Design and development of a silicon microfabricated flow-through dispenser for on-line picolitre sample handling

The development of a piezoactuated flow-through microdispenser is described. The dispenser can be used for on-line sampling in a continuous-liquid-flow system. A major application area is rapid sample handling in chemical microsystems, e.g. automated high-throughput analysis or screening systems. The microdispenser is constructed of two joined silicon structures forming a Bow-through channel. One channel wall couples the impulse movement of a piezoceramic element into the flow channel, generating a pressure pulse. Droplets (of typically 100 picolitres) are ejected from an orifice in the opposite channel wall. The sequential improvements of the dispenser over three generations are presented. The actuation voltage could be lowered from 150 V to approximately 50 V. The Anal version of the dispenser had an internal volume of 2.6 microlitres. The impact on droplet stability and directivity of introducing a protruding pn etch-stop-defined nozzle and a means of matching surface properties to the dispensed liquid for improved performance are discussed. The maximum frequency for stable droplet formation was found to be approximately 500 Hz.