Coated Au Nanoparticles Research Articles

Cheap, reliable, reusable, thermally and chemically stable fluorinated hexagonal boron nitride nanosheets coated Au nanoparticles substrate for surface enhanced Raman spectroscopy

In this study, multi-layered fluorinated hexagonal boron nitride nano-sheets (F-BN) coated gold-nanoparticles (AuNPs/glass) SERS-active substrate is presented. Thermal and chemical stabilities with reusability tests of F-BN/AuNPs/glass SERS-active substrate were performed. The AuNPs on glass substrate (AuNPs/glass) was first prepared by combining ion-sputtering technique with a rapid annealing treatment. Second step involved the spin coating of a thin film of F-BN as a shielding layer on AuNPs/glass substrate. It was seen that Raman performance of FBN/AuNPs/glass substrate is more stable and efficient as compared to bare AuNPs/glass substrate under strong chemical and oxidative environments. Moreover, outcome of cycle tests indicated that F-BN as a protecting layer, could recover the long-term stability of the bare AuNPs/glass SERS-active substrate. DFT based calculations were also performed and theory supported our experimental results that R6G on F-BN/glass has higher adsorption capability as compared to BN/glass. Consequently, our proposed multi-layered F-BN is found to be an excellent wrapping material on AuNPs/glass substrate for cost effective production and reliable fabrication of capable SERS. It is also useful for the detection of particular sensing molecules at high temperatures or in extreme acidic conditions that are too complicated to be analyzed by means of conventional SERS. Hence, our proposed method will promote the wider usage of functionalized BN/metal based SERS in multidisciplinary fields.

Background-Free Quantitative Surface Enhanced Raman Spectroscopy Analysis Using Core-Shell Nanoparticles with an Inherent Internal Standard.

Surface enhanced Raman spectroscopy (SERS) is an ultrasensitive label-free analytical technique that can provide unique chemical and structural fingerprint information. However, gaining reliable quantitative analysis with SERS remains a huge challenge because of poor reproducibility and the instability of nanostructured SERS active surfaces. Herein, an effective strategy of coating Au nanoparticles (NPs) with ultrathin and uniform Prussian blue (PB) shell (Au@PB NPs) was developed for quantitative detection of dopamine (DA) concentrations in blood serum and crystal violet (CV) contaminants in lake water. The only intense PB Raman signal at 2155 cm-1 served as an ideal and interference-free internal standard (IS) for correcting fluctuations in the Raman intensities of analytes. Also, the stability of Au@PB NPs was investigated, exhibiting good functionality in strong acid solutions and thermal stability at 100 °C. This work demonstrates a convenient and fast quantitative SERS technique for detecting analyte concentrations in complex systems and has a great number of potential applications for use in analytical chemistry.

Mitochondrial dysfunction, autophagy stimulation and non-apoptotic cell death caused by nitric oxide-inducing Pt-coated Au nanoparticle in human lung carcinoma cells

BackgroundReactive oxygen species (ROS)-mediated cancer therapeutic has been at higher appreciation than those mediated by reactive nitrogen species. Cytotoxic mechanism of a novel nitric oxide (NO) inducing-Pt coated Au nanoparticle (NP) has been comparatively studied with the well-established ROS inducing Pt-based anticancer drug cisplatin in human lung A549 carcinoma cells. MethodsCytotoxicity was evaluated by MTT assay, lactate dehydrogenase (LDH) release, thiobarbituric acid substances (TBARS) and C11-Boron dipyrromethene (BODIPY). ROS (O2·− and H2O2) was measured with dihydroethidium (DHE) and H2O2-specific sensor. Nitric oxide (NO) and mitochondrial dysfunction were evaluated respectively by NO-specific probe DAR-1 and JC-1. Autophagy was determined by lysotracker (LTR) and monodansylcadaverine (MDC) applied tandemly whereas apoptosis/necrosis by Hoechst/PI and caspase 3 activity. ResultsIC50 (concentration that inhibited cell viability by 50%) of Pt coated Au NP came to be 0.413 μM whereas IC50 of cisplatin came out to 86.5 μM in A549 cells treated for 24 h meaning NPs toxicity was over 200 times higher than cisplatin. However, no significant stimulation of intracellular ROS was observed at the IC50 of Pt coated Au NPs in A549 cells. However, markers like LDH release, TBARS, BODIPY and ROS were significantly higher due to cisplatin in comparison to Pt coated Au NP. ConclusionsPt coated Au NP caused NO-dependent mitochondrial dysfunction and autophagy. Mode of cell death due to NP was much different from ROS-inducing cisplatin. General significancePt coated Au NP offer promising opportunity in cancer therapeutic and warrants advanced study in vivo models of cancer.

Electrochemical modulation of plasmon-induced charge separation behaviour at Au-TiO2 photocathodes.

Plasmon-induced charge separation (PICS) at the interface between a plasmonic nanoparticle and a semiconductor becomes less efficient as the plasmon resonance wavelength increases, because the energy of a photon may not be sufficiently higher than the interfacial Schottky barrier height. In this study, we developed PICS photocathodes by coating Au nanoparticles of different sizes on an ITO electrode with a thin TiO2 layer, and applied negative potentials to those photocathodes so as to suppress back electron transfer and improve the PICS photocurrent responses. The photocurrent enhancement factor was increased as the particle size was decreased, and enhancement of about two orders of magnitude was observed for small Au nanoparticles when bias voltage of 0.5 V was applied. In some cases the photocurrent enhancement was accompanied by a slight redshift of the photocurrent peak, which was caused by a lowered barrier. This technique would be useful for tuning the photocurrents when it is applied to devices such as electrochemical LSPR sensors and photodetectors.

Au nanoparticles supported on Bi2WO6 nanosheets for broad-band absorption and good solar thermal conversion

Photothermal conversion is one of the most effective ways of absorbing and utilizing solar energy. The key issues of photothermal conversion are seeking for nanofluids with strong and wide-range sunlight harvesting. In this work, near-infrared (NIR) light absorbed Bi2WO6 is first exploited for solar thermal conversion. However, the photothermal conversion efficiency is low owing to its insufficient NIR-light absorption. After coating Au nanoparticles on Bi2WO6 nanosheets, the localized surface plasmon resonance effect of Au nanoparticles enable Bi2WO6 show strong optical absorption. Au/Bi2WO6–H2O nanofluids have higher temperature rise and better photothermal conversion efficiency than Bi2WO6 and the base fluid water. The present work not only explore a new way for improving the photothermal conversion efficiency of NIR-light nanofluids, but also help design and prepare novel broad-band sunlight absorption nanofluids.

Gold Nanoparticles Cure Bacterial Infection with Benefit to Intestinal Microflora.

Antibiotics that are most used to cure bacterial infections in the clinic result in the imbalance of intestinal microflora, destroy the intestinal barrier, and induce bacterial resistance. There is an urgent need for antibacterial agent therapy for bacterial infections that does not destroy intestinal microflora. Herein, we applied 4,6-diamino-2-pyrimidinethiol (DAPT)-coated Au nanoparticles (D-Au NPs) for therapy of bacterial infection induced by Escherichia coli ( E. coli) in the gut. We cultured D-Au NPs and E. coli in an anaerobic atmosphere to evaluate their bactericidal effect. We studied the microflora, distribution of Au, and biomarkers in mice after a 28-day oral administration to analyze the effect of Au NPs on mice. D-Au NPs cured bacterial infections more effectively than levofloxacin without harming intestinal microflora. D-Au NPs showed great potential as alternatives to oral antibiotics.

Shell thickness-dependent Au@Ag nanoparticles aggregates for high-performance SERS applications

Plasmonic core-shell nanomaterials have attracted great attention and offered wide applications in surface-enhanced Raman spectroscopy (SERS) due to their unique localized surface plasmon resonance (LSPR) characteristics. In this study, the SERS performance of Ag coated Au nanoparticles aggregates (Au@AgNAs) substrate was explored. The fabrication of Au@AgNAs involved using spherical Au nanocrystals of 32 nm in diameter as the seeds, and ascorbic acid was used as the reductant. The thickness of the Ag shell deposited onto the Au surface was finely tuned from 3 to 13 nm by changing the amount of AgNO3 precursor. Results in this study suggested that the LSPR of the Au core was rapidly attenuated with increasing Ag shell thickness, while the LSPR bands for Ag shell blue-shifted from 390 to 420 nm. Au@AgNAs with the Ag shell thickness of 8.5 nm exhibited excellent SERS activity, which could realize detecting R6G at an ultralow concentration of 1 × 10−12 M. Besides, the prepared Au@AgNAs showed well homogeneity and reproducibility, and the limit of detection of thiram was calculated as 1.09 × 10−9 M, indicating that the Au@AgNAs substrate could be potentially used for high-performance SERS sensing applications.

Surface Plasmon Resonance Characteristics of Au Nanoparticles Layered Sensor Chip for Direct Detection of Stress Hormone Conjugated by Nanoparticles

In this study, localized surface plasmon resonance (LSPR) effect was characterized for immuneassay to detect cortisol conjugated nanoparticles (NPs) using a cuvette-compatible Au NPs layered sensor chip. A neuro stress hormone, cortisol, as target molecule was conjugated to 2 nm, 5 nm, 30 nm, and 40 nm Au NPs or 14 nm zinc oxide (ZnO) NPs to enhance the LSPR detection signals as plasmonic coupling elements with respect to cortisol monoclonal antibody (c-Mab) of probe molecule, which was immobilized on the Au NPs layered sensor. The cortisol conjugated 2 nm and 5 nm Au NPs and 14 nm ZnO NPs, which were selectively immune- bound to the c-Mab coated Au NPs sensor, showed LSPR effects to induce absorbance increases under UV-Vis spectroscopy. Also, the cortisol conjugated 2 nm, 5 nm, 30 nm and 40 nm Au NPs could show disparate plasmonic coupling effects to shift maximum absorbance wavelength peaks. Even though the cortisol conjugated 14 nm ZnO NPs could show increased absorbance only, the conjugation of cortisol to both Au and ZnO NPs was proved to enhance direct LSPR detection of the cortisol, which could not be explicitly sensed by itself for direct LSPR signal.

Assessing the synergy effect of additive and matrix on single-crystal growth: Morphological revolution resulted from gel-mediated enhancement on CIT-calcite interaction

It is well known that in biomineralization, the inorganic solids crystallized in the presence of organic phases, which are generally recognized as additives and matrix, leading to the crystal morphology modification. However, the synergy effects of both soluble additive and insoluble matrix on regulating the morphology of synthetic single-crystals are less studied. Here, we examine the morphological revolution of calcite single crystals induced by the additive, citrate (CIT), or/and the matrix, agarose gel network. The agarose gel matrix is inert to the crystal morphology in the sense that the agarose gel-grown calcite crystals maintain in characteristic rhombohedra. In contrast, CIT additives are active in crystal morphology modification and crystals begin to exhibit curved rough surfaces when grown in solution with the concentration of CIT coated Au nanoparticles ([CIT-Au NPs]) of more than 2.25mg/mL. Interestingly, once agarose gel and CIT-Au NPs are simultaneously introduced, the curved morphological feature emerges at a much lower [CIT-Au NPs] of around 0.2mg/mL. Increasing the gel concentrations further reduce the [CIT-Au NPs] needed to trigger calcite morphological modification, suggesting that the gel networks reduce the CIT diffusion and thereby enhance the kinetic effects of CIT on crystallization. As such, this work may have implications for understanding the mechanism of hierarchical biominerals construction and provide rational strategy to control single-crystal morphologies.

Enhanced CO2 reduction activity of polyethylene glycol-modified Au nanoparticles prepared via liquid medium sputtering

The electrochemical conversion of CO2 into useful chemicals such as CO is a promising strategy to reduce CO2 emissions from fossil fuel consumption and to mitigate the impacts of global warming. Although tremendous effort has been devoted to the practical use of CO2conversion techniques, these techniques still suffer from deficient catalytic activity toward CO2 reduction as well as a complex catalyst synthesis procedure. In this study, an effective strategy to enhance the catalytic CO2 reduction activity with a unique synthesis method is proposed. Polyethylene glycol (PEG)-coated Au nanoparticles supported on a porous carbon support are prepared by a facile, cost-effective, and biocompatible one-step sputtering deposition method, termed liquid medium sputtering. The use of PEG as a liquid medium is advantageous in terms of catalytic activity and stability by producing PEG layers on the Au surface. The prepared PEG-coated Au nanoparticle catalyst exhibits a CO Faradaic efficiency of 100% at −0.57 VRHE and excellent stability during 10 h of operation due to the high solubility of PEG for CO2.

Robust Multimetallic Plasmonic Core–Satellite Nanodendrites: Highly Effective Visible-Light-Induced Colloidal CO2 Photoconversion System

The present report demonstrated the synthesis of trimetallic Pt-nanodots (PtNDs, 3–4 nm) and TiO2 (4–5 nm) coated Au nanoparticles (Pt@TiO2–AuNPs) with spherical dendritic shape, robust structure, and high colloidal stability. Prepared plasmonic nanodendrites were tested for CO2 photoconversion to HCOOH in the aqueous medium at room temperature and showed significant conversion rate with 3.12% of chemical yield and 1.84% of quantum yield. There was a remarkable improvement in the photocatalytic efficiency of TiO2–AuNPs after PtNDs decoration as 312-fold increase in the CO2 photoconversion efficiency with trimetallic Pt@TiO2–AuNPs nanodendrites in comparison to bare AuNPs in the presence of Xe lamp (visible light). Prepared nanodendrites also showed notable efficiency in NIR light and solar simulator illumination. The action spectra (quantum yield vs wavelength of monochromatic light) has shown plasmon-enhanced reaction progress and robustness of prepared colloidal nanodendrites. The spherical nanodendrites have been tested for at least five reaction cycles and showed consistent conversion efficiency with exceptional morphological and colloidal stability.

Effects of Surface Coating on Nanoparticle-Protein Adsorption Selectivity

Negatively charged, uni-sized naked gold (Au) and coated poly (acrylic acid) (PAA)—polyethyleneimine (PEI)-Au (PPAu) nanoparticles (NP)s were incubated with four proteins of different molecular weights: bovine serum albumin (BSA) ~ 67 kDa, cationic trypsin ~ 23.3 kDa, LL-37 peptide ~ 4.5 kDa, and PK(FK)5PK peptide ~ 1.9 kDa. Different interaction kinetics were observed and analyzed by cryogenic transmission electron microscopy (cryoTEM) and UV-Vis spectroscopy. The naked Au NPs adsorbed all four proteins showing no selectivity towards any specific protein category, while PPAu NPs adsorbed only the LL-37 and PK(FK)5PK peptides (they did not adsorb BSA and cationic trypsin), thereby expressing selectivity to positively charged low molecular weight (LMW) proteins. Applying an interpretation of the Hill model, we showed that PPAu and naked Au NPs have similar affinity and cooperative binding behavior toward the PK(FK)5PK peptide. This study also supports the assumption that NP chemical composition may be a tunable property in NP design for specific applications such as LMW proteins’ harvesting, biosensing, and drug delivery systems. Although it may be speculated that surface structure may be shaped to enhance selective adsorption, this feature has not been demonstrated in the present study. Protein-NP interaction is an emerging field in biomedical research. Particularly Au NPs-protein interaction, due to the Au NPs promising medical applications inherited from their easy-to-make and surface functionalizing processes. This interaction depends on several factors, such as NP size, surface charge, and surface chemical composition and morphology. Herein, we studied the effect of NP surface coating on the adsorption behavior of various proteins of similar size, negatively charged naked Au, and coated PPAu NPs. Our findings suggest that the NPs’ surface morphology may play a major role in molecular weight (MW)-based NP-protein adsorption selectivity. Future work will focus on engineering new coated Au NPs with different polymers to gain better understanding regarding the effects of surface composition and manipulated morphology on the selective adsorption of proteins. Additionally, we will explore the potential role of selective protein adsorption in regenerative medicine bioresearch and applications.

Label-Free Photoelectrochemical "Off-On" Platform Coupled with G-Wire-Enhanced Strategy for Highly Sensitive MicroRNA Sensing in Cancer Cells.

MicroRNA (miRNAs) quantification, especially at low abundance, is vital for disease diagnosis, prognosis, and therapy. Herein we develop a distinctive label-free "off-on" configuration for photoelectrochemical (PEC) sensing platform fabrication, coupled with DNA four-way junction (4J) architecture as well as G-wire superstructure for signal amplification. In addition, ultrathin copper phosphate nanosheets (CuPi NSs) coating Au nanoparticles (Au-CuPi NSs) serve as a highly efficient photocathode substrate. To improve the sensitivity, and avoid the false positive signals, the quencher, gold nanoparticles (GNPs), is utilized to switch off the PEC signal because of the commendable surface plasmon resonance (SPR) absorption. Subsequently, ingenious DNA 4J architecture is applied to export proportional c-myc regions for target quantification. Assisted with the G-wire superstructure formation, the enhancer 5,10,15,20-tetra(4-sulfophenyl)-21H,23H-porphyrin (TSPP) is coupled on the substrate to switch on the PEC signal, thus realizing the miRNA assay with persuasive accuracy, high sensitivity, and low detection limit. In addition, we execute the miRNA detection in prostate carcinoma cell line 22Rv1, and acquire desirable quantitative capability. Remarkably, the prepared PEC sensing platform not only realizes the highly efficient miRNAs quantification, but also uncovers a marvelous horizon for sensing platform fabrication.

Colorimetric and SERS dual-readout for assaying alkaline phosphatase activity by ascorbic acid induced aggregation of Ag coated Au nanoparticles

As an essential enzyme, alkaline phosphatase (ALP) has attracted considerable attention for its regulating effect to the dephosphorylation process in living organisms. Here, we present a colorimetric and surface enhanced Raman scattering (SERS) dual-readout approach for assaying ALP activity. The major advantage of dual-readout assay is the perfect combination of the merit of colorimetric and SERS, which not only allow rapid preliminary discrimination of ALP activity by the naked eye but also greatly improved the detection sensitivity by SERS. Specifically, 4-mercaptophenylboronic acid modified Ag coated gold nanoparticles (4-MPBA-Au@Ag NPs) are employed as the colorimetric and SERS bifunctional reporting nanoprobes. Upon the presence of ALP, the phosphate group in the ascorbic acid 2-phosphate (AAP) is cleaved to produce ascorbic acid (AA), which acted as boronic acid moieties receptors to control the aggregation of 4-MPBA-Au@Ag NPs. The color of 4-MPBA-Au@Ag NPs solutions had changed from bright orange to light brown to dark gray, simultaneously accompanied by a substantial enhancement of SERS-readouts for the strong Raman hot-spots between the aggregation of 4-MPBA-Au@Ag NPs. A distinguishable change in the color was observed at an ALP activity of 5.0U/L, meanwhile, SERS-readout sensing method showed a good linear relationship from 0.50 to 10.0U/L (R=0.997) with an exciting detection limit of 0.10U/L (signal-to-noise ratio of 3). In addition, the dual-readout approach developed here was applied for ALP inhibitor evaluation. With the simple, rapid/direct readout yet outstanding sensitivity, we anticipate that this method would greatly promote practical application in ALP-related early-stage diseases diagnosis.

Leakage-free polypyrrole-Au nanostructures for combined Raman detection and photothermal cancer therapy.

A bifunctional gold-coated polypyrrole (PPy-Au) nanostructure with Raman and photothermal activity was developed, in which polypyrrole spheres (PPy NSs) were used as the core and coated with small Au NPs to form polypyrrole-Au (PPy-Au) nanostructures. As a result of the contribution from the coated Au nanoparticles (Au NPs), coupling occurred between the Au NPs and the PPy NSs, leading to an enhanced pyrrole Raman signal. PPy-Au nanostructures were thus used as Raman tags without requiring additional Raman dyes labeling and leaking the cargo dyes even in the absence of a complicated encapsulation process. When conjugated with aptamer S2.2, the nanostructures could specifically bind with the membrane protein MUC1, a kind of tumor-related biomarker that is overexpressed on the surface of human breast cancer cells (MCF-7). The specific detection of MCF-7 cells was thus achieved based on the pyrrole Raman signal. Moreover, the capacity of the PPy-Au nanostructures for transforming NIR light into heat was also greatly enhanced because of the coupling between the Au NPs and the PPy NSs, as indicated by the efficiency of the photothermal conversion up to 70.0% compared to 44.7% for the pure PPy NSs. Photothermal experiments proved that MCF-7 cells incubated with the nanostructures nearly died under 808 nm irradiation (0.5 W cm-2) for 20 min, and the tumors bearing on the mice were also effectively inhibited after the PTT.

Tunable Electromagnetic Enhancement of Gold Nanoparticle Arrays

In this paper, triblock copolymer polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PI-b-PS-b-P2VP) micelles containing HAuCl4 were spin-coated on silicon wafers followed by calcination to form gold nanoparticle arrays. Subsequently the surface optical performances of poly(3-hexylthiophene) (P3HT)-coated Au nanoparticle arrays were investigated. The particle size and the interparticle distance of the gold nanoparticle arrays could be controlled by adjusting the molar ratio of HAuCl4 precursor to vinyl pyridine units in PI-b-PS-b-P2VP and the spin speed during spin-coating. The results demonstrated that Au nanoparticle arrays with large nanoparticle size were able to produce strong electromagnetic field enhancement. Furthermore, the ratio of average particle size to average interparticle distance increased with decreasing spin speed, resulting in strong electromagnetic field enhancement for metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS).

Surface dipole enhanced instantaneous charge pair generation in triboelectric nanogenerator

Developing a successful strategy to maximize the surface charge density is crucial to speed-up the commercialization success of triboelectric nanogenerator. Here, for the first time, the fabrication of positive triboelectric material to donate electrons efficiently to dielectrics is reported, by increasing the stretchability for the uniform contact and by introducing a functional group for the surface potential control. A highly stretchable and conductive film with Ag nanowires and PDMS was fabricated as a base material, in which the portion of nanowires exposed above the embedding surface should be accurately controlled. In specific, positively charged 4-(dimethylamino)pyridine (DMAP) coated Au nanoparticles, prepared by phase transfer method, are coated. The DMAP lowers the effective work function of the nanoparticles by a permanent dipole induced at the DMAP-Au interface and enhances the electron transfer to the dielectrics, confirmed by the Kelvin probe force microscope measurement. The designed nanogenerator gives an output performance up to 80V and 86μA, and 2.5mW in output power, 2.5 times enhancement compared with the conventional TENG. With the integration with AC to DC converting circuit and buck-boost circuit, the nanogenerator produces a constant voltage of 2.6V. The wireless sensing system, which operates the remote controller, were also demonstrated, turning on a siren.

Enhanced spectrophotometric detection of Hg in water samples by surface plasmon resonance of Au nanoparticles after preconcentration with vortex-assisted liquid-liquid microextraction

This article presents an efficient, simple, and cost-effective method for the determination of trace amounts of Hg by vortex-assisted liquid-liquid microextraction (VALLME) coupled to microvolume UV–Vis spectrophotometry. This method correlates changes in the intensity of localized surface plasmon resonance (LSPR) of tetraoctylammonium bromide (TOABr) coated Au nanoparticles (NPs) after interaction with Hg2+ ion. Spectroscopic measurements of the TOABr-coated Au NPs phase with particular absorption properties (strong and well-defined absorption bands) after analyte extraction by VALLME, provide an accurate and sensitive determination of Hg in water samples, comparable with measurements obtained by atomic absorption spectrometry (AAS). Different variables including sample volume, extraction time, and TOABr-coated Au NPs dispersion volume were carefully studied; final experimental conditions were 5mL, 120μL and 5min respectively. The limit of detection (LOD) was 0.8ngmL−1. The calibration curve was linear at concentrations between the limit of quantification (LOQ) (4.9ngmL−1) and up to at least 120ngmL−1 of Hg. The relative standard deviation for six replicate determinations of 20ngmL−1 of Hg was 4.7%. This method exhibited an excellent analytical performance in terms of selectivity and sensitivity and it was finally applied for Hg determination in spiked tap and mineral water samples.

Characterization of hydrophilic coated gold nanoparticles via capillary electrophoresis and Taylor dispersion analysis. Part II: Determination of the hydrodynamic radius distribution – Comparison with asymmetric flow field-flow fractionation

In the first paper of this series we have shown for hydrophilic coated Au nanoparticles that capillary electrophoresis in combination with Taylor dispersion analysis in fused silica capillaries with an inner diameter of 75μm allows for the unbiased precise determination of the number-weighted mean hydrodynamic diameter, the zeta potential and the effective charge number, although mobility corrected double layer polarization has to be taken into account.In this second paper we investigate whether the modified approximate analytic expression developed by Ohshima (2001) permits the calculation of calibration lines and the concomitant conversion of electropherograms into number-weighted particle radius distributions. We show that with the method developed size distributions are obtained which are independent of the measurement conditions. These size distributions are much narrower than those obtained via dynamic light scattering and data evaluation by the CONTIN algorithm. Capillary electrophoresis together with the proposed data evaluation method reveals that the analyzed nanoparticle populations have very narrow size distributions with a width of 2–4nm. The hydrodynamic radius distributions of the coated NPs are only slightly broader than the solid particle radius distribution of the Au-NP cores. The presence of monomodal/bimodal size distributions is confirmed by asymmetric flow field-flow fractionation.

Preparation of SiO2@ Au nanorod array as novel surface enhanced Raman substrate for trace pollutants detection**Project supported by the National Basic Research Program of China (Grant No. 2013CB934301), the National Natural Science Foundation of China (Grant No. 50931002), the Research Project of Chinese Ministry of Education (Grant No. 113007A), and the Initiative Scientific Research Program of Tsinghua University, China

An effective surface enhanced Raman scattering (SERS) substrate is designed and fabricated by synthesis of SiO2 nanorods array via glancing angle deposition, followed by coating Au nanoparticles onto SiO2 surface in order to create numerous “hot spots”. The detecting sensitivity of such substrate could be optimized by simply adjusting the deposition time of Au. Thus, it can be used for detection of Rhodamine 6G at concentration as low as 10−9 M. Furthermore, our SERS substrate is applied to detect 5 μg/g polychlorinated biphenyls in soil sample, which proves its potential for trace environmental pollutants detection.