Triangular Gold Nanoparticles Research Articles

An Investigation of the Effect of Embedded Gold Nanoparticles in Different Geometric Shapes on the Directivity of THz Photoconductive Antennas

This study aims to show how Terahertz (THz) Photoconductive Antennas (PCAs) affect the radiation directivity when gold nanoparticles of various geometric shapes are embedded in the gap region between the electrodes of THz PCAs. Three different PCAs, in the frequency range of 0.1 to 2 THz, conventional and after the addition of cylindrical, triangular, square, and hexagonal geometric gold nanoparticles to the antenna gap region between the electrodes, were built and simulated. The antenna directivity increased from 4.71 dBi to 4.92 dBi when square nanoparticles were added to the bowtie PCA, from 4.33 dBi to 4.45 dBi when triangular nanoparticles were added to the dipole PCA, and from 7.18 dBi to 7.52 dBi when square nanoparticles were added to the Vivaldi PCA.

Behind the Optimization of the Sensor Film: Bioconjugation of Triangular Gold Nanoparticles with Hemoproteins for Sensitivity Enhancement of Enzymatic Biosensors.

Electrochemical biosensors are widely used in a multitude of applications, such as medical, nutrition, research, among other fields. These sensors have been historically used and have not undergone many changes in terms of the involved electrochemical processes. In this work, we propose a new approach on the immobilization and enhancement of the electrochemical properties of the sensing layers through the control and bioconjugation of hemoproteins (hemoglobin, myoglobin, and cytochrome C) on anisotropic gold nanoparticles (gold nanotriangles (AuNTs)). The hemeproteins and the AuNTs are mixed in a solution, resulting in stable bioconjugates that are deposited onto the electrode surface to obtain the biosensors. All the systems proposed herein exhibited direct well-defined redox responses, highlighting the key role of the AuNTs acting as mediators of such electron transfers. Several protein layers surrounding the AuNTs are electroactive, as demonstrated from the charge measured by cyclic voltammetry. The retention of the stability of the hemeproteins once they are part of the bioconjugates is evidenced towards the electrocatalytic reduction of hydrogen peroxide, oxygen, and nitrite. The parameters obtained for the proposed biosensors are similar or even lower than those previously reported for similar systems based on nanomaterials, and they exhibit attractive properties that make them potential candidates for the latest developments in the field of sensing devices.

Symmetry-breaking in patch formation on triangular gold nanoparticles by asymmetric polymer grafting

Synthesizing patchy particles with predictive control over patch size, shape, placement and number has been highly sought-after for nanoparticle assembly research, but is fraught with challenges. Here we show that polymers can be designed to selectively adsorb onto nanoparticle surfaces already partially coated by other chains to drive the formation of patchy nanoparticles with broken symmetry. In our model system of triangular gold nanoparticles and polystyrene-b-polyacrylic acid patch, single- and double-patch nanoparticles are produced at high yield. These asymmetric single-patch nanoparticles are shown to assemble into self-limited patch‒patch connected bowties exhibiting intriguing plasmonic properties. To unveil the mechanism of symmetry-breaking patch formation, we develop a theory that accurately predicts our experimental observations at all scales—from patch patterning on nanoparticles, to the size/shape of the patches, to the particle assemblies driven by patch‒patch interactions. Both the experimental strategy and theoretical prediction extend to nanoparticles of other shapes such as octahedra and bipyramids. Our work provides an approach to leverage polymer interactions with nanoscale curved surfaces for asymmetric grafting in nanomaterials engineering.

Assessing the Efficiency of Triangular Gold Nanoparticles as NIR Photothermal Agents In Vitro and Melanoma Tumor Model.

Photothermal therapy (PTT) is gaining a lot of interest as a cancer treatment option with minimal side effects due to the efficient photothermal agents employed. They are based on nanomaterials that, upon laser irradiation, absorb photon energy and convert it into heat to induce hyperthermia, which destroys the cancer cells. Here, the unique light-to-heat conversion features of three different gold nanotriangular nanoparticles (AuNTs) are evaluated with respect to their absorption properties to select the most efficient nanoheater with the highest potential to operate as an efficient photothermal agent. AuNTs with LSPR response in- and out- of resonance with the 785 nm near-infrared (NIR) excitation wavelength are investigated. Upon 15 min laser exposure, the AuNTs that exhibit a plasmonic response in resonance with the 785 nm laser line show the highest photothermal conversion efficacy of 80%, which correlates with a temperature increase of 22 °C. These photothermal properties are well-preserved in agarose-based skin biological phantoms that mimic the melanoma tumoral tissue and surrounding healthy tissue. Finally, in vitro studies on B16.F10 melanoma cells prove by fluorescence staining and MTT assay that the highest phototoxic effect after NIR laser exposure is induced by AuNTs with LSPR response in resonance with the employed laser line, thus demonstrating their potential implementation as efficient photothermal agents in PTT.

Performance evaluation of rose bengal dye-decorated plasmonic gold nanoparticles-coated fiber-optic humidity sensor: A mechanism for improved sensing

Low-cost fiber-optic humidity sensors with fast response became demanding. Thus, well-dispersed pruned triangular plasmonic gold nanoparticles (AuNPs) of mean size 16.4 ± 7.3 nm were prepared in Rose Bengal dye (RBD) using pulsed laser ablation in liquid method at laser fluence of 7.9 ± 0.3 J/cm 2 . These stable RBD molecules-decorated AuNPs (RBD-AuNPs) showed enhanced fluorescence (lifetime decay ranged from 7.1 ± 0.9–6.4 ± 0.2 ns) and localized surface plasmon resonance absorption. The fabricated RBD-AuNPs-coated fiber-optic relative humidity sensor (FO-RHS) when tested against polyvinyl alcohol (PVA) at intensity modulation of 40–100 % RH) displayed higher sensitivity (0.08 a.u./%RH) and linearity (0.86 a.u./%RH) compared to the one coated with pure AuNPs. This improvement was mainly due to the adherence mechanism of –OH and COOH functional groups of RBD onto AuNPs surface, enabling in binding strongly the PVA molecules via hydrogen bonds. • Gold nanoparticles (AuNPs) were made in rose Bengal dye (RBD) medium by PLAL method. • These RBD-AuNPs showed improved fluorescence and LSPR absorption. • Fluorescence lifetime decay was varied from 7.1 to 6.4 ns. • Presence of –OH and –COOH groups on AuNPs surface enabled strong binding of PVA molecules by hydrogen bonding. • RBD-AuNPs-coated fiber-optic relative humidity sensor (FO-RHS) showed fast response. • Obtained FO-RHS displayed a good sensitivity (0.08 %) and linearity (0.86 %).

TiB2 derived nanosheets co-immobilized with triangular gold nanoparticles elicit fast and stable photocatalytic hydrogen evolution

Transition metal diborides are recently being revisited from the viewpoint of yielding 2D nanostructures owing to their layered topology and the inherent presence of boron honeycomb planes. In this report, we show that nanosheets derived from titanium diboride (TiB2), when co-immobilized with anisotropic gold nanoparticles, demonstrate an impressive photocatalytic behavior towards hydrogen evolution. We found that this novel nano construct could achieve H2 evolution rates of up to 1.13 mmol g−1h−1 at neutral pH and simulated light irradiation. This production rate is significant considering the fact that we neither employed any co-catalyst or electron/hole scavenging chemical species nor applied any external bias. In addition, the catalyst could continuously produce H2 for at least 30 h. We also found that the construct was active under direct sunlight exposure. The co-immobilized construct also showed photocatalytic activity under UV and NIR irradiations. This is the first report wherein TiB2 derived nanosheets have been employed towards catalyzing the HER. We attribute the mechanism of photocatalytic H2 evolution to either better electron/hole pair separation or direct electron transfer from the photosensitive gold nanoparticles to the nanosheets (through the formation of a Schottky barrier). This report showcases the rich potential of functionalized metal diboride nanosheets and their constructs for next-generation photocatalysts.

Nanoscale Biocompatible Structures Generated from Fluorinated Tripodal Phenylenes on Gold Nanoprisms.

Modification of gold substrates with a stable, uniform and ultrathin layer of biocompatible materials is of tremendous interest for the development of bio‐devices. We present the fabrication of hybrid systems consisting of triangular prism gold nanoparticles (Au@NTPs) covalently covered with tripod‐shaped oligo(p‐phenylenes) featuring trifluoromethyl groups. Their synthesis is accomplished using a biphenyl boronic ester as the key compound. Au@NTPs were prepared through a seedless procedure using 3‐butenoic acid and benzyldimethyl ammonium chloride, and modified with aminothiol groups. Coverage of this amine‐modified gold substrate with a self‐assembled monolayer (SAM) of tripod‐shaped molecules is carried out in ethanolic solution. The hybrid system avoids up to 70 % of protein corona formation, and allows unspecific attachment for bulky adsorbates, providing an optimal biosensing platform. Chemical composition and morphology are analyzed by transmission electron microscopy (TEM), UV‐visible spectroscopy and field emission scanning electron microscopy (FESEM).

Particle size and convergent electron diffraction patterns of triangular prismatic gold nanoparticles

Convergent beam diffraction (CBED) patterns of nanoparticles are possible. CBED of triangular prismatic shaped Au nanoparticle with focus on diffraction pattern symmetry and forbidden reflections observed along [111] and [112] zone axes are reported in this work. It is well known that the CBED patterns of nanoparticles of 30 nm or less in size only show bright kinematical discs. The dynamic contrast with Kikuchi and sharp HOLZ lines within the bright discs, as observed in CBED of volumetric materials, is well observed in particles larger of 500 nm in size. In addition, it is shown that the 1/3[422] and 1/2[311] weak forbidden reflections observed in the [111] and [112] electron diffraction patterns of these particles do not modify the symmetry of the CBED patterns, but they disappear as the size of the particle increases. The symmetry of the CBED patterns are always observed in concordance with the space group Fm3m (No. 225) of the Au unit cell. The possible explanations for observing forbidden reflections are the incomplete ABC stacking due to surface termination and the stacking faults in the fcc structure.

Machine-Free Polymerase Chain Reaction with Triangular Gold and Silver Nanoparticles.

Photothermal effects of metal nanoparticles (NPs) are used for various biotechnological applications. Although NPs have been used in a polymerase chain reaction (PCR), the effects of shape on the photothermal properties and its efficiency on PCR are less explored. The present study reports the synthesis of triangular gold and silver NPs, which can attain temperatures up to ∼90 °C upon irradiation with 808 nm laser. This photothermal property of synthesized nanoparticles was evaluated using various concentrations, irradiation time, and power to create a temperature profile required for variable-temperature PCR. This study reports a cost-effective, machine-free PCR using both gold and silver triangular NPs, with efficiency similar to that of a commercial PCR machine. Interestingly, addition of triangular NPs increases PCR efficiency in commercial PCR reactions. The higher PCR efficiencies are due to the direct binding and unfolding of double-stranded DNA as suggested by circular dichroism and UV spectroscopy. These findings suggest that triangular NPs can be used to develop cost-effective, robust machine-free PCR modules and can be used in various other photothermal applications.

Green synthesis of non-spherical gold nanoparticles using Solidago canadensis L. extract

In the present article, we reported the application of the extract of leaves from Solidago canadensis L. for the green synthesis of triangular and hexagonal gold nanoparticles (AuNPs). The phytochemical characterization, by reaction with HAuCl4 solutions, showed that the extract of Solidago canadensis L. contained the secondary metabolites that can act both as reducing and as stabilizing agents. For the synthesis of AuNPs, the effects of the HAuCl4 concentration (0.25–0.975 mM) and the reaction time (10–180 min) were investigated. The formation of AuNPs is confirmed by the color change from yellowish to purple-red. Photoluminescence measurements of Au nanocolloids showed a continuous emission band ranging from violet to red. UV–Vis characterization of AuNPs in the prepared nanocolloids showed surface plasmon resonance peaks at 530 and > 870 nm. TEM revealed that the AuNPs are in the range of 8–200 nm, they have spherical, triangular, and hexagonal forms of varying sizes. AFM and STM showed a non-ideal relief of large triangular and hexagonal gold nanoprisms. The EDX analysis, XRD and SAED patterns confirmed the face-center cubic structure of AuNPs.

Facile Synthesis of Triangular and Hexagonal Anionic Gold Nanoparticles and Evaluation of Their Cytotoxicity.

Comprehension of the shape-dependent properties of gold nanoparticles (AuNPs) could benefit the advancements in cellular uptake efficiency. Spherical AuNPs have generally been used for drug delivery, and recent research has indicated that the cellular uptake of triangular AuNPs was higher than that of spherical ones. Previous reports have also revealed that chemically synthesized AuNPs were cytotoxic. Therefore, we have developed a facile, cost-effective, and environmentally friendly method for synthesizing triangular and hexagonal anionic AuNPs. The zeta potential of the synthesized AuNPs was negative, which indicated that their surface could be easily functionalized with positively charged molecules to upload drugs or biomolecules. Transmission electron microscopy (TEM) images illustrated that the largest particle size of the synthesized quasi-hexagonal AuNPs was 61 nm. The TEM images also illustrated that two types of equilateral-triangular AuNPs were synthesized: One featured sharp and the other rounded corners. The sides of the smallest and largest triangular AuNPs were 23 and 178 nm, respectively. Energy-dispersive X-ray spectra of the green-synthesized AuNPs indicated that they consisted entirely of elemental Au. The cytotoxicity of the green-synthesized AuNPs was evaluated using 3T3-L1 adipocytes. Using cell viability data, we determined that the green-synthesized AuNPs did not exhibit any cytotoxic effects on 3T3-L1 adipocytes.

Hybrid surfaces active in catalysis based on gold nanoparticles modified with redox-active pendants and polymer brushes

We present hybrid systems bearing both plasmonic colloids and redox-active molecules that have demonstrated excellent performances in the catalytic reduction of nitrophenol (Nip) to aminophenol (Amp) in the presence of sodium borohydride. First, amino-functionalized spherical and triangular gold nanoparticles (AuNSs and AuNTs, respectively) were covalently incorporated onto polyacrylic acid (PAA) brushes attached to silicon surfaces. Next, a redox-active anthraquinone derivative (AQ-COOH) was immobilized onto the AuNPs surface by amidation reactions. The AuNP concentrations were varied to increase the incorporation and distribution of gold onto the PAA brushes. The catalytic activity in the reduction of 3-Nip and 4-Nip to Amp by NaBH4 was evaluated by 1H NMR spectroscopy. Colloidal size and morphology are analyzed by transmission electron microscopy (TEM) and UV–visible spectroscopy. Particle distribution on the silicon wafer was analyzed by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The presence of bonded cysteamine (Cys) and anthraquinone (AQ) derivatives on the gold surface was confirmed by X-ray photoelectron spectroscopy (XPS) and surface-enhanced Raman spectroscopy (SERS). The hybrid system could perform seven consecutive catalytic runs without loss of catalytic activity with conversions higher than 80%.

Efficient approach to in-situ preparation of anisotropic and assemblable gold nanoparticles mediated by stimuli-responsive PDMAEMA

Nowadays, stimuli-responsive materials have attracted much attention because of their potential applications in various fields, specifically when a plasmonic nanoparticle is chemically bonded to a polymeric chain. On the other hand, preparation of assemblable anisotropic gold nanoparticles is an interesting challenge and also, synthetic methods and tunability of the plasmonic properties are usually multi-step and complicated. Here, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) was used as a stimuli-responsive polymer substrate for in-situ reduction of chloroauric acid (HAuCl4) and synthesis of smart Au-PDMAEMA nanocomposites with anisotropic shapes. pH- and temperature-sensitive PDMAEMA played its role as a reducing, stabilizing and shape controlling agent to produce triangular gold nanoparticles with tunable UV–Vis absorption domain. Effect of some structural parameters like molar ratio of reducing group to Au ions, addition type and seed-mediated growth methods were studied comprehensively. Responsivity of Au-PDMAEMA nanocomposites to some stimuli like temperature and pH and also their reversibility were examined. Optical investigations revealed reversible and reproducible shifts between UV–Vis (550 nm) and near-IR (700 nm) absorptions by triggering with pH and temperature. The introduced strategy may facilitate synthesis of smart plasmonic nanoparticles with multi-responsivity. Assembly and disassembly of triangular plate-like nanoparticles with several stimulants may open up new fields due to their orientation/packing toward self-assembly.

Triangular gold nanoparticles modify shell characteristics and increase antioxidant enzyme activities in the clam Ruditapes decussatus

Context: Nanoparticles may cause adverse environmental effects but there is limited information on their interactions with marine organisms.Objective: Our aim was to examine the effects of triangular gold nanoparticles (Tr-Au NPs) on the clam, Ruditapes decussatus.Materials and methods: Clams were exposed to Tr-Au1 = 5 µg/L and Tr-Au2 = 10 µg/L for 2 and 7 days. Effects on shell structure were investigated. Superoxide dismutase (SOD), catalase (CAT), glutathione transferase (GST) activities, protein carbonyl levels and malondialdehyde content were used to assess biochemical status.Results: Transmission electron microscopy (TEM) and electron dispersive X-ray microanalysis (EDX) showed that Tr-Au NPs modified shell structure and morphology. Tr-Au NPs size increased forming aggregate particles. Tr-Au NPs increased SOD, CAT and GST activities in gill and digestive gland in a concentration- and time-dependent manner indicating defence against oxidative stress. Enhanced lipid peroxidation and protein carbonyl levels confirmed oxidative stress.Conclusion: Tr-Au NPs cause oxidative stress and affect shell structure of clams. These findings may have relevance to other marine species.

Bio-synthesis of triangular and hexagonal gold nanoparticles using palm oil fronds’ extracts at room temperature

Development of bio-reduction techniques for nanoparticles (NPs) synthesis in medical application remains a challenge to numerous researchers. This work reports a novel technique for the synthesis of triangular and hexagonal gold nanoparticles (AuNP) using palm oil fronds’ (POFs) extracts. The functional groups in the POFs’ extracts operate as a persuasive capping and reducing agent to growth AuNPs. The prepared AuNPs were characterized using UV–vis spectrophotometry, Fourier-transform infrared (FTIR) spectroscopy, dynamic light scattering, energy filtered transmission electron microscopy (EFTEM), and x-ray diffraction (XRD). The analysis of FTIR validates the coating of alkynes and phenolic composites on the AuNPs. This shows a feasible function of biomolecules for efficient stabilization of the AuNPs. EFTEM clearly show the triangular and hexagonal shapes of the prepared AuNPs. The XRD patterns display the peaks of fcc crystal structures at (111), (200), (220), (311) and (222), with average particle sizes of 66.7 and 79.02 nm for 1% and 5% POFs extracts concentrations respectively at room temperature. While at 120 °C the average particles size recorded for 1% and 5% of POFs extract concentrations were 32.17 nm and 45.66 nm respectively, and the reaction completed in less than 2 min. The prepared NPs could be potentially applied in biomedical application, due to their excellent stability and refine morphology without agglomeration.

Chemists create colloidal clathrate crystals

As denizens of DNA, Chad A. Mirkin and his group at Northwestern University have used the biopolymer in combination with metal nanoparticles to assemble hundreds of differently shaped micrometer-scale colloidal crystals. Even so, they have just come up with one that hasn’t been seen before: a colloidal clathrate. The trick in making the clathrates, which are known for their cavities that can house molecules for storing, delivering, and sensing applications, was tuning the nanoparticle shape and the length and sequence of the DNA connectors. The engineering was guided by simulations carried out by Sharon C. Glotzer and her team at the University of Michigan (Science 2017, DOI: 10.1126/science.aal3919). The researchers prepared anisotropic, triangular bipyramidal gold nanoparticles that align into tetramers. Attaching a DNA monolayer to the gold leads to assembly of nanoparticle clusters that form the colloidal crystals with patterns that, rather than become densely packed, leave polygon-shaped holes. The

Visual detection of glucose using triangular silver nanoplates and gold nanoparticles

A sensitive spectrophotometric detection of glucose based on triangular silver nanoplates (Ag TNPs) coupled with gold nanoparticles (Au NPs) was carried out.

Reverse Size Dependences of the Cellular Uptake of Triangular and Spherical Gold Nanoparticles.

Gold nanoparticles (GNPs) show promise as both drug and imaging carriers with applications in both diagnosis and therapy. For the safe and effective use of such gold nanomaterials in the biomedical field, it is crucial to understand how the size and shape of the nanomaterials affect their biological features, such as in vitro cellular uptake speed and accumulation as well as cytotoxicity. Herein, we focus on triangular gold nanoparticles (TNPs) of four different sizes (side length 46, 55, 72, and 94 nm; thickness 30 nm) and compare the cellular internalization efficiency with those of spherical nanoparticles (SNPs) of various diameters (22, 39, and 66 nm). Both surfaces were coated with anionic thiol ligands. Inductively coupled plasma-emission spectrometry (ICP-ES) data demonstrated that TNPs with longer sides showed higher levels of uptake into RAW264.7 and HeLa cells. On the other hand, in the case of SNPs, those with smaller diameters showed higher levels of uptake in both cells. Our results support the notion of a reverse size dependence of TNPs and SNPs in terms of cellular uptake. For HeLa cells, in particular, 20-fold more efficient internalization was observed for TNPs with longer sides (72 nm side length) compared to SNPs (66 nm) with a similar surface area. These results highlight the importance of the shape of nanomaterials on their interactions with cells and provide a useful guideline for the use of TNPs.

Characterization of Triangular Gold Nanoparticles Using Aloe arborescens Leaf Extract: A Green Synthesis Approach

Herein, the authors show the use of the Aloe arborescens leaf extract for green synthesis of gold nanoparticles in water at room temperature under very mild conditions. The synthesis of the gold nanoparticles was complete in several minutes, and no extra stabilizing or capping agents were necessary. The size of the nanoparticles could be controlled by varying the concentration of the leaf extract. The silver nanoparticles and reaction process were characterized by UV-vis spectrometer, Fourier transform infrared spectroscopy, and transmission electron microscopy. The UV-visible spectra of synthesized nanoparticles showed absorption maxima at 540 nm. Transmission electron microscopy images confirm that the nanoparticles are spherical and triangular in shape.

Parametric Study on Gold Nanoparticle Synthesis Using Aqueous Elaise Guineensis (Oil palm) Leaf Extract: Effect of Precursor Concentration

In this study, gold nanoparticles (AuNPs) were synthesized by using aqueous extract of Elaise guineensis (oil palm) leaves without addition of any external stabilizing agent. Effects of precursor concentrations (0.51 mM- 4.055mM) on SPR absorbance and AuNP particle size distribution were investigated. The synthesis reaction was monitored by measuring time-variant SPR spectrum of the reaction medium with a UV-vis spectrophotometer. Biosynthesized AuNPs were characterized using TEM, DLS, UV-vis and FTIR spectroscopy. TEM image analysis showed formation of predominantly spherical gold nanoparticles with mean particle diameter of 27.89±14.59nm were formed using 1.53mM gold concentration. DLS data showed that AuNPs with hydrodynamic diameter 55.22 ± 42.86nm were formed, indicating formation of multilayer coatings of biomolecules present in the leaf extract on nanoparticles. Spherical, triangular, pentagonal and hexagonal gold nanoparticles with mean particle diameter 22.88 ±8.21nm were formed when higher gold (III) precursor concentrations (4.055mM) were used. FTIR analysis revealed that carboxylic and phenolic compounds present in leaf extract played dual roles as reducing and stabilizing agents during synthesis of AuNPs.