High accuracy particle analysis using sheathless microfluidic impedance cytometry

This paper describes a new design of microfluidic impedance cytometer enabling accurate characterization of particles without the need for focusing. The approach uses multiple pairs of electrodes to measure the transit time of particles through the device in two simultaneous different current measurements, a transverse (top to bottom) current and an oblique current. This gives a new metric that can be used to estimate the vertical position of the particle trajectory through the microchannel. This parameter effectively compensates for the non-uniform electric field in the channel that is an unavoidable consequence of the use of planar parallel facing electrodes. The new technique is explained and validated using numerical modelling. Impedance data for 5, 6 and 7 μm particles are collected and compared with simulations. The method gives excellent coefficient of variation in (electrical) radius of particles of 1% for a sheathless configuration. A new microfluidic impedance cytometer chip is demonstrated, giving high quality impedance signals without the need for any particle focusing.