Biomedical subjects

B C Blake-Coleman

Publications and source records attributed to B C Blake-Coleman.

5 recordsLinked to original sources

PubMed1994

Harmonic generation in "non-linear" biological systems.

We describe a high performance, low frequency Fourier Transform based spectrum analyser, with design features particularly suited to the harmonic analysis of the non-linear amplitude transfer functions of various biological systems. A previous published method, using general purpose systems to produce reference and signal plus reference "power" spectra, was susceptible to ambiguous interpretation of results. Unlike that design, the present spectrometer derives quantitative complex voltage (amplitude and phase) harmonics of sampled voltage data, maintaining potentially important information. Based on the use of a basic IBM or compatible PC, it features high sensitivity, high speed data processing and large dynamic range, is compact, easy to use, flexible in operation and low in cost. Its precision current signal source eliminates harmonics generated at the drive electrodes from the measurement. Use of the instrument leads us to conclude that, contrary to previous assertions, no repeatable dielectric or conductive non-linearity is exhibited in the bulk cell suspensions tested under the field and frequency conditions reported.

Electric Impedance↗

PubMed1994

Harmonic 'signatures' of microorganisms.

The frequency/amplitude effect of various microorganisms exposed to periodic (time varying) electric fields, when proximate to immersed electrodes, has been studied using a novel analytical instrument. The harmonic distribution, in complex signals caused by cells exposed to harmonic free waveforms and occupying part of the electrode/suspension interface volume, was shown to be almost entirely due to the change in the standing interfacial transfer function by the (dielectrically nonlinear) presence of cells. Thus, the characteristic interfacial non-linearity is viewed as variable, being uniquely modulated by the presence of particular cells in the interfacial region. Little can be attributed to bulk (far field) effects. The tendency for subtle (characteristic) signal distortion to occur as a function of particulate (cell or molecular) occupancy of the near electrode interfacial region under controlled current conditions leads to the method of sample characterisation by harmonic (Fourier) analysis. We report here, as a sequel to our original studies (Hutchings et al., 1993; Hutchings and Blake-Coleman, 1993), preliminary results of the harmonic analysis of microbial suspensions under controlled signal conditions using a three-electrode configuration. These data provide three-dimensional graphical representations producing harmonic 'surfaces' for various microorganisms. Thus, cell type differences are characterised by their 'harmonic signature'. The visual distinction provided by these 'surface' forming three-dimensional plots is striking and gives a convincing impression of the ability to identify and enumerate specific microorganisms by acquisition of cell-modulated electrode interfacial Fourier spectra.

Candida↗

PubMed1990

Oscillometric instrument for the non-invasive detection of low-level microbial activity. Part 2: Growth characteristics, detection limits and impedimetric assays.

Instrument performance and application was evaluated with a variety of microbial suspensions. Data were compared with those obtainable from current commercial apparatus in terms of resolution and detection times. Trials with growing and non-growing cultures indicated periodic synchronous ion exchange processes. Media composition, particularly salt and nutrient ratios, remain crucial to early and rapid detection of viable microbial activity at low concentrations. With appropriate conditions very significant improvements in detection times with typical detection thresholds of 300 min for start concentrations of 10(2) are shown. It is concluded that with regard to resolution and stability, the system out-performs current systems and is superior in terms of potential test costs, sample handling and sample transport.

Asparaginase↗

PubMed1989

Apparatus for the electrical characterisation of conductive fluids.

Non-invasive and fully automated conductimetric measurements of electrolyte and bacterial samples were achieved in a closed volume test cell, comprising a magnetic field coil and detector. By monitoring field induced currents in sample electrolytes the magnitude of the sample current was shown to vary as the inverse of the sample impedance. The impedance characteristic was shown to be that of an LCR resonant circuit. This characteristic is primarily a function of the applied frequency and the solution/cell properties being dependent on the solution conductivity and dielectric permittivity at any given concentration. Small changes in sample dielectric permittivity in the presence of a large background conductivity are shown to be significant. The apparatus described can provide fixed or swept frequency conductivity measurements in the range 1 kHz to 2.25 MHz with a lower conductivity sensitivity of 0.9 x 10(-3) Scm-1. Bulk impedimetric characteristics of cell suspensions are derived by a two stage measurement.

Bacillus megaterium↗

PubMed1985

The development and application of biosensing devices for bioreactor monitoring and control.

Presently, few of the reported (bio)chemical sensor devices have found application in fermentation monitoring and control. Although many devices with desirable selectivities have been reported, few have demonstrated reliability sufficient to encourage significant and widespread application. Chemical sensors (ion-selective electrodes, amperometric detectors, piezoelectric, field-effect transistors, semiconductor, Optrode and optoelectronic sensors), biosensors (based on potentiometric, amperometric, field-effect transistor and conductiometric detectors) and physical detection methods are reviewed with the aim of highlighting the problems of their application in this area. Physical detection principles appear to show promise as reliable and direct monitoring principles. However, even the more reliable discrete (bio)chemical sensor devices require the development of on-line flow sampling and autocalibration methods to demonstrate the necessary reliability. Biosensor devices appear most problematical and it is concluded that continued development of more direct biosensing principles is likely to prove most fruitful.

Biological Products↗