Abstract
High-speed liquid micro-jets are used to rapidly and repeatedly deliver protein microcrystals to focused and pulsed X-ray beams in the method of serial femtosecond crystallography. However, the current continuous flow of crystals is mismatched to the arrival of X-ray pulses, wasting vast amounts of an often rare and precious sample. Here, we introduce a method to address this problem by periodically trapping and releasing crystals in the liquid flow, creating locally concentrated crystal bunches, using an optical trap integrated in the microfluidic supply line. We experimentally demonstrate a 30-fold increase of particle concentration into 10 Hz bunches of 6.4 μm diameter polystyrene particles. Furthermore, using particle trajectory simulations, a comprehensive description of the optical bunching process and parameter space is presented. Adding this compact optofluidics device to existing injection systems would thereby dramatically reduce sample consumption and extend the application of serial crystallography to a greater range of protein crystal systems that cannot be produced in high abundance. Our approach is suitable for other microfluidic systems that require synchronous measurements of flowing objects.
Highlights
The method of serial femtosecond crystallography (SFX) uses intense and short pulses from X-ray free-electron lasers (XFELs), to record many snapshot X-ray diffraction patterns of protein crystals that flow across the focused beam [1,2]
The liquid flow field in the channel can be determined experimentally or for simple channel geometry like ours, it can be calculated numerical by solving the Navier–Stokes equations using finite-element solver, such as COMSOL Multiphysics [35]. In these simulations we employed an experimental approach known as particle image velocimetry (PIV) [36], where the fluid velocity is computed by tracking the motion of multiple micro-particles flowing through the liquid stream in the y=0 plane of the channel
A plot of the bunching efficiency versus laser power and flow rate showed discrete phases of permanent trapping, bunching, and deflecting without bunching. These results served as the basis for the construction of an optimized optofluidics device, used to experimentally demonstrate particle bunching in excellent agreement with simulations
Summary
The method of serial femtosecond crystallography (SFX) uses intense and short (femtosecondduration) pulses from X-ray free-electron lasers (XFELs), to record many snapshot X-ray diffraction patterns of protein crystals that flow across the focused beam [1,2]. A typical duty ratio of the length of the pulse train to the time between trains in an SFX experiment at the European XFEL is 3 × 10-3 This means that about times the number of crystals must be injected in such an experiment than will contribute to the measured diffraction. Most experiments typically run at a lower than optimal concentration, adding further inefficiencies The root of these inefficiencies lies in delivering sample into a pulsed X-ray beam with a continuous flow. We carried out and analyzed optical particle bunching in our prototype device to validate a numerical exploration of bunching and trapping behaviors as a function of laser power, duty cycle, and liquid flow rate, and found conditions that limit subsequent dispersion of pulses
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
