Electrostatic assembly of CTAB-capped silver nanoparticles along predefined λ-DNA template

Cetyltrimethylammonium bromide (CTAB)-capped positively-charged silver nanoparticles synthesized in water-ethanol system was electrostatic assembled on predefined aligned λ-DNA template. Silver nanowire can be obtained by changing the reaction time and the particles concentration. In our work, the length of the silver nanowire obtained is about 10 μm, and the dimension of the wires is about 20 nm. AFM data reveal that the assembly of CTAB-capped silver nanoparticles on DNA is ordered, but there is space between two particles absorbed on the DNA template. X-ray photoelectron spectroscopy (XPS) was applied to characterize the linear silver clusters, which provides an additional proof that the silver particles were assembled onto DNA template with fine order.     

Temperature dependence of transport behavior of a short DNA molecule

DNA molecules may work as novel devices due to their interesting electronic transport properties. We here propose a theoretical method to deal with the temperature dependence of the transport behavior of a short DNA molecule, taking into account Coulomb interaction of electrons and the coupling between electrons and the two-level system in the DNA molecule. The nonlinear current-voltage curves are derived by using the Landauer formulae. We find that the voltage gap of the current-voltage curves is sensitive to the parameters of the two-level system. We also find that Coulomb blockade peaks can be controlled by varying the temperature, which relates to particular features of the DNA molecule.     

Possible mechanisms of the influence of hexylresorcinol on the structure-dynamic and functional properties of lysozyme protein

The influence of hexylresorcinol on the structure, equilibrium fluctuations, and functional activity of water-soluble enzyme lysozyme was studied over a wide range of hexylresorcinol concentrations. Hexylresorcinol was found to be not only a stabilizer of lysozyme. At low hexylresorcinol concentrations (2 to 10 molecules per lysozyme globule), the activity of lysozyme sharply increased; activity began to decrease as the concentration grew. The influence of hexylresorcinol on the structural, dynamic, and functional lysozyme characteristics is well described by models of preferential hydration and preferential protein interaction with hexylresorcinol. The hexylresorcinol molecule consists of hydrophobic (alkyl radical) and hydrophilic (aromatic nucleus) moieties, which has additional regulatory action on the functional activity of lysozyme. As the concentration of hexylresorcinol increases, the effect of regions with preferential hydration begins to noticeably predominate over the effect of preferential interaction with hexylresorcinol. At hexylresorcinol concentrations higher than 100 molecules per lysozyme globule, the activity of lysozyme is fully inhibited. This is caused by the preferential hydration of the protein with the displacement of hexylresorcinol from direct contacts with it. The displacement of hexylresorcinol causes the formation of high-density hexylresorcinol micelles. Dense micelles interfere with the approach of substrates to the protein and fully inhibit its functional activity. The complete inhibition of lysozyme activity occurs at hexylresorcinol concentrations lower by an order of magnitude than glycerol inhibiting concentrations.     

Controlled assembly of DNA nanostructures on silanized silicon and mica surfaces for future molecular devices

In order to establish key technology for future molecular devices, we have explored the assembly behaviour of λ-deoxyribonucleic acid (DNA) molecules adsorbed on silanized mica and silanized oxide silicon surfaces by using atomic force microscopy (AFM). AFM experiments show that λ-DNA molecules can be hardly adsorbed on untreated mica and oxidized silicon surfaces, but can be strongly adsorbed onto aminosilanized mica and oxidized silicon surfaces. Importantly, DNA molecules can be assembled into linear DNA alignment, and can also self-assemble into various network structures on the silanized surfaces. Our experimental observations have demonstrated the feasibility of assembling DNA-based nanostructures by varying surface chemistry of substrates, and offer useful clues in constructing DNA-based nanodevices for nanoelectronics and biomolecular computation as well as quantum computation.     

用单分子技术研究Sso7d与DNA的相互作用

为了维持基因的稳定性,每种生物体都含有一套独特的染色质蛋白来保护脱氧核糖核酸(DNA)的结构,观察染色质蛋白对DNA结构的作用过程和结果,可以帮助人们了解这些蛋白的具体功能和作用机理.硫化叶菌是一种能在高温下存活的古细菌,Sso7d是硫化叶菌的一种染色质蛋白.深入地了解Sso7d和DNA链的相互作用,有助于解释硫化叶菌的DNA为何能在高温环境下保持活性,本文通过原子力显微镜(AFM)和磁镊两种单分子操作手段,研究了Sso7d与DNA的相互作用.AFM的实验结果给出了Sso7d与DNA的作用过程:结合Sso7d后,DNA首先发生弯折,然后出现loop结构,最终DNA会团聚为致密的核结构.利用磁镊装置测量了Sso7d的结合对打开DNA双链的影响,实验结果表明Sso7d的结合导致打开DNA双链的力的增大,经过数据分析,计算出Sso7d与DNA结合的结合能?G=3.1k_BT,平均每5.5个碱基对(bp)结合一个Sso7d,较高的结合密度和较大的结合能,两方面的作用结果,解释了Sso7d能够稳定DNA结构的原因.     

Effective long-range attraction between protein molecules in solutions studied by small angle neutron scattering

Small angle neutron scattering intensity distributions taken from cytochrome C and lysozyme protein solutions show a rising intensity at a very small wave vector Q, which can be interpreted in terms of the presence of a weak long-range attraction between protein molecules. This interaction has a range several times that of the diameter of the protein molecule, much greater than the range of the screened electrostatic repulsion. We show evidence that this long-range attraction is closely related to the type of anion present and ion concentration in the solution.     

Altering protein surface charge with chemical modification modulates protein–gold nanoparticle aggregation

Gold nanoparticles (AuNP) can interact with a wide range of molecules including proteins. Whereas significant attention has focused on modifying the nanoparticle surface to regulate protein–AuNP assembly or influence the formation of the protein “corona,” modification of the protein surface as a mechanism to modulate protein–AuNP interaction has been less explored. Here, we examine this possibility utilizing three small globular proteins—lysozyme with high isoelectric point (pI) and established interactions with AuNP; α-lactalbumin with similar tertiary fold to lysozyme but low pI; and myoglobin with a different globular fold and an intermediate pI. We first chemically modified these proteins to alter their charged surface functionalities, and thereby shift protein pI, and then applied multiple methods to assess protein–AuNP assembly. At pH values lower than the anticipated pI of the modified protein, AuNP exposure elicits changes in the optical absorbance of the protein–NP solutions and other properties due to aggregate formation. Above the expected pI, however, protein–AuNP interaction is minimal, and both components remain isolated, presumably because both species are negatively charged. These data demonstrate that protein modification provides a powerful tool for modulating whether nanoparticle–protein interactions result in material aggregation. The results also underscore that naturally occurring protein modifications found in vivo may be critical in defining nanoparticle–protein corona compositions.     

Humidity Effects on Imaging and Nanomanipulation of Individual DNA Molecules on HOPG Surface

Single DNA molecules are aligned on highly ordered pyrolytic graphite （HOPG） surface in ambient air. It is shown that environmental humidity has a remarkable influence on the measured height of DNA by atomic force microscopy （AFM）, probably due to the conformation transition of DNA. We also demonstrate that DNA molecules deposited on HOPG surface can be ＇pushed＇ much more easily by AFM tip at high humidity than at 10W one.     

In Situ Evaluation of Nanoparticle–Protein Interactions by Dynamic Magnetic Susceptibility Measurements

The use of dynamic magnetic susceptibility measurements is reported to study nanoparticle–protein interactions in situ. The technique consists of measuring the rotational diffusivity of thermally blocked magnetic nanoparticles (MNPs) in protein solutions. To illustrate the technique, the effect of nanoparticle zeta potential in carboxymethyl‐dextran‐coated MNPs and their interaction with model anionic and cationic proteins, such as bovine serum albumin (BSA), immunoglobulin G (IgG), fibrinogen (FIBR), apo‐transferrin (TRANS), lysozyme (LYZ), and histone (HIS), in a range of protein concentrations is studied. Experiments indicate that interactions between the negatively charged particles and the negatively charged proteins BSA, IgG, FIBR, and TRANS are negligible. However, positively charged proteins LYZ and HIS readily absorb onto the nanoparticles, as evidenced by an increase in size and eventual aggregation of the particles. Onset of this effect seems to happen at a lower concentration of HIS compared with LYZ. The technique could be applied to other particle surface coatings and to particles in complex protein mixtures, such as whole blood and serum, allowing systematic in situ studies of nanoparticle–protein interactions.     

Structural investigation of n-hexadecanoic acid multilayers on mica surface: Atomic force microscopy study

The structure of n-hexadecanoic acid (HA) multilayers formed by spreading an ethanol solution containing this molecule onto a freshly cleaved mica surface has been studied by atomic force microscopy (AFM). AFM images of multilayers obtained with different coating time showed that HA molecules first formed some sporadic domains on mica surface. With the proceeding of the coating process, these domains gradually enlarged and coalesced, until formed a continuous film finally. It was observed that HA molecules were always adsorbed on mica surface with tilted even-numbered layers structure. The height of the repeated tilted bilayer film was measured to be approximately 3.8 ± 0.2 nm, which implied a ∼60° tilt molecular conformation of the HA bilayers on mica surface. Phase image confirmed that the HA multilayers terminated with the hydrophilic carboxylic acid groups. The formation mechanism of the HA multilayers was discussed in detail. Thus, resulted hydrophilic surfaces are of special interest for further study in biological or man-made member systems.     

Biocidal action of ozone-treated polystyrene surfaces on vegetative and sporulated bacteria

Surfaces of materials can be modified to ensure specific interaction features with microorganisms. The current work discloses biocidal properties of polystyrene (PS) Petri-dish surfaces that have been exposed to a dry gaseous-ozone flow. Such treated PS surfaces are able to inactivate various species of vegetative and sporulated bacteria on a relatively short contact time. Denaturation of proteins seems likely based on a significant loss of enzymatic activity of the lysozyme protein. Characterization of these surfaces by atomic-force microscopy (AFM), Fourier-transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) reveals specific structural and chemical modifications as compared to untreated PS. Persistence of the biocidal properties of these treated surfaces is observed. This ozone-induced process is technically simple to achieve and does not require active precursors as in grafting.     

一种改进型单分子操纵装置及其应用

改进了单分子横向磁镊装置,可以直接用于观察单个DNA分子的伸长和扭转并随时更换样品池内的溶液,还可以同时操纵多个DNA分子,大大提高实验效率.此方法可以提供01到40pN范围的拉力,足以满足大部分单分子DNA实验的要求.用该装置实时观测到了DNA分子在拉力作用下的伸长以及在旋转磁场作用下的扭转,并成功地观察到了分子马达拉动DNA的动力学过程,从而验证了该装置的实用性. 关键词： 横向磁镊 单分子操纵 DNA拉伸 DNA扭转     

Interaction between nanobuds and hydrogen molecules: A first-principles study

Hydrogen storage materials are crucial for the wide application of hydrogen in fuel cells. In this Letter, the interaction between hydrogen molecules and nanobuds has been studied using the Dmol3 package. The results show that the adsorption energies of hydrogen molecules onto nanobuds range from 0.069 eV to 0.115 eV, and that the adsorption energies are not sensitive to the nanobuds' structures but closely related to the number of carbon atoms around H₂ molecules. The energy barrier of a hydrogen molecule entering C176 is 2.38 eV. Each C176 nanobud can accommodate four H₂ molecules. The stress existing in nanobuds induces alterative charge distribution, which can improve the hydrogen storage performance of nanobuds to a certain extent.     

Immobilization of protein molecules on step-controlled sapphire surfaces

We have studied effects of surface morphology on immobilization of protein molecules using step-controlled sapphire surfaces. Preferential adsorption of avidin molecules on the step edges was observed on the single-stepped sapphire surface. A randomly-stepped sapphire surface was found to be suitable for high-density immobilization of protein molecules. These results indicate atomic scale structures of the substrate surface influence the adsorption efficiency of the proteins. By using an atomic force microscopy (AFM) equipped with a biotin-modified cantilever, we have confirmed that the immobilized avidin molecules on the substrates keep their biological activity. This means that the ligand-receptor interaction can be detected using the phase image mode of a standard AFM.     

Electrospray deposition in vacuum

We have used the established technique of electrospray in developing a portable vacuum electrospray system which can deposit, in vacuo, dissolved molecules onto a sample which may then be analysed by UHV techniques. As an initial test of the system we have analysed silicon samples with an electrosprayed layer of poly(ethylene) oxide (PEO) using atomic force microscopy (AFM). The polymer forms different structures depending on the voltage applied to the emitter, and solution composition. The system is part of our ongoing effort to deposit other materials such as nanoparticles, and large dye molecules for developing molecular dye sensitised solar cells.     

Coagulation rate of protein fragments in a liquid with gas inclusions

A model of association of protein fragments and molecules in liquid on neutral and charged spherical inhomogeneities, including gas bubbles with stabilizing ion sheaths (bubstons), was developed. Association rates were comparatively estimated for three processes: self-coagulation of noninteracting protein molecules (fragments), self-coagulation of molecules charged as a result of the interaction with surrounding electrolyte, and association of charged molecules on bubstons. Estimation of coagulation of biomolecules on bubstons shows the possibility to control the biomolecule association rate by varying the bubston concentration.     

Forces with submolecular resolution between the probing tip and Cu-TBPP molecules on Cu(100) observed with a combined AFM/STM

Combined STM/AFM experiments were performed on monolayer islands of Cu-TBPP molecules on Cu(100). Pulling of single molecules on the substrate was observed and the imaging parameters were compared to STM studies. Local frequency shift vs. distance curves reveal three types of curves, which can be related to the interaction of the tip above the Cu(100) substrate, the centre of the molecule and the leg of the molecule. The frequency vs. distance curves above the legs reveal two minima, which are associated with the bending of the legs above a certain threshold value. Quantitative analysis yields force values of about 0.4 nN.     

Electrostatic assembly of Cu2O nanoparticles on DNA templates

In this paper, a method for highly ordered assembly of cuprous oxide (Cu₂O) nanoparticles (NPs) by DNA templates was reported. Cetyltrimethylammonium bromide (CTAB)-capped Cu₂O NPs were adsorbed onto well-aligned λ-DNA chains to form necklace-like one-dimensional (1D) nanostructures. UV-vis, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the nanostructure. The Cu₂O nanostructures fabricated with the method are both highly ordered and quite straight.     

Quantitative atomic force microscopy with carbon monoxide terminated tips

Noncontact atomic force microscopy (AFM) has recently progressed tremendously in achieving atomic resolution imaging through the use of small oscillation amplitudes and well-defined modification of the tip apex. In particular, it has been shown that picking up simple inorganic molecules (such as CO) by the AFM tip leads to a well-defined tip apex and to enhanced image resolution. Here, we use the same approach to study the three-dimensional intermolecular interaction potential between two molecules and focus on the implications of using molecule-modified AFM tips for microscopy and force spectroscopy experiments. The flexibility of the CO at the tip apex complicates the measurement of the intermolecular interaction energy between two CO molecules. Our work establishes the physical limits of measuring intermolecular interactions with scanning probes.