Hybrid Monolayer Research Articles

Selective Functionalization of Graphene Peripheries by using Bipolar Electrochemistry

AbstractWe present a contactless strategy based on bipolar electrochemistry for the local chemical modification of monolayer graphene sheets supported on a substrate. Specifically, peripheral graphene regions are directly modified by copper nanoparticles, the characteristics of which are controllable through the bipolar deposition parameters. This functionalization route provides access to hybrid monolayer graphene modified, for example, with two different metals on opposing peripheries. The presented strategy constitutes a new way to functionalize graphene and an avenue for systematically studying bipolar electrochemistry at the nanoscale.

Gold nanoparticles modified with self-assembled hybrid monolayer of triblock aptamers as a photoreversible anticoagulant

We demonstrated that thrombin-binding aptamer-conjugated gold nanoparticles (TBA–Au NPs), prepared from a self-assembled hybrid monolayer (SAHM) of triblock aptamers on Au NPs (13nm), can effectively inhibit thrombin activity toward fibrinogen. The first block poly(adenine) at the end of the triblock TBA was used for the self-assembly on Au NP surface. The second block, in the middle of TBA, was composed of oligonucleotides that could hybridize with each other. The third block, containing TBA15 (15-base, binding to the exosite I of thrombin) and TBA29 (29-base, binding to the exosite II of thrombin) provided bivalent interaction with thrombin. The SAHM triblock aptamers have optimal distances between TBA15 and TBA29, aptamer density, and orientation on the Au NP surfaces. These properties strengthen the interactions with thrombin (Kd=1.5×10−11M), resulting in an extremely high anticoagulant potency. The thrombin clotting time mediated by SAHM TBA15/TBA29–Au NPs was >10 times longer than that of four commercially available drugs (heparin, argatroban, hirudin, or warfarin). In addition, the rat-tail bleeding assay time further demonstrated that the SAHM TBA15/TBA29–Au NPs were superior to heparin. The SAHM TBA15/TBA29–Au NPs exhibited excellent stability in the human plasma (half-life >14days) and good biocompatibility (low cytotoxicity and hemolysis). Most interestingly, the inhibition by SAHM TBA15/TBA29–Au NPs was controllable by the irradiation of green laser, via heat transfer-induced TBA release from Au NPs. Therefore, these easily prepared (self-assembled), low cost (non-thiolated aptamer), photo-controllable, multivalent TBA15/TBA29–Au NPs (high density of TBA15/TBA29 on Au NPs) show good potential for the treatment of various diseases related to blood-clotting disorders. Our study opens up the possibility of regulation of molecule binding, protein recognition, and enzyme activity using SAHM aptamer-functionalized nanomaterials.

Tuning molecule-substrate coupling via deposition of metal adatoms.

Organic-inorganic hybrids constitute an important class of functional materials. The fundamentals at the molecular levels are, however, relatively unexplored. PTCDA (perylene-3,4,9,10-tetracarboxylic dianhydride) is a colorant and extensively applied in organic-based optoelectronic devices. PTCDA/Cu(111) and Fe-PTCDA/Cu(111) metal-organic hybrid monolayers are studied by low temperature scanning tunneling microscopy and spectroscopy (STS) and density functional theory (DFT). The former exhibits Moiré pattern-modulated molecular density of states while the latter adapts a commensurate adlattice. Both imaging and spectroscopic results suggest a strong hybridization between PTCDA molecules and Cu(111) substrate. Weak PTCDA-Cu(111) coupling can be obtained by the introduction of Fe adatoms. Compared to PTCDA/Cu(111), STS spectra of Fe-PTCDA/Cu(111) exhibit a higher energy and sharper features of the frontier orbitals. Together with the DFT results, we found that the PTCDA-Cu(111) coupling is attenuated by the presence of Fe adatoms and Fe-PTCDA coordination.

Interaction of Nano-Clay Platelets with a Phospholipid in Presence of a Fluorescence Probe

This paper reports the interaction of nano-clay platelets with a phospholipid in presence of a fluorescence probe. The surface pressure vs. time characteristic studies were done to monitor the progress of reaction. In-situ fluorescence imaging microscope (FIM) was employed to visualize the domain structure formed at the air-water interface with the progress of reaction. At the end of the reaction, clay induced hybrid monolayer at the air-water interface was transferred onto solid substrate to form Langmuir Blodgett (LB) film. Fluorescence spectroscopic studies revealed the close proximity of RhB molecules resulting in the formation of dimeric species.

Electromechanical response at polar zigzag boundaries in hybrid monolayers

First-principles calculations are used to demonstrate electromechanical control of charge and spin at zigzag-edged interfaces between graphene and boron-nitride domains in hybrid monolayers. We show how, through a direct piezoelectric effect, the interfacial bound charges and associated electric fields can be tuned by application of an external mechanical force (stress) on the system. This results in mechanical control of the edge magnetization (piezomagnetic effect), and the possibility to transform a semiconducting heterostructure into a half-metal. The inverse effect (application of an external electric field to induce a mechanical deformation) goes together with a magnetoelectric response, which under ideal conditions we estimate to be comparable to that of prototypical ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. These effects originate from the magnetic properties of graphene's zigzag edges and the dielectric properties of the boron-nitride domain, and can also be expected in any other coplanar heterostructures with polar discontinuities.

Stable negative differential resistance in porphyrin based σ–π–σ monolayers grafted on silicon

Two Si–porphyrin hybrid monolayers showed room temperature negative differential resistance (NDR) property. The monolayer with a fluorophenyl porphyrin moiety showed a better peak-to-valley ratio due to compact packing.

Optical properties of B x N y C z monolayers

We apply first-principles methods, based on the density functional theory, to investigate the optical properties of B x N y C z hybrid monolayers containing domains. It is observed that the energy structure of such compounds exhibits bound excitons in the near-infrared region. Moreover, such compounds present an extraordinary absorptive capacity in the visible spectrum, which makes them important candidates for future solar cells applications.

Combined concurrent photodynamic and gold nanoshell loaded macrophage‐mediated photothermal therapies: An in vitro study on squamous cell head and neck carcinoma

Treatment modalities, such as hyperthermia and photodynamic therapy (PDT) have been used in the treatment of a variety of head and neck squamous cell carcinoma (HNSCC), either alone or as an adjuvant therapy. Macrophages loaded with gold nanoshells, which convert near-infrared light to heat, can be used as transport vectors for photothermal hyperthermia of tumors. The purpose of this study was to investigate the effects of combined macrophage mediated photothermal therapy (PTT) and PDT on HNSCC cells. Gold nanoshell loaded rat macrophages either alone or combined with human FaDu squamous cells in hybrid monolayers were subjected to PTT, PDT, or a simultaneous combination of the two light treatments. Therapies were given concurrently employing two laser light sources of λ = 670 nm (PDT) and λ = 810 nm (PTT), respectively. Significant uptake of gold nanospheres (AuNS) by rat alveolar macrophages was observed thus providing the rationale for their use as delivery vectors. Viability of the AuNS-loaded Ma was reduced to 35 and 12% of control values at an irradiance of 14 or 28 W/cm(2) administered over a 5 minute period respectively. No significant cytotoxicity was observed for empty Ma for similar PTT exposure. AlPcS2a mediated PDT at a fluence level of 0.25 J/cm(2) and PTT at 14 W/cm(2) irradiance had little effect on cell viability for the FaDu/Ma (ratio 2:1) hybrid monolayers. In contrast, combined treatment reduced the cell viability to less than 40% at these same laser power settings. The results of this study provide proof of concept for the use of macrophages as a delivery vector of AuNS for photothermal enhancement of the effects of PDT on squamous cell carcinoma. A significant synergy was demonstrated with combined PDT and PTT compared to each modality applied separately.

Surface molecular imprinting on dye–(NH2)–SiO2 NPs for specific recognition and direct fluorescent quantification of perfluorooctane sulfonate

A perfluorooctane sulfonate (PFOS, C8F17SO3−) molecularly imprinted (MIP) fluorescence sensor was developed by anchoring the MIP polymer on the surface of SiO2 NPs via a surface molecular imprinting process. Fluorescence dye and organic amine were covalently immobilized onto the surface of MIP–SiO2 NPs to form a hybrid monolayer of dye fluorophores and amine ligands which acted as the receptor sites to bind PFOS(C8F17SO3−) species through the acid–base pairing and hydrogen-bond interaction under acid condition (pH∼3.5). The specific binding of PFOS into the recognition cavities in the polymer matrixes results in the fluorescence quenching due to the electron transfer from the fluorescence dye to PFOS. This proposed method can selectively and sensitively detect down to 5.57μgL−1 of PFOS in water, and a linear relationship has been obtained covering the concentration range of 5.57–48.54μgL−1 (10.36–90.2nM).

Structural and electronic properties of hybrid graphene and boron nitride nanostructures on Cu

Recently, two-dimensional nanostructures consisting of alternating graphene and boron nitride (BN) domains have been synthesized. These systems possess interesting electronic and mechanical properties, with potential applications in electronics and optical devices. Here, we perform a first-principles investigation of models of BN-C hybrid monolayers and nanoribbons deposited on the Cu(111) surface, a substrate used for their growth in said experiments. For the sake of comparison, we also consider BN and BC2N nanostructures. We show that BN and BC2N monolayers bind weakly to Cu(111), whereas monolayers with alternating domains interact strongly with the substrate at the B-C interface, due to the presence of localized interface states. This binding leads to a deformation of the monolayers and sizable n-doping. Nanoribbons exhibit a similar behaviour. Furthermore, they also interact significantly with the substrate at the edge, even in the case of passivated edges. These findings suggest a route to tune the band gap and doping level of BN-C hybrid models based on the interplay between nanostructuring and substrate-induced effects.

Molecular orientation of Ru(II) complexes introduced in hybrid Langmuir–Schaefer films of clay nanosheets and alkylammonium cations

Ternary component hybrid films of amphiphilic alkylammonium cations, clay nanosheets, and ruthenium(II) complex cations were prepared by the modified Langmuir–Schaefer method. When a solution of the amphiphilic ammonium salt (octadecylammonium chloride, ODAH+Cl−) was spread at an air–clay dispersion interface, the clay nanosheets in the dispersion were adsorbed on the floating molecular film of ODAH+ by the electrostatic interaction. Then the floating film of ODAH+ and the clay was deposited on a glass plate and immersed in an aqueous solution of [RuL3]Cl2 (L=2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (dmphen), and 4,7-diphenyl-1,10-phenanthroline (dpp)) to form a ternary component hybrid monolayer. By repeating these procedures, a hybrid multilayer was fabricated. Characterization of the hybrid multilayers was carried out by electronic and IR spectral measurements and X-ray diffraction (XRD) method. Areas per [RuL3]2+ estimated from the analysis of the electronic spectra suggested that the Ru(II) complex cations interacted with each other through hydrophobic interaction. IR and XRD data indicated disordered alkylchains of ODAH+ which would occupy spaces between the [RuL3]2+ cations in the film. The tilt angles of 3-fold axes of [RuL3]2+ were determined to be 32–35° by analyzing electronic spectra measured with p- and s-polarized beams. An orientation model of the [RuL3]2+ cations in the film was proposed, in which substitution groups at 4- or 5-positions of 1,10-phenanthroline ligand were in contact with the clay nanosheet layers. It was likely that the sizes of the ligands and the interaction between the ligands affected the structure of the hybrid film.

Semitransparent organic solar cells with hybrid monolayer graphene/metal grid as top electrodes

Hybrid transparent monolayer graphene/metal grid is proposed as top electrode of semitransparent organic solar cells. The hybrid electrode using gold grid on flexible polyethylene terephthalate substrate shows very low sheet resistance of 22 ± 3 Ω/□ and high optical transmittance of 81.4%, which is comparable to conventional indium tin oxide/glass electrode. Using lamination process, the layer of poly(3,4-ethylenedioythiophene):poly(styrenesulfonate) doped with D-sorbitol plays an important role in the electrical performance of the laminated devices. In addition, the devices show best power convention efficiency of 3.1% and fill factor of 55.0%, which are much better than those of similar graphene-based semitransparent organic solar cells.

Interaction of a Laser Dye with a Floating Phospholipid Monolayer

This communication reports the interaction of the well known laser dye RhB with a zwitterionic phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (abbreviated as DPPC). Reaction kinetics was studied at the air-water interface by measuring the increase in surface pressure with time while the Langmuir barrier was kept fixed. In-situ Fluorescence Imaging Microscopic (FIM) technique was employed to visualize the domain structure formed at the air-water interface with progress of reaction. After completion of the reaction, RhB-DPPC hybrid monolayer at the air-water interface was transferred onto solid substrates to form Langmuir-Blodgett (LB) films. UV-Vis absorption and fluorescence spectroscopic studies confirmed the presence of RhB molecules in the hybrid LB films.

G-B3N3C: a novel two-dimensional graphite-like material

A novel crystalline structure of hybrid monolayer hexagonal boron nitride (BN) and graphene is predicted by means of the first-principles calculations. This material can be derived via boron or nitrogen atoms which are substituted by carbon atoms evenly in the graphitic BN with vacancies. The corresponding structure is constructed from a BN hexagonal ring linking an additional carbon atom. The unit cell is composed of seven atoms, three of which are boron atoms, three are nitrogen atoms, and one is a carbon atom. It shows a similar space structure as graphene, which is thus coined as g-B3N3C. Two stable topological types associated with the carbon bond formation, i.e., C-N or C-B bonds, are identified. Interestingly, distinct ground states of each type, depending on C-N or C-B bonds, and electronic bandgap as well as magnetic properties within this material have been studied systematically. Our work demonstrates a practical and efficient access to electronic properties of two-dimensional nanostructures, providing an approach to tackling open fundamental questions in bandgap-engineered devices and spintronics.

Synthesis And Organic Functionalization Approaches For Magnetite (Fe3O4) Nanoparticles

Several new techniques are invented in recent years to attach organic, bio-organic functionalities to the nanostructures such as the nanoparticles. This approach of adding surface reactivity to the particles enables to tune the properties and reactivity of the resulting hybrid monolayer protected nanoparticles. Magnetic iron oxide nanoparticles of various sizes are reported which bears different organic or polymeric groups. In the present note we have revised the important methods of synthesis of magnetite (Fe3O4) nanoparticles and highlighted the most common strategies for the functionalization of these nanoparticles with organic compounds from very recent literature. This short note will help the students and researchers to screen and choose methods for the synthesis and functionalization of magnetite nanoparticles. Copyright © 2012 VBRI Press.

Elastic properties of hybrid graphene/boron nitride monolayer

Recently hybridized monolayers consisting of hexagonal boron nitride (h-BN) phases inside graphene layer have been synthesized and shown to be an effective way of opening band gap in graphene monolayers [1]. In this letter, we report an ab initio density functional theory (DFT)- based study of h-BN domain size effect on the elastic properties of graphene/boron nitride hybrid monolayers (h-BNC). We found both inplane stiffness and longitudinal sound velocity of h-BNC linearly decrease with h-BN concentration.

Clay-protein ultrathin films: Design and bio-catalytic performance study

In recent years, immense interest has been paid to the biomolecular architecture with the aim of protein assembly in two dimensions on solid substrates, and the constructions of clay-protein ultrathin films (CPUFs) are particularly concerned. This paper gives an overview of the recent research concerning the protein molecules (lysozyme, papain, protamine, bovine serum albumin) immobilized on clay mineral (Na-saponite) platelets and assembled in monolayered or multilayered hybrid ultrafilms or nanofilms. Two techniques including alternate layer-by-layer (LbL) assembly and the Langmuir-Blodgett (LB) are described in detail. A variety of means, including UV-vis absorption, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, XRD, AFM and surface chemistry techniques, have been described for characterization of the films in terms of quantification of protein and clay. The result reveals that electrostatic interaction is a prominent but not the only driving force in CPUF construction. In the case of LB technique, we managed to manipulate the elementary clay mineral platelets (1.3 nm in thickness) and assemble proteins into CPUFs with the aid of surfactants, and the formation of CPUFs was monitored via surface pressure vs. time ( π-t) kinetics curves and surface pressure vs. area (π-A) isotherms. The factors that influence protein adsorption on the clay layer, such as surfactants, the concentration of clay, equilibrium time, categories of protein, and injection methods, were investigated. The parameters such as protein amount (n S ), packing density (Θ), and average surface area per molecule (Ω) of deposited CPUFs were measured via method of surface chemistry and spectroscopy. By comparing the results of surface chemistry with those of adsorption experiments, we demonstrate that the surface chemistry method is a useful tool in investigating CPUFs. We also found that the water soluble protein molecules could form protein-clay hybrid monolayer over the dilute clay dispersions without addition of surfactants, and CPUFs containing elementary clay sheets and protein with great homogeneity were easily prepared by controlling certain surface pressure. To investigate the bio-catalytic performance of the immobilized lysozyme in CPUFs, we deposited CPUFs onto a cover glass, and installed the cover glass in a flow cell-grown reactor for Comamonas testosteroni (WDL7-GFP) incubation. The results show that the proliferation of WDL7-GFP is greatly suppressed by lysozyme, which demonstrates that lysozyme still retains its bioactivity after it is immobilized in the CPUFs.

Thermal conductivity of silicon and carbon hybrid monolayers: a molecular dynamics study

Thermal conductivities of graphene-like silicon and carbon hybrid nanostructures with silicon atom percentages varying from 0 % (graphene) to 100 % (silicene) are investigated using the reserve non-equilibrium molecular dynamic (RNEMD) method and Tersoff bond order potentials. The thermal conductivity of graphene is dramatically reduced with increasing silicon concentration, and the reduction appears to be related more to the topological structures formed than the amount of doped silicon atoms present. The reduction is collectively contributed to by reduced phonon group velocities (v), phonon free paths (l∞), and the specific heat capacity (c) of the material. For systems with high symmetry, thermal conductivity is mainly influenced by v and c. For systems with low symmetry, thermal conductivity is dominated by l∞; such materials are also more direction-dependent on thermal flux than highly symmetric materials.

EXCITON–PLASMON INTERACTION IN MONOLAYERS OF METAL-SEMICONDUCTOR NANOSTRUCTURES

Effect of shape and density on the energy transfer between metallic nanoparticles and semi conducting nanostructures was studied by observing the photoluminescence spectra using near field scanning optical microscope. The monolayers of gold nanoparticles, CdSe nanorods and composite with different number ratios were prepared using Langmuir Blodgett method. The spectra collected from the films with different number ratios of CdSe and gold shows a systematic variation of peak position and intensity as a function of number density of CdSe . The photoluminescence spectra collected from composite monolayer is blue shifted compared to the spectra from CdSe nanorods monolayer. Further we observed a blue shift in peak position and reduction emission intensity with respect to increase in the fraction of gold nanoparticles and surface density. We have provided explanation for the observed behavior in terms of strong exciton–plasmon interactions in the compact hybrid monolayers.

Photoluminescence enhancement and quenching in metal-semiconductor quantum dot hybrid arrays

Hybrid monolayer arrays of metal and semiconductor quantum dots have been prepared to study the exciton-plasmon interaction. We observed crossover from strong quenching to enhancement in photoluminescence of the quantum dots as a function of the emission wavelength for fixed interparticle spacings. Remarkably, the enhancement is observed even for extremely short separation at which strong quenching has been observed and predicted earlier. A significant redshift in emission maxima is also observed for quantum dots with quenched emission. The possible role of collective phenomena as well as strong interactions in such ordered hybrid arrays in controlling the emission is discussed.