Sub-attolitre nanodroplet deposition using a silicon-based nanoelectrospray emitter tip

We demonstrate that low voltage (< 200 V) nanoelectrospray tips can be used to deposit sub-attolitre (al) nanodroplets. By applying microtechnology, we have fabricated and studied novel silicon-based electrospray emitter tips for this purpose; such emitter tips incorporate triangular cantilevers which form a central microfluidic capillary slot; electrospraying occurs at the end of the slot. Electrospraying tests involving such silicon-based structures indicate that deposited electrosprayed droplets can have a volume as small as 0.3 ± 0.03 al and a diameter of 83 ±2.4 nm. These droplets can be directly deposited onto a chromium coated silicon wafer to give a spot size of the order of 190 nm; we have calculated these values using an original method based on scanning electron microscopy observations of the resultant electrospray trace which the charged droplets leave on the Cr surface.