Electroosmosis-based nanopipettor

Decreasing the volume of reagent solutions consumed in each assay is an effective means to reduce the overall cost in high-throughput analysis laboratories. Recently, increasing attention has been paid to investigate the behavior of individual cells. If one wishes to transfer solution to or from a single cell, a picoliter pipettor is needed since the entire cell volume is commonly less than 1 nL. While pressure ejection and iontophoresis have been used to deliver picoliter volumes of solutions, these techniques cannot yield routine pipettors which perform both solution "picking up" and "dispensing" functions. The state-of-the-art pipettors can handle liquids down to similar to 100 nL, although the pipetting accuracy and precision deteriorate considerably from microliters to nanoliters. If one wishes to pipet reagents of less than 100 nL, new pipettors need to be developed. Electroosmosis has been utilized to pump solutions at flow rates of nanoliters to approximately picoliters per second, which is ideal for nanopipettors. The issue is how to arrange fluidic/electrical connections so that pipetting functions can be performed conveniently. In this paper, we present the results of our initial attempt to develop an electroosmosis-based nanopipettor. The first version of this pipettor consists of a microfabricated electroosmotic (EO) flow pump, a polyacrylamide grounding interface, and a nanoliter-to-picoliter pipet tip. The detailed configuration and fabrication process of the pipettor are discussed. An excellent feature of an EO-driven pipettor is that it has no moving parts. Good reproducibilities (RSD = 6% at 140 pL, 2% at 950 pL, and 2% at 13 nL) and accuracies (9% at 0.13 nL, 4% at 1.0 nL, and 3% at 10 nL) of this pipettor have been demonstrated to aliquot/transport nanoliter-to-picoliter solutions.