Oriented immobilization of antibodies onto the gold surfaces via their native thiol groups

The general approach for site-oriented immobilization of antibodies onto gold supports is reported. The immobilization is carried out using the native sulfide groups of immunoglobulin (IgG). To liberate the thiol groups, the intact IgG was split into two half-IgG fragments without destruction of the binding site of the antibody. The immobilization of half-IgG fragments on the gold surface was carried out by simple adsorption. The antigen binding capacity of the half-IgG modified gold supports is similar to that of the gold surfaces with the traditionally linked antibodies and is much higher than for nonspecifically adsorbed intact IgGs. The immobilized antibodies, according to the proposed approach, maintain high antigen binding constants. The immobilization procedure provides orientation of IgG fragments in terms of the similar distance between the binding site of the antibody and the surface of the gold support, which does not cause the distribution of the apparent affinity constants. The high operational stability of half-IgG modified gold electrodes makes them applicable for analytical applications.     

Evolution of atomic and electronic structure of magnetic Gd-doped gold clusters

The evolution of atomic and electronic structure of small Au _n (n = 1–16, and 55) clusters doped with a Gd atom has been investigated using density functional theory within generalized gradient approximation for the exchange–correlation energy. Pure gold neutral clusters with n up to 15 are planar. However, with the doping of a Gd atom, the atomic structure of gold clusters changes, and there is a transition from planar-like structures to three dimensional structures at n = 10. The electronic structure of Gd-doped gold clusters shows a sharp increase in the highest occupied–lowest unoccupied molecular orbital (HOMO–LUMO) gap for certain sizes giving rise to their magic behavior. All clusters are magnetic with large magnetic moments ranging from 6 to 8 μ_B primarily due to the localized 4f electrons on Gd. This makes such clusters with large HOMO–LUMO gaps magnetic superatoms. The main interaction between gold and gadolinium atoms in the clusters is due to hybridization between Au-6s and Gd-5d6s orbitals. Our results indicate the emergence of a wheel structure for Gd@Au₇, a symmetric cage structure at n = 15 for Gd@Au₁₅ and n = 16 for Gd@Au₁₆ ⁺ and Eu@Au₁₆ corresponding to an electronic shell closing at 18 valence electrons leaving aside the f electrons on Gd while for Gd-doped Au₅₅ corresponding to 58 valence electrons, a Au₉Gd@Au₄₆ core–shell structure is obtained in which the Gd atom connects the core of Au₉ with the Au₄₆ shell. The binding energy shows odd–even oscillations with enhancement due to Gd doping compared with pure gold clusters. Such magnetic clusters of gold could have multifunctional biological applications in drug delivery, sensor, imaging, and cancer treatment.     

Adsorption characteristics of self-assembled thiol and dithiol layer on gold

Monolayers of functional proteins are important in many fields related to pure and applied biochemistry and biophysics. The formation of extended uniform protein monolayers by single- or multiple-step self-chemisorption depends on the quality of the functionalized gold surface. The optical and the electrical properties of the 1-nonanethiol and 1,9-nonanedithiol deposited on gold with the self-assembled technique were investigated. We use cyclic voltammetry and impedance spectroscopy to characterize the insulating properties of the two layers. The analysis of the impedance spectra in terms of equivalent circuit of the gold/electrolyte and gold/SAM/electrolyte interface allows defining the thickness of the two thiols and the percentage of coverage area. Atomic force microscopy, contact angle measurement and Fourier transform infra-red spectroscopy have been used for homogeneity, hydrophobic properties and molecular structure of the formed thiols layer, respectively. The measured thickness with impedance spectroscopy fit well the results found with atomic force microscopy.     

Nanopatterning the electronic properties of gold surfaces with self-organized superlattices of metallic nanostructures

The self-organized growth of nanostructures on surfaces could offer many advantages in the development of new catalysts, electronic devices and magnetic data-storage media. The local density of electronic states on the surface at the relevant energy scale strongly influences chemical reactivity, as does the shape of the nanoparticles. The electronic properties of surfaces also influence the growth and decay of nanostructures such as dimers, chains and superlattices of atoms or noble metal islands. Controlling these properties on length scales shorter than the diffusion lengths of the electrons and spins (some tens of nanometres for metals) is a major goal in electronics and spintronics. However, to date, there have been few studies of the electronic properties of self-organized nanostructures. Here we report the self-organized growth of macroscopic superlattices of Ag or Cu nanostructures on Au vicinal surfaces, and demonstrate that the electronic properties of these systems depend on the balance between the confinement and the perturbation of the surface states caused by the steps and the nanostructures' superlattice. We also show that the local density of states can be modified in a controlled way by adjusting simple parameters such as the type of metal deposited and the degree of coverage.     

First-principles electronic structure calculations for peanut-shaped C120 molecules

Using the first-principles real-space finite-difference method, we have theoretically examined optimized structures and electronic energy levels of three peanut-shaped C₁₂₀ molecules (C₆₀ dimers), namely, P55-, P56-, and P66-C₁₂₀ molecules. Our calculations show that as the number of eight-membered rings included in each C₁₂₀ molecule increases, the total energy becomes large and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap becomes small. For the P56-C₁₂₀ molecule, the LUMO is found to be localized at one C₆₀ component, while for the other molecules, the LUMOs are extended over the entire molecule. This fact is understood from the symmetry/asymmetry in the atomic configuration of the three C₁₂₀ molecules.     

Quantitative detection of individual cleaved DNA molecules on surfaces using gold nanoparticles and scanning electron microscope imaging

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) labeling of the cleavage products. The individual RCA amplicon molecules were counted on the surface using fluorescence microscopy. Two principal limitations of such single-molecule counting are the variability in the amplicon size, which results in a large variation in fluorescence signal intensity from the dye-labeled DNA molecules, and a high level of background fluorescence. It is shown here that an excellent alternative to RCA labeling is tagging with gold nanoparticles followed by imaging with a scanning electron microscope. Gold nanoparticles have a uniform diameter (15 +/- 0.5 nm) and provide excellent contrast against the background of the silicon substrate employed. Individual gold nanoparticles are readily counted using publicly available software. The results demonstrate that the labeling efficiency is improved by as much as approximately 15-fold, and the signal-to-noise ratio is improved by approximately 4-fold. Detection of individual cleaved DNA molecules following surface-invasive cleavage was linear and quantitative over 3 orders of magnitude in amount of target DNA (10(-18)-10(-15) mol).     

Effect of surface capping molecules on the electronic structure of CdSe nanocrystal film

The optical band gap and the valence band of CdSe nanocrystals were investigated with respect to surface capping molecules by using photoluminescence and synchrotron photoemission spectroscopy. The optical band gap was shown to be mainly dependent on the size of the molecule controlling the inter-particle distance; the valence band, however, mainly depended on the chemical bonding nature of the molecule. UV in air and anneal under ultra high vacuum (UHV) were carried out to control the surface capping pyridine content on CdSe nanocrystal films. With UV treated film, a great reduction in the pyridine content was found, but extra oxygen was absorbed onto the naked CdSe surface. The surface absorbed oxygen exerted a strong influence on the electronic structure of CdSe nanocrystal films. This extra oxygen was successfully removed though UHV-anneal, and it was possible to distinguish the effect of oxygen from the effect of surface capping pyridine on the electronic structure of CdSe nanocrystal film. A quantitative relationship between the valence band maximum of CdSe nanocrystal films and the content of surface-absorbed oxygen could be given.     

First-principles study of the stability and the electronic structure of NiO/MgO interface

First-principles full potential linearized augmented plane wave method (FP-LAPW) based on density functional theory has been performed to study the stability and the electronic structure of NiO/MgO interface. The surface energy, strain energy and the separation energy are calculated and discussed. The results reveal that NiO(0 0 1)/MgO(0 0 1) interface is more stable than NiO(1 1 1)/MgO(1 1 1) interface. Also examined were the electronic structure and the atomic spin magnetic moment of the NiO/MgO interface. It is found that the interface system significantly affects the electronic structure and magnetic properties of the oxide/oxide interface.     

Directed deposition of single molecules on surfaces

Scanning probe microscopy-based techniques can address and manipulate individual molecules. This makes it possible to use them for building nanostructures by assembling single molecules. Recently the formation of surface structures by positioning single molecules with the Atomic Force Microscope (AFM) was demonstrated on an irreversible delivery process. This inherits the drawback, that the transfer has to occur between differently functionalized surfaces and allows no proofreading of the built structures. Here we demonstrate a procedure for directed deposition of single DNA molecules, which intrinsically allows a reversible positioning. This method uses specific interactions between complementary DNA oligonucleotides for symmetric coupling of the transport molecules to the support and AFM tip, respectively. Thus, it allows for a simple "drag-and-drop" procedure, which relies on the statistical breakage of the molecular interaction under a force load. In addition, the delivery of the transport molecules was observed in real-time by single-molecule fluorescence microscopy.     

Atomic structure and electronic properties of the GaN/ZnO (0001) interface

The stability and electronic structure of cation- and anion-compensated interfaces between (0001) lattice-matched slabs of GaN and ZnO have been considered. It was found that, irrespective of interfacial polarity, cation-compensated interfaces are by approximately 20 meV/unit cell more stable than the corresponding anion-compensated interfaces. Valence band offsets of 1.0 and 0.5 eV have been found at the cation- and anion-compensated interfaces, respectively.     

小分子化合物表面修饰对金/二氧化硅纳米核壳粒子结构的影响

分别使用带有巯基的化合物半胱胺(Cys)、胱胺(CYS)、巯基丁二酸(MSA)和巯基乙醇(ME)对金/二氧化硅纳米核壳粒子(GNs)进行表面化学修饰。利用动态光散射(DLS)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)和紫外-可见吸收光谱(UV-Vis)对修饰后的GNs进行表征。研究结果显示Cys和CYS修饰后GNs胶体溶液稳定性下降,核壳结构完整性破坏,从而导致其在近红外区最大吸收峰消失。而MSA和ME修饰的GNs胶体溶液稳定,金壳结构完整,光学性质稳定。这可能是由于Cys和CYS的胺基通过与金壳之间产生静电力作用和配位作用,破坏了GNs表面金壳。     

First-principles electronic structure calculations for peanut-shaped C120 molecules

Using the first-principles real-space finite-difference method, we have theoretically examined optimized structures and electronic energy levels of three peanut-shaped C₁₂₀ molecules (C₆₀ dimers), namely, P55-, P56-, and P66-C₁₂₀ molecules. Our calculations show that as the number of eight-membered rings included in each C₁₂₀ molecule increases, the total energy becomes large and the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap becomes small. For the P56-C₁₂₀ molecule, the LUMO is found to be localized at one C₆₀ component, while for the other molecules, the LUMOs are extended over the entire molecule. This fact is understood from the symmetry/asymmetry in the atomic configuration of the three C₁₂₀ molecules.     

Organic molecules reconstruct nanostructures on ionic surfaces

Modification and functionalization of the atomic-scale structure of insulating surfaces is fundamental to catalysis, self-assembly, and single-molecule technologies. Specially designed syn-5,10,15-tris(4-cyanophenylmethyl)truxene molecules can reshape features on an ionic KBr (001) surface. Atomic force microscopy images demonstrate that both KBr monolayer islands and pits can reshape from rectangular to round structures, a process which is directly facilitated by molecular adsorption. Simulations reveal that the mechanism of the surface reconstruction consists of collective atomic hops of ions on the step edges of the islands and pits, which correlate with molecular motion. The energy barriers for individual processes are reduced by the presence of the adsorbed molecules, which cause surface structural changes. These results show how appropriately designed organic molecules can modify surface morphology on insulating surfaces. Such strongly adsorbed molecules can also serve as anchoring sites for building new nanostructures on inert insulating surfaces.     

Effect of thiol chemisorption on the transport properties of gold nanotubule membranes

An electroless gold deposition method was used to deposit Au nanotubules within the pores of a polycarbonate template membrane. Membranes containing Au nanotubules with inside diameters of 2 and 3 nm were prepared for these studies. Thiols were chemisorbed to the inside tubule walls in order to change the chemical environment within the tubules. The effect of the chemical environment within the tubules on the transport properties of the tubule-containing membrane was investigated. Membranes modified with HS-C(16)H(33) preferentially transported hydrophobic permeant molecules. When a homologous series of permeant molecules was used, the most hydrophobic permeant was preferentially partitioned into and transported by the HS-C(16)H(33) derivatized membrane. In addition, the effect of alkyl chain length (R), in a homologous series of thiols R-SH, was investigated. Hydrophobic permeant molecules were preferentially partitioned into and transported by membranes containing the largest alkyl group. In contrast, membranes modified with HS-C(2)H(4)OH preferentially transported the more hydrophilic permeant pyridine. Finally, we show here that the HS-C(16)H(33) derivatized membrane can be used to separate hydrophobic species from hydrophilic species.     

Surfactant mediated assembly of gold nanowires on surfaces

The potential of surfactant interactions to direct both the placement and orientation of gold nanowires onto surfaces from solution has been investigated. Gold nanowires were synthesized by template electrodeposition in porous aluminum oxide membranes. Their assembly onto surfaces was controlled by functionalizing the nanowires and surfaces with self-assembled monolayers of thiol based surfactants. Nanowires were assembled from solution onto patterned functional surfaces, and after excess solvent had evaporated the arrangement of nanowires on the surface was observed. A variety of assembly techniques, based upon wettability, electrostatic, or chemical interactions have been studied. Nanowire assembly onto surfaces with patterned wettability resulted in the placement of nanowires on hydrophilic regions with a specific orientation. Hydrogen bonding and carboxylate salt attachment of mercaptoundecanoic acid functionalized nanowires to reactive regions of patterned surfaces has been demonstrated, with unbound wires removed by washing. Similarly, electrostatic interactions between charged nanowires and surfaces have been demonstrated to preferentially assemble nanowires onto oppositely charged surface regions. Although selective attachment of nanowires to reactive surface regions was achieved by both chemical and electrostatic assembly techniques, these methods did not control the orientation of assembled nanowires.     

Formation of gold nanoparticles via a thiol functionalized polyoxometalate

A useful method for the synthesis of Au nanoparticles is presented. The synthesis of Au nanoparticles with various morphologies was carried out at room temperature using gamma radiolysis and NaBH₄ reduction of HAuCl₄ in N,N′-dimethylformamide:water solutions containing polyoxometalate (POM). The results demonstrated that by controlling the rate of reduction and ratio of DMF and water, metal particle size and shape can be further tailored. It is shown that gold nanoparticles with controllable size can be synthesized. In principle, the general finding of this work can be extended to other transition/noble metal nanoparticles.