Silica coated hard-magnetic strontium hexaferrite nanoparticles

Stable colloids of hard magnetic particles are newly developed and very promising materials. Surface functionalization of these particles remains challenging because the particles tend to aggregate during reaction due to strong magnetic interactions. Herein we report on a synthesis of strontium hexaferrite hard magnetic nanoparticles coated with silica by hydrolysis of tetraethoxysilane. As a source of hexaferrite we used stable colloid of plate-like nanoparticles with mean diameter of 40 nm and thickness of 5 nm, which were prepared by a glass-ceramic process. We have shown that to successfully coat each hexaferrite particle individually the hydrolysis conditions should provide heterogeneous nucleation of silica with rate higher than the aggregation rate of the colloidal nanoparticles. The resulting materials represent single crystal hexaferrite cores wrapped in silica shell with mean thickness of 18 and 23 nm depending on synthesis conditions. The obtained core-shell particles can be easily dispersed as stable aqueous colloids. The materials can be used as magnetic sorbents or nanocontainers and, furthermore, they are very promising colloidal building blocks for various magnetically assembled nanostructures.     

Determination of the potency of hexyl‐ciprofloxacin molecules that interact with gold nanoparticles in a reversible manner

This work determined the potency of hexyl‐ciprofloxacin molecules that reversibly interact with gold nanoparticles (AuNPs) passivated with 11‐mercaptoundecanoic acid (MUA) on Escherichia coli cells. For this, partition of modified antibiotic between different compartments of the gold colloid was determined using analytical techniques. First, concentration of hexyl‐ciprofloxacin was determined in the continuous phase of the colloid. Subsequently, the colloid was exposed to a volume of organic immiscible solvent and concentration of the transferred molecules was determined in the organic phase. Comparison of the amount of hexyl‐ciprofloxacin in each phase revealed that interaction between molecules and nanoparticles was reversible. Later, this work determined the potency of a population of hexyl‐ciprofloxacin molecules contained in a volume of the colloid, and the potency of other population of molecules that only interact with the continuous phase of the colloid. The absolute difference between these two values was proportional to the potency of a number of molecules that interact with the nanoparticles of the colloid.Inspec keywords: organic compounds, nanoparticles, gold, colloids, microorganisms, molecular biophysics, drug delivery systems, nanomedicineOther keywords: continuous phase, hexyl‐ciprofloxacin molecules, gold nanoparticles, gold colloid, 11‐mercaptoundecanoic acid, Escherichia coli cells, modified antibiotics, RP‐HPLC, organic immiscible solvent, reversible interaction, Au     

Bovine serum albumins (BSA) induced aggregation and separation of gold colloid nanoparticles

Plasmonic absorption spectrometry has been applied to study the bovine serum albumins (BSA) induced aggregation and separation of gold colloid nanoparticles. When the concentration of the BSA is relative low in the gold colloid, the binding molecules only lead to the dispersive gold nanoparticles aggregate. The formation of the gold nanochain leads to the absorption peak red shift rapidly, and the corresponding limit of the detection can reach to 20 ng/mL. As the concentration of the BSA is too great, the increasing thickness of the coated BSA layer results in the separation of the gold nanochain and then leads to the blue shift of the plasmonic absorption. The physical mechanism based on quasi-static approximation and coupled dipole method has been investigated to illuminate the aggregation dependent plasmonic shifting of bio-coated gold colloids. Gold nanoparticles with larger size and coated by a thin dielectric layer present better potential for biosensing based on the plasmonic response of binding molecules induced aggregation.     

Gold/palladium and silver/palladium colloids as novel metallic substrates for surface-enhanced Raman scattering

New surface-enhanced Raman scattering (SERS) substrates, composed of gold or silver colloidal nanoparticles doped with palladium, were prepared. These novel colloids are stable and maintain a satisfactory SERS efficiency, even after long aging. The interest in doping the coinage metal nanoparticles with palladium is due to the well-known catalytic activity of this metal. Transmission electron microscopy (TEM) and ultraviolet-visible absorption spectroscopy were used to characterize the shape and size of the metal particles. It was found that these bimetallic colloidal nanoparticles have a core-shell structure, with gold or silver coated with palladium clusters.     

肿瘤靶向纳米四氧化三铁造影剂的制备及其磁共振成像应用

环氧氯丙烷交联法制备交联葡聚糖与多肽偶联的肿瘤新生血管靶向的纳米Fe3O4造影剂,考察其体内肿瘤靶向性并进行磁共振成像试验。以共沉淀法制备6～8nm的Fe3O4粒子,采用油酸钠和葡聚糖二次包覆,用环氧氯丙烷使葡聚糖交联并与靶向多肽偶联,进行了肿瘤细胞结合实验和荷瘤动物磁共振成像实验。结果表明,包覆后纳米Fe3O4复合粒子为20～30nm,水动力学粒径小于80nm,仍表现为超顺磁性;葡聚糖交联的时间4～8h,造影剂在体内血浆半衰期从2.8h延长到6.2h;主要通过肝脏和肾脏代谢。与无靶的比较,靶向多肽偶联后与肿瘤细胞特异性结合能力提高了10～30倍,MR成像信号密度是无靶的3.68倍。     

Immobilization of gold nanoparticles on solid supports utilizing DNA hybridization

Self-organization of colloidal metal nanoparticles into micro- and nanostructured assemblies is currently of tremendous interest promising to find new size- and structure-dependent physical properties. Owing to its unique recognition capabilities and physicochemical stability, DNA can be used as a molecular linker for gold nanoparticles and is a promising construction material for their precise spatial positioning. Due to the enormous specificity of nucleic acid hybridization, the site-specific immobilization of DNA-functionalized gold colloids (1–40 nm) to solid supports, previously functionalized with a complementary DNA array, allows the fabrication of novel nanostructured surface architectures. Scanning force microscopy (SFM), used to characterize the intermediate steps of the DNA-directed immobilization (DDI) on a gold substrate, provides initial insight into the specificity and efficiency of this technique.     

Reversible tuning of plasmon coupling in gold nanoparticle chains using ultrathin responsive polymer film

We demonstrate large and reversible tuning of plasmonic properties of gold nanoparticles mediated by the reversible breaking and making of linear and branched chains of gold nanoparticles adsorbed on an ultrathin (1 nm) responsive polymer film. Atomic force microscopy revealed that at pH below the isoelectric point of the polybase (extended state of the polymer chains), gold nanoparticles adsorbed on the polymer layer existed primarily as individual nanoparticles. On the other hand, at higher pH, the polymer chains transition from coil to globule (collapsed) state, resulting in the formation of linear and branched chains with strong interparticle plasmon coupling. Reversible aggregation of the nanoparticles resulted in large and reversible change in the optical properties of the metal nanostructure assemblies. In particular, we observed a large redistribution of the intensity between the individual and coupled plasmon bands and a large shift (nearly 95 nm) in the coupled plasmon band with change in pH. Large tunability of plasmonic properties of the metal nanostructure chains reported here is believed to be caused by the chain aggregates of nanoparticles and un-cross-linked state of the adsorbed polymer enabling large changes in polymer chain conformation.     

Finite frequency f-sum rule for assessment of number density of gold nanoparticles (AuNPs) and Kramers-Kronig relation for refractive index of colloidal gold

Absorption spectra from colloids containing different concentrations of spherical gold nanoparticles in water were measured with a spectrophotometer. The absorption spectra were used to calculate the number density of nanoparticles (NPs) with the aid of an unconventional finite spectral band f-sum rule applied for gold colloid. Good correlation between the number density of dispersion electrons, obtained from the f-sum rule, and the number density of nanoparticles was found. The effective absolute refractive index of the gold colloid was obtained with the aid of a singly subtractive Kramers-Kronig relation, and in addition the refractive index change due to the nanoparticles was obtained with the aid of a conventional Kramers-Kronig relation. Such optical properties are valuable in studies of light interaction with nanoparticles.     

Third-harmonic generation from single gold nanoparticles

We report the first observation of third-harmonic signals from individual gold colloids down to 40 nm diameter. Excited with 1-ps pulses at 1500 nm, the colloids generate 500-nm light, close to the plasmon resonance. The third-harmonic intensity varies as the square of the colloid surface area. Although weak, the third-harmonic signals of gold labels as small as 15 nm in diameter are expected to be accessible with 100-fs pulses. They could be used in microscopy for single-biomolecule tracking.     

Size characterization of bentonite colloids by different methods

The size and shape of colloids released from a natural bentonite into a low-mineralized groundwater are investigated using various colloid characterization methods. For the applied methods such as atomic force microscopy (AFM), laser-induced breakdown detection (UBD), photon correlation spectroscopy (PCS), and flow field-flow fractionation coupled to ICP-mass spectrometric detection (FFFF-ICPMS), the respective raw size data have to be corrected in order to consider chemical composition and shape of the colloids as well as instrumental artifacts. Noncontact mode AFM of the bentonite colloids shows disklike shapes of stacked smectite platelets with a mean height-to-diameter proportion (aspect ratio) of approximately 1/10. A broad particle number size distribution is determined by image processing with a mean particle diameter of 73 nm. In agreement with AFM, a broad size distribution is also found by PCS and FFFF-ICPMS. Likewise, mean particle sizes found by LIBD (67 +/- 13 nm) and FFFF-ICPMS (maximum in the number size distribution, approximately 70 nm) are in fair agreement with the AFM data. Somewhathigher values are obtained by PCS, where mean particle diameters of the intensity-weighted size distributions of larger than 200 nm are found (depending on the algorithm used for data processing). The influence of the disklike particle shape on the results of the individual methods is discussed. As a conclusion, the application of different colloid characterization methods is a prerequisite to get complementary information about colloid size and shape, which is essential for the understanding of natural colloidal systems.     

Magnetically triggered clustering of biotinylated iron oxide nanoparticles in the presence of streptavidinylated enzymes

This work deals with the production and characterization of water-compatible, iron oxide based nanoparticles covered with functional poly(ethylene glycol) (PEG)-biotin surface groups (SPIO-PEG-biotin). Synthesis of the functionalized colloids occurred by incubating the oleate coated particles used as precursor magnetic fluid with anionic liposomes containing 14?mol% of a phospholipid-PEG-biotin conjugate. The latter was prepared by coupling dimyristoylphosphatidylethanolamine (DC(14:0)PE) to activated α-biotinylamido-ω -N-hydroxy-succinimidcarbonyl-PEG (NHS-PEG-biotin). Physical characterization of the oleate and PEG-biotin iron oxide nanocolloids revealed that they appear as colloidal stable clusters with a hydrodynamic diameter of 160?nm and zeta potentials of -?39?mV (oleate coated particles) and -?14?mV (PEG-biotin covered particles), respectively, as measured by light scattering techniques. Superconducting quantum interference device (SQUID) measurements revealed specific saturation magnetizations of 62-73?emu?g(-1) Fe(3)O(4) and no hysteresis was observed at 300?K. MR relaxometry at 3?T revealed very high r(2) relaxivities and moderately high r(1) values. Thus, both nanocolloids can be classified as small, superparamagnetic, negative MR contrast agents. The capacity to functionalize the particles was illustrated by binding streptavidin alkaline phosphatase (SAP). It was found, however, that these complexes become highly aggregated after capturing them on the magnetic filter device during high-gradient magnetophoresis, thereby reducing the accessibility of the SAP.     

Synthesis and agglomeration of gold nanoparticles in reverse micelles

Reverse micelles prepared in the system water, sodium bis-(2-ethylhexyl) sulfoccinate (AOT), and isooctane were investigated as a templating system for the production of gold nanoparticles from Au(III) and the reducing agent sulfite. A core-shell Mie model was used to describe the optical properties of gold nanoparticles in the reverse micelles. Dynamic light scattering of gold colloids in aqueous media and in reverse micelle solution indicated agglomeration of micelles containing particles. This was verified theoretically with an analysis of the total interaction energy between pairs of particles as a function of particle size. The analysis indicated that particles larger than about 8?nm in diameter should reversibly flocculate. Transmission electron microscopy measurements of gold nanoparticles produced in our reverse micelles showed diameters of 8-10?nm. Evidence of cluster formation was also observed. Time-correlated UV-vis absorption measurements showed a red shift for the peak wavelength. This was interpreted as the result of multiple scattering and plasmon interaction between particles due to agglomeration of micelles with particles larger than 8?nm.     

Detection of gold nanoparticles using an immunoglobulin-coated piezoelectric sensor

Since the existence of nanoparticles in our environment has already attracted considerable attention due to their possible toxic impact on biological systems, the field detection of nanoparticles is becoming a technology that will be much in need. We have constructed a piezoelectric sensor with an antibody-coated electrode. The antiserum can bind gold nanoparticles with a high degree of selectivity and sensitivity. The biosensor thus constructed can detect 4, 5, or 6?nm gold nanoparticles (GNPs) depending on the coated antiserum. The sensitivity for the detection of 5?nm GNPs was 10.3 ± 0.9?ng?Hz(-1), with the low limit of detection at 5.5?ng. A quartz crystal microbalance (QCM) sensor was capable of detecting GNPs and other types of nanoparticle, such as ZnO, or Fe(3)O(4). The current study provides, for the first time, a platform for detecting nanoparticles in a convenient, economical manner.     

Association of radionuclides with the colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Associations of radionuclides with colloidal particles of various sizes, isolated from underground waters of the Lake Karachai contamination area, were studied. Analysis by photon correlation spectroscopy showed that the total content of colloidal matter in deeper horizons is higher by an order of magnitude than in near-surface horizons. The mean particle radius also increases with the depth. The major fraction of Pu, Am, and Cm is associated with colloids (40–90%). U and Np are associated with colloidal particles to a lesser extent (2–20%), which determines their higher migration mobility in underground waters. The amount of actinides associated with coarse colloidal particles of size from 450 to 200 nm is insignificant. A considerable fraction of actinides is in the deep-lying water (depth ≥40 m) is associated with colloidal particles of size from 200 to 50 nm. No more than 30% of Pu and Am in water of these horizons is associated with finer colloids (from 10 kDa to 50 nm). With approaching the surface, the amount of actinides in the fraction of nanometer-sized particles (50 nm-10 kDa) increases (to 50%).     

Development of an aggregation-based immunoassay for anti-protein A using gold nanoparticles

A unique, sensitive, and highly specific immunoassay system for antibodies using gold nanoparticles has been developed. The assay is based on the aggregation of gold nanoparticles that are coated with protein antigens in the presence of their corresponding antibodies. The aggregation of the gold nanoparticles results in an absorption change at 620 nm that is monitored using an absorption plate reader. To demonstrate the analytical capabilities of the new technique, monodispersed protein A-coated gold particles, averaging 10 nm in diameter, were used to determine the level of anti-protein A in serum samples. The effects of the pH, the temperature, and the concentration of protein A-coated gold nanoparticles on the sensitivity of the assay were investigated using transmission electron microscopy (TEM) and UV/vis absorption spectroscopy. A dynamic range of 2 orders of magnitude and a limit of detection of 1 microg/mL of anti-protein A were observed. The new technique could be used for fast, high-throughput screening of antibodies in clinical diagnostic applications.     

Visual sensing of proteins using gold nanoparticles coated with polyphenolic glycoside

Gold nanoparticles combined with a polyphenolic glycoside (α-glucosylrutin) were prepared and applied for the selective detection of proteins. Glucosylrutin was coated onto gold nanoparticles with a particle size of 40 nm, without aggregates and color changes. The glucosylrutin-coated gold surface was preferentially adsorbed with concanavalin A, which has specificity against glucosides and mannosides. When the glucosylrutin-coated gold nanoparticles were mixed with concanavalin A, the color of the dispersion changed from red to reddish violet. The level of chromatic change was dependent on the concentration of concanavalin A. When other proteins (bovine serum albumin and peanut agglutinin) were added to the dispersion, no color change was observed. The molecular recognition site for detection of concanavalin A was the glycoside moiety, because the catechin-coated gold nanoparticles have no function in the detection of concanavalin A. Urchin-shaped glucosylrutin-coated gold nanoparticles were also useful for the visual sensing of concanavalin A.     

Fabrication of nanoplasmonic arrays with square symmetry using spin-coating method

A spin-coating method was applied for the first time to prepare a colloid monolayer on the optical crossed gratings used as a template. Four polystyrene colloids of various nominal sizes and different surface charges were spin-coated on templates with periods matched to the particles size. Three types of coverage were described depending on the spin-coating parameters and particles type. The optimal coverage was obtained for all four particles sizes. A way of finding the right spin-coating parameters was proposed. The analysis of a coverage capability of polystyrene particles showed that neutral particles have the highest ability to order on the templates used. Large monolayered areas of ordered particles were used as a lithographic mask for generating a pattern of gold nanoparticles with a square symmetry. A few hundred square micrometers large, continuous and fully defect-free areas of gold nanoparticles were produced on the nearly entire surface of the templated substrates.     

Controlled aggregation of superparamagnetic iron oxide nanoparticles for the development of molecular magnetic resonance imaging probes

A method for synthesizing superparamagnetic iron oxide (SPIO) multi-nanoparticle aggregates as molecular magnetic resonance imaging (MRI) contrast agents is described. The approach utilizes organic acid/base interactions in the colloid to induce highly controllable nanoparticle aggregation. Monodisperse aggregates with diameters as large as 100?nm are synthesized by manipulating the interfacial surface chemistry of the SPIO nanoparticles in tetrahydrofuran solvent. Subsequent phospholipid micelle encapsulation yields micellar multi-SPIO (mmSPIO) aggregates with enhanced T(2) relaxivity (368.0?s(-1)?mmol(-1)?Fe) as compared to micellar single particle SPIO (302.0?s(-1)?mmol(-1)?Fe). mmSPIO conjugated to anti-CA125 monoclonal antibodies were incubated with ovarian carcinoma cell lines to demonstrate targeted in vitro molecular MRI, resulting in a?66% shortening in T(2) time for CA125 positive NIH:OVCAR-3 cells and a less than?3% change in T(2) time for CA125 negative SK-OV-3 cells. The controllable aggregation of mmSPIO shows potential for the development of molecular MRI contrast agents with optimal sizes for specific diagnostic imaging applications.     

The effect of gold colloid on the fluorescence spectrum from Safranine T: a physical mechanism based on resonance light scattering

The non-monotonic change of fluorescence intensity from Safranine T was observed experimentally by adding gold colloids to the Safranine T aqueous solution. Increasing the content of gold colloids leads to the fluorescence emission peak red shift and increases first and then decreases. We believe that one of the important reasons of the fluorescence changing and shifting is due to the resonance light scattering from gold nanoparticles which is stimulated by the fluorescence of Safranine T and is tunable by the shell thickness of the ST that coated around the gold particles.     

Electroless preparation of macroporous Cu thin film from large-scale-orderly colloid monolayer

A facile method to fabricate the highly ordered colloid monolayer of a large scale is demonstrated. The colloidal template involves the ordered array of ∼ 100 nm silica colloids functioned with 3-mercaptopropyltrimethoxysilane (MPTMS) by spin coating on the silicon wafer etched square pattern with an ∼ 100 nm depth. Based on the new nanostructure, highly ordered macroporous Cu thin film can be prepared from Pd nanoparticles-based electroless deposition. By the deposition time, the macroporous thin film of various thicknesses can be prepared. Additionally, the Cu film with (111) strong texture is deposited on the gold substrate of single crystalline (111) orientation.