We measured the electroosmotic flow through

the nanochannel array under the applied electric voltage in the range of 0 to 3 V with a step of 0.5 V. A time series of the flow process was recorded for determination of the flow rate. Figure  4 shows a typical dynamic process of the pumping effect with respect to the time when an electric potential of 3 V was applied. At the initial stage (Figure  4a), channel A appeared bright green while channel B was dark since channel A was filled click here with 50 nM FITC in 0.05× PBS and channel B was filled with 0.05× PBS. As the time elapsed, the fluid containing FITC was gradually pumped from channel A to channel B via the nanochannel array which was evident by the increase in the fluorescent intensity in Figure  4b,c,d. The diffusion of FITC from channel A to channel B was very weak CHIR-99021 compared to the effect of electroosmotic flow. No obvious fluorescent light was detected with the same acquisition setting when no electric field was MK0683 molecular weight applied. Figure 4 Optical images (a-d) of the process of electroosmotic pumping from channel A to channel B. An electric potential of 3 V was applied. Channel A contained an electrolyte solution made from 50 nM FITC dissolved in 0.05× PBS while channel B contained 0.05× PBS only. The time interval between two successive images was 40 s. The averaged velocity for EO flow through the nanochannel array was determined from the

temporal evolution of the pumping effect of FITC from channel A to channel B. Images were taken at every 10 s. Using Equation 6, the EO flow rates for different applied electric field values were calculated and the plot shown in Figure  5. The EO flow rate increased with the increasing electric voltage. The results were in agreement with our prediction using Equation 1 that the EO velocity is linearly proportional to the electric field strength. This relation is simply shown as v EO = 2.9776 × V

EO - 0.7148 by linear-fitting these data in Origin. Figure  5 suggests that the precision of pumping rate can be very high (in the order of 0.1 pl/s) under the varying electric voltage. In other words, the results have implied that electric voltage could be used as a convenient means to control fluid transport with high precision, and the fabricated picoinjector has a promising potential in delivering precise selleck products control of minute amount of fluid for biochemical reactions and drug delivery systems. It is important to note that the EO mobility slightly varies at different electric field strengths [22], leading to a slight deviation especially when field strength is high, which in turns explains the fact that the interception of the line in Figure  5 was slightly smaller than the ideal number (zero). Figure 5 Relation of EOF rate to the applied voltage when the electrolyte solution was 0.05× PBS. A linear relation was obtained by fitting these data using Origin.