An improved 24 channel picoliter dispenser based on direct liquid displacement

For the first time we present a systematic study concerning the relation between nozzle diameter and ejected droplet volume of a highly parallel picoliter dispenser. Such dispensers are essential parts for the mass fabrication of microarrays and are able to dispense up to 96 different reagents at a pitch of 500 /spl mu/m simultaneously. In contrast to an earlier design we investigated different nozzle diameters. The change from 35 /spl mu/m to 60 /spl mu/m in nozzle diameter resulted in a doubling of dispensed volume for most used elastomers and irrespective of actuation parameters. Minimum and maximum of dispensed volumes have been determined to be 125 pl and 1700 pl. Those results are based on a new design, which also includes passive microstructures for droplet homogeneity as well as modified microchannels for improved priming and prevention of cross-contamination. Based on this, the CV of droplet velocity could be reduced from 50% down to less than 5%. The CV of droplet volume is clearly below the measurement error (8%).