Speaker
Description
Imaging the structure and observing the dynamics of isolated proteins using single-particle X-ray diffractive imaging (SPI) is one of the potential applications of X-ray free-electron lasers (XFELs). Currently, SPI experiments on isolated proteins are limited by three factors: low signal strength, limited data and high background from gas scattering. The last two factors are largely due to the shortcomings of the aerosol sample delivery methods in use. Here we present our modified electrospray ionization (ESI) source, which we dubbed helium-ESI (He-ESI). With it, we decreased the gas load in the interaction chamber corresponding to an 80% reduction in gas scattering when compared to the original ES and increased particle delivery into the interaction region by a factor of 10, for 26 nm-sized biological particles. The increased particle delivery was measured using light scattering and also to measure the size and location of single viruses and protein complexes forming an aerosol beam. We were able to detect individual particles down to 16 nm in diameter. The primary purpose of our scattering instrument is to monitor the delivery of single bioparticles to the focus on an X-ray laser and using the He-ESI to potentially increase the quality and quantity of SPI diffraction patterns in future experiments resulting in higher-resolution structures.
In November 2023 we performed an SPI experiment at the SQS endstation on various samples based on low gas background gas scattering. We reduced the background from the gas scattering by a factor of ~ 5 and obtained many diffraction patterns from Bacteriophage MS2, a small virus. Most significantly, we have collected the first dataset of a protein complex, Photosystem I, an important membrane protein, by X-ray SPI. The recorded diffraction patterns match that of photosystem I and we estimated a resolution of 6 nm by phase retrieval transfer function.
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