Uwe Pliquett

Institute for Bioprocessing and Analytical Measurement Techniques, Heiligenstadt, Thuringia, Germany

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Publications (82)172.32 Total impact

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    Uwe Pliquett, Richard Nuccitelli
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    ABSTRACT: Experimental evidence shows that nanosecond pulsed electric fields (nsPEF) trigger apoptosis in skin tumors. We have postulated that the energy delivered by nsPEF is insufficient to impart significant heating to the treated tissue. Here we use both direct measurements and theoretical modeling of the Joule heating in order to validate this assumption. For the temperature measurement, thermo sensitive liquid crystals (TLC) were used to determine the surface temperature while a micro-thermocouple (made from 30 μm wires) was used for measuring the temperature inside the tissue. The calculation of the temperature distribution used an asymptotic approach with repeated calculation of the electric field, Joule heating and heat transfer, and subsequent readjustment of the electrical tissue conductivity. This yields a temperature distribution both in space and time. It can be shown that for the measured increase in temperature an unexpectedly high electrical conductivity of the tissue would be required, which was indeed found by using voltage and current monitoring during the experiment. Using impedance measurements within tafter = 50 μs after the pulse revealed a fast decline of the high conductivity state when the electric field ceases. The experimentally measured high conductance of a skin fold (mouse) between plate electrodes was about 5 times higher than the maximally expected conductance due to fully electroporated membrane structures (Gmax/Gelectroporated) ≈ 5. Fully electroporated assumes that 100 % of the membranes are conductive which is estimated from impedance measurement at 10 MHz where membranes are capacitively shorted. Since the temperature rise in B-16 mouse melanoma tumors due to equally spaced (Δt = 2 s) 300 ns-pulses with E = 40 kV/cm usually does not exceed ΔΤ = 3 K at all parts of the skin fold between the electrodes, a hyperthermic effect on the tissue can be excluded.
    Bioelectrochemistry (Amsterdam, Netherlands) 12/2014; DOI:10.1016/j.bioelechem.2014.03.001 · 3.87 Impact Factor
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    ABSTRACT: Numerous studies have shown electromyographic signals (EMGs) as useful for controlling prostheses and ortheses. Their great potential stems from the degree of voluntary control we wield over these signals, even if limbs are missing, especially in the EMGs of skeletal muscles. However, despite several decades of exploration, the potential of electrical myoimpedance (EMI) as a separate control signal has been largely ignored. The greatest barrier to utilizing this signal is that skin-based measurements suffer from low-sensitivity with the only alternative being invasive methods, such as needles. Since the EMI signal is known to correlate with the passive properties of materials under test, specifically their geometry, it is expected to be highly sensitive to the morphologic changes which occur during concentric contractions. In contrast, EMG signals occur any time a muscle is contracted, whether or not this results in morphologic changes. Therefore, the EMI and EMG signals should not be highly-correlated, suggesting an additional control channel. To test this, we developed a non-invasive procedure for making simultaneous skin-based measurements of EMG and EMI signals during both concentric and isometric contractions. A video camera was synchronized with the measurement system to facilitate the correlation of signal features with muscle actions. We conclude that the two signals can be distinguished.
    15th International Conference on Electrical Bio-Impedance, Heilbad Heiligenstadt, Germany; 04/2013
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    ABSTRACT: This study presents the further establishment of impedimetric biosensors with aptamers as receptors. Aptamers are short single-stranded oligonucleotides which bind analytes with a specific region of their 3D structure. Electrical impedance spectroscopy is a sensitive method for analyzing changes on the electrode surface, e.g. caused by receptor-ligand-interactions. Fast and inexpensive prototyping of electrodes on the basis of commercially available compact discs having a 24 carat gold reflective layer was investigated. Electrode structures (CDtrodes [1]) in the range from few millimetres down to 100 microns were realized. The well-studied thrombin-binding aptamer (TBA) was used as receptor for characterizing these micro- and macro-electrodes. The impedance signal showed a linear correlation for concentrations of thrombin between 1.0 nM to 100 nM. This range corresponds well with most of the references and may be useful for the point-of-care testing (POCT).
    Journal of Physics Conference Series 04/2013; 434(1):2091-. DOI:10.1088/1742-6596/434/1/012091
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    ABSTRACT: Electrolytic conductivity of cell-based suspensions is an important parameter which can be easily and non-destructively measured as part of the electrical impedance. The low frequency conductivity of a cell suspension with very low cell density equals nearly the medium conductivity. However, a high cell density decreases the low frequency conductivity due to the insulating behaviour of the cell membranes. Here we use miniaturized electrode structures, smaller than the size of typical cells for impedometric conductivity measurement which allows an impedance measurement independent of the electrical properties of suspended cells or particles.
    Journal of Physics Conference Series 04/2013; 434(1):2093-. DOI:10.1088/1742-6596/434/1/012093
  • Uwe Pliquett
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    ABSTRACT: While most applications of bio-impedance measurements for characterization of cells or tissue do not have any time requirements, newer developments like real time monitoring of moving cells or membrane recovery after high voltage application depend on fast measurement. This is not compatible with sweeping the frequency through the desired range while assessing magnitude and phase of the material under test (MUT). A high speed is only achievable by using broad-bandwidth excitation signals and monitoring the response in time-domain. Time-domain based methods can be distinguished by the excitation signals as well as by assessing the transmission or reflection behavior of the MUT. Although there is good agreement regarding the advantages of fast measurements, time-domain measurements are often rejected because of low precision and noise sensitivity. This paper points not only the advantages of impedance measurements in time domain but shows also drawbacks together with possible solutions.
    Journal of Physics Conference Series 04/2013; 434(1):2092-. DOI:10.1088/1742-6596/434/1/012092
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    ABSTRACT: Electrodes are an important part of the impedance measurement chain but their influence is often underestimated. Electrochemical reactions or polarization effects, especially for galvanically coupled systems are sometimes completely neglected. The most important features of electrodes to be considered are the geometry with respect to the structure of the material to be tested and the electrochemistry at the electrode surface. Especially drift and corrosion effects may yield misleading results. If applicable, sophisticated electrode systems should be used in order to prevent the distorting influence of electrode polarization, for extending the useful frequency range of the electrodes or for enhancing the signal-to-noise ratio.
    Journal of Physics Conference Series 12/2012; 407(1):2027-. DOI:10.1088/1742-6596/407/1/012027
  • Uwe Pliquett, Andreas Barthel
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    ABSTRACT: The AD5933 [1], a specialized single chip impedance analyzer, made by Analog Devices, is basically not intended for use with four electrode interface. Due to electrochemical phenomena at the electrodes connecting the material under test (MUT), especially in the low frequency region below 100 kHz, a two electrode interface generates considerable errors during the measurement. Thus, for most application in bio-impedance measurement only a four electrode interface can guarantee reliable results. Here we show how a four electrode interface with galvanostatic excitation but also for potentiostatic excitation can be realized by just a few external components.
    Journal of Physics Conference Series 12/2012; 407(1):2019-. DOI:10.1088/1742-6596/407/1/012019
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    ABSTRACT: The incorporation of photoactive molecules in thin layers enables photoinduced changes in wettability, e.g. azobenzenes, or micropatterning by deprotection of functional groups, e.g. applying nitroveratryl compounds. This paper describes a synthetic route for obtaining an azobenzene with a silane anchor. The chemical synthesis, including all intermediates, is characterized by NMR and IR. The photoisomerization of all products was investigated by UV/Vis spectroscopy. Ellipsometry and contact angle measurements give information about monolayers of the synthesized organosilanes.
    RSC Advances 05/2012; 2(11):4792-4801. DOI:10.1039/C2RA20151H · 3.71 Impact Factor
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    ABSTRACT: Proper illumination is essential for light microscopy. Whereas in early years incandescent light was the only illumination, today, more and more specialized light sources, such as lasers or arc lamps are used. Because of the high efficiency and brightness that light-emitting diodes (LED) have reached today, they have become a serious alternative for almost all kinds of illumination in light microscopy. LED have a high durability, do not need expensive electronics, and they can be switched in nanoseconds. Besides this, they are available throughout the UV/Vis/NIR-spectrum with a narrow bandwidth. This makes them ideal light sources for fluorescence microscopy. The white LED, with a color temperature ranging from 2,600 up to 5,000 K is an excellent choice for bright-field illumination with the additional advantage of simple brightness adjustments without changing the spectrum. This review discusses the different LED types, their use in the fluorescence microscope, and discusses LED as specialized illumination sources for Förster resonance energy transfer and fluorescent lifetime imaging microscopy.
    Cytometry Part A 03/2012; 81(3):188-97. DOI:10.1002/cyto.a.22023 · 3.07 Impact Factor
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    ABSTRACT: Square wave excitation is an excellent choice for excitation signal in broad bandwidth and fast impedance measurement. The advantages are simple scalability, easy generation and straight forward data reduction by non-uniform sampling. The often cited disadvantage of low signal energy at high frequency is only partially relevant because a high sampling rate at fast changing portions of the measured signal guarantees a sufficient signal-to-noise ratio throughout the frequency range determined by the sampling speed, the slew rate of the amplifiers used and the time duration of the excitation signal. Although briefly looking at spectra of other signals suggests their better performance, having a well-designed system from signal generation through sampling and processing up to proper data mining shows the advantages of square wave excitation, especially if speed and bandwidth is important. Here we describe a method for obtaining an estimate of a broadband spectrum over several orders of magnitude while only requiring a minimum of computing power.
    Electronics Conference (BEC), 2012 13th Biennial Baltic; 01/2012
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    ABSTRACT: Fast impedance measurements are often performed in time domain utilizing broad bandwidth excitation signals. Other than in frequency domain measurements harmonic distortion cannot be compensated which requires careful design of the analog front end. In order to minimize the influence of electrode polarization and noise, especially in low-frequency measurements, current injection shows several advantages compared to voltage application. Here, we show an active front end based on a voltage-controlled current source for a wide range of impedances. Using proper feedback, the majority of the parasitic capacitances are compensated. The bandwidth ranges from dc to 20 MHz for impedance magnitude below 5 kΩ. The output is a symmetric signal without dc-offset which is accomplished by combination of a current conveyor and a voltage inverter. An independent feedback loop compensates the offset arising from asymmetries within the circuitry. We focused especially on the stability of the current source for usage with small metal electrodes in aqueous solutions. At the monitor side two identical, high input impedance difference amplifiers convert the net current through the object and the voltage dropping across into a 50 Ω symmetric output. The entire circuitry is optimized for step response making it suitable for fast time domain measurements.
    Physiological Measurement 07/2011; 32(7):927-44. DOI:10.1088/0967-3334/32/7/S15 · 1.62 Impact Factor
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    ABSTRACT: The initial effect of nanosecond pulsed electric fields (nsPEFs) on cells is a change of charge distributions along membranes. This first response is observed as a sudden shift in the plasma transmembrane potential that is faster than can be attributed to any physiological event. These immediate, yet transient, effects are only measurable if the diagnostic is faster than the exposure, i.e., on a nanosecond time scale. In this study, we monitored changes in the plasma transmembrane potential of Jurkat cells exposed to nsPEFs of 60 ns and amplitudes from 5 to 90 kV/cm with a temporal resolution of 5 ns by means of the fast voltage-sensitive dye Annine-6. The measurements suggest the contribution of both dipole effects and asymmetric conduction currents across opposite sides of the cell to the charging. With the application of higher field strengths the membrane charges until a threshold voltage value of 1.4-1.6 V is attained at the anodic pole. This indicates when the ion exchange rates exceed charging currents, thus providing strong evidence for pore formation. Prior to reaching this threshold, the time for the charging of the membrane by conductive currents is qualitatively in agreement with accepted models of membrane charging, which predict longer charging times for lower field strengths. The comparison of the data with previous studies suggests that the sub-physiological induced ionic imbalances may trigger other intracellular signaling events leading to dramatic outcomes, such as apoptosis.
    Biophysics of Structure and Mechanism 05/2011; 40(8):947-57. DOI:10.1007/s00249-011-0710-7 · 2.47 Impact Factor
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    ABSTRACT: The electrical properties of nanostructured silicon electrodes in contact with phosphate buffered saline were examined using small signal impedance together with cyclic voltammetry. The highest electrode impedance appears at thermodynamic equilibrium, i.e. at zero current potential. Biasing the electrode in both directions decreases the magnitude of the electrode impedance without showing a clear rectifier effect within ± 3V. The impact of nanostructures on the electrode impedance was negligible given the variability between single electrodes.
    IFMBE proceedings 01/2011; 37:1246-1249. DOI:10.1007/978-3-642-23508-5_322
  • tm - Technisches Messen 01/2011; 78:3-14. DOI:10.1524/teme.2011.0077 · 0.26 Impact Factor
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    ABSTRACT: In this paper, a modular concept for measureing broadband impedance spectroscopy is introduced with a detailed description of measurement examples
    Lecture Notes on Impedance Spectroscopy Measurement, Modeling and Applications, Volume 1, Edited by Olfa Kanoun, 01/2011: chapter 12: pages 83--88; CRC Press., ISBN: 978-0-415-68405-7
  • Uwe Pliquett
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    ABSTRACT: Electrical measurement is a simple innocuous tool for material characterization. Unlike for instance milk or dairy products, the majority of naturally grown food is composed of cells. The cells of meat or vegetables are surrounded by an insulating membrane, while the cytosol and the extracellular fluids are electrolytes. Despite the high permittivity of water, electrolytes behave like ohmic resistors up to hundreds of MHz. In contrast, membranes form capacitive elements due to their high resistance. The typical time constant for charging cell membranes is of the order of a microsecond. Thus, cells influence the impedance in a frequency range up to several MHz. At higher frequencies, the cytosolic content, i.e., macromolecules, gives rise to characteristic relaxation processes. Using the impedance in the microwave range where water dipoles show a distinct dispersion, humidity of dried matter can be addressed. Moreover, with sensitive measurement setup and proper models, one can determine the dry content in mashes and slurries as well. Several quality standards correlate well with the permeability of the membranes or the total water content. Because of the comparatively simple measurement of the electrical impedance together with advanced mathematical modeling, it is often a good approach in quality assessment of agricultural products. The change in conductivity of a culture medium contains information about the metabolism of incubated cells. Using specific culture media and time-lapse conductivity monitoring allows a high sensitivity and selectivity in microbial detection. Because the electrical impedance is very sensitive to the permeability of cell membranes, it is a great choice for the assessment of changes due to high voltage application. Today, many attempts to use impedance measurement in food technology show fast success in research but fail in practice. The reason is often an overestimation especially of the selectivity while underestimating the uncertainties in a harsh environment of a food-processing plant. Established, however, is the use of robust process measurement systems and the limitation of impedance measurement to applications with highly significant outcome or as supplemental measurement in a multiparameter approach. This review introduces the basics of bioimpedance measurement, points to sources of uncertainty, and presents successful applications in food industry. KeywordsBioimpedance-Food quality-Drip loss-Microbial detection-Water content
    Food Engineering Reviews 06/2010; 2(2):74-94. DOI:10.1007/s12393-010-9019-z · 3.04 Impact Factor
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    ABSTRACT: Miniaturized electrodes are introduced in life sciences in a great number and variety. They are often designed for a special purpose without the need of quantitative analysis, such as for detecting cells or water droplets in a fluid channel. Other developments aim in monitoring a single quantity in a process where all other factors held constant. To use miniaturized electrodes for quantitative measurements, their behavior should be known in detail and stable over time in order to allow a mathematical correction of the data measured. Here we show test procedures for evaluating macroscopic but also microscopic electrodes. The most important quality parame-ters for electrode systems used in life science are the electrode impedance, its stability, the useful frequency range as well as the limits for applied stimulus without driving the electrode system into a non-linear region of the current/voltage relation. Proper electrode design allows a bandwidth from 100 Hz up to some MHz for impedances ranging over decades from 50 Ohm up to several MOhm.
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    ABSTRACT: Despite conventional neuromonitoring, the recurrent laryngeal nerve (RLN) is still at risk for damage during thyroid surgery. The feasibility of continuous RLN monitoring by vagal nerve (VN) stimulation with a new anchor electrode should be shown, and electromyographic signal alterations of stressed RLN were analyzed to be alerted to imminent nerve failure whereby the nerve damage becomes reversible. VN stimulation was achieved in 23 pigs. Sensed signals were analyzed and stored as real-time audio/video feedback EMG system. RLN was stressed by mechanical and thermal injury; signal alterations were evaluated. VNs were successfully real-time stimulated by using the anchor electrode. No complications or side effects during stimulation were detected. RLN injury led to an alteration of signal amplitude and latency period but signal restitution after injury. Real-time monitoring of the RLN is technically feasible to perceive imminent nerve failure. The anchor electrode was safely and easy to handle. Its implementation is being tested in an ongoing clinical trial.
    American journal of surgery 04/2010; 199(4):507-14. DOI:10.1016/j.amjsurg.2009.04.036 · 2.41 Impact Factor
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    ABSTRACT: In order to minimize the influence of electrode polarization and noise in impedance measurements, especially in the low frequency region, current injection shows several advantages compared to voltage application. Although the existence of a great variety of current sources, they meet our requirements only partially. We developed a voltage controlled current source for active front ends for a wide range of impedances, from Ω up to TΩ. A broad bandwidth from dc to 100 MHz was ensured by minimizing the parasitic capacitances. The current source outputs a symmetric signal without dc-offset. This is accomplished by a differential driver where the non-inverting branch was used for creating a current conveyor while the inverting branch host the feedback for offset control. We focused especially on the stability of the current source for usage with small metal electrodes in aqueous solutions.
    Journal of Physics Conference Series 04/2010; 224(1). DOI:10.1088/1742-6596/224/1/012009

Publication Stats

2k Citations
172.32 Total Impact Points


  • 2006–2012
    • Institute for Bioprocessing and Analytical Measurement Techniques
      Heiligenstadt, Thuringia, Germany
  • 2006–2011
    • Old Dominion University
      • Frank Reidy Research Center for Bioelectrics
      Norfolk, Virginia, United States
  • 1998–2007
    • Bielefeld University
      • Faculty of Chemistry
      Bielefeld, North Rhine-Westphalia, Germany
  • 1995–2002
    • Massachusetts Institute of Technology
      • Division of Health Sciences and Technology
      Cambridge, Massachusetts, United States
  • 1996
    • University of Leipzig
      • Institut für Medizinische Physik und Biophysik
      Leipzig, Saxony, Germany
  • 1995–1996
    • Harvard University
      Cambridge, Massachusetts, United States