Surface Plasmon Resonance Coupling Research Articles

Engineering the Blackbody Absorption of the Au-Branch-on-Au-Plate Heterostructures.

Utilizing the strong ligand control effects of l-cysteine (l-Cys), the growth of Au on Au triangular nanoplate (AuTN) seeds was continuously tuned from layer-by-layer (the Frank-van der Merwe) to layer-plus-island (the Stranski-Krastanov), and island (the Volmer-Weber) growth modes, leading to the formation of a series of Au-on-AuTN heterostructures. Within the window of VW growth mode (featured by the growth of Au spikes and branches on AuTNs), the effective localized surface plasmon resonance (LSPR) coupling led to the selective strengthening of the "valley" absorptions, leading to smooth and flat absorption curves. Interestingly, through engineering the number/density, size, and branching degree of the Au branches, except for the black color, full spectrum absorption within 400-1300 nm wavelength was achieved on Au-branch-on-AuTN structures. Mechanistic studies revealed that the blackbody absorption property of the Au-branch-on-AuTN originates from the well-balanced intraparticle LSPR couplings among the neighboring Au branches. The tunable blackness and the full spectrum absorption property made the Au-branch-on-AuTN heterostructure a suitable candidate for various plasmonic-related applications, such as a wide spectrum light absorber, photoacoustic imaging contrast agent, and photothermal therapy medium. In addition, our strong ligand control in Au-branch-on-AuTN heterostructures could be extended to other hybrid systems with diverse material combinations, so long as to find the proper strong ligand.

Surface Plasmon-Coupled Directional Emission Enhanced Raman Scattering Based on Waveguide Coupling Surface Plasmon Resonance Configuration

Surface Plasmon-Coupled Directional Emission Enhanced Raman Scattering Based on Waveguide Coupling Surface Plasmon Resonance Configuration

Dual-ligand Eu-MOF/CuS@Au Heterostructure Array-based ECL Sensor for MiRNA-128 Detection in Glioblastoma Tissues

In this work, the dual-ligand lanthanide metal-organic framework (MOF)-based electrochemiluminescence (ECL) sensor was constructed for the detection of miRNA-128 in glioblastoma (GBM) diagnosis. The luminescent Eu-MOF (EuBBN) was synthesized with terephthalic acid (BDC) and 2-amino terephthalic acid (BDC-NH2) as dual-ligand. Due to the antenna effect, EuBBN with conjugated-π structure exhibited strong luminescent signal and high quantum efficiency, which can be employed as ECL nanoprobe. Furthermore, the novel plasmonic CuS@Au heterostructure array has been prepared. The localized surface plasmon resonance coupling effect of the CuS@Au heterostructure array can amplify the ECL signal of EuBBN significantly. The EuBBN/CuS@Au heterostructure array-based sensing system has been prepared for the detection of miRNA-128 with a wide linear range from 1 fM to 1 nM and a detection limit of 0.24 fM. Finally, miRNA-128 in the clinic GBM tissue sample has been analysis for the distinguish of tumor grade successfully. The results demonstrated that the dual-ligand MOF/CuS@Au heterostructure array-based ECL sensor can provide important support for the development of GBM diagnosis.

Harmonic Generation up to Fifth Order from Al/Au/CuS Nanoparticle Films.

Dual heterostructures integrating noble-metal and copper chalcogenide nanoparticles have attracted a great deal of attention in nonlinear optics, because coupling of their localized surface plasmon resonances (LSPRs) substantially enhances light-matter interactions through local-field effects. Previously, enhanced cascaded third-harmonic generation was demonstrated in Au/CuS heterostructures mediated by harmonically coupled surface plasmon resonances. This suggests a promising approach for extending nonlinear enhancement to higher harmonics by adding an additional nanoparticulate material with higher-frequency harmonic resonances to the hybrid films. Here we report the first observation of enhanced cascaded fourth- and fifth-harmonic generation in Al/Au/CuS driven by coupled LSPRs at the fundamental (1050 nm), second harmonic (525 nm), and third harmonic (350 nm) of the pump frequency. An analytical model based on incoherent dipole-dipole interactions among plasmonic nanoparticles accounts for the observed enhancements. The results suggest a novel design for efficiently generating higher harmonics in resonant plasmonic structures by means of multiple sum-frequency cascades.

Enhanced laser-induced fluorescence and Raman spectroscopy with gold nanoparticles for the diagnosis of oral squamous cell carcinoma

BackgroundThe incidence, mortality, and recurrence rates of oral cancer are high worldwide. It is a common and aggressive type of tumor. Owing to the challenges associated with early illness diagnosis, squamous cell carcinoma, a kind that is prevalent of oral cancer, has an unacceptably high fatality rate. The management of the condition and the prevention of cancer, on the other hand, depend greatly on early detection. Therefore, alternative methods for the treatment and early diagnosis are essential for oral cancer. The detection of tongue squamous cell carcinoma is aided by coupled surface plasmon resonance, which can occur in gold nanoparticles (AuNPs). Compared to the currently utilized imaging contrast chemicals, AuNPs are more biocompatible and capable of targeting specific surface molecules. In the current study, AuNPs were synthesized in one step via citrate reduction and applied to tongue samples of a Caucasian man's Homo sapiens (Squamous cell carcinoma from ATCC cell-lines) in order to improve early detection using and laser-induced fluorescence and Raman spectroscopy.ResultsUV–visible spectroscopy, Zeta potential, TEM, and FTIR spectroscopic technique were used to characterize the synthesized nanoparticles. The synthesized AuNPs measured 13 ± 3 nm with uniform size distribution and high stability. Results demonstrate the significance of AuNPs in improving the identification of tongue squamous cell carcinoma.ConclusionObtained results revealed that the use of AuNPs modifies the emitted spectra in the two employed spectroscopic techniques and provides more significant receiver operating characteristic curve parameters, hence a higher detection rate of cancer.

Polarization independent tunable bandwidth absorber based on single-layer graphene

As the demand for cognitive understanding of the THz band continues to grow, there is significant potential for practical applications in designing optical devices operating in this frequency range. This paper proposes a polarization-independent tunable bandwidth absorber based on a monolayer graphene, capable of achieving an absorption rate higher than 0.9 in the 3–6 THz band. The absorber exhibits polarization incoherence due to the structural symmetry. Analysis of the electric field distribution indicates that the strong absorption effect of the absorber primarily arises from the coupling of localized surface plasmon resonance (LSPR). The absorber also demonstrates excellent tunability, both in terms of physical and chemical properties, while maintaining optimal absorption performance at a 45° incidence angle. This implies that the absorber holds significant potential for applications in fields such as biomedicine and communications.

Transparent grating-based metamaterials for dynamic infrared radiative regulation smart windows.

Dynamic infrared radiation regulation has been widely explored for smart windows because of its vital importance for comfortable and energy-efficient buildings. However, it remains a great challenge to synchronously achieve high visible transmittance and pronounced infrared tunability. Here, we propose a dynamic infrared tunable metamaterial composed of indium tin oxide (ITO) gratings, an air insulator, and an ITO reflector. The ITO grating-based infrared radiation regulator exhibits a high emissivity tunability of 0.73 at 8-13 μm while maintaining a high visible transmittance of 0.65 and 0.72 before and after actuation, respectively. By adjusting the geometric parameters, the tunable bandwidth can be further extended to 3-30 μm and the ultra-broadband tunability reaches 0.62. The excellent infrared tunable performance arises from the insulator thickness-dependent effect of Fabry-Pérot and propagating surface plasmon resonance coupling and decoupling, which lead to perfect and low absorption, respectively. This work provides potential for the advancement of smart window technology and makes a significant contribution to sustainable buildings.

Spectrally Selective Ultra‐Broadband Solar Absorber Based on Pyramidal Structure

Here, a spectrally selective solar absorber is explored and an ultra‐broadband solar absorber is proposed based on pyramidal structure. The finite‐difference in time domain (FDTD) software is used to model the spectral characteristics and magnetic absorption patterns of this absorber. The emissivity of the absorber is less than 20% in the far‐infrared band over 6000 nm, showing good selectivity, and the total solar thermal conversion efficiency is very close to that of an ideal truncated selective solar absorber by analyzing the performance of our proposed absorber‐related indexes. By studying the high absorption band of the absorber, the selectivity can be better investigated in depth. Here, 200–4000 nm is chosed as the depth study band. The absorber possesses an ultra‐wide bandwidth of 3554 nm and an average absorption of over 97.4%, and in the 200–3754 nm band, the absorber has an ultra‐high absorption rate of more than 98.3%, and its thermal emitter has a high emission efficiency of 94% at a temperature of 1000 K. Notably, the weighted average absorption in the 280–4000 nm band at AM1.5 is as high as 98.86%, with a loss of only 1.14%. The ultra‐broadband absorption property of this solar absorber is mainly a joint effect of surface plasmon resonance coupling.

Advanced Integration of Glutathione-Functionalized Optical Fiber SPR Sensor for Ultra-Sensitive Detection of Lead Ions.

It is crucial to detect Pb2+ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb2+ concentration, in which the refractive index (RI) sensitivity of the multimode-singlemode-multimode (MSM) hetero-core fiber is largely enhanced by the gold nanoparticles (AuNPs)/Au film coupling SPR effect. The GSH is modified on the fiber as the sensing probe to capture and identify Pb2+ specifically. Its working principle is that the Pb2+ chemically reacts with deprotonated carboxyl groups in GSH through ligand bonding, resulting in the formation of stable and specific chelates, inducing the variation of the local RI on the sensor surface, which in turn leads to the SPR wavelength shift in the transmission spectrum. Attributing to the AuNPs, both the Au substrates can be fully functionalized with the GSH molecules as the probes, which largely increases the number of active sites for Pb2+ trapping. Combined with the SPR effect, the sensor achieves a sensitivity of 2.32 × 1011 nm/M and a limit of detection (LOD) of 0.43 pM. It also demonstrates exceptional specificity, stability, and reproducibility, making it suitable for various applications in water pollution, biomedicine, and food safety.

Giant lateral photovoltaic effect in Ag/porous silicon/Si structure for high-performance near-infrared detection

The lateral photovoltaic effect demonstrates versatility across various applications, including photodetectors, imaging, spectroscopy, biosensing, and environmental monitoring. Challenges arise from the low energy of near-infrared photons, regarded as a bottleneck for high-sensitivity photodetector development in this spectrum, limiting applications like optical fiber communication and image sensors. However, this study achieved a remarkable 720.57 mV/mm sensitivity for the lateral photovoltaic effect in the near-infrared region with a 980 nm laser irradiation on an Ag/Porous Silicon/Si structure. This sensitivity surpasses previous observations several to hundreds of times and even outperforms many other structures in the short-wavelength spectrum, further emphasizing its significance in this field. The use of a unique fluoro-amino electrolysis technique ensures consistent porosity, mitigating the adverse effects of photoluminescence. Combined with surface Ag, it induces local surface plasmon resonance and efficient plasmon coupling, markedly increasing electron density. This highly sensitive structure propels advancements in near-infrared photodetectors and Raman signal enhancement, establishing a robust foundation for potential applications in highly sensitive photodetectors and biological sensors.

Detection of backside coupled propagating surface plasmon resonance on the sidewall of a wafer

We proposed a surface plasmon resonance (SPR) sensor structure that utilized a glass wafer with a diffraction grating and an n-type silicon piece bonded near the SPR coupling site. This configuration enabled surface plasmon excitation from the back of the substrate without the unwanted interaction between the excitation light and the sample, and electrical detection of the SPR response by a 0.7-eV Schottky barrier at the Au/n-Si interface formed on the sidewall of the silicon piece was achieved. Experimental evaluation of the surface plasmon coupling performance was conducted, showing clear peaks in the photocurrent for various wavelengths in the NIR-II window, ranging from 1100 to 1300 nm. The device’s ability to detect propagating surface plasmons as a photocurrent was confirmed; the results indicated a consistent trend with theoretical and numerical calculations. Since the device was composed of a glass substrate, the use of wavelengths shorter than the near-infrared wavelength was possible, including visible wavelengths where the optical absorption by water is negligible. Thus, our proposed sensor provides a compact and efficient solution for SPR sensing in aqueous solutions.

Faraday rotation enhancement for colloidal spherical Au and Ag nanoparticles and their mixtures

So far, magnetooptical (MO) properties of silver nanoparticles (AgNPs) have been studied only by magnetic circular dichroism (MCD) spectroscopy at the surface plasmon resonance (SPR) band. However, direct knowledge of the Faraday rotation effect (FR) is very important in fundamental research and applications. In the present work, we study an enhancement of FR of individual gold nanoparticles (AuNPs) and AgNPs and their mixture of colloidal aqueous suspension. The Au and Ag spherical NPs were synthesized independently as colloids in an aqueous suspension and then such mixtures were studied (AgNPs were also studied as a suspension in hexane). The noble metal NPs were characterized by TEM, UV–Vis, and refraction methods. The enhancement of FR of individual NPs was observed and it is consistent with available MCD results. For the mixtures, observed changes of magnitude of FR is small, and coupling of both SPR is rather weak. The obtained FR spectra associated with SPR band have been successfully converted to MCD spectra using the Kramers-Kronig transformation. Calculated MCD spectra are consisted with that obtained by direct measurements.

Enhancing upconversion luminescence of rare earth ions by the activation of the antenna effect in plasmonic cuprous sulfide nanoparticles

To modulate the local electromagnetic field in the upconversion luminescence (UCL) of rare earth ions is one of the most effective ways to improve the luminescence intensity of upconversion nanocrystals (UCNs). Herein, the luminescence intensity of UCNs was increased by 5.8 times by activating the antenna effect of near-infrared plasma in cuprous sulfide nanoparticles. By simulating the local electromagnetic field distribution of the core-shell composites under 980 nm excitation light, the UCL enhancement mechanism of rare earth ions was studied. It showed that the antenna effect of plasmonic cuprous sulfide nanoparticles enhanced the absorption and utilization of excited light by UCNs, and the optical field in the vicinity of the core-shell composites was significantly optimized by inducing the localized surface plasmon resonance coupling between cuprous sulfide nanoparticles. Finally, our results provide a novel way to effectively regulate the local electromagnetic field in the UCL of rare earth ions.

Nanobiosensing Based on Electro-Optically Modulated Technology.

At the nanoscale, metals exhibit special electrochemical and optical properties, which play an important role in nanobiosensing. In particular, surface plasmon resonance (SPR) based on precious metal nanoparticles, as a kind of tag-free biosensor technology, has brought high sensitivity, high reliability, and convenient operation to sensor detection. By applying an electrochemical excitation signal to the nanoplasma device, modulating its surface electron density, and realizing electrochemical coupling SPR, it can effectively complete the joint transmission of electrical and optical signals, increase the resonance shift of the spectrum, and further improve the sensitivity of the designed biosensor. In addition, smartphones are playing an increasingly important role in portable mobile sensor detection systems. These systems typically connect sensing devices to smartphones to perceive different types of information, from optical signals to electrochemical signals, providing ideas for the portability and low-cost design of these sensing systems. Among them, electrochemiluminescence (ECL), as a special electrochemically coupled optical technology, has good application prospects in mobile sensing detection due to its strong anti-interference ability, which is not affected by background light. In this review, the SPR is introduced using nanoparticles, and its response process is analyzed theoretically. Then, the mechanism and sensing application of electrochemistry coupled with SPR and ECL are emphatically introduced. Finally, it extends to the relevant research on electrochemically coupled optical sensing on mobile detection platforms.

Gold nanohole arrays with ring-shaped silver nanoparticles for highly efficient plasmon-enhanced fluorescence

To enhance the interaction between electromagnetic fields and reduce photoluminescence (PL) lifetime in plasmon-enhanced fluorescence, this study presents a novel approach involving the fabrication of gold (Au) nanohole arrays (ANA) decorated with ring-shaped silver nanoparticles (AgNPs) on a silicon-dioxide (SiO2)/silver (Ag) substrate. The surface plasmon resonance coupling in terms of the PL reactions of ANA substrates with and without ring-shaped AgNPs is investigated via experiments and numerical simulations. The remarkable enhancement of PL intensity of the proposed substrate is attributed to increased absorption, which enables the tuning of surface-enhanced electromagnetic fields. Specifically, the Raman signal of rhodamine 6G (R6G) dye and the PL intensity of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) molecules are significantly enhanced 3.7 and 2.2 times, respectively, compared to those of the bare ANA substrate. Meanwhile, the PL lifetime is reduced by 46.15%. These results confirm that ANAs decorated with ring-shaped AgNPs can significantly improve plasmon-enhanced fluorescence. The findings presented herein demonstrate the potential to revolutionize biosensing, imaging, and photonics.

Symmetrical dual D-shape fiber for waveguide coupled surface plasmon resonance sensing

A waveguide-coupled surface plasmon resonance (WCSPR) sensor consisting of two D-shape single-mode fibers is designed and analyzed by the finite element method (FEM). The optical field of the surface plasmon polaritons (SPPs) mode is confined in the dielectric cavity between the dual metallic thin films. Therefore, the effective refractive index of the SPP mode depends largely on the refractive index of the analyte and an anomalous dispersion relationship is observed between the SPP mode and x-polarized core-guide mode of the dual D-shape fiber. The excitation mechanism of surface plasmon resonance (SPR) in the coupling region is attributed to phase matching of the two modes. Further analysis shows that the narrow bandwidth peak in the loss spectrum of the core mode is determined by the sensor dimensions contributed jointly by the thicknesses of the silver film, dielectric layer, and titanium dioxide film. Compared to the single-fiber structure, the optimized dual D-shape WCSPR sensor achieves a maximum wavelength sensitivity of 52,200 nm/RIU with a full-width at half-minimum (FWHM) of 9.47 nm and a figure of merit (FOM) of 346.6 RIU−1 in the analyte refractive index range of 1.32–1.42.

Temperature-Responsive Nanoassemblies for Self-Regulated Photothermal Therapy and Controlled Copper Release to Accelerate Chronic Wound Healing.

Photothermal therapy (PTT) is an effective therapeutic method against multidrug-resistant bacteria. The heating temperature is of great significance to completely eliminate bacteria but not damage surrounding healthy tissue. To meet the need for chronic wound management, a pH and temperature dual-responsive copper-gold nanoassembly (sCuAu NAs) was constructed by cross-linking the CuAu nanoparticles (CuAu NPs) with small molecules involved in the Edman degradation reaction. At room temperature, the sCuAu NAs could quickly heat up to eliminate the biofilm upon laser irradiation due to the surface plasmon resonance coupling effect. On arriving at the degradation temperature of around 50 °C, the sCuAu NAs are disassembled into CuAu NPs in the wound infection site, which not only prevents overheating but also promotes deep penetration and accelerates copper-ion release to remove residual bacteria and promote wound healing. This study not only provides an effective treatment that can simultaneously alleviate wound infection and accelerate wound healing but also brings up an idea on the development and application of temperature self-regulated photothermal agents in various diseases.

Characterization of the material and electrical properties depending on the Mg:Ag ratio as a cathode for TEOLED

In this study, Mg:Ag mixed alloy films were comprehensively analyzed as a potential transparent cathode, depending on the deposition ratio of Mg:Ag atoms. It was determined that the work function, refractive index, and film formation characteristics varied depending on the deposition ratio of Mg:Ag, and affected electro-optical characteristics such as transmittance and sheet resistance. In addition, the applicability of the proposed transparent cathode for top emitting organic light-emitting diodes (TEOLEDs) was analyzed by comprehensively considering the TEOLED performance in relation to the Mg:Ag deposition ratio. The TEOLED performance was optimized by adjusting the Mg:Ag transmittance, sheet resistance and appropriate work function, and the emission spectrum could be controlled by localized surface plasmon resonance (LSPR) and cavity mode coupling effect.

Coupling doping and localized surface plasmon resonance toward acidic pH-preferential catalase-like nanozyme for oxygen-dominated synergistic cancer therapy

Hypoxia increases patient treatment resistance and favors cancer progression. Nanozymes have received unprecedented attention in alleviating hypoxia via catalase (CAT)-mimicking catalytic reaction. However, the oxygen production capability of CAT-like nanozymes undergoes the deficiency and even absolute loss in acidic tumor microenvironment. Herein, we propose a doping-localized surface plasmon resonance (LSPR) coupling strategy to shatter the acidic pH limitation and reinforce the catalytic activity of CAT-like nanozyme for oxygen-dominated synergistic cancer therapy. Platinum-doped plasmonic gold nanostar modified with glucose oxidase (Pt-AuNS-GOx) is constructed as a proof-of-concept. Density functional theory calculations reveal the *O-assisted and *OH-assisted CAT-like reaction paths in Pt-AuNS-GOx, and demonstrate that Pt doping-induced energy barrier reduction accounts for the oxygen generation in acidity. Furthermore, the CAT-like reaction kinetics of Pt-AuNS-GOx can be significantly enhanced upon plasmon irradiation resulted from the excited hot electrons and local heating accompanied with LSPR decay. Such outstanding acidic pH-preferential oxygen generation capability of Pt-AuNS-GOx significantly boosts the efficiency of synergistic tumor aerobic therapeutics of glutathione oxidation-medicated oxidative stress and GOx-activated starvation in vitro. Remarkably, Pt-AuNS-GOx substantially reverses the hypoxic microenvironment of tumor tissue, and enables greatly accelerated apoptosis and suppressed metastasis of cancer in vivo, possessing conspicuous therapeutic efficiency. The proposed doping-LSPR coupling strategy offers a powerful modality to modulate the restricted reaction pH of CAT-like nanozymes, and provides a paradigm shift for hypoxia alleviation-boosted cancer synergistic treatment.

Design and fabrication of pH-responsive monodisperse gold/peptide/gold sandwich nanoparticles

Integrating stimuli-responsive molecules and plasmonic nanoparticles into a single nanoscale platform for stimuli-adaptive functionality is of great importance in nanotechnology. However, existing strategies for constructing stimuli-responsive molecule/noble metal composite nanoparticles based on a solution or solid-phase methods result in limited separation efficiency and low structural precision. Here, we propose a solid-solution combined strategy to prepare monodisperse pH-adaptive gold/peptide/gold sandwich nanoparticles with precisely controlled layered structures. Wafer-scale gold/peptide/gold layered structure was first deposited on a silicon wafer and then etched by argon plasma using silica nanoparticles as a mask. Sandwich nanoparticles can be easily released from silicon wafers by a wet etching reaction and then purified by centrifugation. The as-prepared gold/peptide/gold nanoparticles exhibit distinct localized surface plasmon resonance (LSPR) coupling peaks at near-infrared wavelengths in acidic and neutral environments, demonstrating their great potential as pH-responsive optical nanodevices. In addition, this flexible and configurable approach enables the precise fabrication of layered nanostructures of different sizes, layer numbers, and compositions, with wide applications in optical actuation and sensors.