Shape evolution of silver nanoplates through heating and photoinduction

Shape conversions of silver nanoplates were realized by heating and subsequent light irradiation. The initial silver nanoprisms were transformed into silver nanodisks gradually in the process of heating, which was possibly achieved through dissolving and readsorption of silver atoms on the surface of silver nanoplates. Subsequently, under light irradiation, the heating induced silver nanodisks were reversed to silver nanoprisms in the same solution. The dissolved oxygen was found to play a pivotal role in the shape conversion from nanoprism to nanodisk. In addition to heating, deionized water could induce the shape conversion of silver nanoplates when it was added to precipitate of the initial silver nanoprisms after centrifugation. Citrate in solution is essential to the photoinduced shape conversion process. Transmission electron microscopy (TEM) and extinction spectroscopy results demonstrated that localized surface plasmon resonance (LSPR) properties of silver nanoplates were effectively tuned through shape conversion.

Variable incidence angle subwavelength grating SPR graphene biosensor

This paper investigates the sensitivity enhancement of a variable incidence angle subwavelength grating based multilayer surface plasmon resonance biosensor (SPRB). In the proposed design, a periodic array of subwavelength grating is integrated on top of a layer of graphene sheet in the multilayer SPR biosensor. The performance of the biosensor is investigated through monitoring the biomolecular interactions of cDNA-ssDNA interactions on its surface. The sensitivity improvement is indicated by the shift of the resonance peak angle.

Functionalization of bamboo pulp fabrics with noble metal nanoparticles

Noble metal (gold and silver) nanoparticles (NPs) were synthesized in-situ on bamboo pulp fabrics. The gold NPs were reduced by bamboo pulp fabrics and bonded to fibers under heating, and an alkaline condition was needed to synthesize silver NPs in the presence of bamboo pulp fabrics. The synthesized gold and silver NPs endowed bamboo pulp fabrics with different colors because of their localized surface plasmon resonance (LSPR) property. The colors of the fabrics treated with metal NPs were extended through complex synthesis of gold and silver NPs in different proportions. The bamboo pulp fabrics treated with noble metal NPs showed good fastness to light and rubbing. In addition, the gold and silver NPs imparted bamboo pulp fabrics excellent UV protection property and remarkable antibacterial activity.

Photoinduced reversible shape conversion of silver nanoparticles assisted by TiO₂.

Silver nanoprisms were transformed into nanodecahedra through photoinduction of ultraviolet (UV) light in the presence of titanium dioxide (TiO2) quantum dots (QDs). Subsequently, the silver nanodecahedra were reconverted to silver nanoprisms under sodium lamp if there was sufficient citrate in the reaction system. The localized surface plasmon resonance (LSPR) optical properties of silver nanoparticles were tuned during photoinduced shape conversion. The photocatalytic activity of TiO2 QDs assisted the conversion of prisms to decahedra upon UV light irradiation. Nevertheless, the presence of TiO2 did not inhibit the photoinduced reconversion from decahedra to prisms by sodium light. It was demonstrated that citrate was indispensable in the photoinduction process. In addition, oxygen in solution played a vital role in the reversible shape conversion of silver nanoparticles. Moreover, simulated sunlight can convert silver nanoprisms to nanodecahedra instead of UV light with assistance of TiO2 QDs, which would promote the photoinduced reaction of silver nanoparticles based on a natural light source.

Silver nanoparticles prepared by gamma irradiation across metal-organic framework templates

In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal-organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10-3 s-1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal-organic frameworks at room temperature with potential applications in environmental science.

A biomimetic sensor for the detection of lead in water.

The monitoring of lead (II) ions (Pb(2+)) in water is essential for both human health and the environment. Herein, a simple yet innovative biosensor for Pb(2+) detection is presented. The sensor is developed by the self-assembly of gold nanoparticles (GNPs) core-satellite structure using naturally occurring tripeptide glutathione (GSH) as linker. The addition of Pb(2+) caused a red-to-blue color change and the localized surface plasmon resonance (LSPR) band was shifted to ca. 650nm. The limit of detection (LOD) is found to be 47.6nM (9.9ppb) by UV-vis spectroscopy with high selectivity against other heavy metals. This method offers a new strategy for heavy metal detection using functionalized GNPs.

In-situ synthesis of gold nanoparticles for multifunctionalization of silk fabrics

A simple in-situ synthesis route for gold nanoparticles (NPs) was developed to realize multifunctions for silk fabrics. The gold NPs were prepared in a heated solution containing white silk fabric samples. The silk fabrics were colored red and brown by the gold NPs because of their localized surface plasmon resonance (LSPR) property. Gold nanospheres on silk were obtained at a low gold content, and gold nanoplates were synthesized as the gold content increased. The silk fabrics treated with gold NPs showed good light fastness. Moreover, the gold NPs endowed silk fabrics with strong antibacterial activity, excellent UV protection property and enhanced thermal conductivity. © 2013 Elsevier Ltd. All rights reserved.

Sunlight-driven synthesis of anisotropic silver nanoparticles

Photoinduced shape conversion of silver nanoparticles was realized using sunlight. The silver seeds were transformed to silver nanoprisms under sunlight when the concentration of citrate was low (≤5.0×10-4M). Nevertheless, sunlight converted the obtained silver nanoprisms to silver nanodecahedrons when the concentration of citrate in reaction system was increased. It was found that the ultraviolet light from sunlight played a vital role in the shape conversion from nanoprism to nanodecahedron. Lighting power density did not influence the shape conversion except for reaction rate. Besides, the silver nanodecahedrons were synthesized in the mixed solution of AgNO3 and citrate in absence of silver seeds through irradiation by simulated sunlight. The mechanism on the sunlight induced synthesis of silver nanoparticles was discussed. Anisotropic silver nanoparticles including nanoprisms and nanodecahedrons were obtained through controlling the citrate concentration and irradiation time by sunlight from green light source.

Functional application of noble metal nanoparticles in situ synthesized on ramie fibers

Different functions were imparted to ramie fibers through treatment with noble metal nanoparticles including silver and gold nanoparticles. The in situ synthesis of silver and gold nanoparticles was achieved by heating in the presence of ramie fibers in the corresponding solutions of precursors. The unique optical property of synthesized noble metal nanoparticles, i.e., localized surface plasmon resonance, endowed ramie fibers with bright colors. Color strength (K/S) of fibers increased with heating temperature. Silver nanoparticles were obtained in alkaline solution, while acidic condition was conducive to gold nanoparticles. The optical properties of treated ramie fibers were investigated using UV-vis absorption spectroscopy. Scanning electron microscopy (SEM) was employed to observe the morphologies of silver and gold nanoparticles in situ synthesized on fibers. The ramie fibers treated with noble metal nanoparticles showed remarkable catalytic activity for reduction of 4-nitrophenol (4-NP) by sodium borohydride. Moreover, the silver nanoparticle treatment showed significant antibacterial property on ramie fibers.

Facile synthesis of silver submicrospheres and their applications

Uniform silver submicrospheres were synthesized under ambient conditions, through reduction of silver nitrate using ascorbic acid as a reducing agent and Tween 20 as a stabilizer. The silver submicroparticles exhibited strong catalytic activity for the reduction of 4-nitrophenol by sodium borohydride (NaBH4). Significantly, the aggregates of a few silver submicroparticles can be used as surface-enhanced Raman scattering (SERS) substrate to improve markedly the Raman signal of crystal violet. The morphologies of silver submicroparticles can be controlled by changing reaction conditions. The formation process of silver submicroparticles was monitored by time-resolved extinction spectroscopy. The influences of concentrations and molar ratios of reaction reagents on the formation of silver submicroparticles are discussed.

Mercury vapor sorption and amalgamation with a thin gold film

Understanding the amalgamation mechanisms between mercury and gold is of fundamental interest and importance to many mercury sensing applications. However, there is only limited and piecemeal discussion in the literature of the mechanisms by which Au-Hg amalgams are formed on thin Au films. Here, we present a comprehensive description of a series of morphological changes occurring in a thin polycrystalline Au film during Au-Hg amalgamation investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). These microscopic investigations enable us to offer a coherent explanation for the features and the mechanisms of amalgamation of Hg with Au in the film. We also use an optical technique (fringes of equal chromatic order, FECO) to observe changes in optical thickness and reflectivity of the film. Amalgamation reactions in the film render it inhomogeneous, thus making optical techniques unsuitable as a method for quantitative monitoring of Hg vapor using Au films of this type.

Sunlight-induced coloration of silk

Silk fabrics were colored by gold nanoparticles (NPs) that were in situ synthesized through the induction of sunlight. Owing to the localized surface plasmon resonance (LSPR) of gold NPs, the treated silk fabrics presented vivid colors. The photo-induced synthesis of gold NPs was also realized on wet silk through adsorbing gold ions out of solution, which provides a water-saving coloration method for textiles. Besides, the patterning of silk was feasible using this simple sunlight-induced coloration approach. The key factors of coloration including gold ion concentration, pH value, and irradiation time were investigated. Moreover, it was demonstrated that either ultraviolet (UV) light or visible light could induce the generation of gold NPs on silk fabrics. The silk fabrics with gold NPs exhibited high light resistance including great UV-blocking property and excellent fastness to sunlight.

Peptide sequence effects control the single pot reduction, nucleation, and growth of Au nanoparticles

Peptides have demonstrated unique capabilities to fabricate inorganic nanomaterials of numerous compositions through noncovalent binding of the growing surface in solution. In this contribution, we demonstrate that these biomolecules can control all facets of Au nanoparticle fabrication, including Au3+ reduction, without the use of secondary reagents. In this regard using the AuBP1 peptide, the N-terminal tryptophan residue is responsible for driving Au3+ reduction to generate Au nanoparticles passivated by the oxidized peptide in solution, where localized residue context effects control the reducing strength of the biomolecule. The process was fully monitored by both time-resolved monitoring of the growth of the localized surface plasmon resonance and transmission electron microscopy. Nanoparticle growth occurs by a unique disaggregation of nanoparticle aggregates in solution. Computational modeling demonstrated that the oxidized residue of the peptide sequence does not impact the biomolecule's ability to bind the inorganic surface, as compared to the parent peptide, confirming that the biomolecule can be exploited for all steps in the nanoparticle fabrication process. Overall, these results expand the utility of peptides for the fabrication of inorganic nanomaterials, more strongly mimicking their use in nature via biomineralization processes. Furthermore, these capabilities enhance the simplicity of nanoparticle production and could find rapid use in the generation of complex multicomponent materials or nanoparticle assembly.

Plasmon eignevalues as a function of nano-spheroids size and elongation

In this paper, the effects of silver nano-spheroid size and elongation on plasmon wavelength are investigated, and the plasmon eigenvalues are formulated as a function of the radius and aspect ratio of the nano-particles. These can be used in eigenmode plasmonic interaction method to study interaction of nano-particles on each other at dipole resonance frequencies.. It is demonstrated that plasmon eigenvalues are partially linear with respect to radius and aspect ratio of the nano-spheroids. In addition, it is shown that the maximum enhancement occurs in the direction of the polarization angle.

Fast colorimetric detection of copper ions using L-Cysteine functionalized gold nanoparticles

This communication reports an efficient visual detection method of Cu²⁺ by L-cysteine functionalized gold nanoparticles in aqueous solution. Upon exposure to Cu²⁺, the gold nanoparticle solution changed from red to blue, in response to surface plasmon absorption of dispersed and aggregated nanoparticles. This colorimetric sensor allows a rapid quantitative assay of Cu²⁺ down to the concentration range of 10⁻⁵ M. Recognition of Cu²⁺ and formation of the aggregates are proposed to occur via a 2 : 1 sandwich complex between L-cysteine and Cu²⁺.