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Biomedical subjects

J P Burt

Publications and source records attributed to J P Burt.

10 recordsLinked to original sources
PubMed1998

Manipulation of herpes simplex virus type 1 by dielectrophoresis.

The frequency-dependent dielectrophoretic behaviour of an enveloped mammalian virus, herpes simplex virus type 1 is described. It is demonstrated that over the range 10 kHz-20 MHz, these viral particles, when suspended in an aqueous medium of conductivity 5 mS m(-1), can be manipulated by both positive and negative dielectrophoresis using microfabricated electrode arrays. The observed transition from positive to negative dielectrophoresis at frequencies around 4.5 MHz is in qualitative agreement with a simple model of the virus as a conducting particle surrounded by an insulating membrane.

Biophysics↗
PubMed1998

Future trends in diagnosis using laboratory-on-a-chip technologies.

There has been an enormous growth in the development of biotechnological applications, where advances in the techniques of microelectronic fabrication and the technologies of miniaturization and integration in semiconductor industries are being applied to the production of Laboratory-on-a-Chip devices. The aim of this development is to create devices that will perform the same processes that are currently carried out in the laboratory in reduced timescales, at a lower cost, requiring less reagents, and with a greater resolution of detection and specificity. The expectations of this Laboratory-on-a-Chip revolution is that this technology will facilitate rapid advances in gene discovery, genetic mapping and gene expression with broader applications ranging from infectious diseases and cancer diagnostics to food quality and environmental testing. A review of the current state of development in this field reveals the scale of the ongoing revolution and serves to highlight the advances that can be perceived in the development of Laboratory-on-a-Chip technologies. Since miniaturization can be applied to such a wide range of laboratory processes, some of the sub-units that can be used as building blocks in these devices are described, with a brief description of some of the fabrication processes that can be used to create them.

Animals↗
PubMed1998

Automatic cell electrorotation measurements: studies of the biological effects of low-frequency magnetic fields and of heat shock.

A computer-aided automatic imaging technique has been developed for measuring the electrorotation spectra of up to 256 particles at the same time. This offers advantages over the conventional manual method, especially when rapidly acquired statistical data are necessary in investigations of the response of cells or test beads to chemical exposure, for example. We have applied this technique to investigate the biological effects of heat shock and low-frequency EM fields reported by others for yeast cells. Although heat shock effects were observed, no changes of the electrorotational behaviour could be detected after exposing the cells to 50 Hz, 8 and 80 microT fields. Although this does not rule out the possibility that the cells were influenced by the magnetic fields, it does limit the number of possible physicochemical changes that might have occurred to their cell walls and membranes.

Automation↗
PubMed1996

Assays for microbial contamination and DNA analysis based on electrorotation.

A new assay is described for determining the concentration and viability of waterborne micro-organisms. The method exploits the fact that when a latex bead coated with a specific binding agent is complexed to the target analyte, the analyte complex formed assumes new dielectric properties that can be monitored by its electrorotation response. This generic technology is applicable to a wide range of organism and toxicological diagnostic tests, as well as to other areas of biotechnology. An example is given of its possible application to DNA sequence analysis.

Animals↗
PubMed1994

The lack of evidence for ELF magnetic-field effects on bilayer membranes and reconstituted membrane channels.

The effects of low-frequency (10-500 Hz) magnetic fields on the electrical properties of channel-free bilayer membranes, and on the single-channel conductance and macroscopic gating characteristics of porin channels incorporated into membranes, have been studied for field strengths in the range 10-100 microT. The field conditions that could in theory give rise to 'cyclotron resonance' effects were also studied. No evidence has been found to support the concept that cyclotron resonance and membrane ion channel effects are involved in the reported biological effects of ELF magnetic fields.

Dose-Response Relationship, Radiation↗
PubMed1993

Membrane changes accompanying the induced differentiation of Friend murine erythroleukemia cells studied by dielectrophoresis.

Dielectrophoresis measurements obtained using an image processing technique are reported over the frequency range 1 Hz to 100 kHz for the Friend murine erythroleukemia cell lines DS19 and R1 before and after treatment with hexamethylene bisacetamide and dimethylsulfoxide, agents that induce terminal differentiation in DS19 but not in R1 cells. Data are analyzed according to the single shell dielectric model of the cell. The membrane capacitance was found to fall by 30% and membrane conductivity by a factor of at least 5 when DS19 cells were induced to differentiate. R1 cells showed no such response. While the theoretical model was found to be useful for comparing differences in data for the different cell lines, several significant discrepancies between its predictions and the experimental data were observed, including positive dielectrophoretic collection at frequencies below 20 Hz and a smaller than predicted response to the membrane permeabilizing agents saponin and valinomycin. Factors that may have accounted for these discrepancies include surface charge effecgs, conduction parallel to the plasma membrane surface, and intracellular compartments.

Cell Differentiation↗
PubMed1992

The SCS/ARS/CES pesticide properties database for environmental decision-making.

The only thing all pesticides have in common is that they are used to control pests. Otherwise, they come from almost every imaginable class of chemical. Everyone associated with pesticide use--farmers, Extension, EPA, state regulatory agencies, manufacturers, and environmentalists--needs information that will allow them to distinguish between pesticides that may be a problem as pollutants in certain situations, and those which may not. There are five basic properties that, when combined with information about site and use, provide much information about the potential of a pesticide to be a pollutant. These five properties are solubility in water, volatility, soil sorption tendency, persistence, and ionization potential. We have compiled the most complete collection of these properties available, using others' compilations but verifying values from the primary literature in many cases. A complete primary literature search was not done. For each parameter we suggest a "Selected Value" which we believe to be the best available, recognizing, however, that persistence and soil sorption are sensitive to specific site conditions. These Selected Values are being incorporated into pesticide environmental-impact risk assessment procedures by state and federal agencies, and are considered to be consensus values. However, there is a serious potential for misuse of these data, particularly the error of using small differences between active ingredients to make regulatory distinctions between them. The ability to relate these data to environmental impact is an essential need and is improving, but is currently at a primitive level.

Animals↗
PubMed1990

Dielectrophoretic characterisation of Friend murine erythroleukaemic cells as a measure of induced differentiation.

Dielectrophoresis measurements, the study of the motion of particles in non-uniform a.c. electrical fields, have been made on three cell lines (DS19, R1 and DR1) of Friend murine erythroleukaemia cells as a function of hexamethylene bisacetamide (HMBA) treatment. The effects of saponin treatment on R1 cells and neuraminidase on human red blood cells were also studied. It is shown that the dielectrophoretic behaviour can be interpreted in terms of cell surface charge and cell membrane conductivity effects. HMBA reduces the cell surface charge on all three cell lines, and in lines DS19 and DR10, where the cells are induced to differentiate, there is an increase in effective cell conductivity. This gain in conductivity is concluded to be associated with either an enhanced lateral electrophoretic motion of delocalised ions or of the polarisability of dipoles at the membrane surface.

Acetamides↗
PubMed1988

Applications of a new optical technique for measuring the dielectrophoretic behaviour of micro-organisms.

It is shown that the dielectrophoretic behaviour (motion in non-uniform a.c. electric fields) of micro-organisms can conveniently and reproducibly be measured by monitoring the decrease in optical absorbance of a cell suspension as the cells are collected at a micro-electrode array. The dielectrophoretic behaviour, as a function of the frequency of the applied electric field and conductivity of the supporting solution, can be determined more quantitatively and rapidly than by methods so far described in the literature. Results are presented for Micrococcus lysodeikticus, Bacillus subtilis and Escherichia coli for the frequency range 20 Hz to 4 MHz and theoretical considerations are presented for the effect of solution conductivity. A value of 0.2 S/m has been derived for the effective conductivity of M. lysodeikticus.

Bacillus subtilis↗