Triangular Silver Nanoplates Research Articles

Localized Surface Plasmon Resonance of Silver Nanotriangles Synthesized by a Versatile Solution Reaction.

The surface plasmon resonance (SPR) of silver nanoparticles can be tuned throughout the visible and near-infrared region by their shape and size. Considering SPR applications, an easy and controllable method for preparing the silver nanocrystals with defined shape and size, is necessary. In this work, the triangular silver nanoplates were synthesized by reducing Ag+ ions with ascorbic acid in the presence of silver seeds and poly(vinylpyrrolidone) (PVP) at room temperature. Both the seeds (as the nucleation sites) and PVP (as the capping reagent) played an important role in determining the edge length of the silver nanotriangles. The SPR of silver nanotriangles showed three distinct bands corresponding to the in-plane dipole, quadrupole, and out-plane quadrupole plasmon resonance, and the SPR shifted to shorter wavelengths with the decreased edge length of the silver nanotriangles as the theoretical calculation.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1058-1) contains supplementary material, which is available to authorized users.

Self-Assembly of High Density of Triangular Silver Nanoplate Films Promoted by 3-Aminopropyltrimethoxysilane

In this work, we studied the structure of synthesized triangular silver nanoplates in solution and the growth of the nanoplates on a silicon surface using 3-aminopropyltrimethoxysilane (APTMS) as a coupling agent. The triangular-shaped colloidal silver nanoplates were simply synthesized by a direct chemical reduction approach. We studied the three characteristic peaks of the unique optical absorbance of triangular silver nanoplates and subsequently measured an average edge length of 26 ± 1 nm. The nanoplate thickness was determined to be 7 ± 2 nm from transmission electron microscopy images. Depositing the nanoplates on a silicon surface was carried out to determine the coverage of triangular nanoplates obtained when adhesion was promoted by a coupling agent. The APTMS film assisted the attachment of the nanoplates to the silicon surface and the coverage of the nanoplates increased with increasing deposition time. The triangular silver nanoplate thin film was a monolayer and a high coverage (near complete) was obtained after eight hours of exposure to the nanoplate solution. The silver film formed was shown to be a good surface-enhanced Raman scattering (SERS) substrate as it gave an enormous Raman enhancement for bisphenol A (BPA).

Highly sensitive C-reactive protein (CRP) assay using metal-enhanced fluorescence (MEF)

Fluorescence has been extensively employed in the area of diagnostic immunoassays. A significant enhancement of fluorescence can be achieved when noble metal nanoparticles are placed in close proximity to fluorophores. This effect, referred to as metal-enhanced fluorescence (MEF), has the potential to produce immunoassays with a high sensitivity and a low limit of detection (LOD). In this study, we investigate the fluorescence enhancement effect of two different nanoparticle systems, large spherical silver nanoparticles (AgNPs) and gold edge-coated triangular silver nanoplates, and both systems were evaluated for MEF. The extinction properties and electric field enhancement of both systems were modeled, and the optimum system, spherical AgNPs, was used in a sandwich immunoassay for human C-reactive protein with a red fluorescent dye label. A significant enhancement in the fluorescence was observed, which corresponded to an LOD improvement of ~19-fold compared to a control assay without AgNPs.

A facile label-free colorimetric sensor for Hg2+ based on Hg-triangular silver nanoplates with amalgam-like structure

In this contribution, we have developed a rapid method for the highly selective detection of mercury ions (Hg2+) using citrate-stabilized triangular silver nanoplates (AgNPs). The colorimetric sensor strategy is based on the aggregation of Hg2+-coated AgNPs with the assistance of two amino groups of lysine, resulting in a color change of AgNP solution from blue to mauve or gray. The sensor enables the analysis of Hg2+ with a minimum detectable concentration that corresponds to 50nM. Meanwhile, the strategy offers excellent selectivity toward Hg2+ against other cations. The validation of this method is carried out by analysis of Hg2+ in tap water with satisfying recoveries over 91.35–106%.

Rapid Determination of Chloride Using Silver Triangular Nanoplates

A sensitive and accurate method for the determination of chloride using citrate-stabilized silver triangular nanoplates was developed. Chloride caused a color change of silver triangular nanoplate solution from blue to yellow by fusion and etching, as confirmed by transmission electron microscopy and ultraviolet-visible absorption spectroscopy. The spectrophotometric determination involved measurement of the spectra involving localized surface plasmon resonance. The change in the ratio of absorption at 642 and 430 nanometers was proportional to the concentration of chloride from 0.10 to 0.30 millimolar with a correlation coefficient of 0.9977. To determine the feasibility of the method, cooling water was analyzed. Good recoveries were obtained with relative standard deviations of 3.09 to 5.42 percent. These results demonstrated that the method was accurate, reliable, and rapid for the determination of chlroide.

Application of triangular silver nanoplates for colorimetric detection of H2O2

In this study, a simple and highly sensitive colorimetric assay of H2O2 using triangular Ag nanoplates has been carried out. In the presence of H2O2, the Ag nanoplates are etched from triangle to round, which leads to the vanishment of the surface plasmon resonance (SPR) absorption at 400nm and significant decrease the absorbance of the band at 670nm. The color change of the reaction system from the initial blue to mauve can be observed. This proposed method can determine H2O2 with a dynamic range of 50nM to 1μM and a low detection limit of 1.36nM. The high sensitivity of the triangular nanoplates can be ascribed to highly reactive edges/tips, and strongly tip sharpness and aspect ratio dependent SPR absorption of the triangular nanostructure. This sensing system is further extended to the detection of glucose by H2O2 generated from the enzymatic oxidation of glucose, and thus holds great promises in clinical applications.

Visual detection of trace copper ions based on copper-catalyzed reaction of ascorbic acid with oxygen

A visual detection method for trace Cu2+ in aqueous solutions using triangular silver nanoplates (abbreviated as TAgNPs) as the probe was developed. The method is based on that TAgNPs could be corroded in sodium thiosulfate (Na2S2O3) solutions. The absorption spectrum of TAgNPs solution changed when it is corroded by Na2S2O3. The reaction of oxygen with ascorbic acid (Vc) in the presence of a low concentration of Cu2+ generates hydrogen peroxide that reacts with Na2S2O3, which leads the concentration of Na2S2O3 in the solution to be decreased. Therefore, the reaction between TAgNPs and the reacted mixture of Na2S2O3/Vc/Cu2+ was prevented efficiently. When the Na2S2O3 concentration and reaction time are constant, the decrease in the concentration of Na2S2O3 is directly proportional to the Cu2+ concentration. Thus, morphology, color, and maximum absorption wavelength of TAgNPs changed with the change of Cu2+ concentration. The changed maximum absorption wavelength of TAgNPs (Δλ) is proportional to Cu2+ concentration in the range from 7.5×10−9 to 5.0×10−7M with a correlation coefficient of r=0.9956. Moreover, color change of TAgNP solution was observed clearly over a Cu2+ concentration range from 7.5×10−8 to 5.0×10−7M. This method has been used to detect the Cu2+ content of a human hair sample, and the result is in agreement with that obtained by the atomic absorption spectroscopy (AAS) method.

Fluorescence Resonance Energy Transfer Detection of Cobalt Ions by Silver Triangular Nanoplates and Rhodamine 6G

In the present paper, the authors studied fluorescence resonance energy transfer (FRET) phenomenon between silver triangular nanoplates and bovine serum albumin (BSA)/Rhodamine 6G fluorescence complex, and established a fluorescence method for the detection of cobalt ions. We found that when increasing the silver triangular nanoplates added to certain concentrations of fluorescent bovine serum albumin (BSA)/Rhodamine 6G complex, the fluorescence of Rhodamine 6G would be quenched up to 80% due to the FRET between the quencher and donor. However, in the presence of cobalt ions, the disassociation of the fluorescent complex from silver triangular nanoplates occurred and the fluorescence of the Rhodamine 6G recovered. The recovery of fluorescence intensity rate (I/I0) has a good relationship with the cobalt ion concentration (cCO2+) added. Thus, the authors developed a fluorescence method for the detection of cobalt ions based on the FRET of silver triangular nanoplates and Rhodamine 6G.

Preparation of Triangular Silver Nanoplates and its Application in Printed Electronics

Conductive ink for inkjet printing has attracted considerable interest for the preparation of advanced electronic circuits. However, high silver content and multiple printing are necessary in order to acquire better conductivity when using spherical silver nanoparticles. In order to reduce manufacturing cost, triangular silver nanoplates were prepared by modified solvothermal method and used for conductive ink. During sintering process of prtinted patterns, the tips of triangular nanoplates were first melted and turned round for high energy of tips. The resistivity of inkjet printed line is 7.6×10-6 Ω·cm when using triangular nanoplates ink with 10 percent content, while it is necessary to use more than 15 percent content for spherical nanoparticles. This is because surface contact between nanoplates can provide more paths for electron transmission relative to spherical nanoparticles.

Preparation of Au-Ag Nanoframe and its Application in SERS

A simple and facile preparation approach of gold-silver nanoframes is described based on triangular silver nanoplates. HAuCl4was used as etching agent and added to boiling nanoplates suspension under stirring. Especially, when different concentrations of HAuCl4was employed, various etching happened and corresponding morphology of gold-silver nanoframes were acquired. The properties of nanoframes were characterized by scanning electron microscopy (SEM) and UV-vis spectra. Then the nanoframes were self-assembled onto the silicon treated with APTMS and used as SERS substrates for detecting p-ATP molecules. The results indicated that nanoframes showed better SERS effects than nanoplates.

Surface enhanced Raman spectroscopy of l-alanyl-l-tryptophan dipeptide adsorbed on Si substrate decorated with triangular silver nanoplates

Raman and surface enhanced Raman spectroscopies have been used to investigate interaction of l-alanyl-l-tryptophan (Ala-Trp) dipeptide with nanostructured silver surface. A highly sensitive surface enhanced Raman scattering (SERS)-based biosensor has been employed for label-free dipeptide detection and its orientation on the nanostructured surface. The synthesis of SERS substrate was based on direct silver ions reduction on hydrofluoric acid etched silicon wafer. Raman and SERS spectra of Ala-Trp were recorded in liquid to keep native environment for dipeptide. To the best of our knowledge, this work is a first attempt to analyze the structure of Ala-Trp dipeptide by Raman spectroscopy.

Visual detection of trace copper(ii) based on its catalytic action in the dissociation of thiosulfate

In this study, we report a new method for the detection of Cu2+based on triangular silver nanoplates (TAg-NPs), which could be corroded by sodium thiosulfate (Na2S2O3).

Towards high quality triangular silver nanoprisms: improved synthesis, six-tip based hot spots and ultra-high local surface plasmon resonance sensitivity.

The great application potential of triangular silver nanoprisms (TSNPRs, also referred to as triangular silver nanoplates) is hampered by the lack of methods to produce well-defined tips with high monodispersity, with easily removable ligands. In this work, a simple one-step plasmon-mediated method was developed to prepare monodisperse high-quality TSNPRs. In this approach, the sole surface capping agent was the easily removable trisodium citrate. Differing from common strategies using complex polymers, OH(-) ions were used to improve the monodispersity of silver seeds, as well as to control the growth process through inhibiting the oxidation of silver nanoparticles. Using these monodisperse high-quality TSNPRs as building blocks, self-assembled TSNPRs consisting of six-tip based "hot spots" were realized for the first time as demonstrated in a high enhancement (∼10(7)) of surface-enhanced Raman scattering (SERS). From the plasmon band shift versus the refractive index, ultra-high local surface plasmon resonance sensitivity (413 nm RIU(-1) or 1.24 eV RIU(-1), figure of merit (FOM) = 4.59) was reached at ∼630 nm, making these materials promising for chemical/biological sensing applications.

Intense Plasmon-induced Cotton Effects in Colloidal Silver Triangular Nanoplates Synthesized by a Ligand-exchange Process

Abstract Chiroptically active Ag triangular nanoplates were synthesized by the ligand-exchange reaction of achiral Ag nanoplates with chiral d- or l-penicillamine molecules. Analysis of the chiroptical properties of the synthesized nanoplates by circular dichroism spectroscopy revealed intense Cotton effects, with wavelengths that corresponded to those of the surface plasmon resonances for the nanoplates. Enantiomeric excess and pH dependence of these effects were also measured to explore the origin of the chiroptical activity of the nanoplates.

Selective Detection of Mercury (II) by Etching the Corners of Silver Triangular Nanoplates

ABSTRACT As confirmed by transmission electron microscopy, we found that Hg2+ has good affinity to etch the sharp corners of silver triangular nanoplates. The etching process induced an apparent absorption peak shift of silver triangular nanoplates from 580 to 530 nm. The shift degree of the absorption peak has a good linear relationship with the amount of Hg2+ added; thus, Hg2+ with a concentration from 0.2 to 1.5 µM can be quantitatively detected by measuring silver triangular absorption. The interaction between mercury and silver triangular nanoplates proposed here is also a new example of silver triangular nanoplate etching and important for explaining the etching mechanism.

Silver nanoplates-based colorimetric iodide recognition and sensing using sodium thiosulfate as a sensitizer

A colorimetric method for the recognition and sensing of iodide ions (I−) has been developed by utilizing the reactions between triangular silver nanoplates (TAg-NPs) and I− in the presence of sodium thiosulfate (Na2S2O3). Specifically, I− together with Na2S2O3 can induce protection of TAg-NPs owing to the formation of insoluble AgI, as confirmed by the high-resolution transmission electron microscopy (HRTEM). In the absence of Na2S2O3, the etching reactions on TAg-NPs were observed not only by I− but also other halides ions. The Na2S2O3 plays as a sensitizer in this system, which improved the selectivity and sensitivity. The desired colorimetric detection can be achieved by measuring the change of the absorption peak wavelength corresponding to localized surface plasmon resonance (LSPR) with UV–vis spectrophotometer or recognized by naked eye observation. The results show that the shift of the maximum absorption wavelength (Δλ) of the TAg-NPs/Na2S2O3/I− mixture was proportional to the concentration of I− in the range 1.0×10−9–1.0×10−6molL−1. Moreover, no other ions besides I− can induce an eye discernible color change as low as 1.0×10−7molL−1. Finally, this method was successfully applied for I− determination in kelp samples.

The influence of triangular silver nanoplates on antimicrobial activity and color of cotton fabrics pretreated with chitosan

The effect of cotton fabric pretreatment with biopolymer chitosan (CHT) on deposition of colloidal triangular silver nanoplates was studied. Also, the influence of deposited silver nanoparticles on color and antimicrobial activity of cotton fabrics was evaluated. Characterization of colloidal silver nanoparticles as well as silver nanoparticles deposited on cotton fabrics was performed using electron microscopy (TEM and FESEM), XRD analysis, atomic absorption spectroscopy, UV–Vis absorption, and reflectance spectroscopy. The cotton fabric turned from white to blue color upon deposition of triangular silver nanoplates. Antimicrobial activity of CHT pretreated cotton fabric impregnated with silver nanoparticles was tested against Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus, and fungi Candida albicans. Deposited silver nanoparticles imparted excellent antimicrobial properties to cotton fabric. The standard sterilization procedure of cotton fabric for antimicrobial activity testing resulted in color change of the fabric from blue to yellow. This color change is most likely consequence of transformation of triangular silver nanoplates into nanodiscs and/or their agglomeration into spheroids.

Visual determination of trace Cysteine based on promoted corrosion of triangular silver nanoplates by sodium thiosulfate

In this study, triangular silver nanoplates (TAg-NPs) were used to detect trace Cysteine concentration in the presence of sodium thiosulfate (Na2S2O3). Study showed that the TAg-NPs could be gently etched by Cysteine with the concentration of 1.0×10−7molL−1 through forming Ag–S covalent bond at the three corners. However, in the presence of Na2S2O3 (only 3.0×10−6molL−1), the corrosion of Cysteine on TAg-NPs can be promoted significantly. It was also found that the color, morphology, and the maximum absorption wavelength of TAg-NPs change clearly with the concentrations of Cysteine as low as 2.5×10−8molL−1. Furthermore, the wavelength shift values (Δλ) of TAg-NPs solution were proportional to the concentrations of Cysteine in the range of 1.0×10−9–1.0×10−7molL−1, and the linear regression equation is Δλ=−0.89+319.94 c (c, μM, n=5) with the correlation coefficient of 0.990. At the same time, the color change of the TAg-NPs solution could be observed clearly by the naked eyes with increasing Cysteine concentrations in the range of 2.5×10−8–1.0×10−7molL−1. Thus, a novel method for the detection of Cysteine by either UV–vis spectrophotometry detection or naked eyes observation is established. It allows determination of Cysteine content in compound amino acid injection sample of 18AA-V.

The nanotoxicity investigation of optical nanoparticles to cultured cells in vitro

Optical nanoparticles (NPs) have the potential to provide new tools for diagnosis and treatment of human diseases, however, their nanotoxicity and biological characteristics are still unclear. Here, we prepared a series of typical NPs (including gold nanospheres, gold nanorods, silver nanopheres, silver triangular nanoplates and quantum dots) with different material and surface chemical modification for nanotoxicity test. Cell proliferation was investigated by SRB assay where the NPs were co-cultured with cancer cells. It was found that NPs’ toxicity was highly correlated to different factors—material selection, physical size/surface area, shape, and surface chemical property, etc. This work has the potential to provide a uniform and systematic information when they are applied as probes in biological and medical fields.

Wash-free highly sensitive detection of C-reactive protein using gold derivatised triangular silver nanoplates

Rapid, wash-free highly sensitive detection of C-reactive protein is reported using nanoplate biosensor sols.