Seed-mediated Synthesis Research Articles

Reducing Agent-Assisted Excessive Galvanic Replacement Mediated Seed-Mediated Synthesis of Porous Gold Nanoplates and Highly Efficient Gene-Thermo Cancer Therapy.

Porous Au nanoplates (pAuNPs) were manufactured by a reducing agent-assisted galvanic replacement reaction on Ag nanoplates using a seed-mediated synthetic approach. Two core additives, poly(vinylpyrrolidone) and l-ascorbic acid, prevented fragmentation and proceeded secondary growth. By controlling the concentration of the additives and the amount of replacing ion AuCl4-, various nanostructures including nanoplates with holes, nanoframes, porous nanoplates, and bumpy nanoparticles with unity and homogeneity were synthesized. The present synthetic method is advantageous, because it can be used to manufacture pAuNPs with ease, robustness, and convenience. The prepared pAuNPs exhibited a highly efficient photothermal conversion effect and cargo loading capacity on exposed surfaces by Au-thiol linkage. By using dual cargo mixed loading of the hepatitis C virus (HCV) targeting gene drug DNAzyme and cell-penetrating peptide TAT onto the surface of the pAuNPs and photothermal conversion-mediated hyperthermic treatment, successful gene-thermo therapy against HCV genomic human hepatocarcinoma cells were demonstrated.

Seed-mediated synthesis of floriated Ag nanoplates as surface enhanced Raman scattering substrate for in situ molecular detection

Novel floriated Ag nanoplates showing numerous ultra-small gaps (6–8nm) on the surfaces were synthesized via a seed-mediated method with the assistance of sodium citrate and etching agent hydrogen peroxide. After inner hotspots were certified by simulation, the floriated Ag nanoplates were employed in surface-enhanced Raman scattering (SERS) detection and exhibit high sensitivity and excellent homogeneity in the analysis of 2-naphthalenethiol. Particularly, a sticker-type SERS substrate was developed by mixed the floriated Ag nanoplates into flexible NaCMC film and applied to in situ survey pesticide residue on the surface of apple.

Seed-mediated synthesis and SERS performance of graphene oxide-wrapped Ag nanomushroom

A facile seed-mediated method was developed to modify core-shell Ag nanosphere@PSPAA with another Ag layer for achieving an enhancement of their surface-enhanced Raman scattering (SERS) activity. Interestingly, an Ag bridge in the polymer shell connected the inner and outer Ag layers, resulting in a mushroom-like nanostructure. The outer Ag grew around the polymer shell to form the cap of the nanomushrooms (NMs) with the extension of the reaction time. The epitaxial growth mechanism of this novel nanostructure was investigated by tuning the type of seed from nanosphere to nanocube and nanorod. With the growth of the outer Ag cap, the SERS intensity of these Ag NMs increased significantly together with the red-shifting and broadening of their typical localized surface plasmon resonance band. Such a phenomenon can be attributed to the formation of SERS hotspots between the inner and outer Ag layers. The Ag NMs were then wrapped with a graphene oxide (GO) shell via static interactions. The GO-wrapped Ag NMs exhibited a further better SERS performance in terms of sensitivity, homogeneity and stability compared with non-wrapped ones, indicating that the heterostructure could be potentially useful for SERS-based immunoassay.

Synthesis of Au-Pd Bimetallic Nanoflowers for Catalytic Reduction of 4-Nitrophenol.

Due to the great potential to improve catalytic performance, gold (Au) and palladium (Pd) bimetallic catalysts have prompted structure-controlled synthesis of Au-Pd nanoalloys bounded by high-index facets. In this work, we prepared Au-Pd bimetallic nanoflowers (NFs) with a uniform size, well-defined dendritic morphology, and homogeneous alloy structure in an aqueous solution by seed-mediated synthesis. The prepared bimetallic NFs were fully characterized using a combination of transmission electron microscopy, Ultraviolet-Visible (UV-vis) spectroscopy, inductively coupled plasma optical emission spectroscopy, and cyclic voltammetry measurements. The catalytic activities of the prepared Au-Pd nanoparticles for 4-nitrophenol reduction were also investigated, and the activities are in the order of Au@Pd NFs > Au-Pd NFs (Au1Pd1 core) > Au-Pd NFs (Au core), which could be related to the content and exposed different reactive surfaces of Pd in alloys. This result clearly demonstrates that the superior activities of Au-Pd alloy nanodendrites could be attributed to the synergy between Au and Pd in catalysts.

Green, Seed-Mediated Synthesis of Au Nanowires and Their Efficient Electrocatalytic Activity in Oxygen Reduction Reaction.

A new, simple, green method for the synthesis of Au nanowires (average diameter 8 nm and several micrometers in length) using Au seeds prepared from bael gum (BG) is reported. The nanowires are characterized using UV-visible absorption spectroscopy, powder X-ray diffraction, transmission electron microscopy (TEM), and high-resolution-TEM. It is observed that the rate of the reduction process might be the decisive factor for the shape selectivity, as evident from the formation of nanowires at a particular concentration of seeds and NaOH. The polysaccharide present in BG is the active ingredient for the synthesis of Au nanowires, while the small molecules present in BG, when used alone, did not result in nanowire formation. The TEM images of the precursor to the Au nanowires suggested that new, nucleated particles align in a linear manner and fuse with one another, resulting in the nanowire. The linear fusion of the newly nucleated particles could be due to the lack of adequate protecting agent and the presence of Au complex adsorbed to the surface. The electrochemical activity of the nanowires for oxygen reduction reaction (ORR) is assessed and compared with that of nanotriangles and spherical nanoparticles of Au. The performance of Au nanowire is better than Au-nanomaterials (heat-treated as well as non-heat-treated), Au seeds, and clusters. The better efficiency of the nanowires when compared to that of the other reported catalysts is attributed to the presence of active (100) facets with numerous corners, edges, and surface defects.

Seed-mediated synthesis of acanthosphere-like gold microstructures with tunable LSPR in the NIR region using gemini surfactants as directing agents for SERS applications

Acanthosphere-like gold microstructures (AGMs) were synthesized using a facile, two-step, seed-mediated method and butanediyl-1,4-bis(dimethylhexadecylammonium bromide) (16-4-16) as a structure-directing agent. The morphologies and sizes of the products were controlled during the synthesis process by adjusting the concentrations of 16-4-16, the AgNO3 feed, HAuCl4, ascorbic acid, the amount of Ag seeds and the types of gemini surfactants used through systematic inquiry; particle sizes ranging from 130 to 800 nm were well prepared. Correspondingly, the morphology of the products changed between regular and irregular AGMs, and the products presented a number of new morphologies, such as open-mouthed submicrostructures and ribbon nanowires. In particular, with the increase in the 16-4-16 concentration, the structural morphology of the thorns clearly changed from a tip to a lamellar structure. A UV-vis spectroscopic analysis indicated that the localized surface plasmon resonance (LSPR) peak of the AGMs could be adjusted by changing the above factors, which extended from 500 to 1350 nm in the near-infrared (NIR) region, enabling a tremendous potential for using the AGMs as platforms for various biomedical applications. Based on the intermediate products, we propose a two-stage growth mechanism for the AGMs in which their solid cores and tips are generated successively. Surface-enhanced Raman scattering (SERS) measurements indicate that the AGMs can serve as sensitive SERS substrates; a SERS detection limit of 5 × 10−7 M is presented for rhodamine B molecules.

Highly Concentrated Seed-Mediated Synthesis of Monodispersed Gold Nanorods

The extremely large optical extinction coefficient of gold nanorods (Au-NRs) enables their use in a diverse array of technologies, rnging from plasmonic imaging, therapeutics and sensors, to large area coatings, filters, and optical attenuators. Development of the latter technologies has been hindered by the lack of cost-effective, large volume production. This is due in part to the low reactant concentration required for symmetry breaking in conventional seed-mediated synthesis. Direct scale up of laboratory procedures has limited viability because of excessive solvent volume, exhaustive postsynthesis purification processes, and the generation of large amounts of waste (e.g., hexadecyltrimethylammonium bromide(CTAB)). Following recent insights into the growth mechanism of Au-NRs and the role of seed development, we modify the classic seed-mediated synthesis via temporal control of seed and reactant concentration to demonstrate production of Au-NRs at more than 100-times the conventional concentration, while maintaining independent control and narrow distribution of nanoparticle dimensions, aspect ratio, and volume. Thus, gram scale synthesis of Au-NRs with prescribed aspect ratio and volume is feasible in a 100 mL reactor with 1/100th of organic waste relative to conventional approaches. Such scale-up techniques are crucial to cost-effectively meet the increased demand for large quantities of Au-NRs in emerging applications.

Effect of Growth Temperature on Tailoring the Size and Aspect Ratio of Gold Nanorods.

The influence of temperature on the gold nanorod synthesis process and its effect on tailoring the size and aspect ratio have not been fully investigated and understood. A comprehensive study, involving SEM and TEM microscopy, Vis-NIR spectroscopy, quantitative data analysis and theoretical simulation, is performed to understand the effect of growth temperature on size, aspect ratio, and shape uniformity of gold nanorods that are synthesized by a recently developed binary-surfactant seed-mediated AuNR synthesis method. It has been demonstrated that the temperature can be used as a simple processing parameter to viably tailor the size and aspect ratio of AuNRs as well as the corresponding surface plasmon resonance behavior. The temperature coefficients for length, diameter, and aspect ratio have been, respectively, determined to be 3.5 nm/°C, 3.9 nm/°C, and -0.18/°C. With a combination of controlling temperature and formulation, the binary surfactant seed-mediated AuNR synthesis method expects to be a convenient way for producing gold nanorods with a large range of size and aspect ratio suitable for different applications.

Exploring the Formation of Symmetric Gold Nanostars by Liquid-Cell Transmission Electron Microscopy.

The shape-dependent properties of gold nanostars (NSs) have motivated massive research efforts in the field of colloidal chemistry to gain a better control over the morphology of these promising nanostructures. Nevertheless, this challenge requires a better understanding of the atomic-scale processes leading to the formation of stellated nanoparticles. We hereby report an unprecedented in situ study focused on the seed-mediated synthesis of symmetric gold NSs performed by radiolysis in methanol. We take advantage of the spatial and temporal resolutions of liquid-cell transmission electron microscopy to unravel the key effects of the growth speed, seed-crystal morphology, and dimethylamine functionalization on the formation mechanisms, shape, and stability of NSs enclosed by high-index facets. Surprisingly, the stellation processes transforming icosahedral nanoparticles into NSs with 20 sharp arms entails a continuous restructuring of NS facets driven by surface diffusion, which provide a fresh look at faceting mechanisms.

Seed-Mediated Synthesis of Gold Nanoparticles of Controlled Sizes To Demonstrate the Impact of Size on Optical Properties

Gold (Au) nanoparticles of varying sizes were synthesized during an outreach activity to introduce students to the size-dependent optical properties of nanomaterials. For the fabrication of Au nanoparticles of varying sizes, a seeded growth method was employed. In the first part of the activity, students performed the Frens method to obtain Au seeds. Students then used these seeds in the second part to conduct a seed-mediated synthesis, and obtained Au nanoparticles of a wide size range. The size differences in the particles were evident by eyesight due to color changes in the nanoparticle solutions. In addition to observations made about color, the nanoparticles were characterized using UV–vis spectroscopy, and a red shift in the peak wavelength of the extinction spectra of the Au nanoparticles was observed when nanoparticles were grown larger in size. This activity demonstrates a straightforward approach to seed-mediated nanoparticle growth and is applicable to both high school and undergraduate students.

Seed-mediated synthesis of ultra-long copper nanowires and their application as transparent conducting electrodes

Owing to a recent push toward one-dimensional nanomaterials, in this study, we report a seed-mediated synthetic strategy for copper nanowires (Cu NWs) production involving thermal decomposition of metal-surfactant complexes in an organic medium. Ultra-long Cu NWs with a high aspect ratio and uniform diameter were obtained by separating nucleation and growth steps. The underlying mechanism for nanowire formation was investigated, in addition, properties of the obtained Cu NWs were also characterized using diverse analysis techniques. The performance of resulting Cu NWs as transparent electrodes was demonstrated for potential application. This article can provide information on both new synthetic pathway and potential use of Cu NWs.

Method for Measuring Platinum Electrochemically Active Surface Area and Understanding Surface Restructuring

Platinum is a widely used catalyst in aqueous environments, particularly in fuel cells as an electrocatalyst for hydrogen oxidation [1] and oxygen reduction [2]. Key to developing new and improved catalysts is a method to accurately measure the surface area of various catalysts so their activity can be properly compared. Further, platinum catalysts can undergo changes in size and shape in an aqueous electrochemical environment, changing the surface area and surface faceting, impacting catalytic performance. We have developed a simple method, based on our prior DFT results [3, 4] which can be used to deconvolute experimentally measured cyclic voltammograms on platinum electrodes in non-adsorbing electrolytes (acid and alkaline) to more accurately estimate electrochemically active surface area (ECSA) than the traditional “H-upd” method, without any additional measurements. This method can also give the relative proportion of 111-terrace sites, 100 step and terrace sites, and 110 step and terrace sites. We validate this method using cyclic voltammograms measured on single crystal electrodes, then extend to Pt nanoparticles and polycrystalline Pt. We also use this method to examine the experimentally measured restructuring of a polycrystalline platinum electrode in an alkaline electrolyte upon potential cycling. To understand the driving forces for restructuring, we use DFT to calculate the surface energy of Pt(111), Pt(100), and Pt(110) in an aqueous environment as a function of potential, considering the adsorption of hydrogen, hydroxide, and oxygen, spanning a large range of potential (the full electrochemical window of water). With these results, we explain the experimentally observed growth in primarily 110 sites, as well as 100 sites, due to the lower energy of these sites near potentials where surface oxide is reduced. We can also use these DFT results to gain insight into nanoparticle growth and restructuring, where for example, the strong binding of hydrogen to Pt(100) at low potentials contributes to the growth of tetrahexahedral nanoparticles on square wave cycling of spherical Pt nanoparticles [5-7]. [1] H. A. Gasteiger, J. E. Panels, and S. G. Yan, "Dependence of PEM fuel cell performance on catalyst loading," Journal of Power Sources, vol. 127, pp. 162-171, 2004. [2] H. A. Gasteiger, S. S. Kocha, B. Sompalli, and F. T. Wagner, "Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs," Applied Catalysis B: Environmental, vol. 56, pp. 9-35, 2005. [3] I. T. McCrum and M. J. Janik, "pH and Alkali Cation Effects on the Pt Cyclic Voltammogram Explained Using Density Functional Theory," The Journal of Physical Chemistry C, vol. 120, pp. 457-471, 2016. [4] I. T. McCrum and M. J. Janik, "First Principles Simulations of Cyclic Voltammograms on Stepped Pt(553) and Pt(533) Electrode Surfaces," ChemElectroChem, vol. 3, pp. 1609-1617, 2016. [5] N. Tian, Z.-Y. Zhou, S.-G. Sun, Y. Ding, and Z. L. Wang, "Synthesis of Tetrahexahedral Platinum Nanocrystals with High-Index Facets and High Electro-Oxidation Activity," Science, vol. 316, pp. 732-735, 2007. [6] S. Liu, N. Tian, A.-Y. Xie, J.-H. Du, J. Xiao, L. Liu, et al., "Electrochemically Seed-Mediated Synthesis of Sub-10 nm Tetrahexahedral Pt Nanocrystals Supported on Graphene with Improved Catalytic Performance," Journal of the American Chemical Society, vol. 138, pp. 5753-5756, 2016. [7] T. Zhu, E. J. M. Hensen, R. A. van Santen, N. Tian, S.-G. Sun, P. Kaghazchi, et al., "Roughening of Pt nanoparticles induced by surface-oxide formation," Physical Chemistry Chemical Physics, vol. 15, pp. 2268-2272, 2013.

Growth of Silver Nanowires from Controlled Silver Chloride Seeds and Their Application for Fluorescence Enhancement Based on Localized Surface Plasmon Resonance.

A "Polyol" method has granted low-cost and facile process-controllability for silver-nanowire (Ag-NW) synthesis. Although homogenous and heterogeneous nucleation and growth during Ag-NW synthesis are possible using polyol methods, heterogeneous nucleation and growth of Ag NW guarantees highly selective growth of nanostructures using silver chloride (AgCl) seeds, which provides a stable source of chloride ions (Cl-) and thermodynamic reversibility. In this paper, a microdroplet has been adopted to synthesize uniform AgCl seeds with different diameter that are used for seed-mediated Ag-NW synthesis. The concentration of two precursors (AgNO3 and NaCl) in the droplets is modulated to produce different sizes of AgCl seeds, which determines the diameter and length of Ag NWs. The process of the seed-mediated growth of Ag NWs has been monitored by observing the peak shift in the time-resolved UV-vis extinction spectrum. Furthermore, the distinct plasmonic property of Ag NWs for transverse and longitudinal localized-surface-plasmon-resonance (LSPR)-mediated fluorescence enhancement is utilized. The high aspect ratio and sharp tips work as simple antennas that induce the enhanced fluorescence emission intensity of a fluorophore, which can be applied in the fields of biological tissue imaging and therapy.

Seed-mediated synthesis of cross-linked Pt-NiO nanochains for methanol oxidation

A simple method was reported for employing NiO nanoparticles act as seeds and then different amounts of Pt2+ were reduced on the NiO nanoparticles, forming a cross-linked Pt-NiO nanocatalysts. These as-prepared catalysts were characterized using different physical-chemical techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results indicate that the morphology of the cross-linked Pt-NiO nanochain was successfully produced regardless of the molar ratio of Pt2+ to NiO precursors. The electrochemical characteristics of Pt-NiO nanochain catalysts were evaluated for the oxidation of methanol as a model reaction, which verify that the Pt-NiO catalysts show enhanced activity and high stability in comparison with the commercial Pt/C catalyst. The optimized ratio of Pt to NiO is 1:1, then tuned by simple adjusting the feed ratio of the precursors as well. The synthesized nanocatalysts will be found the great potential applications as electrocatalysts for fuel cells owe to their enhanced catalytic performance and long-term stability.

Monodisperse Ag/Pd core/shell nanoparticles assembled on reduced graphene oxide as highly efficient catalysts for the transfer hydrogenation of nitroarenes

Addressed herein is a facile seed-mediated synthesis of Ag/Pd core/shell nanoparticles (NPs) and their assembly on reduced graphene oxide (rGO) to catalyze the transfer hydrogenation of nitroarenes to anilines using ammonia borane (AB) as a hydrogen donor under ambient conditions. Monodisperse Ag/Pd core/shell NPs with controllable Pd shell-thickness were synthesized by the means of thermal decomposition of palladium(II) bromide over as-prepared Ag NPs in the mixture of oleylamine and oleic acid at 220°C. As-synthesized Ag/Pd core/shell NPs were characterized by TEM, HR-TEM, XRD, XPS, UV–Vis spectroscopy and ICP-MS and then they were assembled on reduced graphene oxide (rGO). Next, rGO@Ag/Pd catalysts were tested in the transfer hydrogenation of nitroarenes in which ammonia borane (AB) was used as a hydrogen donor at room temperature. It was demonstrated that the thickness of the Pd shell has a significant effect on the catalytic activity of rGO@Ag/Pd catalysts and the 1.75nm Pd shell provided the highest performance in the transfer hydrogenation reactions. The rGO@Ag/Pd catalyzed transfer hydrogenation reactions were tested over a variety of nitroarenes (total 16 examples) and they were all converted to the corresponding aniline derivatives with high yields in 5–15min under ambient conditions.

Seedless Synthesis of Monodispersed Gold Nanorods with Remarkably High Yield: Synergistic Effect of Template Modification and Growth Kinetics Regulation.

Gold nanorods (AuNRs) are versatile materials due to their broadly tunable optical properties associated with their anisotropic feature. Conventional seed-mediated synthesis is, however, not only limited by the operational complexity and over-sensitivity towards subtle changes of experimental conditions but also suffers from low yield (≈15 %). A facile seedless method is reported to overcome these challenges. Monodispersed AuNRs with high yield (≈100 %) and highly adjustable longitudinal surface plasmon resonance (LSPR) are reproducibly synthesized. The parameters that influence the AuNRs growth were thoroughly investigated in terms of growth kinetics and soft-template regulation, offering a better understanding of the template-based mechanism. The facile synthesis, broad tunability of LSRP, high reproducibility, high yield, and ease of scale-up make this method promising for the future mass production of monodispersed AuNRs for applications in catalysis, sensing, and biomedicine.

Understanding the Seed-Mediated Growth of Gold Nanorods through a Fractional Factorial Design of Experiments.

Since the development of simple, aqueous protocols for the synthesis of anisotropic metal nanoparticles, research into many promising, valuable applications of gold nanorods has grown considerably, but a number of challenges remain, including gold-particle yield, robustness to minor impurities, and precise control of gold nanorod surface chemistry. Herein we present the results of a composite fractional factorial series of experiments designed to screen seven additional potential avenues of control and to understand the seed-mediated silver-assisted synthesis of gold nanorods. These synthesis variables are the amount of sodium borohydride used and the rate of stirring when producing seed nanoparticles, the age of and the amount of seeds added, the reaction temperature, the amounts of silver nitrate and ascorbic acid added, and the age of the reduced growth solution before seed nanoparticles are added to initiate rod formation. This statistical experimental design and analysis method, besides determining which experimental variables are important and which are not when synthesizing gold nanorods (and quantifying their effects), gives further insight into the mechanism of growth by measuring the degree to which variables interact with each other by mapping out their mechanistic connections. This work demonstrates that when forming gold nanorods by the reduction of auric ions by ascorbic acid onto seed nanoparticles, ascorbic acid determines how much gold is reduced, and the amount of seeds determine how it is divided, yet both influence the intrinsic growth rates, in both width and length, of the forming nanorods. Furthermore, this work shows that the reduction of gold proceeds via direct reduction on the surface of seeds and not through a disproportionation reaction. Further control over the length of gold nanorods can be achieved by tuning the amount of silver nitrate or the reaction temperature. This work shows that silver does not directly influence rod length or width, and a new primary role for silver is proposed as a catalyst promoting the reduction of gold on the ends of forming nanorods. Furthermore, this silver catalyst is removed from the reaction by adsorption onto the surface of the growing nanorod. This work also demonstrates the importance of freshly prepared silver nitrate and ascorbic acid solutions, free from even a few hours of photodegradation, in preparing gold nanorods with high shape purity and gold yield.

Fabrication and Photoelectrochemical Properties of a Cu2O/CuO Heterojunction Photoelectrode for Hydrogen Production from Solar Water Splitting

We report on the fabrication and characterization of a novel Cu2O/CuO heterojunction structure with CuO nanorods embedded in Cu2O thin film as an efficient photocathode for photoelectrochemical (PEC) solar water splitting. A CuO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method; then, a Cu2O thin film was electrodeposited onto the CuO nanorod array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were examined using X-ray diffraction and scanning electron microscopy, as well as Raman scattering. The PEC properties of the fabricated Cu2O/CuO heterojunction photocathode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the Cu2O/CuO photocathode was found to exhibit negligible dark current and high photocurrent density, e.g. −1.05 mA/cm2 at −0.6 V vs. Hg/HgCl2 in 1 mM Na2SO4 electrolyte, revealing the effective operation of the oxide heterostructure. The photocurrent conversion efficiency of the Cu2O/CuO photocathode was estimated to be 1.27% at −0.6 V vs. Hg/HgCl2. Moreover, the PEC current density versus time (J-T) profile measured at −0.5 V vs. Hg/HgCl2 on the Cu2O/CuO photocathode indicated a 3-fold increase in the photocurrent density compared to that of a simple Cu2O thin film photocathode. The improved PEC performance was attributed to a certain synergistic effect of the bilayer heterostructure on the light absorption and electron-hole recombination processes.

Size-controlled hydrothermal synthesis of monodispersed BaZrO3 sphere particles by seeding

Monodispersed barium zirconate (BaZrO3) fine particles with a spherical shape have been synthesized by hydrothermal reactions using barium hydroxide and a Zr-triethanolamine (TEOA) complex. The particle mean diameter was gradually controlled in a range from 0.20μm to 3.5μm by change in the added amount of seed nanoparticles. The mechanistic characterization of the seed-mediated BaZrO3 sphere synthesis revealed that the particle growth obeyed a simple seed growth mechanism. In the present system, utilization of the Zr-TEOA complex played an important rule to prevent uncontrollable nucleation to form the uniform BaZrO3 fine particles with narrow size distributions.

“Green” seed-mediated synthesis and morphology of Au nanoparticles using β-cyclodextrin

Gold nanoparticles (NPs) with dendritic morphology were synthesized by a “green” seed-mediated approach in the presence of β-cyclodextrin (β-CD) as stabilizing biocompatible capping agent. First, 50 mL of an aqueous solution containing 5 mM of β-CD were prepared, to which a variable amount of HAuCl4 was added. The β-CD/Au molar ratio was monitored from 20 to 200. Optical properties, including Surface-Enhanced Raman Scattering (SERS) activity, of the synthesized structures were characterized by Raman and UV-vis spectroscopies. Morphology was studied by transmission electron microscopy (TEM). Samples prepared using this procedure presents an increase of their SERS signal with respect to samples without peak-rich morphology. Optimized nanodendrites were obtained at a β-CD/Au molar ratio of 100. Moreover, a growth mechanism is proposed to describe the β-cyclodextrin role in the synthesis of Au nanodendrites. The “green” seed-mediated synthesis technique used herein produces Au NPs with good biocompatibility pointing them out for biomedical applications.