On-chip thermopneumatic pressure for discrete drop pumping

A class of "lab-on-a-chip" devices use external air pressure for pumping di screte drops in a microchannel network. External air connectors can be cumb ersome and are real-estate intensive. We have developed an on-chip techniqu e to generate pressures required for metering and pumping of nanoliter-volu me discrete drops. This is achieved by heating of trapped air in a pressure -generating chamber, The pressure-generating chamber is connected to the po int of pressure application in the liquid-conveying microchannel through an air-delivery channel. The trapped air volume on the order of 100 nL is hea ted by resistive metal heaters by tens of degrees celcius to generate air p ressures on the order of 7.5 kN/m(2). The rate of discrete drop pumping is electronically controlled in the microchannel device by controlling the rat e of air heating. Flow rates on the order of 20 nL/s are obtained in the mi crochannel (300 mum x 30 mum) by heating the air chamber at the rate of sim ilar to6 degreesC/s. In this paper, we describe the design, fabrication, an d operation of this new technique of generating on-chip air pressure, used for metering and pumping nanoliter discrete drops in microchannels.