidity is an increase in the solubility of molecular (i.e., neutral) ethanol.