Electrical resistance fluctuations as a probe to monitor colloidal flows

Impedance measurements are widely used to detect particles or cells in a flow and to measure their various properties. The approach typically focuses on individual cell counting and sizing by passing the cells through artificial constrictions in which the channel diameter D is comparable to particle size d (D~d). Here, we explore the electrical impedance sensing technique to characterize colloidal flows in microchannels at different D/d limits. Our measurement is based on a standard four-wire probe of the mean electrical resistance R_m and its fluctuations ΔR(t) across the channel. We have applied this approach to measure flows with microbead and red blood cell suspensions in microchannels with different diameters. Flow properties such as flow rate, shear stress, concentration and composition are varied while monitoring the microchannel optically and electrically. Our results suggest that concentration can be inferred from R_m , while ΔR/R_m and its probability distribution contains information about other flow parameters, such as flow rate, particle composition and its properties. Based on our preliminary data, we will discuss how impedance sensing can be used to monitor flow parameters in vasculature networks.