Femtoliter injector for DNA mass spectrometry

Abstract The fabrication of a front-end injection device based on a fully three-dimensional ring-shaped nozzle as well as the reduction of the nozzle aperture to the micron scale are presented. This new configuration allows to manipulate accurately very small amounts of liquids, in the femtoliter range (1 fl=10 −15 l). The manipulation of the liquid has been tested with two different operating modes: a dynamic method based on the piezo injection technique and a static method based on the variation of the hydrostatic pressure in the liquid reservoir. The size distribution of the droplets generated at 0.5 MHz using the piezo technique is centered at 3.6 fl (∅ drop =1.9 μm) and about 25% of the droplets have a volume less than 1 fl (∅ drop =1.24 μm). On the other hand, the free nozzle extremity was used as an ultra-small liquid reservoir for static liquid handling, allowing us to perform a controlled fluid manipulation at the femtoliter level. A syringe connected to the injection device, via a Teflon tube, is used manually to increase quasi-statically the pressure in the nozzle channel. With this simple method it has been possible to monitor and to visualize the drop formation at the nozzle extremity in an Environmental Scanning Electron Microscope (ESEM®).