Search Results (101)

Sensitive and on-site detection of pesticide residues remains a critical challenge for food safety, particularly in developing regions where rapid screening tools are urgently needed. Herein, we report a flexible surface-enhanced Raman scattering (SERS) platform based on triangular silver nanoplates (TSNPs) integrated onto a polydimethylsiloxane (PDMS) substrate, enabling sensitive and conformal detection of paraquat residues on agricultural surfaces. TSNPs were synthesized via a seed-mediated photochemical growth method and formulated into a TSNP ink, which was directly deposited onto oxygen-plasma-treated and thiol-functionalized PDMS substrates. Owing to the highly anisotropic geometry and sharp edges of TSNPs, the flexible SERS substrate exhibits strong localized surface plasmon resonance (LSPR) enhancement and mechanically stable electromagnetic hot spots. Systematic optimization of TSNP optical absorbance revealed that uniform nanoplate distribution and optimal hotspot density were achieved at an absorbance of 2.0. The SERS performance was evaluated using rhodamine 6G under front-side and back-side illumination configurations, demonstrating good signal reproducibility and a detection limit of approximately 10⁻⁵ M. Notably, back-side illumination through the PDMS layer provided superior SERS responses due to improved optical transmission and light–matter interaction. The practical applicability was further demonstrated through back-side SERS detection of paraquat on aluminum foil as a model surface, achieving a lowest detectable concentration of 5 × 10⁻⁶ M, followed by damage-free detection on Chinese pear peels. This work highlights a reliable and nondestructive flexible SERS platform for on-site pesticide residue monitoring. Full article

In this paper, a notch bandpass filter based on spoof surface plasmon polaritons (SSPPs) is presented and systematically analyzed. The bandpass response is realized by a momentum-matched SSPP transition section and two SSPP resonant units. An annular slot defected ground structure (DGS), evolved from the conventional dumbbell DGS is etched on the ground plane to introduce an in-band notch. The notch frequency can be controlled independently by the DGS geometric parameters while the passband edges remain nearly unchanged. A prototype is fabricated and measured. The measured results agree well with the simulations. Two passbands are obtained from 0.67 to 3.40 GHz and from 3.67 to 4.77 GHz. The insertion loss is 0.48 dB at 2.00 GHz and 1.11 dB at 4.22 GHz. The return loss on both sides of the notch is better than −10 dB. A notch centered at 3.50 GHz provides −25 dB rejection. The compact structure and the independently controllable notch frequency make the proposed filter suitable for narrowband interference suppression in microwave and millimeter-wave front ends. Full article

The synthesis of continuous non-linear metal nanostructures at the micro and nanoscale remains a challenging frontier in nanotechnology due to inherent synthetic constraints. This study introduces an innovative chemical methodology for fabricating continuous rings and diverse geometries via the chemical fusion of gold nanorods (AuNRs) on a solid substrate. Initially, aqueous solutions of cetyltrimethylammonium bromide (CTAB)-coated AuNRs were deposited and dried on a solid substrate, resulting in the self-assembly of ring-like arrays. Subsequent chemical growth of the AuNRs in all dimensions was achieved using an aqueous solution of Au(I)/CTAB/Ascorbic Acid (AA), enabling their fusion into continuous structures. This approach permits the formation of arbitrary shapes by pre-arranging AuNRs, thereby opening new avenues for the exploration of non-linear nanostructures with potentially novel plasmonic and electronic properties. The capability to engineer such complex nanostructures is pivotal for advancing fields such as photonics, electronics, and sensing, where the unique optical and electronic properties of gold nanostructures can be exploited for cutting-edge applications. Furthermore, this technique shows a significant promise for the fabrication of various micro- and nanodevices and the seamless interconnection of components in integrated electronic circuits, potentially leading to more efficient and miniaturized electronic systems. The broader implications of this research are significant, offering a potential pathway to the development of nanomaterials and devices that could benefit various industries and technological processes. Full article

The development of anisotropic gold nanostructures supporting localized surface plasmon (LSP) resonances in the near-infrared (NIR) biological window is of great interest for diagnostic and therapeutic nanotechnologies. Here, we report gold open-shell nanoparticles (AuOSNs), a symmetry-broken nanoshell architecture exhibiting strong NIR surface-enhanced Raman scattering (SERS) activity. AuOSNs were fabricated via a surfactant-free strategy combining bottom-up silica sphere assembly with a simple top-down gold deposition process, without using highly cytotoxic surfactants such as cetyltrimethylammonium bromide (CTAB). Boundary element method (BEM) simulations revealed that the asymmetric open-shell geometry induces NIR LSP resonances with pronounced electromagnetic field localization near the opening edges, depending on excitation configuration. Consistent with these predictions, extinction spectra of AuOSNs dispersed in water showed an LSP resonance peak at ~793 nm, close to the 785 nm excitation wavelength for SERS. In aqueous dispersion, AuOSNs modified with 4-mercaptobenzoic acid (4-MBA) exhibited strong SERS activity with enhancement factors of ~10⁶. Furthermore, polyethylene glycol (PEG)-modified MBA/AuOSNs showed negligible cytotoxicity in vitro. SERS imaging confirmed that PEG/MBA/AuOSNs enable visualization of HeLa cells via characteristic MBA SERS signals. These results demonstrate that surfactant-free AuOSNs provide a biocompatible platform for NIR-excited SERS sensing and cellular imaging, highlighting their potential in plasmonic bioimaging applications. Full article

Gold nanorods (AuNRs) were synthesized and optimized with the aim of obtaining strongly hydrophilic nanomaterials, suitable as a drug delivery system (DDS) for copper-based drugs. After careful purification, AuNRs were characterized by ultraviolet–visible–near-infrared spectroscopy (UV–Vis–NIR), showing two typical localized surface plasmon resonance (LSPR) bands in the range 550–750 nm. Fourier Transform Infrared (FT-IR) and high-resolution X-ray photoelectron (HR-XPS) spectroscopies verified the surface functionalization. Transmission electron microscopy (TEM) showed AuNRs with regular shape and size, with an aspect ratio (AR) of 2.6. Dynamic Light Scattering (DLS) measurements confirmed the size and the stability in water for up to 3 months. The AuNRs were conjugated with copper(I) drugs, i.e., [Cu(PTA)₄]BF₄ (PTA = 1,3,5-triaza-7-phosphadamantane). The drug loading procedures and efficiency were optimized, and the best loading was η (%) = 50 ± 7%. The non-covalent interactions of the Cu(I) complex with the AuNRs were studied by means of UV–Vis–NIR, ζ-potential, HR-TEM, FT-IR, synchrotron radiation-induced X-ray photoelectron (SR-XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. The MTT assay performed on Vero E6 cells showed that AuNRs and AuNR-Cu(I) conjugates had no significant effect on cell viability, being biocompatible, causing a reduction in cell viability only after prolonged exposure. Full article

Negative refraction of nanolight (e.g., polaritons, hybrid light, and matter excitation) provides a promising building block for nanophotonics, as it paves the way for developing cutting-edge nanoscale applications, such as super-resolution and subwavelength imaging. In the visible regime, negative refraction of surface plasmon polaritons has been extensively studied in conventional plasmonic and metamaterial systems; however, the inherent metallic losses remain a challenge that hinders their practical applications. Herein, we demonstrate negative refraction of low-loss and highly confined hyperbolic plasmon polaritons (HPPs) in a lateral heterojunction of a natural hyperbolic van der Waals material, molybdenum dioxide chloride (MoOCl₂). Owing to the exotic and ray-like propagating properties of HPPs, the negative refraction-inspired superlens can easily reach into the deep subwavelength scale, with spatial confinement of 800 nm near-infrared light wavelengths to below 150 nm focal spots. By elaborately adjusting the orientation directions of two-sided MoOCl₂, the mirror-symmetric superlensing effect can be tilted, and therefore, the focal spots are tuned and steered to deviate from the vertical interfacial lines. Our results applying the concepts of in-plane negative refraction with vdW materials achieve deep subwavelength light confinement and manipulation, offering new possibilities for constructing efficient and compact nanophotonic and opto-electronic devices. Full article

Low-temperature Ag₂Se is a narrow-band semiconductor, with its transport and optical properties significantly influenced by the local coordination environment. This study investigates the effects of La and Gd incorporation using DFT+U calculations and Ag-K edge EXAFS analysis. Analysis of electron localization function (ELF) and charge density differences reveals increased electron localization at dopant sites. Additionally, k³χ(k) and wavelet transforms demonstrate that the first M-Se shell shifts from approximately 1.346 Å in Ag-Se to around 1.386 Å and 1.291 Å for La-Se and Gd-Se, respectively (phase-uncorrected), thereby confirming dopant-specific lattice distortions while maintaining the orthorhombic framework. The observed changes are associated with an increase in dielectric strength, with ε₂ increasing from approximately 30–40 in pristine Ag₂Se to around 50–60 for La and 70–80 for Gd at low photon energies, alongside enhanced absorption nearing 1.32–1.34 × 10⁵ cm⁻¹. The characteristic plasmon resonance in the range of 15–20 eV is maintained. Rare-earth substitution effectively adjusts local bonding and low-energy optical response in Ag₂Se, with Gd demonstrating the most significant impact among the examined dopants. Full article

Au–ZnO heterogeneous nanoparticles (NPs) were successfully synthesized, and the intrinsic correlation between their spectral evolution and interfacial growth mechanism was systematically elucidated. With increasing Au content, the SPR absorption peak of Au exhibits a pronounced red shift, while the defect-related emission of ZnO is suppressed and the band-edge emission becomes broadened. These spectral variations are closely coupled with the interfacial growth process. Interfacial electron transfer and the formation of a Schottky barrier induce charge redistribution within ZnO and reduce oxygen vacancies, enabling ZnO to preferentially nucleate on the Au surface and subsequently evolve into a pyramidal structure. The resulting morphological transformation further enhances electron depletion and plasmonic coupling, lowering the effective plasmonic energy of Au and deepening the SPR red shift. Quantitative analysis based on Mie theory shows that approximately 12% of the free electrons in Au participate in interfacial transfer, confirming the cooperative role of strong electronic coupling in governing both growth dynamics and optical responses. This study provides deeper insight into the photophysical mechanisms of Au–ZnO heteronanocrystals and offers guidance for designing noble metal–semiconductor composites with tunable optoelectronic properties. Full article

Biosensing technology serves as a cornerstone in biomedical diagnostics, environmental monitoring, personalized medicine, and wearable devices, playing an indispensable role in precise detection and real–time monitoring. Compared with traditional sensing platforms, functional nanomaterials—by virtue of their ultra–large specific surface area, exceptional optoelectronic properties, and superior catalytic activity—significantly enhance the sensitivity, selectivity, and response speed of biosensors. This has enabled ultrasensitive, rapid, and even in situ detection of disease biomarkers, pollutants, and pathogens. This review summarizes recent advances in five key categories of functional nanomaterials—metallic, semiconductor, carbon–based, two–dimensional, and stimulus–responsive materials—for advanced biosensing applications. It elucidates the structure–property relationships governing sensing performance, such as the surface plasmon resonance of gold nanoparticles and the high carrier mobility of graphene, and analyzes the core mechanisms behind optical sensing, electrochemical sensing, and emerging multimodal sensing strategies. With a focus on medical diagnostics, wearable health monitoring, and environmental and food safety surveillance, the review highlights the application value of functional nanomaterials across diverse scenarios. Current research is progressively moving beyond single–performance optimization toward intelligent design, multifunctional integration, and real–world deployment, though challenges related to industrial application remain. Finally, the review outlines existing issues in the development of functional nanomaterial–based biosensors and offers perspectives on the integration of nanomaterials with cutting–edge technologies and the construction of novel sensing systems. This work aims to provide insights for the rational design of functional nanomaterials and the cross–disciplinary translation of biosensing technologies. Full article

Optical skyrmions, as topologically protected quasiparticles, hold great promise for on-chip photonic technologies. However, achieving programmable control over their properties through subtle structural changes remains challenging. This study introduces a minimal perturbation engineering strategy on a plasmonic metasurface. By applying controlled geometric perturbations (either continuous shortening or discrete segmentation) to a single edge of a hexagonal groove structure, combined with incident phase perturbations, we systematically manipulate the evolution of the skyrmion texture. These minimal perturbations induce reproducible shifts in the skyrmions’ center intensity and peak position, yielding up to ~32% center suppression, while the global topological charge remains conserved. This “geometry × phase” dual-perturbation approach provides a straightforward and efficient approach for engineering programmable topological light fields on a chip, with promising applications in integrated photonic devices. Full article

The pervasive environmental contamination by micro- and nanoplastics (MNPs) presents a formidable analytical challenge, necessitating the development of rapid and sensitive detection methods. While conventional techniques often suffer from limitations in sensitivity and throughput, fluorescent probe-based technology has emerged as a powerful alternative. This review charts the evolution of these probes, from initial stains relying on hydrophobic adsorption to advanced molecular designs engineered for specific chemical recognition. We critically examine key operational mechanisms, including the solvatochromic response of Nile Red, polarity-discriminatory probes enabling a “microplastic rainbow,” and targeted systems achieving turn-on fluorescence via restriction of intramolecular rotation. Furthermore, we highlight cutting-edge signal enhancement strategies, such as plasmon- and metal-enhanced fluorescence, which amplify detection to the femtogram level. Special emphasis is placed on the distinct challenges posed by nanoplastics, including their propensity for aggregation in aqueous matrices that exacerbates false positives and their superior ability to breach biological barriers, and how AIE luminogens and PEF/MEF strategies mitigate these issues through enhanced signal-to-noise ratios and subcellular resolution, differing from their application to microplastics. Critically, we address the imperative for low-toxicity probe designs, emphasizing biocompatibility and biodegradability criteria to facilitate safe, long-term in vivo tracking and widespread ecological surveillance. The integration of these sophisticated probes with smart, “activate-on-target” systems is paving the way for next-generation MNP analysis, offering critical insights for environmental monitoring and toxicological assessment. Full article

Recent theoretical studies have shown that gapped Dirac materials (such as gapped monolayer graphene) optically pumped with circularly polarized light can host edge-localized plasmon modes with nonreciprocal dispersions driven by valley population imbalance. Here, we extend this framework to Bernal-stacked bilayer graphene. Using the Wiener–Hopf method, we compute the exact edge plasmon dispersion, confinement length, and electric potential. Our results show that bilayer graphene exhibits stronger nonreciprocity in edge plasmons, requiring approximately one order of magnitude lower pump amplitude to achieve splitting compared with monolayer Dirac systems. Furthermore, the gate-tunable energy gap of bilayer graphene provides an additional degree of control, positioning optically pumped bilayer graphene as a versatile platform for magnet-free nonreciprocal plasmonics. Full article

Surface-enhanced Raman spectroscopy (SERS) enables ultra-sensitive molecular detection and has broad analytical and biomedical applications; recent advances focus on high-performance substrates and innovative detection strategies. However, achieving controllable and reproducible substrate fabrication—particularly using natural templates such as hair—remains challenging, limiting SERS application in trace analysis and on-site detection. This study developed a single-hair in situ SERS platform using a natural hair template. Confinement within hair cuticle grooves and capillary-evaporation assembly enables dense arrangement of cetyltrimethylammonium bromide-coated Au nanorods and polyvinylpyrrolidone-coated Au nanoparticles, forming uniform plasmonic nanoarrays. Spectroscopy and microscopy analyses confirmed the regular alignment of nanostructures along the hair axis with denser packing at the edges. The platform detected crystal violet at 10⁻⁹ M, yielding clear signals, negligible background, and stable peaks after repeated washing. For p-phenylenediamine, enhancement was observed down to 10⁻⁶ M. On the platform, a concentration-dependent response appeared within 10⁻³–10⁻⁵ M, with spatial Raman imaging along the hair axis. Capillary-evaporation coupling and interfacial wettability facilitated solute enrichment from larger to smaller gap hotspots, improving signal-to-noise ratio and reproducibility. This portable, low-cost, and scalable method supports rapid on-site screening in complex matrixes, offering a general strategy for hotspot engineering and programmable assembly on natural templates. Full article

Nanophotonics, the study of light–matter interactions at the nanometer scale, has emerged as a transformative field that bridges photonics and nanotechnology. Using engineered nanomaterials—including plasmonic metals, high-index dielectrics, two-dimensional (2D) materials, and hybrid systems—nanophotonics enables light manipulation beyond the diffraction limit, unlocking novel applications in sensing, imaging, and quantum technologies. This review provides a comprehensive overview of recent advances (post-2020) in nanophotonic materials, fabrication methods, and their cutting-edge applications. We first discuss the fundamental principles governing nanophotonic phenomena, such as localized surface plasmon resonances (LSPRs), Mie resonances, and exciton–polariton coupling, highlighting their roles in enhancing light–matter interactions. Next, we examine state-of-the-art fabrication techniques, including top-down (e.g., electron beam lithography and nanoimprinting) and bottom-up (e.g., chemical vapor deposition and colloidal synthesis) approaches, as well as hybrid strategies that combine scalability with nanoscale precision. We then explore emerging applications across diverse domains: quantum photonics (single-photon sources, entangled light generation), biosensing (ultrasensitive detection of viruses and biomarkers), nonlinear optics (high-harmonic generation and wave mixing), and integrated photonic circuits. Special attention is given to active and tunable nanophotonic systems, such as reconfigurable metasurfaces and hybrid graphene–dielectric devices. Despite rapid progress, challenges remain, including optical losses, thermal management, and scalable integration. We conclude by outlining future directions, such as machine learning-assisted design, programmable photonics, and quantum-enhanced sensing, and offering insights into the next generation of nanophotonic technologies. This review serves as a timely resource for researchers in photonics, materials science, and nanotechnology. Full article

In this paper, the electronic structure and photoelectric properties of graphdiyne nanotubes with armchair (A-GDYNT) and zigzag (Z-GDYNT) types have been studied. Calculations show that as n decreases, the divergence in gap values between (n)-A-GDYNT and (n)-Z-GDYNT increases. This is mainly attributed to the edge effect arising from their different boundaries. Plasmon spectra are generated in all three directions of X, Y, and Z, with the spectra along the Z direction being more prominent. The optical absorption process exhibits not only the nonlinear nature of the GDYNTs, but also a good regularity, especially in the infrared region. As the pore size increases, the A-GDYNT and Z-GDYNT exhibit striking differences in how their charge self-organizes. Likewise, notable distinctions emerge in the evolutionary pattern of their charge difference density under excitation. The porous structure and excellent sorption ability in various light regions make GDYNTs have great potential application in the field of photocatalysis and far infrared detection. Full article