On-demand droplet spotter for preparing pico- to femtoliter droplets on surfaces.

A droplet spotter for on-demand generation of pico- to femtoliter droplets was developed to meet the requirement for high-density spotting of chemicals on a surface. Our droplet spotter involves applying a approximately 1000-V and approximately 10-ms pulse voltage to the tip of a capillary tube (o.d. approximately 18 microns; i.d. approximately 11 microns) supplied with water or a dye solution. The capability of the spotter was demonstrated by preparing a microarray of dye molecules. The microarray was prepared by spotting approximately 30-fL droplets of a dye solution on a surface at the density of one spot per 20 x 20 micron 2.