Abstract: An apparatus that couples automated injection with flow feedback to provide nanoliter accuracy in controlling microliter volumes. The apparatus comprises generally a source of hydraulic fluid pressure, a fluid isolator joined to the outlet of the hydraulic pressure source and a flow sensor to provide pressure-driven analyte metering. For operation generally and particularly in microfluidic systems the hydraulic pressure source is typically an electrokinetic (EK) pump that incorporates gasless electrodes. The apparatus is capable of metering sub-microliter volumes at flowrates of 1-100 ?L/min into microsystem load pressures of up to 1000-50 psi, respectively. Flowrates can be specified within 0.5 ?L/min and volumes as small as 80 nL can be metered.

Abstract: Gas bubble-free electrodes are necessary for stable long-term operation of millimeter-scale electrokinetic (EK) pumps when currents exceed 10-50 ?A. An accompanying Technical Advance describes EK pumps that draw 1-3 mA. We have developed gasless and gas bubble-free electrodes that can run millimeter-scale (and smaller) EK pumps continuously at high current densities. Two types of gasless electrodes based on porous carbon and ruthenium/tantalum-on-titanium oxides have been developed that are supercapacitors which store ions from a fluid electrolyte. The gas bubble-free electrodes isolate gas generated by water electrolysis of the pump fluid from the fluid channels by means of an electrically-conductive polymer. Nafion® tubing is a cationic-selective polymer that is used to pass currents and water for electrolysis at titanium and platinum surfaces. The gas bubble-free electrodes are easy to fabricate and can operate well even with typical, low-conductivity electrolytes.

Abstract: Electrokinetic (“EK”) pumps convert electric to mechanical work when an electric field exerts a body force on ions in the Debye layer of a fluid in a packed-bed, which then viscously drags the fluid. Porous silica and polymer monoliths (2.5-mm O.D., and 6-mm to 10-mm length) having a narrow pore size distribution have been developed that are capable of large pressure gradients (250-500 psi/mm) when large electric fields (1000-1500 V/cm) are applied. Flowrates up to 200 ?L/min and delivery pressures up to 1200 psi have been demonstrated. Forces up to 5 lb-force at 0.5 mm/s (12 mW) have been demonstrated with a battery-powered DC-DC converter. Hydraulic power of 17 mW (900 psi@ 180 uL/min) has been demonstrated with wall-powered high voltage supplies. The force and stroke delivered by an actuator utilizing an EK pump are shown to exceed the output of solenoids, stepper motors, and DC motors of similar size, despite the low thermodynamic efficiency.

Abstract: A device for measuring fluid flow rates over a wide range of flow rates (<1 nL/min to >10 ?L/min) and at pressures at least as great as 2,000 psi. The invention is particularly adapted for use in microfluidic systems. The device operates by producing compositional variations in the fluid, or pulses, that are subsequently detected downstream from the point of creation to derive a flow rate. Each pulse, comprising a small fluid volume, whose composition is different from the mean composition of the fluid, can be created by electrochemical means, such as by electrolysis of a solvent, electrolysis of a dissolved species, or electrodialysis of a dissolved ionic species. Measurements of the conductivity of the fluid can be used to detect the arrival time of the pulses, from which the fluid flow rate can be determined. A pair of spaced apart electrodes can be used to produce the electrochemical pulse.