[Show abstract][Hide abstract] ABSTRACT: Aimed at utilizing high-magnetization nanospheres for magnetic field-enhanced cellular labeling, core-shell structured sandwich-like magnetic mesoporous silica nanospheres were developed. While the magnetite cluster core can provide a high magnetic response for overcoming Brownian motion in cell culture media, the layered silica shell facilitates an efficient fluorescent dye labeling. However, the problem of particle aggregation in cell media, which is strongly enhanced under a magnetic field, significantly impeded the uptake by cells, resulting in difficulties in the precise analysis of the degree of particle internalization by fluorescence-based techniques (flow cytometry and confocal microscopy). To overcome this, reflection-based assessment was employed. Further, emphasis was put on utilizing the unique role of surface-hyperbranched polyethylenimine (PEI) in efficient prevention of particle aggregation prior to cell internalization in the presence of an external magnetic field. The interparticle attraction forces originating from magnetic dipole-dipole interactions are hereby balanced by the steric and electrostatic repulsion forces provided by the PEI functionalization, which leads to dispersed nanospheres in cell culture media during the magnetic-field induced cell labeling. As a consequence, PEI functionalization and the presence of the magnetic field synergistically enhanced the efficiency of MRI-fluorescence dual-mode labeling for cellular tracking.
[Show abstract][Hide abstract] ABSTRACT: Plasmonic core-shell Au@SiO2 nanoparticles have previously been shown to enhance the performance of dye-sensitized solar cells (DSSCs). A thin silica coating can provide a better stability during thermal processing and chemical stability to survive the corrosive electrolyte used in DSSCs. However, the thickness and completeness of the silica shell has proven crucial for the performance of the plasmonic particles and is largely controlled by the linking chemistry between the gold core and silica shell. We have evaluated four different silica coating procedures of ∼15nm gold nanoparticles for usage in DSSCs. The chemical stability of these core-shell nanoparticles was assessed by dispersing the particles in iodide/triiodide electrolyte solution and the thermal stability by heating the particles up to 500°C. In order to maintain stable gold cores a complete silica coating was required, which was best obtained by using a mercaptosilane as a linker. In situ TEM characterization indicated that the heating process only had minor effects on the core-shell particles. The final step was to evaluate how the stable Au@SiO2 nanoparticles were influencing a real DSSC device when mixed into the TiO2 photoanode. The plasmon-incorporated DSSCs showed a ∼10% increase in efficiency compared to devices without core-shell nanoparticles.
Journal of Colloid and Interface Science 12/2013; · 3.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent advances within materials science and its interdisciplinary applications in biomedicine have emphasized the potential of using a single multifunctional composite material for concurrent drug delivery and biomedical imaging. Here we present a novel composite material consisting of a photoluminescent nanodiamond (ND) core with a porous silica (SiO2) shell. This novel multifunctional probe serves as an alternative nanomaterial to address the existing problems with delivery and subsequent tracing of the particles. Whereas the unique optical properties of ND allows for long-term live cell imaging and tracking of cellular processes, mesoporous silica nanoparticles (MSNs) have proven to be efficient drug carriers. The advantages of both ND and MSNs were hereby integrated in the new composite material, ND@MSN. The optical properties provided by the ND core rendered the nanocomposite suitable for microscopy imaging in fluorescence and reflectance mode, as well as super-resolution microscopy as a STED label; whereas the porous silica coating provided efficient intracellular delivery capacity, especially in surface-functionalized form. This study serves as a demonstration how this novel nanomaterial can be exploited for both bioimaging and drug delivery for future theranostic applications.
[Show abstract][Hide abstract] ABSTRACT: A multifunctional core-shell nanocomposite platform consisting of a photoluminescent nanodiamond (ND) core with uniform porous silica coatings is presented. This design intended for drug delivery applications allows simultaneous stable fluorescent imaging with high loading capacity of bioactive molecules. Despite irregularly shaped starting cores, well-dispersed and uniformly shaped nanocomposite particles can be produced. Moreover, after optimization of the silica source-to-diamond ratio, the thickness of the porous layer can be tuned by adjusting the ethanol amount, allowing rational nanoparticle size control. The ND key property, photoluminescence, is not quenched regardless of coating with thick silica layers. The high loading capacity for incorporation of active agents, provided by the introduced porous layer, is demonstrated by adsorption of a hydrophobic model drug into the composite particles. The loading degree, as compared to pure ND, increased with two orders of magnitude from 1wt-% for the
[Show abstract][Hide abstract] ABSTRACT: Strongly luminescent silver nanoclusters with tunable emission are directly synthesized in organic polar and apolar solvents. We show that an amphiphilic polystyrene-block-poly(methacrylic acid) block copolymer can be universally used as their support medium. A remarkable similarity in spectroscopic properties is observed between these clusters and charge-transfer organic dyes.
[Show abstract][Hide abstract] ABSTRACT: Silver nanoclusters composed of only a few metal atoms present appealing properties such as fluorescence. We have previously reported on aqueous solutions of this fluorophore using poly(methacrylic acid) as scaffold and their sensing properties. Here we report on the preparation of organic solutions of fluorescent silver nanoclusters by quantitative transfer from aqueous solution to an immiscible organic solvent. The fluorescent silver nanoclusters in the organic phase present enhanced emission properties and increased purity, which may expand the range of applications of this promising fluorophore.
[Show abstract][Hide abstract] ABSTRACT: The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O2 reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies.
[Show abstract][Hide abstract] ABSTRACT: Colorful clusters: Silver nanoclusters consisting of only a few atoms exhibit large chemical-environment-responsive shifts of their optical absorption and emission bands, that is, large solvatochromism (see picture). The photophysical characteristics and electrochemiluminescence of the Ag clusters give them remarkable advantages over larger nanoparticles in applications such as molecular sensing.
Angewandte Chemie International Edition 03/2009; 48(12):2122-5. · 11.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report a simple memory device in which the fullerene-derivative [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) mixed with inert polystyrene (PS) matrix is sandwiched between two aluminum (Al) electrodes. Transmission electron microscopy (TEM) images of PCBM:PS films showed well controlled morphology without forming any aggregates at low weight percentages (<10 wt%) of PCBM in PS. Energy dispersive x-ray spectroscopy (EDX) analysis of the device cross-sections indicated that the thermal evaporation of the Al electrodes did not lead to the inclusion of Al metal nanoparticles into the active PCBM:PS film. Above a threshold voltage of <3 V, independent of thickness, a consistent negative differential resistance (NDR) is observed in devices in the thickness range from 200 to 350 nm made from solutions with 4-10 wt% of PCBM in PS. We found that the threshold voltage (V(th)) for switching from the high-impedance state to the low-impedance state, the voltage at maximum current density (V(max)) and the voltage at minimum current density (V(min)) in the NDR regime are constant within this thickness range. The current density ratio at V(max) and V(min) is more than or equal to 10, increasing with thickness. Furthermore, the current density is exponentially dependent on the longest tunneling jump between two PCBM molecules, suggesting a tunneling mechanism between individual PCBM molecules. This is further supported with temperature independent NDR down to 240 K.
[Show abstract][Hide abstract] ABSTRACT: Preparation of L-leucine nanoparticles by a process based on physical vapor deposition has been presented. In an aerosol flow reactor method, aqueous L-leucine droplets were first dried followed by the sublimation of L-leucine to produce vapor that upon vapor deposition resulted in L-leucine nanoparticles with size ranging from 40 to 200 nm. Onset temperature for the sublimation of L-leucine at concentrations from 0.02 to increased from 135 to , respectively. The formation of nanoparticles was initiated in three different ways: (i) via droplet drying, (ii) via heterogeneous nucleation of L-leucine vapor on solid L-leucine particles, and (iii) via homogeneous nucleation of L-leucine vapor to form new-born nanoparticles. Consequently, the saturation conditions of L-leucine vapor in the reactor determined the resulting particle size, size distribution and number concentration, those depending very much on nucleation mode. In general, the both nucleation modes produced narrow size distributions, that is, geometric standard deviation (GSD) was <1.8 although the number concentration increased with the increased amount of L-leucine vapor. Upon desublimation and vapor deposition, L-leucine formed leafy crystals whose size was the largest when produced from the heated section at the vicinity of the onset temperature and the smallest far above the onset temperature. All the particles prepared in the conditions (i)–(iii) were crystalline. However, X-ray diffraction analysis showed preferential direction for crystal growth according to the way of particle formation.
[Show abstract][Hide abstract] ABSTRACT: Amphiphilic thermally responsive gold nanoparticles have been prepared by protecting the particles with both polystyrene, PS, and poly(N-isopropylacrylamide), PNIPAM, chains. Particles form a monolayer on a water surface in a Langmuir trough, and according to in situ spectroscopic measurements, the surface plasmon resonance, SPR, band undergoes a blue-shift during the monolayer compression. The compression-induced blue-shift is related to a change in the conformation of tethered PNIPAM chains; the phenomenon is discussed on the basis of Mie-Drude theory. In contrast, a red-shift in the SPR of the multilayers of the same nanoparticles transferred at different temperatures has been observed with increasing the deposition cycle, attributed to the presence of a weak interparticle coupling in the multilayer.
[Show abstract][Hide abstract] ABSTRACT: Two techniques for crystallographic image processing are introduced aiming at determining the crystal structure and defect
structure respectively at atomic resolution. The techniques are based on a simple image contrast theory that extends the weak
object approximation to thicker crystals. Dynamical effect and other intensity distortions are properly corrected. Examples
of applications to crystal structure and defect structure are given.
[Show abstract][Hide abstract] ABSTRACT: Poly- and nearly monocrystalline hematite particles having diameters of around 2 and 0.1 m, respectively, were prepared by the gel-sol method and coated with a uniform silica layer by the sol-gel method. The core in the silica shell was reduced to iron without agglomerate formation between the particles by using a hydrogen stream. The microstructure and morphology of these cores and the silica layers were examined by high-resolution transmission electron microscopy, and electron and X-ray diffraction analysis. In hematite particles, around 2 m in diameter, the reduced products were mostly -Fe, but partially magnetite. In hematite particles, around 0.1 m in diameter, only -Fe was observed. Most of the raw hematite and iron particles produced were monocrystalline, and part of core grew hexagonal prism-shaped monocrystalline particles. In the case of the growth of a crystal to a hexagonal prism, a nanometer-scaled space at the interface between the iron crystal core and the silica layer was discovered.
[Show abstract][Hide abstract] ABSTRACT: Two types of amphiphilic gold nanoparticles (AuNP-1 and -2) grafted with a mixture of poly(N-isopropylacrylamide) (PNIPAM) and polystyrene (PS) chains in two different compositions have been successfully prepared with the “grafting-to” method in a homogeneous THF phase. These AuNPs were thoroughly characterized by FTIR, 1H NMR, UV−vis, high-resolution transmission electron microscopy, thermogravimetric analysis, and dynamic light scattering to determine the total number of polymer chains bound to the gold nanoparticles, the ratio between PNIPAM and PS chains, and the size of the gold core. Langmuir monolayer experiments at the air−water interface of the two types of AuNPs revealed different compression isotherms of the surface pressure vs particle area (π−A curve) conducted at 20 °C. These amphiphilic gold nanoparticles can be regarded as analogues of amphiphilic diblock copolymers at the air−water interface. The compression isotherm of AuNP-2 with a PNIPAM:PS ratio of 2:1 showed several characteristic regions that can be attributed to the polymer conformational transitions from the pancake, the pancake to brush transition, to the brush. However, the monolayer of AuNP-1, with a ratio of 5:1 of PNIPAM:PS, never reaches a brush stage but showed an extension of the pseudoplateau region upon compression. These differences may be due to the more hydrophilic nature and the more stretched PNIPAM chains. Furthermore, the sessile drop contact angle measurements, conducted at room temperature on both upper and lower surfaces of the AuNP-2 monolayer transferred at 35 mN/m onto either hydrophilic or hydrophobic substrates, are slightly different, 82 ± 2° and 77 ± 2°, respectively. After comparing with the literature data of the contact angles of water on either the pure PS film or the PNIPAM brush, we concluded that the chemically different PNIPAM and PS chains grafted on the surface of the gold core tend to be phase-separated.
[Show abstract][Hide abstract] ABSTRACT: This article reports the use of the scanning electrochemical microscope (SECM) to investigate the electronic properties of Langmuir monolayers of alkane thiol protected gold nanocrystals (NCs). A substantial increase in monolayer conductivity upon mechanical compression of the Au NC monolayer is reported for the first time. This may be the room temperature signature of the insulator to metal transition previously reported for comparable silver NC monolayers. Factors influencing the conductivity of the monolayer NC array are discussed.
Journal of the American Chemical Society 07/2004; 126(22):7126-32. · 10.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The preparation of poly(N-isopropylacrylamide)-monolayer-protected clusters (PNIPAM-MPC) of gold nanoparticles was carried out in a homogeneous phase using three methods, in which three types of PNIPAM ligands were employed. The first type was comprised of PNIPAMs with narrow molar mass distributions, synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerization and thus bearing a dithiobenzoate at the chain end. These polymers were used directly to passivate the gold nanoparticles upon the Schiffrin reaction in a one-pot synthesis. The second type of ligand was derived from the first one through hydrazinolysis, and they therefore contained a thiol end group. The third type of ligand was PNIPAMs obtained through conventional radical polymerization, postmodified to contain thiol end groups. The PNIPAM-MPCs were characterized by high-resolution transmission electron microscopy, UV−vis spectroscopy, and dynamic light scattering. The one-pot synthesis utilizing the ligands of the first type turned out to be a simple and facile method compared with the other two ways, with which the size of the gold nanoparticles can be easily manipulated mainly by adjusting the molar ratios of PNIPAM/HAuCl4. PNIPAM is a more efficient ligand to stabilize the gold nanoparticles in water and in organic solvents than alkanethiols. The surface density of PNIPAM chains ranged from 1.8 to 2.5 chain/nm2, which is much lower than that typical for alkanethiols. The thickness of a PNIPAM monolayer bound to the gold core is somewhat larger than the size of the random coil of the corresponding free PNIPAM in aqueous solution, which suggests that the conformation of a PNIPAM chain bound to the gold core is extended.
[Show abstract][Hide abstract] ABSTRACT: This work focuses on the synthesis method of Au nanoparticles protected by a well-defined polymer monolayer. Nanosized, spherical gold clusters coated with poly(N-isopropylacrylamide) (PNIPA) grafts were prepared by controlled radical polymerization. The polymerization of N-isopropylacrylamide was initiated from the surface of a gold nanoparticle modified with 4-cyanopentanoic acid dithiobenzoate for a reversible-addition-fragmentation chain-transfer polymerization. The number mean diameter of the Au core was 3.2 nm as observed by high-resolution transmission electron microscopy. The molar mass of the PNIPA ligand was 21000 g/mol by gel permeation chromatography. The changes in the surface plasmon of gold were investigated in different media, and as functions of particle concentration, as well as of temperature in aqueous solutions. The particles were soluble at least slightly in water, forming aggregates. The area and the maximum wavelength of the plasmon band in water decreased with dilution and increasing temperature. During the collapse of PNIPA ligands the surroundings of the gold surface change from hydrophilic to hydrophobic.