Biomedical subjects

S Douglass Gilman

Publications and source records attributed to S Douglass Gilman.

6 recordsLinked to original sources

PubMed2006

Measuring electroosmotic flow in microchips and capillaries.

Electrophoretic migration and electroosmotic flow (EOF) combine to determine the migration rate of charged compounds in capillary electrophoresis (CE) and microchip capillary electrophoresis (MCE). Uncontrolled and unmeasured changes in EOF will lead to irreproducible peak migration times and poor peak quantitation. The two most common methods for measuring EOF for CE and MCE are detailed. Experimental results for application of the neutral marker method and the current monitoring method to EC are presented, and related calculations of EOF rates and electroosmotic mobility are described. The strengths and shortcomings of these two EOF measurement techniques are discussed. Additional approaches for studying and measuring EOF and for improving the reproducibility of migration times for CE and MCE are summarized.

Electrochemistry↗

PubMed2003

Experimental studies of electroosmotic flow dynamics during sample stacking for capillary electrophoresis.

Electroosmotic flow dynamics during a field-amplified sample stacking experiment have been studied experimentally using the periodic photobleaching of a dilute, neutral fluorophore added to the separation buffer. The effects of hydrodynamically injecting different sample plug lengths containing a mixture of arsenic compounds dissolved in 0.125 mM (120, 240, and 600 s) and 41.7 microM (27, 45, and 74 s) phosphate buffer with a separation buffer concentration of 12.5 mM phosphate buffer were examined. Changes in electroosmotic flow during sample stacking and separation were monitored at a rate of 1 Hz. The observed effects of increasing the sample plug length on electroosmotic flow and electrophoretic current agreed qualitatively with predictions by theoretical models presented in the literature. Electroosmotic flow changes on the order of 100% (1.6-3.3 mm/s) were observed. Broadening of the flow monitoring peaks has been used to examine parabolic flow due to the discontinuous buffer systems used for sample stacking.

Journal Article↗

PubMed2003

Experimental studies of electroosmotic flow dynamics in microfabricated devices during current monitoring experiments.

Electroosmotic flow (EOF) was monitored in glass microfluidic devices at rates up to 2 Hz with a precision of 0.2-1.0% using a technique based on the periodic photobleaching of a dilute, neutral fluorophore added to the running buffer. This EOF monitoring method was used to examine the performance of the current monitoring technique for measuring an average electroosmotic flow in a microfluidic device with a cross-T design. Flow measurements made with the current monitoring method gave a precision of 0.4-2.2%, but the periodic photobleaching method shows that the current monitoring technique causes changes in EOF as high as 41% during a single experiment. The periodic photobleaching method for EOF monitoring was also used to study EOF in channels on opposite sides of a cross-channel intersection. The opposite channels were shown to exhibit substantially different EOF dynamics during a current monitoring experiment as well as different steady-state EOF rates during normal operating conditions.

Journal Article↗

PubMed2003

Ultrasound-mediated release of iron from ferritin.

We investigated the release of iron from ferritin in aqueous solutions exposed to high-frequency ultrasound (US). Our data suggests that superoxide produced as a result of ultrasonic cavitation acts as a reducing agent, enabling the release of iron from ferritin. We also found that the release of ferritin iron during US exposure is enhanced by the addition of 5-hydroxy-1,4-naphthoquinone. We hypothesize that this quinone is ultrasonically transformed into a semiquinone radical capable of directly and indirectly reducing Fe(3+) in ferritin to soluble Fe(2+). Our proposed mechanism for the release of iron from ferritin adds new insight to the synergistic effect of quinone-containing cancer drugs with US.

Antineoplastic Agents↗

PubMed2002

Studies of reversible inhibition, irreversible inhibition, and activation of alkaline phosphatase by capillary electrophoresis.

Reversible inhibition, irreversible inhibition, and activation of calf intestinal alkaline phosphatase (EC 3.1.3.1) have been studied by capillary electrophoresis. The capillary electrophoretic enzyme-inhibitor assays were based on electrophoretic mixing of inhibitor and enzyme zones in a substrate-filled capillary. Enzyme inhibition was indicated by a decrease in product formation detected in the capillary by laser-induced fluorescence. Reversible enzyme inhibitors could be quantified by Michaelis-Menten treatment of the electrophoretic data. Reversible, competitive inhibition of alkaline phosphatase by sodium vanadate and sodium arsenate has been examined, and reversible, noncompetitive inhibition by theophylline has been studied. The K(i) values determined for these reversible inhibitors using capillary electrophoresis are within the range of values reported in the literature for the same enzyme-inhibitor combinations. Irreversible inhibition of alkaline phosphatase by EDTA at concentrations of 1.0mM and above has been observed. Activation of alkaline phosphatase has also been observed for EDTA at concentrations from 20 to 400 microM.

Alkaline Phosphatase↗

PubMed2002

Laser ablation construction of on-column reagent addition devices for capillary electrophoresis.

A simple and reproducible technique for constructing perfectly aligned gaps in fused-silica capillaries has been developed for postcolumn reagent addition with capillary electrophoresis. This technique uses laser ablation with the second harmonic of a Nd:YAG laser (532 nm) at 13.5 mJ/pulse and a repetition rate of 15 Hz to create these gaps. A capillary is glued to a microscope slide and positioned at the focal point of a cylindrical lens using the focused beam from a laser pointer as a reference. Gaps of 14.0 +/- 2.2 microm (n = 33) at the bore of the capillary are produced with a success rate of 94% by ablation with 400 pulses. This simple method of gap construction requires no micromanipulation under a microscope, hydrofluoric acid etching, or use of column fittings. These structures have been used for reagent addition for postcolumn derivatization with laser-induced fluorescence detection and have been tested for the separation of proteins and amino acids. Detection limits of 6 x 10(-7) and 1 x 10(-8) M have been obtained for glycine and tranferrin, respectively. Separation efficiencies obtained using these gap reactors range from 38,000 to 213,000 theoretical plates.

Electrophoresis, Capillary↗