  Serial diffraction of proteins requires an injection method to deliver
protein molecules - preferably uncharged, fully hydrated, spatially oriented,
and with high flux - into the crossed beams of an alignment laser and a focused
probe beam of electrons or X-rays of typically only a few tens of microns
diameter. The aim of this work has been to examine several potential droplet
sources as to their suitability for this task. We compare Rayleigh droplet
sources, electrospray sources, nebulizers and aerojet-focused droplet sources
using time-resolved optical images of the droplet beams. Shrinkage of droplets
by evaporation as a means of removing most of the water surrounding the
proteins is discussed. Experimental measurements of droplet size, conformation
of proteins after passing through a Rayleigh jet, and triboelectric charging
are presented and conclusions are drawn about the source configuration for
serial diffraction. First experimental X-ray diffraction patterns from Rayleigh
droplet beams doped with 100nm gold balls are shown.
