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

The ergodicity question when imaging DNA conformation using liquid cell electron microscopy

Assessing the ergodicity of graphene liquid cell electron microscope measurements, we report that loop states of circular DNA interconvert reversibly and that loop numbers follow the Boltzmann distribution expected for this molecule in bulk solution, provided that the electron dose is low (80-keV electron energy and electron dose rate 1-20 e- Å-2 s-1). This imaging technique appears to act as a "slow motion" camera that reveals equilibrated distributions by imaging the time average of a few molecules without the need to image a spatial ensemble.

Direct Imaging of "Patch-Clasping" and Relaxation in Robust and Flexible Nanoparticle Assemblies

Polymer patching on inorganic nanoparticles (NPs) enables multifunctionality and directed self-assembly into nonclosely packed optical and mechanical metamaterials. However, experimental demonstration of such assemblies has been scant due to challenges in leveraging patch-induced NP-NP attractions and understanding NP self-assembly dynamics. Here we use low-dose liquid-phase transmission electron microscopy to visualize the dynamic behaviors of tip-patched triangular nanoprisms upon patch-clasping, where polymer patches interpenetrate to form cohesive bonds that connect NPs. Notably, these bonds are longitudinally robust but rotationally flexible. Patch-clasping is found to allow highly selective tip-tip assembly, interconversion between dimeric bowtie and sawtooth configurations, and collective structural relaxation of NP networks. The integration of single particle tracking, polymer physics theory, and molecular dynamics simulation reveals the macromolecular origin of patch-clasping-induced NP dynamics. Our experiment-computation integration can aid the design of stimuli-responsive nanomaterials, such as topological metamaterials for chiral sensors, waveguides, and nanoantennas.

Exploration of Organic Nanomaterials with Liquid-Phase Transmission Electron Microscopy

ConspectusOrganic, soft materials with solution-phase nanoscale structures, such as emulsions, hydrogels, and thermally responsive materials, are inherently difficult to directly image via dry state and cryogenic-transmission electron microscopy (TEM). Therefore, we lack a routine microscopy method with sufficient resolution that can, in tandem with scattering techniques, probe the morphology and dynamics of these and many related systems. These challenges motivate liquid cell (LC) TEM method development, aimed at making the technique generally available and routine. To date, the field has been and continues to be dominantly focused on analyzing solution-phase inorganic materials. These mostly metallic nanoparticles have been studied at electron fluxes that can allow for high-resolution imaging, in the range of hundreds to thousands of e- Å-2 s-1. Despite excellent contrast, in these cases, one often contends with knock-on damage, direct radiolysis, and sensitization of the solvent by virtue of enhanced secondary electron production by the impinging electron beam. With an interest in soft materials, we face both related and distinct challenges, especially in achieving a high-enough contrast within solvated liquid cells. Additionally, we must be aware of artifacts associated with high-flux imaging conditions in terms of direct radiolysis of the solvent and the sensitive materials themselves. Regardless, with care, it has become possible to gain real insight into both static and dynamic organic nanomaterials in solution. This is due, in large part, to key advances that have been made, including improved sample preparation protocols, image capture technologies, and image analysis, which have allowed LCTEM to have utility. To enable solvated soft matter characterization by LCTEM, a generalizable multimodal workflow was developed by leveraging both experimental and theoretical precedents from across the LCTEM field and adjacent works concerned with solution radiolysis and nanoparticle tracking analyses. This workflow consists of (1) modeling electron beam-solvent interactions, (2) studying electron beam-sample interactions via LCTEM coupled with post-mortem analysis, (3) the construction of "damage plots" displaying sample integrity under varied imaging and sample conditions, (4) optimized LCTEM imaging, (5) image processing, and (6) correlative analysis via X-ray or light scattering. In this Account, we present this outlook and the challenges we continue to overcome in the direct imaging of dynamic solvated nanoscale soft materials.

Goethite Mineral Dissolution to Probe the Chemistry of Radiolytic Water in Liquid-Phase Transmission Electron Microscopy

Liquid-Phase Transmission Electron Microscopy (LP-TEM) enables in situ observations of the dynamic behavior of materials in liquids at high spatial and temporal resolution. During LP-TEM, incident electrons decompose water molecules into highly reactive species. Consequently, the chemistry of the irradiated aqueous solution is strongly altered, impacting the reactions to be observed. However, the short lifetime of these reactive species prevent their direct study. Here, the morphological changes of goethite during its dissolution are used as a marker system to evaluate the influence of radiation on the changes in solution chemistry. At low electron flux density, the morphological changes are equivalent to those observed under bulk acidic conditions, but the rate of dissolution is higher. On the contrary, at higher electron fluxes, the morphological evolution does not correspond to a unique acidic dissolution process. Combined with kinetic simulations of the steady state concentrations of generated reactive species in the aqueous medium, the results provide a unique insight into the redox and acidity interplay during radiation induced chemical changes in LP-TEM. The results not only reveal beam-induced radiation chemistry via a nanoparticle indicator, but also open up new perspectives in the study of the dissolution process in industrial or natural settings.

Moisture-Induced Degradation of Quantum-Sized Semiconductor Nanocrystals through Amorphous Intermediates

Elucidating the water-induced degradation mechanism of quantum-sized semiconductor nanocrystals is an important prerequisite for their practical application because they are vulnerable to moisture compared to their bulk counterparts. In-situ liquid-phase transmission electron microscopy is a desired method for studying nanocrystal degradation, and it has recently gained technical advancement. Herein, the moisture-induced degradation of semiconductor nanocrystals is investigated using graphene double-liquid-layer cells that can control the initiation of reactions. Crystalline and noncrystalline domains of quantum-sized CdS nanorods are clearly distinguished during their decomposition with atomic-scale imaging capability of the developed liquid cells. The results reveal that the decomposition process is mediated by the involvement of the amorphous-phase formation, which is different from conventional nanocrystal etching. The reaction can proceed without the electron beam, suggesting that the amorphous-phase-mediated decomposition is induced by water. Our study discloses unexplored aspects of moisture-induced deformation pathways of semiconductor nanocrystals, involving amorphous intermediates.

pH-Mediated Size-Selective Adsorption of Gold Nanoparticles on Diblock Copolymer Brushes

Precise control of nanoparticles at interfaces can be achieved by designing stimuli-responsive surfaces that have tunable interactions with nanoparticles. In this study, we demonstrate that a polymer brush can selectively adsorb nanoparticles according to size by tuning the pH of the buffer solution. Specifically, we developed a facile polymer brush preparation method using a symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer deposited on a grafted polystyrene layer. This method is based on the assembly of a PS-b-P2VP thin film oriented with parallel lamellae that remains after exfoliation of the top PS-b-P2VP layer. We characterized the P2VP brush using X-ray reflectivity and atomic force microscopy. The buffer pH is used to tailor interactions between citrate-coated gold nanoparticles (AuNPs) and the top P2VP block that behaves like a polymer brush. At low pH (∼4.0) the P2VP brushes are strongly stretched and display a high density of attractive sites, whereas at neutral pH (∼6.5) the P2VP brushes are only slightly stretched and have fewer attractive sites. A quartz crystal microbalance with dissipation monitored the adsorption thermodynamics as a function of AuNP diameter (11 and 21 nm) and pH of the buffer. Neutral pH provides limited penetration depth for nanoparticles and promotes size selectivity for 11 nm AuNP adsorption. As a proof of concept, the P2VP brushes were exposed to various mixtures of large and small AuNPs to demonstrate selective capture of the smaller AuNPs. This study shows the potential of creating devices for nanoparticle size separations using pH-sensitive polymer brushes.

Boswellic acid coated zinc nanoparticles attenuate NF-κB-mediated inflammation in DSS-induced ulcerative colitis in rats

INTRODUCTION

Ulcerative colitis (UC) is a chronic non-specific inflammatory bowel disease, and until now therapeutic agents for UC still cannot exert satisfied effects. Therefore, this study aimed to investigate the ameliorative effect of boswellic acid coated zinc nanoparticles (BAs-ZnNPs) on dextran sodium sulphate (DSS) induced-UC in rats.

METHODS

Rats were divided into five groups; control, BAs-ZnNPs, DSS, DSS+BAs, and DSS + BAs-ZnNPs. The activity of alkaline phosphatase (ALP) was determined colorimetrically, while the concentration of IgM, IgG, TNF-α, IL-1β, and IL-8 were measured by ELISA. Levels of gene expression of NF-κB and COX-2 genes were evaluated by RT-qPCR, while the expression of protein levels of PI3K and STAT-3 were done by western blotting. Finally, histopathological examination of colon tissues of different groups of rats was done.

RESULTS

The depicted ball-like structure of the BAs-ZnNPs in the TEM images ranging in size from 50 to 100 nm in diameter while their formation was confirmed by UV-visible spectroscopy with a sharp peak of maximum absorbance at 266 nm. Our results revealed that BAs-ZnNPs exerted an anti-inflammatory effect in the experimental model of colitis, demonstrated histologically and biochemically as shown by the improvement of ALP, IgM, IgG, and the gene expression levels of NF-κB and COX-2. Also, this beneficial effect was associated with the reduction in the expression of TNF-α, IL-1β, IL-8, PI3K, and STAT-3. Thus, this effect improves the altered immune response associated with the colonic inflammation.

CONCLUSION

BAs-ZnNPs can be proposed as a therapeutic candidate to attenuate UC. The potential underlying mechanism includes suppression of ALP, IgM, IgG, IL-1β, and IL-8 levels via regulation of NF-κB and COX-2 gene expression and STAT-3 and PI3K protein expression in a UC rat model.

Conformation Dynamics of Single Polymer Strands in Solution

Conformational changes in macromolecules significantly affect their functions and assembly into high-level structures. Despite advances in theoretical and experimental studies, investigations into the intrinsic conformational variations and dynamic motions of single macromolecules remain challenging. Here, liquid-phase transmission electron microscopy enables the real-time tracking of single-chain polymers. Imaging linear polymers, synthetically dendronized with conjugated aromatic groups, in organic solvent confined within graphene liquid cells, directly exhibits chain-resolved conformational dynamics of individual semiflexible polymers. These experimental and theoretical analyses reveal that the dynamic conformational transitions of the single-chain polymer originate from the degree of intrachain interactions. In situ observations also show that such dynamics of the single-chain polymer are significantly affected by environmental factors, including surfaces and interfaces.

Coalescence dynamics of platinum group metal nanoparticles revealed by liquid-phase TEM

Coalescence, one of the major pathways observed in the growth of nanoparticles, affects the structural diversity of the synthesized nanoparticles in terms of sizes, shapes, and grain boundaries. As coalescence events occur transiently during the growth of nanoparticles and are associated with the interaction between nanoparticles, mechanistic understanding is challenging. The ideal platform to study coalescence events may require real-time tracking of nanoparticle growth trajectories with quantitative analysis for coalescence events. Herein, we track nanoparticle growth trajectories using liquid-cell transmission electron microscopy (LTEM) to investigate the role of coalescence in nanoparticle formation and their morphologies. By evaluating multiple coalescence events for different platinum group metals, we reveal that the surface energy and ligand binding energy determines the rate of the reshaping process and the resulting final morphology of coalesced nanoparticles. The coalescence mechanism, based on direct LTEM observation explains the structures of noble metal nanoparticles that emerge in colloidal synthesis.

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Image processing of in situ liquid cell TEM image

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Size-dependent coalescence behaviors of metal nanoparticles

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Different kinetics of Pt and Pd nanoparticles owing to their different surface energies

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Reshaping kinetics determines the final morphology of coalesced nanoparticles

Microreactor-Based TG-TEM Synchronous Analysis

It is challenging to measure the heating-induced mass change of the material during its morphological/structural evolution process. Herein, a silicon microreactor is developed for thermogravimetric-transmission electron microscopy synchronous analysis (TG-TEM synchronous analysis). A self-heating resonant microcantilever for mass-change detection and a dummy microcantilever with electron-beam transparent SiN_x windows for in situ TEM imaging are integrated back-to-back inside the microreactor. The TEM resolution of the microreactor reaches the Ångström level in an air atmosphere of 100 mbar, and the TGA function is realized by the heatable resonant microcantilever. The TG-TEM synchronous analysis has been successfully used to characterize two Ni(OH)₂ samples. During the in situ TEM observing process, the desorption of the intercalated H₂O molecules and dehydration of the lattice OH groups in the amorphous Ni(OH)₂·xH₂O nanosheets can be clearly distinguished from the microcantilever-based TGA. For single-crystal Ni(OH)₂ nanosheets, the TG-TEM synchronous analysis can distinguish the desorption of physiosorbed water, the condensation of surface OH groups, and the dehydration of lattice OH groups. The amorphous Ni(OH)₂ nanosheets transformed to polycrystalline NiO completed at 290 °C, and the decomposition from the single-crystalline Ni(OH)₂ nanoplates to NiO at 315 °C is also clearly recognized. The proposed microreactor-based TG-TEM synchronous analysis provides an interrelated characterization platform to obtain more comprehensive information on materials.