Generation and delivery of monodisperse pico-liter droplets out of PDMS microchip into Accelerator Mass Spectrometry (AMS)

We have developed a drop-on-demand microdroplet generator for the discrete dispensing of bio-samples into a bio-analytical unit, Accelerator Mass Spectrometry (AMS). The disposable PDMS microfluidic device can generate monodisperse droplets of pico-liter volume directly out of a plane sidewall of the microfluidic chip by an electrohydrodynamic mechanism. The droplet generation was accomplished without using either an inserted capillary or built-in tip. The minimum droplet volume was around 4 pico-liters, and the droplet generation was repeatable and stable for at least 30 minutes, with a typical variation of less than 2.0% of drop size. A computational simulation of the droplet generation verified the importance of controlling the surface wetting conditions for the droplet formation. Our microdroplet generator can be effective interfacing mechanism from a microfluidic chip to a non-chip bio-sensing unit, such as AMS or MALDI-MS.