Gold Nanotriangles Research Articles

Surface Enhanced Raman Scattering and Gated Materials for Sensing Applications: The Ultrasensitive Detection of Mycoplasma and Cocaine.

We present herein a novel combination of gated mesoporous silica nanoparticles (MSNs) and surface-enhanced Raman scattering (SERS) for sensing applications. As a proof-of-concept, we show the design of a system comprising MSNs loaded with crystal violet (CV), a molecule with high Raman cross section acting as SERS reporter, and capped with either a suitable DNA sequence for the detection of Mycoplasma genomic DNA or with an aptamer that selectively coordinates cocaine. In both cases the presence of the corresponding target analyte in solution (i.e., genomic DNA or cocaine) resulted in the release of CV. CV delivery was detected by SERS upon adsorption on gold nanotriangles (AuNTs), which display an efficient electromagnetic field enhancement and a high colloidal stability. By using this novel procedure a limit of detection of at least 30 copies DNA per μL was determined for the detection of Mycoplasma genomic DNA, whereas cocaine was detected at concentrations as low as 10 nm.

Direct self-assembly of CTAB-capped Au nanotriangles

Densely packed and ordered “suprastructures” are new types of nanomaterials exhibiting broad applications. The direct self-assembly of cetyltrimethylammonium bromide (CTAB)-capped gold nanotriangles to form “suprastructures” was systematically investigated by varying the temperature and tilt angle of the silicon wafer used in the assembly process. Under optimal conditions, nanotriangles form into regular patterns, maintain their integrity, and form edge-to-edge, point-to-point, and face-to-face connections to form ordered “suprastructures” within an area of hundreds of square microns, achieving a high level of regularity. The formation of the “suprastructures” under optimal conditions could be mainly attributed to the complex balance between multiple temperature-dependent factors, including the atom diffusion rate, solvent evaporation rate, self-assembly rate, and the time for which the nanoparticle stays in the wet medium.

Quantum emitter coupled to plasmonic nanotriangle: Spatially dependent emission and thermal mapping

Herein we report on our studies of radiative and non-radiative interaction between an individual quantum emitter and an anisotropic plasmonic nanostructure: a gold nanotriangle. Our theoretical and three-dimensional electromagnetic simulation studies highlight an interesting connection between: dipole-orientation of the quantum emitter, anisotropy of the plasmonic nanostructure and, radiative and non-radiative energy transfer processes between the emitter and the plasmonic geometry. For the out of plane orientation of quantum emitter, the total decay rate and non-radiative decay rate was found to be maximum, showing radiation extraction efficiency of 0.678. Also the radiative decay rate was greater for the same orientation, and showed a pronounced spatial dependence with respect to the nanotriangle. Our study has direct implication on two aspects: designing nanoparticle optical antennas to control emission from individual atoms and molecules and geometrical control of quenching of emission into plasmonic decay channels.

Two‐Photon Cycloreversion Reaction of Diarylethene on Gold Nanotriangles

Two‐Photon Cycloreversion Reaction of Diarylethene on Gold Nanotriangles

Polyampholyte-mediated synthesis of anisotropic gold nanoplatelets

This paper focused on the synthesis of triangular nanoplatelets in the presence of a tubular network structure. The tubular network structure is formed by adding a strongly alternating polyampholyte, i.e., PalPhBisCarb, to a mixed vesicle system with a negatively charged bilayer containing phosphatidylcholin and AOT. Using the tubular network as a reducing agent in a one-step procedure, triangular and hexagonal nanoplatelets are formed. One can show that the nanoplatelet yield is enhanced by increasing the temperature and decreasing the reaction time. The platelet edge length can be decreased by heating the system up to 100 °C. Due to specific interactions between PalPhBisCarb and the AOT/phospholipid bilayer, stacking and welding effects lead to the formation of ordered platelet structures. The reaction pathway to flat gold nanotriangles is discussed with regard to the twin plane growth model of gold nanoplates.

Extracellular synthesis gold nanotriangles using biomass of Streptomyces microflavus.

Applications of nanotechnology and nano-science have ever-expanding breakthroughs in medicine, agriculture and industries in recent years; therefore, synthesis of metals nanoparticle (NP) has special significance. Synthesis of NPs by chemical methods are long, costly and hazardous for environment so biosynthesis has been developing interest for researchers. In this regard, the extracellular biosynthesis of gold nanotriangles (AuNTs) performed by use of the soil Streptomycetes. Streptomycetes isolated from rice fields of Guilan Province, Iran, showed biosynthetic activity for producing AuNTs via in vitro experiments. Among all 15 Streptomyces spp. isolates, isolate No. 5 showed high biosynthesis activity. To determine the bacterium taxonomical identity at genus level, its colonies characterised morphologically by use of scanning electron microscope. The polymerase chain reaction (PCR) molecular analysis of active isolate represented its identity partially. In this regard, 16S rRNA gene of the isolate was amplified using universal bacterial primers FD1 and RP2. The PCR products were purified and sequenced. Sequence analysis of 16S rDNA was then conducted using National Center for Biotechnology Information Basic Local Alignment Search Tool method. The AuNTs obtained were characterised by ultraviolet-visible spectroscopy, atomic force microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction spectroscopy analyses. The authors results indicated that Streptomyces microflavus isolate 5 bio-synthesises extracellular AuNTs in the range of 10-100 nm. Synthesised SNPs size ranged from 10 to 100 nm. In comparison with chemical methods for synthesis of metal NPs, the biosynthesis of AuNTs by Streptomyces source is a fast, simple and eco-friendly method. The isolate is a good candidate for further investigations to optimise its production efficacy for further industrial goals in biosynthesis of AuNTs.

“Green” gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering

The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs.

Gnidia glauca Leaf and Stem Extract Mediated Synthesis of Gold Nanocatalysts with Free Radical Scavenging Potential

Development of eco-friendly and novel method for the synthesis of metal nanoparticles is one of the most popular and emerging aspect of nanobiotechnology. In this report, Gnidia glauca leaf and stem extract are used to synthesize gold nanoparticles (AuNPs). As compared to other biological methods, the syntheses were extremely rapid leading to complete reduction within 20 min. Transmission and high resolution transmission electron micrographs clearly indicated that majority of the bioreduced nanoparticles were spherical within a size range of 10 to 60 nm. Exotic shapes like gold nanotriangles and nanohexagons were found in a range between 100 to 300 nm. Dynamic light scattering validated the size range that was observed in TEM and HRTEM. Unique pattern confirming the self-assembly of spheres into anisotropic nanoparticles of larger dimensions was exhibited in HRTEM images. X-ray diffraction pattern and energy dispersive spectroscopic analysis confirmed the purity of elemental gold in the bioreduced nanoparticles. Fourier infrared spectral analysis indicated the role of the phenolic groups in reduction of chloroauric acid into AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs and NaBH4 with apparent rate constants (k) 1.99 × 10-3 min-1 and 4.498 × 10-3 min-1, for AuNPs reduced by GGLE and GGSE, respectively provided strong evidence for the catalytic potential. AuNPs synthesized by GGSE and GGLE showed a second order rate constant of 1.78 × 107 and 1.31 × 107 respectively confirming the scavenging of ABTS•+ radicals.

A two-step approach to realize size- and shape-selective separation of crude gold nanotriangles with high purification

A two-step separation strategy that combined CTAB and CTAC has been proposed that enables the purification of gold nanotriangles effectively.

Gold nanotriangles decorated with superparamagnetic iron oxide nanoparticles: a compositional and microstructural study.

The combination of iron oxide and gold in a single nanoparticle results in both magnetic and plasmonic properties that can stimulate novel applications in bio-sensing, medical imaging, or therapeutics. Microwave assisted heating allows the fabrication of multi-component, multi-functional nanostructures by promoting selective heating at desired sites. Recently, we reported a microwave-assisted polyol route yielding gold nanotriangles decorated with iron oxide nanoparticles. Here, we present an in-depth microstructural and compositional characterization of the system using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). A method to remove the iron oxide nanoparticles from the gold nanocrystals and some insights on crystal nucleation and growth mechanisms are also provided.

Rapid Non-Crosslinking Aggregation of DNA-Functionalized Gold Nanorods and Nanotriangles for Colorimetric Single-Nucleotide Discrimination.

Gold nanoparticles modified with DNA duplexes are rapidly and spontaneously aggregated at high ionic strength. In contrast, this aggregation is greatly suppressed when the DNA duplex has a single-base mismatch or a single-nucleotide overhang located at the outermost surface of the particle. These colloidal features emerge irrespective of the size and composition of the particle core; however, the effects of the shape remain unexplored. Using gold nanorods and nanotriangles (nanoplatelets), we show herein that both remarkable rapidity in colloidal aggregation and extreme susceptibility to DNA structural perturbations are preserved, regardless of the shape and aspect ratio of the core. It is also demonstrated that the DNA-modified gold nanorods and nanotriangles are applicable to naked-eye detection of a single-base difference in a gene model. The current study corroborates the generality of the unique colloidal properties of DNA-functionalized nanoparticles, and thus enhances the feasibility of their practical use.

Multiphoton Plasmonics: Regioselective Localization and Tracking of Biomolecules on Single Gold Nanoparticles (Adv. Sci. 11/2015)

In article number 1500232, Y. B. Zheng and co-workers extend the scope of multi-photon plasmonic lithography to immobilize biomolecules. Protein hydrogels are precisely immobilized at the tips of a single gold nanotriangle. This process is tracked on single nanoparticles using dark-field scattering spectroscopy. These protein nano-anchors can serve as frameworks to study plasmon–molecule interactions and to assemble functional materials with hierarchical structures.

Plasmon-Enhanced Fluorescence from Single Proteins in Living Bacteria

The sensitivity and resolution of single-molecule fluorescence imaging in biology are mainly limited by two known weaknesses of fluorescent proteins: label brightness and photostability. In this work, we use patterned gold substrates to achieve plasmon-enhanced emission from intrinsically fluorescent proteins in living pathogenic bacteria cells. By coupling membrane-bound single fluorescent protein fusions to the virulence regulator TcpP in living Vibrio cholerae bacteria to extracellular gold nanotriangle arrays, we use plasmonics to improve our measurements of this important question in pathogenesis: how does V. cholerae produce its deadly toxin? Based on a simple experimental geometry, we observe a 1.3× enhancement in the rate of emission and a 1.4× enhancement in the number of photons detected prior to photobleaching. Furthermore, by enhancing both the rate of emission and the total number of photons detected from single-molecule fluorescent probes in live cells, we show that plasmon-enhanced fluoresc...

Regioselective Localization and Tracking of Biomolecules on Single Gold Nanoparticles.

Selective localization of biomolecules at the hot spots of a plasmonic nanoparticle is an attractive strategy to exploit the light–matter interaction due to the high field concentration. Current approaches for hot spot targeting are time‐consuming and involve prior knowledge of the hot spots. Multiphoton plasmonic lithography is employed to rapidly immobilize bovine serum albumin (BSA) hydrogel at the hot spot tips of a single gold nanotriangle (AuNT). Regioselectivity and quantity control by manipulating the polarization and intensity of the incident laser are also established. Single AuNTs are tracked using dark‐field scattering spectroscopy and scanning electron microscopy to characterize the regioselective process. Fluorescence lifetime measurements further confirm BSA immobilization on the AuNTs. Here, the AuNT‐BSA hydrogel complexes, in conjunction with single‐particle optical monitoring, can act as a framework for understanding light–molecule interactions at the subnanoparticle level and has potential applications in biophotonics, nanomedicine, and life sciences.

A novel and greener approach for shape controlled synthesis of gold and gold–silver core shell nanostructure and their application in optical coatings

Green and facile synthetic methods have gained marvellous fame for the production of polyhedral, anisotropic and spherical gold, and gold–silver bimetallic nanostructures. The useful pivotal characteristics of a green procedure are the usage of environment benign solvent medium, reducing and stabilising agents, and shorter reaction time. We describe here a novel, and greener method for the production of gold and gold–silver core shell nanostructures using aqueous fish scales extract of the Labeo rohita. The effect of various reaction parameters, such as temperature and concentration for the synthesis of the nanostructures were studied. Results indicated that triangular and decahedron gold nanostructures were formed at a lower temperature (40°C) and concentration (10%). While, icosahedral and spherical gold nanostructures were produced at a comparatively higher temperature (100°C) and concentration (40%). The study also revealed that the core–shell bimetallic nanostructures with different morphologies (spherical and oval-shape) were formed at different ratios of chloroaurate and silver nitrate solution. Thus, the present study indicated a simple shape controlled synthesis of gold and gold silver core–shell nanostructures. The synthesised gold nanotriangles were coated over the glass substrate and found to be highly efficient in absorbing infra-red radiations for potential architectural applications. Therefore, the study demonstrated the facile usage of gold nanotriangles for optical coatings. The present strategy depicted the dual functional ability of the fish scale extract as reducing and stabilising agents. This strategy also eliminates the usage of hazardous chemicals, toxic solvents and harsh reducing and stabilizing agents.

Magnetic gold nanotriangles by microwave-assisted polyol synthesis.

Simple approaches to synthesize hybrid nanoparticles with magnetic and plasmonic functionalities, with high control of their shape and avoiding cytotoxic reactants, to target biomedical applications remain a huge challenge. Here, we report a facile, fast and bio-friendly microwave-assisted polyol route for the synthesis of a complex multi-material consisting of monodisperse gold nanotriangles around 280 nm in size uniformly decorated by superparamagnetic iron oxide nanoparticles of 5 nm. These nanotriangles are readily dispersible in water, display a strong magnetic response (10 wt% magnetic fraction) and exhibit a localized surface plasmon resonance band in the NIR region (800 nm). Moreover, these hybrid particles can be easily self-assembled at the liquid-air interfaces.

Well-oriented epitaxial gold nanotriangles and bowties on MoS2 for surface-enhanced Raman scattering.

We report on epitaxial growth of Au nanotriangles (AuNTs) and bowties consisting of opposing tip-to-tip AuNTs with a few-nanometer gap on n-layer MoS2. These AuNTs exhibit well-defined crystallographic orientations with the average size determined by the MoS2 thickness. Monolayer (1L) MoS2 shows the weakest coalescence, corroborating the layer-dependent interactions among Au and n-layer MoS2. High-resolution transmission electron microscopy characterization confirms the lattice directing of thin MoS2 sheets on the AuNT formation with [111]Au||[001]MoS2 and <211>Au||<210>MoS(2). By introducing misfit dislocation arrays, the system with an 8.8% lattice misfit is stress-free. In particular, subwavelength-sized gold bowtie nanoantennas can be easily found on the MoS2 surface with a spacing gap down to 3 nm and a density up to 1.6 × 10(13) m(-2). This technique is low cost, time-saving and free of impurities compared to the conventional lithography technologies. Meanwhile, the equilateral AuNTs can enhance Raman signals of thin MoS2 sheets far stronger than that by ordinary gold films, indicating the potential use of AuNTs as SERS substrates for SERS applications.

Near-field plasmonic coupling for enhanced nonlinear absorption by femtosecond pulses in bowtie nanoantenna arrays

Plasmonic bowtie nanoantennas (BNAs) can exhibit a strong enhancement of optical field, leading to large nonlinear effects. We investigated the nonlinear optical absorption of an array of BNA by femtosecond pulses, using the open-aperture Z-scan technique. The BNA array composed of paired gold nanotriangles was fabricated by nanosphere lithography. We experimentally demonstrated that upon decreasing the gap width, nonlinear absorption is enhanced due to both the enhancement of near-field coupling of nanoantennas and the minimum of the spectral detuning between the center wavelength of the laser for excitation and the localized surface plasmon resonances. The role of near-field resonant plasmonic coupling in BNA is analyzed theoretically and confirmed by our simulations.

Biogenic gold nano-triangles: Cargos for anticancer drug delivery

We present synthesis of biogenic gold nano triangles (GNTs) using Azadirachta indica leaf extract at inherent pH (5.89) and its application in efficient drug delivery of doxorubicin (DOX) (anticancer drug). The main idea was to take advantage of large surface area of GNTs which has 3 dimensions and use the plant peptides coated on these triangles as natural linkers for the attachment of DOX. Sucrose density gradient centrifugation (SDGC) and dialysis methods were used for separation of the GNT from mixture of GNPs. Flocculation parameter (FP) was used to check stability of GNT which was found to be exceptionally high (0–0.75) due to the biological capping agents. DOX attachment to GNT was verified using Fourier transformed infra-red (FTIR) spectroscopy. The complex thus formed was found to be less toxic to normal cells (MDCK cells) and significantly toxic for the cancerous cells (HeLa cells). Drug loading efficiency was found to be 99.81% and DOX release followed first order release kinetics. Percentage drug release was found to be more than 4.5% in both acidic (5.8) as well as physiological pH (7.2) which is suitable for tumor targeting.

Monodisperse gold nanotriangles: size control, large-scale self-assembly, and performance in surface-enhanced Raman scattering.

Au nanotriangles display interesting nanoplasmonic features with potential application in various fields. However, such applications have been hindered by the lack of efficient synthetic methods yielding sufficient size and shape monodispersity, as well as by insufficient morphological stability. We present here a synthesis and purification protocol that efficiently addresses these issues. The size of the nanotriangles can be tuned within a wide range by simply changing the experimental parameters. The obtained monodispersity leads to extended self-assembly, not only on electron microscopy grids but also at the air-liquid interface, allowing transfer onto centimeter-size substrates. These extended monolayers show promising performance as surface-enhanced Raman scattering substrates, as demonstrated for thiophenol detection.