Characterizing Microfluidic Valve Electrical Properties

Microfluidic valves were assembled according to Figure 1, and filled with testing solution (1 M KCl, 5 mM HEPES at pH 7.4). Microfluidic valve operation was controlled by a 3-way micro solenoid valve (ASCO, Florham Park, NJ) toggling between vacuum (open) and pressurized (closed) states.^{20 (link)} Electrical performance was evaluated using an EPC-8 patch clamp amplifier (HEKA Electronics, Bellmore, NY) with an ITC-16 DAQ board (Instrutech, New York). Opening and closing times (t_10-90 and t_90-10, respectively) were calculated from current vs. time plots for at least 3 valves per surface modification. To measure the electrical resistance, an increasing potential was applied across the valve ranging from −100 mV to +100 mV in 10 mV increments for 100 ms per increment.^{32 (link)} Resistance was calculated from the slope of i-V curves (n = 3). Valve opening and closing and the corresponding noise values were evaluated via application of a 10 mV holding potential.