An automated stream-centres dielectrophoretic system

Dielectrophoresis has been shown to be potentially useful as a technique for identifying dielectric properties of particles and separating them on that basis. Particles range from simple polystyrene microspheres to the more complex biological cells. An automated system which allows the characterization and potential separation of particles/biological cells on a continuous basis is described. Here, a narrow sample stream suspended within a large sheath is injected between a pair of isomotive electrodes. Upon application of an AC field the sample particles undergo a positive or negative displacement, depending on their polarization characteristics relative to the medium. This deflection is detected using a linear 1024-element photodiode array and laser light source, to provide a measure of the response over a range of frequencies (110 Hz-50 MHz) under computer control. This enables the dielectrophoretic spectra to be obtained with very little human intervention. Details of the design and preliminary test results, based on inert and biological test particles, are presented and potential applications discussed