Circadian rhythms organize many aspects of cell biology and physiology to a daily temporal program that depends on clock gene expression cycles in most mammalian cell types. However, circadian rhythms are also observed in isolated mammalian red blood cells (RBCs), which lack nuclei, suggesting the existence of post-translational cellular clock mechanisms in these cells. Here we show using electrophysiological and pharmacological approaches that human RBCs display circadian regulation of membrane conductance and cytoplasmic conductivity that depends on the cycling of cytoplasmic K+ levels. Using pharmacological intervention and ion replacement, we show that inhibition of K+ transport abolishes RBC electrophysiological rhythms. Our results suggest that in the absence of conventional transcription cycles, RBCs maintain a circadian rhythm in membrane electrophysiology through dynamic regulation of K+ transport.

Induced particle motion by dielectrophoresis has been assessed on a microelectrode system consisting of two facing planes, one with circular apertures which we have termed "dots". Dot diameters ranging between 150µm -500µm have been used to show positive and negative dielectrophoresis, and have shown differences in particle velocities which is also influenced by the concentration of the suspended particles in the system. Simulations of the electric field morphology within the system showed a characteristic dome-shape distribution over the centre of the dot for smaller diameters which becomes distorted as the diameter increases. The design of the microelectrode geometry has effective spatial electric field penetrating capabilities over planar dielectrophoretic electrode geometries, with the potential for novel on chip processes such as particle characterisation which is described in this paper.

1347in [7]. Sequence data for type III collagen come from bovine skin collagen and was kindly given to us by Dr. J. Chapman and Dr. M. Humphries. Although these sequence data do not come from the same species used in this work this is not a problem, as a substantial measure of homology between species exists.Five liver and six skin images from two different species are analyzed using the proposed approach. For each image we derive a single average D-period, so that each set is described by a small number of average D-periods. The D-periods of each set are being aligned to each other and to model I as reference. We then average them and get an overall average D-period for each set (total set). Next, we employ the proposed pattern analysis procedure to derive type I tendencies for each average D-period, i.e., for each set. Table I summarizes our results. The field named "number of periods" records the number of periods that the D-period extraction algorithm samples from the current image. The subsequent "type I proportion" field records the proportion a of model I at the mixture model that was found to correlate at the highest degree with the corresponding average D-period, and the field "correlation coefficient" encodes the degree of correlation between this mixture model and the average image D-period. The row labeled "Total Set" presents the results corresponding to the overall D-period of the entire set. A first comparison indicates that the relative amount of type I periods is larger in liver than in skin fibrils. Indeed, the relative type I tendencies for liver and skin sets are respectively 94% and 91%. Our results are in good agreement with those derived from biochemical methods [3] confirming that liver contains an assortment of collagen types, usually with type I predominating, though this is not always the case. Skin has a different overall profile from other tissues. Two collagen types, I and III, are the main constituents accompanied by other minor types.The significance of the derived linear proportion coefficients is tested via statistical hypothesis tests. We validate the ability of a single average period (for the total set) to represent the sample population, in respect to proportion of and correlation with the mixture model. In order to assess results concerning the agreement of a sample mean x with the overall D-period measure derived (tested mean), we set up a statistical hypothesis test for type I proportion of the form H 0: x = ; versus H 1:For sample size and standard deviation m and s, respectively, the test statistic t1 = j( x 0 )=(s= p m)j is compared against the one-sided threshold for the significance level a, which is specified as the upper a=2 percentile of the t-distribution with m01 degrees of freedom. The test statistics with the corresponding thresholds at 10% significance are also in the Table I. Overall, it is derived that the total set measures are in good agreement with the sample means, i.e., the test statistic cannot reject the null hypotheses. V. CONCLUSIONIn this work we...

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.

Dielectrophoresis (DEP) has been used for many years for the analysis of the electrophysiological properties of cells. However, such analyses have in the past been time-consuming, such that it can take 30 min or more to collect sufficient data to make valid interpretations from a single DEP spectrum. This has limited the application of the technology to a rapid tool for non-invasive, label-free research in areas from drug discovery to diagnostics. In this paper we present the development of a programmable, multi-channel DEP system for rapid biophysical assessment of populations of biological cells. A new assay format has been developed for continuous near-real-time monitoring, using simultaneous application of up to eight alternating current electrical signals to independently addressable dot microelectrodes in an array format, allowing a DEP spectrum to be measured in 20 s, with a total cycle time between measurements of 90 s. To demonstrate the system, human leukaemic K562 cells were monitored after exposure to staurosporine and valinomycin. The DEP response curves showed the timing and manner in which the membrane properties changed for the actions of these two drugs at the early phase of induction. This technology shows the great potential for increasing our understanding of the role of electrophysiology in drug action, by observing the changes in electrical characteristics as they occur.

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Spatial patterning of cells is of great importance in tissue engineering and biotechnology, enabling, for example the creation of bottom-up histoarchitectures of heterogeneous cells, or cell aggregates for in vitro high-throughput toxicological and therapeutic studies within 3D microenvironments. In this paper, a single-step process for creating peelable and resilient hydrogels, encapsulating arrays of biological cell aggregates formed by negative DEP has been devised. The dielectrophoretic trapping within low-energy regions of the DEP-dot array reduces cell exposure to high field stresses while creating distinguishable, evenly spaced arrays of aggregates. In addition to using an optimal combination of PEG diacrylate pre-polymer solution concentration and a novel UV exposure mechanism, total processing time was reduced. With a continuous phase medium of PEG diacrylate at 15% v/v concentration, effective dielectrophoretic cell patterned arrays and photo-polymerisation of the mixture was achieved within a 4 min period. This unique single-step process was achieved using a 30 s UV exposure time frame within a dedicated, wide exposure area DEP light box system. To demonstrate the developed process, aggregates of yeast, human leukemic (K562) and HeLa cells were immobilised in an array format within the hydrogel. Relative cell viability for both cells within the hydrogels, after maintaining them in appropriate iso-osmotic media, over a week period was greater than 90%.

Detection of pathogens from environmental samples is often hampered by sensors interacting with environmental particles such as soot, pollen, or environmental dust such as soil or clay. These particles may be of similar size to the target bacterium, preventing removal by filtration, but may non-specifically bind to sensor surfaces, fouling them and causing artefactual results. In this paper, we report the selective manipulation of soil particles using an AC electrokinetic microfluidic system. Four heterogeneous soil samples (smectic clay, kaolinitic clay, peaty loam, and sandy loam) were characterised using dielectrophoresis to identify the electrical difference to a target organism. A flow-cell device was then constructed to evaluate dielectrophoretic separation of bacteria and clay in a continous flow through mode. The average separation efficiency of the system across all soil types was found to be 68.7% with a maximal separation efficiency for kaolinitic clay at 87.6%. This represents the first attempt to separate soil particles from bacteria using dielectrophoresis and indicate that the technique shows significant promise; with appropriate system optimisation, we believe that this preliminary study represents an opportunity to develop a simple yet highly effective sample processing system