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High speed simultaneous optical and impedance analysis of single particles

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In this work we report on the development of biochips for the rapid analysis of single cells and other particules. We have developed a device that can simultaneously measure the optical and electrical properties of single cells or other micron-scale particules. The micro flow-cytometer chip consists of a planar electrode array onto which a micro-fluidic channel is fabricated from polyimide. The electrodes are used to measure the impedance of single cells flowing through the channel at hundreds per second. The impedance of single particlesis simultaneously measured at typically two separate frequencies (e.g. 0.5MHz and 2MHz) using a lock-in system and high specification instrumentation amplifiers mounted on top of the micro-fluidic chip. The impedance data provides information on the membrane chracteristics of cells and also the size of the particle. In addition a three-wavelength confocal optical system has been developed which is used to simultaneously interrogate the optical properties of particles. The device can detect small numbers of fluorescently labelled rare particles in a sample that has been used for the analysis of blood and suspensions of latex beads.

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