Atomic Force Microscopy Characterization Research Articles

A benzoxazine surfactant exchange for atomic force microscopy characterization of two dimensional materials exfoliated in aqueous surfactant solutions

Surfactant exchange was utilized to successfully deposit 2D flakes from liquid phase exfoliation for AFM characterization.

Combined “post-infiltration, subsequent photochemical cross-linking” and “cross-linking and selective etching” strategies to fabricate nanoporous layer-by-layer assembled multilayers

This study reports a new method combining a “post-infiltration, subsequent photochemical cross-linking” strategy and a “cross-linking and selective etching” approach to fabricate porous multilayers incorporating weak polyelectrolytes poly(allylamine hydrochloride) (PAH), polyethyleneimine (PEI), and poly(sodium-p-styrenesulfonate) (PSS). The multilayer film is fabricated by layer-by-layer (LbL) assembly of a blend of PAH and PEI in alternation with PSS to construct a composite multilayer film as a precursor. Then, 4,4′-diazido-2,2′-stilbenedisulfonic acid disodium (DAS) is infiltrated into the multilayer films, and subsequent photochemical cross-linking is applied under UV irradiation. By taking advantage of the differences between PAH/PSS and PEI/PSS, the multilayer films are immersed into a basic solution to selectively dissolve PEI. UV-visible spectroscopy, atomic force microscopy and cyclic voltammogram characterization results prove formation of nanoporous structures in the LbL assembled multilayer films. This novel way to fabricate porous films is anticipated to have potential applications in polymer and interface science.

Carbon Allotrope Nanomaterials Based Catalytic Micromotors

Carbon allotropes nanomaterials are explored here for the preparation of highly efficient tubular micromotors: 0D (C60 fullerene), 1D (carbon nanotubes), 2D (graphene), and 3D (carbon black, CB). The micromotors are prepared by direct electrochemical reduction or deposition of the nanomaterial into the pores of a membrane template. Subsequent electrodeposition of diverse inner catalytic layers (Pt, Pd, Ag, Au, or MnO2) allows for efficient bubble-propulsion in different media (seawater, human serum, and juice samples). Atomic-force microscopy (AFM) and scanning electron microscopy characterization reveals that the micromotors exhibit a highly rough outer surface and highly microporous inner catalytic structures. A key aspect derived from the AFM characterization is the demonstration that the rough outer surface of the micromotors can greatly affect their overall speed. To date, the literature has only focused on studying the effect of the inner catalytic layer upon their speed and performance and has unde...

Poroelasticity of cell nuclei revealed through atomic force microscopy characterization

With great potential in precision medical application, cell biomechanics is rising as a hot topic in biology. Cell nucleus, as the largest component within cell, not only contributes greatly to the cell's mechanical behavior, but also serves as the most vital component within cell. However, cell nucleus' mechanics is still far from unambiguous up to now. In this paper, we attempted to characterize and evaluate the mechanical property of isolated cell nuclei using Atomic Force Microscopy with a tipless probe. As indicated from typical indentation, changing loading rate and stress relaxation experiment results, cell nuclei showed significant dynamically mechanical property, i.e., time-dependent mechanics. Furthermore, through theoretical analysis, finite element simulation and stress relaxation experiment, the nature of nucleus' mechanics was better described by poroelasticity, rather than viscoelasticity. Therefore, the essence of nucleus' mechanics was clarified to be poroelastic through a sophisticated analysis. Finally, we estimated the poroelastic parameters for nuclei of two types of cells through a combination of experimental data and finite element simulation.

The synergic role of collagen and citrate in stabilizing amorphous calcium phosphate precursors with platy morphology.

Citrate is an important component of the bone organic matrix but its specific role in bone mineralization is presently unclear. In this work, bioinspired in vitro collagen mineralization experiments in the presence of citrate have been carried out and the combined role of collagen and citrate in controlling mineral formation has been addressed for the first time. Through X-ray scattering and Atomic Force Microscopy characterizations on mineralized and non-mineralized collagen fibrils, we have found that citrate in synergy with collagen stabilizes an amorphous calcium phosphate (ACP) phase with platy morphology over one week and controls its deposition on collagen fibrils.

Atomic force microscopy characterization of kinase-mediated phosphorylation of a peptide monolayer.

We describe the detailed microscopic changes in a peptide monolayer following kinase-mediated phosphorylation. A reversible electrochemical transformation was observed using square wave voltammetry (SWV) in the reversible cycle of peptide phosphorylation by ERK2 followed by dephosphorylation by alkaline phosphatase. A newly developed method for analyzing local roughness, measured by atomic force microscope (AFM), showed a bimodal distribution. This may indicate either a hole-formation mechanism and/or regions on the surface in which the peptide changed its conformation upon phosphorylation, resulting in increased roughness and current. Our results provide the mechanistic basis for developing biosensors for detecting kinase-mediated phosphorylation in disease.

The effect of annealing temperature on the structural, morphological, mechanical and surface properties of intermetallic NiTi alloy thin films

In this work, we report our studies on intermetallic NiTi thin films grown on silicon (1 0 0) substrates by glancing angle DC-magnetron sputtering technique using separate sputter targets Ni and Ti. The as prepared intermetallic NiTi thin films were vacuum annealed for one hour at four different temperatures, i.e. 350, 450, 550 and 650°C. The crystallization and surface morphology were studied using X-ray diffraction technique (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Atomic Force Microscopy (AFM). It was observed that the annealing temperatures had a significant influence on structural, morphological, mechanical and surface properties of intermetallic NiTi thin films. XRD studies revealed that the degree of crystallization increased with the increase in annealing temperature. The surface mean height (Ra), root mean square (RMS) and maximum peak to valley height (P-V) values have been obtained by AFM characterization. Nanoindentation tests on annealed intermetallic NiTi thin films were performed at room temperature. The hardness and elastic moduli increased from 8.32 to 10.24GPa and from 154.60 to 164.49GPa, respectively, with respect to the increase in annealing temperature. X-ray photo-electron spectroscopy (XPS) was used to study the composition and surface chemistry of the annealed films. From HR-XPS investigations, it was observed that intermetallic NiTi thin films had higher affinity to form Titanium dioxide (TiO2) layer on the film surface leaving a Nickel enriched matrix immediately behind the metal oxide layer.

A Cost-Effective Method to Immobilize Hydrated Soft-Tissue Samples for Atomic Force Microscopy

Immobilizing hydrated soft tissue specimens for atomic force microscopy (AFM) is a challenge. Here, we describe a simple and very cost-effective immobilization method, based on the use of transglutaminase in an aqueous environment, and successfully apply it to AFM characterization of human native Wharton's Jelly (nWJ), the gelatinous connective tissue matrix of the umbilical cord. A side-by-side comparison with a widely used polyphenolic protein-based tissue adhesive (Corning Cell-Tak), which is known to bind strongly to virtually all inorganic and organic surfaces in aqueous environments, shows that both adhesives successfully immobilize nWJ in its physological hydrated state. The cost of transglutaminase, however, is over 3000-fold lower than that of Cell-Tak, making it a very attractive method for immobilizing soft tissues for AFM characterization.

A novel approach for extracting viscoelastic parameters of living cells through combination of inverse finite element simulation and Atomic Force Microscopy

Dynamic mechanical behaviour of living cells has been described by viscoelasticity. However, quantitation of the viscoelastic parameters for living cells is far from sophisticated. In this paper, combining inverse finite element (FE) simulation with Atomic Force Microscope characterization, we attempt to develop a new method to evaluate and acquire trustworthy viscoelastic index of living cells. First, influence of the experiment parameters on stress relaxation process is assessed using FE simulation. As suggested by the simulations, cell height has negligible impact on shape of the force–time curve, i.e. the characteristic relaxation time; and the effect originates from substrate can be totally eliminated when stiff substrate (Young’s modulus larger than 3 GPa) is used. Then, so as to develop an effective optimization strategy for the inverse FE simulation, the parameters sensitivity evaluation is performed for Young’s modulus, Poisson’s ratio, and characteristic relaxation time. With the experiment data obtained through typical stress relaxation measurement, viscoelastic parameters are extracted through the inverse FE simulation by comparing the simulation results and experimental measurements. Finally, reliability of the acquired mechanical parameters is verified with different load experiments performed on the same cell.

Study of DNA binding and bending by Bacillus subtilis GabR, a PLP-dependent transcription factor

BackgroundGabR is a transcriptional regulator belonging to the MocR/GabR family, characterized by a N-terminal wHTH DNA-binding domain and a C-terminal effector binding and/or oligomerization domain, structurally homologous to aminotransferases (ATs). In the presence of γ-aminobutyrate (GABA) and pyridoxal 5′-phosphate (PLP), GabR activates the transcription of gabT and gabD genes involved in GABA metabolism. MethodsHere we report a biochemical and atomic force microscopy characterization of Bacillus subtilis GabR in complex with DNA. Complexes were assembled in vitro to study their stoichiometry, stability and conformation. ResultsThe fractional occupancy of the GabR cognate site suggests that GabR binds as a dimer with Kd of 10nM. Upon binding GabR bends the DNA by 80° as measured by anomalous electrophoretic mobility. With GABA we observed a decrease in affinity and conformational rearrangements compatible with a less compact nucleo-protein complex but no changes of the DNA bending angle. By employing promoter and GabR mutants we found that basic residues of the positively charged groove on the surface of the AT domain affect DNA affinity. ConclusionsThe present data extend current understanding of the GabR-DNA interaction and the effect of GABA and PLP. A model for the GabR-DNA complex, corroborated by a docking simulation, is proposed. General SignificanceCharacterization of the GabR DNA binding mode highlights the key role of DNA bending and interactions with bases outside the canonical direct repeats, and might be of general relevance for the action mechanism of MocR transcription factors.

Novel strategy for sulfapyridine detection using a fully integrated electrochemical Bio-MEMS: Application to honey analysis

Sulfapyridine (SPy) is a sulfonamide antibiotic largely employed as veterinary drugs for prophylactic and therapeutic purposes. Therefore, its spread in the food products has to be restricted. Herein, we report the synthesis and characterization of a novel electrochemical biosensor based on gold microelectrodes modified with a new structure of magnetic nanoparticles (MNPs) coated with poly(pyrrole-co-pyrrole-2-carboxylic acid) (Py/Py-COOH) for high efficient detection of SPy. This analyte was quantified through a competitive detection procedure with 5-[4-(amino)phenylsulfonamide]-5-oxopentanoic acid-BSA (SA2-BSA) antigens toward polyclonal antibody (Ab-155). Initially, gold working electrodes (WEs) of integrated biomicro electro-mechanical system (BioMEMS) were functionalized by Ppy-COOH/MNPs, using a chronoamperometric (CA) electrodeposition. Afterward, SA2-BSA was covalently bonded to Py/Py-COOH/MNP modified gold WEs through amide bonding. The competitive detection of the analyte was made by a mixture of a fixed concentration of Ab-155 and decreasing concentrations of SPy from 50µgL−1 to 2ngL−1. Atomic Force Microscopy characterization was performed in order to ensure Ppy-COOH/MNPs electrodeposition on the microelectrode surfaces. Electrochemical measurements of SPy detection were carried out using electrochemical impedance spectroscopy (EIS). This biosensor was found to be highly sensitive and specific for SPy, with a limit of detection of 0.4ngL−1. This technique was exploited to detect SPy in honey samples by using the standard addition method. The measurements were highly reproducible for detection and interferences namely, sulfadiazine (SDz), sulfathiazole (STz) and sulfamerazine (SMz). Taking these advantages of sensitivity, specificity, and low cost, our system provides a new horizon for development of advanced immunoassays in industrial food control.

Pressure induced directional transformations on close spaced vapor transport deposited SnS thin films

In this work, SnS thin films were deposited by employing the Close Spaced Vapor Transport (CSVT) technique under air atmosphere. Single-phase, p-type SnS thin films were synthesized by varying the final pressure in the chamber and its effect on the properties of SnS were studied. The pressure impact on the directional preferred orientation (DPO) of grains is presented for the first time. The analysis of different pressure values on deposited film properties was performed by X-ray diffraction analysis, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, optical measurements and electric characterization techniques.

Purely Armchair or Partially Chiral: Noncontact Atomic Force Microscopy Characterization of Dibromo-Bianthryl-Based Graphene Nanoribbons Grown on Cu(111).

We report on the atomic structure of graphene nanoribbons (GNRs) formed via on-surface synthesis from 10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on Cu(111). By means of ultrahigh vacuum noncontact atomic force microscopy with CO-functionalized tips we unveil the chiral nature of the so-formed GNRs, a structure that has been under considerable debate. Furthermore, we prove that-in this particular case-the coupling selectivity usually introduced by halogen substitution is overruled by the structural and catalytic properties of the substrate. Specifically, we show that identical chiral GNRs are obtained from 9,9'-bianthryl, the unsubstituted sister molecule of DBBA.

Effects of germination and high hydrostatic pressure processing on mineral elements, amino acids and antioxidants in vitro bioaccessibility, as well as starch digestibility in brown rice (Oryza sativa L.)

The effects of germination and high hydrostatic pressure (HHP) processing on the in vitro bioaccessibility of mineral elements, amino acids (AAs), antioxidants and starch in brown rice (BR) were investigated. Germinated BR (GBR) was obtained by incubating at 37°C for 36h and then subjected to HHP treatments at 0.1, 100, 300 and 500MPa for 10min. The in vitro bioaccessibility of calcium and copper was increased by 12.59–52.17% and 2.87–23.06% after HHP, respectively, but bioaccessible iron was decreased. In addition, HHP significantly improved individual AAs, particularly indispensable AAs and gama-aminobutyric acid, as well as bioaccessible total antioxidant activities and starch resistance to enzymatic hydrolysis. However, germination greatly increased starch digestibility. Atomic force microscopy characterization suggested an obvious structural change in bran fraction at pressures above 300MPa. These results can help to understand the effects of germination and HHP technologies on nutrients bioaccessibility and develop appropriate processing conditions.

Large-Scale Synthesis of a Uniform Film of Bilayer MoS2 on Graphene for 2D Heterostructure Phototransistors

The large-scale synthesis of atomically thin, layered MoS2/graphene heterostructures is of great interest in optoelectronic devices because of their unique properties. Herein, we present a scalable synthesis method to prepare centimeter-scale, continuous, and uniform films of bilayer MoS2 using low-pressure chemical vapor deposition. This growth process was utilized to assemble a heterostructure by growing large-scale uniform films of bilayer MoS2 on graphene (G-MoS2/graphene). Atomic force microscopy, Raman spectra, and transmission electron microscopy characterization demonstrated that the large-scale bilayer MoS2 film on graphene exhibited good thickness uniformity and a polycrystalline nature. A centimeter-scale phototransistor prepared using the G-MoS2/graphene heterostructure exhibited a high responsivity of 32 mA/W with good cycling stability; this value is 1 order of magnitude higher than that of transferred MoS2 on graphene (2.5 mA/W). This feature results from efficient charge transfer at the interface enabled by intimate contact between the grown bilayer MoS2 (G-MoS2) and graphene. The ability to integrate multilayer materials into atomically thin heterostructures paves the way for fabricating multifunctional devices by controlling their layer structure.

Monitoring Volumetric Changes in Silicon Thin-Film Anodes through In Situ Optical Diffraction Microscopy.

A high-resolution in situ spectroelectrochemical optical diffraction experiment has been developed to understand the volume expansion/contraction process of amorphous silicon (a-Si) thin-film anodes. Electrodes consisting of 1D transmissive gratings of silicon have been produced through photolithographic methods. After glovebox assembly in a home-built Teflon cell, monitoring of the diffraction efficiency of these gratings during the lithiation/delithiation process is performed using an optical microscope equipped with a Bertrand lens. When the diffraction efficiency along with optical constants obtained from in situ spectroscopic ellipsometry is utilized, volume changes of the active materials can be deduced. Unlike transmission electron microscopy and atomic force microscopy characterization methods of observing silicon's volume expansion, this experiment allows for real-time monitoring of the volume change at charge/discharge cycles greater than just the first few along with an experimental environment that directly mimics that of a real battery. This technique shows promising results that provide needed insight into understanding the lithium alloying reaction and subsequent induced capacity fade during the cycling of alloying anodes in lithium-ion batteries.

Direct Evidence of Divalent Manganese Ion‐Induced DNA Condensation at Room Temperature

Whether manganese ion can induce DNA condensation at room temperature has not been clarified. In this study, direct evidence of Mn2+ ion‐induced DNA condensation is provided by single‐molecule measurements and atomic force microscopy characterization. It is shown that elevated temperature is not a requirement to induce DNA condensation, but helps to promote the process at the ensemble level. The finding suggests the failure of the Manning theory in explaining Mn2+‐DNA interactions and refreshes the view that divalent metal ions cannot cause DNA condensation. The localized binding of Mn2+ on DNA is believed to induce condensation. image

Self-assembly of monodisperse composite microgels with bimetallic nanorods as core and PNIPAM as shell into close-packed monolayers and SERS efficiency

In this study, monolayer film of composite microgels with bimetallic nanorods as core and PNIPAM as shell (Au@AgNR@PNIPAM) assembly on a modified surface of silicon wafer was formed by a dip coating method. The effects of temperature, pH and concentration of KCl on the surface morphology of monolayer were discussed. And when the temperature was 50°C; pH value was 4.0; concentration of KCl was 10mM, a monolayer film would be formed much better. By the characterization of atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM), the monolayer structure of Au@AgNR@PNIPAM composite microgels assembled products was confirmed. The analysis of attenuated total reflection Fourier transform infrared absorption spectrum (ATR-FTIR) confirmed that the chemical composition of monolayer film on the silicon wafer surface was PNIPAM. And the UV–visible spectroscopy showed Au@AgNR in the monolayer film still maintained their LSPR optical performance. Assembled product has high stability, the surface morphology and coverage of the monolayer film did not change significantly when testing in a swing speed of 100rpm Rocking Shaker within 30min. The assembled monolayer was used as SERS substrates to trace the 10−1M to 10−4M 1-naphthol in aqueous solution, and the analysis results was with good reproducibility.

Improvement of pentathiophene/fullerene planar heterojunction photovoltaic cells by improving the organic films morphology through the anode buffer bilayer

Organic photovoltaic cells (OPVCs) are based on a heterojunction electron donor (ED)/electron acceptor (EA). In the present work, the electron donor which is also the absorber of light is pentathiophene. The typical cells were ITO/HTL/pentathiophene/fullerene/Alq 3 /Al with HTL (hole transport layer) = MoO 3 , CuI, MoO 3 /CuI. After optimisation of the pentathiophene thickness, 70 nm, the highest efficiency, 0.81%, is obtained with the bilayer MoO 3 /CuI as HTL. In order to understand these results the pentathiophene films deposited onto the different HTLs were characterized by scanning electron microscopy, atomic force microscopy, X-rays diffraction, optical absorption and electrical characterization. It is shown that CuI improves the conductivity of the pentathiophene layer through the modification of the film structure, while MoO 3 decreases the leakage current. Using the bilayer MoO 3 /CuI allows cumulating the advantages of each layer.

Advanced mechanical and electrical characterization of piezoelectric ZnO nanowires for electro-mechanical modeling of enhanced performance sensors

Nano-scale devices based on zinc oxide (ZnO) are expected to be widely used as building-blocks of future innovative sensors due to outstanding properties of this semiconductive material including presence of a direct bandgap, piezoelectricity, pyroelectricity, biocompatibility. Zinc oxide nanostructures can be also conceived as ultra-high efficiency nanogenerators to harvest electrical energy from the strain vibrational energy in order to drive an array of nanosensors. In fact most applications are based on the cooperative and average response of a large number of ZnO elongated micro/nanostructures, such as wires, rods and pillars. In order to assess the quality of the materials and their performance it is fundamental to characterize and then accurately model the specific electrical and piezoelectric properties of single ZnO structures, in an integrated manner. In this paper, we report on the brittle-to-ductile transition that occurs when reducing the size down to the nanoscale, which has been rarely documented. Then we report on focused ion beam machined of high aspect ratio nanowires and pillars and their mechanical and electrical (by means of conductive atomic force microscopy) characterization. Finally, we present new simulation results concerning ZnO nanowires under lateral bending obtained through the classical approach and the finite element method. Here we use a new power-law design concepts to accurately model the relevant electrical and mechanical size-effects whose existence has been emphasized in recent reviews.