Biomedical subjects

M Gaitan

Publications and source records attributed to M Gaitan.

6 recordsLinked to original sources

PubMed2001

Temperature measurement in microfluidic systems using a temperature-dependent fluorescent dye.

A technique is described for the measurement of fluid temperatures in microfluidic systems based on temperature-dependent fluorescence. The technique is easy to implement with a standard fluorescence microscope and CCD camera. In addition, the method can be used to measure fluid temperatures with micrometer spatial resolution and millisecond time resolution. The efficacy of the method is demonstrated by measuring temperature distributions resulting from Joule heating in a variety of microfluidic circuits that are electrokinetically pumped. With the equipment used for these measurements, fluid temperatures ranging from room temperature to 90 degrees C were measured with a precision ranging from 0.03 to 3.5 degrees C-dependent on the amount of signal averaging done. The spatial and temporal resolutions achieved were 1 microm and 33 ms, respectively.

Journal Article↗

PubMed2001

Laser modification of preformed polymer microchannels: application to reduce band broadening around turns subject to electrokinetic flow.

A pulsed UV excimer laser (KrF, 248 nm) was used to modify the surface charge on the side wall of hot-embossed microchannels fabricated in a poly(methyl methacrylate) substrate. Subablation level fluences, less than 2,385 mJ/cm2, were used to prevent any changes in the physical morphology of the surface. It is shown that the electroosmotic mobility, induced by an electric field applied along the length of the channel, increases by an average of 4% in the regions that have been exposed to UV laser pulses compared to nonexposed regions. Furthermore, application of UV modification to electroosmotic flow around a 90 degrees turn results in a decrease in band broadening, as measured by the average decrease in the plate height of 40% compared to flow around a nonmodified turn. The ability to modify the surface charge on specific surfaces within a preformed plastic microchannel allows for fine control, adjustment, and modulation of the electroosmotic flow without using wall coatings or changing the geometry of the channel to achieve the desired flow profile.

Journal Article↗

PubMed2000

Control of flow direction in microfluidic devices with polyelectrolyte multilayers.

Electroosmotic flow (EOF) is commonly utilized in microfluidics. Because the direction of the EOF can be determined by the substrate surface charge, control of the surface chemical state offers the potential, in addition to voltage control, to direct the flow in microfluidic devices. We report the use of polyelectrolyte multilayers (PEMs) to alter the surface charge and control the direction of flow in polystyrene and acrylic microfluidic devices. Relatively complex flow patterns with simple arrangements of applied voltages are realized by derivatization of different arms of a single device with oppositely charged polyelectrolytes. In addition, flow in opposite directions in the same channel is possible. A positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows. Derivatization of the two sides of a plastic microchannel with oppositely charged polyelectrolytes was used to achieve side-by-side opposite flows. The flow is characterized using fluorescence imaging and particle velocimetry.

Journal Article↗

PubMed2000

Room-temperature imprinting method for plastic microchannel fabrication

A new plastic imprinting method using a silicon template is demonstrated. This new approach obviates the necessity of heating the plastic substrate during the stamping process, thus improving the device yield from approximately 10 devices to above 100 devices per template. The dimensions of the imprinted microchannels were found to be very reproducible, with variations of less than 2%. The channel depths were dependent on the pressures applied and the materials used. Rather than bonding the open channels with another piece of plastic, a flexible and adhesive poly(dimethylsiloxane) film is used to seal the microchannels, which offers many advantages. As an application, isoelectric focusing of green fluorescence protein on these plastic microfluidic devices is illustrated.

Journal Article↗

PubMed1998

Growing pains: status of emergency medicine in Nicaragua.

Nicaragua is one of the poorest nations in the Western Hemisphere. The health of the population suffers as a result of poor nutrition, epidemic diseases, natural and manmade disasters, sporadic violence, urban industrial growth, and inadequate government funding for even basic medical equipment and supplies. Within this environment, emergency services development has been recognized as an important and cost-effective public health intervention. In recent years, government and nongovernmental agencies working together have had a dramatic positive impact on the quality of emergency care provided.

Delivery of Health Care↗

PubMed1997

Fabrication of plastic microfluid channels by imprinting methods.

Microfluidic devices have been fabricated on poly(methyl methacrylate) substrates by two independent imprinting techniques. First-generation devices were fabricated using a small-diameter wire to create an impression in plastics softened by low-temperature heating. The resulting devices are limited to only simple linear channel designs but are readily produced at low cost. Second-generation devices with more complex microchannel arrangements were fabricated by imprinting the plastic substrates using an inverse three-dimensional image of the device micromachined on a silicon wafer. This micromachined template may be used repeatedly to generate devices reproducibly. Fluorescent analtyes were used to demonstrate reproducible electrophoretic injections. An immunoassay was also performed in an imprinted device as a demonstration of future applications.

Indicators and Reagents↗