Direct growth of shape-controlled nanocrystals on nanotubes via biological recognition

The new biological approach was examined to fabricate shape-controlled Ag nanocrystals grown directly on surfaces, inspired by nature that various shapes of nanocrystals are produced accurately and reproducibly in biological systems. Here we demonstrate the direct growth of hexagon-shaped Ag nanocrystals on sequenced peptide-coated nanotubes via biological recognition. When the peptide, Asn-Pro-Ser-Ser-Leu-Phe-Arg-Tyr-Leu-Pro-Ser-Asp, recognizing and effecting the Ag nanocrystal growth on the (111) face, was sequenced and incorporated onto template nanotube surfaces, the biomineralization of Ag ions on the nanotubes led the isotropic hexagon-shaped Ag nanocrystal coating under pH control of the growth solution. Multiple Ag nanocrystal shapes were observed when the peptide mineralized Ag ions without the template nanotubes, and therefore the template nanotube has a significant influence on regulating the majority of Ag nanocrystals into the hexagonal shape. This biological approach, using specific peptide sequences on surfaces to control nanocrystal shapes, may be developed as a simple and economical method to produce building blocks with desired physical properties for new generation of electronics, sensors, and optical devices.     

Application of host-guest chemistry in nanotube-based device fabrication: photochemically controlled immobilization of azobenzene nanotubes on patterned alpha-CD monolayer/Au substrates via molecular recognition

Azobenzene-functionalized nanotubes recognized and attached onto well-defined complementary regions of thiolated alpha-CD SAM/Au substrates via host-guest molecular recognition. The binding between the azobenzene nanotubes and the alpha-CD SAM/Au substrates was controlled by UV irradiation. The light-induced attachment-detachment of the azobenzene nanotubes on the alpha-CD SAMs was reversible. Some of the nanotubes were capable of interconnecting two Au substrates. This smart building block may be applied to build photoactive nanometer-sized mechanical switches in electronics.     

Influence of antibody immobilization strategy on molecular recognition force microscopy measurements

A systematic evaluation of the effects of antibody immobilization strategy on the binding efficiency and selectivity (e.g., ability to distinguish between specific and nonspecific interactions) of immunosurfaces prepared with F(ab') antibody fragments of rabbit Immunoglobulin G (IgG) is described. F(ab') was attached to gold surfaces either (1) directly via the formation of a gold-thiolate bond or (2) indirectly through a series of a bifunctional linkers containing an alkane chain or ethylene glycol spacer. Immobilization of F(ab') via the sulfhydryl reactive group located opposite the antigen binding site ensured optimum orientation of the antigen binding site. X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) were used to confirm surface modification with the bifunctional linkers and antibody immobilization, respectively. Binding efficiency assays performed with SPR indicated that increasing the length of the linker increased the antigen binding efficiency. Atomic force microscopy (AFM) adhesion force measurements indicated that AFM probes functionalized with directly immobilized F(ab') more effectively discriminated between specific and nonspecific surface-bound proteins than probes modified indirectly via linker-immobilized F(ab'). In addition, a greater number of antibody-antigen binding events were observed with directly immobilized F(ab')-functionalized probes.     

One-step vs stepwise immobilization of 1-d coordination-based rh-rh molecular wires on gold surfaces

Reaction of dimeric [Rh(II)(2)(phen)(2)(μ-OAc)(2)(MeCN)(2)](BF(4))(2) (phen =1,10-phenanthroline) with pyrazine (pz) in a 1:2 ratio leads to the new 1-D metal-metal-bonded coordination oligomer {[Rh(II)(2)(phen)(2)(μ-OAc)(2)(pz)](BF(4))(2)}(n) (Rh-Rhpz)(n) (1), where each Rh atom of the dimeric unit (Rh-Rh) is coordinated in the equatorial plane to a nitrogen atom of a rigid and linear bifunctionalized organic linker (pz). Single X-ray diffraction analysis reveals the 1-D straight oligomeric chain structure (molecular wire, MW) consists of alternating (Rh-Rh) units and pz linking ligands with free BF(4)(-) as counteranions, and each metal center has a slightly distorted octahedral arrangement. The presence of accessible labile MeCN groups on both ends of these MWs ("free ends") enables functionalization of a 4-mercaptopyridine-gold coordinating platform (Au/MP) to form in one step a layer of coordination oligomer (Au/MP(Rh-Rhpz)(n); n ≈ 50). Furthermore (Rh-Rhpz)(n) (n = 1-6) MWs were grafted to Au/MP surfaces by a conventional step-by-step assembly construction involving coordination reactions between the Rh dimer ([Rh(2)(phen)(2)(μ-OAc)(2)(MeCN)(2)](BF(4))(2) (2)) and pz. A detailed physicochemical study (UV-vis, RAIR, QCM-D, ellipsometry, contact angle measurements, as well as impedance spectroscopy and cyclic voltammetry) has been made during both assembly methods to characterize the resulting surface-anchored coordination molecular wire (CMW) layers (Au/MP(Rh-Rhpz)(n)). The results indicate that the immobilized molecular assemblies (MAs) were successfully fabricated using both methods of assembly. The efficiency of the two methods is discussed.     

Simultaneous quartz crystal microbalance-electrochemical impedance spectroscopy study on the adsorption of anti-human immunoglobulin G and its immunoreaction at nanomaterial-modified Au electrode surfaces.

The quartz crystal microbalance method (QCM), in combination with electrochemical impedance spectroscopy (EIS), has been utilized to monitor in situ anti-human IgG adsorption on several Au-based surfaces, bare Au, nanogold/4-aminothiophenol (4AT)/Au, and multi-walled carbon nanotubes (MWCNT)/Au, and succeeding human IgG reactions. Also, the immobilization protocol of anti-human IgG via its glutaraldehyde (GA) cross-linking with self-assembled 4AT on an Au electrode and the subsequent surface immunoreaction were examined. The resonant frequency (f(0)) and the motional resistance (R(1)) of the piezoelectric quartz crystal (PQC) as well as electrochemical impedance parameters were measured and discussed. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the ferricyanide/ferrocyanide couple were examined before and after electrode modification, the antibody adsorption and antibody-antigen reactions. We found that the amount for antibody adsorption was the greatest on the colloid Au modified surface, and that at MWCNT ranked the second, while specific bioactivity was almost identical on the four kinds of surfaces. Two parameters simultaneously obtained at the colloid Au modified surface, Deltaf(0) and DeltaC(s) (interfacial capacitance), have been used to estimate the association constant of the immunoreaction.     

Influence of surfactants and antibody immobilization strategy on reducing nonspecific protein interactions for molecular recognition force microscopy

Specific and nonspecific interactions between antibody-modified probes and substrate-immobilized proteins were monitored by atomic force microscopy (AFM). Probes were modified with anti-ovalbumin IgG antibodies immobilized in either an oriented or a random manner. The oriented immobilization of whole IgG was accomplished through the use of Protein A, and random immobilization was carried out with glutaraldehyde. Nonspecific interactions may lead to false detection of antibody-antigen binding events even when the antigen binding sites are properly positioned by an oriented immobilization strategy. Thus, nonionic and zwitterionic surfactants, including Tween 20, Tween 80, Triton X-100, and CHAPS, were evaluated to determine if nonspecific binding events could be reduced without compromising the desired specific antibody-antigen binding. Enzyme-linked immunosorbent assay and surface plasmon resonance assays were also employed to study antibody-antigen binding as a function of immobilization strategy and surfactant concentration. The data from these studies indicate that Protein A can be used to immobilize whole IgG onto AFM probes for force measurement experiments and that a surfactant is useful for improving the selectivity for such measurements.     

Formation of smooth, conformal molecular layers on ZnO surfaces via photochemical grafting

We have investigated the photochemical grafting of organic alkenes to atomically flat ZnO(10 ?10) single crystals and ZnO nanorods as a way to produce functional molecule-semiconductor interfaces. Atomic force microscopy shows that photochemical grafting produces highly conformal, smooth molecular layers with no detectable changes in the underlying structure of the ZnO terraces or steps. X-ray photoelectron spectroscopy measurements show that grafting of a methyl ester-terminated alkene terminates near one monolayer, while alkenes bearing a trifluoroacetamide-protected amine form very smooth multilayers. Even with multilayers, it is possible to deprotect the amines and to link a second molecule to the surface with excellent efficiency and without significant loss of molecules from the surface. This demonstrates that the use of photochemical grafting, even in the case of multilayer formation, enables multistep chemical processes to be conducted on the ZnO surface. Photoresponse measurements demonstrate that functionalization of the surface does not affect the ability to induce field effects in the underlying ZnO, thereby suggesting that this approach to functionalization may be useful for applications in sensing and in hybrid organic-inorganic transistors and related devices.     

Aqueous ionic and complementary zwitterionic soluble surfactants: molecular dynamics simulations and sum frequency generation spectroscopy of the surfaces

An aqueous ionic surfactant, 1-dodecyl-4-(dimethylamino)pyridinium (DMP) bromide, and the corresponding zwitterion 2-[4-(dimethylamino)pyridinio]dodecanoate (DPN) were explored by means of molecular dynamics (MD) simulations and, for the ionic system, by infrared-visible sum frequency generation (IR-vis SFG). The molecular structure of the interfacial layer was investigated for the ionic and zwitterionic systems as a function of surfactant concentration, both in water and in salt (KF or KBr) solutions, by MD simulations in a slab geometry. The buildup of the surface monolayer and a sublayer was monitored, and density and orientational profiles of the surfactants were evaluated. The difference between the ionic and zwitterionic systems and the effect of the added salt were analyzed at the molecular level. The results of MD simulations were compared to those of nonlinear optical spectroscopy measurements. IR-vis SFG was employed to study the DMP ionic surfactant in water and upon addition of simple salts. The influence of added salts on the different molecular moieties at the interface was quantified in detail experimentally.     

Layer-by-layer electrostatic deposition of biomolecules on surfaces for molecular recognition, redox mediation and signal generation

Layer-by-layer supramolecular structures composed of alternate layers of negatively charged enzymes and cationic redox polyelectrolyte have been assembled. Glucose oxidase (GOx), lactate oxidase (LOx) and soybean peroxidase (SBP) have been electrically wired to the underlying electrode by means of poly(allylamine) with [Os(bpy)2ClPyCOH]+ covalently attached (PAA-Os) in organized structures with high spatial resolution. Biotinylated glucose oxidase has also been used to assemble step-by-step on antibiotin goat immunoglobulin (IgG) layers and the enzyme was electrically wired by PAA-Os. These spatially organized multilayers with mono- and bienzymatic schemes can work efficiently in molecular recognition, redox mediation and generation of an electrical signal. The concentration of redox mediator integrated into the multilayers, obtained from the voltammetric charge and an estimation of the layer thickness, exceeds by 100-fold the amount of deposited enzyme assessed by quartz crystal microbalance. Differences in GOx electrical wiring efficiency have been detected with the different assembling strategies. The surface concentration of electrically wired enzyme represents a small proportion of all the enzyme molecules present in the multilayers which can be oxidized by the soluble mediator [Os(bpy)2Cl PyCOOH]Cl. This proportion, as well as the rate of FADH2 oxidation by PAA-Os, increases with the number of electrically wired enzyme layers and with the spatial accessibility of the Os moiety to the enzyme active center.     

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

This work presents a detailed study of the photo-induced spin-state dynamics of the photochromic iron(II) complex 1, where the metal ion is in the field of a tripodal hexa-imine ligand with protolysable phenol groups. The nature of the complex’s ground state has been identified as a spin singlet by ¹H NMR and steady-state UV/vis spectroscopies, and its distorted octahedral structure was analyzed via crystal structure determination. Sub-picosecond and nanosecond time-resolved laser flash photolysis experiments identify the long-lived quintet state of 1 as the selective product of photoexcitation in the UV/vis spectral region. Thermal barriers of spin-state interconversion as a function of solvent and added base are derived from temperature-dependent rates of transient decay. Ground-state recovery is found to be significantly affected by the solvent and is strongly enhanced, in particular, by base-driven solvolysis of the ligand’s phenol groups. Partial spontaneous deprotonation of the phenolic hydroxyl groups of 1 seems to prevail on metal oxide surfaces, i.e. on alumina. Composite materials, like 1 at Al₂O₃, that retain the characteristic spectral features of the parent iron(II) complex can be readily obtained by wet impregnation of hydrous alumina with solutions of 1.     

Formaldehyde adsorption on the interior and exterior surfaces of CN nanotubes

Using density functional theory, we have investigated the adsorption of formaldehyde (H₂CO) on the interior and exterior walls of a carbon nitride nanotube (CNNT) in terms of energetic, geometric, and electronic properties. It was found that the adsorption is more preferential on the exterior surface of the tube with maximum adsorption energy of ?7.4 kcal/mol. It has also been found that the adsorption energy per molecule is increased by increasing the number of adsorbed molecules. The results reveal that the electronic properties of CNNT are very sensitive to the presence of formaldehyde so that the HOMO/LUMO gap is reduced from 4.02 eV in the free tube to 2.44 eV in the most stable configuration of 3H₂CO/CNNT complex. Also, we have showed that the response of the tube may depend on concentration of the H₂CO molecules, suggesting that the CNNT might produce an electrical signal in the presence of H₂CO molecules.     

Current development of analytical affinity chromatography: Design and biotechnological uses of molecular recognition surfaces

Analytical high performance liquid affinity chromatography (analytical HPLAC) has been investigated as an experimental guide to both synthetic design and affinity technological use of peptide and protein recognition surfaces. This work has progressed from the ongoing use of analytical affinity chromatography to study interaction mechanisms of naturally-occurring peptides and proteins, including enzyme fragment complexes and neuroendocrine biosynthetic precursors. We recently initiated a study to use analytical HPLAC for de novo design of recognition peptides called “anti-sense peptides”. Present data suggest the potential to use anti-sense peptides as “synthetic antibodies”, in immobilized forms, for biomolecular separation and analysis. Analogous studies have been started with immobilized natural antibodies in analytical immuno HPLAC. Our present data typify the growing usefulness of analytical HPLAC when designing recognition molecules, analyzing their interaction characteristics, and devising ways to use them in affinity technology.     

Mesomorphic phases obtained through molecular recognition of complementary adenine and thymine nucleobases functionalized with long aliphatic chains

Complementary adenine and thymine nucleobases were functionalized with long aliphatic chains. The materials exhibited a mesomorphic character which was attributed to the formation of supramolecular architectures. Molecular recognition through hydrogen bonding of the complementary ends of the molecules was the driving force for their formation. It was also found that these structures are affected by the crystallization medium.     

Mesomorphic phases obtained through molecular recognition of complementary adenine and thymine nucleobases functionalized with long aliphatic chains

Abstract

Complementary adenine and thymine nucleobases were functionalized with long aliphatic chains. The materials exhibited a mesomorphic character which was attributed to the formation of supramolecular architectures. Molecular recognition through hydrogen bonding of the complementary ends of the molecules was the driving force for their formation. It was also found that these structures are affected by the crystallization medium.     

Adsorption model of atomic hydrogen on the surfaces of carbon nanotubes

A model for the adsorption of atomic hydrogen on the surfaces of single-walled zig-zag and armchair carbon nanotubes is constructed on the basis of the single-impurity periodic Anderson model. Features of the bands caused by the adsorption of hydrogen atoms in the structure of carbon nanotubes are studied. A reduction in the forbidden gap as a result of adsorption is revealed, and its dependence on the diameter of the semiconducting nanotubes is established. It is concluded that the model can be used to study the adsorption of other monovalent atoms on the surfaces of carbon particles.     

Electrochemical characteristics of the immobilization of calf thymus DNA molecules on multi-walled carbon nanotubes

Immobilization of DNA on carbon nanotubes plays an important role in the development of new types of miniature DNA biosensors. Electrochemical characteristics of the immobilization of calf thymus DNA molecules on the surfaces of multi-walled carbon nanotubes (MWNTs) have been investigated by cyclic voltammetry and electrochemical impedance analysis. The peak currents for Fe(CN)(6)(3-)/Fe(CN)(6)(4-) redox couple observed in the cyclic voltammograms decrease and the electron-transfer resistance (R(et)) obtained from the Nyquist plots increase due to the immobilization of DNA molecules (dsDNA or ssDNA) on the surfaces of MWNTs. Most of calf thymus DNA are covalently immobilized on MWNTs via diimide-activated amidation between the carboxylic acid groups on the carbon nanotubes and the amino groups on DNA bases, though the direct adsorption of the DNA molecules on MWNTs can be observed. Additionally, the interaction between DNA molecules immobilized on MWNTs and small biomolecules (ethidium bromide) can be observed obviously by cyclic voltammetry and electrochemical impedance analysis. This implies that the DNA molecules immobilized at the surface of MWNTs, with little structure change, still has the ability to interact with small biomolecules.     

Electrochemical determination of nitrite via covalent immobilization of a single-walled carbon nanotubes and single stranded deoxyribonucleic acid nanocomposite on a glassy carbon electrode

A novel method has been developed for determination of nitrite by modifying the surface of a glassy carbon electrode (GCE) using single-walled carbon nanotubes with covalently immobilized single-strand deoxyribonucleic acid. The modified electrodes were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical techniques. The results demonstrate that the nanotube-DNA nanocomposite has been successfully immobilized on the surface of the GCE. The new electrode, under optimum conditions at room temperature, exhibits excellent electrocatalytic activity towards the oxidation of nitrite, with a significantly reduction of the overpotential. The linear range for the detection of nitrite is from 0.6 to 540 μM, with a sensitivity of 0.216 μA?μM^?1, and a detection limit as low as 0.15 μM. The electrode showed good reproducibility and high stability and was successfully used to analyze nitrite in water and sausage samples.     

Phosphocreatine immobilization of the surface of silica and magnetite nanoparticles for targeted drug delivery

Russian Chemical Bulletin - A method is proposed for immobilization of anti-ischemic drug phosphocreatine on the surface of aminated silica and magnetite nanoparticles of similar size and shape....     

A chirality indicator for the walls and the surfaces of silica nanotubes

Single-handed helical silica nanotubes were prepared according to the literature procedures,using the self-assemblies of a pair of chiral cationic low-molecular-weight gelators as the templates.A chirality indicator,4,4’-bis(triethoxysilyl)-1,1’-biphenyl,was developed to determine the chirality of the silica nanotubes.The chirality of the surfaces and the bulky walls of the silica nanotubes were understood from the twist of the biphenylene rings.     

Self-complementary recognition of supramolecular urea-aminotriazines in solution and on surfaces

The recognition of self-complementary quadruple urea-aminotriazine (UAT)-based hydrogen-bonded arrays was investigated in solution and at surfaces. For this purpose, an UAT-based donor-acceptor-donor-acceptor (DADA) array and complementary receptors were synthesized. Two-dimensional proton nuclear magnetic resonance ((1)H NMR) measurements in CDCl(3) pointed at an intramolecular hydrogen-bond stabilization of the UAT, which promotes a planar molecular geometry and, thereby, results in a significant stabilization of the dimeric complex. The bond strength of the UAT dimers at surfaces was determined by atomic force microscopy-based single molecule force spectroscopy (AFM-SMFS) in hexadecane. The UAT receptor was immobilized on gold surfaces using an ultrathin layer of ethylene glycol terminated lipoic acid and isocyanate chemistry. The layers obtained and the reversible self-complementary recognition were thoroughly characterized with contact angle measurements, grazing angle Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and AFM. Loading rate-dependent SMFS measurements yielded a barrier width x(β) and a bond lifetime at zero force t(off)(0) of 0.29 ± 0.02 nm and 100 ± 80 ms, respectively. The value of the corresponding off-rate constant k(off) suggests a substantially larger value of the dimerization constant compared to theoretical predictions, which is fully in line with the additional intramolecular hydrogen-bond stabilization detected in solution by (1)H NMR spectroscopy.