Optical Enhancing Properties Research Articles

Surface-enhanced photoluminescence and Raman spectroscopy of single molecule confined in coupled Au bowtie nanoantenna

Optical nanoantennas possess broad applications in the fields of photodetection, environmental science, biosensing and nonlinear optics, owing to their remarkable ability to enhance and confine the optical field at the nanoscale. In this article, we present a theoretical investigation of surface-enhanced photoluminescence spectroscopy for single molecules confined within novel Au bowtie nanoantenna, covering a wavelength range from the visible to near-infrared spectral regions. We employ the finite element method to quantitatively study the optical enhancement properties of the plasmonic field, quantum yield, Raman scattering and fluorescence. Additionally, we systematically examine the contribution of nonlocal dielectric response in the gap mode to the quantum yield, aiming to gain a better understanding of the fluorescence enhancement mechanism. Our results demonstrate that altering the configuration of the nanoantenna has a significant impact on plasmonic sensitivity. The nonlocal dielectric response plays a crucial role in reducing the quantum yield and corresponding fluorescence intensity when the gap distance is less than 3 nm. However, a substantial excitation field can effectively overcome fluorescence quenching and enhance the fluorescence intensity. By optimizing nanoantenna configuration, the maximum enhancement of surface-enhanced Raman can be turned to 9 and 10 magnitude orders in the visible and near-infrared regions, and 3 and 4 magnitude orders for fluorescence enhancement, respectively. The maximum spatial resolutions of 0.8 nm and 1.5 nm for Raman and fluorescence are also achieved, respectively. Our calculated results not only provide theoretical guidance for the design and application of new nanoantennas, but also contribute to expanding the range of surface-enhanced Raman and fluorescence technology from the visible to the near-infrared region.

Boosting the analytical properties of gold nanostars by single particle confinement into yolk porous silica shells.

Herein we illustrate an effective protocol to boost the optical enhancing properties of gold nanostars. By coating single nanostars with a mesoporous silica layer of the appropriate size (yolk capsules), to localize them under optical microscopy, it is possible to enumerate single particles and design SERS quantitative methods with minute amounts of metallic particles.

Plasmon Tunability of Gold Nanostars at the Tip Apexes.

Herein, we present an optimized bottom-up approach to fabricate homogeneous Au nanostars with plasmon resonances fully tunable between the red and the infrared. The synthetic method relies on the kinetic control of the reaction upon optimization of the reactant concentrations (i.e., gold seeds, reducing agent, and gold salt). Optical enhancing properties of the obtained materials are demonstrated by using SERS with visible and infrared lasers.

Fabrication and optical enhancing properties of discrete supercrystals.

Discrete gold nanoparticle crystals with tunable size and morphology are fabricated via a fast and inexpensive template-assisted method. The highly precise hierarchical organization of the plasmonic building blocks yields superstructures with outstanding behaviour for surface-enhanced Raman scattering analysis.

Investigation of maximum optical enhancement in single gold nanowires and triple nanowire arrays

This work thoroughly investigates gold nanowires with various cross-sectional geometries and patterns. The study has determined the effect of the cross section aspect ratio on its maximum optical enhancement. The plasmonic optical enhancement properties of single gold nanowires and an array of three nanowires were investigated using finite element method simulations. The results indicate a significant dependence of the optical enhancement on both the thickness and width of the nanowires. From the simulation data, an equation for each geometry (single and triple array) was found that relates the dimensions and incident wavelength to the optical enhancement. These relationships can be a valuable resource while designing nanowires to optimize the dimensions and provide the maximum possible optical enhancement.

Gold Nanorod-pNIPAM Hybrids with Reversible Plasmon Coupling: Synthesis, Modeling, and SERS Properties.

The thermoresponsive optical properties of Au nanorod-doped poly(N-isopropylacrylamide) (Au NR-pNIPAM) microgels with different Au NR payloads and aspect ratios are presented. Since the volume phase transition of pure pNIPAM microgels is reversible, the optical response reversibility of Au NR-pNIPAM hybrids is systematically analyzed. Besides, extinction cross-section and near-field enhancement simulations for Au NR-microgel hybrids are performed using a new numerical method based on the surface integral equation method of moments formulation (M3 solver). Additionally, the Au NR-microgel hybrid systems are expected to serve as excellent broadband surface-enhanced Raman scattering (SERS) substrates due to the temperature-controlled formation of hot spots and the tunable optical properties. The optical enhancing properties related to SERS are tested with three laser lines, evidencing excitation wavelength-dependent efficiency that can be easily controlled by either the aspect ratio (length/width) of the assembled Au NR or by the Au NR payload per microgel. Finally, the SERS efficiency of the prepared Au NR-pNIPAM hybrids is found to be stable for months.

Fabrication of stable network-like gold nanostructures in solution and their assessment as efficient NIR-SERS platforms for organic pollutants detection

In this work we report a facile, rapid and low-cost procedure to fabricate network-like gold nanostructures and demonstrate their effectiveness as surface-enhanced Raman scattering (SERS) platforms for organic pollutants detection. The typical procedure starts with the preparation of standard colloidal gold nanoparticles solution followed by addition of zinc acetate which induces formation of novel and useful morphology for SERS substrates. The fabricated plasmonic nanoarchitectures exhibit high stability in water and strong optical enhancing properties in near-infrared (NIR). The NIR-SERS efficiency is assessed against two representative organic dyes, methylene blue and basic fuchsin. The study demonstrates that the as prepared platform can detect minute amounts of organic pollutants in aqueous solution with excitation at 785nm diode laser line from a portable Raman spectrometer. The results are promising for integration in ultrasensitive optical devices for NIR-SERS detection of organic pollutants in watercourses.

Organized Solid Thin Films of Gold Nanorods with Different Sizes for Surface-Enhanced Raman Scattering Applications

Gold nanorods are among the most efficient structures for optical applications, especially in surface-enhanced Raman scattering applications. Notably, their use directly in colloidal solutions decreases their optical enhancing properties because of the impossibility of generating hot spots and the passivation of their surfaces by the surfactants used during their preparation, hindering the interaction of the analyte with the plasmonic surface. We present an easy and fast method for preparing organized lying-down nanorod films with particles of different aspect ratios, yielding efficient and clean plasmonic films populated with a large number of homogeneous hot spots.

Modulation of Localized Surface Plasmons and SERS Response in Gold Dumbbells through Silver Coating

We describe the modulation of localized surface plasmons in gold nanodumbbells through stepwise silver coating, along with a detailed discussion regarding the experimental parameters affecting the final core−shell morphology. Interestingly, whereas conformal growth was observed for thin coatings, for intermediate and high silver salt concentrations, the final nanoparticles end up with either rod-like or irregular faceted morphologies as a consequence of anisotropic silver growth. Upon silver reduction, pronounced changes in the optical properties were observed, which could be modeled using the boundary element method (BEM), which also allowed the assignment of different plasmon modes. Such core−shell Au@Ag nanoparticles are expected to serve as excellent SERS substrates, as significantly higher enhancement factors are expected for silver as compared to gold. Optical enhancing properties for SERS were tested with two laser lines, evidencing significantly larger enhancement factors for the bimetallic nanopa...

Growth of Sharp Tips on Gold Nanowires Leads to Increased Surface-Enhanced Raman Scattering Activity.

We report the formation of gold nanoparticles with a novel and useful morphology, comprising nanowires fully covered with sharp tips (thorned nanowires). The synthesis is based on a seeded-growth approach based the rapid overgrowth of ultrathin gold wires in N,N-dimethylformamide, in the presence of poly(vinylpyrrolidone). The process allows a fine control over the thickness of the final wires, as well as the tunability of the number and sharpness of the thorns. These new plasmonic nanostructures display extremely strong optical enhancing properties and can be readily used as platforms for SERS and for integration in ultrasensitive optical devices.

Single-Molecule SERRS Detection Platforms Obtained via Galvanic Displacement on Silver Fractals

Nanostructured metallic architectures have unique and highly attractive properties, including large optical field enhancements resulting in strong light scattering and absorption. Modification of prefabricated nanostructures by simple galvanic displacement (GD) allows for the design of new nanomaterials with enhanced optical properties. In this paper, we have studied the optical properties of two families of Ag fractals before and after GD in a Au(III) solution. The new nanomaterials showed significantly improved optical enhancing properties that allowed for straightforward and highly reproducible single-molecule detection by surface-enhanced resonance Raman scattering (SERRS).

Optical Enhancing Properties of Anisotropic Gold Nanoplates Prepared with Different Fractions of a Natural Humic Substance

The results of this work demonstrate the properties of suspensions of humic substances (HS) used as reducing and templating agent for the formation of gold nanostructures. It is further established that a considerable degree of control over the size and shape of the nanoparticles can be achieved by selecting the appropriate humic fraction and adjusting the pH of the working suspension. These gold nanostructures can sustain surface plasmon resonances and exhibit optical enhancing properties that make them suitable for plasmonic applications and optical enhancement such as surface-enhanced Raman scattering (SERS). The efficiency of the nanostructures as a SERS substrate is illustrated enhancing the Raman spectrum of 2-mercaptobenzothiazole (MBT), a common organic pollutant.