Electron inelastic mean free path in water

Exploring Biomineralization Processes Using In Situ Liquid Transmission Electron Microscopy: A Review

Liquid transmission electron microscopy (TEM) is a newly established technique broadly used to study reactions in situ. Since its emergence, complex and multifaceted biomineralization processes have been revealed with real-time resolution, where classical and non-classical mineralization pathways have been dynamically observed primarily for Ca and Fe-based mineral systems in situ. For years, classical crystallization pathways have dominated theories on biomineralization progression despite observations of non-traditional routes involving precursor phases using traditional- and cryo-TEM. The new dynamic lens provided by liquid TEM is a key correlate to techniques limited to time-stamped, static observations - helping shift paradigms in biomineralization toward non-classical theories with dynamic mechanistic visualization. Liquid TEM provides new insights into fundamental biomineralization processes and essential physiological and pathological processes for a wide range of organisms. This review critically reviews a summary of recent in situ liquid TEM research related to the biomineralization field. Key liquid TEM preparation and imaging parameters are provided as a foundation for researchers while technical challenges are discussed. In future, the expansion of liquid TEM research in the biomineralization field will lead to transformative discoveries, providing complementary dynamic insights into biological systems.

Liquid Phase Electron Microscopy of Bacterial Ultrastructure

Recent advances in liquid phase scanning transmission electron microscopy (LP-STEM) have enabled the study of dynamic biological processes at nanometer resolutions, paving the way for live-cell imaging using electron microscopy. However, this technique is often hampered by the inherent thickness of whole cell samples and damage from electron beam irradiation. These restrictions degrade image quality and resolution, impeding biological interpretation. Using graphene encapsulation, scanning transmission electron microscopy (STEM), and energy-dispersive X-ray (EDX) spectroscopy to mitigate these issues provides unprecedented levels of intracellular detail in aqueous specimens. This study demonstrates the potential of LP-STEM to examine and identify internal cellular structures in thick biological samples. Specifically, it highlights the use of LP-STEM to investigate the radiation resistant, gram-positive bacterium, Deinococcus radiodurans using various imaging techniques.

Optimizing Contrast in Automated 4D STEM Cryotomography

4D STEM is an emerging approach to electron microscopy. While it was developed principally for high-resolution studies in materials science, the possibility to collect the entire transmitted flux makes it attractive for cryomicroscopy in application to life science and radiation-sensitive materials where dose efficiency is of utmost importance. We present a workflow to acquire tomographic tilt series of 4D STEM data sets using a segmented diode and an ultrafast pixelated detector, demonstrating the methods using a specimen of a T4 bacteriophage. Full integration with the SerialEM platform conveniently provides all the tools for grid navigation and automation of the data collection. Scripts are provided to convert the raw data to mrc format files and further to generate a variety of modes representing both scattering and phase contrasts, including incoherent and annular bright field, integrated center of mass, and parallax decomposition of a simulated integrated differential phase contrast. Principal component analysis of virtual annular detectors proves particularly useful, and axial contrast is improved by 3D deconvolution with an optimized point spread function. Contrast optimization enables visualization of irregular features such as DNA strands and thin filaments of the phage tails, which would be lost upon averaging or imposition of an inappropriate symmetry.

Nanoscale architecture of synaptic vesicles and scaffolding complexes revealed by cryo-electron tomography

The spatial distribution of proteins and their arrangement within the cellular ultrastructure regulates the opening of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in response to glutamate release at the synapse. Fluorescence microscopy imaging revealed that the postsynaptic density (PSD) and scaffolding proteins in the presynaptic active zone (AZ) align across the synapse to form a trans-synaptic "nanocolumn," but the relation to synaptic vesicle release sites is uncertain. Here, we employ focused-ion beam (FIB) milling and cryoelectron tomography to image synapses under near-native conditions. Improved image contrast, enabled by FIB milling, allows simultaneous visualization of supramolecular nanoclusters within the AZ and PSD and synaptic vesicles. Surprisingly, membrane-proximal synaptic vesicles, which fuse to release glutamate, are not preferentially aligned with AZ or PSD nanoclusters. These synaptic vesicles are linked to the membrane by peripheral protein densities, often consistent in size and shape with Munc13, as well as globular densities bridging the synaptic vesicle and plasma membrane, consistent with prefusion complexes of SNAREs, synaptotagmins, and complexin. Monte Carlo simulations of synaptic transmission events using biorealistic models guided by our tomograms predict that clustering AMPARs within PSD nanoclusters increases the variability of the postsynaptic response but not its average amplitude. Together, our data support a model in which synaptic strength is tuned at the level of single vesicles by the spatial relationship between scaffolding nanoclusters and single synaptic vesicle fusion sites.

Observing the Dynamics of an Electrochemically Driven Active Material with Liquid Electron Microscopy

Electrochemical liquid electron microscopy has revolutionized our understanding of nanomaterial dynamics by allowing for direct observation of their electrochemical production. This technique, primarily applied to inorganic materials, is now being used to explore the self-assembly dynamics of active molecular materials. Our study examines these dynamics across various scales, from the nanoscale behavior of individual fibers to the micrometer-scale hierarchical evolution of fiber clusters. To isolate the influences of the electron beam and electrical potential on material behavior, we conducted thorough beam-sample interaction analyses. Our findings reveal that the dynamics of these active materials at the nanoscale are shaped by their proximity to the electrode and the applied electrical current. By integrating electron microscopy observations with reaction-diffusion simulations, we uncover that local structures and their formation history play a crucial role in determining assembly rates. This suggests that the emergence of nonequilibrium structures can locally accelerate further structural development, offering insights into the behavior of active materials under electrochemical conditions.

Quantitative atomic cross section analysis by 4D-STEM and EELS

We demonstrate the use of a 4-dimensional scanning transmission electron microscope (4D-STEM) to extract atomic cross section information in amorphous materials. We measure the scattering amplitudes of 200 keV electrons in several representative specimens: amorphous carbon, silica, amorphous ice of pure water, and vitrified phosphate buffer solution. Diffraction patterns are recorded by 4D-STEM with or without energy filter at the zero-loss peak. In addition, Electron Energy Loss Spectroscopy (EELS) data are acquired at several thicknesses and energies. Mixed elastic and inelastic contributions for thick samples can be decoupled based on a convolution model. Measured differential cross sections between 1 and 3 mrad are due primarily to plasmon excitations and follow precisely a 1/θ2 angular distribution. The measured intensities match Inokuti's calculations of total dipole matrix elements for discrete dipole transitions alone, i.e., transitions to bound states of the atom and not to continuum states. We describe the fundamental mechanism of plasmon excitation in insulators as a two-step interaction process with a fast electron. First, a target electron in the specimen is excited, the probability for which follows from the availability of atomic transitions, with a strong dependence on the column of the periodic table. Second, the dielectric response of the material determines the energy loss. The energy of the loss peak depends primarily on the valence electrons. Elastic scattering is dominant at higher angles, and can be fitted conveniently to 1/θ3.7 with a linear dependence on atomic number for light atoms. In order to facilitate the interpretation of 4D STEM measurements in terms of material composition, we introduce two key parameters. Zeta is an analytical equivalent of classical STEM Z-contrast, determined by the ratio of elastic to inelastic scattering coefficients, while eta is the elastic coefficient divided by thickness. The two parameters may serve for identification of basic classes of materials in biological and other amorphous organic specimens.

High-resolution and analytical electron microscopy in a liquid flow cell via gas purging

Liquid-phase transmission electron microscopy (LPTEM) technique has been used to perform a wide range of in situ and operando studies. While most studies are based on the sample contrast change in the liquid, acquiring high qualitative results in the native liquid environment still poses a challenge. Herein, we present a novel and facile method to perform high-resolution and analytical electron microscopy studies in a liquid flow cell. This technique is based on removing the liquid from the observation area by a flow of gas. It is expected that the proposed approach can find broad applications in LPTEM studies.

Correlating cryo-super resolution radial fluctuations and dual-axis cryo-scanning transmission electron tomography to bridge the light-electron resolution gap

Visualization of organelles and their interactions with other features in the native cell remains a challenge in modern biology. We have introduced cryo-scanning transmission electron tomography (CSTET), which can access 3D volumes on the scale of 1 micron with a resolution of nanometers, making it ideal for this task. Here we introduce two relevant advances: (a) we demonstrate the utility of multi-color super-resolution radial fluctuation light microscopy under cryogenic conditions (cryo-SRRF), and (b) we extend the use of deconvolution processing for dual-axis CSTET data. We show that cryo-SRRF nanoscopy is able to reach resolutions in the range of 100 nm, using commonly available fluorophores and a conventional widefield microscope for cryo-correlative light-electron microscopy. Such resolution aids in precisely identifying regions of interest before tomographic acquisition and enhances precision in localizing features of interest within the 3D reconstruction. Dual-axis CSTET tilt series data and application of entropy regularized deconvolution during post-processing results in close-to-isotropic resolution in the reconstruction without averaging. The integration of cryo-SRRF with deconvolved dual-axis CSTET provides a versatile workflow for studying unique objects in a cell.

Observing ion diffusion and reciprocating hopping motion in water

When an ionic crystal dissolves in solvent, the positive and negative ions associated with solvent molecules release from the crystal. However, the existing form, interaction, and dynamics of ions in real solution are poorly understood because of the substantial experimental challenge. We observed the diffusion and aggregation of polyoxometalate (POM) ions in water by using liquid phase transmission electron microscopy. Real-time observation reveals an unexpected local reciprocating hopping motion of the ions in water, which may be caused by the short-range polymerized bridge of water molecules. We find that ion oligomers, existing as highly active clusters, undergo frequent splitting, aggregation, and rearrangement in dilute solution. The formation and dissociation of ion oligomers indicate a weak counterion-mediated interaction. Furthermore, POM ions with tetrahedral geometry show directional interaction compared with spherical ions, which presents structure-dependent dynamics.

Tailoring the Acidity of Liquid Media with Ionizing Radiation: Rethinking the Acid-Base Correlation beyond pH

Advanced in situ techniques based on electrons and X-rays are increasingly used to gain insights into fundamental processes in liquids. However, probing liquid samples with ionizing radiation changes the solution chemistry under observation. In this work, we show that a radiation-induced decrease in pH does not necessarily correlate to an increase in acidity of aqueous solutions. Thus, pH does not capture the acidity under irradiation. Using kinetic modeling of radiation chemistry, we introduce alternative measures of acidity (radiolytic acidity π* and radiolytic ion product K_W*), that account for radiation-induced alterations of both H⁺ and OH^- concentration. Moreover, we demonstrate that adding pH-neutral solutes such as LiCl, LiBr, or LiNO₃ can trigger a significant change in π*. This provides a huge parameter space to tailor the acidity for in situ experiments involving ionizing radiation, as present in synchrotron facilities or during liquid-phase electron microscopy.

Bringing Structure to Cell Biology with Cryo-Electron Tomography

Recent advances in cryo-electron microscopy have marked only the beginning of the potential of this technique. To bring structure into cell biology, the modality of cryo-electron tomography has fast developed into a bona fide in situ structural biology technique where structures are determined in their native environment, the cell. Nearly every step of the cryo-focused ion beam-assisted electron tomography (cryo-FIB-ET) workflow has been improved upon in the past decade, since the first windows were carved into cells, unveiling macromolecular networks in near-native conditions. By bridging structural and cell biology, cryo-FIB-ET is advancing our understanding of structure-function relationships in their native environment and becoming a tool for discovering new biology.

Plasma FIB milling for the determination of structures in situ

Structural biology studies inside cells and tissues require methods to thin vitrified specimens to electron transparency. Until now, focused ion beams based on gallium have been used. However, ion implantation, changes to surface chemistry and an inability to access high currents limit gallium application. Here, we show that plasma-coupled ion sources can produce cryogenic lamellae of vitrified human cells in a robust and automated manner, with quality sufficient for pseudo-atomic structure determination. Lamellae were produced in a prototype microscope equipped for long cryogenic run times (> 1 week) and with multi-specimen support fully compatible with modern-day transmission electron microscopes. We demonstrate that plasma ion sources can be used for structural biology within cells, determining a structure in situ to 4.9 Å, and characterise the resolution dependence on particle distance from the lamella edge. We describe a workflow upon which different plasmas can be examined to further streamline lamella fabrication.

Radiolysis-Driven Evolution of Gold Nanostructures - Model Verification by Scale Bridging In Situ Liquid-Phase Transmission Electron Microscopy and X-Ray Diffraction

Utilizing ionizing radiation for in situ studies in liquid media enables unique insights into nanostructure formation dynamics. As radiolysis interferes with observations, kinetic simulations are employed to understand and exploit beam-liquid interactions. By introducing an intuitive tool to simulate arbitrary kinetic models for radiation chemistry, it is demonstrated that these models provide a holistic understanding of reaction mechanisms. This is shown for irradiated HAuCl4 solutions allowing for quantitative prediction and tailoring of redox processes in liquid-phase transmission electron microscopy (LP-TEM). Moreover, it is demonstrated that kinetic modeling of radiation chemistry is applicable to investigations utilizing X-rays such as X-ray diffraction (XRD). This emphasizes that beam-sample interactions must be considered during XRD in liquid media and shows that reaction kinetics do not provide a threshold dose rate for gold nucleation relevant to LP-TEM and XRD. Furthermore, it is unveiled that oxidative etching of gold nanoparticles depends on both, precursor concentration, and dose rate. This dependency is exploited to probe the electron beam-induced shift in Gibbs free energy landscape by analyzing critical radii of gold nanoparticles.

MeasureIce: accessible on-the-fly measurement of ice thickness in cryo-electron microscopy

Ice thickness is arguably one of the most important factors limiting the resolution of protein structures determined by cryo-electron microscopy (cryo-EM). The amorphous atomic structure of the ice that stabilizes and protects biological samples in cryo-EM grids also imprints some additional noise in cryo-EM images. Ice that is too thick jeopardizes the success of particle picking and reconstruction of the biomolecule in the worst case and, at best, deteriorates eventual map resolution. Minimizing the thickness of the ice layer and thus the magnitude of its noise contribution is thus imperative in cryo-EM grid preparation. In this paper we introduce MeasureIce, a simple, easy to use ice thickness measurement tool for screening and selecting acquisition areas of cryo-EM grids. We show that it is possible to simulate thickness-image intensity look-up tables, also usable in SerialEM and Leginon, using elementary scattering physics and thereby adapt the tool to any microscope without time consuming experimental calibration. We benchmark our approach using two alternative techniques: the "ice channel" technique and tilt-series tomography. We also demonstrate the utility of ice thickness measurement for selecting holes in gold grids containing an Equine apoferritin sample, achieving a 1.88 Ångstrom resolution in subsequent refinement of the atomic map.

Imaging biological macromolecules in thick specimens: The role of inelastic scattering in cryoEM

We investigate potential improvements in using electron cryomicroscopy to image thick specimens with high-resolution phase contrast imaging. In particular, using model experiments, electron scattering theory, Monte Carlo and multislice simulations, we determine the potential for improving electron cryomicrographs of proteins within a cell using chromatic aberration (Cc) correction. We show that inelastically scattered electrons lose a quantifiable amount of spatial coherence as they transit the specimen, yet can be used to enhance the signal from thick biological specimens (in the 1000 to 5000 Å range) provided they are imaged close to focus with an achromatic lens. This loss of information quantified here, which we call "specimen induced decoherence", is a fundamental limit on imaging biological molecules in situ. We further show that with foreseeable advances in transmission electron microscope technology, it should be possible to directly locate and uniquely identify sub-100 kDa proteins without the need for labels, in a vitrified specimen taken from a cell.

Elastic and inelastic mean free paths for scattering of fast electrons in thin-film oxides

Quantitative transmission electron microscopy (TEM) often requires accurate knowledge of sample thickness for determining defect density, structure factors, sample dimensions, electron beam and X-ray photons signal broadening. The most common thickness measurement is by Electron Energy Loss Spectroscopy which can be applied effectively to crystalline and amorphous materials. The drawback is that sample thickness is measured in units of Inelastic Mean Free Path (MFP) which depends on the material, the electron energy and the collection angle of the spectrometer. Furthermore, the Elastic MFP is an essential parameter for selecting optimal sample thickness to reduce dynamical scatterings, such as for short-range-order characterization of amorphous materials. Finally, the Inelastic to Elastic MFP ratio can predict the dominant mechanism for radiation damage due to the electron beam. We implement a fast and precise method for the extraction of inelastic and elastic MFP values in technologically important oxide thin films. The method relies on the crystalline Si substrate for calibration. The Inelastic MFP of Si was measured as a function of collection semi-angle (β) by combining Energy-Filtered TEM thickness maps followed by perpendicular cross-sectioning of the sample by Focused-Ion-Beam. For example, we measured a total Inelastic MFP (β∼157 mrad) in Si of 145 ± 10 nm for 200 keV electrons. The MFP of the thin oxide films is determined by their ratio at their interface with Si or SiO₂. The validity of this method was verified by direct TEM observation of cross-to-cross sectioning of TEM samples. The high precision of this method was enabled mainly by implementing a wedge preparation technique, which provides large sampling areas with uniform thickness. We measured the Elastic and Inelastic Mean Free Paths for 200 keV and 80 keV electrons as a function of collection angle for: SiO₂ (Thermal, CVD), low-κ SiOCH, Al₂O₃, TiO₂, ZnO, Ta₂O₅ and HfO₂. The measured MFP values were compared to calculations based on models of Wenzel, Malis and Iakoubovskii. These models deviate from measurements by up to 30%, especially for 80 keV electrons. Hence, we propose functional relations for the Elastic MFP and Inelastic MFP in oxides with respect to the mass density and effective atomic number, which reduce deviations by a factor of 2-3. In addition, the effects of sample cooling on the measurements and sample stability are examined.

Nanofluidic chips for cryo-EM structure determination from picoliter sample volumes

Cryogenic electron microscopy has become an essential tool for structure determination of biological macromolecules. In practice, the difficulty to reliably prepare samples with uniform ice thickness still represents a barrier for routine high-resolution imaging and limits the current throughput of the technique. We show that a nanofluidic sample support with well-defined geometry can be used to prepare cryo-EM specimens with reproducible ice thickness from picoliter sample volumes. The sample solution is contained in electron-transparent nanochannels that provide uniform thickness gradients without further optimisation and eliminate the potentially destructive air-water interface. We demonstrate the possibility to perform high-resolution structure determination with three standard protein specimens. Nanofabricated sample supports bear potential to automate the cryo-EM workflow, and to explore new frontiers for cryo-EM applications such as time-resolved imaging and high-throughput screening.

Benchmarking the ideal sample thickness in cryo-EM

The relationship between sample thickness and quality of data obtained is investigated by microcrystal electron diffraction (MicroED). Several electron microscopy (EM) grids containing proteinase K microcrystals of similar sizes from the same crystallization batch were prepared. Each grid was transferred into a focused ion beam and a scanning electron microscope in which the crystals were then systematically thinned into lamellae between 95- and 1,650-nm thick. MicroED data were collected at either 120-, 200-, or 300-kV accelerating voltages. Lamellae thicknesses were expressed in multiples of the corresponding inelastic mean free path to allow the results from different acceleration voltages to be compared. The quality of the data and subsequently determined structures were assessed using standard crystallographic measures. Structures were reliably determined with similar quality from crystalline lamellae up to twice the inelastic mean free path. Lower resolution diffraction was observed at three times the mean free path for all three accelerating voltages, but the data quality was insufficient to yield structures. Finally, no coherent diffraction was observed from lamellae thicker than four times the calculated inelastic mean free path. This study benchmarks the ideal specimen thickness with implications for all cryo-EM methods.

Real-space imaging of nanoparticle transport and interaction dynamics by graphene liquid cell TEM

Thermal motion of colloidal nanoparticles and their cohesive interactions are of fundamental importance in nanoscience but are difficult to access quantitatively, primarily due to the lack of the appropriate analytical tools to investigate the dynamics of individual particles at nanoscales. Here, we directly monitor the stochastic thermal motion and coalescence dynamics of gold nanoparticles smaller than 5 nm, using graphene liquid cell (GLC) transmission electron microscopy (TEM). We also present a novel model of nanoparticle dynamics, providing a unified, quantitative explanation of our experimental observations. The nanoparticles in a GLC exhibit non-Gaussian, diffusive motion, signifying dynamic fluctuation of the diffusion coefficient due to the dynamically heterogeneous environment surrounding nanoparticles, including organic ligands on the nanoparticle surface. Our study shows that the dynamics of nanoparticle coalescence is controlled by two elementary processes: diffusion-limited encounter complex formation and the subsequent coalescence of the encounter complex through rotational motion, where surface-passivating ligands play a critical role.

A cryo-TSEM with temperature cycling capability allows deep sublimation of ice to uncover fine structures in thick cells

The scanning electron microscope (SEM) has been reassembled into a new type of cryo-electron microscope (cryo-TSEM) by installing a new cryo-transfer holder and anti-contamination trap, which allowed simultaneous acquisition of both transmission images (STEM images) and surface images (SEM images) in the frozen state. The ultimate temperatures of the holder and the trap reached − 190 °C and − 210 °C, respectively, by applying a liquid nitrogen slush. The STEM images at 30 kV were comparable to, or superior to, the images acquired with conventional transmission electron microscope (100 kV TEM) in contrast and sharpness. The unroofing method was used to observe membrane cytoskeletons instead of the frozen section and the FIB methods. Deep sublimation of ice surrounding unroofed cells by regulating temperature enabled to emerge intracellular fine structures in thick frozen cells. Hence, fine structures in the vicinity of the cell membrane such as the cytoskeleton, polyribosome chains and endoplasmic reticulum (ER) became visible. The ER was distributed as a wide, flat structure beneath the cell membrane, forming a large spatial network with tubular ER.

Advanced Materials for Energy-Water Systems: The Central Role of Water/Solid Interfaces in Adsorption, Reactivity, and Transport

The structure, chemistry, and charge of interfaces between materials and aqueous fluids play a central role in determining properties and performance of numerous water systems. Sensors, membranes, sorbents, and heterogeneous catalysts almost uniformly rely on specific interactions between their surfaces and components dissolved or suspended in the water-and often the water molecules themselves-to detect and mitigate contaminants. Deleterious processes in these systems such as fouling, scaling (inorganic deposits), and corrosion are also governed by interfacial phenomena. Despite the importance of these interfaces, much remains to be learned about their multiscale interactions. Developing a deeper understanding of the molecular- and mesoscale phenomena at water/solid interfaces will be essential to driving innovation to address grand challenges in supplying sufficient fit-for-purpose water in the future. In this Review, we examine the current state of knowledge surrounding adsorption, reactivity, and transport in several key classes of water/solid interfaces, drawing on a synergistic combination of theory, simulation, and experiments, and provide an outlook for prioritizing strategic research directions.

Mapping and Controlling Liquid Layer Thickness in Liquid-Phase (Scanning) Transmission Electron Microscopy

Liquid-Phase (Scanning) Transmission Electron Microscopy (LP-(S)TEM) has become an essential technique to monitor nanoscale materials processes in liquids in real-time. Due to the pressure difference between the liquid and the microscope vacuum, bending of the silicon nitride (SiN_x ) membrane windows generally occurs. This causes a spatially varying liquid layer thickness that makes interpretation of LP-(S)TEM results difficult due to a locally varying achievable resolution and diffusion limitations. To mediate these difficulties, it is shown: 1) how to quantitatively map liquid layer thickness for any liquid at less than 0.01 e^- Å^-2 total dose; 2) how to dynamically modulate the liquid thickness by tuning the internal pressure in the liquid cell, co-determined by the Laplace pressure and the external pressure. It is demonstrated that reproducible inward bulging of the window membranes can be realized, leading to an ultra-thin liquid layer in the central window area for high-resolution imaging. Furthermore, it is shown that the liquid thickness can be dynamically altered in a programmed way, thereby potentially overcoming the diffusion limitations towards achieving bulk solution conditions. The presented approaches provide essential ways to measure and dynamically adjust liquid thickness in LP-(S)TEM experiments, enabling new experiment designs and better control of solution chemistry.

Accessing local electron-beam induced temperature changes during in situ liquid-phase transmission electron microscopy

A significant electron-beam induced heating effect is demonstrated for liquid-phase transmission electron microscopy at low electron flux densities using Au nanoparticles as local nanothermometers. The obtained results are in agreement with theoretical considerations. Furthermore, the impact of beam-induced heating on radiolysis chemistry is estimated and the consequences of the effect are discussed.

Unhindered Brownian Motion of Individual Nanoparticles in Liquid-Phase Scanning Transmission Electron Microscopy

Liquid-phase transmission electron microscopy (LPTEM) offers label-free imaging of nanoparticle (NP) processes in liquid with sub-nanometer spatial and millisecond temporal resolution. However, LPTEM studies have reported only on NPs moving orders of magnitude slower than expected from bulk aqueous liquid conditions, likely due to strong interactions with the LPTEM liquid-enclosing membranes. We demonstrate how scanning transmission electron microscope (STEM) imaging can be used to measure the motion of individual NPs and agglomerates, which are not hindered by such interactions. Only at low electron flux do we find that individual NPs exhibit Brownian motion consistent with optical control experiments and theoretical predictions for unhindered passive diffusive motion in bulk liquids. For increasing electron flux, we find increasingly faster than passive motion that still appears effectively Brownian. We discuss the possible origins of this beam-sample interaction. This establishes conditions for the use of STEM as a reliable tool for imaging nanoscale hydrodynamics in situ TEM.