Nickel-Induced Reduced Graphene Oxide Nanoribbon Formation on Highly Ordered Pyrolytic Graphite for Electronic and Magnetic Applications.

The development of nanoribbon-like structures is an effective strategy to harness the potential benefits of graphenic materials due to their excellent electrical properties, advantageous edge sites, rapid electron transport, and large specific area. Herein, parallel and connected magnetic nanostructured nanoribbons are obtained through the synthesis of reduced graphene oxide (rGO) using NiCl2 as a precursor with potential applications in nascent electronic and magnetic devices. Several analytical techniques have been used for the thorough characterization of the modified surfaces. Atomic force microscopy (AFM) shows the characteristic topographical features of the nanoribbons. While X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy provided information on the chemical state of Ni and graphene-like structures, magnetic force microscopy (MFM) and scanning Kelvin probe microscopy (SKPFM) confirmed the preferential concentration of Ni onto rGO nanoribbons. These results indicate that the synthesized material shows 1D ordering of nickel nanoparticles (NiNPs)-decorating tiny rGO flakes into thin threads and the subsequent 2D arrangement of the latter into parallel ribbons following the topography of the HOPG basal plane.

Electrode Potential-Dependent Studies of Protein Adsorption on Ti6Al4V Alloy.

This article presents the potential-dependent adsorption of two proteins, bovine serum albumin (BSA) and lysozyme (LYZ), on Ti6Al4V alloy at pH 7.4 and 37 °C. The adsorption process was studied on an electropolished alloy under cathodic and anodic overpotentials, compared to the open circuit potential (OCP). To analyze the adsorption process, various complementary interface analytical techniques were employed, including PM-IRRAS (polarization-modulation infrared reflection-absorption spectroscopy), AFM (atomic force microscopy), XPS (X-ray photoelectron spectroscopy), and E-QCM (electrochemical quartz crystal microbalance) measurements. The polarization experiments were conducted within a potential range where charging of the electric double layer dominates, and Faradaic currents can be disregarded. The findings highlight the significant influence of the interfacial charge distribution on the adsorption of BSA and LYZ onto the alloy surface. Furthermore, electrochemical analysis of the protein layers formed under applied overpotentials demonstrated improved corrosion protection properties. These studies provide valuable insights into protein adsorption on titanium alloys under physiological conditions, characterized by varying potentials of the passive alloy.

TiO2 nanoparticle coatings on glass surfaces for the selective trapping of leukemia cells from peripheral blood.

Photodynamic therapy (PDT) using TiO2 nanoparticles has become an important alternative treatment for different types of cancer due to their high photocatalytic activity and high absorption of UV-A light. To potentiate this treatment, we have coated commercial glass plates with TiO2 nanoparticles prepared by the sol-gel method (TiO2 -m), which exhibit a remarkable selectivity for the irreversible trapping of cancer cells. The physicochemical properties of the deposited TiO2 -m nanoparticle coatings have been characterized by a number of complementary surface-analytical techniques and their interaction with leukemia and healthy blood cells were investigated. Scanning electron and atomic force microscopy verify the formation of a compact layer of TiO2 -m nanoparticles. The particles are predominantly in the anatase phase and have hydroxyl-terminated surfaces as revealed by Raman, X-ray photoelectron, and infrared spectroscopy, as well as X-ray diffraction. We find that lymphoblastic leukemia cells adhere to the TiO2 -m coating and undergo amoeboid-like migration, whereas lymphocytic cells show distinctly weaker interactions with the coating. This evidences the potential of this nanomaterial coating to selectively trap cancer cells and renders it a promising candidate for the development of future prototypes of PDT devices for the treatment of leukemia and other types of cancers with non-adherent cells.

Electrografting of 4-Nitrobenzenediazonium Salts on Al-7075 Alloy Surfaces-The Role of Intermetallic Particles.

In this work, the electrografting of Al-7075 aluminium alloy substrates with 4-nitrobenzenediazonium salt (4-NBD) films was studied on a complex aluminium alloy surface. Prior to the electrografting reaction, the substrates were submitted to different surface treatments to modify the native aluminium oxide layer and unveil intermetallic particles (IMPs). The formation of the 4-NBD films could be correlated with the passive film state and the distribution of IMPs. The corresponding electrografting reaction was performed by cyclic voltammetry which allowed the simultaneous analysis of the redox reaction by a number of complementary surface-analytical techniques. Spatially resolved thin film analysis was performed by means of SEM-EDX, AFM, PM-IRRAS, Raman spectroscopy, XPS, and SKPFM. The collected data show that the 4-NBD film is preferentially formed either on the Al oxide layer or the IMP surface depending on the applied potential range. Potentials between -0.1 and -1.0 VAg/AgCl mostly generated nitrophenylene films on the oxide covered aluminium, while grafting between -0.1 and -0.4 VAg/AgCl favours the growth of these films on IMPs.

Effect of DNA Origami Nanostructures on hIAPP Aggregation.

The aggregation of human islet amyloid polypeptide (hIAPP) plays a major role in the pathogenesis of type 2 diabetes mellitus (T2DM), and numerous strategies for controlling hIAPP aggregation have been investigated so far. In particular, several organic and inorganic nanoparticles (NPs) have shown the potential to influence the aggregation of hIAPP and other amyloidogenic proteins and peptides. In addition to conventional NPs, DNA nanostructures are receiving more and more attention from the biomedical field. Therefore, in this work, we investigated the effects of two different DNA origami nanostructures on hIAPP aggregation. To this end, we employed in situ turbidity measurements and ex situ atomic force microscopy (AFM). The turbidity measurements revealed a retarding effect of the DNA nanostructures on hIAPP aggregation, while the AFM results showed the co-aggregation of hIAPP with the DNA origami nanostructures into hybrid peptide-DNA aggregates. We assume that this was caused by strong electrostatic interactions between the negatively charged DNA origami nanostructures and the positively charged peptide. Most intriguingly, the influence of the DNA origami nanostructures on hIAPP aggregation differed from that of genomic double-stranded DNA (dsDNA) and appeared to depend on DNA origami superstructure. DNA origami nanostructures may thus represent a novel route for modulating amyloid aggregation in vivo.

Altering model cell membranes by means of localized magnetic heating.

Isolated iron oxide magnetic nanoparticles (MNPs), 12 nm in diameter, coated with oleic acid molecules as capping agents have been deposited by the Langmuir-Blodgett (LB) method onto a model cell membrane incorporating 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and Cholesterol (Chol) in the 1:1 ratio, which was also fabricated by the LB technique. Atomic Force Microscopy (AFM) experiments showed that the application of an alternating magnetic field results in the embedding of the MNPs through the phospholipidic layer. These experimental results reveal that the heating of individual MNPs may induce a local increase in the fluidity of the film with a large control of the spatial and temporal specificity.

Effect of Terminal Modifications on the Adsorption and Assembly of hIAPP(20-29).

The assembly of peptides and proteins into nanoscale amyloid fibrils via formation of intermolecular ß-sheets not only plays an important role in the development of degenerative diseases but also represents a promising approach for the synthesis of functional nanomaterials. In many biological and technological settings, peptide assembly occurs in the presence of organic and inorganic interfaces with different physicochemical properties. In an attempt to dissect the relative contributions of the different molecular interactions governing amyloid assembly at interfaces, we here present a systematic study of the effects of terminal modifications on the adsorption and assembly of the human islet amyloid polypeptide fragment hIAPP(20-29) at organic self-assembled monolayers (SAMs) presenting different functional groups (cationic, anionic, polar, or hydrophobic). Using a selection of complementary in situ and ex situ analytical techniques, we find that even this well-defined and comparatively simple model system is governed by a rather complex interplay of electrostatic interactions, hydrophobic interactions, and hydrogen bonding, resulting in a plethora of observations and dependencies, some of which are rather counterintuitive. In particular, our results demonstrate that terminal modifications can have tremendous effects on peptide adsorption and assembly dynamics, as well as aggregate morphology and molecular structure. The effects exerted by the terminal modifications can furthermore be modulated in nontrivial ways by the physicochemical properties of the SAM surface. Therefore, terminal modifications are an important factor to consider when conducting and comparing peptide adsorption and aggregation studies and may represent an additional parameter for guiding the assembly of peptide-based nanomaterials.

Electrically transmissive alkyne-anchored monolayers on gold.

Well-ordered, tightly-packed (surface coverage 0.97 × 10-9 mol cm-2) monolayer films of 1,4-bis((4-ethynylphenyl)ethynyl)benzene (1) on gold are prepared via a simple self-assembly process, taking advantage of the ready formation of alkynyl C-Au σ-bonds. Electrochemical measurements using [Ru(NH3)6]3+, [Fe(CN)6]3-, and ferrocenylmethanol [Fe(η5-C5H4CH2OH)(η5-C5H5)] redox probes indicate that the alkynyl C-Au contacted monolayer of 1 presents a relatively low barrier for electron transfer. This contrasts with monolayer films on gold of other oligo(phenylene ethynylene) derivatives of comparable length and surface coverage, but with different contacting groups. Additionally, a low voltage transition (Vtrans = 0.51 V) from direct tunneling (rectangular barrier) to field emission (triangular barrier) is observed. This low transition voltage points to a low tunneling barrier, which is consistent with the facile electron transport observed through the C-Au contacted self-assembled monolayer of 1.

Unconventional Single-Molecule Conductance Behavior for a New Heterocyclic Anchoring Group: Pyrazolyl.

Electrical conductance across a molecular junction is strongly determined by the anchoring group of the molecule. Here we highlight the unusual behavior of 1,4-bis(1H-pyrazol-4-ylethynyl)benzene that exhibits unconventional junction current versus junction-stretching distance curves, which are peak-shaped and feature two conducting states of 2.3 × 10-4 G0 and 3.4 × 10-4 G0. A combination of theory and experiments is used to understand the conductance of single-molecule junctions featuring this new anchoring group, i.e., pyrazolyl. These results demonstrate that the pyrazolyl moiety changes its protonation state and contact binding during junction evolution and that it also binds in either end-on or facial geometries with gold contacts. The pyrazolyl moiety holds general interest as a contacting group, because this linkage leads to a strong double anchoring of the molecule to the gold electrode, resulting in enhanced conductance values.

Towards molecular electronic devices based on 'all-carbon' wires.

Nascent molecular electronic devices based on linear 'all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me3Si-(C[triple bond, length as m-dash]C)4-SiMe3 (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe3 (Au|C8SiMe3). In the second stage, treatment of Au|C8SiMe3 with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH (Au|C8H). The reactive terminal C[triple bond, length as m-dash]C-H moiety in Au|C8H can be modified by 'click' reactions with (azidomethyl)ferrocene (N3CH2Fc) to introduce a redox probe, to give Au|C6C2N3HCH2Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C8H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures Au|C8|GNP in which the monolayer of linear, 'all-carbon' C8 chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C6C2N3HCH2Fc systems and after formation of the gold top-contact electrode in Au|C8|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices Au|C8|GNP featuring 'all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.

Adsorption and Fibrillization of Islet Amyloid Polypeptide at Self-Assembled Monolayers Studied by QCM-D, AFM, and PM-IRRAS.

Aggregation and fibrillization of human islet amyloid polypeptide (hIAPP) plays an important role in the development of type 2 diabetes mellitus. Understanding the interaction of hIAPP with interfaces such as cell membranes at a molecular level therefore represents an important step toward new therapies. Here, we investigate the fibrillization of hIAPP at different self-assembled alkanethiol monolayers (SAMs) by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). We find that hydrophobic interactions with the CH3-terminated SAM tend to retard hIAPP fibrillization compared to the carboxylic acid-terminated SAM where attractive electrostatic interactions lead to the formation of a three-dimensional network of interwoven fibrils. At the hydroxyl- and amino-terminated SAMs, fibrillization appears to be governed by hydrogen bonding between the peptide and the terminating groups which may even overcome electrostatic repulsion. These results thus provide fundamental insights into the molecular mechanisms governing amyloid assembly at interfaces.

High surface coverage of a self-assembled monolayer by in situ synthesis of palladium nanodeposits.

Nascent metal|monolayer|metal devices have been fabricated by depositing palladium, produced through a CO-confined growth method, onto a self-assembled monolayer of an amine-terminated oligo(phenylene ethynylene) derivative on a gold bottom electrode. The high surface area coverage (85%) of the organic monolayer by densely packed palladium particles was confirmed by X-ray photoemission spectroscopy (XPS) and atomic force microscopy (AFM). The electrical properties of these nascent Au|monolayer|Pd assemblies were determined from the I-V curves recorded with a conductive-AFM using the Peak Force Tunneling AFM (PF-TUNA™) mode. The I-V curves together with the electrochemical experiments performed rule out the formation of short-circuits due to palladium penetration through the monolayer, suggesting that the palladium deposition strategy is an effective method for the fabrication of molecular junctions without damaging the organic layer.

Reversible Monolayer-Bilayer Transition in Supported Phospholipid LB Films under the Presence of Water: Morphological and Nanomechanical Behavior.

Mixed monolayer Langmuir-Blodgett (LB) films of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (Chol) in the 1:1 ratio have been prepared onto solid mica substrates. Upon immersion in water or in an aqueous HEPES solution (pH 7.4) the monolayer LB films were spontaneously converted into well-organized bilayers leaving free mica areas. The process has been demonstrated to be reversible upon removal of the aqueous solution, resulting in remarkably free of defects monolayers that are homogeneously distributed onto the mica. In addition, the nanomechanical properties exhibited by the as-formed bilayers have been determined by means of AFM breakthrough force studies. The bilayers formed by immersion of the monolayer in an aqueous media exhibit nanomechanical properties and stability under compression analogous to those of DPPC:Chol supported bilayers obtained by other methods previously described in the literature. Consequently, the hydration of a monolayer LB film has been revealed as an easy method to produce well-ordered bilayers that mimic the cell membrane and that could be used as model cell membranes.

All-Carbon Electrode Molecular Electronic Devices Based on Langmuir-Blodgett Monolayers.

Nascent molecular electronic devices, based on monolayer Langmuir-Blodgett films sandwiched between two carbonaceous electrodes, have been prepared. Tightly packed monolayers of 4-((4-((4-ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid are deposited onto a highly oriented pyrolytic graphite electrode. An amorphous carbon top contact electrode is formed on top of the monolayer from a naphthalene precursor using the focused electron beam induced deposition technique. This allows the deposition of a carbon top-contact electrode with well-defined shape, thickness, and precise positioning on the film with nm resolution. These results represent a substantial step toward the realization of integrated molecular electronic devices based on monolayers and carbon electrodes.

Design and Synthesis of Aviram-Ratner-Type Dyads and Rectification Studies in Langmuir-Blodgett (LB) Films.

The design and synthesis of Aviram-Ratner-type molecular rectifiers, featuring an anilino-substituted extended tetracyanoquinodimethane (exTCNQ) acceptor, covalently linked by the σ-spacer bicyclo[2.2.2]octane (BCO) to a tetrathiafulvalene (TTF) donor moiety, are described. The rigid BCO spacer keeps the TTF donor and exTCNQ acceptor moieties apart, as demonstrated by X-ray analysis. The photophysical properties of the TTF-BCO-exTCNQ dyads were investigated by UV/Vis and EPR spectroscopy, electrochemical studies, and theoretical calculations. Langmuir-Blodgett films were prepared and used in the fabrication and electrical studies of junction devices. One dyad showed the asymmetric current-voltage (I-V) curve characteristic for rectification, unlike control compounds containing the TTF unit but not the exTCNQ moiety or comprising the exTCNQ acceptor moiety but lacking the donor TTF part, which both gave symmetric I-V curves. The direction of the observed rectification indicated that the preferred electron current flows from the exTCNQ acceptor to the TTF donor.

Nanomechanical characterization of nanostructured bainitic steel: Peak Force Microscopy and Nanoindentation with AFM.

The full understanding of the deformation mechanisms in nanostructured bainite requires the local characterization of its mechanical properties, which are expected to change from one phase, bainitic ferrite, to another, austenite. This study becomes a challenging process due to the bainitic nanostructured nature and high Young's modulus. In this work, we have carried out such study by means of the combination of AFM-based techniques, such as nanoindentation and Peak Force Quantitative Nanomechanical Mapping (PF-QNM) measurements. We have addressed critically the limits and advantages of these techniques and been able to measure some elastoplastic parameters of both phases. Specifically, we have analyzed by PF-QNM two nanostructured bainitic steels, with a finer and a coarser structure, and found that both phases have a similar Young's modulus.

Evaluation of nanostructure and microstructure of bone regenerated by BMP-2-porous scaffolds.

In this study, three systems containing BMP-2 were fabricated, including two electrospun sandwich-like-systems of PLGA 75:25 and PLGA 50:50 and a microsphere system of PLGA 50:50 to be implanted in a critical size defect in rat calvaria. The in vivo BMP-2 release profiles of the three systems were similar. The total dose was released during the first two weeks. To evaluate the nano and microstructure of the regenerated bone a multi-technique analysis was used, including stereo microscope, X-Ray; AFM, micro-CT, and histological analyses. The progression of bone regeneration was followed at 4, 8, and 12 weeks after the microsphere system implantation whereas the two electrospun systems were evaluated at fixed 12 weeks. All the techniques applied showed high bone regeneration. The average values of bone volume density, bone mineral density, Young's modulus, and the percent of bone repair were ∼70% of the values of the native bone. Besides, SEM-EDX analysis indicated that the main chemical elements in the new bone were oxygen, calcium, and phosphorus in a ratio similar to that of native bone. In comparison, the micro-CT may provide an alternative to histology for the evaluation of bone formation at the defect size.

Quinone-rich poly(dopamine) magnetic nanoparticles for biosensor applications.

Novel core-shell quinone-rich poly(dopamine)-magnetic nanoparticles (MNPs) were prepared by using an in situ polymerization method. Catechol groups were oxidized to quinone by using a thermal treatment. MNPs were characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, magnetic force microscopy, UV/Vis, Fourier-transform infrared spectroscopy, and electrochemical techniques. The hybrid nanomaterial showed an average core diameter of 17 nm and a polymer-film thickness of 2 nm. The core-shell nanoparticles showed high reactivity and were used as solid supports for the covalent immobilization of glucose oxidase (Gox) through Schiff base formation and Michael addition. The amount of Gox immobilized onto the nanoparticle surface was almost twice that of the nonoxidized film. The resulting biofunctionalized MNPs were used to construct an amperometric biosensor for glucose. The enzyme biosensor has a sensitivity of 8.7 mA M(-1) cm(-2) , a low limit of detection (0.02 mM), and high stability for 45 days. Finally, the biosensor was used to determine glucose in blood samples and was checked against a commercial glucometer.

Self-assembly of flagellin on Au(111) surfaces.

The adsorption of flagellin monomers from Pseudomonas fluorescens on Au(111) has been studied by Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Surface Plasmon Resonance (SPR), and electrochemical techniques. Results show that flagellin monomers spontaneously self-assemble forming a monolayer thick protein film bounded to the Au surface by the more hydrophobic subunit and exposed to the environment the hydrophilic subunit. The films are conductive and allow allocation of electrochemically active cytochrome C. The self-assembled films could be used as biological platforms to build 3D complex molecular structures on planar metal surfaces and to functionalize metal nanoparticles.

On the influence of the culture conditions in bacterial antifouling bioassays and biofilm properties: Shewanella algae, a case study.

BACKGROUND: A variety of conditions (culture media, inocula, incubation temperatures) are employed in antifouling tests with marine bacteria. Shewanella algae was selected as model organism to evaluate the effect of these parameters on: bacterial growth, biofilm formation, the activity of model antifoulants, and the development and nanomechanical properties of the biofilms.The main objectives were: 1) To highlight and quantify the effect of these conditions on relevant parameters for antifouling studies: biofilm morphology, thickness, roughness, surface coverage, elasticity and adhesion forces. 2) To establish and characterise in detail a biofilm model with a relevant marine strain. RESULTS: Both the medium and the temperature significantly influenced the total cell densities and biofilm biomasses in 24-hour cultures. Likewise, the IC50 of three antifouling standards (TBTO, tralopyril and zinc pyrithione) was significantly affected by the medium and the initial cell density. Four media (Marine Broth, MB; 2% NaCl Mueller-Hinton Broth, MH2; Luria Marine Broth, LMB; and Supplemented Artificial Seawater, SASW) were selected to explore their effect on the morphological and nanomechanical properties of 24-h biofilms. Two biofilm growth patterns were observed: a clear trend to vertical development, with varying thickness and surface coverage in MB, LMB and SASW, and a horizontal, relatively thin film in MH2. The Atomic Force Microscopy analysis showed the lowest Young modulii for MB (0.16 ± 0.10 MPa), followed by SASW (0.19 ± 0.09 MPa), LMB (0.22 ± 0.13 MPa) and MH2 (0.34 ± 0.16 MPa). Adhesion forces followed an inverted trend, being higher in MB (1.33 ± 0.38 nN) and lower in MH2 (0.73 ± 0.29 nN). CONCLUSIONS: All the parameters significantly affected the ability of S. algae to grow and form biofilms, as well as the activity of antifouling molecules. A detailed study has been carried out in order to establish a biofilm model for further assays. The morphology and nanomechanics of S. algae biofilms were markedly influenced by the nutritional environments in which they were developed. As strategies for biofilm formation inhibition and biofilm detachment are of particular interest in antifouling research, the present findings also highlight the need for a careful selection of the assay conditions.