Coupling Of Gold Nanoparticles Research Articles

Unveiling the Synergy of Coupled Gold Nanoparticles and J-Aggregates in Plexcitonic Systems for Enhanced Photochemical Applications.

Plexcitonic systems based on metal nanostructures and molecular J-aggregates offer an excellent opportunity to explore the intriguing interplay between plasmonic excitations and excitons, offering unique insights into light-matter interactions at the nanoscale. Their potential applications in photocatalysis have prompted a growing interest in both their synthesis and the analysis of their properties. However, in order to construct a high-performing system, it is essential to ensure chemical and spectral compatibility between both components. We present the results of a study into a hybrid system, achieved through the coupling of gold nanobipyramids with organic molecules, and demonstrate the strengthened photochemical properties of such a system in comparison with purely J-aggregates. Our analysis includes the absorbance and photoluminescence characterization of the system, revealing the remarkable plexcitonic interaction and pronounced coupling effect. The absorbance spectroscopy of the hybrid systems enabled the investigation of the coupling strength (g). Additionally, the photoluminescence response of the J-aggregates and coupled systems reveals the impact of the coupling regime. Utilizing fluorescence lifetime imaging microscopy, we established how the photoluminescence lifetime components of the J-aggregates are affected within the plexcitonic system. Finally, to assess the photodegradation of J-aggregates and plexcitonic systems, we conducted a comparative analysis. Our findings reveal that plasmon-enhanced interactions lead to improved photostability in hybrid systems.

MMP simulation of coupled gold nanoparticles as nanoantennae: Efficient tuning of localized surface plasmon resonances

We study localized surface plasmon excitations on a set of two coupled two-dimensional (2D) gold nanoparticles as a nanoantenna by using the multiple multipoles (MMP) method. We investigate the plasmon spectrum as a function of the nanoparticle's size, the background index of refraction, and the separating gap between the nanoparticles in order to provide proper means to tune the underlying plasmon resonance efficiently. Accurate multiple multipoles (MMP) computations are conducted with precise control over error measures, particularly for configurations of coupled particles with varying inter-particle distances and illumination conditions. Our findings demonstrate that by selecting these parameters carefully, nanoantennae can amplify emitter radiation across a wide range of spectra from ultraviolet to near-infrared. Numerical calculations have revealed that the MMP method is accurate, easy to handle, and efficient even on a low-cost, state-of-the-art PC.

Synthesis of Graphene Quantum Dots Coupled to Au Nanoparticles: A Facile and Versatile Route Using Different Carbon Sources

A top-down synthesis of graphene quantum dots (GQD) was carried out by hydrothermal method from different carbon sources (graphene, multi-walled carbon nanotubes, and black carbon) and H2O2 as an oxidizing agent, with an N source added in the reaction to modify the chemical surface of the GQD, giving rise to the nanomaterial N-GQD. The modified chemical surface of N-GQD partially allowed the nucleation and coupling of gold nanoparticles from a HAuCl4 solution. The X-ray diffraction spectrogram confirms the amorphization of the precursor materials, while the functionalized surface of N-GQD was characterized through UV-Vis, Fourier transform infrared, and photoluminescense spectrometry; TEM and FE-SEM show particle sizes between 8 and 15 nm. N-GQD@AuNP presence can be confirmed by UV-Vis spectroscopy and TEM analysis, showing partial coupling and nanoparticle nucleation of Au in the structure with particle sizes between 20 and 40 nm.

Coupled Gold Nanoparticles with Aptamers Colorimetry for Detection of Amoxicillin in Human Breast Milk Based on Image Preprocessing and BP-ANN.

Antibiotic residues in breast milk can have an impact on the intestinal flora and health of babies. Amoxicillin, as one of the most used antibiotics, affects the abundance of some intestinal bacteria. In this study, we developed a convenient and rapid process that used a combination of colorimetric methods and artificial intelligence image preprocessing, and back propagation-artificial neural network (BP-ANN) analysis to detect amoxicillin in breast milk. The colorimetric method derived from the reaction of gold nanoparticles (AuNPs) was coupled to aptamers (ssDNA) with different concentrations of amoxicillin to produce different color results. The color image was captured by a portable image acquisition device, and image preprocessing was implemented in three steps: segmentation, filtering, and cropping. We decided on a range of detection from 0 µM to 3.9 µM based on the physiological concentration of amoxicillin in breast milk and the detection effect. The segmentation and filtering steps were conducted by Hough circle detection and Gaussian filtering, respectively. The segmented results were analyzed by linear regression and BP-ANN, and good linear correlations between the colorimetric image value and concentration of target amoxicillin were obtained. The R2 and MSE of the training set were 0.9551 and 0.0696, respectively, and those of the test set were 0.9276 and 0.1142, respectively. In prepared breast milk sample detection, the recoveries were 111.00%, 98.00%, and 100.20%, and RSDs were 6.42%, 4.27%, and 1.11%. The result suggests that the colorimetric process combined with artificial intelligence image preprocessing and BP-ANN provides an accurate, rapid, and convenient way to achieve the detection of amoxicillin in breast milk.

Ultrafast Dynamics of Multiple Plexcitons in Colloidal Nanomaterials: The Mediating Action of Plasmon Resonances and Dark States.

Plexcitons, that is, mixed plasmon-exciton states, are currently gaining broad interest to control the flux of energy at the nanoscale. Several promising properties of plexcitonic materials have already been revealed, but the debate about their ultrafast dynamic properties is still vibrant. Here, pump–probe spectroscopy is used to characterize the ultrafast dynamics of colloidal nanohybrids prepared by coupling gold nanoparticles and porphyrin dyes, where one or two sets of plexcitonic resonances can be selectively activated. We found that these dynamics are strongly affected by the presence of a reservoir of states including plasmon resonances and dark states. The time constants regulating the plexciton relaxations are significantly longer than the typical values found in the literature and can be modulated over more than 1 order of magnitude, opening possible interesting perspectives to modify rates of chemically relevant molecular processes.

Multiple plasmonic hot spots platform: Nanogap coupled gold nanoparticles

Au-polymer-Au nanogap (Au-P-Au)-coupled gold nanoparticle (Au NP) platforms are fabricated via a combination of nanoskiving and polymer-assisted assembly. The structure consists of multiple types of nanogaps, specified as nanogaps within Au-P-Au, narrow nanogaps between assembled Au NPs, and nanogaps between Au NPs and the edge of the nanogap. The electric field is strongly enhanced in the nanogaps due to the confinement of incident light, generating multiple “hot spots”. The Au-P-Au-coupled Au NP platform promotes a significant surface-enhanced Raman scattering (SERS) performance, achieving a maximum enhancement factor of 1.36 × 108 and a sensitive detection of glucose. The united nanofabrication technology for Au-P-Au-coupled Au NP platforms with a considerable SERS enhancement would facilitate the applications of nonlinear optics, nano-photonics, and surface-enhanced spectroscopy.

Enhanced photoluminescence of a CsPbBr3/Al2O3 film heterojunction enabled by coupling of gold nanoparticles

We studied an enhanced photoluminescence (PL) effect of CsPbBr3/Al2O3 heterojunction by using gold nanoparticls (NPs). The CsPbBr3/Al2O3 heterojunction and CsPbBr3/Au/Al2O3 heterojunction were respectively prepared on porous Al2O3 film by using a colloidal self-assembly method. The defect fluorescence of CsPbBr3/Al2O3 heterojunction was enhanced up to 40 times due to the transfer of photo-generated carriers from the CsPbBr3 quantum dots (QDs) to the porous Al2O3 film. To suppress the defect fluorescence of heterojunction, the CsPbBr3/Au/Al2O3 heterojunction was prepared by loading the gold NPs between the CsPbBr3 QDs film and the porous Al2O3 film. The results showed that the gold NPs facilitated the transfer of the photo-generated carriers from the CsPbBr3 QDs to the surface of porous Al2O3 film. Compared with the porous Al2O3 film and CsPbBr3/Al2O3 heterojunction, the peak fluorescence of CsPbBr3/Au/Al2O3 heterojunction was enhanced to 6.4 times and 2.8 times, respectively. This method of enhanced fluorescence of QD heterojunction provides a new pathway in the applications of photovoltaic, photodetector, LED, image sensor, photocatalysis.

Sensitivity enhanced D-type large-core fiber SPR sensor based on Gold nanoparticle/Au film co-modification

A D-type large core optical fiber sensor with high sensitivity and good stability based on the coupling of gold nanoparticles and Au film was proposed and demonstrated by simulation and experiments. The proposed sensor is numerically simulated based on the finite element method. The simulation shows that the electric field intensity of the gap coupling between gold nanoparticles and Au film is 4–5 times higher than that of Au film, and the electric field intensity on the surface of gold nanoparticles is twice as strong as that on the surface of Au films. The electric field coupling effect between the Au film surface plasmon resonance (SPR) and the gold nanoparticle localized surface plasmon resonance (LSPR) can improve the refractive index sensitivity of the sensor. Experimental results show that the refractive index sensitivity of D-type optical fiber/Au film/gold nanoparticles sensor reaches 3074 nm/refraction index unit (RIU), which is 1.4 times that of D-type optical fiber/Au film sensor. SPR–LSPR coupling effect is a good method to improve the sensing performance of optical fiber sensors, especially for detecting the refractive index changes of surrounding media. Compared with existing similar biosensors, the designed biosensor has higher sensitivity and the sensor proposed in this paper has great application prospects in the field of biological detection.

Gold Nanoparticles Functionalized with Fully Conjugated Fullerene C60 Derivatives as a Material with Exceptional Capability of Absorbing Electrons

We report a highly electron-absorbing material (“electron-sponge”) obtained by coupling gold nanoparticles (AuNPs, 8 nm in diameter) with fullerene C60 spheres by fully conjugated linker molecules. This goal has been achieved through synthesis of a new class of conducting thionoester-substituted and thioketone-substituted azahomo-[60]fullerenes. The obtained C60 derivatives have been found to possess the capability of binding covalently to the surface of gold. Thus, for the first time, we show that thioketone and thionoester moieties can be successfully employed as new anchoring groups for conjugated fullerene derivatives. High-resolution X-ray photoelectron spectroscopy studies have revealed that the ligands are attached to the gold surface of AuNPs through strong Au–S bonding. One of the synthesized C60 derivatives, O-butyl 4-(azahomo(C60-Ih)fullerene)benzothioate (C60-BCT-OBu), has been investigated in detail. The C60-BCT-OBu-coated AuNPs form a highly insoluble precipitate, which can be easily dissolv...

Coupling gold nanoparticles to Dye-Sensitized Solar Cells for an increased efficiency

New approaches for coupling Au NPs to the photoanode of dye sensitized solar cells (DSSCs) were proposed herein, aiming to improve the typical energy conversion efficiency of these cells. For this purpose, colloidal Au NPs with different particles sizes, ∼5 nm and ∼22 nm, were chemically synthesized and attached (i) directly to titanium dioxide (TiO2) or (ii) to TiO2 surface modified with siliceous shells enriched in dithiocarbamate moieties (SiO2/SiDTC). Photoanodes composed by films of TiO2 anatase, TiO2@Au NPs (∼5 nm and ∼22 nm), or TiO2 functionalized with SiO2/SiDTC, loaded with colloidal Au NPs, were made. DSSCs were set-up in a typical sandwich configuration, using the photoanode, a Pt counter electrode, and an iodide electrolyte solution (I−/I3−).In general, a relevant contribution in the plasmonic DSSC performance was evidenced by using Au NPs of ∼22 nm loaded in different amounts 23.9 wt%, 31.0 wt% and 44.0 wt%. Photoanodes composed by 23.9% of Au yielded an increment of 14.40% in photocurrent and of 11.21% in the overall power conversion efficiency (PCE), when compared to the conventional one. In turn, the new strategy used in the chemical modification of the conventional photoanodes with dithiocarbamate groups showed also a significant improvement of the DSSC parameters.

Detection of Mycobacterium tuberculosis purified ESAT-6 (Rv3875) by magnetic bead-coupled gold nanoparticle-based immuno-PCR assay.

PurposeImmuno-PCR (I-PCR), an ultrasensitive method, combines the versatility of ELISA with the exponential amplification capacity of PCR. Coupling of detection antibodies with the reporter DNA is a critical step of I-PCR. Gold nanoparticles (GNPs) and magnetic beads (MBs) are relatively easy to attach with the antibodies and DNA. Therefore, we designed MB-coupled GNP-based I-PCR (MB-GNP-I-PCR) assay for the detection of Mycobacterium tuberculosis antigen.MethodsGNPs were synthesized by chemical reduction and seed-mediated synthesis. Functionalized GNPs were prepared by coupling GNPs with the detection antibodies and reporter DNA and were characterized. Detection limit of M. tuberculosis-specific purified early secreted antigenic target-6 (ESAT-6) (Rv3875) was determined by MB-GNP-I-PCR.ResultsTransmission electron microscopy revealed spherical and slightly polydispersed GNPs of ~20 and ~60 nm size. Coupling of antibodies to GNPs was indicated by a shift in absorption maxima from 524 to 534 nm, which was confirmed by transmission electron microscopy. A color reaction with ELISA and the presence of 76 bp product by PCR further validated the coupling of detection antibodies and signal DNA to the functionalized GNPs. Also, attachment of capture antibodies with MBs was confirmed by magneto-ELISA. Detection limit of purified ESAT-6 by MB-GNP-I-PCR was determined to be 10 fg/mL, 105-fold lower than analogous ELISA. Notably, no sample matrix effect was observed in the saliva samples of healthy individuals spiked with the purified ESAT-6.ConclusionUnlike conventional I-PCR (solid format), MB-GNP-I-PCR (liquid format) is relatively simple with the reduced background signals, which can be further exploited for the clinical diagnosis of tuberculosis.

Application of Gold Nanoparticle to Plasmonic Biosensors.

Gold nanoparticles (GNPs) have been widely utilized to develop various biosensors for molecular diagnosis, as they can be easily functionalized and exhibit unique optical properties explained by plasmonic effects. These unique optical properties of GNPs allow the expression of an intense color under light that can be tuned by altering their size, shape, composition, and coupling with other plasmonic nanoparticles. Additionally, they can also enhance other optical signals, such as fluorescence and Raman scattering, making them suitable for biosensor development. In this review, we provide a detailed discussion of the currently developed biosensors based on the aforementioned unique optical features of GNPs. Mainly, we focus on four different plasmonic biosensing methods, including localized surface plasmon resonance (LSPR), surface-enhanced Raman spectroscopy (SERS), fluorescence enhancement, and quenching caused by plasmon and colorimetry changes based on the coupling of GNPs. We believe that the topics discussed here are useful and able to provide a guideline in the development of novel GNP-based biosensors in the future.

Imaging rotational dynamics of nanoparticles in liquid by 4D electron microscopy.

In real time and space, four-dimensional electron microscopy (4D EM) has enabled observation of transient structures and morphologies of inorganic and organic materials. We have extended 4D EM to include liquid cells without the time resolution being limited by the response of the detector. Our approach permits the imaging of the motion and morphological dynamics of a single, same particle on nanometer and ultrashort time scales. As a first application, we studied the rotational dynamics of gold nanoparticles in aqueous solution. A full transition from the conventional diffusive rotation to superdiffusive rotation and further to a ballistic rotation was observed with increasing asymmetry of the nanoparticle morphology. We explored the underlying physics both experimentally and theoretically according to the morphological asymmetry of the nanoparticles.

Highly Selective and Ultrasensitive Turn-on Luminescence Chemosensor for Mercury (II) Determination Based on the Rhodamine 6G Derivative FC1 and Au Nanoparticles.

A method for the detection and quantitation of Hg2+ in aqueous samples by fluorescence spectroscopy is presented. It consists of a turn-on sensor developed by coupling Gold nanoparticles (AuNPs) with the rhodamine 6G derivative FC1, in which the response is generated by a mercury-induced ring-opening reaction. The AuNPs were included in order to improve the sensitivity of the method towards the analyte, maintaining its high selectivity. The method was validated in terms of linearity, precision and accuracy, and applied to the quantitation of Hg2+ in Milli-Q and tap water with and without spiked analyte. The limit of detection and quantitation were 0.15 μg·L−1 and 0.43 μg·L−1, respectively, constituting a substantial improvement of sensitivity in comparison with the previously reported detection of Hg2+ with free FC1.

Nonlinear Absorption and Fluorescence in ZnO and ZnO–Au Nanostructures

This paper investigates whether coupling gold nanoparticles to nanostructured zinc oxide enhances fluorescence emission, to produce efficient nanoscale UV emitters that radiate through nonlinear optical absorption processes. The z‐scan technique is used to measure nonlinear absorption simultaneously with measurements of nonlinear‐absorption‐induced fluorescence in zinc oxide nanostructures and hybrid zinc oxide–gold nanostructures. This allows for better determination of the nonlinear excitation and energy dissipation pathways. The measurements show that the nonlinear absorption of the hybrid structures is enhanced by up to two orders of magnitude compared to the pure zinc oxide nanostructures. However, it is found that the increase in nonlinear absorption does not correspond to an equivalent increase in fluorescence due to the competition between two‐photon absorption and excited state absorption.

Colorimetric detection of glucose based on gold nanoparticles coupled with silver nanoparticles

We have coupled gold nanoparticles (AuNPs) with silver nanoparticles (AgNPs) to assemble a plasmonic sensing platform for colorimetric detection of glucose. In this system, small AuNPs (~4nm) can act as glucose oxidase (GOD) mimic enzyme to catalytically oxidize glucose in the presence of oxygen, producing hydrogen peroxide, which dissolves AgNPs to lead the color changes. Glucose can be detected not only by naked eyes (from yellow to red) but also by spectrophotometer in the concentration range of 5–70μM, with detection limit of 3μM. More importantly, we found that l-cysteine added in the system can markedly improve the selectivity for the detection of glucose. The proposed method was used to application for the detection of glucose in human serum with satisfactory results. This system is simple and low cost without using any enzymes and organic chromogenic agents.

The role of morphology and coupling of gold nanoparticles in optical breakdown during picosecond pulse exposures.

This paper presents a theoretical study of the interaction of a 6 ps laser pulse with uncoupled and plasmon-coupled gold nanoparticles. We show how the one-dimensional assembly of particles affects the optical breakdown threshold of its surroundings. For this purpose we used a fully coupled electromagnetic, thermodynamic and plasma dynamics model for a laser pulse interaction with gold nanospheres, nanorods and assemblies, which was solved using the finite element method. The thresholds of optical breakdown for off- and on-resonance irradiated gold nanosphere monomers were compared against nanosphere dimers, trimers, and gold nanorods with the same overall size and aspect ratio. The optical breakdown thresholds had a stronger dependence on the optical near-field enhancement than on the mass or absorption cross-section of the nanostructure. These findings can be used to advance the nanoparticle-based nanoscale manipulation of matter.

Plasmonic coupling-dependent SERS of gold nanoparticles anchored on methylated DNA and detection of global DNA methylation in SERS-based platforms

Global DNA methylation is in the spotlight as a treatment and diagnostic strategy for several severe diseases. However, conventional methods entail laborious work, high costs, and high concentrations at a nanomolar range. We developed a new method based on surface-enhanced Raman spectroscopy (SERS) to detect global DNA methylation. This was chosen due to the following two reasons: (i) genomic DNA has many neighbouring methylcytosine (mCpG) sites in CpG islands, and (ii) anti-mCpG immunogold colloids are coupled to amplify plasmon coupling and then enhance SERS intensity when they bind to the mCpG sites on the genome. We first used a DNA backbone with well-defined distances between different mCpG sites to study the link between plasmon coupling and a SERS signal as a basis for plasmonic coupling-dependent SERS. The plasmon shift and SERS enhancement were monitored by plasmon coupling with different mCpG spacing on a genomic DNA backbone. Global DNA methylation was then detected via SERS in a coupled gold nanoparticle–silver nanowire (AgNW) and a simple glass-based system on a multi-channel chamber. DNA samples were simply absorbed onto a cetyltrimethylammonium bromide (CTAB)-positive-charge AgNW surface and a microscopic glass, and immunogold colloids were then used to detect the methylation status by recognizing mCpG sites. The detection limits for global methylated DNA on the platform of glass and the silver nanowire were 195 fg ml−1 and 18 fg ml−1, respectively. Moreover, the approach of aligning gold nanoparticles on methylated DNA could be applied for biomolecular templates that can assemble themselves, and a proportional correlation between the concentration and SERS intensity could allow for a quantitative assay of DNA methylation from various samples.

Reversible Aptamer-Au Plasmon Rulers for Secreted Single Molecules.

Plasmon rulers, consisting of pairs of gold nanoparticles, allow single-molecule analysis without photobleaching or blinking; however, current plasmon rulers are irreversible, restricting detection to only single events. Here, we present a reversible plasmon ruler, comprised of coupled gold nanoparticles linked by a single aptamer, capable of binding individual secreted molecules with high specificity. We show that the binding of target secreted molecules to the reversible plasmon ruler is characterized by single-molecule sensitivity, high specificity, and reversibility. Such reversible plasmon rulers should enable dynamic and adaptive live-cell measurement of secreted single molecules in their local microenvironment.

Plasmomechanics: A Colour-Changing Device Based on the Plasmonic Coupling of Gold Nanoparticles

We have carried out an experiment on a flexible polymeric substrate, coated with a monolayer of gold nanoparticles, which demonstrates how the combined effect of nanoparticle growth and stretching influences the average normalized gap between particles, thus modifying the extinction spectra of the sample. The study paves the way for the realization of a plasmonic strain sensor based on the plasmonic coupling of gold nanoparticles deposited onto elastomeric films: application of a mechanical stretching induces a change of colour of the device and a fine control of the applied strain allows a continuous tuning of the colour.