A molecular dynamics simulation of the adsorption of water molecules surrounding an Au nanoparticle

This study uses molecular dynamics simulations performed in a parallel computing environment to investigate the adsorption of water molecules surrounding Au nanoparticles of various sizes. An observation of the oxygen and hydrogen atom distributions reveals that the adsorption of the water molecules creates two shell-like formations of water in close vicinity to the Au nanoparticle surface. These shell-like formations are found to be more pronounced around smaller Au nanoparticles. The rearrangement of water molecules in this region reduces the local hydrogen bond strength to below that which is observed in the bulk region. Finally, the simulation results indicate that the absolute value of the interaction energy between the water molecules and the Au nanoparticle is reduced when the water molecules surround a nanoparticle of larger diameter. This observation implies that a stronger adsorption effect exists between smaller Au nanoparticles and water molecules. Hence, the value of the adsorption constant increases for smaller Au nanoparticles.     

NMR studies into colloidal stability and magnetic order in fatty acid stabilised aqueous magnetic fluids

We report the physico-chemical characterisation of fatty acid stabilised aqueous magnetic fluids, which are ideal systems for studying the influence of nanoparticle aggregation on the emergent magnetic resonance properties of the suspensions. Stable colloids of superparamagnetic magnetite, Fe(3)O(4), nanoparticle clusters in the 80 to 100 nm size range were produced by in situ nanoparticle growth and stabilisation, and by suspending pre-formed nanoparticles. NMR relaxation analysis shows that the magnetic resonance properties of the two types of suspension differ substantially and provides new insights into how the relaxation mechanisms are determined by the organisation of the nanoparticles within the clusters.     

Preparation and controlled self-assembly of Janus magnetic nanoparticles

Janus magnetic nanoparticles (~20 nm) were prepared by grafting either polystyrene sodium sulfonate (PSSNa) or polydimethylamino ethylmethacrylate (PDMAEMA) to the exposed surfaces of negatively charged poly(acrylic acid) (PAA)-coated magnetite nanoparticles adsorbed onto positively charged silica beads. Individually dispersed Janus nanoparticles were obtained by repulsion from the beads on reversal of the silica surface charge when the solution pH was increased. Controlled aggregation of the Janus nanoparticles was observed at low pH values, with the formation of stable clusters of approximately 2-4 times the initial size of the particles. Cluster formation was reversed, and individually dispersed nanoparticles recovered, by restoring the pH to high values. At intermediate pH values, PSSNa Janus nanoparticles showed moderate clustering, while PDMAEMA Janus nanoparticles aggregated uncontrollably due to dipolar interactions. The size of the stable clusters could be controlled by increasing the molecular weight of the grafted polymer, or by decreasing the magnetic nanoparticle surface availability for grafting, both of which yielded larger cluster sizes. The addition of small amounts of PAA-coated magnetic nanoparticles to the Janus nanoparticle suspension resulted in a further increase in the final cluster size. Monte Carlo simulation results compared favorably with experimental observations and showed the formation of small, elongated clusters similar in structure to those observed in cryo-TEM images.     

Wash-free magnetic oligonucleotide probes-based NMR sensor for detecting the Hg ion

An easily applied and sensitive sensor for the detection of heavy metal ion residues based entirely on magnetic nanoparticle and oligonucleotide was developed. The tool is established on the relaxation of magnetic nanoparticles with different dispersion states. The target analyte, Hg ions, induce the aggregation of the MNP oligonucleotide probes. Accordingly, the light produced by the magnetic relaxation image and the transverse relaxation time (T(2)) all change due to the effect of the aggregation. The limit of qualitative detection of the sensor is 0.15 ppt. The recoveries from test samples range between 97.1-101.8%. Using the nuclear resonance instrument, the method is a high throughput and sensitive sensor.     

DNA-based magnetic nanoparticle assembly acts as a magnetic relaxation nanoswitch allowing screening of DNA-cleaving agents

Monodisperse magnetic nanoparticles conjugated with complementary oligonucleotide sequences self-assemble into stable magnetic nanoassemblies resulting in a decrease of the spin-spin relaxation times (T2) of neighboring water protons. When these nanoassemblies are treated with a DNA cleaving agent, the nanoparticles become dispersed, switching the T2 of the solution back to original values. These qualities render the developed nanoparticles and their nanoassemblies as magnetic relaxation switches capable of screening for DNA-cleaving compounds by magnetic resonance methods such as MRI and NMR.     

Probing the surfaces of core‐shell and hollow nanoparticles by solvent relaxation NMR

Measurement of the spin–spin NMR relaxation time (or its inverse, the rate) of water molecules in aqueous nanoparticle dispersions has become a popular approach to probe of the nature and structure of the particle surface and any adsorbed species. Here, we report on the characterisation of aqueous dispersions of hollow amorphous nanoparticles that have two liquid accessible surfaces (inner cavity surface and outer shell surface) plus the solid (silica) and core‐shell (titania–silica) nanoparticle precursors from which the hollow particles have been prepared. In all cases, the observed water relaxation rates scale linearly with particle surface area, with the effect being more pronounced with increasing levels of titania present at the particle surface. Two distinct behaviours were observed for the hollow nanoparticles at very low volume fractions, which appear to merge with increasing surface area (particle concentration). Herewith, we further show the versatility of solvent NMR spectroscopy as a probe of surface character.     

Molecular and electronic structures and magnetic properties of multilayer graphene nanoclusters and their changes under the influence of adsorbed molecules

The results of investigations of the structures and properties of multilayer graphene nano-clusters (nanographites), structural blocks of activated carbon fibers, and their changes under the influence of adsorbed molecules are presented. The presence of specific edge p-electron-ic states in the nanographites and a reversible decrease in their density at the Fermi level upon the interaction of the graphite nanoparticles with adsorbed molecules of oxygen, chlorine, and water were found. The explanation of the discovered effect was proposed in the terms of the model of spin splitting of edge p-electronic states initiated by the transfer of a small fraction of the electron density from the nanographites to adsorbed molecules. The change in the sign of the temperature coefficient of current carrier spin relaxation rate in the presence of adsorbates can be accounted for by their interaction with edge spin-split (magnetically ordered) states. The preservation of peripheral p-electronic states of the nanographites of free (dangling) s-orbitals of edge carbon atoms at saturation with chlorine was substantiated.     

Preparation of drug nanoparticles by co-grinding with cyclodextrin: formation mechanism and factors affecting nanoparticle formation

The aim of this study was to investigate the factors affecting the formation of pranlukast nanoparticle prepared by co-grinding with beta-cyclodextrin (beta-CD) and to elucidate the mechanism of nanoparticle formation. The effects of grinding time, moisture content and CD content on the nanoparticle formation were evaluated by means of UV quantitative determination and particle size analysis. High-resolution scanning electron microscopy (HRSEM) was employed to observe drug nanoparticles in the ground mixture. Nanoparticle recovery was higher than 95% for 2 : 1 molecular mixtures of beta-CD : pranlukast which had been ground for 10 min with moisture levels between 10 and 15%. While that of the 1 : 2 ground mixture prepared at 8% moisture level was only 57%. Nanoparticle recovery from beta-CD : pranlukast 2 : 1 mixture ground for 1 min was 2.5%, while that of the 10 min ground mixture was as high as 95%. HRSEM demonstrated that primary drug nanoparticles having a particle size around 50 nm were observed in the ground mixture. The grinding time, the moisture content, and the CD content had significant influences on the formation of drug nanoparticles. The CD matrix may form and stabilize primary particles by its interaction with the particle surface through water molecules. Primary nanoparticles existed in the ground mixture as 50 nm drug nanocrystallites.     

Mesoporous silica-coated hollow manganese oxide nanoparticles as positive T1 contrast agents for labeling and MRI tracking of adipose-derived mesenchymal stem cells

Mesoporous silica-coated hollow manganese oxide (HMnO@mSiO(2)) nanoparticles were developed as a novel T(1) magnetic resonance imaging (MRI) contrast agent. We hypothesized that the mesoporous structure of the nanoparticle shell enables optimal access of water molecules to the magnetic core, and consequently, an effective longitudinal (R(1)) relaxation enhancement of water protons, which value was measured to be 0.99 (mM(-1)s(-1)) at 11.7 T. Adipose-derived mesenchymal stem cells (MSCs) were efficiently labeled using electroporation, with much shorter T(1) values as compared to direct incubation without electroporation, which was also evidenced by signal enhancement on T(1)-weighted MR images in vitro. Intracranial grafting of HMnO@mSiO(2)-labeled MSCs enabled serial MR monitoring of cell transplants over 14 days. These novel nanoparticles may extend the arsenal of currently available nanoparticle MR contrast agents by providing positive contrast on T(1)-weighted images at high magnetic field strengths.     

Growth and characterization of highly branched nanostructures of magnetic nanoparticles

Magnetite nanoparticles of Fe(3)O(4) have been found to grow into large highly branched nanostructures including nanochains and highly branched nanotrees in the solid state through a postannealing process. By varying the preparation conditions such as annealing time and temperature, the nanostructures could be easily manipulated. Changing the starting concentration of the magnetic nanoparticle solution also caused significant changes of the nanoarchitectures. When the magnetic nanoparticle concentration is low, the nanoparticles formed straight rods mainly with an average diameter of 80 nm and a length of several microns. With increasing concentration of the nanoparticles, treelike structures began to form. With further increase of the concentration, well-ordered nanostructures with the appearance of snowflakes were generated. The driving force for the formation of the highly ordered nanostructures includes interaction between the nanoparticles and interaction through surface-capping molecules. This experiment demonstrates that novel nanostructures can be generated by self-assembly of magnetic nanoparticles under the solid state.     

Transfer of foreign genes by electroporation and their expression in mammalian cells

Expression of foreign genes transferred into mammalian cells by electroporation has been studied. The pX1TK gene, pSV2Neo gene and pUCEJ oncogene have been introduced into MLTK- cells and NIH/3T3 cells, respectively. Stable transformation transient expression of TK gene by MLTK- cells as well as stable and malignant transformation of NIH/3T3 cells have been obtained. Transient expression frequency is about 80% and stable transformation frequency is about 10(-4). Integration of foreign genes into the cellular genome was verified with molecular hybridization. Tumor development was observed after inoculation of transformed cells into nude mice.     

Effects of surface coordination chemistry on the magnetic properties of MnFe(2)O(4) spinel ferrite nanoparticles

To understand the influence of surface interactions upon the magnetic properties of magnetic nanoparticles, the surface of manganese ferrite, MnFe(2)O(4), nanoparticles have been systematically modified with a series of para-substituted benzoic acid ligands (HOOC-C(6)H(4)-R; R = H, CH(3), Cl, NO(2), OH) and substituted benzene ligands (Y-C(6)H(5), Y = COOH, SH, NH(2), OH, SO(3)H). The coercivity of magnetic nanoparticles decreases up to almost 50% upon the coordination of the ligands on the nanoparticle surface, whereas the saturation magnetization has increased. The percentage coercivity decrease of the modified nanoparticles with respect to the native nanoparticles strongly correlates with the crystal field splitting energy (CFSE) Delta evoked by the coordination ligands. The ligand inducing largest CFSE results in the strongest effect on the coercivity of magnetic nanoparticles. The change in magnetic properties of nanoparticles also correlates with the specific coordinating functional group bound onto the nanoparticle surface. The correlations suggest the decrease in spin-orbital couplings and surface anisotropy of magnetic nanoparticles due to the surface coordination. Such surface effects clearly show the dependence on the size of nanoparticles.     

High-density assembly of gold nanoparticles on multiwalled carbon nanotubes using 1-pyrenemethylamine as interlinker

In this article, we describe the formation of carbon nanotube (CNT)-gold nanoparticle composites in aqueous solution using 1-pyrenemethylamine (Py-CH2NH2) as the interlinker. The alkylamine substituent of 1-pyrenemethylamine binds to a gold nanoparticle, while the pyrene chromophore is noncovalently attached to the sidewall of a carbon nanotube via pi-pi stacking interaction. Using this strategy, gold nanoparticles with diameters of 2-4 nm can be densely assembled on the sidewalls of multiwalled carbon nanotubes. The formation of functionalized gold nanoparticles and CNT-Au nanoparticle composites was followed by UV-vis absorption and luminescence spectroscopy. After functionalization of gold nanoparticles with 1-pyrenemethylamine, the distinct absorption vibronic structure of the pyrene chromophore was greatly perturbed and its absorbance value was decreased. There was also a corresponding red shift of the surface plasmon resonance (SPR) absorption band of the gold nanoparticles after surface modification from 508 to 556 nm due to interparticle plasmon coupling. Further reduction of the pyrene chromophore absorbance was observed upon formation of the CNT-Au nanoparticle composites. The photoluminescence of 1-pyrenemethylamine was largely quenched after attaching to gold nanoparticles; formation of the CNT-Au nanoparticle composites further lowered its emission intensity. The pyrene fluoroprobe also sensed a relatively nonpolar environment after its attachment to the nanotube surface. The present approach to forming high-density deposition of gold nanoparticles on the surface of multiwalled carbon nanotubes can be extended to other molecules with similar structures such as N-(1-naphthyl)ethylenediamine and phenethylamine, demonstrating the generality of this strategy for making CNT-Au nanostructure composites.     

Selective Control of Cell Activity with Hydrophilic Polymer‐Covered Cationic Nanoparticles

Cationic polymers exhibit high cytotoxicity via strong interaction with cell membranes. To reduce cell membrane damage, a hydrophilic polymer is introduced to the cationic nanoparticle surface. The hydrophilic polymer coating of cationic nanoparticles resulted in a nearly neutral nanoparticle. These particles are applied to mouse fibroblast (3T3) and human cervical adenocarcinoma (Hela) cells. Interestingly, nanoparticles with a long cationic segment decrease cell activity regardless of cell type, while those with a short segment only affect 3T3 cell activity at lower concentrations less than 500 µg mL^?1. Most nanoparticles are located inside 3T3 cells but on the cell membrane of Hela cells. The short cationic nanoparticle shows negligible cell membrane damage despite its high accumulation on Hela cell membranes. Cell activity changed by hydrophilic polymer‐coated cationic nanoparticles is caused by incorporated nanoparticle accumulation in the cells, not cell membrane damage. To suppress the cytotoxicity from the cationic polymer, cationic nanoparticle needs to completely cover with hydrophilic polymer so as not to exhibit the cationic effect and applies to cell with low concentrations to reduce the nonselective cytotoxicity from the cationic polymer.     

Ultrasensitive Fluorescence Polarization Aptasensors Based on Exonuclease Signal Amplification and Polystyrene Nanoparticle Amplification

Here, we combine T7 exonuclease (T7 Exo) signal amplification and polystyrene nanoparticle (PS NP) amplification to develop novel fluorescence polarization (FP) aptasensors. The binding of a target/open aptamer hairpin complex or a target/single‐stranded aptamer complex to dye‐labeled DNA bound to PS NPs, or the self‐assembly of two aptamer subunits (one of them labeled with a dye) into a target/aptamer complex on PS NPs leads to the cyclic T7 Exo‐catalyzed digestion of the dye‐labeled DNA or the dye‐labeled aptamer subunit. This results in a substantial decrease in the FP value for the amplified sensing process. Our newly developed aptasensors exhibit a sensitivity five orders of magnitude higher than that of traditional homogeneous aptasensors and a high specificity for the target molecules. These distinct advantages of our proposed assay protocol make it a generic platform for the design of amplified aptasensors for ultrasensitive detection of various target molecules.     

Dithiol-mediated incorporation of CdS nanoparticles from reverse micellar system into Zn-doped SBA-15 mesoporous silica and their photocatalytic properties

CdS nanoparticles, as prepared in reverse micellar systems, were incorporated into alkanedithiol-modified Zn-doped SBA-15 mesoporous silica (dtz.sbnd;ZnSBA-15; pore diameter, ca. 4 nm), which were themselves prepared via hydrolysis of tetraethylorthosilicate (TEOS) in the presence of Zn(NO(3))(2) and triblock copolymer, as a nonsurfactant template and pore-forming agent, followed by contact with dithiol molecules. A particle-sieving effect for the dtz.sbnd;ZnSBA-15 was observed, in that the incorporation of the nanoparticles was remarkably decreased with increasing the nanoparticle size. The resulting CdSz.sbnd;ZnSBA-15 composite was then used as photocatalysts for the generation of H(2) from 2-propanol aqueous solution. Under UV irradiation (lambda>300 nm), a high photocatalytic activity was observed for this composite material. This is effected by electron transfer from the photoexcited ZnS (dithiol-bonded Zn on SBA-15) to CdS nanoparticles. The photocatalytic activity is increased with a decrease in the number of methylene groups in the dithiol molecules, according to the rank order 1,10-decanedithiol < 1,6-hexanedithiol < 1,2-ethanedithiol.     

Hemoprotein bioconjugates of gold and silver nanoparticles and gold nanorods: structure-function correlations

Bioconjugates of the hemoproteins, myoglobin, and hemoglobin have been synthesized by their adsorption on spherical gold and silver nanoparticles and gold nanorods. The adsorption of hemoproteins on the nanoparticle surface was confirmed by their molecular ion signatures in matrix assisted laser desorption ionization mass spectrometry and specific Raman features of the prosthetic heme b units. High-resolution transmission electron microscopy (HRTEM) and UV-visible spectroscopy showed that the particles retain their morphology and show aggregation only in the case of silver. The binding of azide ion to the Fe(III) center of the prosthetic heme b moiety caused a red shift of the Soret band, both in the case of the bioconjugates and in free hemoproteins. This was further confirmed by the characteristic signature at 2050 cm-1 in the Fourier-transform infrared spectra, which corresponds to the asymmetric stretching of the Fe(III) bound azide. The retention of the chemical behavior of the prosthetic heme group after adsorption on the nanoparticle is interesting due to its implications in nanoparticle supported enzyme catalysis. The absence of morphology changes after the reaction of bioconjugates with azide ion observed in HRTEM studies implies the stability of nanoparticles under the reaction conditions. All these studies indicate the retention of protein structure after adsorption on the nanoparticle surface.     

Atomistic simulations of calcite nanoparticles and their interaction with water

Molecular dynamics (MD) simulations have been used to study the stability of calcite nanoparticles ranging in size from 18 to 324 f.u., both in vacuo and in the presence of explicit water molecules. In vacuo, the smallest particles become highly disordered during the MD simulation due to rotation and translation of the undercoordinated CO(3) (2-) anions at the edges of the particles. As the nanoparticle size increases, the influence of the fully coordinated bulk ions begins to dominate and long-range order is seen both in the Ca-C pair distribution functions and in the degree of rotational order of the CO(3) (2-) anions. However, when explicit water is added to the system, the molecules in the first hydration layer complete the coordination shell of the surface ions, preserving structural order even in the smallest of the nanoparticles. Close to particle surface, the structure of the water itself shows features similar to those seen close to planar periodic (1014) surfaces, although the molecules are far less tightly bound.     

Investigation of the hydration of nonfouling material poly(ethylene glycol) by low-field nuclear magnetic resonance

The strong surface hydration layer of nonfouling materials plays a key role in their resistance to nonspecific protein adsorption. Poly(ethylene glycol) (PEG) is an effective example of materials that can resist nonspecific protein adsorption and cell adhesion. Thus, the strong interaction between water molecules and PEG was investigated through each T(2) component in water/PEG mixtures using multiexponential inversion of T(2) relaxation time measured by the Carr-Purcell-Meiboom-Gill (CPMG) sequence of low-field nuclear magnetic resonance (LF-NMR). Results show that about one water molecule is tightly bound with one ethylene glycol (EG) unit, and additional water molecules over 1:1 ratio mainly swell the PEG matrix and are not tightly bound with PEG. This result was also supported by the endothermic behavior of water/PEG mixtures measured by differential scanning calorimetry (DSC). It is believed that the method developed could be also applied to investigate various interactions between macromolecules and other small molecules without using deuterium samples, which might open a novel route to quantitatively measure guest-host interactions in the future.     

Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers: from micelles to vesicles

We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.