Silver Nanotriangles Research Articles

A Sensitive SERS Quantitative Analysis Method for Amino Acids Using Ruhemann’s Purple as Molecular Probe in Triangle Nanosilver Sol Substrate

The stable silver nanotriangle (AgNT) sol was prepared by reduction of silver ions with sodium borohydride in the presence of H2O2 and sodium citrate. Under the action of NaCl, AgNTs were aggregated to a highly surface-enhanced Raman scattering (SERS) active substrate. In pH 6.0 Na2HPO4-NaH2PO4 buffer solution (PBS) at 80 °C water bath, ninhydrin reacted with amino acids to form blue-violet complex Ruhemann’s purple (RP), and the RP molecules adsorbed on the aggregated AgNT surfaces that exhibited a strong SERS peak at 657 cm−1. The peak was linear to amino acid concentration in the range of 0.7–99.8 μmol/L, with a detection limit (DL) of 0.5 μmol/L. This SERS method was applied to detect amino acid in samples, with satisfactory results. In addition, the analytical system was also investigated by resonance Rayleigh scattering (RRS), absorption, and electron microscope techniques.

Modulation of the shape and localized surface plasmon resonance of silver nanoparticles via halide ion etching and photochemical regrowth

In the present study, modulation of the shape and their localized surface plasmon resonance (LSPR) properties of silver nanoparticles (AgNPs) were realized by halide ion etching and subsequent photochemical regrowth. Silver nanotriangles were chemically etched into nanodisks, and were then transformed into nanohexagons, truncated nanotriangles, and nanotriangles with sharp corners by photochemical regrowth process. By changing the excitation wavelength applied in the photochemical regrowth process, the LSPR properties of AgNPs were tuned in the range from 490 to 800nm.

High Current Density Chronopotentiometric Electrosynthesis and SEM Characterization of Hexanethiol-Monolayer-Protected Silver Planar Nanotriangles (Ag@C6SH)

This work reports for the first time electrosynthesis of hexanethiol capped silver nanotriangles cores (Ag@C6SH NCs) by a rapid, clean, and simple Double Pulse Chronopotentiometric (DCP) method in nonaqueous media, using a Taguchi orthogonal arrayL8design to identify the optimized experimental conditions. It was found that the size and shape of the product could be tuned by the current density, electrolysis time, electrode distance, and amount of NaBH4% used. The Ag@C6SH NCs in different shapes and sizes (in the range of 30 to 44 nm as an average estimation) were synthesized, under different experimental conditions. Finally, the as-prepared nanoclusters electrosynthesized at optimized conditions were characterized by SEM, XRD, and UV-Vis spectroscopy. The average particle size of the triangular/pyramidal shape (Ag@C6SH NCs), obtained under optimized experimental conditions, was30.5±2.0 nm but the majority of nanoparticles in TC3SEM are so much finer.

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.

Multipolar and dark-mode plasmon resonances on drilled silver nano-triangles.

Dark-mode plasmon resonances can be excited by positioning a suitable nano-antenna above a nanostructure to couple a planar incident wave-front into a virtual point source. We explore this phenomenon using a prototypical nanostructure consisting of a silver nanotriangle into which a hole has been drilled and a rod-like nano-antenna of variable aspect ratio. Using numerical simulations, we establish the behavior of the basic drilled nanotriangle under plane wave illumination and electron beam irradiation to provide a baseline, and then add the nano-antenna to investigate the stimulation of additional dark-mode plasmon resonances. The introduction of a suitably tuned nano-antenna provides a new and general means of exciting dark-mode resonances using plane wave light. The resulting system exhibits a very rich variety of radiant and sub-radiant resonance modes.

Surface-enhanced fluorescent immunoassay on 2D silver nanotriangles array

Long range ordered silver nanotriangles array was fabricated for surface-enhanced fluorescent immunoassay in this paper. By polystyrene (PS) microspheres based LB template method, the silver nanotriangle array with about 100nm in height was constructed on the surface of glass slide. On the surface of Ag nanotriangles array, the immune reaction of antigens and labeled antibodies was carried out. Based on the interaction of fluorophores from antibodies with the plasmon resonance from Ag nanotriangles and the enrichment effect of this patterned array, 3.11 times enhancement of the fluorescent intensity of the target antibodies was obtained. According to the fitting curve of fluorescent intensities and logarithmic concentrations of labeled antibodies from 100pg/mL to 10μg/mL, it concludes that the limit of detection by this Ag nanotriangles array for immune complex is 100pg/mL. Due to the advantages of high sensitivity, good reproducibility, and convenient fabrication, the 2D silver nanotriangles array could be an exciting platform for bioassays in proteomics, drug discovery and diagnostics.

Folic Acid-Conjugated, SERS-Labeled Silver Nanotriangles for Multimodal Detection and Targeted Photothermal Treatment on Human Ovarian Cancer Cells

The effectiveness of a therapeutic agent for cancer stands in its ability to reduce and eliminate tumors without harming the healthy tissue nearby. Nanoparticles peripherally conjugated with targeting moieties offer major improvements in therapeutics through site specificity. In this study we demonstrate this approach by targeting the folate receptor of NIH:OVCAR-3 human ovary cancer cell line. Herein we used silver nanotriangles which were biocompatibilized with chitosan (bio)polymer, labeled with para-aminothiophenol (pATP) Raman reporter molecule, and conjugated with folic acid. The nanoparticles conjugation and efficient labeling was investigated by localized surface plasmon resonance (LSPR), zeta potential, and surface-enhanced Raman scattering (SERS) measurements. Conjugated particles were proven to be highly stable in aqueous and cellular medium. The targeted uptake of conjugated nanoparticles by human ovary cancer cells was confirmed by dark field microscopy and scattering spectra of the particles inside cells. Comparative studies revealed specific internalization of the conjugated nanoparticles in comparison with similar bare nanoparticles. Moreover, the SERS identity of the particles was proven to be highly conserved inside cells. Targeted cancer cell treatment conducted by irradiating the nanoparticle-treated cells with a continuous wave-nearinfrared (cw-NIR) laser in resonance with their plasmonic band proved an efficient therapeutic response. By integrating the advantages of multimodal optical imaging and SERS detection with hyperthermia capabilities through site specificity, these nanoparticles can represent a real candidate for personalized medicine.

Electron–Phonon Scattering in 2D Silver Nanotriangles

Electron−phonon energy exchanges are investi- gated in 2D silver nanotriangles of thickness ranging from 5 to 8 nm and lateral size ranging from 25 to 85 nm, using time-resolved femtosecond spectroscopy in the low-perturbation regime. The measured electron−phonon decay time is smaller in 2D nano- triangles than in bulk silver, and its value corresponds to the decay time measured in isolated nanospheres with a diameter equal to the thickness of the nanotriangles. These results show that the electron−phonon energy exchanges in 2D nanosystems are strongly accelerated by confinement and this acceleration is directly governed by the smallest dimension of the nano-object.

Green Synthesis of Gold and Silver Nanoparticles Using <I>Achyranthes aspera</I> L. Leaf Extract

The importance of leaf extract of Achyranthes aspera L. as reducing agent in the synthesis of gold, silver nanoparticles (NPs) in quantitative yield, by the reaction of aqueous chloroaurate ions and aqueous silver ions with a small quantity of leaf extract is demonstrated. Changes in concentration of leaf extract can modify the phase morphology and the size of the nanoparticles can be tuned. UV-Visible spectra of the solution evidenced the variation in the dimension of anisotropic nanostructures. The formation of spherical nanostructures and nanotriangles of noble metal gold and silver nanoparticles is confirmed by transmission electron microscopy (TEM) investigations. The gold nanoparticles are poly dispersed and the average size of spherical nanoparticles is found to be 18 3±1 0 nm. The average edge length of the triangle is 27 2±2 0 nm. Selected area diffraction pattern (SAED) confirmed the polycrystalline molecular structure. SAED diffraction patterns of biogenic silver nanotriangles revealed the orientation of nanotriangles top surface normal to the electron beam.

Chitosan-coated triangular silver nanoparticles as a novel class of biocompatible, highly sensitive plasmonic platforms for intracellular SERS sensing and imaging

There is a need for new strategies for noninvasive imaging of pathological conditions within the human body. The approach of combining the unique physical properties of noble-metal nanoparticles with their chemical specificity and an easy way of conjugation open up new routes toward building bio-nano-objects for biomedical tracking and imaging. This work reports the design and assessment of a novel class of biocompatible, highly sensitive SERS nanotags based on chitosan-coated silver nanotriangles (Chit-AgNTs) labeled with para-aminothiophenol (p-ATP). The triangular nanoparticles are used as Raman scattering enhancers and have proved to yield a reproducible and strong SERS signal. When tested inside lung cancer cells (A549) this class of SERS nanotags presents low in vitro toxicity, without interfering with cell proliferation. Easily internalized by the cells, as demonstrated by imaging using both reflected bright-light optical microscopy and SERS spectroscopy, the particles are proved to be detectable inside cells under a wide window of excitation wavelengths, ranging from visible to near infrared (NIR). Their high sensitivity and NIR availability make this class of SERS nanotags a promising candidate for noninvasive imaging of cancer cells.

Fluorescence Enhancement Using Silver Nanotriangle Arrays

We describe the fabrication of silver nanotriangle array using angle resolved nanosphere lithography and utilizing the same for enhancing fluorescence. The well established nanosphere lithography is modified by changing the angle of deposition between the nanosphere mask and the beam of silver being deposited resulting in nanotriangles of varying surface area and density. The 470 nm plasmon resonance wavelength of the substrate was determined using minimum reflectivity method which closely matches with excitation wavelength of the fluorophore. Ten times enhancement in fluorescence emission intensity is obtained from fluorescein isothiocyanate coated on top of silver nanotriangle array separated by a spacer layer of poly vinyl alcohol as compared to glass. The enhanced fluorescence emission is attributed to the increase in local field enhancement.

Excitation Polarization Sensitivity of Plasmon-Mediated Silver Nanotriangle Growth on a Surface

In this contribution, we report an effective and relatively simple route to grow triangular flat-top silver nanoparticles (NPs) directly on a solid substrate from smaller NPs through a wet photochemical synthesis. The method consists of fixing small, preformed nanotriangles (NTs) on a substrate and subsequently irradiating them with light in a silver seed solution. Furthermore, the use of linearly polarized light allows for exerting control on the growth direction of the silver nanotriangles on the substrate. Evidence for the role of surface plasmon resonances in governing the growth of the NTs is obtained by employing linear polarized light. Thus, this study demonstrates that light-induced, directional synthesis of nanoparticles on solid substrates is in reach, which is of utmost importance for plasmonic applications.

Probing plasmon polarization-mediated photoluminescence enhancement on metal–semiconductor hybrid optical nanostructures

The emission properties of CdSe quantum dots coupled to silver nanotriangles (AgNT) plasmon modes are reported. In the presence nanoparticles, the quantum dots exhibit 14-fold luminescence enhancements at an excitation wavelength of 442 nm which overlap with both AgNT dipole and quadrupole plasmon resonance frequencies. The distance-dependent transition between enhancements and quenching and the polarization dependence of plasmon-mediated CdSe emission are also investigated. The modifications on CdSe emission are explained in terms of electromagnetic coupling with the surface plasmon modes of nanoparticles and an increase in the excitation efficiency due to the enhanced local incident field intensity at the excitation wavelength.

Chitosan-coated triangular silver nanoparticles as a novel class of biocompatible, highly effective photothermal transducers for in vitro cancer cell therapy

One of the relevant directions that nanotechnology is taking nowadays is connected with nanomedicine and specifically related to the use of light and nanoparticles in early diagnosis and effective therapeutics of cancer. Noble-metal nanoparticles can act under laser irradiation as effective photothermal transducers for triggering localized hyperthermia of tumors. In this work we report the performance of newly synthesized chitosan-coated silver nanotriangles (Chit-AgNTs) with strong resonances in near-infrared (NIR) to operate as photothermal agents against a line of human non-small lung cancer cells (NCI-H460). The hyperthermia experiments were conducted by excitation of nanoparticles-loaded cells at 800 nm wavelength from a Ti:Sapphire laser. We found that the rate of cell mortality in the presence of Chit-AgNTs is higher than in the presence of thiolated poly(ethylene) glycol capped gold nanorods (PEG-AuNRs) – a common hyperthermia agent used as reference-, while no destructive effects were noticed on the control sample (cells without nanoparticles) under identical irradiation conditions. Additionally, we conducted cytotoxicity assays and found Chit-AgNTs to be efficiently uptaken by the cells while exhibiting good biocompatibility for healthy human embryonic cells (HEK), which is essential for any in vivo applications. Our results reveal a novel class of biocompatible plasmonic nanoparticles with high potential to be implemented as effective phototherapeutic agents in the battle against cancer.

Measurement and Optimization of Metal‐Nanoparticle‐Induced Luminescence Enhancement Factors in a Crossed‐Optical Fiber Configuration

A crossed‐optical‐fiber configuration comprised of silver nanoparticles covalently attached to the core of an optical fiber and labeled with luminescent ruthenium molecules is reported. A second optical fiber was placed at right angle of the fiber containing the nanoparticle/ruthenium, to form a fiber‐fiber junction, and it was used to detect the luminescence from the ruthenium molecules bound to the first fiber. To employ the effect of metal‐enhanced luminescence, the ruthenium complex was kept at an appropriate distance from the nanoparticles by polyelectrolyte spacer layers. For silver nanospheres, nanotriangles and nanorods and for spacer‐layer thicknesses from 2–14 nm luminescence‐enhancement factors were determined. A 27‐fold luminescence enhancement was found when the ruthenium complex was placed 4 nm from silver nanotriangles. Finally, a calibration curve for the oxygen dependence of luminescence intensities and lifetimes of ruthenium complex is presented suggesting that the oxygen sensing capabilities of the nanoengineered‐ruthenium complex are maintained.

Mapping surface plasmons on a single metallic nanoparticle

Understanding how light interacts with matter at the nanometre scale is a fundamental issue in optoelectronics and nanophotonics. In particular, many applications (such as bio-sensing, cancer therapy and all-optical signal processing) rely on surface-bound optical excitations in metallic nanoparticles. However, so far no experimental technique has been capable of imaging localized optical excitations with sufficient resolution to reveal their dramatic spatial variation over one single nanoparticle. Here, we present a novel method applied on silver nanotriangles, achieving such resolution by recording maps of plasmons in the near-infrared/visible/ultraviolet domain using electron beams instead of photons. This method relies on the detection of plasmons as resonance peaks in the energy-loss spectra of subnanometre electron beams rastered on nanoparticles of well-defined geometrical parameters. This represents a significant improvement in the spatial resolution with which plasmonic modes can be imaged, and provides a powerful tool in the development of nanometre-level optics.

Overlayers on Silver Nanotriangles: Field Confinement and Spectral Position of Localized Surface Plasmon Resonances

We studied the spectral evolution of plasmon modes associated with silver nanotriangles as a function of dielectric overlayer thickness in the range of 5-300 nm. A substantial red-shift of the resonance is observed that oscillates with increasing over-layer thickness. We explain this previously unreported oscillation through the cavity quantum electrodynamical effect of the array of triangles combined with the dielectric overlayer. The red-shift, though substantial, is less than expected. Comparison with numerical models indicates that this discrepancy is due to very tight field confinement around the tips of the triangles.