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[Display omitted] Colloidal gold nanoparticles (AuNPs) functionalised with hydrophilic thiols can be used as drug delivery probes, thanks to their small size and hydrophilic character. AuNPs possess unique properties for their use in nanomedicine, especially in cancer treatment, as diagnostics and therapeutic tools. Thiol functionalised AuNPs were synthesised and loaded with methotrexate (MTX). Spectroscopic and morphostructural characterisations evidenced the stability of the colloids upon interaction with MTX. Solid state (GISAXS, GIWAXS, FESEM, TEM, FTIR-ATR, XPS) and dispersed phase (UV–Vis, DLS, ζ-potential, NMR, SAXS) experiments allowed to understand structure-properties correlations. The nanoconjugate was tested in vitro (MTT assays) against two neuroblastoma cell lines: SNJKP and IMR5 with overexpressed n -Myc. Molar drug encapsulation efficiency was optimised to be >70%. A non-covalent interaction between the π system and the carboxylate moiety belonging to MTX and the charged aminic group of one of the thiols was found. The MTX loading slightly decreased the structural order of the system and increased the distance between the AuNPs. Free AuNPs showed no cytotoxicity whereas the AuNPs-MTX nanoconjugate had a more potent effect when compared to free MTX. The active role of AuNPs was evidenced by permeation studies: an improvement on penetration of the drug inside cells was evidenced. [ABSTRACT FROM AUTHOR]

[Display omitted] Hybridized periodic mesoporous organosilica (PMO) nanoparticles are expected to provide a multifunctional theranostic platform for precision medicine by combining the advantages of different organic and inorganic components. In this work, double-shell-structured PMO nanotheranostics composed of ethane- and thioether-bridged organosilica shells were synthesized. Gold colloids were generated in situ by the thioether groups on the inner shell. The obtained double-shell PMO@Au (DSPA) has uniform size, large surface areas, ordered mesochannels and photothermal conversion capability. After being encapsulated with perfluorohexacene (PFH), DSPA-PFH produced a strong ultrasound signal upon laser irradiation due to the phase transit of PFH during hyperthermia. DSPA-PFH showed enhanced photothermal therapeutic efficacy, great ultrasound contrast, and minimal toxicity both i n vitro and in vivo. These results demonstrated the distribution of different organosilica could be delicately adjusted in hybridized PMO nanoparticles. Furthermore, it showed the potential of using hybridized PMO nanoparticles as a theranostic platform for biomedical applications by combining unique characteristics of different organosilica through rational design. [ABSTRACT FROM AUTHOR]

Simple, low-cost, robust, and scalable fabrication of microscopic linear barcodes with high levels of complexity and multiple authentication layers is critical for emerging applications in information security and anti-counterfeiting. This manuscript presents a novel approach for fabrication of microscopic linear barcodes that can be visualized under Raman microscopy. Microfluidic channels are used as molds to generate linear patterns of end-grafted polymers on a substrate. These patterns serve as templates for area-selective binding of colloidal gold nanoparticles resulting in plasmonic arrays. The deposition of multiple taggant molecules on the plasmonic arrays via a second microfluidic mold results in a linear barcode with unique Raman fingerprints that are enhanced by the underlying plasmonic nanoparticles. The width of the bars is as small as 10 μm, with a total barcode length on the order of 100 μm. The simultaneous use of geometric and chemical security layers provides a high level of complexity challenging the counterfeiting of the barcodes. The additive, scalable, and inexpensive nature of the presented approach can be easily adapted to different colloidal nanomaterials and applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Hypothesis Reversible addition fragmentation chain transfer (RAFT) - assisted encapsulating emulsion polymerization (REEP) has received considerable attention as an efficient strategy to prepare colloidal stable shell@core nanoparticles. Generally, amphipathic macroRAFT agents are used but the effect of working above or below the critical micelle concentration (CMC) of macroRAFT agents needs to be addressed. Hence, it is necessary to understand if this parameter has an impact not only on the stability of the colloids but also on the molecular mass of the polymer shell. Methods Here, the CMC of three different macroRAFT agent was determined and the effect of macroRAFT agents concentration on the colloidal stability of gold nanoparticles coated with macroRAFT agents (macroRAFT@Au) assessed. The subsequent chain extension from macroRAFT@Au NPs, resulting in encapsulated Au nanoparticles (copolymer@Au), has also been systematically studied. Findings Using the REEP approach it was possible to obtain stable encapsulated Au NPs. Moreover, this strategy opens the possibility of adjusting the macroRAFT agents concentration to tune the length of the polymer chains grown around Au cores which is of major interest for the design of biosensors based on responsive polymer shells, such as pH, temperature and photoluminescence quenching. [ABSTRACT FROM AUTHOR]

Graphical abstract High yield of spiral gold nanowires are grown from Au nanoparticles in solution. The versatile system allows systematic adjustment and thus enables syntheses of complex Au hybrid nanostructures. Abstract Synthesis of asymmetric nanostructures has always been a great challenge. In particular, there are only limited approaches for growing spiral nanowires in solution, and almost all of them require templates. Here, as a step in advancing the synthetic capability at the nanoscale, we report a wet chemistry template-free approach for growing hybrids spiral gold nanowires. The spiral gold nanowires were grown from the surface of colloidal gold nanoparticles, forming hybrid Au nanostructures. As an application of the active surface growth mechanism, the mechanistic understanding enables systematic adjustment of the nanowire morphology. The length and width of the spiral nanowires could be readily adjusted. Furthermore, the number of spiral nanowire on each Au nanoparticle, could be tuned by the pre-hydrolysis of the surface modification reagent. Such versatile system allows creation of complex nanostructures like the octopus-like and spider-like Au hybrids. [ABSTRACT FROM AUTHOR]

Hypothesis Nanoparticle adsorption at the oil–water interface in an unstable, coalescing emulsion leads to cluster formation. Experiments Stable suspensions of clusters are prepared using a facile, two-step procedure involving few reagents and neither thiolated compounds nor chlorinated solvents. First, colloidal gold nanoparticles are assembled at the aqueous–hexanol interface in an emulsion that rapidly coalesces and spontaneously deposits a film on the interior surface of the glass container. The film is dissolved in ethanol with sonication to disperse the clusters. The film and clusters are characterized by transmission electron and atomic force microscopies as well as ultraviolet–visible spectrometry. Findings Clusters are observed to contain as few as 8 to as many as 24 Au nanoparticles. The clusters are anisotropic and can also be formed from larger nanoparticles. Hydrophobic and hydrophilic interactions are implicated in the formation of these clusters within the interfacial tension gradients of a coalescing emulsion. The clusters can be re-suspended in ethanol and water, maximizing the utility of these clusters with an extinction band in the near-Infrared region of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

Highlights: [•] Stable gold sols were prepared by reducing [AuCl4]− with nitrilotriacetic acid (NTA). [•] The concentration of reductant dictates the size of gold nanoparticles. [•] A large NTA excess is necessary to prevent the aggregation of Au nanoparticles. [•] Stable sols with a concentration up to 1.5×10−3 moldm−3 have been prepared. [ABSTRACT FROM AUTHOR]

Highlights: [•] Surface modification of gold colloid by adsorption of pH responsive polymer. [•] pH responsive reversible aggregation of core–shell particles. [•] Flexible technique for the construction of stimuli responsive composite particles. [ABSTRACT FROM AUTHOR]

Abstract: Water-soluble gold nanoparticles (AuNPs) have gained considerable attention because they offer a myriad of potential applications, especially in the fields of biology and medicine. One method to prepare such gold nanoparticles is through the well-known Murray place-exchange reaction. In this method, precursor gold nanoparticles, bearing labile ligands and with very good size distribution, are synthesized first, and then reacted with a large excess of the desired ligand. We report a comparison of the reactivity of several known precursor gold nanoparticles (citrate-stabilized, pentanethiol-stabilized, tetraoctylammonium bromide-stabilized, and 4-dimethylaminopyridine-stabilized) to several biologically relevant ligands, including amino acids, peptides, and carbohydrates. We found that citrate-stabilized and 4-dimethylaminopyridine-stabilized gold nanoparticles have broader reactivities than the other precursors studied. Citrate-stabilized gold nanoparticles are more versatile precursors because they can be prepared in a wide range of sizes and are very stable. The hydrophobic pentane-stabilized gold nanoparticles made them “inert” toward highly water-soluble ligands. Tetraoctylammonium bromide-stabilized gold nanoparticles exhibited selective reactivity, especially for small, unhindered and amphiphilic ligands. Depending on the desired ligand and size of AuNPs, a judicious selection of the available precursors can be made for use in place-exchange reactions. In preparing water-soluble AuNPs with biologically relevant ligands, the nature of the incoming ligand and the size of the AuNP should be taken into account in order to choose the most suitable place-exchange procedure. [Copyright &y& Elsevier]

Abstract: This paper reports the preparation of superhydrophobic SiO2 layers with a micro-nano hierarchical surface structure. SiO2 layers, which were rough on the microscale, were prepared using an electrospraying method combined with a sol–gel chemical route. To create a nanoscale structure, the surface of the SiO2 layers was coated with Au nanoparticles using an ultraviolet-enhanced chemical reduction process, resulting in a micro-nano hierarchical surface structure. A subsequent fluorination treatment with a solution containing trichloro(1H,1H,2H,2H-perfluorooctyl)silane resulted in fluorination of the micro-nano hierarchical SiO2 layers. The resulting SiO2 layers showed outstanding repellency toward a range of liquid droplets, for example, a water-repellency of 170°. The surface fraction and work of adhesion of the fluorinated, micro-nano hierarchical SiO2 layers were estimated using the Cassie–Baxter and Young–Dupre equations, respectively. The long-term durability and ultraviolet resistance of the superhydrophobic SiO2 layers prepared in this study highlight their potential in a range of practical applications. [Copyright &y& Elsevier]

Abstract: This study examines and quantifies the effect of cationic polyelectrolyte adsorption on paper on the aggregation and retention of gold nanoparticles (AuNPs) to optimize their Surface Enhanced Raman Scattering (SERS) enhancement factor and sensitivity. Aggregation of metallic nanoparticles is known as a key factor for intense SERS enhancement. Paper substrates were treated with aqueous solutions of cationic polyacrylamide (CPAM) varying in concentration, charge density, and molecular weight to control the AuNPs’ aggregate size distribution and surface coverage on paper. The Raman Enhancement Factor of AuNPs-CPAM paper was almost an order of magnitude greater than for the untreated AuNPs paper. The high loading and uniform distribution of AuNPs aggregates on CPAM pre-treated paper contributed toward the excellent SERS reproducibility, sensitivity, and high enhancement factor. This configuration of AuNP on paper was favoured by treating the substrate with CPAM solutions of higher concentrations, higher charge density, and greater molecular weight. [Copyright &y& Elsevier]

Abstract: Highly dispersed gold–silver core–shell nanoparticles were synthesized in a two-step process. The stabilizer-free gold core particles with an average diameter of ∼30nm were first precipitated by rapid reduction of HAuCl4 with l-ascorbic acid. Thin continuous silver shells of variable thickness were subsequently obtained by reducing controlled amounts of silver nitrate added in the gold sol. The plasmon band of gold gradually blue-shifted and a peak characteristic for silver eventually emerged as the amount of deposited silver increased. A strong and well-defined silver absorption band was recorded when the Ag content exceeded 60wt.%. It is shown that the concentration of Cl− ions in the gold precursor solution plays a critical role in the stability of the bi-metallic sol and the structure of the deposited silver shell. [Copyright &y& Elsevier]

Abstract: There is a growing interest in identifying biomacromolecules such as proteins and peptides to functionalize metallic surfaces through noncovalent binding. One method for functionalizing materials without fundamentally changing their inherent structure is using biorecognition moieties. Here, we proved a general route to select a biomolecule adhesive motif for surface functionalization by comprehensively screening phage displayed peptides. In particular, we selected a genetically engineered M13 bacteriophage and a linear dodecapeptide derived from its pIII domain for recognizing gold surfaces in a specific and selective manner. In the phage context, we demonstrated the adhesive motif was capable to adsorb on gold in a preferential way with a morphological and viscoelastic signature of the adsorbed layer as evidenced by QCM-D and AFM investigations. Out of the phage context, the linear dodecapeptide is reproducibly found to adhere to the gold surface, and by quantitative SPR measurements, high affinity constants (K eq∼ 106M−1, binding energy ∼−8kcal/mol) were determined. We proved that the interactions occurring at gold interface were mainly hydrophobic as a consequence of high frequency of hydrophobic residues in the peptide sequence. Moreover, by CD, molecular dynamics and steered molecular dynamics, we demonstrated that the molecular flexibility only played a minor role in the peptide adsorption. Such noncovalent but specific modification of inorganic surfaces through high affinity biomolecule adsorption represents a general strategy to modulate the functionality of multipurpose metallic surfaces. [Copyright &y& Elsevier]

Abstract: Gold nanoparticles from commercially available colloids were deposited onto a hydrogen-terminated silicon substrate without the use of a polyelectrolyte linker by the addition of HF acid. The deposition density was shown to be controlled over three orders of magnitude by varying the colloid concentration, and finer control is achieved by varying the deposition time. In order to minimise agglomeration, however, we show that deposition times should be minimised since nanoparticle agglomeration increases rapidly over the first 2min after the addition of HF. To increase nanoparticle density without increasing agglomeration, we show that successive depositions of short times linearly increase the deposition density without increasing the agglomeration of nanoparticles. [Copyright &y& Elsevier]

Abstract: Continuous platinum shells consisting of ∼5 atomic layers were deposited onto preformed gold seeds in aqueous medium by reducing hexachloroplatinic acid with ascorbic acid. By controlling the reduction kinetics of Pt(IV) species and the properties of the substrate, it was possible to ensure a slow and controlled deposition of platinum atoms onto the gold cores. Electrochemical evaluations revealed the presence of a compact platinum shell. The mass specific oxygen reduction activity of platinum in the AuPt core–shell nanoparticles was found to be four times higher than that of platinum black and comparable to that of polycrystalline bulk metal. [Copyright &y& Elsevier]

Abstract: A facile method for controlling the density and site of attachment of gold nanoparticles onto the surface of carbon nanotubes is demonstrated. Nitric acid based oxidation was carried out to create carboxylic groups exclusively at the ends of carbon nanotubes, whereas oxidation using a mixture of nitric and sulfuric acid with varied reaction time was carried out to control the population of carboxylic groups on the side walls of nanotubes. In turn, 4-aminothiophenol modified gold nanoparticles were covalently interfaced to these carboxylated multi-walled carbon nanotubes in the presence of a zero length cross-linker, 1-ethylene-3-(3-dimethylaminopropyl) carbodiimide. Raman spectroscopic results showed increase in height of disorder band with each of these successive steps, indicating the increase in degree of functionalization of the carbon nanotubes. Fourier transformed infrared spectroscopic analysis affirmed the functionalization of nanostructures and the formation of nanohybrid. Transmission electron and field emission scanning electron microscopic analysis ascertained the attachment of gold nanoparticles to the ends and side walls of the multi-walled carbon nanotubes. The new hybrid nanostructures may find applications in electronic, optoelectronic, and sensing devices. [Copyright &y& Elsevier]

Abstract: This study demonstrates a facile but efficient approach to deposit metallic (gold) nanoparticles on β-FeOOH nanorods to obtain Au/β-FeOOH nanocomposites without the assistance of any polymers or surfactants at ambient conditions. In this method, a strong reducing agent (NaBH4) can be used to extensively produce Au nanoparticles, converting β-FeOOH into Fe3O4 and depositing gold particles onto magnetic Fe3O4 simultaneously. The microstructure, composition, and chemical properties of the obtained nanocomposites are characterized by various advanced techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV–vis spectroscopy. Moreover, the Au/β-FeOOH nanocomposite can be used to detect trace melamine using UV spectrum in the ultraviolet wavelength range (190–260nm), in which the nanocomposites show a higher sensitivity toward melamine due to the promotion of symmetry-forbidden bands (n → π *) of melamine molecules and also avoid the disturbance of commercial products containing solid colloids or food colorings that distort visual spectrum during the detection of chemical sensing. The deposition mechanisms and their sensing detection toward melamine are discussed. [Copyright &y& Elsevier]

Abstract: Green synthesis of gold nanospheres with uniform diameter and triangular nanoprisms with optically flat surface was carried out using a non-pathogenic bio-control agent Trichoderma asperellum for reduction of HAuCl4. Kinetics of the reaction was monitored by UV–Vis absorption spectroscopy. No additional capping/complexing agent was used for stabilizing the gold nanoparticles. Evolution of morphology from pseudospherical nanoparticles to triangular nanoprisms was studied by transmission electron microscopy (TEM). It revealed that three or more pseudospheres fused to form nanoprisms of different shapes and sizes. Slow rate of reduction of HAuCl4 by constituents of cell-free fungal extract was instrumental in producing such exotic morphologies. Isolation of gold nanotriangles from the reacting masses was achieved by differential centrifugation. [Copyright &y& Elsevier]

Abstract: Continuous flow synthesis of gold nanoparticles was demonstrated using a microchannel reactor with glucose reduction in aqueous alkaline medium. Particle size, morphology, and visual/optical properties of the dispersion liquid were controlled dynamically by tuning of the rate of NaOH addition. Characteristic star-like nanoparticles formed spontaneously as a quasi-stable state, but they changed the morphology to round shape and showed spectral change over time. [Copyright &y& Elsevier]

Abstract: In this study, we partially grafted geminal silanol groups in the protecting organic shells on the surfaces of gold nanoparticles (AuNPs) and then assembled the alkyl-AuNP-Si(OH)4 particles onto the surfaces of silicon (Si) wafers. The density of assembled AuNPs on the Si surface was adjusted by varying the geminal silanol group content on the AuNP surface; at its optimal content, it approached the high assembly density (0.0254particles/nm2) of an AuNP assembled monolayer. Using reactive-ion etching (RIE) with the templates as masks, we transferred the patterned AuNP assemblies to form large-area, size-tunable, Si nanopillar arrays, the assembly density of which was controlled by the dimensions of the AuNPs. Using this colloidal lithography (CL) process, we could generate Si nanopillars having sub-10-nm diameters and high aspect ratios. The water contact angles of the high-aspect-ratio Si nanopillars approached 150°. We used another fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate hydrophilic 200-nm-resolution line patterns on a Si surface to assemble the AuNPs into 200-nm-resolution dense lines for use as an etching mask. Subsequent CL provided a patterned Si nanopillar array having a feature size of 200nm on the Si surface. Using this approach, it was possible to pattern sub-10-nm Si nanopillar arrays having densities as high as 0.0232nm−2. [Copyright &y& Elsevier]

Abstract: Well-defined hexangularly faced CdS nanorod arrays have been grown directly on a conductive ITO glass via a facile one-step and non-template hydrothermal approach. Gold nanoparticles were decorated onto the nanorods to enhance the electron transfer process of electrode. Glucose oxidase (GOD) was then immobilized on the CdS through crosslinking with chitosan (CS), which resulted in a glucose biosensor with high enzyme loading and excellent sensitivity. Such a chitosan-encapsulated GOD-based biosensor revealed a relatively rapid response time of less than 50s, and an approximate linear detection range of glucose concentration, from 50 to 500μmolL−1 with a detection limit of 38μmolL−1 and an electrode sensitivity of 5.9μAmM−1. [Copyright &y& Elsevier]

Abstract: This study constitutes a demonstration of the biological route to controlled nano-fabrication via modular multi-functional inorganic-binding peptides. Specifically, we use gold- and silica-binding peptide sequences, fused into a single molecule via a structural peptide spacer, to assemble pre-synthesized gold nanoparticles on silica surface, as well as to synthesize nanometallic particles in situ on the peptide-patterned regions. The resulting film-like gold nanoparticle arrays with controlled spatial organization are characterized by various microscopy and spectroscopy techniques. The described bio-enabled, single-step synthetic process offers many advantages over conventional approaches for surface modifications, self-assembly and device fabrication due to the peptides’ modularity, inherent biocompatibility, material specificity and catalytic activity in aqueous environments. Our results showcase the potential of artificially-derived peptides to play a key role in simplifying the assembly and synthesis of multi-material nano-systems in environmentally benign processes. [Copyright &y& Elsevier]

Abstract: We present a simple, novel procedure to selectively deposit gold nanoparticles using pure water. It enables patterning of nanoparticle monolayers with a remarkably high degree of selectivity on flat as well as microstructured oxide surfaces. We demonstrate that water molecules form a thin “capping” layer on exposed thiol molecules within the mercaptan self-assembled layer. This reversible capping of water molecules locally “deactivates” the thiol groups, therewith inhibiting the binding of metallic gold nanoparticles to these specific areas. This amazing role of water molecules can be used as a tool to pattern flat as well as structured surfaces with gold nanoparticles. [Copyright &y& Elsevier]

Abstract: The influence of pH value on gold nanoparticle production in the presence of Pluronic stabilizers is systematically investigated. The reactions are studied as a function of pH and at fixed concentrations of the two reactants, HAuCl4 and P123 block copolymer. Results indicate that the reaction pathway during the nanoparticle formation can be controlled by varying pH. The nanoparticles synthesized at pH=11.12 have an average diameter of 9.6nm with a narrow size distribution, and the Pluronics are adsorbed on individual gold particle surfaces to form core–shell structures via hydrophobic interactions. The present work provides an economic way to improve the dispersion and stabilization of gold nanoparticles and throws further light on the understanding of gold nanoparticle production using block copolymers. [Copyright &y& Elsevier]

Abstract: Intracellular uptake of serum-coated gold nanoparticles (AuNPs) in a single mammalian cell was examined in order to investigate the interactions of cell culture media and aromatic thiol-functionalized gold surfaces using micro-spectroscopic tools. The AuNPs modified by the aromatic thiols of para-aminobenzenethiol (ABT), para-hydroxy benzenethiol (HBT), and para-carboxylic benzenethiol (CBT, para-mercaptobenzoic acid) bearing NH2, OH, and COOH surface functional groups are presumed to adsorb the serum proteins as indicated from the compiled quartz crystal microbalance (QCM) data. The QCM results indicate that among the constituents, fetal bovine serum (FBS) should be the major adsorbate species on AuNPs incubated in Roswell Park Memorial Institute (RPMI) medium. The functionalized AuNPs were found to be internalized as an aggregation state in mammalian cells as evidenced by transmission electron microscopy (TEM) images. We monitored such cellular uptake behaviors of aromatic thiol-modified AuNPs using dark-field microscopy (DFM)-guided confocal surface-enhanced Raman scattering techniques in order to identify the three-dimensional localization inside the single cell. We found that the uptake amounts of ABT, HBT, and CBT were similar by counting up to 70 particles inside the cells incubated in the solution mixture of the aromatic thiol and 1,4-phenylenediisocyanide (PDIC) as a reference. This result indicates for the short aromatic thiol compounds, the AuNPs should enter the cell after the serum-coating regardless of the surface functional groups. Considering that the aromatic thiols have little effect on the serum coating, the DFM/SERS method is an effective tool for monitoring the localization of AuNPs inside a single cell. [Copyright &y& Elsevier]

Abstract: We depict a novel strategy exploiting the chemistry of metal ion adsorption for detection and sequestration of toxic heavy metal from processed water using gold nanoparticles capped with 4-aminothiophenol. The interaction between 4-aminothiophenol capped gold nanoparticles and heavy metal ions was studied as a function of time and concentration using TEM, HRTEM, SEM, EDS, and I–V characterization. Experiments confirmed that pH is one of the crucial controlling parameters. Adsorption capacity was monitored using AAS, UV–vis spectroscopy and I–V measurement. In the absence of any alloy formation between Au and heavy metal ions, the desorption of the heavy metal ions from 4-aminothiophenol capped gold nanoparticles surface by pH modulation serves as a mean of collection of heavy metal ions. Experiments revealed that the concentration of heavy metal ions in processed water after adsorption is below the maximum permissible limit set by the WHO. [Copyright &y& Elsevier]

Abstract: A novel method was designed for the determination of trace protein with high sensitivity. This sensing method combined the principle of biomineralization and the resonance scattering (RLS) assay of gold nanoparticles (AuNPs). AuNPs were synthesized in the presence of polpyropylneimine hexadeacamnie dendrimers (PPIHA). Meanwhile, they were superficially modified with the amine group, which was confirmed by Fourier transform infrared spectra (FTIR). The specific covalent coupling between bovine serum albumin (BSA) and amine-AuNPs assembles a hyperefficient crystal core. Based on the principle of biomineralization, Au3+ ions were reduced to Au at the surface of bioconjugates in the HAuCl4–NH4OH·HCl redox system. Thus, the size of AuNPs–BSA was selectively enhanced. Meanwhile, the concentration signal of BSA was converted to the RLS intensity of AuNPs, which was enhanced through this process. The selective amplification of RLS signal laid the foundation of the detection method, as it intensified with the increase of AuNPs–BSA concentration. Experimental results show that the peak intensity at 548nm is proportional to the concentration gradient of the bioconjugates from 0.268μg/ml to 1.608μg/ml under the optimized conditions. Additionally, the method has high sensitivity with detection limit as low as 0.096μg/ml. The specific coupling with high sensitivity and good stability of this method indicates its possibility for the assay of other proteins. Moreover, the novel method achieves quantitative detection of trace proteins, suggesting the potential of AuNPs-based analytical methods in further application. [Copyright &y& Elsevier]

Abstract: Well-aligned ZnO nanorods (NRs) were grown on indium–tin-oxide (ITO) slide by the hydrothermal method and used as templates for preparing ZnO/Au composite nanoarrays. The optical and morphological properties of ZnO/Au composites under various HAuCl4 concentrations were explored via UV–vis absorption spectroscopy, photoluminescence (PL) and scanning electron microscopy (SEM). The density and size of gold nanoparticles (Au NPs) on ZnO NRs can be controlled by adjusting the concentration of HAuCl4. The optimal ZnO/Au composites display complete photocatalytic degradation of methyl blue (MB) within 60min, which is superior to that with pure ZnO NRs prepared by the same method. The reason of better photocatalytic performance is that Au NPs act as electron traps and it prevents the rapid recombination of electrons and holes, resulting in the improvement of photocatalytic efficiency. The photocatalytic performance of ZnO/Au composites is mainly controlled by the density of Au NPs formed on ZnO NRs. The application in rapid photodegradation of MB shows the potential of ZnO/Au composite as a convenient catalyst for the environmental purification of organic pollutants. [Copyright &y& Elsevier]

Abstract: Gold nanoparticles were fabricated by reduction of highly concentrated Au(III) ions (200mM) with casein proteins from milk. The gold nanoparticles were converted to nanoparticle-powders after washing and subsequent vacuum drying without aggregation. The nanoparticle-powders completely re-dispersed in aqueous solution, and stable colloidal gold nanoparticles were obtained. UV–vis extinction spectra and dynamic light scattering (DLS) measurements revealed that large assemblies (size, ca. 3μm) and subaggregates (size, <0.5μm) composed of gold nanoparticle–casein protein chain–Au(III) ion were dynamically formed and disintegrated over the course of the growth of the gold nanoparticles. Fourier transform infrared (FT-IR) spectra indicated conformational changes of casein proteins induced by the interaction of casein protein–Au(III) ion and -gold nanoparticle. Finally, rapid, one-pot, and highly concentrated synthetic procedures of gold and silver nanoparticle powders protected by casein (mean diameters below 10nm) were successfully developed using 3-amino-1-propanol aqueous solutions as reaction media. Dense colloidal gold (40gL−1) and silver (22gL−1) nanoparticle aqueous solutions were obtained by re-dispersing the metal nanoparticle powders. [Copyright &y& Elsevier]

Abstract: The reduction of tetrachloroaurate by citrate ions in aqueous solutions yielding gold nanoparticles (GNPs) has been studied using in situ tapping mode atomic force microscopy (AFM), UV–vis absorption and dynamic light scattering (DLS) spectroscopies, small-angle X-ray scattering (SAXS) along with ex situ TEM, EDX and XPS. Special attention is given to mesoscale intermediates responsible for the intense coloring of the transient solutions and their role in nucleation and crystal growth. AFM detects liquid droplet-like domains, globules 30–50nm in diameter arranged in submicrometer aggregates in the gray and blue solutions, and well separated individual particles in the final red sols. DLS shows abrupt appearance of species about 30nm and larger but not growing Au nanoparticles, while SAXS reveals gradually increasing nanoparticles and no aggregates. The mesoscale structures observed in TEM become looser as the reaction proceeds; they contain signatures of oxidized Au and other solutes. The results are interpreted in terms of decomposition of supersaturated solutions to afford domains (“dense droplets”) enriched by gold, and then, after nucleation and coalescence of Au nuclei inside them, rather slow growth of gold nanoparticles within the associated globules; the color changes of the transient solutions are due to increasing interparticle distances. [Copyright &y& Elsevier]

Abstract: A sensitive and selective biosensor for dengue serotyping was successfully developed. The biosensor uses a novel gold nanoparticles-polyaniline hybrid composite (AuNpPANI) for the immobilization of Bauhinia monandra lectin (BmoLL). The nanocomposite was applied to a bare gold electrode surface by chemical adsorption, and BmoLL was subsequently electrostatically adsorbed to the nanocomposite-modified surface. Atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance (EI) techniques were applied to evaluate the immobilization of BmoLL on AuNpPANI. The AFM images for AuNpPANI-BmoLL-DEN systems indicate a homogenous, compact and dense film of the conjugate. In the EI analyses, an obvious difference of the electron transfer resistance between the AuNpPANI-modified electrode and the bare gold electrode was observed. Among three dengue serotypes studied, dengue serotype 2 (DEN2) has higher values for R CT, and lower values for both n and Q. These are indications of a larger blocking effect and smaller capacitive dispersion, resulting from the higher agglutination of glycoproteins from the DEN2 sera. The selective BmoLL recognition for various dengue serotypes may be attributed to different patterns of glycoproteins in the sera produced by the glycoprotein immunoresponse from patients infected by the dengue virus. [Copyright &y& Elsevier]

Abstract: Mesoporous TiO2 nanocontainers (NCs) covered with polyelectrolyte multilayers were adsorbed on self-assembled monolayer (SAM) modified gold substrates at different values of pH and ionic strength. The adsorption process was followed in situ by means of a quartz crystal microbalance (QCM) and the morphology of the adsorbate was investigated by means of FE-SEM images taken of the substrates after each adsorption process. Deposition could be achieved if either the particles and the surface had opposite charge, or if the salt concentration was sufficiently high, reducing the repulsion between the spheres and the surface. In the latter case the adsorption kinetics could be explained in the context of the DLVO-theory. Using conditions of like charges, one has a means to control the speed of deposition by means of ionic strength. However, interparticle aggregation and cluster deposition on the surface were observed at high ionic strength. Such conditions have to be avoided to obtain a uniform deposition of separated nanocontainers on the surface. [Copyright &y& Elsevier]

Abstract: Gold nanoparticle-doped poly(2-vinylpyridine) (P2VP) microcapsules and foam films were synthesized and assembled at the P2VP chloroform solution/HAuCl4 aqueous solution interface at 25°C. It was found that Au nanoparticles with the average diameter of 2.1nm were homogeneously embedded in and adsorbed on the walls of the capsules and foams, the nanoparticles were composed of Au(0) and Au(III) with the molar ratio of about 75/25, and the mass percent of Au elements was measured to be 19.65%. The formation of the nanostructures was attributed to the self-assembly of P2VP at the liquid/liquid interface, the simultaneous reduction of ions by a small amount of ethanol in the chloroform and adsorption of ions. After irradiated by UV-light for 1h, the average diameter of the nanoparticles was found to be 2.2nm, and the ions were transformed to Au(0) completely. The catalytic performance of these composite nanostructures were evaluated by using the reduction of 4-nitrophenol (4-NP) by potassium borohydride in aqueous solutions. The catalytic activity was very high in the first cycle, decreased rapidly and slightly in the second and third cycles, respectively, due to the aggregation of some nanoparticles, and stabilized after the third cycle. [Copyright &y& Elsevier]

Abstract: Photocatalytic and in situ microbial activityofthe amorphous and annealed states of Ag-doped and un-doped titania were examined. Studiesontheir structure, morphology, composition, and the photo-absorption characteristics of these materials were performed. Theseresultswere correlated with the photocatalytic and microbial activity against methicillin resistant Staphylococcus aureus K324 (MRSA), methicillin susceptible S. aureus ATCC 25923 (MSSA), Escherichia coli PA 170, and yeasts Candida albicans ATCC 90028. The annealed powders containing anatase form of titania exhibited relatively higher photocatalytic activity,correspondingto activity against MRSA,when exposed to UV-A radiation. In comparison, amorphous powders exhibited low photoactivity and showed poor antibacterial performance against MRSA under UV-A exposure. Doping of amorphous titania with Ag resulted in an anti-MRSA effectwithoutexposure to UV radiation. In the Ag-doped crystalline anatase samples, the size of Ag primary nanocrystallites increased, which led tothedecrease in the surface concentration of Aganddetrimentanti-MRSA activity. [Copyright &y& Elsevier]

Abstract: We report the development of a new selective and specific electrochemical biosensor for bacterial lipolysaccharide (LPS). An electrode interface was constructed using a l-cysteine-gold nanoparticle (AuNpCys) composite to be immobilized by electrostatic interaction in the network of a poly(vinyl chloride-vinyl acetate maleic acid) (PVM) layer on a gold bare electrode. The impedimetric biosensor is fabricated by self-assembled CramoLL lectin on the PVM–AuNpCys–modified gold electrode through electrostatic interaction. CramoLL is used as the recognition interface. AFM images showed that LPS was specifically recognized on the PVM–AuNpCys–CramoLL system surface. The measurements of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the electrochemical response of a redox probe system (K4[Fe(CN)6]4−/K3[Fe(CN)6]3−) were blocked, due to the procedures of modified electrode with PVM–AuNpCys–CramoLL. In the majority of the experiments the lectin retained its activity as observed through its interaction with LPS from Escherichia coli, Serratia marcescens, Salmonella enterica and Klebsiella pneumoniae. The results are expressed in terms of the charge transfer resistance and current peak anodic using the EIS and CV techniques for the development of a biosensor for contamination by endotoxins. A new type of sensor for selective discrimination of LPS types with a high sensitivity has been obtained. [Copyright &y& Elsevier]

Abstract: A one-phase and/or two-phase method were used to prepare the stable ionic liquid-based nanofluids containing same volume fraction but different sizes or surface states of gold nanoparticles (Au NPs) and their thermal conductivities were investigated in more detail. Five significant experiment parameters, i.e. temperature, dispersion condition, particle size and surface state, and viscosity of base liquid, were evaluated to supply experimental explanations for heat transport mechanisms. The conspicuously temperature-dependent and greatly enhanced thermal conductivity under high temperatures verify that Brownian motion should be one key effect factor in the heat transport processes of ionic liquid-based gold nanofluids. While the positive influences of proper aggregation and the optimized particle size on their thermal conductivity enhancements under some specific conditions demonstrate that clustering may be another critical effect factor in heat transport processes. Moreover, the remarkable difference of the thermal conductivity enhancements of the nanofluids containing Au NPs with different surface states could be attributed to the surface state which has a strong correlation with not only Brownian motion but also clustering. Whilst the close relationship between their thermal conductivity enhancements and the viscosity of base liquid further indicate Brownian motion must occupy the leading position among various influencing factors. Finally, a promisingly synergistic effect of Brownian motion and clustering based on experimental clues and theoretical analyses was first proposed, justifying different mechanisms are sure related. The results may shed lights on comprehensive understanding of heat transport mechanisms in nanofluids. [Copyright &y& Elsevier]

Abstract: The Turkevich method for synthesizing gold nanoparticles, using sodium citrate as the reducing agent, is renowned for its ability to produce biocompatible colloids with mean size>10nm. Here we show that monodisperse gold nanoparticles in the 5–10nm size range can be synthesized by simply reversing the order of addition of reactants, i.e. adding chloroauric acid to citrate solution. Kinetic studies and electron microscopic characterization revealed that the reactivity of chloroauric acid, initial molar ratio of citrate to chloroauric acid (MR), and reaction mixture pH play an important role in producing monodisperse gold nanoparticles. Reversing the order of addition also enhanced the stabilization of nanoparticles at high MR values. Remarkably, the system exhibits a ‘memory’ of the order of addition, even when the timescale of mixing is much shorter than the timescale of synthesis. [Copyright &y& Elsevier]

Abstract: We report for the first time on the templating effect of β-lactoglobulin amyloid-like fibrils to synthesize gold single crystals of several decades of μm in dimensions. The gold single crystals were produced by reducing an aqueous solution of chloroauric acid by β-lactoglobulin amyloid protein fibrils. Atomic force microscopy, conventional and scanning transmission electron microscopy, electron diffraction and optical microscopy techniques were combined to characterize the structure of the gold crystals. The single-crystalline features of these macroscopic gold crystals are witnessed by their distinctive hexagonal and triangular shape and are confirmed by selected area electron diffraction (SAED). UV–vis absorption spectrum, recorded after a reaction time of 6h at the heating temperature of 55°C showed a surface plasmon resonance peak at 540nm. With the increase of reaction time to 24h, the absorption spectrum peaks shift to a very broad and higher wavelength region extending up to near infrared region. Remarkably, these single crystalline gold crystals show auto fluorescence when illuminated to UV lamp. Further increase in β-lactoglobulin amyloid fibrils concentration above the isotropic-nematic transition, drives the formation of gold single crystals microplates stacking together and self-assembling into new hierarchical, layered protein-gold hybrid composites. [Copyright &y& Elsevier]

Abstract: Gold nanoclusters (Au NCs) have attracted intensive attention for their molecular-like properties such as luminescence and unique charging behavior. A facile route has been developed for the preparation of ultrafine Au NCs at room temperature. Bis(p-sulfonatophenyl)phenylphosphine dihydrate dipotassium was used to stabilize the Au NCs obtained by NaBH4 reduction of HAuCl4 at pH of ∼12 and facilitated the phase transfer of Au NCs from aqueous phase to an organic medium based on electrostatic interaction. From the analyses of TEM, HRTEM, and XRD patterns, the formation of fcc structured Au NCs dominated by {200} facets was identified. The Au NCs transferred into toluene could be used as seeds for the formation of core–shell Au@Ag2S nanoparticles, providing for a promising strategy for the metal doping in semiconductor nanocrystals. [Copyright &y& Elsevier]

Abstract: Amphiphilic gold nanoparticles grafted with V-shaped brushes (Au-V-brushes) were prepared by grafting a polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer with a trithiocarbonate group as the junction to the Au surface. The obtained Au-V-brushes were subjected to solubility test and UV–vis, FT-IR, TEM and DLS characterizations. It is found that the Au-V-brushes are soluble in both water and organic solvents. In the common solvent DMF, the size of the Au-V-brushes is about 17nm, whereas in selective solvents (toluene and water) aggregates of 70–90nm are formed. Phase transfer of the Au-V-brushes from the water phase into the toluene phase occurs upon addition of Na2SO4 into water and the Au-V-brushes can also transfer from the toluene phase to the interface of toluene and water phases after addition of citric acid in the water phase. [Copyright &y& Elsevier]

Abstract: We report an enzymatic method to control the plasmon resonance absorbance of gold nanoparticle (AuNP) arrays assembled on hyaluronic acids. While multiple electrostatic interactions between cysteamine on the AuNPs and the carboxylic acid residues in the whole intact hyaluronic acid induced the formation of large aggregates, precise control of the plasmon absorbance was possible by tailoring the size of the bio-polymeric templates with hyaluronidase, almost over the entire range of the resonant coupling wavelengths. It was possible to precisely tune the position of the second plasmon absorbance by manipulating the amount of the template and the enzymatic hydrolysis time. Finally, we were able to produce a chain-like array of AuNPs, which was nearly one dimensional, with a maximum shift of up to 189nm in the plasmon absorbance at the optimal hydrolysis time of the templates. This enzymatic method can be used as a useful tool to tailor the plasmonic properties of the nanostructures required for specific applications. [Copyright &y& Elsevier]

Abstract: The utilization of metal nanoparticles (NPs) to fabricate metal electrodes under mild conditions is one of the most studied topic in recent years. In this work, colloidal Au NPs were deposited on two isostructural molecular crystals, namely 1,2,3,4-tetrafluoro-7-thiomethyl-acridine (MeSAcr) and 1,2,3,4-tetrafluoro-7-methoxy-acridine (MeOAcr), exposing S atoms and O atoms, respectively, at their largest crystal faces. The depositions were carried out mainly by drop casting under ambient conditions, increasing the contact time from 1 to 120min, and the samples were then analyzed by atomic force microscopy (AFM) to evaluate the coverage. Thanks to the affinity between S and Au atoms, Au NPs are observed to adhere on the MeSAcr surface within 1-min contact time, whereas at least 1h is required to find NPs on the MeOAcr surface. NP adsorption is also affected by the substrate surface morphology; indeed, step edges represent preferential adsorption sites even in the absence of Au–S interaction. Experiments under different conditions were performed to maximize the coverage on MeSAcr, reaching values up to 13%. AFM equipped with fluid cell was also employed to simultaneously depositing and imaging NPs, achieving a better understanding of the adsorption mechanism. [Copyright &y& Elsevier]

Abstract: We report a novel strategy on the controlled assembly of gold nanoparticles (NPs) at the air–water interface by designing a concentration gradient of electrolytes utilizing volatile weak acidic electrolytes. Films of close-packed Au NPs can be facilely obtained by exposing citrate-protected gold colloids to the vapor of formic acid for several hours in an airtight desiccator at room temperature. Both the higher interfacial concentration of formic acid and the buffer effect of citrate solution play the key roles in the assembly. They engender a gradient distribution of hydrogen ions such that to trigger the interfacial assembly of gold NPs while preventing the bulk colloid from aggregation and coagulation. Comparative investigations have also been performed either using other volatile electrolytes like weaker acetic acid and stronger hydrochloric acid or adding an electrolyte directly into the colloids. The as-prepared films of gold NPs can serve as good substrates for surface-enhanced Raman scattering (SERS). This strategy has also been applied to the assembly of some other NPs like colloidal Pt at the air–water interface. [Copyright &y& Elsevier]

Abstract: The preparation and characterisation of a series of well-defined low generation (poly)amidoamine (PAMAM)-based dendrimers with end-grafted ethylene glycol ether moieties of type N(CH2CH2C(O)NHCH2CH2NR2)3 (3a, R=CH2CH2C(O)OCH2CH2OCH3; 3b, R=CH2CH2C(O)O(CH2CH2O)2C2H5; 3c, R=CH2CH2C(O)O(CH2CH2O)9CH3), [CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2 (4, R=CH2CH2C(O)O(CH2CH2O)2C2H5) and (R2NCH2CH2NHC(O)CH2CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NR2)2]2 (5a, R=CH2CH2C(O)OCH2CH2OCH3; 5b, R=CH2CH2C(O)O(CH2CH2O)2C2H5; 5c, R=CH2CH2C(O)O(CH2CH2O)9CH3) and their application for the stabilisation of gold nanoparticles (Au NPs) is described. These dendrimers were prepared by a consecutive divergent synthesis methodology including Michael addition and amidation cycles. For comparison, amidoamine related model compounds N(C3H7)R2 (1, R=CH2CH2C(O)O(CH2CH2O)2C2H5) and [CH2NR2]2 (2, R=CH2CH2C(O)O(CH2CH2O)2C2H5) were also synthesised to estimate the minimum required donating capabilities of the stabiliser. Loading the appropriate dendritic templates with H[AuCl4] (12) and subsequent reduction of the respective metallodendrimers with Na[BH4] produced dendrimer encapsulated gold colloids. The dendrimeric scaffold, the length of the ethylene glycols, the adjusted stabilizer:gold ratio and the duration of reaction time affects the average Au particle diameter in a range of 4.0 (±0.9) to 58.5 (±14.5) nm. Furthermore, depending on the nature of the stabiliser, nanoparticles were formed having spherical or multiple morphologies. Characterisation by transmission electron microscopy (TEM), dynamic light scattering (DLS), UV/vis, and IR spectroscopy revealed that Au NPs are formed and protected inside the dendrimer scaffold. [Copyright &y& Elsevier]

Abstract: Gold nanoparticles were prepared using peptide–biphenyl hybrids (PBHs) as capping agents. AuNPs were characterized by different techniques including UV–Vis, TEM, EDX, FT-IR, elemental analysis, 1H NMR and 13C CP/MAS NMR spectroscopy. TEM analysis showed that AuNPs present diameters in the range of 1.8–3.7nm, depending on the structure and the amount of the capping PBH used. FT-IR spectroscopy and solid-state 13C NMR revealed that the carboxylic group of PBHs, especially in the case of the acid ligands, interacts with the gold surface (in the form of carboxylate). The results confirm that PBHs are excellent stabilizers of AuNPs, being one of the first examples on the use of peptidomimetics–gold hybrid materials. [Copyright &y& Elsevier]

Abstract: The growth of gold nanoparticles without chemical reduction of gold (III) ions was achieved by the disruption of thermoresponsive polymers conjugated with the gold nanoparticles through the phase transition of the polymers. When a solution of gold nanoparticles coated with thermoresponsive polymers was heated, chains of the thermoresponsive polymers were disrupted because of dehydration, resulting in the fusion of gold nanoparticles to form larger nanoparticles. The evolution of the extinction band around 550nm evidenced the formation of these large (post-fusion) gold nanoparticles, which were characterized by transmission electron microscope (TEM) and dynamic light scattering (DLS). TEM images verified the formation of the large gold nanoparticles having particle sizes of 80–100nm, whereas DLS indicated the existence of large nanoparticles with hydrodynamic diameters exceeding 200nm. The deposition did not require the addition of reductants or trivalent gold ions for the formation of the large gold nanoparticles. Both the heating and the solution conditions were studied to elucidate the mechanism of the formation of large gold nanoparticles. [Copyright &y& Elsevier]

Abstract: We report the bioassisted synthesis of gold nanoparticle/silica (Au NP/silica) tubes using layer-by-layer (LBL) assembled poly(l-lysine)/poly(l-tyrosine) (PLL/PLT) multilayer films deposited on the polycarbonate (PC) membrane pores as both mediating agents and templates. The novelty of this approach is the in situ synthesis of Au NP/silica tubes using PLL/PLT multilayer films for sequential growth of Au NPs and silicas. The experimental data revealed that the buildup of the LBL multilayer films was mainly driven by the formation of hydrogen bond and the polypeptide macromolecular assemblies adopted mainly β-sheet conformation. The as-prepared Au NP/silica tubes possessed promising catalytic activity toward the reduction of p-nitrophenol. The synthesis conditions such as the concentration of gold precursor and polypeptide molecular weight were found to influence the gold weight ratio and particle size in the tubes and the catalytic properties of the Au NP/silica tubes. This approach provides a facile, robust, and green method to obtain nonaggregated metal nanoparticles immobilized in porous oxide network at ambient conditions. Using the synergy between biomimetic or bioassisted synthesis of nanostructured materials and LbL assembly technique, a variety of structures such as films, tubes, and capsules comprising of multiple compositions can be obtained. [Copyright &y& Elsevier]

Abstract: Thin films composed of oleylamine (OLA) and double-stranded deoxyribonucleic acid (dsDNA from Salmon testes) have been successfully constructed on polycrystalline Au surfaces using the electrostatic adsorption and self-assembly (SA) technique. The formation of the Au/OLA/dsDNA films was followed step-by-step by Quartz Crystal Microbalance with energy dissipation (QCM-D), Atomic Force Microscopy (AFM), and electrochemical techniques such as Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The use of these techniques allowed the characterization and the follow up of the successful construction of the OLA/dsDNA composite film. The main advantages of the proposed methodology are the simplicity of the modification procedure, the stability of the dsDNA self-assembled film, and the potential employment of the dsDNA modified gold electrodes to study the interactions of DNA with target molecules. [Copyright &y& Elsevier]

Abstract: We present a process for the phase-transfer of gold nanoparticles from an aqueous to an organic medium with normal alkanethiols. This method can be applied not only to large nanospheres (d ∼100nm) but also to anisotropic nanoparticles like nanorods and nanoplates. It allows the comparison of the nanoparticle optical properties when they are dispersed in both aqueous and organic media. [Copyright &y& Elsevier]

Abstract: This paper describes a performance of precise control of shell thickness in silica-coating of Au nanoparticles based on a sol–gel process, and an investigation into X-ray imaging properties for the silica-coated Au (Au/SiO2) particles. The Au nanoparticles with a size of 16.9±1.2nm prepared through a conventional citrate reduction method were used as core particles. The Au nanoparticles were silica-coated with a sol–gel reaction using tetraethylorthosilicate (TEOS) as a silica source, sodium hydroxide (NaOH) as a catalyst, and (3-aminopropyl) trimethoxysilane (APMS) as a silane coupling agent. An increase in TEOS concentration resulted in an increase in shell thickness. Under certain concentrations of Au, H2O, NaOH, and APMS, the Au/SiO2 particles with silica shell thickness of 6.0–61.0nm were produced with varying TEOS concentration. Absorption peak wavelength of surface plasmon resonance of the Au/SiO2 colloid solution depended on silica shell thickness, which agreed approximately with the predictions by Mie theory. The as-prepared colloid solution could be concentrated up to an Au concentration of 0.19M with salting-out and centrifugation. The concentrated colloid solution showed an X-ray image with high contrast, and a computed tomography value for the colloid solution with an Au concentration of 0.129M was achieved 1329.7±52.7HU. [Copyright &y& Elsevier]