Rapid Acquisition of X-Ray Scattering Data from Droplet- Encapsulated Protein Systems

Encapsulating reacting biological or chemical samples in microfluidic
droplets has the great advantage over single-phase
flows of providing separate reaction compartments. These
compartments can be filled in a combinatoric way and prevent
the sample from adsorbing to the channel walls. In recent
years, small-angle X-ray scattering (SAXS) in combination with
microfluidics has evolved as a nanoscale method of such systems.
Here, we approach two major challenges associated with
combining droplet microfluidics and SAXS. First, we present
a simple, versatile, and reliable device, which is both suitable
for stable droplet formation and compatible with in situ X-ray
measurements. Second, we solve the problem of “diluting” the
sample signal by the signal from the oil separating the emulsion
droplets by multiple fast acquisitions per droplet and data
thresholding. We show that using our method, even the
weakly scattering protein vimentin provides high signal-tonoise
ratio data.