Biomedical subjects

Andrew A Gewirth

Publications and source records attributed to Andrew A Gewirth.

22 records · Page 2Linked to original sources

PubMed2003

Peroxide electroreduction on bi-modified Au surfaces: vibrational spectroscopy and density functional calculations.

The mechanism of the electroreduction of peroxide on Bi-submonolayer-modified Au(111) surfaces is examined using surface-enhanced Raman scattering (SERS) measurements along with detailed density functional theory (DFT) calculations. The spectroscopy shows the presence of Bi-OH and Bi-O species at potentials just positive of that where peroxide is reduced. These species are not present in solutions absent either peroxide or Bi. DFT calculations show that peroxide is unstable relative to Bi-OH when Bi is present in the (2 x 2) configuration on Au(111) known from previous work to be catalytically active. The spacing between Bi adatoms is such that peroxide association with two Bi cannot occur without O-O bond cleavage. The full Bi monolayer is catalytically inactive and exhibits none of the Bi-OH or Bi-O signals seen for the active surface. The calculations show that as the Bi coverage becomes greater and the Bi adatom spacing becomes smaller, peroxide can adsorb on Bi without O-O bond rupture. These results indicate an important role for M-OH species in peroxide electroreduction.

Journal Article↗

PubMed2002

Materials science of the gel to fluid phase transition in a supported phospholipid bilayer.

We report the results of in situ AFM measurements examining the phase transition of bilayers formed from the zwitterionic phospholipid, DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine, supported on mica. The images show that the fluid to gel phase transition process features substantial tearing of the bilayer due to the density change between the two phases. The gel to fluid transition is strongly affected by the resultant stress introduced into the gel phase, which changes the degree of cooperativity, the shape of developing fluid phase regions, and the course of the transition.

Aluminum Silicates↗

PubMed2002

A split microchannel design and analytical model to compensate for electroosmotic instabilities in micro-separations.

Organic polymers offer many advantages as materials for the construction of microfluidic devices but suffer frequently from the limitation that the electrodynamic flow they support can exhibit considerable instability. This article describes a split-channel microfluidic device that can be used to compensate for changes in electroosmotic flow. The design of the separation system divides an analyte plug after injection between two separation channels of differing length. The two channels are later recombined for single point detection, eliminating the need for a scanning optical detection system. The utility of this simple design lies in the fact that the migration time of any analyte can be referenced to its twin in the parallel separation channel. This eliminates the need for a separate electroosmotic marker and allows mobilities measured in multiple devices to be compared quantitatively. Using a model adopted from the literature, the data from the split channel system can be used to precisely account for the drift that characterizes electrophoretic separations made in a polymer chip. The relative standard deviations of the analyte mobilities measured for replicate runs on multiple devices were reduced from values as high as 20% to ca. 1% RSD. This internal standardization procedure also appears to address other sources of drift in the electroosmotic flow (EOF) supported by the polymer microchannel, eliminating the need for careful monitoring of either the temperature or reservoir pH between separation runs.

Journal Article↗

PubMed2002

Indirect fluorescence detection of simple sugars via high-pH electrophoresis in poly(dimethylsiloxane) microfluidic chips.

This article describes the successful electrophoretic separation of simple carbohydrates in a polymeric microfluidic chip. The device fabricated in poly(dimethylsiloxane) (PDMS) is found to be stable in high-pH solutions. This allows sugars to be separated electrophoretically at pH values at or above their pK(a) using indirect fluorescence detection. Signal-to-noise values greater than 10:1 were obtained using a mercury arc lamp excitation source and a fluorescein-containing mobile phase for the detection of sugars at concentrations as low as 5 mM. The results obtained compare favorably with published results for the same system using a traditional fused-silica capillary. Analysis of the data revealed a significant experimental sensitivity of the migration times measured in these PDMS devices, an aging effect that leads to considerable systematic drift over the course of a series of replicate measurements. These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device. Channel priming at high pH provides a necessary, but by itself insufficient, means by which this instability can be minimized.

Carbohydrates↗