Observation of reactions in single molecules/nanoparticles using light microscopy

Recent techniques for direct observation of single molecules or nanoparticles provide methodologies for imaging the activation sites of heterogeneous catalysts (spatially resolved) and observing intermediates that are not visible in the ensemble average (temporally resolved). Accordingly, the primary challenge for related experiments is obtaining sufficient spatial and temporal resolutions for microscopic observation of the chemical reaction of interest. This review discusses recent advances in fluorescence-for example, total internal reflection fluorescence (TIRF)-and dark-field microscopy-for example, imaging plasmonic probes-used for observing organic, inorganic, and biological reactions. The following key factors for microscopic observation of chemical reactions are discussed: (1) design of the chemical reaction and probe, (2) selection of microscope based on reaction's temporal information, and (3) use of machine learning algorithms to analyze the sequence imaging data. This review summarizes experimental techniques and detailed examples of reactions at the single molecule and nanoparticle level. Furthermore, it discusses avenues of development. These observations can guide the development of new and systematic methodological approaches for investigating important unsolved problems in chemistry. © 2022 Korean Chemical Society, Seoul & Wiley-VCH GmbH.FALS

DEVELOPMENT OF LEAD SLOWING DOWN SPECTROMETER FOR ISOTOPIC FISSILE ASSAY

A lead slowing down spectrometer (LSDS) is under development for analysis of isotopic fissile material contents in pyro-processed material, or spent fuel. Many current commercial fissile assay technologies have a limitation in accurate and direct assay of fissile content. However, LSDS is very sensitive in distinguishing fissile fission signals from each isotope. A neutron spectrum analysis was conducted in the spectrometer and the energy resolution was investigated from 0.1eV to 100keV. The spectrum was well shaped in the slowing down energy. The resolution was enough to obtain each fissile from 0.2eV to lkeV. The detector existence in the lead will disturb the source neutron spectrum. It causes a change in resolution and peak amplitude. The intense source neutron production was designed for similar to E12 n's/sec to overcome spent fuel background. The detection sensitivity of U238 and Th232 fission chamber was investigated. The first and second layer detectors increase detection efficiency. Thorium also has a threshold property to detect the fast fission neutrons from fissile fission. However, the detection of Th232 is about 76% of that of U238. A linear detection model was set up over the slowing down neutron energy to obtain each fissile material content. The isotopic fissile assay using LSDS is applicable for the optimum design of spent fuel storage to maximize burnup credit and quality assurance of the recycled nuclear material for safety and economics. LSDS technology will contribute to the transparency and credibility of pyro-process using spent fuel, as internationally demanded.close0

Activation analysis of targets and lead in a lead slowing down spectrometer system

A neutron generation system was developed to induce fissile fission in a lead slowing down spectrometer (LSDS) system. The source neutron is one of the key factors for LSDS system work. The LSDS was developed to quantify the isotopic contents of fissile materials in spent nuclear fuel and recycled fuel. The source neutron is produced at a multilayered target by the (e,γ)(γ,n) reaction and slowed down at the lead medium. Activation analysis of the target materials is necessary to estimate the lifetime, durability, and safety of the target system. The CINDER90 code was used for the activation analysis, and it can involve three-dimensional geometry, position dependent neutron flux, and multigroup cross-section libraries. Several sensitivity calculations for a metal target with different geometries, materials, and coolants were done to achieve a high neutron generation rate and a low activation characteristic. Based on the results of the activation analysis, tantalum was chosen as a target material due to its better activation characteristics, and helium gas was suggested as a coolant. In addition, activation in a lead medium was performed. After a distance of 55 cm from the lead surface to the neutron incidence, the neutron intensity dramatically decreased; this result indicates very low activation

Temporal Patterns of Angular Displacement of Endosomes: Insights into Motor Protein Exchange Dynamics

Abstract The material transport system, facilitated by motor proteins, plays a vital role in maintaining a non‐equilibrium cellular state. However, understanding the temporal coordination of motor protein activity requires an advanced imaging technique capable of measuring 3D angular displacement in real‐time. In this study, a Fourier transform‐based plasmonic dark‐field microscope has been developed using anisotropic nanoparticles, enabling the prolonged and simultaneous observation of endosomal lateral and rotational motion. A sequence of discontinuous 3D angular displacements has been observed during the pause and run phases of transport. Notably, a serially correlated temporal pattern in the intermittent rotational events has been demonstrated during the tug‐of‐war mechanism, indicating Markovian switching between the exploitational and explorational modes of motor protein exchange prior to resuming movement. Alterations in transition frequency and the exploitation‐to‐exploration ratio upon dynein inhibitor treatment highlight the relationship between disrupted motor coordination and reduced endosomal transport efficiency. Collectively, these results suggest the importance of orchestrated temporal motor protein patterns for efficient cellular transport

Sunlight-Activatable ROS Generator for Cell Death Using TiO2/c-Si Microwires

Solar-driven reactive oxygen species (ROS) generation is an attractive disinfection technique for cell death and water purification. However, most photocatalysts require high stability in the water environment and the production of ROS with a sufficient amount and diffusion length to damage pathogens. Here, a ROS generation system was developed consisting of tapered crystalline silicon microwires coated with anatase titanium dioxide for a conformal junction. The system effectively absorbed >95% of sunlight over 300-1100 nm, resulting in effective ROS generation. The system was designed to produce various ROS species, but a logistic regression analysis with cellular survival data revealed that the diffusion length of the ROS is similar to 9 mu m, implying that the most dominant species causing cell damage is H2O2. Surprisingly, a quantitative analysis showed that only 15 min of light irradiation on the system would catalyze a local bactericidal effect comparable to the conventional germicidal level of H2O2 (similar to 3 mM)

Combinatorial selective synthesis and excitation experiments for quantitative analysis of effects of Au on a semiconductor photocatalyst

Despite its chemical stability, Au can significantly augment the catalytic properties of heterogeneous photocatalysts owing to its excellent optical properties in the visible region and localized surface plasmon resonance at the nanometer scale. However, experimental demonstration and quantitation of Au-semiconductor electron/energy-transfer pathways remain challenging. Herein, we report an optical microscopy-based combinatorial synthesis and excitation strategy to study Au@Cu2O plasmonic nanocatalysts under light irradiation at the single-particle level. Moreover, we studied the reaction kinetics of the hybridized catalyst, a property that is often difficult to investigate among the other parameters of molecular transport, and measured the individual contributions of the plasmon and excitation effects toward the intrinsic catalytic efficiency. Based on this, we propose an electron-transfer mechanism for Au-semiconductor nanoparticles. This simple and systematic strategy is a better alternative to the conventional electron microscopy technique and aids in investigating chemical reactions at the single-molecule and single-particle level. © 2022 Elsevier Inc.11Nsciescopu

Two GPSes in a Ball: Deciphering the Endosomal Tug-of-War Using Plasmonic Dark-Field STORM

Live video recording of intracellular material transport is a promising means of deciphering the fascinating underlying mechanisms driving life at the molecular level. Such technology holds the key to realizing real-time observation at appropriate resolutions in three-dimensional (3D) space within living cells. Here, we report an optical microscopic method for probing endosomal dynamics with proper spatiotemporal resolution within 3D space in live cells: plasmonic dark-field STORM (pdf-STORM). We first confirmed that pdf-STORM has a spatial resolution comparable to that of scanning electron microscopy. Additionally, by observing two optical probes within a single organelle, we were able to track rotational movements and demonstrate the feasibility of using pdf-STORM to observe the angular displacements of an endosome during a ???tug-of-war??? over an extended period. Finally, we show various biophysical parameters of the hitherto unelucidated dynamics of endosomes???angular displacement is discontinuous and y-axis movement predominates and follows a long-tail distribution

From Homogeneity to Turing Pattern: Kinetically Controlled Self-Organization of Transmembrane Protein

Understanding the spatial organization of membrane proteins is crucial for unraveling key principles in cell biology. The reaction–diffusion model is commonly used to understand biochemical patterning; however, applying reaction–diffusion models to subcellular phenomena is challenging because of the difficulty in measuring protein diffusivity and interaction kinetics in the living cell. In this work, we investigated the self-organization of the plasmalemma vesicle-associated protein (PLVAP), which creates regular arrangements of fenestrated ultrastructures, using single-molecule tracking. We demonstrated that the spatial organization of the ultrastructures is associated with a decrease in the association rate by actin destabilization. We also constructed a reaction–diffusion model that accurately generates a hexagonal array with the same 130 nm spacing as the actual scale and informs the stoichiometry of the ultrastructure, which can be discerned only through electron microscopy. Through this study, we integrated single-molecule experiments and reaction–diffusion modeling to surpass the limitations of static imaging tools and proposed emergent properties of the PLVAP ultrastructure

From Homogeneity to Turing Pattern: Kinetically Controlled Self-Organization of Transmembrane Protein

Understanding the spatial organization of membrane proteins is crucial for unraveling key principles in cell biology. The reaction–diffusion model is commonly used to understand biochemical patterning; however, applying reaction–diffusion models to subcellular phenomena is challenging because of the difficulty in measuring protein diffusivity and interaction kinetics in the living cell. In this work, we investigated the self-organization of the plasmalemma vesicle-associated protein (PLVAP), which creates regular arrangements of fenestrated ultrastructures, using single-molecule tracking. We demonstrated that the spatial organization of the ultrastructures is associated with a decrease in the association rate by actin destabilization. We also constructed a reaction–diffusion model that accurately generates a hexagonal array with the same 130 nm spacing as the actual scale and informs the stoichiometry of the ultrastructure, which can be discerned only through electron microscopy. Through this study, we integrated single-molecule experiments and reaction–diffusion modeling to surpass the limitations of static imaging tools and proposed emergent properties of the PLVAP ultrastructure