Nanoscopic Changes Research Articles

Detour to success: photoswitching via indirect excitation.

Photoswitchable molecules that undergo nanoscopic changes upon photoisomerisation can be harnessed to control macroscopic properties such as colour, solubility, shape, and motion of the systems they are incorporated into. These molecules find applications in various fields of chemistry, physics, biology, and materials science. Until recently, research efforts have focused on the design of efficient photoswitches responsive to low-energy (red or near-infrared) irradiation, which however may compromise other molecular properties such as thermal stability and robustness. Indirect isomerisation methods enable photoisomerisation with low-energy photons without altering the photoswitch core, and also open up new avenues in controlling the thermal switching mechanism. In this perspective, we present the state of the art of five indirect excitation methods: two-photon excitation, triplet sensitisation, photon upconversion, photoinduced electron transfer, and indirect thermal methods. Each impacts our understanding of the fundamental physicochemical properties of photochemical switches, and offers unique application prospects in biomedical technologies and beyond.

Photocontrolled DNA nanotubes as stiffness tunable matrices for controlling cellular behavior.

Cell behavior is determined by a variety of properties of the extracellular environment like ligand spacing, nanotopography, and matrix stiffness. Matrix stiffness changes occur during many biological processes like wound healing, tumorigenesis, and development. These spatio-temporal dynamic changes in stiffness can cause significant changes in cell morphology, cell signaling, migration, cytoskeleton etc. In this paper, we have created photocontrolled stiffness-tunable DNA nanotubes which can undergo reversible changes in their conformation upon UV and VIS irradiation. When used as a substrate for cell culture, the photocontrolled DNA nanotubes can tune the cell morphology of HeLa cells from a long spindle-shaped morphology with long filopodia protrusions to a round morphology with short filopodia-like extrusions. Such a photocontrolled nanosystem can give us deep insights into the cell-matrix interactions in the native extracellular matrix caused by nanoscopic changes in stiffness.

Contraction and Expansion of Nanocomposites during Ion Exchange Reactions.

The next generation of advanced functional materials can greatly benefit from methods for realizing the right chemical composition at the right place. Nanocomposites of amorphous silica and metal carbonate nanocrystals (BaCO3/SiO2) form an attractive starting point as they can straightforwardly be assembled in different controllable three-dimensional (3D) shapes, while the chemical composition of the nanocrystals can be completely converted via ion exchange. Nevertheless, it is still unknown—let alone predictable—how nanoscopic changes in the lattice volume of the nanocrystals translate to changes in the microscopic dimensions of 3D BaCO3/SiO2 structures during ion exchange. Here, we demonstrate that the microscopic shape adapts to contraction and expansion of the atomic spacing of nanocrystals. Starting from BaCO3/SiO2, we systematically decrease and increase lattice volumes by converting the BaCO3 nanocrystals into a range of chalcogenides and perovskites. Based on geometrical analysis, we obtain a precise prediction for how the microscopic nanocomposite volume follows the change in nanoscopic crystal volume. The silica matrix facilitates mechanical flexibility to adapt to nanoscopic volume changes, while preserving the 3D morphology and fine details of the original composite with high fidelity. The versatility and predictability of shape-preserving conversion reactions open up exciting opportunities for using nanocomposites as functional components.

A Practical Guide for Using Electrochemical Dilatometry as Operando Tool in Battery and Supercapacitor Research.

Lithium‐ion batteries and related battery concepts show an expansion and shrinkage (“breathing”) of the electrodes during cell cycling. The dimensional changes of an individual electrode or a complete cell can be continuously measured by electrochemical dilatometry (ECD). The obtained data provides information on the electrode/cell reaction itself but can be also used to study side reactions or other relevant aspects, e.g., how the breathing is influenced by the electrode binder and porosity. The method spans over a wide measurement range and allows the determination of macroscopic as well as nanoscopic changes. It has also been applied to supercapacitors. The method has been developed already in the 1970s but recent advancements and the availability of commercial setups have led to an increasing interest in ECD. At the same time, there is no “best practice” on how to evaluate the data and several pitfalls exist that can complicate the comparison of literature data. This review highlights the recent development and future trends of ECD and its use in battery and supercapacitor research. A practical guide on how to evaluate the data is provided along with a discussion on various factors that influence the measurement results.

Nanoscopic changes in the lattice structure of striated muscle sarcomeres involved in the mechanism of spontaneous oscillatory contraction (SPOC)

Muscles perform a wide range of motile functions in animals. Among various types are skeletal and cardiac muscles, which exhibit a steady auto-oscillation of force and length when they are activated at an intermediate level of contraction. This phenomenon, termed spontaneous oscillatory contraction or SPOC, occurs devoid of cell membranes and at fixed concentrations of chemical substances, and is thus the property of the contractile system per se. We have previously developed a theoretical model of SPOC and proposed that the oscillation emerges from a dynamic force balance along both the longitudinal and lateral axes of sarcomeres, the contractile units of the striated muscle. Here, we experimentally tested this hypothesis by developing an imaging-based analysis that facilitates detection of the structural changes of single sarcomeres at unprecedented spatial resolution. We found that the sarcomere width oscillates anti-phase with the sarcomere length in SPOC. We also found that the oscillatory dynamics can be altered by osmotic compression of the myofilament lattice structure of sarcomeres, but they are unchanged by a proteolytic digestion of titin/connectin—the spring-like protein that provides passive elasticity to sarcomeres. Our data thus reveal the three-dimensional mechanical dynamics of oscillating sarcomeres and suggest a structural requirement of steady auto-oscillation.

Effect of Silica Nanofluid on Nanoscopic Pore Structure of Low-Permeability Petroleum Reservoir by Nitrogen Adsorption Technique: A Case Study

Silica nanofluids have proven to be successful in improving hydrocarbon recovery in the petroleum industry, and increased demand for hydrocarbons has necessitated its application in low-permeability reservoirs. In recent times, surface coating of nanoparticles has been employed to reduce its retention in porous media, but this does not entirely eliminate nanoparticle attachment to pore walls. Knowledge of changes that occur in pore wall and structure such as specific surface area (SSA), pore size distribution and total pore volume (TPV) would be useful in understanding retention mechanisms. This study used nitrogen adsorption technique in studying changes in pore structure due to silica nanofluid treatment. The Brunauer–Emmett–Teller theory and Barrett–Joyner–Halenda adsorption model were used in determining SSAs and TPVs, respectively. SSA, adsorbability and TPV increased in treated samples compared to untreated samples and the rates of change increased with treatment time due to extra pores induced by nanoparticle coagulation. Percent changes in TPV matched closely with SSA and was responsible for increments in the latter. Scanning electron micrographs confirmed coagulation of nanoparticles which increased with treatment time and introduced pseudo-pores on pore walls, resulting in increase in TPV. Increase in differential pore volume was observed for the entire studied range of 2–100 nm except for 3–4 nm which showed no changes in all samples. Severity of differential pore volume increased with treatment time. This study provides insights into nanoscopic changes that occur on pore walls and structure when employing silica nanoparticles in improving hydrocarbon recovery in low-permeability hydrocarbon reservoirs.

The Global Relationship between Chromatin Physical Topology, Fractal Structure, and Gene Expression

Most of what we know about gene transcription comes from the view of cells as molecular machines: focusing on the role of molecular modifications to the proteins carrying out transcriptional reactions at a loci-by-loci basis. This view ignores a critical reality: biological reactions do not happen in an empty space, but in a highly complex, interrelated, and dense nanoenvironment that profoundly influences chemical interactions. We explored the relationship between the physical nanoenvironment of chromatin and gene transcription in vitro. We analytically show that changes in the fractal dimension, D, of chromatin correspond to simultaneous increases in chromatin accessibility and compaction heterogeneity. Using these predictions, we demonstrate experimentally that nanoscopic changes to chromatin D within thirty minutes correlate with concomitant enhancement and suppression of transcription. Further, we show that the increased heterogeneity of physical structure of chromatin due to increase in fractal dimension correlates with increased heterogeneity of gene networks. These findings indicate that the higher order folding of chromatin topology may act as a molecular-pathway independent code regulating global patterns of gene expression. Since physical organization of chromatin is frequently altered in oncogenesis, this work provides evidence pairing molecular function to physical structure for processes frequently altered during tumorigenesis.

Hofmeister Effects on RAFT-Like Domains

We have studied ion-specific effects of monovalent salts on coexisting liquid-ordered (Lo)/liquid-disordered (Ld) domains using small-angle X-ray scattering. In particular, we focused on nanoscopic changes in domain properties in mixtures of dioleophosphatidylcholine, distearophosphatidylcholine and cholesterol brought about by Cl-, Br- and I- at various concentrations. Global data analysis in terms of the scattering length density model resulted in highly-resolved data on domain thickness, area per lipid and bending fluctuations in Lo and Ld domains. In accordance with previous experiments on homogenous bilayers changes in structural parameters within a given phase – either Lo, or Ld – follow the well-known Hofmeister series (Cl-< Br-< I-). Interestingly, however, these effects are expressed to different levels in coexisting Lo/Ld domains. In particular, Ld domains are much more susceptible to ion-specific interactions than Lo domains. For example the area per lipid decreases rapidly for Ld domains but not for Lo domains. This suggests a significant role of the ionic composition of the aqueous phase in structuring complex lipid membranes.

Characterization of the Distance Relationship Between Localized Serotonin Receptors and Glia Cells on Fluorescence Microscopy Images of Brain Tissue.

We here present two new methods for the characterization of fluorescent localization microscopy images obtained from immunostained brain tissue sections. Direct stochastic optical reconstruction microscopy images of 5-HT1A serotonin receptors and glial fibrillary acidic proteins in healthy cryopreserved brain tissues are analyzed. In detail, we here present two image processing methods for characterizing differences in receptor distribution on glial cells and their distribution on neural cells: One variant relies on skeleton extraction and adaptive thresholding, the other on k-means based discrete layer segmentation. Experimental results show that both methods can be applied for distinguishing classes of images with respect to serotonin receptor distribution. Quantification of nanoscopic changes in relative protein expression on particular cell types can be used to analyze degeneration in tissues caused by diseases or medical treatment.

Three‐Dimensional Concentration Mapping of Organic Blends

AbstractThe three‐dimensional morphology of mixed organic layers are quantitatively measured using high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) with electron tomography for the first time. The mixed organic layers used for organic photovoltaic applications have not been previously imaged using STEM tomography as there is insufficient contrast between donor and acceptor components. Contrast is generated by substituting fullerenes with endohedral fullerenes that contain a Lu3N cluster within the fullerene cage. The high contrast and signal‐to‐noise ratio, in combination with use of the discrete algebraic reconstruction technique (DART), allows generation of the most detailed and accurate three‐dimensional map of BHJ morphology to date. From the STEM‐tomography reconstructions it is determined that three distinct material phases are present within the BHJs. By observing changes to morphology and mixing ratio during thermal and solvent annealing, the effects of mutual solubility and fullerene crystallization on morphology and long term stability are determined. This material/technique combination shows itself as a powerful tool for examining morphology in detail and allows for observation of nanoscopic changes in local concentration.

Low-Loss, High-Permittivity Composites Made from Graphene Nanoribbons

A new composite material was prepared by incorporation of graphene nanoribbons into a dielectric host matrix. The composite possesses remarkably low loss at reasonably high permittivity values. By varying the content of the conductive filler, one can tune the loss and permittivity to desirable values over a wide range. The obtained data exemplifies how nanoscopic changes in the structure of conductive filler can affect macroscopic properties of composite material.

Acute hyperoxia increases lipid peroxidation and induces plasma membrane blebbing in human U87 glioblastoma cells

Atomic force microscopy (AFM), malondialdehyde (MDA) assays, and amperometric measurements of extracellular hydrogen peroxide (H 2O 2) were used to test the hypothesis that graded hyperoxia induces measurable nanoscopic changes in membrane ultrastructure and membrane lipid peroxidation (MLP) in cultured U87 human glioma cells. U87 cells were exposed to 0.20 atmospheres absolute (ATA) O 2, normobaric hyperoxia (0.95 ATA O 2) or hyperbaric hyperoxia (HBO 2, 3.25 ATA O 2) for 60 min. H 2O 2 (0.2 or 2 mM; 60 min) was used as a positive control for MLP. Cells were fixed with 2% glutaraldehyde immediately after treatment and scanned with AFM in air or fluid. Surface topography revealed ultrastructural changes such as membrane blebbing in cells treated with hyperoxia and H 2O 2. Average membrane roughness (R a) of individual cells from each group ( n=35 to 45 cells/group) was quantified to assess ultrastructural changes from oxidative stress. The R a of the plasma membrane was 34±3, 57±3 and 63±5 nm in 0.20 ATA O 2, 0.95 ATA O 2 and HBO 2, respectively. R a was 56±7 and 138±14 nm in 0.2 and 2 mM H 2O 2. Similarly, levels of MDA were significantly elevated in cultures treated with hyperoxia and H 2O 2 and correlated with O 2-induced membrane blebbing ( r 2=0.93). Coapplication of antioxidant, Trolox-C (150 μM), significantly reduced membrane R a and MDA levels during hyperoxia. Hyperoxia-induced H 2O 2 production increased 189%±5% (0.95 ATA O 2) and 236%±5% (4 ATA O 2) above control (0.20 ATA O 2). We conclude that MLP and membrane blebbing increase with increasing O 2 concentration. We hypothesize that membrane blebbing is an ultrastructural correlate of MLP resulting from hyperoxia. Furthermore, AFM is a powerful technique for resolving nanoscopic changes in the plasma membrane that result from oxidative damage.

Nanoscopic Morphological Changes in Yeast Cell Surfaces Caused by Oxidative Stress: An Atomic Force Microscopic Study

Nanoscopic changes in the cell surface morphology of the yeasts Saccharomyces cerevisiae (strain NCYC 1681) and Schizosaccharomyces pombe (strain DVPB 1354), due to their exposure to varying concentrations of hydrogen peroxide (oxidative stress), were investigated using an atomic force microscope (AFM). Increasing hydrogen peroxide concentration led to a decrease in cell viabilities and mean cell volumes, and an increase in the surface roughness of the yeasts. In addition, AFM studies revealed that oxidative stress caused cell compression in both S. cerevisiae and Schiz. pombe cells and an increase in the number of aged yeasts. These results confirmed the importance and usefulness of AFM in investigating the morphology of stressed microbial cells at the nanoscale. The results also provided novel information on the relative oxidative stress tolerance of S. cerevisiae and Schiz. pombe.

Using Localized Surface Plasmon Resonances to Probe the Nanoscopic Origins of Adsorbate-Driven Ordering Transitions of Liquid Crystals in Contact with Chemically Functionalized Gold Nanodots

We report that localized surface plasmon resonances (LSPRs) of gold nanodots immersed under liquid crystals (LCs) can be used to characterize adsorbate-induced ordering transitions of the LCs on the surfaces of the nanodots. The nanoscopic changes in ordering of the LCs, as measured by LSPR, were shown to give rise to macroscopic ordering transitions of the LCs that were observed by polarized light microscopy. The results reported herein suggest that (i) LCs may be useful for enhancing the sensitivity of LSPR-based detection of binding events and (ii) that LSPR measurements of gold nanodots provide a means to characterize the nanoscopic origins of macroscopic, adsorbate-induced LC ordering transitions.

A Step‐Flow Model for the Heteroepitaxial Growth of Strained, Substitutional, Binary Alloy Films with Phase Segregation: I. Theory

We develop a step‐flow model for the heteroepitaxy of a generic, strained, substitutional, binary alloy. The underlying theory is based on the fundamental principles of modern continuum thermodynamics. In order to resolve the inherent disparity in the spatial scales—continuous in the lateral directions vs. atomistically discrete along the epitaxial axis—we represent the film as a layered structure, with the layer height equal to the lattice parameter along the growth direction, thus extending the classical BCF framework [W. K. Burton, N. Cabrera, and F. C. Frank, Philos. Trans. Roy. Soc. London Ser. A, 243 (1951), pp. 299–358] to growth situations in which the bulk behavior impacts the surface evolution. Our discrete‐continuum model takes the form of a free‐boundary problem for the evolution of monoatomic steps on a vicinal surface, in which interfacial effects on the terraces and along the step edges couple to their bulk counterparts (i.e., within both film and, indirectly, substrate). In particular, the proposed constitutive theory is such that the film layers are endowed with (generalized) Ginzburg–Landau free energies that account for phase segregation and, concomitantly, competition between gradient‐driven coarsening and elastic refining of the separated domains. Importantly, the bulk and terrace effects are intertwined with the step dynamics via novel boundary conditions at the step edges derived from separate balance laws for configurational and microforces. Specifically, the former forces are associated with the evolution of defects (in the present setting, the steps), whereas the latter forces accompany micro‐ and nanoscopic changes in an order parameter (for a binary alloy subject to diffusion‐mediated phase separation, the atomic density of one of its components or, equivalently, the relative atomic density), and the postulated balances should be viewed as generalizations to a dynamic, dissipative setting—such as epitaxial growth, a far‐from‐equilibrium process—of more standard variational calculations.

STM and LEED observations of the surface structure ofTiO2(110)following crystallographic shear plane formation

Extended vacuum annealing of rutile ${\mathrm{TiO}}_{2}(110)$ produces macroscopic and nanoscopic changes in the surface morphology. These result from the ordering of oxygen ${\mathrm{v}\mathrm{a}\mathrm{c}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{s}/\mathrm{T}\mathrm{i}}^{n+}$ interstitials in bulk ${\mathrm{TiO}}_{2}$ into crystallographic shear (CS) planes. We have employed low-energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) to identify the surface termination of CS planes produced in the bulk. The directions of the planar defects along the surface indicate the {132} series of shear planes dominate the STM images, which is also supported by the LEED results. The spacing between planes gradually varies across the surface suggesting that a series of Magn\'eli phases are formed. LEED patterns confirm the coexistence of both relatively large areas of a single phase and a continuum of separations between planes. Formation of CS planes also leads to extensive facetting of the crystal, which is visible to the naked eye as a rippled surface finish. Some Ca segregation is observed during CS plane formation; however, when removed the CS planes remain, indicating they are not significantly stabilized by the Ca.

Phase transformation and bonding of ceramic nanoparticles in a TEM

Remarkable nanoscopic changes were observed in-situ in metastable oxide particles on the room temperature stage of a TEM under as electron beam intensity of 10 19 e/cm 2sec. Particles of 10–15 nm diameter α-Al 2O 3 and 5nm diameter Al metal were obtained from 100nm metastable θ-Al 2O 3 particles by a process dependent on the electron beam intensity. Al nanoparticles were bonded by continuous irradiation via surface diffusion of Al atom and the formation of 2 nm sized Al clusters The effects of the electron beam are the irradiation induced increase of the oxygen mobility and localized heating.