Controlled electrospray pulsation for deposition of femtoliter fluid droplets onto surfaces

The ability to atomize a liquid sample into femtoliter droplets and deposit them precisely on a surface is a key problem in microfluidics and chemical analysis. Here we show that control of stable oscillations in an unforced electrospray is a high accuracy drop-on-demand method of depositing femtoliter droplets. Examples are presented of a liquid jet, formed for 35μs, in a discontinuous spray mode controlled using electrostatic fields of short duration; no liquid pump was employed. Each transient jet ejects femtoliter volumes of material, which was deposited on a nearby surface. The volumes ejected by pulsating sprays on a range of nozzle sizes are predicted from electrospray scaling laws. Using the modified nanoelectrospray method, we have printed 1.4μm wide features onto a surface in a drop-on-demand fashion with a placement accuracy of a few micrometers. We anticipate that our technique could produce biological microarrays and precisely deliver ultra-small samples for lab-on-a-chip analysis.