Figure 3
Results of characterization experiments. (a) Photograph of the flow monitoring device with a modified microSD memory card allowing electrical connections to off-the-shelf capacitors. (b) Graphs showing the correlation of the measured capacitance values to nominal values of smaller capacitors (<100 pF) and to values of larger capacitors (>1 nF) measured using a multimeter. (c) Capacitance measurements of a capillary-driven microfluidic chip in dry state, showing zero drift in 30 min and <3 pF peak-to-peak variation, and the temperature of the microfluidic chip measured using an infrared thermopile, showing about 1.5 °C increase during continuous capacitance measurements. (d) Measured capacitance and the calculated change in the capacitance during the capillary flow of PBS with 1% BSA and 0.05% Tween 20 for two straight channels having different channel and electrode dimensions. (e) Flow rate estimation using capacitance measurements for 4 designs with different flow resistors (50 µm wide and 10, 20, 30, 40 mm long, the flow path is illustrated using the simplified chip layout on top). Inset: Plot showing the slope of the change in the capacitance in the capillary pump with respect to the reciprocal of the length of the flow resistor.
