Seeded Growth Approach Research Articles

Synthesis and characterisation of non-bonded 1.7 μm thin-shell (TS1.7-100 nm) silica particles for the rapid separation and analysis of uric acid and creatinine in human urine by hydrophilic interaction chromatography

A rapid chromatographic method for the simultaneous determination of uric acid (UA) and creatinine (Cr) in human urine is described, using a non-bonded 1.7μm thin-shell (TS1.7-100nm) silica particle prepared by the seeded-growth approach. The new shell particle was characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) and BET analysis. TEM reveals 1.5μm solid core and 100nm shell thickness. DLS shows polydispersity index <0.2. Expanded pore size of 88Å and specific surface area of 78m2/g were determined by BET. Chromatographic results demonstrate that UA, Cr and hypoxanthine (Hyp, as internal standard) can be separated in less than 1min on the in-house packed TS1.7-100 column (4.6 ID x 100mm), using chromatographic conditions with mobile phase 70% acetonitrile, 10mM ammonium acetate buffer, pH 6.78, flow rate 1.25ml/min and UV detection at 254nm. A linear relationship between the ratio of the peak area of the standard UA and Cr to that of the internal standard (Hyp) and the concentration of standards was obtained for both UA and Cr with the square of the correlation coefficients, R2=0.998 for both renal biomarkers. The calculated detection limits were 0.03μg/ml and 0.05μg/ml for UA and Cr respectively. Urine samples tested were found to contain UA and Cr in the concentration range of 782–1206μg/ml and 535–862μg/ml respectively. The recovery ranges for spiked urine standards were 85.7–93.2% for UA and 91.9–94.6% for Cr and the relative standard deviations (RSD) for both biomarkers were 3.05% and 0.88% respectively. The developed rapid HILIC method can have application in determining the concentrations of UA and Cr for early prediction in patients with developing disease conditions, including acute kidney injury (AKI).

Multicolor immunochromatographic strip test based on gold nanoparticles for the determination of aflatoxin B1 and fumonisins

The authors describe the preparation of desert rose-like gold nanoparticles (DR-GNPs) with a plasmon resonance band at 620 nm which gives them a blue color. They have a hydrodynamic diameter of ∼72 nm and were prepared by a seeding growth approach. The DR-GNPs were characterized by UV-vis spectroscopy, transmission electron microscopy and dynamic light scattering. These nonspherical GNPs were used as a label for the antibody in an immunochromatographic strip test (ICST). Despite their particular shape and the higher surface area compared to spherical gold nanoparticles, the DR-GNPs are useful blue labels for the GNP-based strip test. A multicolor ICST for aflatoxin B1 and fumonisins is described that employs both blue DR-GNPs and red spherical GNPs. It allows for simultaneous rapid determination of the two mycotoxins in maize flour, with visual cut-off levels of 2 μg⋅kg-1 for aflatoxin B1 and of 1000 μg⋅kg-1 for fumonisins.

Two-dimensional assemblies from crystallizable homopolymers with charged termini.

The creation of shaped, uniform and colloidally stable two-dimensional (2D) assemblies by bottom-up methods represents a challenge of widespread current interest for a variety of applications. Herein, we describe the utilization of surface charge to stabilize self-assembled planar structures that are formed from crystallizable polymer precursors by a seeded growth approach. Addition of crystallizable homopolymers with charged end-groups to seeds generated by the sonication of block copolymer micelles with crystalline cores yields uniform platelet micelles with controlled dimensions. Significantly, the seeded growth approach is characterized by a morphological memory effect whereby the origin of the seed, which can involve a quasi-hexagonal or rectangular 2D platelet precursor, dictates the observed 2D platelet shape. This new strategy is illustrated using two different polymer systems, and opens the door to the construction of 2D hierarchical structures with broad utility.

Polyethyleneimine-mediated seed growth approach for synthesis of silver-shell silica-core nanocomposites and their application as a versatile SERS platform

PEI-mediated seed growth approach for synthesis of high performance silver-shell silica-core nanocomposites.

Galvanic Replacement onto Complex Metal-Oxide Nanoparticles: Impact of Water or Other Oxidizers in the Formation of either Fully Dense Onion-like or Multicomponent Hollow MnOx/FeOx Structures

Multicomponent metal-oxide nanoparticles are appealing structures from applied and fundamental viewpoints. The control on the synthetic parameters in colloidal chemistry allows the growth of complex nanostructures with novel morphologies. In particular, the synthesis of biphase metal-oxide hollow nanoparticles has been reported based on galvanic replacement using an organic-based seeded-growth approach, but with the presence of H2O. Here we report a novel route to synthesize either fully dense or hollow core/shell metal-oxide nanoparticles (MnOx/FeOx) by simply adding or not oxidants in the reaction. We demonstrate that the presence of oxidants (e.g., O2 carried by the not properly degassed H2O or (CH3)3NO) allows the formation of hollow structures by a galvanic reaction between the MnOx and FeOx phases. In particular, the use of (CH3)3NO as oxidant allows for the first time a very reliable all-organic synthesis of hollow MnOx/FeOx nanoparticles without the need of water (with a somewhat unreliable oxidation role). Oxidants permit the formation of MnOx/FeOx hollow nanoparticles by an intermediate step where the MnO/Mn3O4 seeds are oxidized into Mn3O4, thus allowing the Mn3+ → Mn2+ reduction by the Fe2+ ions. The lack of proper oxidative conditions leads to full-dense onion-like core/shell MnO/Mn3O4/Fe3O4 particles. Thus, we show that the critical step for galvanic replacement is the proper seed oxidation states so that their chemical reduction by the shell ions is thermodynamically favored.

Controlled growth of high-density CdS and CdSe nanorod arrays on selective facets of two-dimensional semiconductor nanoplates.

The rational synthesis of hierarchical three-dimensional nanostructures with specific compositions, morphologies and functionalities is important for applications in a variety of fields ranging from energy conversion and electronics to biotechnology. Here, we report a seeded growth approach for the controlled epitaxial growth of three types of hierarchical one-dimensional (1D)/two-dimensional (2D) nanostructures, where nanorod arrays of II-VI semiconductor CdS or CdSe are grown on the selective facets of hexagonal-shaped nanoplates, either on the two basal facets of the nanoplate, or on one basal facet, or on the two basal facets and six side facets. The seed engineering of 2D hexagonal-shaped nanoplates is the key factor for growth of the three resulting types of 1D/2D nanostructures. The wurtzite- and zinc-blende-type polymorphs of semiconductors are used to determine the facet-selective epitaxial growth of 1D nanorod arrays, resulting in the formation of different hierarchical three-dimensional (3D) nanostructures.

Role of Collagen Concentration in Stability of Star-Shaped Silver@Gold Nanoparticles

In this report, star-shaped silver@gold (Ag@Au) nanoparticles were synthesized in collagen (Coll) suspensions by a seeding growth approach. The silver nanoparticles were used as seeds for Au development. Coll was used as a protecting agent and the effect of its concentration on stability was also examined. Obtained nanoparticles were then characterized by UV-Vis, TEM, XRD and FTIR. The result was confirmed by the maximum surface plasmon resonance peak at 566-580 nm for each sample indicating the formation of branched Ag@Au@Coll NPs. The average diameters of the branched Ag@Au@Coll NPs were revealed to be 30-50 nm depending on the corresponding component ratio and the pH value. It is interesting to note that the concentration of Coll plays a critical role in the stability of the star-shaped gold nanoparticles. The results offer an understanding of the handling of the electronic and the silver@gold based nanoparticles stability properties.

Synthesis and catalytic properties of highly branched palladium nanostructures using seeded growth.

In order to develop nanocatalysts with enhanced catalytic performance, it is important to be able to synthesize nanocrystals enclosed by high-index surface facets, due to their high density of low coordinated atoms at step, ledge and kink sites. Here, we report a facile seed-mediated route to the synthesis of highly branched Pd nanostructures with a combination of {113}, {115} and {220} high-index surface planes. The size of these nanostructures is readily controlled by a simple manipulation of the seed concentration. The selective use of oleylamine and oleic acid was also found to be critical to the synthesis of these structures, with Pd icosahedra enclosed by low-index {111} facets being produced when hexadecylamine was employed as capping ligand. The structure-property relationship of these nanostructures as catalysts in Suzuki-cross coupling reactions was then investigated and compared, with the high-index faceted branched Pd nanostructures found to be the most effective catalysts.

Size-dependent production of radicals in catalyzed reduction of Eosin Y using gold nanorods

Gold nanostructures have been widely used as catalysts for chemical processes, energy conversion, and pollution control. The size of gold nanocatalysts is thus paramount for their catalytic activity. In this paper, gold nanorods with different sizes were prepared by means of the improved seeding growth approach by adding aromatic additive. The sizes and aspect ratios of the obtained gold nanorods were calculated according to the TEM characterization. Then, we studied the catalytic activities of gold nanorods using a model reaction based on the reduction of Eosin Y by NaBH4. By monitoring the absorption intensities of the radicals induced by gold nanorods in real time, we observed the clear size-dependent activity in the conversion of EY2− to EY3−. The conversion efficiency indicated that the gold nanorods with the smallest size were catalytically the most active probably due to their high number of coordinatively unsaturated surface atoms. In addition, a compensation effect dominated by the surface area of nanorods was observed in this catalytic reduction, which could be primarily attributed to the configuration of Eosin Y absorbed onto the surfaces of gold nanorods.

Seeded Growth Synthesis of Composition and Size-Controlled Gold–Silver Alloy Nanoparticles

We propose a novel methodology to synthesize monodisperse gold–silver alloy nanoparticles (NPs) with fine control of size and composition. The synthesis is based on a combination of the coreduction of gold and silver salts for the formation of alloys and the seeded growth approach for the formation of size-controlled NPs. While the simple use of coreduction gives alloy NPs limited to ∼30 nm, the combination of both methods yields spherical alloy NPs with a size that can be controlled between ∼30 and ∼150 nm, with a coefficient of variation smaller than 15%. The alloy NPs can be synthesized to any composition between pure silver and pure gold. We also show that the alloy composition is nonhomogeneous, with a gold-rich core and a silver-rich surface. The transition in the alloy composition is gradual from the core to the surface, resulting in optical properties very similar to the optical properties of a homogeneous alloy, except for the smaller (∼30 nm) NPs. A multilayer Mie model has been introduced to st...

Au–Ag core–shell nanoparticles with controllable shell thicknesses for the detection of adenosine by surface enhanced Raman scattering

In this study, we report a feasible aqueous chemical method to synthesize Au core–Ag shell nanoparticles (NPs) by seeding growth approach. The concentration of Au NPs plays an important role in growing the different thicknesses of Ag shells. The design of signaling aptamer utilizes the target-induced switching between an aptamer/DNA duplex and an aptamer/target complex. The surface enhanced Raman scattering (SERS) signal was enhanced upon the hybridization of the Raman reporter-labeled DNA released from the target-induced displacement with the captured DNA immobilized on the silicon substrate with Au–Ag core–shell NPs. This substrate with 12.4nm Ag shell shows high reproducibility, strong enhancement, and a low detection limit (1nM). The enhancement in DNA-based adenosine detection properties shall be advantageous in applications for other aptamer sensing systems.

Controlled synthesis of monodisperse gold nanorods with different aspect ratios in the presence of aromatic additives

This paper reports the synthesis of monodisperse gold nanorods (GNRs) via a simple seeded growth approach in the presence of different aromatic additives, such as 7-bromo-3-hydroxy-2-naphthoic acid (7-BrHNA), 3-hydroxy-2-naphthoic acid (HNA), 5-bromosalicylic acid (5-BrSA), salicylic acid (SA), or phenol (PhOH). Effects of the aromatic additives and hydrochloric acid (HCl) on the structure and optical properties of the synthesized GNRs were investigated. The longitudinal surface plasmon resonance (LSPR) peak wavelength of the resulting GNRs was found to be dependent on the aromatic additive in the following sequence: 5-BrSA (778 nm) > 7-BrHNA (706 nm) > SA (688 nm) > HNA (676 nm) > PhOH (638 nm) without the addition of HCl, but this was changed to 7-BrHNA (920 nm) > SA (890 nm) > HNA (872 nm) > PhOH (858 nm) > 5-BrSA (816 nm) or 7-BrHNA (1,005 nm) > PhOH (995 nm) > SA (990 nm) > HNA (980 nm) > 5-BrSA (815 nm) with the addition of HCl or HNO3, respectively. The LSPR peak wavelength was increased with the increasing concentration of 7-BrHNA without HCl addition; however, there was a maximum LSPR peak wavelength when HCl was added. Interestingly, the LSPR peak wavelength was also increased with the amount of HCl added. The results presented here thus established a simple approach to synthesize monodisperse GNRs of different LSPR wavelengths.

A naked eye aggregation assay for Pb2+ detection based on glutathione-coated gold nanostars

Gold nanostars (AuNS) with a mean hydrodynamic size of 40 nm, obtained with a seed-growth approach using a zwitterionic surfactant (laurylsulfobetaine, LSB), were successfully coated with glutathione (GSH), obtaining a stable and purified solid product which can be easily stored and re-dissolved on need in 0.1 M aqueous solution of Hepes buffered at pH 7. Upon exposure to micromolar concentrations of Pb2+ cation, the GSH-coated nano-objects undergo a fast aggregation followed by sedimentation leading to complete precipitation in about an hour. The subsequent disappearing of the intense LSPR extinction can of course be followed spectrophotometrically but, most importantly, can be easily detected with the naked eye. No signs of this event are noticed when other divalent cations are added to the colloidal suspension in the same condition. A careful investigation was performed to study this selectivity and the behaviour of aggregation as a function of time and Pb2+ cation concentration. We demonstrate that an easy, rapid, instrument-free, visual detection of micromolar levels of Pb2+ is thus possible with this assay, showing a good selectivity towards other investigated metal cations.

Seeding Growth Approach to Gold Nanoparticles with Diameters Ranging from 10 to 80 Nanometers in Organic Solvent

AbstractTo accommodate the high demand for gold nanoparticles, which is generated by the extraordinary optical properties of plasmonic metamaterials, a focus has been placed on their large‐scale synthesis for several years. In this work, a simple method for the preparation of nearly monodisperse gold nanoparticles with diameters of up to 80 nm is presented. For this purpose, gold nanoparticles with an average diameter of 9 nm were synthesized in toluene by using oleylamine both as a reducing and stabilizing agent. These gold nanoparticles act as seeds for a subsequent growth reaction in which the same precursors are slowly added to the reaction vessel. During the reaction, the gold nanoparticles start to agglomerate when they reach a certain size (ca. 20 nm). Despite their agglomeration, they can be grown further without impairing their size distribution or morphology. The gold nanoparticle agglomerates can be separated by stabilization with thiol‐terminated polystyrene.

Fabrication of gold-nanoshell/polycaprolactonecomposite films with high electrical conductivity

Gold nanoshells on 1.1µm diameter silica cores were produced via a seeded growth approach and their quality evaluated using optical measurements. The particles were combined with polycaprolactone to produce a flexible biocompatible composite film with high conductivity (1.51Scm−1) and relatively low effective gold loading (16.86wt%) in comparison with other reports in the literature. The morphology of the composite was shown to comprise nanoshell-filled pores percolating a polymer-rich matrix. The obtained films have potential for biomedical applications such as in patches for cardiac tissue engineering, combining biocompatibility, flexibility and electrical conductivity.

Synthesis of Highly Monodisperse Citrate-Stabilized Silver Nanoparticles of up to 200 nm: Kinetic Control and Catalytic Properties

Highly monodisperse sodium citrate-coated spherical silver nanoparticles (Ag NPs) with controlled sizes ranging from 10 to 200 nm have been synthesized by following a kinetically controlled seeded-growth approach via the reduction of silver nitrate by the combination of two chemical reducing agents: sodium citrate and tannic acid. The use of traces of tannic acid is fundamental in the synthesis of silver seeds, with an unprecedented (nanometric resolution) narrow size distribution that becomes even narrower, by size focusing, during the growth process. The homogeneous growth of Ag seeds is kinetically controlled by adjusting reaction parameters: concentrations of reducing agents, temperature, silver precursor to seed ratio, and pH. This method produces long-term stable aqueous colloidal dispersions of Ag NPs with narrow size distributions, relatively high concentrations (up to 6 × 1012 NPs/mL), and, more important, readily accessible surfaces. This was proved by studying the catalytic properties of as-synthesized Ag NPs using the reduction of Rhodamine B (RhB) by sodium borohydride as a model reaction system. As a result, we show the ability of citrate-stabilized Ag NPs to act as very efficient catalysts for the degradation of RhB while the coating with a polyvinylpyrrolidone (PVP) layer dramatically decreased the reaction rate.

Influence of amount of CTAB and ascorbic acid concentration on localized surface plasmon resonance property of gold nanorod

Gold nanorods (AuNRs) are prepared through seeded growth approach. Synthesis parameters of the amount of cetyltrimethylammonium bromide (CTAB), and concentration of ascorbic acid (AA) were studied. We were aiming for an aspect ratio of 3 which could be achieved by a nanorod feature in the range of 45nm length and 15nm width. The absorption spectra are observed with an UV–visible NIR spectrophotometer and analysed theoretically. It is known that there are two plasmon resonance peaks for gold nanorod corresponding to transverse surface plasmon resonance (TSPR) and longitudinal surface plasmon resonance (LSPR), respectively. It is found that as the concentration of CTAB increases, the yield of NRs increases. As the concentration of AA increased from 0.05 to 0.2M, LSP shifts to longer wavelength but upon further increasing the concentration, LSP shifts back to shorter wavelength. A linear relationship between LSPR wavelength and surrounding medium dielectric constant is obtained, which is in good agreement with the theoretical results.

“Flash” Synthesis of CdSe/CdS Core–Shell Quantum Dots

We report on the “flash” synthesis of CdSe/CdS core–shell quantum dots (QDs). This new method, based on a seeded growth approach and using an excess of a carboxylic acid, leads to an isotropic and epitaxial growth of a CdS shell on a wurtzite CdSe core. The method is particularly fast and efficient, allowing the controllable growth of very thick CdS shells (up to 6.7 nm in the present study) in no more than 3 min, which is considerably shorter than in previously reported methods. The prepared materials present state-of-the-art properties with narrow emission and high photoluminescence quantum yields, even for thick CdS shells. Additionally, Raman analyses point to an alloyed interface between the core and the shell, which, in conjunction with the thickness of the CdS shell, results in the observed considerable reduction of the blinking rate.

Aptamer based surface enhanced Raman scattering detection of adenosine using various core sizes of Au–Ag core–shell nanoparticles

The combination of the varied sizes of Au NPs and seeding growth approach can be exploited to control the sizes of Au–Ag core–shell NPs. The silicon substrates with self-assembled Au–Ag core–shell NPs can be used to detect adenosine by a structures-switch aptamer.

Fe2O3/Cu2O heterostructured nanocrystals

We report the synthesis of colloidal γ-Fe2O3/Cu2O hetero-nanocrystals (HNCs) using a solution-phase seeded-growth approach. The structural and electronic properties of these materials are investigated by HRTEM and photoelectron spectroscopy. A type II band alignment was found between the p-Cu2O and n-Fe2O3 domains making the particles potentially attractive candidates for applications in solar energy conversion.