Search Results (132)

The interaction between light and chiral plasmonic metasurfaces provides a powerful mechanism for controlling polarization states at the nanoscale. Utilizing displacement Talbot lithography for large-area fabrication, we characterized the chiroptical response by measuring the evolution of Stokes parameters to quantify phase retardation between orthogonal polarization components. To elucidate the underlying physical mechanism, we employ a hybrid finite element method and rigorous coupled-wave analysis approach to investigate the behavior of the far-field and local-field configurations. Our results reveal that the phase shift is highly sensitive to symmetry-breaking features, where the interplay between different modes dictates the overall circular dichroism signal. Furthermore, the analysis of local field plots suggests specific contributions of plasmonic modes to the chiroptical response. We conclude that the phase shift effects, characterized via Stokes parameters and modal analysis, provide a robust metric for engineering chiroptical properties in these systems. This work establishes a fundamental framework for developing compact polarization-control elements and enhances the understanding of phase-modulated light-matter interactions in chiral plasmonic metasurfaces. Full article

The growing request for more sustainable materials and environmentally friendly nanofabrication methods in the electronics field has recently driven the scientific community in the development of bio-derived materials as an alternative to conventional lithographic resists. In this work, we used chitosan, a biodegradable and biocompatible polysaccharide, as a green direct-write resist material for Atomic Force Microscopy-based nanolithography. Chitosan thin layers were obtained by spin coating and systematically characterized, in terms of thickness and surface roughness, demonstrating nanoscale smoothness and tunable film thickness. Three Pulse–Atomic Force Lithography (P-AFL) approaches, i.e., Constant Pulse, Gradient Pulse, and Raster Pulse AFL methods, were used to pattern nanostructures with constant-depth nanogrooves, variable-depth (2.5D) profile, and three-dimensional nanoholes on chitosan films. The results reveal high pattern fidelity, reproducibility, and tunability of feature dimensions as a function of applied force and scanning direction. Moreover, the RP-AFL technique enabled the fabrication of well-defined 3D nanostructures with depths matching the film thickness, which is a prerequisite for subsequent pattern transfer. This experimental work provided a first proof-of-concept to adopt chitosan as a more sustainable alternative with respect to conventional resists. Moreover, the results highlight P-AFL methods as a versatile and low-impact nanofabrication strategy, contributing to the development of greener micro- and nano-manufacturing technologies. Full article

Reliable quality control of adeno-associated virus (AAV) vectors remains a major bottleneck in gene therapy manufacturing, particularly for resolving subtle differences in genome loading and conformation at the single-particle level. Existing approaches often struggle to distinguish AAV populations with similar mass and charge, such as capsids carrying self-complementary versus single-stranded DNA. Here, we introduce an AC plasmonic nanopore sensing framework for AAV9 characterization. Individual AAV capsids were optically trapped within a plasmonic double-nanohole nanopore and interrogated using multi-frequency AC pulse trains spanning 500 Hz to 100 kHz. To enhance sensitivity to localized particle–field interactions, a nanofabricated Ag/AgCl ring electrode was integrated concentrically with the plasmonic nanopore. Relative to a conventional wire electrode, the ring electrode produced broader and more robust analyte-dependent differences across multiple frequency-dependent parameters, enabling reliable discrimination of empty capsids (AAV_empty) and genome-loaded capsids carrying either self-complementary (AAV_scDNA) or single-stranded DNA (AAV_ssDNA), despite their near-identical genome mass. Concentration titration experiments further demonstrated that the extracted multivariate AC features remained largely concentration-independent over the tested range. Together, these results demonstrate that ring-electrode-enabled AC plasmonic nanopore sensing provides a multidimensional framework for resolving closely related AAV populations and advances plasmonic nanopores toward practical single-particle quality control of gene therapy vectors. Full article

Localized surface plasmon resonance (LSPR) is an optical phenomenon that occurs when light interacts with free electrons on the surface of metallic thin films, producing intensified electromagnetic fields at specific sites, often called “hot spots”. LSPR-based sensing technologies respond to chemical and associated optical interfacial changes. Inherent advantages include enhanced sensitivity, compact size, low production cost, and strong potential for integration into portable, point-of-care diagnostic systems. This study focuses on a detailed investigation into the surface functionalization of localized surface plasmon resonance (LSPR)-based nanohole array (NHA) sensors for biomedical applications. Gold-coated NHA surfaces were functionalized using polyethylene glycol (PEG) self-assembled monolayers (SAMs), enabling specific attachment of biomolecular species. As a proof-of-concept, bovine serum albumin (BSA) and SARS-CoV-2 nanobody proteins were successfully immobilized on the PEGylated surfaces. Individual steps of surface modification including PEGylation, protein immobilization and nanobody immobilization were validated through a dual-method approach which combined measurement of LSPR optical spectral shifts and x-ray photoelectron spectroscopy (XPS) chemical analyses. Reproducibility was assessed across multiple sensors and repeated trials, confirming the repeatability of each functionalization and binding process. The sensor system, consisting of NHA-based plasmonic platform, microfluidics, and a portable optical spectrometer, exhibits the capability for reliable and sensitive, label-free detection of biomolecular targets, including viral antigens, in liquid-phase environments. Full article

A reflective plasmonic humidity sensor based on an Au–PVA–Au nanohole sandwich structure is investigated. The device consists of a periodic gold nanohole array, a poly(vinyl alcohol) (PVA) spacer, and a continuous gold film. A humidity-dependent model considering both the refractive-index decrease and thickness swelling of PVA is established to analyze the optical response and resonance-modulation mechanism. Within the relative humidity range of 20–98%RH, the reflection resonance dip exhibits a continuous blueshift with a total wavelength shift of approximately 135 nm. Piecewise linear fitting shows sensitivities of 1.3857 nm/%RH in the 20–74%RH range and 2.5000 nm/%RH in the 74–98%RH range. At approximately 74%RH, the resonance wavelength, full width at half maximum, and quality factor are about 830 nm, 19 nm, and 43.7, respectively. Decoupling analysis confirms that both PVA refractive-index reduction and thickness swelling contribute to the blueshift, while their combined effect produces the largest response. These results demonstrate that the proposed structure converts humidity-induced optical and geometric variations in PVA into a pronounced wavelength response, providing a mechanism-guided design route for reflective nanoplasmonic humidity sensors based on polymer-assisted cavity modulation. Full article

Realizing high-quality-factor (high-Q) plasmonic resonances in the visible regime is critical for enhancing light-matter interactions and advancing biochemical sensing. However, traditional localized surface plasmon resonances (LSPRs) typically suffer from broad spectral linewidths due to severe radiative damping. In this work, we propose a simple two-dimensional symmetric gold nanohole-array metasurface that supports a symmetry-protected bound state in the continuum (SP-BIC) at normal incidence. By introducing extrinsic symmetry breaking via oblique incidence, this non-radiative dark state is successfully transformed into an observable high-Q quasi-BIC Fano resonance. Cartesian multipole decomposition reveals that this sharp mode ($\lambda \approx 688$ nm) is predominantly driven by a tightly confined Magnetic Dipole (MD) excitation, which drastically suppresses radiative leakage compared to the highly damped Electric Dipole (ED)-dominated LSPR. Consequently, the quasi-BIC mode exhibits an ultra-narrow spectral linewidth ($\mathrm{FWHM}\approx 17.4$ nm). While its bulk sensitivity ($236.9$ nm/RIU) is slightly lower than that of the LSPR mode, the exceptionally sharp resonance yields a remarkably low Limit of Detection (LOD) of $7.35\times {10}^{-3}$ RIU, achieving a nearly five-fold improvement over the traditional LSPR. Furthermore, the quasi-BIC mode maintains an outstanding Figure of Merit (FOM up to ∼19.7 ${\mathrm{RIU}}^{-1}$) across the entire sensing range. By eliminating the need for complex asymmetric nanofabrication, this robust angle-tuned design strategy provides a highly promising platform for the development of high-resolution, low-cost optical biosensors. Full article

Recent advances in metasurface-based research have enabled significant reductions in the size and weight of optical devices. By employing metallic nanostructures with subwavelength dimensions, color filtering can be achieved through phenomena such as extraordinary optical transmission (EOT), which allows specific bands of visible light to pass through. However, conventional EOT-based color filters often suffer from strong side peaks outside the desired transmission band, degrading color purity and hindering accurate color reproduction. In this study, we propose an ultrathin, polarization-independent color filter based on a nanohole array that utilizes the EOT effect while effectively suppressing unwanted side peaks. To achieve this, we introduce a modified design in which additional metallic triangular edges are placed around a hole in a conventional hole array. This configuration suppresses higher-order diffraction modes and enables selective transmission at RGB wavelengths, thereby improving spectral selectivity and overall color performance. Full article

Surface plasmon resonance (SPR) sensors based on nanostructured metasurfaces offer enhanced sensitivity through engineered electromagnetic responses. In this study, we present an analytical and numerical investigation of the plasmonic behavior of gold nanopillar (Au-NP) and nanohole (Au-NH) arrays under both p- and s-polarized illumination, employing the Effective Medium Theory (EMT) in combination with the Transfer Matrix Method (TMM). The study combines Effective Medium Theory (EMT) and the Transfer Matrix Method (TMM) to describe the macroscopic optical response of multilayer plasmonic systems. For p-polarization, the nanostructure geometry strongly modulates the real and imaginary parts of the effective permittivity, with nanoholes supporting stronger SPR coupling and reduced optical losses compared to nanopillars. Under s-polarization, the effective permittivity remains largely invariant, primarily driven by the filling fraction. The analysis reveals that polarization-dependent behavior arises from boundary-condition-mediated coupling mechanisms governing surface plasmon excitation, aligning with classical plasmonic theory. Benchmarking against analytical dispersion relations and published experimental data for Au/BK7 systems shows close agreement within ±2°, confirming the physical consistency of the EMT–TMM framework. These results provide a systematic description of how polarization and filling fraction jointly modulate SPR coupling. The results offer a foundation for the rational design of plasmonic coatings and SPR-supporting metasurfaces by elucidating macroscopic coupling trends; however, no quantitative sensor performance metrics, such as refractive index sensitivity or figure of merit, are evaluated in this work. Full article

Dielectric-engineered plasmonic nano-hole arrays (NHAs) offer an effective approach for precisely controlling subwavelength light confinement. Here, we investigate wavelength compression in aluminum NHAs filled with three different dielectric materials such as Al₂O₃, MoO₃, and TiO₂ under illumination by a 1.5 µm lightwave. The hole radius varies from 300 nm to 500 nm to analyze the combined effects of geometry and dielectric environment on the plasmonic response. The NHAs filled with Al₂O₃ exhibit a pronounced and monotonic increase of the compressed wavelength with decreasing hole radius, indicating strong geometric tunability of the dominant plasmonic mode. Meanwhile, the structures filled with MoO₃ or TiO₂ show weak wavelength variations over the same radius range. Spatially resolved analysis at these nano-holes reveals nearly position-independent wavelength squeezing for Al₂O₃, whereas noticeable spatial variations appear for MoO₃ and TiO₂ at hole radii of 450 nm and 400 nm, respectively. The observed wavelength compression is attributed to hybrid plasmonic modes originating from the interplay between in-hole-like compressed cavity modes and localized surface plasmon polaritons. Our findings demonstrate how dielectric composition tunes wavelength compression in plasmonic NHAs, offering practical guidelines for designing the near-infrared plasmonic devices. Full article

The detection of chiral properties is crucial for pharmacology and biochemistry, yet standard circular dichroism spectroscopy suffers from low sensitivity when probing minute sample volumes. While complex asymmetric chiral nanostructures can enhance these Circular Dichroic (CD) signals, their fabrication is intricate and costly. In this work, we analyzed an alternative based on extrinsic chirality in achiral square arrays of plasmonic circular NHAs realized via Displacement Talbot Lithography (DTL), thus exploring the chiroptical response arising from symmetry breaking induced by oblique illumination. Unlike isolated nanoparticles, nanohole arrays (NHAs) support propagating Surface Plasmon Polaritons (SPPs), allowing for unique light confinement capabilities essential for high-throughput sensing. A careful characterization in terms of Stokes parameters has been performed over a selected range of different optical angles of incidence and sample orientation to disentangle extrinsic chiral contribution from spurious effects related to sample imperfections. By optimizing such extrinsic chiral contributions, enhanced chiroptical response could be engineered by significantly amplifying the interaction between light and chiral biomolecules trapped within the holes. This methodology establishes DTL-fabricated achiral NHAs as an ultrasensitive, cost-effective platform for the detection and discrimination of enantiomers in biosensing applications. Full article

The operational ability of a unit or mechanism depends mainly on the quality of the mechanically produced working surfaces. Many materials can be assigned to a group of hard-to-cut materials that includes titanium- and aluminum-based alloys, a new class of heat-resistant alloys, SiCp/Al composites, hard alloys, and other alloys. The difficulties in their machining are related not only to the high temperatures achieved on the contact pads under mechanical load and the extreme cutting conditions but also to the properties of those materials, which affect the adhesion of the chip to the tool faces, hindering chip flow. One of the possible solutions to reduce those effects and improve the operational life of the tool, and as a consequence, the final quality of the working surface of the unit, is texturing the rake face of the tool with microgrooves or nanogrooves, microholes or nanoholes (pits, dimples), micronodes, cross-chevron textures, and other microtextures, the depth of which is in the range of 3.0–200.0 µm. This review is addressed at systematizing the data obtained on micro- and nanotexturing of PCD tools for cutting hard-to-cut materials by different techniques (fiber laser graving, femto- and nanosecond laser, electrical discharge machining, fused ion beam), additionally subjected to fluorination and dip- and drop-based coatings, and the effect created by the use of the textured PCD tool on the machined surface. Full article

We introduce an equal-phase method to design the polarization-insensitive metasurface lens, composed of subwavelength nano-holes etched into a silver film. By calculating the intensity distribution under linearly, circularly, and elliptically polarized light illumination, we demonstrate that the designed metasurface lens can effectively focus incident light with different polarization states. Moreover, we confirm that this polarization-insensitive property of the designed lens maintains stable focus ability across the entire visible light bandwidth, exhibiting a broadband performance. It is important to note that the metasurface lens design based on the equal-phase method is not limited by specific nanostructure units and exhibits considerable flexibility. For some complex application conditions, we also explore the design of polarization-insensitive lenses capable of generating longitudinal and transverse dual focal spots. The metasurface lenses and the design method proposed in this paper may provide a reference for the development and application of polarization-independent components in integrated photonic devices. Full article

Plasmonic nanohole arrays (NAs) integrating Au and hydrogen-responsive Mg enable dynamic spectral tuning via the Mg → MgH₂ transition. Using finite-difference time-domain (FDTD) numerical simulations, we systematically investigate how layer sequence, Au/Mg ratio, total thickness, and stacking number govern extraordinary optical transmission (EOT) resonances. Mg–Au–Mg architectures exhibit the strongest hydrogen response, delivering resonance shifts up to 275 nm and FoM > 1, owing to direct plasmon–hydride coupling at surface Mg layers. Varying the Au/Mg ratio reveals a trade-off: Mg-rich stacks maximize spectral tunability but suffer from broadened, unstable resonances, while Au-rich stacks sustain sharp modes with limited sensitivity; optimal performance arises at intermediate compositions. Thickness dependence shows that ultrathin films (<50 nm) achieve giant shifts (>600 nm) with high contrast, whereas thicker multilayers lose responsiveness. Finally, stacking analysis uncovers an odd–even effect, with Mg-terminated arrays providing larger shifts than Au-terminated ones. These results establish design rules for hydrogen plasmonic sensors, emphasizing resonance engineering through rational layer ordering and composition control. Full article

Local droplet etching and subsequent refilling enables the fabrication of highly symmetric quantum dots with low fine structure splitting, suitable for generating polarization entangled photons. While well established in GaAs/Al_xGa_1−xAs, this approach does not yield emission in the telecom bands required for low loss fiber-based quantum communication. To achieve emission at 1.55 μm, local droplet etching must be adapted to alternative material platforms such as InP. Here, we systematically investigate how the etching material deposition rate and etching time influence nanohole morphology in In_0.52Al_0.48As layers lattice-matched to InP. In the first experiment, InAl was deposited at fluxes of 0.2–4.0 Å s⁻¹ at $T_{etch} = 350 °\mathrm{C}$ and 460 °C. Lower fluxes produced nanoholes with lower density and larger ring diameters, indicating fewer and larger initial droplets, consistent with scaling theory. The average nanohole diameter decreased monotonically with increasing flux, whereas the average depth showed no clear dependence on flux. In the second experiment, etching times of 30–600 s were tested for InAl, In, and Al droplets. Average nanohole diameters remained constant for Al across all etching times, but decreased for In and InAl with increasing etching time, suggesting sidewall redeposition during etching. For all droplet types, depths peaked at intermediate times and decreased for prolonged etching, consistent with material diffusion into the nanohole after droplet consumption. Full article

The electromagnetic density of states (EM-DOS) plays a crucial role in understanding light–matter interactions, especially at metal–dielectric interfaces. This study explores the impact of interface geometry, material properties, and nanostructures on EM-DOS, with a focus on surface plasmon polaritons (SPPs) and evanescent waves. Using a combination of analytical and numerical methods, the behavior of EM-DOS is analyzed as a function of distance from metal–dielectric interfaces, showing exponential decay with penetration depth. The influence of different metals, including copper, gold, and silver, on EM-DOS is examined. Additionally, the effects of dielectric materials, such as Ti${\mathrm{O}}_2$, PMMA, and ${\mathrm{Al}}_2$${\mathrm{O}}_3$, on the enhancement of electromagnetic field confinement are discussed. The study also investigates the effect of nanostructures, like nanohole and nanopillar arrays, on EM-DOS by calculating effective permittivity and analyzing the interaction of quantum emitters with these structures. Results show that nanopillar arrays enhance EM-DOS more effectively than nanohole arrays, especially in the visible spectrum. The findings provide insights into optimizing plasmonic devices for applications in sensing, quantum technologies, and energy conversion. Full article