Impedance microflow cytometry for viability studies of microorganisms
2011
Impedance-based Coulter counters and its derivatives are widely used cell analysis tools in many laboratories and use
normally DC or low frequency AC to perform these electrical analyses. The emergence of micro-fabrication technologies
in the last decade, however, provides a new means of measuring electrical properties of cells. Microfluidic approaches
combined with impedance spectroscopy measurements in the radio frequency (RF) range increase sensitivity and
information content and thus push single cell analyses beyond simple cell counting and sizing applications towards
multiparametric cell characterization. Promising results have been shown already in the fields of cell differentiation and
blood analysis. Here we emphasize the potential of this technology by presenting new data obtained from viability
studies on microorganisms. Impedance measurements of several yeast and bacteria strains performed at frequencies
around 10 MHz enable an easy discrimination between dead and viable cells. Moreover, cytotoxic effects of antibiotics
and other reagents, as well as cell starvation can also be monitored easily. Control analyses performed with conventional
flow cytometers using various fluorescent dyes (propidium iodide, oxonol) indicate a good correlation and further
highlight the capability of this device. The label-free approach makes on the one hand the use of usually expensive
fluorochromes obsolete, on the other hand practically eliminates laborious sample preparation procedures. Until now,
online cell monitoring was limited to the determination of viable biomass, which provides rather poor information of a
cell culture. Impedance microflow cytometry, besides other aspects, proposes a simple solution to these limitations and
might become an important tool for bioprocess monitoring applications in the biotech industry.
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