Biomedical subjects

Jason Shih

Publications and source records attributed to Jason Shih.

3 recordsLinked to original sources

PubMed2005

Microfluidic platform for liquid chromatography-tandem mass spectrometry analyses of complex peptide mixtures.

A microfluidic chip that integrates all the fluidic components of a gradient liquid chromatography (LC) system is described. These chips were batch-fabricated on a silicon wafer using photolithographic processes and with Parylene as the main structural material. The fabricated chip includes three electrolysis-based electrochemical pumps, one for loading the sample and the other two for delivering the solvent gradient; platinum electrodes for delivering current to the pumps and establishing the electrospray potential; a low-volume static mixer; a column packed with silica-based reversed-phase support; integrated frits for bead capture; and an electrospray nozzle. The fabricated structures were able to withstand pressures in excess of 250 psi. The device was used to perform a liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of a mixture of peptides from the trypsin digestion of bovine serum albumen (BSA). Gradient elution through the 1.2-cm column was performed at a flow rate of 80 nL/min. Compared to the analysis of the same sample using a commercial nanoflow LC system, the chromatographic resolution was nearly as good, and the total cycle time was significantly reduced because of the minimal volume between the pumps and the column. Results demonstrate the potential of mass-produced, low-cost microfluidic systems capable of performing LC separations for proteomics applications.

Amino Acid Sequence↗

PubMed2004

Surface micromachined electrostatically actuated micro peristaltic pump.

An electrostatically actuated micro peristaltic pump is reported. The micro pump is entirely surface micromachined using a multilayer parylene technology. Taking advantage of the multilayer technology, the micro pump design enables the pumped fluid to be isolated from the electric field. Electrostatic actuation of the parylene membrane using both DC and AC voltages was demonstrated and applied to fluid pumping based on a 3-phase peristaltic sequence. A maximum flow rate of 1.7 nL min(-1) and an estimated pumping pressure of 1.6 kPa were achieved at 20 Hz phase frequency. A dynamic analysis was also performed with a lumped-parameter model for the peristaltic pump. The analysis results allow a quantitative understanding of the peristaltic pumping operation, and correctly predict the trends exhibited by the experimental data. The small footprint of the micro pump is well suited for large-scale integration of microfluidics. Moreover, because the same platform technology has also been used to fabricate other devices (e.g. valves, electrospray ionization nozzles, filters and flow sensors), the integration of these different devices can potentially lead to versatile and functional micro total analysis systems (microTAS).

Equipment Design↗

PubMed2004

An electrochemical pumping system for on-chip gradient generation.

Within the context of microfluidic systems, it has been difficult to devise pumping systems that can deliver adequate flow rates at high pressure for applications such as HPLC. An on-chip electrochemical pumping system based on electrolysis that offers certain advantages over designs that utilize electroosmotic driven flow has been fabricated and tested. The pump was fabricated on both silicon and glass substrates using photolithography. The electrolysis electrodes were formed from either platinum or gold, and SU8, an epoxy-based photoresist, was used to form the pump chambers. A glass cover plate and a poly(dimethylsiloxane) (PDMS) gasket were used to seal the chambers. Filling of the chambers was accomplished by using a syringe to inject liquid via filling ports, which were later sealed using a glass cover plate. The current supplied to the electrodes controlled the rate of gas formation and, thus, the resulting fluid flow rate. At low backpressures, flow rates >1 microL/min have been demonstrated using <1 mW of power. Pumping at backpressures as high as 200 psi have been demonstrated, with 20 nL/min having been observed using <4 mW. By integrating two electrochemical pumps with a polymer electrospray nozzle, we have confirmed the successful generation of a solvent gradient via a mass spectrometer.

Coated Materials, Biocompatible↗