Perspectives: DOD Inkjets at High and Ultra-Brilliant Light Sources

Abstract

Droplets generated by inkjets can serve as carriers for biological solutions and objects including nanocrystals. X-ray scattering from ballistic droplets loaded with biological matter provides conformational and structural information in the absence of confining walls of microfluidic systems. Such experiments have been performed stroboscopically on a stream of droplets of sub-nL volume using quasi-continuous synchrotron radiation microbeams in order to obtain sufficient counting statistics. We will discuss methodological and scientific perspectives of X-ray scattering with micro-and nanobeams from individual droplets down to aL volumes based on pulsed ultra-brilliant X-ray free electron laser and 4 th generation synchrotron radiation sources.

Wall-free droplet microfluidics for probing biological processes by high-brilliance X-ray scattering techniques

“…A complementary microbeam endstation with a ∼1.5 μm FWHM focal spot and ∼1.5∗10 5 photons/s/nm 2 flux-density based on refractive optics should allow further reducing Q min due to a lower beam divergence (expected range: Q min ∼0.06 nm −1 ; d max ∼100 nm), well into the resolution range of third generation SR source SAXS beamlines. Scanning experiments are currently performed using fast framing pixel detectors in continuous-scanning mode, averaging across X-ray flashes emitted by the SR source ( Graceffa and Accardo, 2018 ). Droplets deposited on a horizontal surface are probed in transmission geometry with the SR beam approximately parallel to the surface ( Figure 2A ).…”

“…mesh-scan of sample array). The high flux density enables in principle single droplet experiments ( Graceffa and Accardo, 2018 ).…”

“…A temperaturegradient driven, Marangoni-type flow in μL droplets provided a quasi-confined local environment, resulting in well-ordered fibrillar pockets at the droplet interface (Zhang and Moretti, 2020). Frontiers in Molecular Biosciences frontiersin.org XFEL application: DOD print-heads developed for SR applications could also be used for XFEL applications, in particular for probing ultrasmall droplet volumes or contact line dynamics during droplet coalescence (Graceffa and Accardo, 2018). These authors discuss also options to mitigate droplet explosions producing fragments perturbing neighbouring droplets shape and trajectory in a train of droplets (Stan et al, 2016).…”

“…XFEL application : DOD print-heads developed for SR applications could also be used for XFEL applications, in particular for probing ultrasmall droplet volumes or contact line dynamics during droplet coalescence ( Graceffa and Accardo, 2018 ). These authors discuss also options to mitigate droplet explosions producing fragments perturbing neighbouring droplets shape and trajectory in a train of droplets ( Stan et al, 2016 ).…”

“…Selected applications will be reviewed and perspectives for the latest generation of SR/XFEL sources discussed. For a review on probing ballistic droplets in flight see: ( Graceffa and Accardo, 2018 ).…”