Atomic Force Microscopy Observations Research Articles

Dosimetry of pulsed magnetic field towards attaining bacteriostatic effect on Enterococcus faecalis: Implications for endodontic therapy.

To examine in a laboratory setting the efficacy of moderate to high strength magnetic fields, as a potential bacteriostatic stimulus, against Enterococcus faecalis, one of the causative agents for infection during root canal treatments. Four different strengths (1, 2, 3 and 4T) of the pulsed magnetic field (PMF) were applied in thirty repetitions to bacterial suspension. A pickup coil setup was used to measure the electromotive force induced inside the bacterial suspensions. The optical density (OD) was monitored over time (for 16h 40min) during the post-treatment period to assess bacterial growth. Along with the change in OD values, live/dead assay, membrane depolarization study, atomic force microscopy (AFM), scanning electron microscopy (SEM) and reactive oxygen species (ROS) assay on selected samples were studied to evaluate the effect of PMFs. All results were analysed using one-way ANOVA followed by post hoc Tukey test and considered significant at p<.05. Regression analysis (at a confidence of 95%, α=0.05) was performed on the bacterial growth and membrane depolarization studies to determine progressive changes of the outcomes. The peak value of the induced electromotive force was recorded as 0.25V, for the 4T magnetic field pulse with a pulse width of 16ms. There was a significant arrest of bacterial cell growth after an exposure to PMFs of 1T, 3T and 4T (ANOVA score: F (4, 495) =395.180 at p=.05). The image-based qualitative results of the live/dead assay using fluorescence microscopy techniques indicated that an exposure to higher PMFs (3T/ 4T) induced a bacteriostatic effect in a longer post-exposure timescale. Evidence of altered membrane potential within the 2h of exposure to 4T PMF was supported by the incidence of elevated ROS. For the ROS assay, a significant difference occurred for 4T exposed samples (ANOVA score: calculated F (1, 3) =20.2749 at p=.05). SEM and AFM observations corroborated with the outcomes, by portraying significant membrane damage. In a laboratory setting, PMFs with higher magnitudes (3T and 4T) were capable of inducing bacteriostatic effects on E.faecalis.

SWCNT network evolution of PEDOT:PSS/SWCNT composites for thermoelectric application

Although conjugated polymer/carbon nanotube (CNT) thermoelectric (TE) composites have witnessed explosive achievements in recent years, the in-depth mechanism of CNT network evolution and its influence on composite TE performance are still unclear. Herein, we systematically investigate the evolution of single-walled CNT (SWCNT) network structure with a wide SWCNT content range for poly (3,4-ethyienedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/SWCNT composites based on TE properties and atomic force microscopic (AFM) observations. The whole curves of TE performance can be divided into three regions with the increase of SWCNT loading. In Region I (< 20 wt% SWCNT), a percolation-like phenomenon is observed with an S-shape change of electrical conductivity and constant Seebeck coefficient, possibly due to the occurrence of SWCNT aggregates besides primary particles. Subsequently, because of energy-filtering effect, in Region II (SWCNT content between 20 wt% and 97.5 wt%), the electrical conductivity decreases, while the Seebeck coefficient gradually increases with increased SWCNT loading. With further increase of SWCNT content (Region III), the TE performances are almost independent of SWCNT content. In addition, the temperature dependence of TE performance and the stability of TE performance against mechanical bending cycles are studied. Finally, a prototype TE device based on PEDOT:PSS/SWCNT composite film is assembled, showing an open-circuit voltage and an output power of 6.6 mV and 1200 nW at a temperature difference of 60 K, respectively. The results are helpful to elucidate the mechanism of structure–property relations for conjugated polymer TE composites, and will benefit their practical applications.

Dominant factors and their action mechanisms on material removal rate in electrochemical mechanical polishing of 4H-SiC (0001) surface

Slurryless electrochemical mechanical polishing (ECMP) has been confirmed as a highly efficient damage-free polishing technique for SiC wafers. To increase the material removal rate of ECMP, it is essential to have a better understanding of the anodic oxidation mechanism of SiC to obtain a much higher anodic oxidation rate. In this study, we investigated the effects of electrolyte temperature, surface damage, doping concentration, and strain on the anodic oxidation rate of SiC. All these factors were found have a promotional effect on the anodic oxidation of SiC. The promotional effects of processing-induced damage and doping on SiC anodic oxidation were attributed to the processing-induced residual strain and doping-induced strain on the SiC surface, which were observed by Raman spectroscopy. The relationship between anodic oxidation rate and strain on the SiC surface was quantitatively investigated by applying a strain-controllable anodic oxidation device. Both compressive and tensile strains were found to increase the anodic oxidation rate of SiC. The promotion mechanism of the strain on the anodic oxidation of SiC was studied by conductive atomic force microscopy observations. This study is expected to be an important guide for improving the efficiency of ECMP and will contribute to the practical application of ECMP.

Structural and ultraviolet photo-detection properties of laser molecular beam epitaxy grown GaN layers using solid GaN and liquid Ga targets

GaN epitaxial layers have been grown on sapphire (0001) substrate by laser molecular beam epitaxy technique using laser ablation of polycrystalline GaN solid and liquid Ga metal targets in the ambient of nitrogen plasma. In-situ reflection high energy electron diffraction and exsitu atomic force microscopy observations revealed that GaN growth using solid target yields rough surface under three-dimensional growth mode while a flat surface GaN is obtained using liquid Ga target. From X-ray rocking curve measurement, it is also observed that the GaN layer grown using solid GaN target has a relatively better structural quality. X-ray photoelectron spectroscopy confirmed Ga–N bond formation and near-stoichiometric composition of the GaN epilayers. The influence of threading dislocation density on the ultraviolet (UV) photoresponse properties of GaN layers have been studied using metal-semiconductor-metal (MSM) based device structure. It is found that the GaN MSM structure obtained using solid GaN target with lesser screw and dislocation densities exhibits a higher responsivity with fast response and recovery time.

Spectroscopic and structural properties of CeO2 nanocrystals doped with La3+, Nd3+ and modified on their surface with Ag nanoparticles

The purpose of this work is to present our efforts focused on applications of chemical synthesis of nanocrystalline cerium dioxide (CeO2) powders doped with La3+ ions and CeO2:Nd3+ modified, on their surface, with Ag nanoparticles (NPs). The synthesized powders were examined by X-ray powder diffraction (XRD), absorption, emission spectroscopy, scanning electron (SEM) and atomic force microscopy (AFM). The relations between crystallographic properties and stability of CeO2 compounds doped by La ions and surface-modified by Ag were studied. XRD patterns revealed that all studied samples are single-phase and crystallized in the cubic fluorite-type structure, in space group Fm-3m. The average crystallite sizes estimated by Rietveld method of series: La-doped CeO2 were in the range of 7–14 nm, and CeO2:1%Nd3+/n-Ag (n: 1- 5wt.%) were found to be in the range of 29–34 nm, respectively. The lattice parameter a for La-doped CeO2 powders varying from 5.416 to 5.482 Å with increasing content of La3+ ions from 0 to 20wt.%, respectively. For series of CeO2:Nd3+/n-Ag materials lattice parameter a was at the same level and in accordance with the standard value a0 = 5.411 Å (ICDD - 43-1002). The SEM and AFM observations depicted the grainy structure of all obtained CeO2-powder samples. The estimated grain size ranged from 50 to 500 nm. The diverse grain shapes and packing was remarked in the samples. According to our knowledge, the relationship between the structural, spectroscopic and morphological characteristics of CeO2 samples was presented in this work for the first time.

Mitigating the negative effects of feldspar slime on spodumene flotation using mixed anionic/cationic collector

Due to the prevalent weathering, spodumene flotation is often susceptible to feldspar slime. In this study, the effect of feldspar slime on spodumene flotation in the NaOL and NaOL/DDA systems was studied. The micro-flotation tests showed that the negative effect of feldspar slime on spodumene flotation could be reduced by using the mixed NaOL/DDA collector with mole ratio of 9/1. The scanning electron microscopic images and the adsorption test results indicated that the decrease of spodumene recovery was attributed to collector consumption by feldspar slime. The mechanism was analyzed by ways of surface tension measurement, atomic force microscopic (AFM) observation and bubble attachment measurements, and the results showed that compared with NaOL alone, the mixed NaOL/DDA collector exhibited a better surface activity owing to a lower value of critical micelle concentration (CMC). The ‘spots’ formed on spodumene surface were thicker, and the formation of TPC was more likely. In addition, the bubble size was smaller and the bubble–particle adhesion was more possibly to occur in the NaOL/DDA system.

High temperature in situ SEM assessment followed by ex situ AFM and EBSD investigation of the nucleation and early growth stages of Fe-Al intermetallics

A dedicated in situ heating setup in a scanning electron microscope (SEM) followed by an ex situ atomic force microscopy (AFM) and electron backscatter diffraction (EBSD) is used to characterize the nucleation and early growth stages of Fe-Al intermetallics (IMs) at 596°C. A location tracking is used to interpret further characterization. Ex situ AFM observations reveal a slight shrinkage and out of plane protrusion of the IM at the onset of IM nucleation followed by directional growth. The formed interfacial IM compounds were identified by ex situ EBSD. It is now clearly demonstrated that the θ-phase nucleates first prior to the diffusion-controlled growth of the η-phase. The θ-phase prevails the intermetallic layer.

In vitro comparison of the surface roughness of polymethyl methacrylate and bis-acrylic resins for interim restorations before and after polishing

Statement of problemPolymethyl methacrylate and bis-acrylic based resins are widely used for interim restorations. Their initial surface roughness is important because it determines their aesthetic properties and the potential for biofilm adhesion. PurposeThe purpose of this in vitro study was to assess the surface roughness and morphology of 6 bis-acrylic and 2 polymethyl methacrylate resins widely used for interim dental restorations, both before and after polishing. Material and methodsSpecimens made of different bis-acrylic resins (Protemp 4, Luxatemp Star, Systemp, Telio, Structur Premium, Structur 3) or of polymethyl methacrylate (Unifast Trad, Unifast 3) were polished using a 2-step polishing system (Diatech). The average surface roughness before and after polishing (10 seconds at low speed in dry conditions) was measured by optical profilometry. Atomic force microscopy and scanning electron microscopy were used to analyze surface morphology. The Mann-Whitney and Kruskal-Wallis tests were used to evaluate the differences in roughness among specimens (α=.05), and the Pearson r correlation was computed to assess the relationship between fillers and average surface roughness. ResultsIn the 8 groups evaluated, the roughness significantly increased (P<.001) for Protemp 4 (from 0.12 to 0.50 μm), Luxatemp Star (0.17 to 1.19 μm), Unifast 3 (0.40 to 1.00 μm), Systemp (0.46 to 1.51 μm), Structur 3 (0.85 to 1.06 μm), Structur Premium (1.00 to 1.74 μm), and Telio (1.13 to 1.21 μm), except for Unifast Trad (9.20 to 2.59 μm). Pairwise multiple comparisons identified Protemp 4 as having the smoothest surface before and after polishing, while Unifast Trad was the roughest in both. Atomic force microscopy and scanning electron microscopy observations showed that the surface roughness of bis-acrylic resins was related to their surface morphology and average filler sizes. A positive relation between fillers and roughness was assessed (r=0.345, P<.001). ConclusionsFor the bis-acrylic interim resins, the surface roughness after polishing was correlated to the material used and its filler sizes. Nanofiller-based resins showed the smoothest surfaces. For the polymethyl methacrylate–based resins, the recently marketed Unifast 3 had the lowest overall roughness values.

Crystallization of Sodium Bicarbonate in the Presence of Trace Amounts of HPMA

AbstractThe effect of trace amounts of hydrolytic polymaleic anhydride (HPMA) on the crystallization of sodium bicarbonate (NaHCO3) has been investigated by molecular simulation and experimental methods. Cooling crystallization experiments show that the trace HPMA molecule effectively promotes the formation of larger NaHCO3 crystals. Besides, the crystal morphology changes from needle‐like to flake‐like. The determination of the metastable zone width of NaHCO3 and Atomic Force Microscopy (AFM) observation confirmed that the spontaneous nucleation processes are suppressed. Molecule simulation was used to explore the interaction of HPMA molecule and different crystal faces of NaHCO3. It was found that the binding energy between HPMA and NaHCO3 surface is greater than the corresponding attachment energy of NaHCO3 surface. The electrostatic interaction energy between double‐bonded oxygen on the HPMA molecule and the Na+ of the NaHCO3 crystal plane plays a dominant role in the additive molecule‘s adsorption on the NaHCO3 crystal surface. This work suggests that HPMA could serve as an inhibitor of nucleation and impact NaHCO3 crystallization.

Split conformation of Chaetomium thermophilum Hsp104 disaggregase

Hsp104 and its bacterial homolog ClpB form hexameric ring structures and mediate protein disaggregation. The disaggregated polypeptide is thought to thread through the central channel of the ring. However, the dynamic behavior of Hsp104 during disaggregation remains unclear. Here, we reported the stochastic conformational dynamics and a split conformation of Hsp104 disaggregase from Chaetomium thermophilum (CtHsp104) in the presence of ADP by X-ray crystallography, cryo-electron microscopy (EM), and high-speed atomic force microscopy (AFM). ADP-bound CtHsp104 assembles into a 65 left-handed spiral filament in the crystal structure at a resolution of 2.7Å. The unit of the filament is a hexamer of the split spiral structure. In the cryo-EM images, staggered and split hexameric rings were observed. Further, high-speed AFM observations showed that a substrate addition enhanced the conformational change and increased the split structure's frequency. Our data suggest that split conformation is an off-pathway state of CtHsp104 during disaggregation.

Investigation on the Electrical Stability of 5,11-Bis(triethylsilylethynyl)anthradithiophene Thin-Film Transistors.

We investigate the effects of environmental conditions on the electrical stability of spin-coated 5,11-bis(triethylsilylethynyl)anthradithiophene (TES-ADT) thin-film transistors (TFTs) in which crosslinked poly(4-vinylphenol-co-methyl methacrylate) (PVP-co-PMMA) was utilized as a gate insulator layer. Atomic force microscopy observations show molecular terraces with domain boundaries in the spin-coated TEST-ADT semiconductor film. The TFT performance was observed to be superior in the ambient air condition. Under negative gate-bias stress, the TES-ADT TFTs showed a positive threshold voltage shift in ambient air and a negative threshold voltage shift under vacuum. These results are explained through a chemical reaction between water molecules in air and unsubstituted hydroxyl groups in the cross-linked PVP-co-PMMA as well as a charge-trapping phenomenon at the domain boundaries in the spin-coated TES-ADT semiconductor.

Construction of Self-Assembled Polyelectrolyte/Cationic Microgel Multilayers and Their Interaction with Anionic Dyes Using Quartz Crystal Microbalance and Atomic Force Microscopy.

This study aimed to reveal the interaction between self-assembled multilayers and dye molecules in the environment, which is closely related to the multilayers’ stable performance and service life. In this work, the pH-responsive poly (N-isopropylacrylamide-co-2-(dimethylamino) ethyl methacrylate) microgels were prepared by free-radical copolymerization and self-assembled with sodium alginate (SA) into multilayers by the layer-by-layer deposition method. Quartz crystal microbalance (QCM) and atomic force microscopy (AFM) results confirmed the construction of multilayers and the absorbed mass, resulting in a decrease in the frequency shift of the QCM sensor and the deposition of microgel particles on its surface. The interaction between the self-assembled SA/microgel multilayers and anionic dyes in the aqueous solution was further investigated by QCM, and it was found that the electrostatic attraction between dyes and microgels deposited on the QCM sensor surface was much larger than that of the microgels with SA in multilayers, leading to the release of the microgels from the self-assembled structure and a mass loss ratio of 27.6%. AFM observation of the multilayer morphology exposed to dyes showed that 29% of the microgels was peeled off, and the corresponding microgel imprints were generated on the surface. In contrast, the shape and size of the remaining self-assembled microgel particles did not change.

Complex coacervation of carboxymethyl konjac glucomannan and ovalbumin and coacervate characterization

Carboxymethyl konjac glucomannan (CMKGM) is an anionic derivative of konjac glucomannan (KGM). Its coacervation with ovalbumin (OVA) was investigated through turbidity and coacervate yield measurements and the resultant CMKGM-OVA coacervates were characterized as a function of phase separation pH. The results indicated that CMKGM could coacervate with OVA in pHs ranging from 2.0 to 4.5. OVA to CMKGM mass ratios higher than 1:1 led to insoluble coacervates, while lower ratios conferred soluble complexes. NaCl suppressed the interaction between CMKGM and OVA and could resuspend their precipitated coacervates. The interaction between the two polyelectrolytes was not affected in temperatures ranging from 25 °C to 55 °C, but was weakened in higher temperatures. The coacervation increased the thermal stability and induced structural changes in both the polyelectrolytes. Atomic force microscope observation revealed that the CMKGM-OVA coacervates separated in mass ratio 1:1 was not susceptible to aggregation, and quartz crystal microbalance with dissipation analysis demonstrated that OVA exhibited the strongest absorption towards CMKGM in pH 3.0 in multilayer mode. Hence, CMKGM is a promising polyelectrolyte for coacervation with proteins and could be used in the construction of targeted delivery systems through the electrostatic interaction with oppositely charged biopolymers.

Interaction between ovalbumin and pectin and coacervate characterization

The interaction between ovalbumin (OVA) and high methoxyl pectin (PEC) was explored according to turbidity and coacervate yield measurements. Coacervation could occur between the two polyelectrolytes in pHs ranging from 2.5 to 4.0 and peaked in pH 2.5. The presence of NaCl suppressed the interaction, and their mass ratio determined the solubility of resultant coacervates. The association between OVA and PEC was highly temperature dependent and hydrophobic interaction played an important role in their complexation. Atomic force microscope observation revealed that serious aggregation occurred to the coacervates separated in pH 2.5, and circular dichroism analysis indicated that coacervation with PEC induced structural changes in OVA, which was positively related to the degree of coacervation. Thermogravimetry analysis demonstrated increased thermal stability of OVA in the coacervates, and quartz crystal microbalance analysis confirmed that the association between OVA and PEC was pH dependent and a rigid layer could be formed between them.

Extraction and Characterization Studies of Cellulose Derived from the Roots of Acalypha Indica L

ABSTRACT The underlying principle of this current research was to characterize the cellulosic fibers that were retted from the roots of Acalypha indica L. plant to find their aptness for making green composites. Physical characterization tests were conducted and reported proving the reinforcing capability of these fibers which has a density of 1.356 g/cm3. Chemical composition tests conducted on these fibers showed the weight % of cellulose as 67.86. Amorphous constituents such as hemicellulose and lignin were present as 0.24 and 18.75 weight %, respectively. Wax, ash, and moisture were respectively present as 0.86, 2.13, and 10.16 weight % of fibers. X-ray diffraction (XRD) studies purported the presence of both amorphous and crystalline contents of cellulose confirming the peaks of Fourier-transform infrared spectroscopy (FTIR) studies. The fibers possessed a crystallinity index of 46.62% and their crystallite size was computed as 3.68 nm from XRD, with a good temperature bearing capacity of 225°C as ascertained from the thermo-gravimetric analysis. Conglomeration of fibrils and the roughness characteristics were evident from the scanning electron microscopic images and atomic force microscopic observations, respectively. Thus, it can be seen that this newly identified fiber are apposite reinforcements and can be explored further by infusing them in polymer matrices for making sustainable products.

Transformation of SH-SY5Y cell line into neuron-like cells: Investigation of electrophysiological and biomechanical changes

SH-SY5Y human neuroblastoma cells are commonly used as neuronal models. Here, we examined different aspects of SH-SY5Y cell differentiation. Various differentiation protocols have been proposed previously, including treatments with retinoic acid, brain-derived neurotrophic factor (BDNF), cholesterol and oestradiol. We examined undifferentiated SH-SY5Y cells (UNDIFF); cells differentiated by the treatment with retinoic acid (RA); retinoic acid + BDNF (RB); and retinoic acid + BDNF + cholesterol + oestradiol (RBCE). We performed whole-cell patch-clamp recordings from these cells and nanomechanically characterised them by using atomic force microscopy (AFM). Our results indicated that Na+ currents become most pronounced in the differentiated RB cells, whereas UNDIFF SH-SY5Y cells had significantly larger K+ currents, which is a characteristic feature of cancer cells. AFM observations of these two groups showed that Young’s moduli of SH-SY5Y cells increased threefold with differentiation. Furthermore, we showed a direct relationship between Na+ channel activity and elasticity in these cells. We conclude that SH-SY5Y human neuroblastoma cells should be used as a neuronal model only when they are differentiated by the treatment with retinoic acid and BDNF.

Highly Regioselective and Helix-Sense Selective Living Polymerization of Phenyl and Alkoxyallene Using Chiral Nickel(II) Catalysts

Facile synthesis of high optically active helical polymers from achiral monomers still remains a great challenge. In this work, two chiral Ni(II) catalysts bearing chiral R- or S-2a ligands were facilely prepared which can efficiently initiate the living/controlled polymerization of allene monomers and afford well-defined polyallenes in high yields with controlled molecular masses (Mₙs) and low molecular mass distributions (Mw/Mₙs). The catalysts showed interesting regioselectivity on the cumulated double bonds of allene monomers, as the polymerizations were highly selective which occurred on 2,3-double bonds. Moreover, the polymerization of achiral allene monomers using chiral Ni(II) catalysts showed remarkable helix-sense selectivity. The yielded polyallenes exhibited high optical activity due to the formation of a predominant one-handed helix as revealed by circular dichroism, UV–vis, and direct atomic force microscopy (AFM) observations as well. The predominant one-handed helicity of the generated polyallenes was solely determined by the chirality of the Ni(II) catalysts.

Investigating the inhibitive effect of Davidia involucrata leaf extract as a biological eco-friendly inhibitor for copper in acidic medium

The inhibitive effect of copper in 0.5 mol/L H2SO4 by Davidia involucrata leaf extract (DLE) as inhibitor was investigated by means of experimental and theoretical methods. The maximun inhibition efficiency (η) acquired by electrochemical measurements are found to be close to 90% at different temperatures. The bonding information are detected by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations illustrate DLE can protect copper by forming an effective film. Also, Langmuir adsorption model is the most suitable to illustrate the adsorption mechanism of DLE on copper surface. The adsorption mechanism is further explained through quantum chemical calculation and molecular dynamics simulation.

In situ measurement of cell stiffness of Arabidopsis roots growing on a glass micropillar support by atomic force microscopy.

Atomic force microscopy (AFM) can measure the mechanical properties of plant tissue at the cellular level, but for in situ observations, the sample must be held in place on a rigid support and it is difficult to obtain accurate data for living plants without inhibiting their growth. To investigate the dynamics of root cell stiffness during seedling growth, we circumvented these problems by using an array of glass micropillars as a support to hold an Arabidopsis thaliana root for AFM measurements without inhibiting root growth. The root elongated in the gaps between the pillars and was supported by the pillars. The AFM cantilever could contact the root for repeated measurements over the course of root growth. The elasticity of the root epidermal cells was used as an index of the stiffness. By contrast, we were not able to reliably observe roots on a smooth glass substrate because it was difficult to retain contact between the root and the cantilever without the support of the pillars. Using adhesive to fix the root on the smooth glass plane overcame this issue, but prevented root growth. The glass micropillar support allowed reproducible measurement of the spatial and temporal changes in root cell elasticity, making it possible to perform detailed AFM observations of the dynamics of root cell stiffness.

Effect of cobalt content on electrodeposition and properties of Co–Ni alloy thin films

Co–Ni thin films alloys were deposited on ruthenium substrates by the electrochemical method from chloride bath at pH 3.8. The effect of cobalt content on the composition, morphology, electrochemical and microstructural properties of the electrodeposited thin films was investigated. Effectively, the conditions of electrodeposition of Ni–Co deposits were determined using the cyclic voltammetry at three ions concentration ratios Co/Ni (5:1, 1:1 and 1:5). Combined results from the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) study, show an excellent corrosion resistance for the deposits obtained when the cobalt concentration is low. The morphology of the electrodeposited Co–Ni alloys thin films is intimately associated with the Co content in the bath. Atomic force microscopy (AFM) observations of the deposits show a granular structure of the electrodeposited thin films and when the amount of Co was decreased in the solution bath; a strong decrease in the grain size was observed. X-ray diffraction measurements (XRD) indicate a small crystallite size with the presence of a mixture of hexagonal close-packed (hcp) and face-centered cubic (fcc) Co–Ni structures. The phase structure gradually changed from fcc to hcp with the increase of cobalt content.