M. Di Berardino

Single cell analysis is an important tool to gain deeper insights into microbial physiology for the characterization and optimization of bioprocesses. In this study a novel single cell analysis technique was applied for estimating viability and membrane potential (MP) of Bacillus megaterium cells cultured in minimal medium. Its measurement principle is based on the analysis of the electrical cell properties and is called impedance flow cytometry (IFC). Comparatively, state‐of‐the‐art fluorescence‐based flow cytometry (FCM) was used to verify the results obtained by IFC. Viability and MP analyses were performed with cells at different well‐defined growth stages, focusing mainly on exponential and stationary phase cells, as well as on dead cells. This was done by PI and DiOC₂(3) staining assays in FCM and by impedance measurements at 0.5 and 10 MHz in IFC. In addition, transition growth stages of long‐term cultures and agar plate colonies were characterized with both methods. FCM and IFC analyses of all experiments gave comparable results, quantitatively and qualitatively, indicating that IFC is an equivalent technique to FCM for the study of physiological cell states of bacteria. Biotechnol. Bioeng. 2012; 109:483–492.

Objectives: Many flow-cytometric cell characterization methods require costly markers and colour reagents. We present here a novel device for cell discrimination based on impedance measurement of electrical cell properties in a microfluidic chip, without the need of extensive sample preparation steps and the requirement of labelling dyes. Materials and methods, Results: We demonstrate that in-flow single cell measurements in our microchip allow for discrimination of various cell line types, such as undifferentiated mouse fibroblasts 3T3-L1 and adipocytes on the one hand, or human monocytes and in vitro differentiated dendritic cells and macrophages on the other hand. In addition, viability and apoptosis analyses were carried out successfully for Jurkat cell models. Studies on several species, including bacteria or fungi, demonstrate not only the capability to enumerate these cells, but also show that even other microbiological life cycle phases can be visualized. Conclusions: These results underline the potential of impedance spectroscopy flow cytometry as a valuable complement to other known cytometers and cell detection systems.