A new microsystem for automated electrorotation measurements using laser tweezers

We have developed a new microsystem for fast, automated studies of reaction s and kinetics of single cells with biochemical or pharmacological agents. A cell spins in an external rotating electric field and the frequency depen dence characterises the passive dielectric properties of membrane and cytop lasm. We use a planar microelectrode chip with microchannel (easily covered with a removable slip) for the application of frequencies exceeding 250 MH z to determine cytoplasmic properties in low and high conductivity electrol yte solutions. The laser tweezers serve as a bearing system, rotation is in duced by microelectrodes and rotation speed is recorded automatically. This opens up new possibilities in biotechnology, e.g. for drug screening as de monstrated by measuring the influence of ionomycin on the passive dielectri c properties of T-lymphoma cells. Additionally, a possible infrared-induced long-term cell damage could be observed by electrorotation and is discusse d. (C) 2000 Elsevier Science B.V. All rights reserved.