Portable viscosity measurement system. (a) The setup consists of a microfluidic device, electronics and laptop computer controlled data acquisition system. (b) A closer look at the silicon-glass microfluidic device. Metal electrodes are evaporated and patterned on the silicon side. The glass side has two open (OC1 and OC2, d ~ 45 μm, w ~ 300 μm, Ltotal ~ 9.0 cm) and two sealed channels (SC1 and SC2, d ~ 45 μm). OC1 and SC1 are used for the calibration liquid (e.g., water) and OC2 and SC2 are used for the sample. Only one drop of the liquid is used for each pair, part of which wicks into the sealed channel while another part wicks into the open channel.