Distributed Gold Nanoparticles Research Articles

Deep-learning-augmented microscopy for super-resolution imaging of nanoparticles.

Conventional optical microscopes generally provide blurry and indistinguishable images for subwavelength nanostructures. However, a wealth of intensity and phase information is hidden in the corresponding diffraction-limited optical patterns and can be used for the recognition of structural features, such as size, shape, and spatial arrangement. Here, we apply a deep-learning framework to improve the spatial resolution of optical imaging for metal nanostructures with regular shapes yet varied arrangement. A convolutional neural network (CNN) is constructed and pre-trained by the optical images of randomly distributed gold nanoparticles as input and the corresponding scanning-electron microscopy images as ground truth. The CNN is then learned to recover reversely the non-diffracted super-resolution images of both regularly arranged nanoparticle dimers and randomly clustered nanoparticle multimers from their blurry optical images. The profiles and orientations of these structures can also be reconstructed accurately. Moreover, the same network is extended to deblur the optical images of randomly cross-linked silver nanowires. Most sections of these intricate nanowire nets are recovered well with a slight discrepancy near their intersections. This deep-learning augmented framework opens new opportunities for computational super-resolution optical microscopy with many potential applications in the fields of bioimaging and nanoscale fabrication and characterization. It could also be applied to significantly enhance the resolving capability of low-magnification scanning-electron microscopy.

Multifunctional Hybrid MoS2-PEGylated/Au Nanostructures with Potential Theranostic Applications in Biomedicine.

In this work, flower-like molybdenum disulfide (MoS2) microspheres were produced with polyethylene glycol (PEG) to form MoS2-PEG. Likewise, gold nanoparticles (AuNPs) were added to form MoS2-PEG/Au to investigate its potential application as a theranostic nanomaterial. These nanomaterials were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoelectron X-ray spectroscopy (XPS), Fourier-transformed infrared spectroscopy (FTIR), cyclic voltammetry and impedance spectroscopy. The produced hierarchical MoS2-PEG/Au microstructures showed an average diameter of 400 nm containing distributed gold nanoparticles, with great cellular viability on tumoral and non-tumoral cells. This aspect makes them with multifunctional characteristics with potential application for cancer diagnosis and therapy. Through the complete morphological and physicochemical characterization, it was possible to observe that both MoS2-PEG and MoS2-PEG/Au showed good chemical stability and demonstrated noninterference in the pattern of the cell nucleus, as well. Thus, our results suggest the possible application of these hybrid nanomaterials can be immensely explored for theranostic proposals in biomedicine.

Photo-Aligned Nematic Liquid Crystals Enable the Modulation of Thermoplasmonic Heating

We experimentally demonstrate that the plasmonic heat delivered by a single layer of homogeneously distributed gold nanoparticles (AuNPs), immobilized on a glass substrate, can be optically tuned by taking advantage of the properties of an organic layer based on azobenzene and nematic liquid crystal (NLC) molecules. The effect, which exploits the dependence of the NLC refractive index value on the molecular director orientation, is realized using the polarization-dependent, light-induced molecular reorientation of a thin film of photo-aligning material that the NLC is in contact with. The reversibility of the optically induced molecular director reorientation of the NLC enables an active modulation of the plasmonic photo-induced heat.

Synthesis of homogeneously distributed gold nanoparticles built-in metal free organic framework: Electrochemical detection of riboflavin in pharmaceutical and human fluids samples

This study describes the synthesis of gold nanoparticles (AuNPs) incorporated melamine based covalent organic framework (MCOF) and their modification on glassy carbon electrode (GCE) for the sensitive and selective detection of riboflavin (RF). The MCOF was synthesized by refluxing melamine and terephthalaldehyde followed by AuNPs were incorporated into MCOF. The synthesized nanocomposite (MCOF-AuNPs) was confirmed by different spectral, microscopic and electrochemical methods. The TEM images show spherical AuNPs with an average diameter of 8 nm on the sheet-like structure of MCOF. The heterogeneous electron transfer rate constant (ket) was calculated for 1 mM K3/K4[Fe(CN)6] containing 0.1 M KCl at bare GC, MCOF and MCOF-AuNPs/GCEs was found to be 1.14, 1.72 and 4.31 × 10-4 cm2 s−1, respectively. The higher ket value achieved at MCOF-AuNPs/GCE indicates that the electron transfer rate reaction was faster at this electrode than others. The MCOF-AuNPs modified electrode was then utilized for the reduction of RF in 0.2 M phosphate-buffered saline (PBS) (pH 7.0). The MCOF-AuNPs/GCE showed 3.0 and 1.7-fold higher reduction current with 40 and 60 mV less positive potential shift against RF than bare GCE and MCOF/GCE. Under the optimized sensing parameters, the linear range concentration was achieved from 5 nM to 0.2 mM with the LOD of 2.0 nM. Finally, the present sensor was applied for the quantitative determination of RF in human biological fluids samples (human blood, urine, and saliva). Besides, the practical application was also demonstrated by determining RF in vitamin B-complex tablets and satisfactory results were obtained.

Coherent optical interaction between plasmonic nanoparticles and small organic dye molecules in microcavities

We investigate the lasing performance of different composite gain materials consisting of small organic molecules, gold nanoparticles, and a polymer matrix mixed on a nanoscale within a spin-coated thin film. We experimentally demonstrate that the localized surface plasmon resonances of randomly distributed gold nanoparticles can oscillate in phase with the standing wave of the surrounding microcavity resonator and contribute to a lower lasing threshold.

LSPR-mediated improved upconversion emission on randomly distributed gold nanoparticles array

The Au thin film was fabricated on silica glass substrate (a) and UCNPs were fabricated over (a) to get the plasmonic resonance (image b) with the coupling of metal. The UC emission enhancement after confinement of metal and NPs were simulated (c).

Plasmonic modulated upconversion fluorescence by adjustable distributed gold nanoparticles

In this research, we designed the core/shell/shell model of NaYF4@SiO2@Au with adjustable gold nanoparticles (different sizes and distributions) on the surface to enhance the up-conversion luminescence (UCL) intensity. The discrete dipole approximation (DDA) simulation results indicate that the position of the model extinction peak can be changed through changing the number of gold nanoparticles. In theory, if the extinction peak is red-shifted without overlapping with the model emission peak, the luminescence will be effectively enhanced. Then, we synthesized composite with different amounts of gold nanoparticles coated on the surface using layer-by-layer (LBL) electrostatic adsorption methods, and the UCL enhancement effect of difference gold nanoparticles is exactly consistent with the results of DDA simulation. When the extinction peak is best crossed with the excitation (near infrared) region and the extinction peak is not crossed with the emission (visible) region, the enhancement achieves the highest. Therefore, the lanthanide-gold composite with effectively improved UCL intensity could be designed and guided by DDA simulation.

Gold nanoparticles incorporated into cryogel walls for efficient nitrophenol conversion

The past several decades have illustrated an enormous interest in noble metal nanoparticles for their superior catalytic activity, however, their industrial use is very restricted due to inefficient recovery leading to potential contamination of products and the environment. Immobilised nanoparticles illustrate promising results for scaling up processes, and can be successfully applied for various catalytic processes including waste industrial water treatment. The aim of the study was to design and study an easy and economically efficient green chemistry approach of preparation of macroporous material, with well distributed gold nanoparticles within the wall of cryogel. Ionic cryogels containing chitosan and tetrachloroaurate complex was reduced by 1.1.3.3-tetramethoxypropane, concurrently allowing chemical cross-linking of the polymer. A mechanism of reduction of noble gold complexes within the cryogel walls by tetramethoxypropane is also studied. Properties of the composite cryogels were evaluated using; differential scanning calorimetry, FT-IR, NMR, compression tests, SEM, TEM), Energy-dispersive X-ray spectroscopy and low temperature nitrogen adsorption. The catalytic activity of the in-situ synthesised gold nanoparticles was comprehensively studied using a model reduction reaction of 4-nitrophenol. Four different concentrations of gold nanoparticles within the cryogel structure were investigated. The turnover number and the turnover frequency parameters for cryogels containing four different concentrations of gold nanoparticles were calculated. The conversion degree of 4-nitrophenol to 4-aminophenol for cryogel containing the lowest of gold nanoparticles reached 96.8% at room temperature. The catalytic activity of incorporated gold nanoparticles for 4-nitrophenol conversion did not decline over 14 consequent testing cycles.

Development of bacteria sensing platform through layered (metal-dielectric-metal) nanoparticles

Trilayer possessing metal-dielectric-metal layer of nanometric thickness was prepared through multiple processes such as direct current (DC) and radio frequency (RF) Sputter Coating. This trilayer was used for a biosensing platform. Metal layer of gold having a thickness of 30 nm was deposited through direct DC Sputter Coating while the dielectric layer of SiO2 having a thickness of 177 nm was deposited through RF Sputter Coating. The trilayer coated sample was subjected to thermal annealing at 470 °C for 2 h in a temperature controlled furnace. The top layer of continuous gold film gets converted into randomly distributed gold nanoparticles (AuNPs) while the bottom gold layer undergoes minor morphological change. The reflectance spectrum of the dewetted trilayer is changed by presence of the Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. The average reflectance of the as-deposited trilayer was found to be 60.06% while presence of E. coli and S. aureus on the trilayer reduces its reflectance to 21.84% and 47.58% respectively. The fabricated platform is more effective for the detection of S. aureus as it produced sharp detectable shift (70 nm to left) in spectra due to the spherical shape of bacterium. The shift in reflectance spectra depends on the incubation period which gives information about the amount of bacteria present on the platform.

Comparing In Situ DIC Results from an Etched Surface with a Gold Speckled Surface

A ferrite-pearlite two-phase steel was investigated using in situ scanning electron microscope (SEM) tensile testing combined with digital image correlation (DIC). Two different speckled patterns were used and compared. The first pattern was achieved by etching a polished surface in order to reveal the microstructural features. Second, a gold speckled pattern was obtained. Here, a continuous layer of gold was applied to a polished surface. This continuous layer was remodeled into gold nanoparticles by keeping the specimen at 180 °C for 96 h with an Ar/Styrene mixture flowing across the specimen surface. The result is randomly distributed gold nanoparticles on the surface. These particles and the etched microstructure were then used by the DIC software to correlate an image series to obtain the local strain field of the material. The differences between the two techniques are numerous. Considering the etched surface, most microstructural features were grain boundaries and pearlite lamellas. As a consequence, large areas within grains did not provide sufficient contrast for DIC, thus restricting maximum resolution. However, the technique is fast and does not expose the material to any elevated temperatures. In contrast, the gold remodeling method provides a finely dispersed gold speckle pattern on the surface, giving excellent contrast across the recorded area. DIC with gold particles achieved a spatial resolution of 0.096 µm, compared to 2.24 µm in the DIC for the etched specimen. As a result, DIC with gold speckles can resolve slip lines. Conversely, DIC with etched microstructure resolves local strains on grain level. However, it is less cumbersome and faster to perform the test on the etched specimen.

Seed-Mediated Electroless Deposition of Gold Nanoparticles for Highly Uniform and Efficient SERS Enhancement.

A seed-mediated electroless deposition (SMED) approach for fabrication of large-area and uniform gold nanoparticle films as efficient and reproducible as surface-enhanced Raman scattering (SERS) substrates was presented. This approach involved a seeding pretreatment procedure and a subsequent growth step. The former referred to activation of polylysine-coated glass slides in gold seed solution, and the latter required a careful control of the reactant concentration and reaction time. With the aid of gold seeds and appropriate reaction conditions, a large-area and uniform nanofilm with evenly distributed gold nanoparticles (Au NPs) was formed on the surface of the substrates after adding a mixed solution containing ascorbic acid and trisodium citrate. The morphology of the Au nanofilm was examined by scanning electron microscopy. The size evolution of Au NPs on the surface of the substrates was analyzed in detail. The nanofilm substrate was prepared by reaction conditions of the seeded activation process: 10 mL ascorbic acid and trisodium citrate mixture and 30 min of soaking time, which exhibited an excellent uniformity and reproducibility of SERS enhancement with relative standard deviation (RSD) values of less than 8% (particularly, a RSD value of 3% can be reached for the optimized measurement). Compared to the common electroless deposition, the seed-mediated electroless deposition possessed inherent advantages in controllability, reproducibility, and economic benefit.

Gold Doping in a Layered Co‐Ni Hydroxide System via Galvanic Replacement for Overall Electrochemical Water Splitting

AbstractThe development of active yet stable bifunctional materials to produce hydrogen and oxygen via electrochemical water splitting is an ongoing challenge. Here, a system based on electrodeposited Ni(OH)2 and Co(OH)2 containing highly distributed gold nanoparticles at less than 0.25 at% to facilitate the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions is developed. The key aspect is using galvanic replacement to deposit gold on a layer of electrodeposited Co(OH)2 prior to electrodepositing Ni(OH)2. The fabrication of a composite system based on Co(OH)2‐Au‐Ni(OH)2 is required for optimal activity for both the HER and OER. The composite is characterized with helium ion microscopy, transmission electron microscopy, depth profiling X‐ray photoelectron microscopy, and a variety of electrochemical techniques. This material exceeds the activity of Pt for the HER at current densities greater than 40 mA cm−2 and is stable for both reactions for prolonged periods of electrolysis. In a two‐electrode configuration, current densities greater than 175 mA cm−2 for overall water splitting could be readily achieved at an applied voltage of 1.90 V in a commercially relevant electrolyte of 6 m NaOH.

Dynamic optical properties of gold nanoparticles/cholesteric liquid crystal arrays

Abstract

Insight on agglomerates of gold nanoparticles in glass based on surface plasmon resonance spectrum: study by multi-spheres T-matrix method

The formation of a localized surface plasmon resonance (SPR) spectrum of randomly distributed gold nanoparticles in the surface layer of silicate float glass, generated and implanted by UV ArF-excimer laser irradiation of a thin gold layer sputter-coated on the glass surface, was studied by the T-matrix method, which enables particle agglomeration to be taken into account. The experimental technique used is promising for the production of submicron patterns of plasmonic nanoparticles (given by laser masks or gratings) without damage to the glass surface. Analysis of the applicability of the multi-spheres T-matrix (MSTM) method to the studied material was performed through calculations of SPR characteristics for differently arranged and structured gold nanoparticles (gold nanoparticles in solution, particles pairs, and core–shell silver–gold nanoparticles) for which either experimental data or results of the modeling by other methods are available. For the studied gold nanoparticles in glass, it was revealed that the theoretical description of their SPR spectrum requires consideration of the plasmon coupling between particles, which can be done effectively by MSTM calculations. The obtained statistical distributions over particle sizes and over interparticle distances demonstrated the saturation behavior with respect to the number of particles under consideration, which enabled us to determine the effective aggregate of particles, sufficient to form the SPR spectrum. The suggested technique for the fitting of an experimental SPR spectrum of gold nanoparticles in glass by varying the geometrical parameters of the particles aggregate in the recurring calculations of spectrum by MSTM method enabled us to determine statistical characteristics of the aggregate: the average distance between particles, average size, and size distribution of the particles. The fitting strategy of the SPR spectrum presented here can be applied to nanoparticles of any nature and in various substances, and, in principle, can be extended for particles with non-spherical shapes, like ellipsoids, rod-like and other T-matrix-solvable shapes.

Conductive connection induced speed-up of localized-surface-plasmon dynamics

Conductive connection of localized surface plasmons (LSPs) was achieved by depositing a layer of continuous gold film onto the top surface of a matrix of randomly distributed gold nanoparticles (AuNPs) that were originally isolated on a glass substrate. Ultrafast spectroscopic response of such plasmonic nanostructures was investigated by femtosecond pump-probe detection technique. The transient-absorption data showed large redshift and broadening of the resonance spectrum of the conductively connected AuNPs with respect to the isolated ones. Such effects led to modulation on the evolution dynamics of LSPs in a transient transition spectral band. Making use of the temporal and spectral dislocation between the edges of transition band, we achieved much increased speed of the plasmonic optical switching effect.

Photo-thermal study of a layer of randomly distributed gold nanoparticles: from nano-localization to macro-scale effects

We present an experimental characterization and a comprehensive theoretical modeling of macroscopic plasmonic heat production that takes place in a single layer of small gold nanoparticles (GNPs), randomly distributed on a glass substrate, covered with different host media and acted on by a resonant radiation. We have performed a detailed experimental study of the temperature variations of three different systems, obtained by varying the density of nanoparticles. Due to the macroscopic dimension of the spot size, the used laser irradiates a huge number of nanoparticles, inducing a broad thermo-plasmonic effect that modifies the thermal conductivity of the entire system; starting from the state of art, we have implemented a simple model that enables to evaluate the resulting new thermal conductivity. We have also extended our theoretical approach to the macroscale, including an analysis of the effects predicted for different NP densities and laser spot size values, as well as for different values of the laser intensity, which can be as low as 0.05 W . Theoretically predicted temperature variations are in excellent agreement with experimental results.

Structuring of Surfaces with Gold Nanoparticles by Using Bessel‐Like Beams

AbstractHere, the structuring of surfaces with gold nanoparticles by using Bessel‐like beam array is demonstrated. The experimental results show that the fabricated microring structures containing gold nanoparticles have a surface plasmon resonance in the spectral range of 520–540 nm, which can be tuned by selecting the laser treatment parameters. Fabricated microring structures exhibit a lower light transmittance comparing with the randomly distributed gold nanoparticles for wavelengths 500–570 nm due to the growth in the size of nanoparticles. In the spectral range of 600–700 nm, the light transmittance through microring structures is higher compared with the randomly distributed gold nanoparticles because of the removal of gold nanoparticles as gold has high reflectivity for wavelengths longer than 600 nm. The demonstrated method enables an easy fabrication of microring structures having tunable plasmonic properties.

Study of the Influence of Incorporation of Gold Nanoparticles on the Modified Porous Silicon Sensor for Petroleum Gas Detection

In this work, the influence of alloying the porous surface with uniform distributed gold nanoparticles on the characteristic porous silicon gas sensors for petroleum gas detection has been fabricated and studied extensively. Well-controlled gold nanoparticles were prepared by employing the simple dipping process of the macro porous silicon surface in diluted concentrations of HAuCl4 salt aqueous solution. The sensing properties of the prepared porous silicon-based sensors, sensitivity response and recovery times at room temperature operating in CO gas were studied. The sensitivity of alloyed porous silicon increased from 38% to about 82% incorporation of gold nanoparticles. The lowest gas pressure detection process of CO molecules was improved from 1 mbar to 0.5 mbar. The surface alloying with rounded gold nanoparticles improved the integrated specific surface area of the alloyed porous silicon/gold nanoparticles structure, so efficient gas developed with the low-cost process.

Thermo-plasmonic effects on E7 nematic liquid crystal

ABSTRACTThe photo-induced heating from a layer of uniformly distributed gold nanoparticles has been characterized to investigate the impact of a direct interaction of the metallic nanostructures with a drop of E7 nematic liquid crystal. A double effect is obtained: an increase of the photo-induced heating due to a change in the refractive index of the medium surrounding the nanoparticles (from air to E7) and a new way of exploiting this heating to induce a phase transition of the E7 NLC (from anisotropic to isotropic phase), with a significant decrease of the necessary energy density in the case of an impinging green radiation.

Biocompatible, Multiresponsive Nanogel Composites for Codelivery of Antiangiogenic and Chemotherapeutic Agents

Single therapy approaches are usually insufficient to treat certain diseases, due to genetic differences between patients or disease resistance. Therefore, such approaches are gradually replaced by combination therapies comprising two or more drugs. In oncology, these include BRAF inhibitors and cytotoxic, antiangiogenic, or immunomodulatory agents, among others. We propose herein the use of multiresponsive nanogel composites for the codelivery of a DNA intercalator (doxorubicin) and an antiangiogenic and immunomodulatory agent (pomalidomide). We introduce a surfactant-free synthetic protocol to decorate biocompatible poly(ethylene glycol)methacrylate nanogels (PEGMA) with evenly distributed gold nanoparticles and explore their ability to deliver drugs upon stimulation by various triggers such as heat, light, and reducing agents present in the intracellular environment. We further demonstrate that an additional polymer coating on the nanogel surface can decrease uncontrolled drug leakage and modulate cell...