Hossein Salimi-Moosavi

A multireflection cell for enhanced absorbance detection in microchip-based capillary electrophoresis devices

The design, fabrication and testing of a photolithographically fabricated, glass‐based multireflection absorbance cell for microfluidic devices, in particular microchip‐based capillary electrophoresis (CE) systems is described. A multireflection cell was fabricated lithographically using a three‐mask process to pattern aluminum mirrors above and below a flow channel in a chip, with 30 μm diameter optical entrance or exit apertures (one in each mirror) positioned 200 μm apart. Source and detector were positioned on opposite sides, and the metal mirrors were made 1 cm square, to reduce stray light effects. Calibration curves using bromothymol blue (BTB) with a 633 nm source (He:Ne laser) were linear to at least 0.5 absorbance units, with typical r2 values of 0.9997, relative standard deviations in the slopes of ± 1.3%, and intercepts of zero within experimental error. Effective optical pathlengths of 50—272 μm were achieved, compared to single‐pass pathlengths of 10—30 μm, corresponding to sensitivity enhancements (i.e., optical path length increase) of 5 to 10‐fold over single‐pass devices. Baseline absorbance noise varied within a factor of two in almost all devices, depending only weakly on path length. This device can give much higher absorbance sensitivity, and should be much easier to manufacture than planar, glass‐based devices previously reported.

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.

Biology Lab-on-a Chip for Drug Screening

A microfluidic device was designed and tested for screening anti-inflammatory drug candidates using the cell rolling method. Channels were coated with either E- or P-Selectin (adhesion molecule), and isolated human neutrophils or lymphocytes were allowed to roll on the Selectin coated surface under flow conditions which mimic blood flow in the vascular capillary. Undiluted human blood was successfully tested for cell rolling and inhibition. Anti E- or P- Selectin, Sialyl Lewisx and Fucoidan were tested for the inhibition of cell rolling.

Single Cell Enzymatic Analysis on a Microchip: Lysing of Single Cells and Identification of Their β-Galactosidase Activity

Microchips are introduced as a platform for performing single cell assays. On-chip lysis and incubation of single HL-60 cells with FDG, a fluorogenic, β-galactosidase specific, substrate, followed by detection of the fluorescence response is demonstrated. The advantages of chip based enzymatic single cell analyses are highlighted.

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.