Scanning dielectrophoretic manipulations of micro objects

There are some advantages of our scanning method for dielectrophoretic manipulations of micro objects, ranging from cells to inorganic particles, over the conventional onchip styles with fixed electrodes patterned on substrates such as microfluidic chips. The scanning system consists of a pair of microneedles connected to waveform generator for arbitrary ac electric fields. As a result, our scanning method places and moves the strong electric field spot between the electrode tips anywhere, just as optical tweezers have done the focus of light beam. To be also noted, the waveform generator can change the temporal patterns of the applied electric fields more easily than the optical control. In this paper, we demonstrate non-contact manipulations unique to our scanning method. We further propose that the use of the frequency modulated electric field provides a novel way for one-step assay of crossover frequency in dielectrophoresis of a single micro object, which has been validated due to our scanning method unambiguously.