Biomedical subjects

Jeremy D Ramsey

Publications and source records attributed to Jeremy D Ramsey.

3 recordsLinked to original sources

PubMed2005

Integrated microfluidic device for solid-phase extraction coupled to micellar electrokinetic chromatography separation.

An integrated microdevice was utilized for the autonomous coupling of solid-phase extraction (SPE) to micellar electrokinetic chromatography (MEKC). Porous plugs of polymethacrylate polymer approximately 200 microm in length) were fabricated by ultraviolet irradiation in microchannels. Microcolumns of hydrophobic beads packed against the polymethacrylate plugs were utilized for the quantitative extraction of rhodamine B, yielding preconcentration factors over 200 for a 90-s extraction. The calculated detection limit for this dye was 60 fM. A sample of coumarin dyes were concentrated by SPE, eluted in a nonaqueous solvent from a separate on-chip reservoir, and injected by a gated valve onto a separate column for MEKC analysis. Using the integrated device, a completely automated sequence of extraction, elution, injection, separation, and detection were performed in less than 5 min. Observed separation efficiencies were high, with plate heights below 2 microm. The analysis was at least 3 times faster than semiautomated, conventional, solid-phase extraction, while requiring no user intervention. The design, fabrication, and autonomous operation of the device is discussed.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2004

Compact, high voltage power supply for the lab-on-a-chip.

The design, construction and operation of a simple, inexpensive and compact high voltage power supply (HVPS) for use in conjunction with a simple cross capillary electrophoresis microchip is presented. The microchip HVPS utilizes a single high voltage power supply (15 kV), a voltage-divider network, to give the voltages necessary to operate a gated injection valve, and two high voltage relays for switching between the open and closed gate sequences of the injection. In order to accommodate the application of different simple cross microchip dimensions, a set of equations for defining the resistor network and ensuring proper gate performance are presented.

Electric Power Supplies↗

PubMed2003

High-efficiency, two-dimensional separations of protein digests on microfluidic devices.

High-efficiency, two-dimensional separations of tryptic digests were achieved using glass microfluidic devices. Following micellar electrokinetic chromatography (MEKC) separations in a 19.6-cm-long serpentine channel, the peptides were rapidly sampled into a 1.3-cm-long second-dimension channel, where they were separated by capillary electrophoresis (CE). The turns in the serpentine channel were asymmetrically tapered to minimize geometrical contributions to band broadening and to provide ample channel length for high-efficiency chromatographic separations. Analysis of rhodamine B injections routinely produced plate numbers of 230000 and 40000 in the first (MEKC) and second (CE) dimensions, respectively, corresponding to plate heights of 0.9 and 0.3 microm. The electric field strengths were 200 V/cm for MEKC and 2400 V/cm for CE. In analysis times less than 15 min, two-dimensional separation of bovine serum albumin tryptic digest produced a peak capacity of 4200 (110 in the first dimension and 38 in the second dimension). The system was used to identify a peptide from a tryptic digest of ovalbumin using standard addition and to distinguish between tryptic digests of human and bovine hemoglobin.

Animals↗