Gold Nanoparticle Dimers Research Articles

Optomechanical motions of gold dimer’s spin, rotation and revolution manipulated by bessel beam

The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs’ spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer’s rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters.

Achiral Plasmonic Antennas Enhance Differential Absorption To Increase Preferential Detection of Chiral Single Molecules.

Plasmonic antennas increase the photon flux in their vicinity, which can lead to plasmon-enhanced fluorescence for molecules near these nanostructures. Here, we combine plasmon-coupled fluorescence and fluorescence-detected circular dichroism to build a specific and sensitive detection strategy for chiral single molecules. Electromagnetic simulations indicate that a two-dimensional gold nanoparticle dimer antenna enhances the electric field and optical chirality of a plane wave in its near field. Furthermore, this optical chirality enhancement can be tuned based on the polarization of the incident electric field, such that enhancing the optical chirality via these antennas will increase the differential absorption of parity-inverted fields. We measured the fluorescence from single molecules of chiral absorbers-Cy5 J-dimers assembled in double-stranded DNA backbones-and achieved increased detectability of these right-handed molecules near achiral gold nanoparticle dimer antennas under right circularly polarized illumination. This strategy offers a new approach to distinguishing weakly fluorescent enantiomers.

Refractometric sensing with plasmon resonances in dimer, trimer and quadrumer ensembles of gold nanoparticles

We studied by FDTD computer simulations the dependence of the surface plasmon resonances in linearly arranged gold nanospheres on incident light polarization, spheres number and diameter, and interparticle gap. The observed scattering spectra of large particles show a particularly interesting behaviour, with coupled plasmon resonances that can be either red or blue shifting with the modification of the interparticle gap. The sensitivity of the various observed coupled plasmon modes to refractive index variations is then evaluated.

DNA Origami-Based Letterpress Printing of Gold Nanostructures with Predesigned Morphologies.

Creating customizable metallic nanostructures in a simple and controllable manner has been a long-standing goal in nanoscience. In this study, we use DNA origami as a letterpress printing plate and gold nanoparticles as ink to produce predesigned gold nanostructures. The letterpress plate is reusable, enabling the repetitive production of predesigned gold nanostructures. Furthermore, by modifying the DNA origami letterpress plate on magnetic beads, we can simplify the printing processes. We have successfully printed gold nanoparticle dimers, trimers, straight and quadrilateral tetramers, and other nanostructures. Our approach improves the flexibility and stability of metallic nanostructures, simplifying both their design and their operation. It promises universal applicability in the fabrication of metamaterials, biosensors, and surface plasma nanooptics.

Polarization Z-Scan Studies Revealing Plasmon Coupling Enhancement Due to Dimer Formation of Gold Nanoparticles in Nematic Liquid Crystals.

We investigate the plasmon coupling of gold nanoparticle (AuNP) dimers dispersed in a nematic liquid crystal matrix using the polarization z-scan technique. Our experimental setup includes the precise control of incident light polarization through polarization angles of 0°, 45°, and 90°. Two distinct cell orientations are examined: parallel and twisted nematic cells. In parallel-oriented cells, where liquid crystal molecules and AuNPs align with the rubbing direction, we observe a remarkable 2-3-fold increase in the nonlinear absorption coefficient when the polarization of the incident light is parallel to the rubbing direction. Additionally, a linear decrease in the third-order nonlinear absorption coefficient is noted as the polarization angle varies from 0° to 90°. In the case of twisted nematic cells, the NPs do not have any preferred orientation, and the enhancement remains consistent across all polarization angles. These findings conclusively establish that the observed enhancement in the nonlinear absorption coefficient is a direct consequence of plasmon coupling, shedding light on the intricate interplay between plasmonic nanostructures and liquid crystal matrices.

Charge-Transfer Plasmon Resonance in a Dimer of Gold Nanoparticles Connected with a Carbon Nanotube

Charge-Transfer Plasmon Resonance in a Dimer of Gold Nanoparticles Connected with a Carbon Nanotube

Charge transfer effect: a new assignment of the abnormal optical absorption band of gold nanoparticles

As a significant accompanying phenomenon of surface-enhanced Raman scattering (SERS), the addition of foreign molecules to colloidal gold or silver nanoparticles results in a new abnormal optical absorption (AOA) band, which usually appears in the long-wavelength region. The assignment of this AOA band has long been debated as an important issue that is desired to be addressed in the SERS field, which is crucial for a clear understanding of the SERS enhancement mechanism and beneficial to surface plasmonics. In this study, both the calculated and measured optical absorptions of gold nanoparticle monomers and dimers as well as their interactions with adsorbed molecules, showed that the AOA band in the long-wavelength region which was assigned to the characteristic longitudinal localized surface plasmon resonance (LSPR) effect of gold nanoparticle chain aggregates in conventional SERS electromagnetic theory, should be attributed to the charge-transfer resonance absorption from gold nanoparticles to adsorbed molecules. This was further confirmed by the corresponding SERS effects. As the excitation wavelength at 785 nm was resonant with the broad AOA band centered at 750 nm, the SERS peaks of the adsorbed pyridine molecules could be dramatically enhanced due to the charge-transfer resonance effect. In contrast, under an excitation wavelength of 532 nm, the SERS peaks appeared very weak, although the excitation wavelength was resonant with the LSPR absorption band of the individual gold nanoparticles.

A novel alternative strategy for monitoring and insight into liver fibrosis progression: The combination of surface-enhanced Raman spectroscopy (SERS) and gut microbiota

Nowadays, the studies on the interaction and relationship between the intestinal microorganisms and liver diseases are increasing. However, it is still a huge challenge for the in-depth investigation and dynamic monitoring of such a complex network. Herein, a significant discovery was made. A strong association between gut microbial structural and functional genomics and SERS spectra of hepatocytes were revealed. Based on the study of gut microbes and SERS spectra, complementary information could be provided for the mechanism analysis of related diseases. Liver fibrosis, a chronic liver disease that lack specific cure was thus comprehensive studied. Liver targeting gold nanoparticle dimers were prepared as the SERS tags, and abundant SERS peak signals were acquired. Meanwhile, the gut microbiomes were also comparative studied. The changes of carbohydrates and lipids in liver cells were observed at the early stages of liver fibrosis, and TLR4 (toll-like receptors 4) was activated to elicit immune responses. Then again, oxidative stress, endotoxin and serum inflammatory factors were the major observations at the late stages. The SERS signals and the microbiome analysis were well confirmed and complemented each other, which suggested that the detection strategy could be another valuable method for the “gut-liver axis” study.

Charge transfer plasmon resonances of conductively linked asymmetric gold nanoparticle dimers

Charge transfer plasmon resonances of conductively linked asymmetric gold nanoparticle dimers

Early warning of Diaporthe infection in kiwifruit soft rot by plasmonic dimer-enhanced Raman spectroscopy.

Diaporthe genus is the dominant pathogens of kiwifruit soft rot with long incubation period and rapid onset and very hard to detect in advance. It is of great significance to develop point-of-care tests for disease prevention and field management. Here we screen a pair of genus-level primers for constructing plasmonic dimer Rayleigh/Raman spectroscopy, which enables rapid, specific, and sensitive detection of Diaporthe genus in real kiwifruits. Dark-filed Rayleigh scattering clearly visualizes the target-induced dimer assembly of nanoprobes. Plasmonic dimer-enhanced Raman spectroscopy has high specificity for 12 common isolates of Diaporthe genus in one batch samples with highly accurate results and much higher sensitivity than polymerase chain reaction (PCR). It realizes the recognition of Diaporthe infection at an early stage of 24h when the kiwifruits do not have any noticeable symptoms. It demonstrates a bright prospect of point-of-care tests for early warning of kiwifruit soft rot infection and quality control.

Carbon capture and biocatalytic oxygen production of photosystem II from thylakoids and microalgae on nanobiomaterials

Enhanced carbon capture and oxygen production via water splitting was observed by controlling the plasmon-induced resonance energy transfer (PIRET) for photosystem II (PSII) in thylakoid extracts and spirulina assembled on gold nanoparticle (AuNP) dimer arrays. The two types of vertical (V) and horizontal (H) AuNP dimer arrays were uniformly inserted inside pore diameter-controlled templates. Based on the theoretical calculations, the longitudinal mode of the H AuNP dimer array was found to be sensitive to the nanogap distances between the two AuNPs in resonance with the absorption at P680 of the PSII. The longitudinal modes that interacted with P680 of PSII increased from the V to the H conformer. The optical properties from the H AuNP dimer array caused overlapping absorbance and photoluminescence with PSII, and the H AuNP dimer arrays exhibited a significant increase in carbon capture and oxygen generation rates in comparison with those of the bare PSII protein complex under light irradiation via the controlled PIRET process.

Thermal Transport through Polymer-Linked Gold Nanoparticles.

Polymer-nanoparticle networks have potential applications in molecular electronics and nanophononics. In this work, we use all-atom molecular dynamics to reveal the fundamental mechanisms of thermal transport in polymer-linked gold nanoparticle (AuNP) dimers at the molecular level. Attachment of the polymers to AuNPs of varying sizes allows the determination of effects from the flexibility of the chains when their ends are not held fixed. We report heat conductance (G) values for six polymers-viz. polyethylene, poly(p-phenylene), polyacene, polyacetylene, polythiophene, and poly(3,4-ethylenedioxythiophene)-that represent a broad range of stiffness. We address the multimode effects of polymer type, AuNP size, polymer chain length, polymer conformation, system temperature, and number of linking polymers on G. The combination of the mechanisms for phonon boundary scattering and intrinsic phonon scattering has a strong effect on G. We find that the values of G are larger for conjugated polymers because of the stiffness in their backbones. They are also larger in the low-temperature region for all polymers owing to the quenching of segmental rotations at low temperature. Our simulations also suggest that the total G is additive as the number of linking polymers in the AuNP dimer increases from 1 to 2 to 3.

Dynamic surface-enhanced Raman spectroscopy of DNA oligomer with a single hotspot from a gold nanoparticle dimer.

Various nanostructures for single-molecule surface-enhanced Raman spectroscopy (SERS) have been fabricated through a random aggregation process using nanoparticles that can stochastically generate multiple hotspots in the laser spot. This leads to multiple molecule detection. In this study, a single gold nanoparticle (AuNP) dimer with a single hotspot was fabricated in a laser spot controlling the position and orientation on a silicon substrate using a nanotrench-guided self-assembly. The Raman peaks of deoxyribonucleic acid (DNA) were dynamically observed, indicating a single DNA oligomer detection composed of adenine, guanine, cytosine, phosphate, and deoxyribose.

Controllable synthesis of gold nanoparticle dimers via site-selective growth.

Random aggregation of nanoparticles follows step-growth kinetics, and thus the synthesis of large nanoparticle dimers is still a challenge. Here, we report a site-selective growth route to producing gold nanoparticle dimers in a high yield of up to 71%. The polymer contraction exposed two tips of gold nanorods, which provided active sites for further growth, setting the ability for a high yield of large dimers. Methods to fine tune the reaction rate allowed us to control the spacing between nanoparticles, giving a good SERS performance. Our method was shown to make up for the shortcomings of the existing synthetic method, and to achieve the synthesis of large dimers in solution.

Few-Molecule Strong Coupling with Dimers of Plasmonic Nanoparticles Assembled on DNA.

Hybrid nanostructures, in which a known number of quantum emitters are strongly coupled to a plasmonic resonator, should feature optical properties at room temperature such as few-photon nonlinearities or coherent superradiant emission. We demonstrate here that this coupling regime can only be reached with dimers of gold nanoparticles in stringent experimental conditions, when the interparticle spacing falls below 2 nm. Using a short transverse DNA double-strand, we introduce five dye molecules in the gap between two 40 nm gold particles and actively decrease its length down to sub-2 nm values by screening electrostatic repulsion between the particles at high ionic strengths. Single-nanostructure scattering spectroscopy then evidence the observation of a strong-coupling regime in excellent agreement with electrodynamic simulations. Furthermore, we highlight the influence of the planar facets of polycrystalline gold nanoparticles on the probability of observing strongly coupled hybrid nanostructures.

Fabrication and measurement of fiber optic localized surface plasmon resonance sensor based on gold nanoparticle dimer

Fiber optic localized surface plasmon resonance (FO LSPR) sensors capable of portable, real-time, and remote sensing are emerging with the progress of lab-on-fiber technology. However, the small area of the substrate by the optical fiber often restricts the sensitivity of the FO LSPR sensors. To improve the performance of the FO LSPR sensors, it is necessary to enhance the interactions between incident light and plasmonic nanostructures within a defined region. Dimer in which two nanoparticles are arranged with nanometer spacing can effectively increase the light-nanostructure interactions. It is well known that the nanogap made in the assembled nanoparticles significantly enhances the intensity of the electromagnetic field in the confined area by the hot spot effect. We fabricate the dimers of gold nanoparticles on the optical fiber with benzenethiol using a method that reduces the repulsive force between the nanoparticles. In the dimers, the strong plasmonic interaction between the two nanoparticles produces a longitudinal plasmon coupling band, which is compared to the transverse plasmon band by the monomer-based FO LSPR sensor with a similar density of gold nanoparticles. In the proposed sensor, the longitudinal band displays approximately 9.1 times improved sensitivity. When two types of sensors are applied to the biosensor application, the dimer-based FO LSPR sensor also proves an improved limit of detection of about 2.6 times. This method is expected to become a milestone in the field of measurement for small molecules and low concentration through the advancement of the yield and density of dimers.

A general scattering proximity immunoassay with the formation of dimer of gold nanoparticle

In this work, we structured a colorimetric ultrasensitive detection of carcinoembryonic antigen (CEA) based on a proximity hybridization-induced gold nanoparticles (Au NPs) dimers structure. Under the dark-field microscope, this method takes advantage of the distinctive and strong distance-relative localized surface plasmon resonance (LSPR) of Au NPs and their oriented assembly. DNA served as a medium showing wonderful flexibility to label antibody and Au NPs, and tune interparticle spacing as well. Two capture probes were formed by the integration of DNA labeled antibody (DNA1-Ab1 or DNA2-Ab2) and asymmetrically assembled DNA (DNA 3 or DNA 4)- Au NPs via partly hybridization between DNA sequences. In the presence of antigen, the reaction between target protein and capture probes could trigger the generation of immunocomplex which led to the proximity hybridization of the DNA1 and DNA2, and then change the distance of interparticle to form Au NP dimers and thus showed a different color under dark-field microscope. A limit of detection of 14.25 pg/mL was obtained for the detection of CEA, which indicated a promising sensing method in clinical diagnosis of protein biomarkers.

Raman Enhancement of Nanoparticle Dimers Self-Assembled Using DNA Origami Nanotriangles.

Surface-enhanced Raman scattering is a powerful approach to detect molecules at very low concentrations, even up to the single-molecule level. One important aspect of the materials used in such a technique is how much the signal is intensified, quantified by the enhancement factor (EF). Herein we obtained the EFs for gold nanoparticle dimers of 60 and 80 nm diameter, respectively, self-assembled using DNA origami nanotriangles. Cy5 and TAMRA were used as surface-enhanced Raman scattering (SERS) probes, which enable the observation of individual nanoparticles and dimers. EF distributions are determined at four distinct wavelengths based on the measurements of around 1000 individual dimer structures. The obtained results show that the EFs for the dimeric assemblies follow a log-normal distribution and are in the range of 106 at 633 nm and that the contribution of the molecular resonance effect to the EF is around 2, also showing that the plasmonic resonance is the main source of the observed signal. To support our studies, FDTD simulations of the nanoparticle’s electromagnetic field enhancement has been carried out, as well as calculations of the resonance Raman spectra of the dyes using DFT. We observe a very close agreement between the experimental EF distribution and the simulated values.

JaSTA-3: Light scattering simulations for heterogeneous aggregate

JaSTA-3: Light scattering simulations for heterogeneous aggregate

Plasmon-Induced Grafting in the Gap of Gold Nanoparticle Dimers for Plasmonic Molecular Junctions

Gold nanoparticle (NP) dimers of various shapes have been fabricated on indium tin oxide (ITO) by electron-beam lithography. The gap separating two NPs was set to 30–50 nm. Oligo(bisthienylbenzene)...