Strong Plasmonic Coupling Research Articles

Tunable enhanced chiroptical response of a twisted L-shaped plasmon nanoparticle system

Chiroptical responses in plasmon systems have aroused widespread interest, manifesting potential application in fields including physics, biology, and pharmacy, as well as other disciplines. However, the enhancement and tunability of chiroptical responses by strong plasmon coupling, which have been seldom discussed, remain wanting. In this paper, we propose a stacked and twisted L-shaped nanoparticle system, which exhibits an enhanced chiroptical response and the dynamic modulation of chiroptical response. By adjusting the twist angle and the gap between L-shaped nanoparticles, the anisotropy factor g, which quantifies the relative strength of the chiroptical response, can reach up to −1.5, and the peak position and linewidth of the g spectrum can be modified. Furthermore, in instances where the chiroptical response is weak, we construct a finite-size 1D chain by using the proposed system as the unit cell. By harnessing the global interaction among the unit cell of the 1D chain, the maximum value of g can be effectively improved and adjusted. Such an L-shaped nanoparticle system as a fundamental structure has potential applications in tunable chiroptical devices and also extends methods for device design.

Enhanced optical nonlinearity in suspensions of dual-resonance gold–copper chalcogenide core–shell nanoparticles

Plasmonic copper chalcogenide (Cu2−xE, E = S, Se, Te) nanoparticles (NPs) possess high potentials in photothermal therapy and photoacoustic tomography for their unique localized surface plasmon resonant absorption in the second near-infrared biologically transparent window. In this study, strong thermal-induced nonlinear negative-lens effect in aqueous suspensions containing Cu2−xSe NPs was observed. Furthermore, the nonlinear absorption was notably enhanced in aqueous suspensions containing Au@Cu2−xSe core–shell NPs, as the positive nonlinear absorption coefficient increased by 20-fold, attributed to the strong plasmonic coupling in Au@Cu2−xSe core–shell NPs. This finding underscores the importance of the nonlinear optical behaviors of plasmonic NPs in biomedical applications, as they offer extra strategy for optimizing systems and incorporating additional functionalities.

Construction of aptamers-modified plasmonic GO/urchin-like Au nanoparticles with enhanced photothermal performance and their efficient capture and elimination of Staphylococcus aureus

Here, aptamers-modified graphene oxide/urchin-like Au nanoparticles (Apt-GUANPs) were developed for efficient capture and photothermal therapy (PTT) of Staphylococcus aureus (S. aureus). Specifically, anisotropic UANPs were first prepared, and the excellent photothermal property was related to the localized surface plasmon resonance (LSPR) in the near infrared (NIR) region caused by sharp branching. Then GO, which was used to enhance the photothermal effect, was added and assembled into GUANPs by electrostatic action. Infrared images showed that GUANPs exhibited a stronger photothermal effect than UANPs. Under the irradiation of 808 nm laser, the photothermal conversion efficiency (η) of GUANPs was as high as 40.5 %, which was attributed to the enhanced optical response of GUANPs at 808 nm and the strong plasmonic coupling effect between tightly packed UANPs loaded on GO surfaces. Aptamers were modified on the surfaces of GUANPs for specific capture of S. aureus, with the capture efficiency of up to 72 %. Utilizing the specific capture ability of aptamers and the excellent photothermal property of GUANPs, Apt-GUANPs exhibited the strong photothermal killing ability against S. aureus. Therefore, Apt-GUANPs will be a promising and efficient photothermal agent, and will have a great application prospect in the treatment of bacterial infections in the future.

Plasmonic coupling dependent sensitivity in localized surface plasmon resonance based optical sensors

This paper investigates the impact of environmental changes on silver nanoparticles (AgNp) immobilized sensor probe within strong and weak plasmonic coupling regimes. To monitor these interaction regimes, evanescent wave absorption based on fiber optic and attenuated total reflection techniques have been employed. In the weak coupling regime, variations in refractive index (RI) primarily affect intensity rather than wavelength. Conversely, in the strong coupling regime, intensity decreases, while wavelength sensitivity increases with changes in RI. Our findings qualitatively agree with a theoretical framework based on the discrete dipole approximation (DDA) for two-particle interacting systems, providing valuable insights for optimizing plasmonic interactions to enhance sensitivity. This information will aid the scientific and industrial community in understanding the plasmonic interaction region for maximizing sensitivity of Localized surface plasmon resonance (LSPR) based photonic devices.

An efficient and miniaturized ultra-thin tunable UWB graphene metasurface absorber for terahertz gap regime

This work introduces an ultra-thin tunable ultra-wideband (UWB) metasurface absorber (MSA) for the terahertz (THz) gap. The polarization-insensitive MSA provides an absorptivity (A(f)) ≥ 90% from 0.1 to 11.5 THz, corresponding to 196.6% fractional bandwidth. The usage of resonant slots engraved on top patterned graphene sheet (Gpat) and strong plasmonic coupling in the Fabry-Perot cavity formed between top Gpat and bottom continuous graphene (Gcont) in bilayer stack configuration ensures absorptivity over a UWB THz spectrum. An equivalent circuit model (ECM) closely follows the A(f) response of the proposed MSA. The proposed DC-biasing mechanism can regulate the chemical potential (μc) of the connected Gcont efficiently. A DC bias voltage of 0 to 6.1 V is adequate to vary μc of Gcont from 0 to 0.6 eV for achieving tunable A(f). The structure maintains its ultra-thin nature and has a thickness of only λ0/1500, where λ0 is the free space wavelength calculated at 0.1 THz. In addition, the periodicity is only λ0/300. The MSA also provides stable absorption response from 0.1 to 11.5 THz with A(f) ≥ 80% for incidence angle (θ) up to 60∘ under both transverse magnetic (TM) and transverse electric (TE) polarization.

Formation of Linear Plasmonic Heterotrimers Using Nanoparticle Docking to DNA Origami Cages.

The fabrication of complex assemblies with interesting collective properties from plasmonic nanoparticles (NPs) is often challenging. While DNA-directed self-assembly has emerged as one of the most promising approaches to forming such complex assemblies, the resulting structures tend to have large variability in gap sizes and shapes, as the DNA strands used to organize these particles are flexible, and the polydispersity of the NPs leads to variability in these critical structural features. Here, we use a new strategy termed docking to DNA origami cages (D-DOC) to organize spherical NPs into a linear heterotrimer with a precisely defined geometrical arrangement. Instead of binding NPs to the exterior of the DNA templates, D-DOC binds the NPs to either the interior or the opening of a 3D cage, which significantly reduces the variability of critical structural features by incorporating multiple diametrically arranged capture strands to tether NPs. Additionally, such a spatial arrangement of the capture strand can work synergistically with shape complementarity to achieve tighter confinement. To assemble NPs via D-DOC, we developed a multistep assembly process that first encapsulates an NP inside a cage and then binds two other NPs to the openings. Microscopic characterization shows low variability in the bond angles and gap sizes. Both UV-vis absorption and surface-enhanced Raman scattering (SERS) measurements showed strong plasmonic coupling that aligned with predictions by electrodynamic simulations, further confirming the precision of the assembly. These results suggest D-DOC could open new opportunities in biomolecular sensing, SERS and fluorescence spectroscopies, and energy harvesting through the self-assembly of NPs into more complex 3D assemblies.

Synthesis of Structure-Adjustable R-Au/Pt-CdS Nanohybrids with Strong Plasmon Coupling and Improved Photothermal Conversion Performance.

Noble metal nanomaterials with a localized surface plasmon resonance effect exhibit outstanding advantages in areas such as photothermal therapy and photocatalysis. As a unique plasmonic metal nanostructure, gold nanobipyramids have been attracting much interest due to their strong specific local electric field intensity, large optical cross sections, and high refractive index sensitivity. In this study, we propose a novel three-component hetero-nanostructure composed of rough gold nanobipyramids (R-Au NBPs), Pt, and CdS. Initially, purified gold nanobipyramids are regrown to form R-Au NBPs that have a certain degree of roughness. These R-Au NBP substrates with a rough surface provide more hotspots and strengthen the intensity of localized electric fields. Subsequently, Pt and CdS nanoparticles are selectively deposited onto the surface of R-Au NBPs. Pt nanoparticles can provide more active sites. Each component of this hetero-nanostructure directly contacts others, creating multiple electron transfer channels. This novel design allows for tunable localized plasmon resonance wavelengths ranging from the visible to near-infrared regions. These factors contribute to the final superior photothermal conversion performance of the R-Au/Pt-CdS nanohybrids. Under the irradiation of near-infrared light (1064 nm), the photothermal conversion efficiency of R-Au/Pt-CdS reached 38.88%, which is 4.49, 1.5, and 1.22 times higher than that of Au NBPs, R-Au NBPs, and R-Au NBPs/Pt, respectively.

Effect of thin MoS2 film with different layer numbers on tip-enhanced photoluminescence spectroscopy

As a novel semiconductor material, Molybdenum disulfide (MoS2) has great application potential in sensors, catalysts and optoelectronic devices. In this study, we aim to investigate the unique optical properties of MoS2 by theoretically exploring the impact of thin MoS2 films with varying layer numbers on the tip-enhanced fluorescence of a single molecule confined within the nanocavity formed by an Au tip over a substrate. The influence of incidence angle, layer numbers, tip radius and tip-MoS2 film distance on the excitation field, quantum yield and fluorescence enhancement are quantitatively analyzed in detail. The results show that the presence of multilayer MoS2 film can significantly improve tip-enhanced fluorescence spectroscopy. In the strong gap-mode plasmon coupling effect, the maximum fluorescence enhancement reaches approximately five orders of magnitude when it consists of six layers under excitation wavelength of 660 nm. Furthermore, the spatial resolution of Raman and fluorescence increases with decreasing tip radius and gap distance, reaching a maximum of 2.6 nm and 3.8 nm, respectively. Our results provide a theoretical guidance for further understanding and application of the two-dimensional material in optical experiments.

Intensifying heat using AgCu core-shell-based black titania with highly efficient photothermal conversion performance for solar-driven seawater desalination

A novel photoreceiver composed of black titania (BT) matrix with biochar for efficient steam production was investigated to measure the desalination efficiency under the illumination of one sun (1 kW m−2). The density of localized hotspots on the surface of the photothermal system is enhanced by the incorporation of AgCu core-shell that promotes photothermal activity and improves the degradation of methyl orange (MO) dye. Assemblages of AgCu nanoparticles on the surface of BT generated a strong stochastic plasmonic coupling and therefore broad-band absorption for much better solar energy consumption. The nanocomposite exhibited an excellent vaporization flux of 1.4 kg m−2 h−1 with high efficiency reaching 95.7 % under the illumination of one sun. AgCu@BT/BC exhibited an excellent surface temperature of 41 °C after only 5 min compared to other prepared photothermal systems. Furthermore, the prepared composites revealed superb degradation of MO dye under UV–vis light with a percentage of 96 %. The band gap energy of white titania decreased from 3.2 eV to 1.86 eV in the case of AgCu@BT/BC nanocomposite. Moreover, the crystalline AgCu@BT/BC demonstrates outstanding photocatalytic performance because of boosted charge migration, reduced electron-hole pair recombination rate, and identifiable shift to the red region.

Embedding plasmonic nanoparticles in soft crystals: an approach exploiting CTAB-I structures.

Embedding nanoparticles with different functionalities into soft substrates is a convenient tool to realize technologically significant multifunctional materials. This study focuses on incorporating bimetallic plasmonic nanoparticles into soft crystals made of cetyltrimethylammonium bromide-iodide. We observed the emergence of a novel symmetry-lowered cetrimonium crystal polymorph that enables the realization of strong interparticle plasmonic coupling in these composite materials. The observed crystal polymorph exhibits a triclinic structure with significantly reduced unit cell volume compared to standard CTAB. Solid-state nuclear magnetic resonance studies revealed an enhanced cetrimonium chain rigidity and a commensurate decrease in the mobility of the methyl groups. This is attributed to iodide incorporation. To study the influence of these interactions on solution phase dynamical properties, we employed light scattering measurements using gold nanospheres as markers, where we observed aggregation of these particles. We then develop a two step synthetic scheme that successfully enables high levels (533 particles per μm2) of incorporation of bimetallic plasmonic particles into the emergent crystal polymorph.

Plasmon mediated SERS and photocatalysis enhancement in Au nanoparticle decorated 2D-TiSe2

The combination of 2D materials and noble metallic nanostructure is becoming an attractive research domain for label-free, highly sensitive surface-enhanced Raman spectroscopy (SERS) applications. This study demonstrated photocatalysis degradation and SERS enhancements of organic fluorophore (Rhodamine 6G) on two-dimensional (2D) TiSe2 using Raman spectroscopy. The Au nanoparticles (NPs) were decorated on TiSe2 thin films by thermal annealing at variable temperatures. The selective deposition of Au NPs on the hexagonal TiSe2 nanocrystals increases surface roughness, creating a larger surface area for molecule adsorption. It has been observed that the Au decoration at 250 °C on TiSe2 exhibits efficient detection capabilities for R6G with the Raman intensity enhancement factors of the order of ≈105 along with the significantly improved visible light-induced photodegradation efficiency. The optimized Au NP size creates large electromagnetic hot spots produced by strong plasmon coupling that assists in the charge transfer mechanism among TiSe2, Au NPs, and R6G for enhanced SERS and photocatalysis activities. It has been observed that the intensity of Raman scattering decreases as the Au NP size increases on the TiSe2 material. A possible charge transfer mechanism is proposed with an energy band diagram. The simultaneous measurement of SERS and photocatalytic dye degradation in Au decorated TiSe2 can be used as a sensitive technique for water pollution treatment and biodegradable organic contaminants for the environmental ecosystem.

Plasmonic Nanocrystal Assembly-Semiconductor Hybrids for Boosting Visible to Near-Infrared Photocatalysis.

Plasmonic metal-semiconductor hybrid photocatalysts have received much attention because of their wide light harvesting range and efficient charge carrier generation capability originating from plasmon energy transfer. Here, we introduce a plasmonic metal-semiconductor hybrid nanostructure consisting of a Au core-satellite assembly and crystalline TiO2. The formation of Au@TiO2-Au core-satellite assemblies using TiO2 as a spacer and the subsequent growth of outer TiO2 shells on the core-satellite assemblies, followed by calcination, successfully generated Au core-satellite assembly@TiO2 nanostructures. Exquisite control over the growth of the TiO2 interlayer enabled the regulation of the gap distance between the core and satellite Au nanocrystals within the same hybrid morphology. Due to the structural controllability of the present approach, the gap-distance-dependent plasmonic and photocatalytic properties of the hybrid nanostructures could be explored. The nanostructures possessing the most closely arranged Au nanocrystals showed high photocatalytic activity under visible to near-infrared light irradiation, which can be attributed to strong plasmon coupling between the core and satellite Au nanocrystals that can expedite the formation of intense plasmon energy and its transfer to TiO2.

Synthesis and Raman Performance Enhancement of Multilayer AuAg Heterostructures with Magnetic Resonance

Significant amplification of surface enhanced Raman scattering (SERS) signals can be achieved mainly by the electric field enhancement in metal core-shell nanostructures, and the enhanced magnetic field is rarely studied. In this study, we prepared multi-gap Au/AgAu core-shell hybrid nanostructures by using gold nanocup as the core. The overgrowth processes to grow one, two, and three layers of AgAu hybrid nanoshells can produce Au/AgAu1, Au/AgAu2, and Au/AgAu3 heteronanostructures. The strong plasmon coupling between the core and shell leads to significant electromagnetic field enhancement. Under the synergistic effect of electromagnetic plasmon resonance and plasmon coupling, Au/AgAu core-shell hybrid nanostructures exhibit excellent SERS signals. We also investigate the effect of the interstitial position of the rhodamine B (RhB) molecule on Raman enhancement in Au/AgAu3 heteronanostructures. This study can provide new ideas for the synthesis of multi-gap Raman signal amplifiers based on magnetic plasmon coupling.

Branched Aluminum Nanocrystals with Internal Hot Spots: Synthesis and Single-Particle Surface-Enhanced Raman Scattering.

Owing to their unique and sustainable surface plasmonic properties, Al nanocrystals have attracted increasing attention for plasmonic-enhanced applications, including single-particle surface-enhanced Raman scattering (SERS). However, whether Al nanocrystals can achieve single-particle SERS is still unknown, mainly due to the synthetic difficulty of Al nanocrystals with internal gaps. Herein, we report a regrowth method for the synthesis of Al nanohexapods with tunable and uniform internal gaps for single-particle SERS with an enhancement factor of up to 1.79 × 108. The uniform branches of the Al nanohexapods can be systematically tuned regarding their dimensions, terminated facets, and internal gaps. The Al nanohexapods generate hot spots concentrated in the internal gaps due to the strong plasmonic coupling between the branches. A single-particle SERS measurement of Al nanohexapods shows strong Raman signals with maximum enhancement factors comparable to that of Au counterparts. The large enhancement factor indicates that Al nanohexapods are good candidates for single-particle SERS.

Analysis and Modeling of Novel Organic Material BOBzBT2 With Strong Coupling of Frenkel Excitons and Surface Plasmon

Analysis and Modeling of Novel Organic Material BOBzBT₂ With Strong Coupling of Frenkel Excitons and Surface Plasmon

Plasmonic-enhanced efficiency of AlGaN-based deep ultraviolet LED by graphene/Al nanoparticles/graphene hybrid structure.

The AlGaN-based deep ultraviolet light-emitting diode (DUV LED) has advantages of environmentally friendly materials, tunable emission wavelength, and easy miniaturization. However, the light extraction efficiency (LEE) of an AlGaN-based DUV LED is low, which hinders its applications. Here, we design a graphene/Al nanoparticles/graphene (Gra/Al NPs/Gra) hybrid plasmonic structure, where the strong resonant coupling of local surface plasmons (LSPs) induces a 2.9-times enhancement for the LEE of the DUV LED according to the photoluminescence (PL). The dewetting of Al NPs on a graphene layer by annealing is optimized, resulting in better formation and uniform distribution. The near-field coupling of Gra/Al NPs/Gra is enhanced via charge transfer among graphene and Al NPs. In addition, the skin depth increment results in more excitons being coupled out of multiple quantum wells (MQWs). An enhanced mechanism is proposed, revealing that the Gra/metal NPs/Gra offers a reliable strategy for improving the optoelectronic device performance, which might trigger the advances of LEDs and lasers with high brightness and power density.

Multi-dimensional plasmonic coupling system for efficient enrichment and ultrasensitive label-free SERS detection of bilirubin based on graphene oxide-Au nanostars and Au@Ag nanoparticles

Rapid and sensitive detection of free bilirubin (BR) is essential for early diagnosis of jaundice and other hepatobiliary diseases. Inspired by sandwich immunoassay strategy, a multi-dimensional plasmonic coupling SERS platform composed of graphene oxide-Au nanostars nanocomposites (GANS NCs) and Au@Ag nanoparticles (NPs) was designed for label-free detection of BR. Specifically, GANS NCs were first prepared, and their excellent SERS activity was ascribed to synergistic enhancement effect of electromagnetic enhancement and chemical enhancement. Furthermore, SERS spectroscopy was used to monitor the adsorption process of BR. Subsequently, secondary reinforcing Au@Ag NPs were directly added, ultimately resulting in a multi-dimensional plasmonic coupling effect. The SERS enhancing mechanism of coupled system was discussed through electromagnetic field simulations. Interestingly, the high-density hotspots generated by strong plasmonic coupling in GANS-Au@Ag substrate could lead to more extraordinary SERS enhancing behavior compared to GANS NCs. Sensing efficiency of the SERS platform was examined by BR with a detection limit down to 10−11 M. Besides, GANS-Au@Ag NCs performed high uniformity and reproducibility. This work not only opens up a new avenue for construction of multi-dimensional plasmonic coupling system, but also offers a new biosensing technology for label-free diagnosis of BR-related diseases, thereby expecting to be applied in clinical diagnosis.

An anisotropic nanobox based core-shell-satellite nanoassembly of multiple SERS enhancement with heterogeneous interface for stroke marker determination

Herein, A novel gold-silver alloy nanobox (AuAgNB)@SiO2-gold nanosphere (AuNP) nanoassembly based on core–shell-satellite structure is fabricated and applied to the surface-enhanced Raman scattering (SERS) detection of S100 calcium-binding protein B protein (S100B). It contains an anisotropic hollow porous AuAgNB core with rough surface, an ultrathin silica interlayer labeled with reporter molecules, and AuNP satellites. The nanoassemblies were systematically optimized by tuning the reporter molecules concentration, silica layer thickness, AuAgNB size, and the size and number of AuNP satellite size. Remarkably, AuNP satellites are adjacent to AuAgNB@SiO2, developing AuAg-SiO2-Au heterogeneous interface. With the strong plasmon coupling between AuAgNB and AuNP satellites, chemical enhancement from heterogeneous interface, and the tip “hot spots” of AuAgNB, the SERS activity of the nanoassemblies was multiply enhanced. Additionally, the stability of nanostructure and Raman signal was significantly improved by the silica interlayer and AuNP satellites. Eventually, the nanoassemblies were applied for S100B detection. It demonstrated satisfactory sensitivity and reproducibility with a wide detection range of 10 fg/mL-10 ng/mL and a limit of detection (LOD) of 1.7 fg/mL. This work based on the AuAgNB@SiO2-AuNP nanoassemblies with multiple SERS enhancements and favorable stability demonstrates the promising application in stroke diagnosis.

Quaternization-Assisted Assembly of Polymer-Tethered Gold Nanoparticles into Superlattices with a Tunable Structure

Programmable organization of functional inorganic nanoparticles (NPs) into well-defined hierarchical superstructures has raised considerable concern due to the enhanced magnetic, electronic, and optical properties arising from the strong plasmonic coupling effect. However, the spontaneous self-assembly of inorganic NPs into uniform superlattices with the desired or tunable shape remains a formidable challenge. Herein, we report the quaternization-assisted hierarchical assembly of gold nanoparticles (AuNPs) tethered with polystyrene (PS) and quaternized poly(2-vinylpyridine) (P2VP) ligands into controllable superstructures in emulsion droplets. The quaternization interaction between bromoalkyl molecular additives (e.g., CnH2n+1Br) and P2VP ligands results in the increase of the hydrophilicity degree of quaternized P2VP ligands and triggers the interfacial instability of emulsion droplets, achieving the continuous transformation of generated superstructures from solid assemblies to hollow colloidosomes and then to the multilayer sheet-like superlattices. Furthermore, the degree of quaternization can be readily tuned by the added content of additives and the length of the alkyl chain, providing a unique and promising approach to prepare contrivable superstructures and functional materials.

Strong coupling of localized surface plasmons and intermolecular vibration mode at terahertz frequencies

Organic molecular vibrations, typically occurring in the terahertz (THz) regime, can resonate with a metastructure. A hallmark Rabi splitting occurs when the coupling strength is sufficiently strong. In this work, we observe the strong coupling of localized surface plasmons (LSPs) and intermolecular vibration mode at THz on a metasurface spin-coated with organic molecule α-lactose monohydrate. Excited by transverse-electric THz waves, dispersive localized surface plasmons interact with nondispersive intermolecular vibrations and form two vibro-polariton modes. The angle-resolved transmission spectra of the coupled system are detected by using a terahertz time-domain spectrometer, demonstrating an anti-crossing effect with a clear Rabi splitting. By retrieving the coupling strength and Hopfield coefficients of polariton bands from the measured data, we further verify that these two bands originate from the strong coupling between LSPs and molecular vibration mode. Moreover, we show that it is possible to implement molecular concentration sensing based on this strong coupling effect. This study demonstrates a unique approach to investigate vibro-polaritons at the terahertz regime and provides a testbed for future applications of strong coupling effects in chemical detection and biosensing.