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Biomedical subjects

Michael P Hughes

Publications and source records attributed to Michael P Hughes.

11 recordsLinked to original sources
PubMed2006

Dielectrophoretic separation of Bacillus subtilis spores from environmental diesel particles.

Isolation of pathogenic bacteria from non-biological material of similar size is a vital sample preparation step in the identification of such organisms, particularly in the context of detecting bio-terrorist attacks. However, many detection methods are impeded by particulate contamination from the environment such as those from engine exhausts. In this paper we use dielectrophoresis--the induced motion of particles in non-uniform fields--to successfully remove over 99% of diesel particulates acquired from environmental samples, whilst letting bacterial spores of B. subtilis pass through the chamber largely unimpeded. We believe that such a device has tremendous potential as a precursor to a range of detection methods, improving the signal-to-noise ratio and ultimately improving detection rates.

Bacillus subtilis↗
PubMed2006

Early detection of oral cancer - Is dielectrophoresis the answer?

The early detection of oral squamous cell carcinoma by non-invasive methods has the potential to hasten diagnosis and thus lessen the morbidity associated with tumour therapy. Dielectrophoresis (DEP) can non-invasively determine electrophysiological parameters such as conductivity and permittivity of cellular cytoplasm and membrane. The present study demonstrates that DEP can be utilised to characterise H357 and UP cells and reveals that there are significant differences in these parameters between malignant and more normal epithelial cell lines. The present results suggest that DEP has potential for the early detection of cancerous from non-cancerous cells in a clinical setting.

Carcinoma, Squamous Cell↗
PubMed2006

Differences in the biophysical properties of membrane and cytoplasm of apoptotic cells revealed using dielectrophoresis.

We have used dielectrophoresis to determine the dielectric properties of human chronic myelogeneous leukaemic (K562) cells during apoptosis (programmed cell death). Our results indicate that K562 cells increase markedly in cytoplasmic conductivity from 0.28 S/m to 0.50 S/m within the first 4 h following treatment with staurosporine, which then lasts beyond 12 h, whilst cell shrinkage increases the capacitance of the membrane from 9.7 mF/m2 to 20 mF/m2. After 24 and 48 h of incubation with staurosporine, multiple sub-populations were detected, highlighted by the dielectric changes that the cell undergoes before death. By comparing these results with those obtained by common apoptosis monitoring techniques Annexin V and TMRE (tetramethylrhodamine ethylester), it is possible to infer the role of ion efflux in the progress of apoptosis. The use of dielectrophoresis for monitoring apoptosis offers a number of benefits as it is both rapid and non-invasive. It can also be used in parallel with other assays in high-throughput screening applications.

Annexin A5↗
PubMed2005

Extraction of dielectric properties of multiple populations from dielectrophoretic collection spectrum data.

In this paper we show how simplifying assumptions can be used to extract useful data from the dielectrophoretic collection spectrum, in particular for the cytoplasm, and hence determine the properties of multiple populations of cells within a sample. Specifically, the observation of the frequencies of onset of dielectric dispersion allows the identification and enumeration of populations of cells according to cytoplasmic conductivity, with particular relevance to the determination of the action of drugs for high-throughput screening applications.

Algorithms↗
PubMed2005

A high-throughput 3-D composite dielectrophoretic separator.

Dielectrophoresis has great potential to offer a range of diverse fields from bioprocessing to clinical medicine, but is hampered by low throughput rates to the micrometer scale of the electrodes required to generate highly nonuniform fields. Here we describe a novel approach to electrode construction, using a drilled laminated structure to form channels bearing electrodes 30 microm across and 150 microm apart. Since these electrodes appear along all sides of the drilled bore, the trapping efficiency is improved over conventional devices. We have developed and demonstrated a separator capable of sorting a 50:50 mixture of viable and nonviable yeast cells into an 86:14 mixture at 25 mLhr(-1).

Cell Biology↗
PubMed2003

Dielectrophoretic assay of bacterial resistance to antibiotics.

The dielectrophoretic collection spectra of antibiotic-sensitive and antibiotic-resistant strains of Staphylococcus epidermidis have been determined. These indicate that in the absence of antibiotic treatment there is a strong similarity between the dielectric properties of sensitive and resistant strains, and that there is a significant difference between the sensitive strains before and after treatment with the antibiotic streptomycin after 24 h exposure. This method offers possibilities for the assessment of bacterial resistance to antibiotics.

Colony Count, Microbial↗
PubMed2003

Assessment of multidrug resistance reversal using dielectrophoresis and flow cytometry.

In cancer, multidrug resistance (MDR) is the simultaneous resistance of tumor cells to different natural product anticancer drugs that have no common structure. This is an impediment to the successful treatment of many human cancers. A common correlate of MDR is the overexpression of a membrane protein, P-glycoprotein. Many studies have shown that MDR can be reversed after the use of substrate analogs, called MDR modulators. However, our understanding of MDR modulation is incomplete. In this article, we examine the electrical properties of the human leukemic cells (K562) and its MDR counterpart (K562AR) using dielectrophoresis and flow cytometry (with a membrane potential sensitive dye, DIOC5), both before and after treatment with XR9576 (a P-glycoprotein-specific MDR-reversal agent). The results show significant differences in the cytoplasmic conductivity between the cell lines themselves, but indicate no significant changes after modulation therapy. We conclude that the process of MDR modulation is not associated with changes in the electrical properties of cancer cells. Moreover, the results demonstrate that using the flow cytometry method alone, with MDR cells, may produce artifactual results--whereas in combination with dielectrophoresis, the results show the role of MDR modulators in preventing drug efflux in MDR cells.

Blotting, Western↗
PubMed2003

Water quality test based on dielectrophoretic measurements of fresh water algae Selenastrum capricornutum.

A method is described whereby dielectrophoresis of algal cells is used to perform rapid water quality analysis, specifically detecting the presence of CuSO4. The dielectric collection spectrum of the fresh water alga Selenastrum capricornutum was determined for a range of concentrations of CuSO4 from 25 mg L(-1) to 0.25 mg L(-1) for exposure times of 15 min and 18 h. In all cases increasing the concentration of CuSO4 reduced cell collection, but a step reduction was observed in collection between 2 mg L(-1) and 5 mg L(-1). This method has potential for forming a rapid, low-cost test for water quality with broad specificity and significantly reduced analysis time compared to current methods.

Chlorophyta↗
PubMed2002

Measuring the dielectric properties of herpes simplex virus type 1 virions with dielectrophoresis.

An investigation has been performed into the biophysical properties of the enveloped mammalian virus, herpes simplex virus type 1 (HSV-1). The dielectrophoretic behaviour of the virus particles was measured as a function of applied frequency (over the range 100 kHz-20 MHz) and conductivity of the suspending medium (over the range 1-100 mS m(-1)). The dielectric properties of the virus were determined from the dielectrophoretic data using the smeared-out shell model. The data suggest that the intact particle has a surface conductance of 0.3 nS, an internal and membrane permittivity of 75varepsilon(o) and 7.5varepsilon(o), respectively, an internal conductivity of approximately 0.1 S m(-1) and a zeta potential of 70 mV. The dielectric properties were measured for intact, fresh virus particles and also for particles following exposure to various modifying agents, such as treatment with enzymes, ionophores and ageing. It is shown that the observed changes in the dielectrophoretic spectrum, and the variations in the dielectric properties of the virus concur with the expected physiological effects of these agents.

Biophysical Phenomena↗
PubMed2002

Strategies for dielectrophoretic separation in laboratory-on-a-chip systems.

Dielectrophoresis--the induced motion of polarizable particles in nonuniform fields--has proven to be an effective method for the separation of bioparticles such as cells, viruses and proteins. In this paper, the application of dielectrophoresis in miniaturized laboratories-on-a-chip is discussed, and strategies are described for using dielectrophoresis both for the binary separation of bioparticles and for the fractionation of many populations in such devices.

Cell Separation↗