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Determination of conductivity of bacteria by using cross-flow filtration
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
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2006 (English)In: Biotechnology letters, ISSN 0141-5492, E-ISSN 1573-6776, Vol. 28, no 8, 601-603 p.Article in journal (Refereed) Published
Abstract [en]

An important property of the bacterial surface is its conductivity. To obtain reliable conductivity values, it is essential to handle the cells as gently as possible during the measurement procedure. We have developed a method where a standard conductivity meter is used in combination with cross-flow filtration, thus avoiding repeated centrifugation and resuspension. With this method, the conductivity of Bacillus subtilis was determined to be 7000 mu S/cm, which is a deviation from previously published data by almost an order of a magnitude.

Place, publisher, year, edition, pages
2006. Vol. 28, no 8, 601-603 p.
Keyword [en]
Bacillus subtilis, conductivity, cross-flow filtration, isoconductance point
National Category
Analytical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5519DOI: 10.1007/s10529-006-0021-8ISI: 000236846800012Scopus ID: 2-s2.0-33645876464OAI: oai:DiVA.org:kth-5519DiVA: diva2:9911
Note
QC 20100908. Uppdaterad från In press till Published (20100908)Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2017-11-21Bibliographically approved
In thesis
1. New Concepts for Dielectrophoretic Separations and Dielectric Measurements of Bioparticles
Open this publication in new window or tab >>New Concepts for Dielectrophoretic Separations and Dielectric Measurements of Bioparticles
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents two new concepts for separation of micro particles using dielectrophoresis, demonstrated by calculated examples, as well as a new method for obtaining dielectric data on living cells. The thesis is based on four papers.

Paper I describes how the trapping efficiency of micro particles may be significantly increased when superpositioned electric fields are employed in a high conductivity medium. Avoiding low conductivity media is important when working with living cells. Calculations were performed to predict trajectories of Escherichia coli bacteria in the system with superpositioned electric fields, and a model was developed which employed two arrays of interdigitated electrodes in a micro channel.

Paper II proposes a new concept for separation of micro particles, based on repetitive dielectrophoretic trapping and release in a flow system. Calculations show that the resolution increases as a direct function of the number of trap and release steps, and that a difference in size will have a larger influence on the separation than a difference in dielectrophoretic properties. Polystyrene beads in deionized water were used as a model, and calculations were performed to predict the particle behavior and the separation efficiency. It should be possible to separate particles with a size difference of 0.2 % by performing 200 trap-and-release steps. The enhanced separation power of multi step dielectrophoresis could have significant applications, not only for fractionation of particles with small differences in size, but also for measuring changes in surface conductivity.

Paper III presents a new calculation method for predicting dielectrophoretic motion of micro particles. The method is based on a soft sphere method often used in molecular dynamics. Results from the calculations are in good agreement with theoretical predictions as well as initial experimental results, showing that the method provides good efficiency and accuracy.

Paper IV describes a new method for measurements of conductivity of living bacteria. To obtain reliable conductivity values, it is important to handle the cells as gently as possible during the measurement process. A standard conductivity meter was used in combination with cross-flow filtration. In this way, repeated centrifugation and resuspension is avoided which otherwise may cause damage to the bacteria. The conductivity of Bacillus subtilis was determined to be 7000 μS/cm by means of the cross-flow filtration method, and the values differ from earlier published values by almost an order of a magnitude.

In addition to the work presented in the papers, some experimental dielectrophoresis work in chip-based systems was performed. The behavior of Escherichia coli and polystyrene beads at different voltages and frequencies were studied. Separation of beads with different sizes was achieved on an array of interdigitated electrodes. Using electrodes with a pointed shape, alignment in different directions, pearl-chain formation, rotation, and other dielectrophoretic motion of E. coli were observed.

Place, publisher, year, edition, pages
Stockholm: Kemi, 2006. 26 p.
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-3894 (URN)91-7178-286-9 (ISBN)
Presentation
2006-03-27, Sal K2, Teknikringen 28, Stokcholm, 10:15
Opponent
Supervisors
Note
QC 20101108Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2010-11-08Bibliographically approved

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