Non-uniform electric field-induced yeast cell electrokinetic behavior

Common dielectrophoresis (c-DEP, i.e. neutral matter motion induced by non-uniform electric fields) has become a basic phenomenon of biochips intended for medical, biological and chemical assays, especially when they imply bioparticle handling. This paper deals with modelling and experimental verification of a castellated, c-DEP-based, microelectrode array intended to handle biological objects. The proposed microsystem was developed employing platinum electrodes patterned by lift-off, silicon micro-machining and photoresin patterning techniques. Saccharomyces cerevisiae were used as test bioparticles for experimental verification. Yeast cells were repelled toward electrode bays and toward interelectrodic gaps tor frequencies around 20 MHz where there is minimum electric field strength, corresponding to a negative dielectrophoretic phenomenon. Yeast cell agglomerations were observed around electrode edges for frequencies of around 2 MHz where there is maximum electric field strength, thereby verifying the positive dielectrophoretic phenomenon. Bioparticles were separated from the electrode edges when the working frequency was reduced and they were dragged towards the electrode centre, remaining there while the frequency was low enough. Such atypical pattern may be explained due to the occurrence of positive dielectrophoresis overlap with electrohydrodynamic effects (i.e. the viscous drag force acting on the particles was greater than the dielectrophoretic force at frequencies where positive dielectrophoresis should occur). The experiments illustrated microsystem convenience in microhandling biological objects, thereby providing these microarrays' possible use with other cells. Liquid motion resulting from electrohydrodynamic effects must also be taken into account when designing bioparticle micromanipulators, and could be used as a mechanism for cleaning electrode surfaces.