Toward cryogenic beams of nanoparticles and proteins

Abstract

To determine the structure of (bio-)nanoparticles, and possibly, the dynamics and function of it, the ultrashort and bright pulses generated from x-ray free-electron lasers can be used. X-ray free-electron lasers provide x-ray pulses with pulse durations of a few tens of femtoseconds and high photon numbers, sufficiently high to record scattering off a single macromolecule. This method of imaging is called single-particle diffractive imaging. The ultrashort pulses outrun radiation damage and an intact particle is imaged. This promising technique has one bottleneck: sample injection. Currently, the output of the experiments is limited by a low number of collected diffraction patterns and a low hit rate. The (bio-)nanoparticles are injected into the x-ray beam with aerosol injectors consisting of an aerosolization source and an aerodynamic lens stack to generate a continuous stream of nanoparticles. One concern despite the low hit rate in these experiments is the purity of the particle beam, that is consisting of clusters of nanoparticles, different charge states and spatial conformers. Within this thesis, sample delivery methods are improved toward the overall goal of imaging single proteins. To study the injector properties, a novel particle-beam characterization method to image the transverse particle beam profile is presented, capable of characterizing the particle flux and the particles’ velocity from an aerodynamic lens stack injector. Improvements on the aerosol sample delivery are made based on existing aerosol injectors to improve the hit rate through better particle focusing. Using simulations, the optimization of the geometry is performed efficiently. The optimized injector geometry is implemented in the setup and used for generating a particle beam of gold nanoparticles. Toward the aim of imaging single proteins, important steps are taken in understanding the particle-beam formation for smaller nanoparticles using particle trajectory calculations and extending the particle-beam detection towards smaller nanoparticles using optical scattering. Another crucial step in sample delivery is taken by generating a particle beam consisting of shock-frozen sub-100 nm particles, opening up the path toward a sample delivery setup that is capable of providing a pure particle beam for single-particle imaging experiments.