Nghia Chiem

Integrated capillary electrophoresis devices with an efficient postcolumn reactor in planar quartz and glass chips.

Methods to fabricate planar capillary electrophoresis devices integrated with a postcolumn reactor in fused silica (quartz) and Pyrex glass are presented. Quartz is etched at ∼1 μm/min with a 2.1:1 width-to-depth ratio using a Cr/Au/Cr metal mask and concentrated HF/HNO(3). On-chip postcolumn reaction of o-phthaldialdehyde (OPA) and amino acids gave theoretical plate numbers up to 83 000 and ∼90 ms peak widths, corresponding to 14 plates/V and a 0.5 μm theoretical plate height. The reactor geometry caused only a 10% degradation in efficiency.

Design of an interface to allow microfluidic electrophoresis chips to drink from the fire hose of the external environment.

An interface design is presented that facilitates automated sample introduction into an electrokinetic microchip, without perturbing the liquids within the microfluidic device. The design utilizes an interface flow channel with a volume flow resistance that is 0.54—4.1 × 106 times lower than the volume flow resistance of the electrokinetic fluid manifold used for mixing, reaction, separation, and analysis. A channel, 300 μm deep, 1 mm wide and 15—20 mm long, was etched in glass substrates to create the sample introduction channel (SIC) for a manifold of electrokinetic flow channels in the range of 10—13 μm depth and 36—275 μm width. Volume flow rates of up to 1 mL/min were pumped through the SIC without perturbing the solutions within the electrokinetic channel manifold. Calculations support this observation, suggesting a leakage flow to electroosmotic flow ratio of 0.1:1% in the electrokinetic channels, arising from 66—700 μL/min pressure‐driven flow rates in the SIC. Peak heights for capillary electrophoresis separations in the electrokinetic flow manifold showed no dependence on whether the SIC pump was on or off. On‐chip mixing, reaction and separation of anti‐ovalbumin and ovalbumin could be performed with good quantitative results, independent of the SIC pump operation. Reproducibility of injection performance, estimated from peak height variations, ranged from 1.5—4%, depending upon the device design and the sample composition.

Protein separation and surfactant control of electroosmotic flow in poly(dimethylsiloxane)-coated capillaries and microchips.

A thermally pyrolyzed poly(dimethylsiloxane) (PDMS) coating intended to prevent surface adsorption during capillary electrophoretic (CE) [Science 222 (1983) 266] separation of proteins, and to provide a substrate for surfactant adsorption for electroosmotic mobility control was prepared and evaluated. Coating fused-silica capillaries or glass microchip CE devices with a 1% solution of 100 cSt silicone oil in CH2Cl2, followed by forced N2 drying and thermal curing at 400 degrees C for 30 min produced a cross-linked PDMS layer. Addition of 0.01 to 0.02% Brij 35 to a 0.020 M phosphate buffer gave separations of lysozyme, cytochrome c, RNase, and fluorescein-labeled goat anti-human IgG Fab fragment. Respective plates/m typically obtained at 20 kV (740 V cm(-1)) were 2, 1.5, 1.25, and 9.4-10(5). In 50 mM ionic strength phosphate, 0.01% Brij 35 running buffer, the electroosmotic flow observed was about 25% of that in a bare capillary, and showed no pH dependence between pH 6.3-8.2. Addition of sodium dodecylsulfate (SDS) or cetyltrimethylammonium bromide (CTAB) to this running buffer allowed ready control of electroosmotic mobility, mu(eo). Concentrations of SDS between 0.005 to 0.1% resulted in mu(eo) ranging from 3 to 5 x 10(-4) cm2 V(-1) s(-1). Addition of 1 to 2.3 x 10(-4)% (2.7-6.3 microM) CTAB caused flow reversal. CTAB concentrations between 3.5 x 10(-4) and 0.05% (0.0014-1.37 mM) allowed control of mu(eo) between -1 x 10(-4) and -5.0 x 10(-4) cm2 V(-1) s(-1). For both surfactants the added presence of 0.01% Brij 35 provided slowly varying changes in mu(eo) with charged surfactant concentration.

Micromachinng chemical and biochemical analysis and reaction systems on glass substrates

Microfluidic systems micromachined in glass chips serve as systems for chemical analysis or sensing. Using electroosmotic pumping, applied voltages control the direction of fluid flow without the need for valves. Mixing of reagent solutions, chemical reactions and separation of compounds in mixtures can be achieved. Demonstration of pre-separation mixing of chemical reagents for reaction on-chip, post-separation fluorescent labelling on-chip, and immunological assays on-chip is presented.

Room temperature bonding of micromachined glass devices for capillary electrophoresis

Abstract We report a simple method to bond glass at room temperature for microfluidic applications, which is based on rigorous cleaning [K. Fluri, G. Fitzpatrick, N. Chiem, D.J. Harrison, Integrated capillary electrophoresis devices with an efficient postcolumn reactor in planar quartz and glass chips, Anal. Chem. 68 (1996) 4285–4290; N. Chiem, D.J. Harrison, Microchip-based capillary, Anal. Chem. 69 (1997) 373–378; D. Sobek, A.M. Young, M.L. Gray, S.D. Senturia, A microfabricated flow chamber for optical measurements influids, Proc. IEEE Micro-Electromechanical Systems Workshop, Fort Lauderdale, FL, Feb 7–10, 1993, pp. 219–224.] of the glass substrates before bonding. Low applied pressure on micromachined glass substrates contacted at 20°C provides devices, which are robustly bonded. These devices are able to withstand routine handling, and be used for capillary electrophoresis for as long as 2 years. Separation efficiencies as high as 90,000 theoretical plates were observed at 6–8 kV applied, comparable to 100,000 observed in devices bonded at 440–650°C. A wide range of the same or different types of commercially available glass can be bonded without heat treatment, alleviating the need for a good match in thermal expansion coefficients between the glasses.

Integrated Microsystem for Sample Introduction, Mixing, Reaction, Separation and Self Calibration of Immunoassays

We present here the development of elements for a fully integrated sample processing system, including a rapid-exchange, sample introduction port for the world-to-chip interface, and an integrated immunoassay reactor, which incorporates a method for performing on-chip calibration, on-chip mixing, reaction and separation of immunoreagents, sample and products.

Developing a Routine Coating Method for Multichannel Flow Networks on a Chip using Pyrolized Poly(dimethylsiloxane)

Thermally pyrolized poly(dimethylsiloxane) coatings prevent surface adsorption during capillary electrophoresis (CE) separation of proteins.

Design Rule Evaluation for Micro-Scale Flow Restrictions: Comparing Experiment and Theory

Control of the direction of fluid flow within a network of flow paths in a microfluidic device is paramount to its proper operation. Pressure driven flow requires either active valving for control, or passive control through variation of the flow resistance of each intersecting channel by adjusting its geometry. In order to achieve rational design of passive flow control, an accurate model describing fluid flow in micron-scale devices must be available. In this report we compare the predictions of the Navier-Stokes equations with experimental results for three-port devices with flow restrictors. The good agreement seen indicates that flow restrictors with 1-µm dimensions can be designed using solutions to the Navier-Stokes equations.

Automated Microchip Platform for Biochemical Analysis

The development of the components and subsystems of an automated microchipbased platform for bioanalysis by immunoassay and gene probe assay is described. The device uses micromachined glass plates for the fabrication of channel networks and combines electroosmotic pumping and capillary electrophoresis for fluid transport and separation. The complete system enables the on-chip integration of the key elements in analytical processing: injection, mixing, separation, detection and elimination. The analysis platform is being designed for use with an on-line aerosol collector for environmental monitoring.