• Instrumentation: Development of a fast, portable bio-impedance Spectrometer

    Motivation. Electrical bio-impedance can be measured using commercially available instruments, which provide a wide range of features, but are relatively expensive and not optimized for specific applications. Small measurement units, using micro controllers connected with a PC, can provide a cheaper alternative, exhibiting the desired speed, measurement accuracy and frequency range and last but not least large flexibility (different probes and standards are able to be measured in a desired sequence).

    Results and discussion: The device developed within our lab is a multi-channel low frequency impedance spectrometer for the detection of analytes of various sizes (from proteins and toxic compounds to whole cells)

  • Quantitative analysis procedure for measuring the impedance spectra on tissues under ischemia conditions

    Motivation: Measurements of different tissue samples exhibit large variations due to biological variability, therefore single examples are usually reported. Our previous results point to similar characteristic behaviour for the evolution of Cole parameters during ischemia reported in a few experiments on heart and liver tissue. It was suggested that nonlinear analysis of the evolution of spectral parameters could lead to a "common language" for comparing and interpreting the data.

    Results and discussion: Even though the absolute values of the Cole parameters are different for various experiments, time evolution displays the same pattern: an initial peak, followed by a plateau. Times corresponding to the peak entrance to the plateau (with distinct absolute values for different experimental conditions) were used to normalize the data.

  • Theoretical and experimental advances in determining cell properties from impedance data

    1. application of fitting algorithms (related to spherical or ellipsoidal models) on simulated data on multi shelled non-spheroids
    2. the assumption that mixed cell suspensions having same shape, same thickness of shells but different sizes might be equivalent to a suspension of unitary cells
    3. linear procedures to correct the experimental noise given by the uneven frequency behavior of the impedance spectrometer
  • Motivation: Many sources of errors can affect the derivation of cell properties from impedance data. Errors are commonly associated with limitations or misuse of models, and to practical limitations of measuring the impedance of cell suspensions. Aiming to determine the evolution of cell parameters during the cell cycle, we have developed a set of microscopic approaches (considering non-spherical & multi-shelled cell models), together with the associated fitting algorithms. We have focused on errors due to:

  • Revealing cell cycle measures via impedance spectroscopy

    Motivation: Lack of accurate measurements and misuse of existing models (e.g., cell shape is often neither spherical nor ellipsoidal) confine most practical applications of Impedance Spectroscopy of cell suspensions to biomass monitoring. The significant influence of cell shape on cell polarizability provides a new and promising challenge: to monitor cell cycle progression under different environmental conditions. Our experience with models of arbitrarily shaped cells was applied to simulate the evolution of a suspension of initially synchronized budding yeast. Impedance measurements were performed on synchronised suspensions of the budding yeast mutant, CDC 28 over several cell cycles at different temperatures.

    Results & Discussion: Nonlinear analysis of time series of averaged cell polarizability at different frequencies (provided by impedance spectroscopy on initially synchronized cells) revealed a measure of synchrony loss which is shown to be the same, irrespective of the physiologic temperatures chosen to perform the experiments.





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