Plasmonics最新文献

Surface-enhanced Raman spectroscopy (SERS) has become a cornerstone technique in nanoplasmonics, enabling ultrasensitive molecular detection through the excitation of localized surface plasmon resonances (LSPRs) in noble metal nanostructures. This review highlights the emerging role of microneedle and nanoneedle-based plasmonic platforms as efficient SERS substrates for applications in biomedical diagnostics, pharmaceutical monitoring, and environmental sensing. We explore the fundamental plasmonic mechanisms underlying electromagnetic field enhancement in needle-like architectures, along with recent progress in fabrication techniques, such as lithographic patterning, template-assisted growth, and chemical etching. Case studies involving cancer cell discrimination, antioxidant molecule detection, and drug level tracking are discussed, demonstrating the capabilities of these 3D plasmonic structures for label-free, in situ analysis. We also address critical challenges such as tip functionalization, penetration depth, and biocompatibility. Finally, future directions are proposed to optimize nanoneedle-based SERS systems for integration into wearable, flexible, and implantable sensing devices.

The design of nanostructure colors is influenced by mechanisms such as quantum size effects, surface plasmon resonance, and structural coloration. These optical properties arise from the interaction between localized magnetic and electric dipole resonances, rendering them highly sensitive to changes in geometric parameters. However, conventional analytical methods are inefficient in optimizing geometric parameters to achieve target colors, particularly when faced with the challenges of large-scale and diverse structural color designs. To address this limitation, we propose a design framework based on a bidirectional deep neural network (DNN) consisting of both a forward network and an inverse design network. The forward network learns the relationship between geometry and color response through parameter scans, enabling precise color prediction for specific geometries. The inverse design network derives the corresponding geometry from target color coordinates (CIE1931 color space) and tackles the multi-solution challenges in inverse design by cross-validating with the forward network. Rigorous computational modeling demonstrates that this approach can generate over one million visible-spectrum nanostructure colors with a theoretically predicted color reproduction rate exceeding 98%. This research presents a highly efficient and accurate framework for the design of high-precision optical components, including those used in silicon-based color processing, optical displays, sensors, and photovoltaic systems.

A comprehensive investigation of both spectral characterizations and sensing performance of a Pd-Au core–shell dimer is conducted theoretically by the finite-difference time-domain (FDTD) numerical tool. The extinction spectrum of the two-particle model exhibits the excitation of three hybrid resonance modes, which introduces a reliable multi-site sensing platform for bio/chemical molecules. Altering either the core size (r_c) or the shell thickness (t) significantly impacts the overall optical properties, illustrating controlled optical tunability over a wide range of frequencies extending from the UV to the visible region. Increasing the shell thickness considerably improves sensing capability to changes in the dielectric properties of the host matrix. To maintain simultaneous and effective sensing standards at several spectral sites, a structural ratio of t ≤ (3/2)r_c should be maintained. Otherwise, the sensing performance of the high-energy site is degraded with any further increase in t. The optimal sensing performance is achieved for a core radius of r_c = 10 nm and a shell thickness of t = 15 nm, where both low- and high-energy plasmonic modes exhibit enhanced sensitivity factors. The structural tunability of the proposed bimetallic dimer provides detailed guidelines for designing plasmon-based nanosensors. Additionally, we conclude that our theoretical observations will have profound implications for the use of extinction cross-section spectra in characterizing bimetallic core–shell dimers.

In this paper, two novel tree-branch spoof surface plasmon polariton (SSPP) units are proposed by adding branches on both sides of the rectangular SSPP unit, and a wideband bandpass filter (BPF) and a dual-band BPF are successively designed based on the proposed SSPP structures. Compared with the rectangular SSPP unit, the proposed tree-branch SSPP unit can effectively excite multiple high-order modes of SSPPs in smaller longitudinal dimension. The designed filter only consists of four tree-branch SSPP units, which do not require the mode conversion transition structure, leading to a miniaturized design. More significantly, by changing the length ratio relationship between the upper and lower branches of the tree-branch SSPP unit, the adjustment of the frequency bandwidth of the high-order modes can be achieved. Therefore, the passband and stopband characteristics of the filter can be flexibly modulated, which is conducive to realize the suppression of unwanted spurious signals.

Early detection of cancer cells is vital for effective treatment and personalized healthcare. This study presents a dual-mode optical biosensor that integrates the Goos-Hänchen (GH) shift with surface plasmon resonance (SPR) for highly sensitive, label-free detection of cancer cells. The system utilizes a red diode laser, a beam splitter, a polarizer, a high-refractive-index prism, and a quadrant detector to measure lateral beam shifts with high precision. Lung (A549) and colon (LS180) cancer cells were cultured on gold-coated glass substrates, and their interaction with the evanescent field under total internal reflection induced measurable optical responses. Compared to normal lung and colon cells, cancer cells produced greater SPR angle shifts (~ 2.2° for A549, ~ 1.6° for LS180) and GH shifts (~ 6.5 μm for A549, ~ 5.8 μm for LS180). Refractive index sensitivities reached 220°/RIU (A549) and 160°/RIU (LS180), with detection limits as low as 2.73 × 10⁻⁵ RIU. The sensor exhibited stable performance with a detection threshold of ~ 5 × 10⁵ cells/cm², a FWHM of ~ 1.5°, and SNR of 20:1. Theoretical modeling and MATLAB-based numerical simulations elucidated coupling between SPR and GH modes, validating enhanced sensitivity over conventional SPR. These results highlight the sensor’s potential for rapid, non-invasive discrimination between cancerous and normal cells, offering a promising tool for clinical diagnostics.

Terahertz (THz) waves hold great promise for next-generation wireless communication systems due to their broadband bandwidth and capability for high-speed data transmission. Here, we propose a symmetric plasmonic waveguide that incorporates low-index dielectric layers sandwiched between the graphene sheet and GaAs microrods, enabling deep subwavelength THz field confinement. The mode properties are systematically optimized through finite element simulations. Our simulations reveal a normalized mode area as low as 10⁻⁴, propagation lengths exceeding 50 µm, and tunable modal characteristics can be achieved within the range of 2 to 4 THz. Furthermore, the proposed structure demonstrates robustness against fabrication misalignment, ensuring practical feasibility. Crosstalk analysis further demonstrates negligible mode coupling even at zero waveguide spacing, highlighting its potential for high-density photonic integration. These results pave the way for ultra-compact, low-loss THz devices, including modulators, waveguides, and sensors.

Metasurfaces, as ultra-thin two-dimensional structures with subwavelength patterns, can achieve flexible control over beam phase, amplitude, and polarization. However, most existing metasurfaces can only control beams from a specific incident direction, limiting their potential applications. This paper proposes a non-interleaved, bidirectional multifunctional Janus metasurface, which can be used to control terahertz waves over the entire space. By integrating photosensitive silicon—a phase-change material whose properties can be modulated by light—the functionality of the Janus metasurface can be dynamically reconfigured through changes in illumination intensity. With two input parameters—electromagnetic wave propagation direction and the state of the photosensitive silicon—four independent beam control functionalities are realized. Based on the proposed four-channel metasurface, a beam focusing characterization half-adder is designed for simple optical computation. The Gerchberg-Saxton (GS) algorithm is then used to design four near-field imaging phase encoding distributions to validate the performance of the proposed four-channel metasurface. A series of simulation results indicate that the reconfigurable Janus metasurface effectively reduces crosstalk between channels, and the simulation results of each channel match the expected design. Our work is of great significance for advancing multifunctional, miniaturized metasurfaces, and the proposed metasurface devices have many potential applications in optical computation, imaging, and communication.

Ascorbic acid, commonly called vitamin C, is a major biomarker of many malfunctions and deficiencies in the human body. This research focuses on enhancing ascorbic acid detection sensitivity using a specialized (single-mode, multimode, and single-mode) SMS fiber structure through enzyme functionalization and leveraging localized surface plasmon resonance (LSPR). The SMS fiber structure, designed for versatility, was modified to increase selectivity by ascorbate oxidase functionalization, which oxidizes the AA in the presence of oxygen, while LSPR techniques were employed to harness plasmonic effects for improved detection capabilities using gold nanoparticles (AuNPs), whose absorbance peak wavelength appeared at 522.8 nm. The resulting sensor probe was examined for various concentrations of AA ranging from 50 to 120 µM in terms of different performance parameters such as sensitivity, limit of detection, selectivity, reproducibility, and repeatability for ascorbic acid detection and such studies could be employed in complex biological matrices for AA detection. The sensor demonstrated a sensitivity of 0.0138 nm/μM and a calibration correlation factor of 0.9181, good linearity over the range of 50–120 µM AA concentrations. Additionally, the resulting fiber structure displayed selective detection of AA, thus ensuring non-interference of other analytes present in the realistic biological matrix. This research holds promise for advanced applications in clinical diagnostics and biomedical research, offering a novel and effective approach to enhance ascorbic acid detection.

This study investigated the influence of the degree of polydispersity of silver nanoparticles on plasmon-enhanced photoluminescence (PL) and surface-enhanced Raman scattering (SERS), which is crucial for the development of sensitive sensors. Experimental and theoretical modeling demonstrate the advantages of silver nanoparticles (~ 30 nm) with higher polydispersity and polymorphicity over monodisperse particles in enhancing the photoluminescence of a "green" luminophore, as well as SERS and resonance SERS (SERRS) of dyes under green light excitation within the resonance range of individual silver nanoparticles. When red excitation (620 nm and 633 nm) within the plasmon resonance of silver nanoparticle aggregates was used, no significant effect of Ag nanoparticle polydispersity on the enhancement of PL, SERS, or SERRS was observed. These findings highlight the importance of considering metal nanoparticle polydispersity when optimizing sensor systems based on plasmonic enhancement and challenge the conventional prioritization of monodispersity in plasmonic sensor design and offer practical guidelines for optimizing enhancement efficiency.