Laboratory of Molecular Nanodynamics

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Microsecond melting and revitrification of cryo samples: protein structure and beam-induced motion

Marcel Drabbels, Oliver Florian Harder, Ulrich Lorenz, Pavel Olshin, Jonathan Mark Voss

A novel approach to time-resolved cryo-electron microscopy (cryo-EM) has recently been introduced that involves melting a cryo sample with a laser beam to allow protein dynamics to briefly occur in the liquid, before trapping the particles in their transient configurations by rapidly revitrifying the sample. With a time resolution of just a few microseconds, this approach is notably fast enough to study the domain motions that are typically associated with the activity of proteins but which have previously remained inaccessible. Here, crucial details are added to the characterization of the method. It is shown that single-particle reconstructions of apoferritin and Cowpea chlorotic mottle virus from revitrified samples are indistinguishable from those from conventional samples, demon- strating that melting and revitrification leaves the particles intact and that they do not undergo structural changes within the spatial resolution afforded by the instrument. How rapid revitrification affects the properties of the ice is also characterized, showing that revitrified samples exhibit comparable amounts of beam-induced motion. The results pave the way for microsecond time-resolved studies of the conformational dynamics of proteins and open up new avenues to study the vitrification process and to address beam-induced specimen move- ment.

2022

Multifunctional Gd2O3:Tm3+, Er3+, Nd3+ particles with luminescent and magnetic properties

Pavel Olshin

Development of novel materials with advanced properties is one of the main research directions of chemistry. New substances are not only crucial for many current technological applications but also should satisfy the needs of tomorrow. Industry often requires reliable, economically effective methods that can provide high quality reproducible results. Here we propose an inexpensive synthesis method that is suitable for synthesis of many types of particles. In this work we focused on Gd2O3:Tm3+, Er3+, Nd3+ particles with luminescence and magnetic properties. Based on the analysis of morphology, structural and optical properties of particles prepared by the standard Pechini methods and its variations, we found that the method with K2CO3 as additive yields particles with smaller sizes (down to tens of nm), higher crystallinity, and up to 1.7 times increased luminescence intensity. We also demonstrate that the unique combination of the particles' characteristics, for example, the intensity ratio of the luminescent bands corresponding to different REI and the mass susceptibility, strongly depends on the composition, synthesis method, and structure. The variety of the combination of the properties makes these particles a promising candidate for safety markers applications.& nbsp;

2022

Accurate time zero determination in an ultrafast transmission electron microscope without energy filter

Marcel Drabbels, Ulrich Lorenz, Pavel Olshin, Jonathan Mark Voss

In this manuscript, we describe a simple and accurate method for finding the temporal overlap of the laser pump and electron probe pulse in ultrafast TEM. Our approach is based on the observation that the outline of a nanoparticle blurs at time zero, a phenomenon that arises from the PINEM effect. Aside from determining time zero, the blurring can also be used to characterize the instrument response, determine the laser polarization in situ, and map the near fields of nanoparticles, all without the help of an energy filter.

2022