Electrostatic assembly of protein lysozyme on DNA visualized by atomic force microscopy

In the present work, atomic force microscopy (AFM) has been used to study the assembly of protein lysozyme on DNA molecule. Based on the electrostatic interaction, the positively charged lysozyme can easily bind onto the negatively charged DNA molecule surface. The protein molecules appear as globular objects on the DNA scaffold, which are distinguishable in the AFM images. At the same time, lysozyme molecules can be assembled onto DNA as dense or sporadic pattern by varying the protein concentration. This work may provide fundamental aspects for building protein nanostructures and studying of DNA-protein interaction.

Adsorption behaviors of methanol, ethanol, n-butanol, n-hexanol and n-octanol on mica surface studied by atomic force microscopy

The adsorption behavior of methanol, ethanol, n-butanol, n-hexanol and n-octanol on mica surface was investigated by atomic force microscopy. All these alcohols have formed homogeneous films with different characteristics. Upright standing bilayer structure was formed on methanol adsorbed mica surface. For ethanol, bilayer structure and monolayer one were simultaneously formed, while for n-butanol and n-hexanol, rough films were observed. What was formed for n-octanol? Close-packed flat film was observed on n-octanol adsorbed mica substrate, the film was assumed to be a tilted monolayer. The possible adsorption model for each alcohol molecule was proposed according to its adsorption behavior.

DNA network structures on various solid substrates investigated by atomic force microscopy

We have fabricated DNA network structures on glass and sapphire substrates. As a comparison, we also formed the network structure on mica substrate. For titanate strontium substrate, however, DNA network can not be obtained even if it is wet-treated by Na2HPO4 solution to make it hydrophilic. We also discuss the factors that affect the DNA networks formed on various substrates.

Conducting probe atomic force microscopy investigation of anisotropic charge transport in solution cast PBD single crystals induced by an external field

2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxdiazole (PBD) is a good electron-transporting material and can form single crystals from solution. In this work, solution cast PBD single crystals with different crystallographic axes (b, c) perpendicular to the Au/S substrates in large area are achieved by controlling the rate of solvent evaporation in the presence and absence of external electrostatic field, respectively. The orientation of these single crystals on Au/S substrate was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Conducting probe atomic force microscopy (CP-AFM) was used to measure the charge transport characteristics of PBD single crystals grown on Au/S substrates. Transport was measured perpendicular to the substrate between the CP-AFM tip and the Au/S substrate. The electron mobility of 3 x 10(-3) cm(2)/(V s) for PBD single crystal along crystallographic b-axis is determined. And the electron mobility of PBD single crystal along the c-axis is about 2 orders of magnitude higher than that along the b-axis due to the anisotropic charge transport at the low voltage region.

Investigation of facilitated ion-transfer reactions at high driving force by scanning electrochemical Microscopy

The kinetics of facilitated ion-transfer (FIT) reactions at high driving force across the water/1,2-dichloroethane (W/DCE) interface is investigated by scanning electrochemical microscopy (SECM). The transfers of lithium and sodium ions facilitated by dibenzo-18-crown-6 (DB18C6) across the polarized W/DCE interface are chosen as model systems because they have the largest potential range that can be controlled externally. By selecting the appropriate ratios of the reactant concentrations (Kr c(M)+/c(DB18C6)) and using nanopipets as the SECM tips, we obtained a series of rate constants (k(f)) at various driving forces (Delta(O)(W) phi(ML+)(0') - Es, Delta(O)(W) phi(ML+)(0') is the formal potential of facilitated ion transfer and Es is the potential applied externally at the substrate interface) based on a three-electrode system. The FIT rate constants k(f) are found to be dependent upon the driving force. When the driving force is low, the dependence of 1n k(f) on the driving force is linear with a transfer coefficient of about 0.3. It follows the classical Butler-Volmer theory and then reaches a maximum before it decreases again when we further increase the driving forces. This indicates that there exists an inverted region, and these behaviors have been explained by Marcus theory.

Use of atomic force microscopy for imaging the initial stage of the nucleation of calcium phosphate in Langmuir-Blodgett films of stearic acid

The nucleation of calcium phosphate on the substrate of steatic acid Langmuir-blodgett film at the initial stage was investigated by atomic force microscopy. Nano-dots, nano-wires and nano-islands were observed in sequence for the first time, reflecting the nucleation of calcium phosphate and the molecular arrangement of carboxylic layer. The nucleation rates perpendicular and parallel to the carboxylic terminal group were estimated from the height and diameter of the calcium phosphate crystals, respectively. And this stage was distinct from the late explosive grown stage, in which the change of the morphology was not obvious. The approaches based on this discovery would lead to the development of new strategies in the controlled synthesis of inorganic nano-phases and the assembly of organized composite and ceramic materials.

Rapid self-assembly of oligo(o-phenylenediamine) into one-dimensional structures through a facile reprecipitation route

The self-assembly of oligo(o-phenylenediamine) (OPD) into 1-D nanostructures on a macroscopic length scale was found when they were transferred from N-methyl pyrrolidone to deionized water. Field emission scanning electron microscopy and confocal fluorescence microscopy were used to investigate the morphology of the precipitates. Results showed that large amounts of OPD 1-D supertructures could be obtained through the simple reprecipitation route, and the length of the fibers could be tuned from microscale to macroscale by adjusting the ratio of two solvents. X-ray diffraction patterns and UV-vis spectra revealed that pi-pi interactions between OPD molecules that facilitated the formation of 1-D structures became predominant when they were transferred from a good solvent to a bad one. Accordingly, a possible formation mechanism was proposed.

Growth of cationic lipid toward bilayer, lipid membrane by solution spreading: scanning probe microscopy study

The growth of cationic lipid dioctadecyldimethylammonium bromide (DODAB) toward bilayer lipid membrane (BLM) by solution spreading on cleaved mica surface was studied by atomic force microscopy (AFM). Bilayer of DODAB was formed by exposing mica to a solution of DODAB in chloroform and subsequently immersing into potassium chloride solution for film developing. AFM studies showed that at the initial stage of the growth, the adsorbed molecules exhibited the small fractal-like aggregates. These aggregates grew up and expanded laterally into larger patches with time and experienced from monolayer to bilayer, finally a close-packed bilayer film (5.4 +/- 0.2 nm) was approached. AFM results of the film growth process indicated a growth mechanism of nucleation, growth and coalescence of dense submonolayer, it revealed the direct information about the film morphology and confirmed that solution spreading was an effective technique to prepare a cationic bilayer in a short time.

Self-assembled monolayer growth of octanol on mica: Atomic force microscopy and Fourier-transform infrared spectroscopy studies

The growth kinetics of self-assembled monolayers formed by exposing freshly cleaved mica to octanol solution has been studied by atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). AFM images of samples immersed in octanol for varying exposure times showed that before forming a complete monolayer the octanol molecules aggregated in the form of small islands on the mica surface. With the proceeding of immersion, these islands gradually grew and merged into larger patches. Finally, a close-packed film with uniform appearance and few defects was formed. The thickness of the final film showed 0.8 nm in height, which corresponded to the 40degrees tilt molecular conformation of the octanol monolayer. The growth mechanisms consisted of nucleation, growth, and coalescence of the submonolayer films. The growth process was also confirmed by FTIR. And the surface coverage of the submonolayer islands estimated from AFM images and FTIR spectra as a function of immersion time was quite consistent.

Surface phase separations of PMMA/SAN blends investigated by atomic force microscopy

The thin films of poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN) and their blends were prepared by means of spin-coating their corresponding solutions onto silicon wafers, followed by being annealed at different temperatures. The surface phase separations of PMMA/SAN blends were characterized by virtue of atomic force microscopy (AFM). By comparing the tapping mode AFM (TM-AFM) phase images of the pure components and their blends, surface phase separation mechanisms of the blends could be identified as the nucleation and growth mechanism or the spinodal decomposition mechanism. Therefore, the phase diagram of the PMMA/SAN system could be obtained by means of TM-AFM. Contact mode AFM was also used to study the surface morphologies of all the samples and the phase separations of the blends occurred by the spinodal decomposition mechanism could be ascertained. Moreover, X-ray photoelectron spectroscopy was used to characterize the chemical compositions on the surfaces of the samples and the miscibility principle of the PMMA/SAN system was discussed.

Study of methanol adsorption on mica, graphite and ITO glass by using tapping mode atomic force microscopy

Tapping mode atomic force microscopy (AFM) was applied to study the adsorption behavior of methanol on mica, highly oriented pyrolytic graphite (HOPG) and indium-tin oxide (ITO) coated glass substrates. On mica and HOPG substrates surfaces, the thin films of methanol with bilayer and multilayer were observed, respectively. The formation of irregular islands of methanol was also found on HOPG surface. On ITO surface only aggregates and clusters of methanol molecules were formed. The influence of sample preparation on the adsorption was discussed.

A relocated technique of atomic force microscopy (AFM) samples and its application in molecular biology

A kind of simple atomic force microscopy (AFM) relocated technique, which takes advantage of homemade sample locator system, is used for investigating repeatedly imaging of some specific species on the whole substrate (over 1 x 1 cm(2)) with resolution about 400 nm. As applications of this sample locator system, single extended DNA molecules and plasmid DNA network are shown in different AFM operational modes: tapping mode and contact mode with different tips after the substrates have been moved.

Study of electron-transfer reactions across an externally polarized water/1,2-dichloroethane interface by scanning electrochemical microscopy

A novel method to study electron-transfer (ET) reactions between ferrocene in 1,2-dichloroethane (DCE) and a redox couple of K3Fe(CN)(6) and K4Fe(CN)(6) in water using scanning electrochemical microscopy (SECM) with a three-electrode setup is reported. In this work, a water droplet that adheres to the Surface of a platinum disk electrode is immersed in a DCE solution. The aqueous redox couple serves both as a reference electrode on the platinum disk and as an electron donor/acceptor at the polarized liquid/liquid inter-face. With the present experimental approach, the liquid/liquid interface can be polarized externally, while the electron-transfer reactions between the two phases can be monitored independently by SECM. The apparent heterogeneous rate constants for the ET reactions were obtained by fitting the experimental approach curves to the theoretical values. These rate constants obey the Butler-Volmer theory i.e., them, are found to be potential dependent.