Reid Brennen

Monolithic porous polymer stationary phases in polyimide chips for the fast high-performance liquid chromatography separation of proteins and peptides

Poly(lauryl methacrylate-co-ethylene dimethacrylate) and poly(styrene-co-divinylbenzene) stationary phases in monolithic format have been prepared by thermally initiated free radical polymerization within polyimide chips featuring channels having a cross-section of 200micromx200microm and a length of 6.8cm. These chips were then used for the separation of a mixture of proteins including ribonuclease A, myoglobin, cytochrome c, and ovalbumin, as well as peptides. The separations were monitored by UV adsorption. Both the monolithic phases based on methacrylate and on styrene chemistries enabled the rapid baseline separation of most of the test mixtures. Best performance was achieved with the styrenic monolith leading to fast baseline separation of all four proteins in less than 2.5min. The in situ monolith preparation process affords microfluidic devices exhibiting good batch-to-batch and injection-to-injection repeatability.

Microfluidic HPLC-Chip devices with integral channels containing methylstyrenic-based monolithic media

Polyimide HPLC-Chip devices containing poly(methylstyrene-bis-p-vinylphenyl)ethane (MS/BVPE) stationary phase within the device channels and with wall attachment were prepared by thermally initiated free radical polymerization. The microfluidic devices were coupled to both UV and MS detectors. The potential of the MS/BVPE monolith as an alternative separation media within chip devices was investigated by side-by-side comparisons to particulate media within commercial devices. The chromatographic behavior of this stationary phase was comparable to particulate media for separations of proteins as the average peak width at half-height was equal (6.2 s) for a separation within 8 min under gradient elution conditions. The ability to control the porosity characteristics of the MS/BVPE monolith with changes in polymerization time also extended its utility into small analyte (< 500 Da) applications, although more optimization is needed to match conventional RP media for these applications. The good mechanical stability of the MS/BVPE monolith within the microdevices enabled excellent run-to-run repeatability (%RSD retention time (< or = 0.16) and chip-to-chip reproducibility (%RSD retention time (1.4). The use of this material within enrichment channels also shows its potential value in more complex work flows.

Designing Corner Compensation for Electrophoresis in Compact Geometries

Recent studies have shown that serpentine microchannels intended to increase the separation efficiency of electrophoresis on microchips may actually decrease efficiency due to band broadening in the corners. We have designed and tested a compensating corner geometry that greatly reduces this so-called “race-track” effect. Initial corner designs were evaluated using a technique that allows sample skew to be determined from properties of the electric field. Optimized versions of the compensating corners were then generated using full simulations of the electrokinetic and diffusional transport of the samples. The corner geometries were validated experimentally using caged- and bleached fluorescence imaging.

Chip-MS: A Polymeric Microfluidic Device with Integrated Mass-Spectrometer Interface

We report the use of direct write UV laser ablation to create microstructures in polymer film substrates. An integrated chip-MS device is fabricated combining a microfluidic channel with an electrospray tip. Mass spectral data is presented demonstrating protein sample compatibility and excellent spray stability.

Micromachined Fused Silica Liquid Core Waveguide Capillary Flow Cell

A planar, chip-based flow cell for UV-vis absorbance detection in HPLC is presented. The device features a microfabricated free-standing liquid core waveguide (LCW) capillary detection tube of long path length that is based on total internal reflection. We report on the linearity and calibration slope characteristics of lithographically produced LCWs with different interior/exterior geometries. 3D ray tracing was indispensable in modeling behavior in the more demanding geometries: multipath behavior may be intrinsic to these waveguides with consequent nonlinearity. Fortunately, nonlinearity in lithographically easy-to-produce waveguide geometries (such as with a flat, concave exterior and a round interior) is not as detrimental as might be initially expected. Experimental performance is predictably affected by the attainable surface quality of the LCW and efficient and reproducible coupling of the input light into the LCW.

Laser-Ablated Microfluidics for Nanoflow Life Science Measurements

An overview of the laser ablation fabrication method for polymer microfluidic chips is presented with a discussion of some of the interesting and useful designs and applications of the technology along with a presentation of measurement results for some life science applications.