Biomedical subjects

Robert H Austin

Publications and source records attributed to Robert H Austin.

25 records · Page 2Linked to original sources

PubMed2003

Parallel microchannel-based measurements of individual erythrocyte areas and volumes.

We describe a microchannel device which utilizes a novel approach to obtain area and volume measurements on many individual red blood cells. Red cells are aspirated into the microchannels much as a single red blood cell is aspirated into a micropipette. Inasmuch as there are thousands of identical microchannels with defined geometry, data for many individual red cells can be rapidly acquired, and the fundamental heterogeneity of cell membrane biophysics can be analyzed. Fluorescent labels can be used to quantify red cell surface and cytosolic features of interest simultaneously with the measurement of area and volume for a given cell. Experiments that demonstrate and evaluate the microchannel measuring capabilities are presented and potential improvements and extensions are discussed.

Cell Size↗

PubMed2002

Bacterial chromosome extraction and isolation.

We have used diffusive mixing and dielectrophoretic trapping to lyse Escherichia coli cells in a microfabricated environment and trap the E. coli chromosome. We characterize the conditions needed for efficient lysis of the cells, and conditions needed for the dielectrophoretic trapping of the chromatin without the trapping of cytoplasmic proteins.

Chromosomes, Bacterial↗

PubMed2002

Role of molecular size in ratchet fractionation.

We show the importance of finite particle size in microfluidic asymmetric continuous-flow diffusion arrays, specifically the critical nature of the particle size with respect to the barrier gaps. We show that particles much smaller than the barrier gap follow individual field lines through narrow gaps and are poorly fractionated. In contrast, particles comparable to the gap size lose memory of their incoming field line and can be fractionated with high resolution. We demonstrate this effect using a new technological approach to create very straight and narrow injection bands in such arrays, and completely resolve bands of DNA of lengths 48,500 and 16,7000 base pairs.

Bacteriophage T4↗

PubMed2002

A DNA prism for high-speed continuous fractionation of large DNA molecules.

The analysis and fractionation of large DNA molecules plays a key role in many genome projects. The standard method, pulsed-field gel electrophoresis (PFGE), is slow, with running times ranging from 10 hours to more than 200 hours. In this report, we describe a thumbnail-sized device that sorts large DNA fragments (61-209 kilobases (kb)) in 15 seconds, with a resolution of approximately 13%. An array of micron-scale posts serves as the sieving matrix, and integrated microfluidic channels spatially shape the electric fields over the matrix. Asymmetric pulsed fields are applied for continuous-flow operation, which sorts DNA molecules in different directions according to their molecular masses, much as a prism deflects light of different wavelengths at different angles. We demonstrate the robustness of the device by using it to separate large DNA inserts prepared from bacterial artificial chromosomes, a widely used DNA source for most genomics projects.

Chemical Fractionation↗

PubMed2002

Continuous separation of biomolecules by the laterally asymmetric diffusion array with out-of-plane sample injection.

The laterally asymmetric diffusion array, a biomolecule sorting device, was used to continuously separate a mixture of T2 and T7 coliphage DNA molecules into its constituents. A two-dimensional array of obstacles (in the presence of an average flow v) can be used to rectify the Brownian motion of particles (in this case DNA molecules) so that they diffuse preferentially in one direction, and perpendicular to the direction of the applied field (in this case an electric field). This type of device had not yet been used for actual fractionation of biomolecules, due to difficulties in injection of the sample. Here we show that with a new injection strategy a well-defined, narrow and continuous stream of molecules can be injected into the separation channel, thus enabling this separation technique to be used in a working device. We expect this type of device could now be employed for separation of a variety of different biomolecules, ranging from long dsDNA to small proteins.

Bacteriophage T4↗

PubMed2002

Electrodeless dielectrophoresis of single- and double-stranded DNA.

Dielectrophoretic trapping of molecules is typically carried out using metal electrodes to provide high field gradients. In this paper we demonstrate dielectrophoretic trapping using insulating constrictions at far lower frequencies than are feasible with metallic trapping structures because of water electrolysis. We demonstrate that electrodeless dielectrophoresis (EDEP) can be used for concentration and patterning of both single-strand and double-strand DNA. A possible mechanism for DNA polarization in ionic solution is discussed based on the frequency, viscosity, and field dependence of the observed trapping force.

Biophysical Phenomena↗

PubMed2001

Excited-state lifetimes of far-infrared collective modes in proteins.

Vibrational excitations of low frequency collective modes are essential for functionally important conformational transitions in proteins. Here we report the first direct measurement on the lifetime of vibrational excitations of the collective modes at 87 microm (115 cm(-1)) in bacteriorhodopsin, a transmembrane protein. The data show that these modes have extremely long lifetime of vibrational excitations, over 500 ps, accommodating 1500 vibrations. We suggest that there is a connection between this relatively slow anharmonic relaxation rate of approximately 10(9) sec(-1) and the similar observed rate of conformational transitions in proteins, which require multilevel vibrational excitations.

Protein Conformation↗