Electrical cell manipulation in microfluidic systems

This dissertation reports on the development of devices and concepts for electrical and microfluidic cell manipulation. In the present context, the term cell manipulation stands for both cell handling and cell modification. The combination of microfluidic channels with micropatterned electrodes allows for the definition of highly localised chemical and electrical environments with spatial resolution comparable to the size of a cell. The devices fabricated in the frame of this thesis employ dielectrophoretic particle handling schemes such as deflection and trapping in pressure-controlled laminar flows to bring cells to – or immobilise them at – locations where cell altering electric fields or chemicals are present. The two concepts of dielectrophoretic cell dipping and cell immersion are introduced and experimentally shown for erythrocytes dipped into Rhodamine in flow, and for individually immobilised Jurkat cells immersed by Trypan Blue. Also, in-situ membrane breakdown in high intensity AC electric fields is optically assessed by efflux of haemoglobin (haemolysis) and by influx of nucleic stains or fluorescence-enhancing ions. The most advanced experiments are on-chip medium exchange followed immediately by electropermeablisation or electrodeformation. The majority of assays presented in this thesis are carried out in microfabricated glass-polymer-glass chips featuring top-bottom electrodes. The devices are fluidically controlled by external gas pressure bridging circuits. Experimental evidence of the unmatched precision of pressure bridging is given in the case of micrometric xy positioning of cells at the intersection of two perpendicular microfluidic channels. Further shown in this document are two methods of optical in-situ temperature measurements, important for bioinstrument characterisation. The two concepts of thermoquenching of a fluorescent dye and the original thermoprecipitation of "smart polymers" are used. The last part of this work deals with the innovative, conceptual engineering tool Liquid Electrode. The general concept and its advantages over solid-state electrodes are given, followed by numerical particle tracking in the case of the novel lateral nDEP particle deflection. The chapter on liquid electrodes concludes with preliminary experimental results of buffer swapping of cells in flow and of AC electropermeabilisation of erythrocytes at frequencies far below the cut-off frequency of corresponding solid-state microelectrodes.

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