Surface Plasmon Research Articles

Compact and voltage-tunable surface plasmon polariton-based optical neural networks

Optical neural networks (ONNs) offer advantages in parallel processing, low power consumption, and high-speed operation. However, existing ONN designs face challenges in miniaturization, stability, tunability, and integration. This study proposes a graphene surface plasmon polariton (GSPP) waveguide switch array for all-optical neural networks. The design features a compact structure with a lateral area of only 0.045 . Numerical simulations show that within the 30.2 to 49.4 THz range, the transmission rate is tunable from 0 to 0.875, accurately simulating synaptic weights in ONNs. The compact switch array achieves a recognition accuracy of 93.83% on the CIFAR-10 dataset, demonstrating its potential for high-speed, low-power, and highly integrated neural network computing platforms.

Wide index optical fiber sensor based on localized surface plasmon resonance

Abstract A wide refractive index (RI) photonic crystal fiber (PCF) sensor based on localized surface plasmon resonance (LSPR) was used to detect the RI of unknown analytes, and the modified sensor was numerically analyzed. The design features a D-type fiber structure with gold nanorods as the sensing layer, which enhances the mode matching between the core mode and the plasmon, thereby effectively promoting the LSPR effect. The results of the full-vector finite element method (FEM) analysis present that the displacement of core mode constraint loss peak is more obvious in Y-polarized mode. The wavelength sensitivity and figure of merit (FOM) are used to better and more accurately evaluate and analyze the output characteristics of the sensor. The results present that the sensor has a maximum wavelength sensitivity (WS) of 26,000 nm/RIU, a resolution of 3.85×10-6 RIU, a maximum FOM of 123.6, a sensor RI range of 1.02~1.39, and excellent transmission characteristics. The sensor has a simple structure and low cost, and its wide RI range has great application potential in molecular biology detection, environmental pollution detection, food safety detection, and drug research.

Landau levels induced by synthetic strain in plasmonic metasurface

The quantum Hall effect arises when electrons in a two-dimensional plane are subjected to a magnetic field, causing them to undergo cyclotron motion and form discrete energy levels, known as Landau levels. These levels play a critical role in condensed matter physics. However, practical limitations of applying a magnetic field have led to the introduction of pseudomagnetic fields, which can similarly induce Landau levels. Such pseudomagnetic fields are typically generated through synthetic strain, achieved by deforming geometric patterns, and have been applied to systems like graphene, photons, and phonon crystals. Building on previous research in electronics and optics, we present a plasmonic metasurface that induces Landau levels via synthetic strain in the microwave frequency range. This strain is realized by printing metal structures of specific shapes on a dielectric substrate using printed circuit board technology. The fundamental unit of the plasmonic metasurface is a C6 symmetric structure composed of six localized surface plasmon patches. By applying a displacement function along the transmission direction, we discretize the dispersion curve, leading to band degeneration and the emergence of edge states. The distribution of these edge states is influenced by the strength of the pseudomagnetic field, which is controlled by the magnitude of the displacement function. We validate our design through fabricated models and demonstrate the existence of edge states using near-field scanning experiments. Our work, which combines synthetic magnetic fields and plasmonic metasurface, provides valuable insights for the development and application of integrated photonic devices.

Localized Surface Plasmon Resonance of Ag-SiO2 Core–Shell Nanowire Tetramers

Localized Surface Plasmon Resonance of Ag-SiO2 Core–Shell Nanowire Tetramers

Gold nanoparticles for theranostic treatment of cancer

The chemical stability, low toxicity, and relative simplicity of methods for the synthesis and modification of gold nanoparticles open up wide possibilities for their use as theranostic agents for the diagnosis and treatment of cancer. The unique properties of gold nanoparticles, known as localized surface plasmon resonance, make it possible to create theranostic agents based on these nanoparticles, combining the capabilities of both in vitro diagnostics and targeted drug delivery. The high surface-area-to-volume ratio of gold nanoparticles significantly facilitates the creation of complex nanoplatforms, which can be used in several therapeutic and diagnostic areas at once.

Refractive index and magnetic field sensing based on bent microfiber functionalized with graphene oxide

A bent tapered multimode fiber structure for refractive index (RI) and magnetic field sensing applications is proposed and investigated. The bent tapered region deposited with gold film to excite surface plasmon resonance (SPR) functions as the sensing area. Further surface functionalization with graphene oxide (GO) enhances the SPR effect. The high sensitivity of 5260.1 nm/RIU in the RI range of 1.33–1.37 is achieved. Magnetic fluid is used as the magneto-sensitive material, and the achieved magnetic field intensity and directional sensitivities are 7.08 nm/mT and 0.15 nm/°, respectively. The surface functionalization of GO extends the magnetic field sensor's detection range up to 30 mT. The proposed sensor features a simple structure, low cost, point-sensing capability, and excellent mechanical properties, making it highly suitable for various practical applications.

Characterization of the surface topography of side-polished fiber surface plasmon resonance sensors, and evaluation of its optical performance

Characterization of the surface topography of side-polished fiber surface plasmon resonance sensors, and evaluation of its optical performance

Improved absorption of phosphates through interface junctions and photothermal–energy–storage capability of Ca(OH)2–[Co3O4–Co3(PO4)2]

Strong absorption in the full solar spectrum is required for efficient usage of solar energy. Near-infrared (NIR) light absorption mainly depends on surface plasmon resonance and a high density of free charge carriers (FCCs). However, increasing FCC density in semiconductors is still a challenge. In this work, we demonstrated that multitudinous S-scheme interface junctions can be constructed within nanoscale Co3O4–Co3(PO4)2, leading to enhanced light absorption of phosphates over the entire solar spectrum due to the increased FCC density and charge-carrier configurations. This absorber can also boost the photothermal performance of Ca(OH)2. The photothermal dehydration conversion of Ca(OH)2 is considerably improved (13.7 times). The reversibility of the photothermal hydration–dehydration cycles of Ca(OH)2 is improved by 39 times. This composite is promising for photothermal conversion and thermal energy storage in one-step.

Plasmonic S-type Bi/TiO2@C Heterojunction Composites for Efficient Visible-Light Photocatalytic Removal of Multi-Antibiotics and Dyes

In this work, two series of plasmonic S-type heterojunction photocatalysts containing Bi, TiO2, and biochar (Bi/TiO2@C) have been developed through a biomass-assisted hydrothermal-calcination strategy, utilizing grapefruit peel as a reducing agent and C resource. The calcination temperature and the mass ratio of biomass were optimized to obtain the optimal nanocomposite, which shows excellent adsorptive and visible-light photocatalytic performance in the removal of diverse antibiotic and dye pollutants, including tetracycline, oxytetracycline, ciprofloxacin, sulfamethoxazole, sulfisoxazole, malachite green, and rhodamine B. The remarkable performance can be attributed to the enhanced absorption of light absorption resulting from the localized surface plasmon resonance effect of the semimetal Bi, and the formation of heterogeneous interface between Bi and TiO2, which accelerates the transfer of photogenerated charge. Furthermore, trapping tests and electron spin resonance (ESR) analysis reveal that ∙O2- and h+ are the primary active species involved in the removal of tetracycline. A plausible charge transfer mechanism has been proposed.

Polarization-independent ultranarrow ultraviolet graphene perfect absorption for temperature controlled high-performance optical switch

We demonstrate a tunable polarization-independent ultranarrow perfect absorption (PA) in a hybrid metasurface consisting of graphene-dielectric nanodisk-metal mirror in the ultraviolet (UV) range. Through near-field interactions between the optical dissipation of graphene and surface plasmon polaritons supported by Al2O3 nanodisk array on UV mirror, the UV Fano-like absorption peak can reach 99.92% with linewidth as low as 3.4 nm, which is predicted by the impedance matching theory and a Fano model. Furthermore, a dynamic tuning of the UV PA and the associated high-performance optical switch are achieved via temperature change of the encapsulated ethanol. Importantly, the modulation depth of almost 100%, the ultralarge modulation intensity of about 2.5×106 and the on/off ratio of 63 dB are reached for the graphene-based switch by a thermal control. Our work holds potential applications on the UV graphene based light modulators such as high-precision optical switch and nanodevices.

Ultra-sensitive early detection of colorectal cancer using surface plasmon resonance sensor: theoretical analysis.

One of the primary causes of cancer-related mortality on a global scale is colorectal cancer. Early colorectal cancer detection can stop the disease from progressing and save lives. Detection of colorectal cancer at an early stage yields significant financial savings, lowers mortality rates, and allows for a broader range of less invasive, more effective treatment options, thereby improving patient outcomes. The copper (Cu), carbon nanotube (CNT), and Hafnium Diselenide (HfSe2) with CaF2 prism-based structure have been proposed for colorectal and other cancer detection. The proposed sensor can detect the refractive index (RI) of the sensing medium (SM) between 1.33 and 1.35. The optimal thickness of Cu, CNT, and HfSe2 has been taken at 41nm, 1nm, and 2nm, respectively. At optimal structure have been determined the sensitivity, detection accuracy (DA), and figure of merit (FoM). The maximum sensitivity 356.66deg/RIU is attained at RI of SM 1.33-1.35. For the detection of colorectal cancer, the sensitivity, DA, and FoM of 387.60deg/RIU, 0.253/deg, and 98.6/RIU, respectively, are obtained. By comparison with the reported work in the literature, the results provide a significant improvement. At optimal structure have been determined the sensitivity, DA, and FoM.

Cu nanoparticle geometry as the key to bicolor behavior in Oregon sunstones: An application of LSPR theory in nanomineralogy

Abstract The coloration mechanism of Oregon sunstone is a classic and controversial topic in mineralogy because of the unique coexistence of anisotropic (green-red) and isotropic (red) color zones within single feldspar crystals. After nearly 50 years of research, no models proposed to date have satisfactorily accounted for all observed optical phenomena. Here, we present high-resolution transmission electron microscopy analyses of samples prepared by focused ion beam extraction along specific crystal directions. In both the anisotropic and the isotropic color zones, we observed Cu nanoparticles (NPs) included within plagioclase but with different geometries. In the isotropic (red) zone, NPs were randomly distributed nano-spheres or nano-ellipsoids (8.7–12 nm in diameter) with an aspect ratio of 1–1.3. In contrast, in dichroic (green/red) zones, NPs were directionally aligned nano-rods (8.5–21 nm along the long axis) with an aspect ratio of ∼2.5. We applied localized surface plasmon resonance (LSPR) theory to simulate absorption spectra and developed a model to explain the observed optical properties. LA-ICP-MS and polarized UV-Vis spectroscopy were also performed to confirm our conclusions. This study systematically reveals the existence and optical influence of variably shaped metal-NP inclusions in feldspar crystals. Furthermore, it demonstrates the necessity of including LSPR in the canon of mineral coloration mechanisms. Cu-NP-bearing labradorite has been shown to exhibit third-order nonlinear optical properties, and approaches that incorporate NP shapes and sizes will assist in designing NP-embedded optical materials with tailored optical properties.

Compact dual-band filter using hybrid transition-free spoof surface plasmon polaritons and substrate integrated waveguide

In this paper, a new hybrid transition-free spoof surface plasmon polaritons (SSPPs)-substrate integrated waveguide(SIW) unit is used to design a compact dual-band filter. Benefiting from the combination of the H-shaped unit and the bilateral T-shaped unit of the proposed hybrid unit, the inherent two-stage wave vector matching is provided to achieve momentum and impedance matching. Thus, the proposed transition-free SSPPs-based filter does not require SSPPs transition units, making the circuit size reduction largely. Moreover, the high-order mode (Mode 1) of the transition-free SSPPs transmission units will not be suppressed by the stopband between the fundamental mode (Mode 0) and Mode 1 of transition-free SSPPs transition unit, making it possible to design a dual-band filter based on Mode 0 and Mode 1. In addition, the cutoff frequency of the filter can be controlled by the geometric size of the hybrid transition-free SSPPs-SIW unit. To verify the design theory, a compact dual-band filter with operating frequencies of 4.4 GHz − 5.6 GHz and 9.0 GHz − 9.6 GHz is designed and fabricated. The simulated results are in good agreement with the test results, indicating the feasibility of the proposed structure and design method.

The evaluation of DNA-linked inhibitor antibody and AlphaScreen assays for high-throughput screening of compounds targeting the cap-binding domain in influenza a polymerase.

The PB2 subunit of the influenza virus polymerase complex is essential for viral replication, primarily through a mechanism known as cap-snatching. In this process, PB2 binds to the 5' cap structure of host pre-mRNAs, enabling the viral polymerase to hijack the host transcriptional machinery. This binding facilitates the cleavage and integration of the capped RNA fragment into viral mRNA, thereby promoting efficient viral replication. Inhibiting the PB2-cap interaction is therefore crucial, as it directly disrupts the viral replication cycle. Consequently, targeting PB2 with specific inhibitors is a promising strategy for antiviral drug development against influenza. However, there are currently no available methods for the high-throughput screening of potential inhibitors. The development of new inhibitor screening methods of potential PB2 binders is the focus of this study. In this study, we present two novel methods, DIANA and AlphaScreen, for screening influenza PB2 cap-binding inhibitors and evaluate their effectiveness compared to the established differential scanning fluorimetry (DSF) technique. Using a diverse set of substrates and compounds based on the previously described PB2 binder pimodivir, we thoroughly assessed the capabilities of these new methods. Our findings demonstrate that both DIANA and AlphaScreen are highly effective for PB2 inhibitor screening, offering distinct advantages over traditional techniques such as isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR). These advantages include improved scalability, reduced sample requirements, and the capacity for label-free detection. Notably, DIANA's ability to determine Ki values from a single-well measurement significantly enhances its practicality and efficiency in inhibitor screening. This research represents a significant step forward in the development of more efficient and scalable screening strategies, helping advance efforts in the discovery of antiviral drugs against influenza.

Loss of PII-dependent control of arginine biosynthesis in Dunaliella salina

In cyanobacteria and most Archaeplastida, Arg regulates its formation via allosteric inhibition of the controlling enzyme, N-acetyl-L-glutamate kinase (NAGK) that requires PII protein to properly sense the feedback inhibitor. Although PII expression has been shown to be reduced in Dunaliella salina compared to other green algae, the potential impact of this protein on DsNAGK activity remains unclear. We here performed coupled enzyme assay and surface plasmon resonance analysis and show that DsNAGK is activated by NAG and inhibited by Arg but is not controlled by DsPII. Moreover, DsPII has likely lost its function as an effective glutamine sensor. Replacement of the C-terminus from DsPII with the C-terminus from Chlamydomonas PII restored sensitivity to glutamine in a recombinant DsPII protein, demonstrating the importance of C-terminal residues close to the Q-loop for PII functions. The findings are discussed in the context of the relationship between NAGK control and the acquisition of salinity tolerance during evolution.

Theoretical Analysis of Diffraction Grating-Based SPR Sensor Using the Rigorous Coupled Wave Analysis Method

Abstract Surface plasmon resonance (SPR) sensors are crucial for highly sensitive, label-free detection in various applications, including biosensing and environmental monitoring. This study investigates the sensitivity and performance of diffraction grating-based SPR sensors using rigorous coupled wave analysis (RCWA). The analysis focuses on single- and bi-layered metallic structures composed of copper, gold, and silver. The results reveal that single-layer silver sensors exhibit the highest sensitivity of 169.37°/RIU followed by Au and Cu with a sensitivity of 168.4°/RIU and 167.9°/RIU respectively. Further, to enhance the stability and reliability, bilayered configurations were introduced, incorporating protective coatings of one metal over the other. Among the bilayered configurations, Ag-Cu demonstrated the greatest sensitivity of 175°/RIU followed by Ag-Au with a sensitivity of 173.25°/RIU and Au-Cu with the sensitivity of 168.5°/RIU. This study establishes the potential of bi-metallic SPR sensors for achieving superior sensitivity and stability, highlighting their applicability in advanced detection systems. The novel insight into the interplay between material properties and sensor performance offers a roadmap for designing next-generation plasmonic sensors.

A multifunctional biosensor for selective identification, sensitive detection and efficient photothermal sterilization of Salmonella typhimurium and Staphylococcus aureus.

The foodborne pathogens, e.g., Salmonella typhimurium (S. typ) and Staphylococcus aureus (S. aureus), pose a serious threat to human health. Accurate identification, rapid detection and efficient inactivation are crucial in the early diagnosis and treatment of S. typ and S. aureus. To date, however, the majority of studies have only concentrated on the construction of single-function biological platform for detection or inactivation of S. typ and S. aureus. Therefore, it is imperative to develop a multifunctional surface-enhanced Raman scattering (SERS) biosensor that can effectively sterilize S. typ and S. aureus while simultaneously achieving sensitive detection and selective identification. Herein, we designed and constructed a multifunctional SERS biosensor based on sandwich structure of "capture probe/bacteria/signal probe" in order to simultaneously identify, detect and kill S. typ and S. aureus. Aptamer-modified ZnO/Ag was used as a capture probe to accurately identify and capture the target bacteria in complex environments. Au@Ag-4-MPBA-Aptamer was employed as signal probe to provide the corresponding bacterial SERS "fingerprint" information. The SERS enhancement mechanism of the sandwich-structure ZnO/Ag-Au@Ag SERS substrate was discussed. The sandwich-type SERS biosensor exhibited the strong localized surface plasmon resonance (LSPR) effect and the detection limit for S. typ and S. aureus was as low as 10cfu/mL. Furthermore, the sandwich-type SERS biosensor offered excellent photothermal conversion efficiency (54.32%), enabling photothermal killing of target bacteria when exposed to laser irradiation. A dual enhancement strategy based on a sandwich structure was proposed to maximize the sensitivity of SERS signals using synergistic action of electromagnetic enhancement and chemical enhancement. SERS enhancement factor (EF) was as high as 4.67×105. In addition, the sandwich-type SERS biosensor not only exhibited negligible cytotoxicity, but also was proved to be a promising tool for photothermally inactivate of S. typ and S. aureus in food samples.

Ginkgolic acid inhibits Ebola virus transcription and replication by disrupting the interaction between nucleoprotein and VP30 protein.

The Ebola virus, a filovirus, has been responsible for significant human fatalities since its discovery. Despite extensive research, effective small-molecule drugs remain elusive due to its complex pathogenesis. Inhibition of RNA synthesis is a promising therapeutic target, and the VP30 protein plays a critical role in this process. The interaction between VP30 and the nucleoprotein (NP) is essential for viral replication. We identified ginkgolic acid as a small molecule with strong affinity for VP30, which was validated through multiple assays, including thermal shift, surface plasmon resonance, fluorescence polarization, pull-down, and co-immunoprecipitation. The antiviral efficacy of ginkgolic acid was demonstrated in the EBOV transcription- and replication-competent virus-like particle (trVLP) system. Furthermore, we resolved the crystal structure of the VP30-ginkgolic acid complex, revealing two ginkgolic acid molecules located at the VP30/NP interaction interface. This structural information provides insight into the molecular basis of ginkgolic acid's antiviral activity and suggests a novel therapeutic strategy targeting the VP30/NP interaction.

A label-free gold nanoparticles functionalized peptide dendrimer biosensor for visual detection of breakthrough infections in COVID-19 vaccinated patients

Given the global implementation of effective COVID-19 vaccines, which do not confer complete immunity, it is crucial to monitor the occurrence of breakthrough infections, particularly against newly emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Hence, we developed a label-free colorimetric assay using gold nanoparticles (GNPs) functionalized with a peptide dendrimer incorporating highly reactive epitopes of the nucleocapsid (N) protein. This assay relies on the tween-20 induced colorimetric changes caused by the aggregation of peptide dendrimer-coated GNPs in the absence of anti- SARS-CoV-2 N antibodies, and vice versa. Transmission electron microscopy, dynamic light scattering, and circular dichroism spectroscopy analyses all showed the formation of a uniform and highly stable coating of the peptide dendrimer over GNPs. Surface plasmon resonance experiments have demonstrated a strong binding affinity for the peptide dendrimer and anti- SARS-CoV-2 N antibodies, with a KD value of 525 nM. To validate the proof-of-concept, we have tested this assay on seventy human serum samples, and receiver operating characteristic curve analysis demonstrated high diagnostic sensitivity (88.89 %) and specificity (100 %). This approach opens up new avenues for the development of simple and rapid diagnostic assays for identifying antibodies against viral infections and other pathogens.

Validation of plasmonic-based biosensors for rapid and in depth characterization of monoclonal antibodies directed against rabbit haemorrhagic and foot-and-mouth disease viruses in biological samples.

ELISA and RT-PCR represent the standard tools for the sensitive identification of viruses in biological samples, but they lack the capacity to finely characterize the binding of viruses or viral antigens to monoclonal antibodies (MAbs). Biosensing technologies are gaining increasing importance as powerful MAb characterization tools in the field of virology. Surface plasmon resonance (SPR) is an optical biosensing technology already used for the in depth characterization of MAbs of diagnostic and therapeutic value. Rabbit haemorrhagic disease virus (RHDV) and foot-and-mouth disease virus (FMDV) are top veterinary issues for which the development of novel methods aimed at the characterization of antiviral MAbs represents a priority with important livestock healthcare and economic implications. With these premises in mind, here we prepared a series of SPR biosensors by immobilizing RHDV2 or its 6S subunit by different strategies that were then used to characterize the binding capacity of a panel of anti-RHDV2 MAbs. From the comparison of the results obtained, the biosensor composed of intact RHDV2 captured with catcher-MAb covalently immobilized to the surface showed the best analytical performances. To evaluate the versatility of the biosensor, the same strategy was then adopted using FMVD in cell extracts. The results obtained are discussed in view of the exploitation of SPR in the rapid and resilient fine characterization of antiviral MAbs for diagnostic or therapeutic purposes in the field of animal virology.