Search Results (87)

ZnO nanostructures have attracted attention as transducer materials in optical biosensing platforms due to their wide bandgap, defect-mediated photoluminescence, high surface-to-volume ratio, and tunable morphology. This review examines how the dimensionality of ZnO nanostructures affects biosensor performance, particularly in terms of charge transport, signal transduction, and biomolecule immobilization. The synthesis approaches are discussed, highlighting how they influence crystallinity, defect density, and surface functionalization potential. The impact of immobilization strategies on sensor stability and sensitivity is also assessed. The role of ZnO in various optical detection schemes, including photoluminescence, surface plasmon resonance (SPR), localized (LSPR), fluorescence, and surface-enhanced Raman scattering (SERS), is reviewed, with emphasis on label-free and real-time detection. Representative case studies demonstrate the detection of clinically and environmentally relevant targets, such as glucose, dopamine, cancer biomarkers, and SARS-CoV-2 antigens, with limits of detection in the pico- to femtomolar range. Recent developments in ZnO-based hybrid systems and their integration into fiber-optic and microfluidic platforms are explored as scalable solutions for portable, multiplexed diagnostics. The review concludes by outlining current challenges related to reproducibility, long-term operational stability, and surface modification standardization. This work provides a framework for understanding structure–function relationships in ZnO-based biosensors and highlights future directions for their development in biomedical and environmental monitoring applications. Full article

Finding high-performance and low-cost materials is essential for high-quality photocatalytic water purification to expand the spectral response and improve light utilization. In this paper, we used relatively inexpensive materials such as Ag and TiO₂. The influence of particle spacing, core radius, shell thickness, environmental refractive index, and incident light direction angle on the light absorption and scattering properties, local electric field enhancement, and photothermal effect of the Ag@TiO₂ core–shell nanosphere dimer is investigated by using the finite element method and the finite difference time domain. The formation mechanism of multipole resonance mode of the dimer is revealed by means of the multipole decomposition theory and the internal current distribution of the particles. The results show that light absorption and scattering of the dimer can be tuned within the visible light range by changing the particle spacing, core radius, and shell thickness. With the azimuth angle of incident light increases, the longitudinal local surface plasmon resonance (L-LSPR) mode will transform into the transverse local surface plasmon resonance (T-LSPR) mode, and the L-LSPR mode makes the dimer have better local electric field enhancement. Strong light absorption can easily cause a sharp increase in the temperature around the dimer, accelerating the rate of catalytic oxidation reactions and the elimination of bacteria and viruses in water. Strong light scattering causes a significant enhancement of the electric field between the particles, making the generation of hydroxyl and other active oxides more efficient and convenient. This work establishes a theoretical basis for designing efficient water purification photocatalysts. Full article

Volatile organic compound (VOC) monitoring is crucial for environmental safety and health, but conventional gas sensors often suffer from poor selectivity or lack spatial information. Here, we report a localized surface plasmon resonance (LSPR) gas sensor based on Au nano-urchins coated with a zeolitic imidazolate framework (ZIF-8) for both the quantitative detection and visualization of VOCs. Substrates were fabricated by immobilizing Au nano-urchins (~90 nm) on 3-aminopropyltriethoxysilane-modified glass and subsequently growing ZIF-8 crystals (~250 nm) for different durations. Scanning electron microscopy and optical analysis revealed that 90 min of ZIF-8 growth provided the optimal coverage and strongest plasmonic response. Using a spectrometer-based LSPR system, the optimized substrate exhibited clear, concentration-dependent responses to three representative VOCs, 2-pentanone, acetic acid, and ethyl acetate, over nine concentrations, with detection limits of 12.7, 14.5, and 36.3 ppm, respectively. Furthermore, a camera-based LSPR visualization platform enabled real-time imaging of gas plumes and evaporation-driven diffusion, with differential pseudo-color mapping providing intuitive spatial distributions and concentration dependence. These results demonstrate that ZIF-8-modified Au nano-urchin substrates enable sensitive and reproducible VOC detection and, importantly, transform plasmonic sensing into a visual modality, offering new opportunities for integrated LSPR–surface-enhanced Raman scattering dual-mode gas sensing in the future. Full article

Background: One of the most widely used metal nanoparticles in biological applications is gold, which has unique physicochemical characteristics. Strong localized surface plasmon resonance (LSPR) endows them with exceptional optical properties that facilitate the development of innovative methods for biosensing, bioimaging, and cancer research, particularly in the context of photothermal and photodynamic therapy. Methods: This study marked the first time that Mandragora autumnalis ethanolic extract (MAE) was utilized in the environmentally friendly synthesis of gold nanoparticles (AuNPs). Several characterization methods, including dynamic light scattering analysis (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and biological methods, were used to emphasize the anti-cancerous activity of the biogenic AuNPs. Results: MAE-AuNPs showed a surface plasmon resonance band at 570 nm. DLS and SEM demonstrated the synthesis of small, spherical AuNPs with a zeta potential of −19.07 mV. The crystalline nature of the AuNPs was confirmed by the XRD pattern, and data from FTIR and TGA verified that MAE-AuNPs played a part in stabilizing and capping the produced AuNPs. In addition, the MAE-AuNPs demonstrated their potential effectiveness as antioxidant and anticancer therapeutic agents by demonstrating radical scavenging activity and anticancer activity against a number of human cancer cell lines, specifically triple-negative breast cancer cells. Conclusions: Green synthesis techniques are superior to other synthesis methods because they are simple, economical, energy-efficient, and biocompatible, which reduces the need for hazardous chemicals in the reduction process. This article highlights the significance of characterizing MAE-AuNPs and evaluating their antioxidant and anticancer properties. Full article

Brain natriuretic peptide (BNP) is an important biomarker for the diagnosis and prediction of chronic heart failure (CHF). Aiming at the problems of the low sensitivity and poor portability of traditional BNP detection methods, this study proposes a Surface-enhanced Raman-scattering (SERS) fiber-optic sensor based on a multimode fiber (MMF)–no core fiber (NCF) structure. The sensor achieves BNP detection by significantly amplifying the Raman signal of the toluidine blue (TB) marker through the synergistic effect of NCF’s unique optical transmission modes and localized surface plasmon resonance (LSPR). To optimize the sensor performance, we first investigated the effect of the NCF length on the Raman signal, using Rhodamine 6G (R6G), and determined the optimal structural parameters. Combined with the microfluidic chip integration technology, the antibody–BNP–antibody sandwich structure was adopted, and TB was used as the Raman label to realize the quantitative detection of BNP. Experimental results demonstrate that the detection limit of the sensor is lower than the clinical diagnostic threshold and exhibits stability. The sensor sensitivity can be adjusted by regulating the laser power. With its stability and high portability, this sensor provides a new solution for the early diagnosis of heart failure and demonstrates broad application prospects in biomarker detection. Full article

Exosomes are nanoscale extracellular vesicles (EVs) that carry biomolecular signatures reflective of their parent cells, making them powerful tools for non-invasive diagnostics and therapeutic monitoring. Despite their potential, clinical application is hindered by challenges such as low abundance, heterogeneity, and the complexity of biological samples. To address these limitations, plasmonic biosensing technologies—particularly propagating surface plasmon resonance (PSPR), localized surface plasmon resonance (LSPR), and surface-enhanced Raman scattering (SERS)—have been developed to enable label-free, highly sensitive, and multiplexed detection at the single-vesicle level. This review outlines recent advancements in nanoplasmonic platforms for exosome detection and profiling, emphasizing innovations in nanostructure engineering, microfluidic integration, and signal enhancement. Representative applications in oncology, neurology, and immunology are discussed, along with the increasingly critical role of artificial intelligence (AI) in spectral interpretation and diagnostic classification. Key technical and translational challenges—such as assay standardization, substrate reproducibility, and clinical validation—are also addressed. Overall, this review highlights the synergy between exosome biology and plasmonic nanotechnology, offering a path toward real-time, precision diagnostics via sub-femtomolar detection of exosomal miRNAs through next-generation biosensing strategies. Full article

Magnetotactic bacteria (MTB), a unique group of Gram-negative prokaryotes, have the remarkable ability to biomineralize magnetic nanoparticles (MNPs) intracellularly, making them promising candidates for various biomedical applications such as biosensors, drug delivery, imaging contrast agents, and cancer-targeted therapies. To fully exploit the potential of MTB, a precise understanding of the structural, surface, and functional properties of these biologically produced nanoparticles is required. Given these concerns, this review provides a focused synthesis of the most widely used microscopic and spectroscopic methods applied in the characterization of MTB and their associated MNPs, covering the latest research from January 2022 to May 2025. Specifically, various optical microscopy techniques (e.g., transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM)) and spectroscopic approaches (e.g., localized surface plasmon resonance (LSPR), surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopy (XPS)) relevant to ultrasensitive MTB biosensor development are herein discussed and compared in term of their advantages and disadvantages. Overall, the novelty of this work lies in its clarity and structure, aiming to consolidate and simplify access to the most current and effective characterization techniques. Furthermore, several gaps in the characterization methods of MTB were identified, and new directions of methods that can be integrated into the study, analysis, and characterization of these bacteria are suggested in exhaustive manner. Finally, to the authors’ knowledge, this is the first comprehensive overview of characterization techniques that could serve as a practical resource for both younger and more experienced researchers seeking to optimize the use of MTB in the development of advanced biosensing systems and other biomedical tools. Full article

This study investigates the effects of substrate flexibility and metal deposition methods on piezoelectric-enhanced Surface-Enhanced Raman Scattering (SERS) in metal-deposited ZnO nanorod (NR) nanocomposites (NCPs). ZnO NRs were grown on both rigid (ITO–glass) and flexible (ITO-PET) substrates, followed by gold (Au) deposition by pulsed-laser-induced photolysis (PLIP) or silver (Ag) deposition by thermal evaporation. Structural analysis revealed that ZnO NRs on flexible substrates exhibited smaller diameters (60–80 nm vs. 80–100 nm on glass), a higher density, and diverse orientations that enhanced piezoelectric responsiveness. Optical characterization showed distinct localized surface plasmon resonance (LSPR) peaks at 420 nm for Ag and 525 nm for Au systems. SERS measurements demonstrated that Ag-ZnO NCPs achieved superior detection limits (10⁻⁹ M R6G) with enhancement factors of 10⁸–10⁹, while Au-ZnO NCPs reached 10⁻⁸ M detection limits. Mechanical bending of flexible substrates induced dramatic signal enhancement (50–100-fold for Au-ZnO/PET and 2–3-fold for Ag-ZnO/PET), directly confirming piezoelectric enhancement mechanisms. This work establishes quantitative structure–property relationships in piezoelectric-enhanced SERS and provides design principles for high-performance flexible sensors. Full article

In this study, we present a novel surface-enhanced Raman scattering (SERS) substrate based on porous silicon microcavities (PSiMCs) decorated with silver nanoparticles (AgNPs) for ultra-sensitive molecule detection. This substrate utilizes a dual enhancement mechanism: the localized surface plasmon resonance (LSPR) of AgNPs and the optical resonance of the PSiMC structure, which together create intense electromagnetic hot spots and prolong photon–molecule interactions. The porous architecture provides a large surface area for uniform nanoparticle distribution and efficient analyte adsorption. The AgNP/PSiMC substrate demonstrates an impressive detection limit of 1.0 × 10⁻¹³ M for rhodamine101 and 1.0 × 10⁻¹⁰ M for methyl parathion, outperforming many previously reported SERS platforms. Furthermore, the substrate exhibits excellent signal uniformity (RSD ≈ 6.14%) and long-term stability, retaining over 50% signal intensity after 28 days. These results underscore the potential of AgNP/PSiMCs as highly efficient, reproducible, and scalable SERS platforms for trace-level chemical and environmental sensing applications. Full article

Noble metal nanostructures have garnered significant attention for their exceptional optical properties, particularly Localized Surface Plasmon Resonance (LSPR), which enables pronounced near-field electromagnetic enhancements. Among these, bowtie nanoantennas (BNAs) are distinguished by their intense plasmonic coupling within nanogap regions, making them highly effective for applications such as surface-enhanced Raman scattering (SERS). However, the practical utility of conventional BNAs is often hindered by small hotspot areas and significant scattering losses at their peak near-field enhancement wavelengths. To overcome these limitations, we have designed a novel notch metal-insulator-metal bowtie nanoantenna (NMIM-BNA) structure. This innovative design integrates dielectric materials with Ag-BNA nanostructures and strategically positions arrays of silver (Ag) nanorods within the central nanogap. By coupling the larger NMIM-BNA framework with these smaller Ag nanorod arrays, higher-order plasmon modes (often referred to as dark modes) are effectively excited. Consequently, the NMIM-BNA exhibits substantial electric field enhancement, particularly at the Fano dip wavelength, arising from the efficient coupling of these higher-order plasmon modes with dipole plasmon modes. Compared to conventional Ag-BNA nanoantennas, our NMIM-BNA provides a significantly larger hotspot region and an enhanced near-field amplification factor, underscoring its strong potential for advanced SERS applications. Full article

This study presents a comprehensive numerical and experimental investigation of electric field enhancement in inverted-pyramidal gold (Au) array substrates, focusing on variable inter-pyramidal spacing for surface-enhanced Raman scattering (SERS) applications. We conducted a series of finite element method (FEM) simulations to model the spatial distribution of electromagnetic fields within plasmonic metasurfaces under 780 nm laser excitation. The results show that reducing the spacing between inverted pyramidal structures from 10 μm to 3.2 μm significantly increases the electric field intensity at both the tip and edge regions of the inverted-pyramidal Au structure, with maximum fields reaching 6.75 × 10⁷ V/m. Experimental SERS measurements utilizing 4-mercaptobenzoic acid as a Raman reporter support the simulation findings, indicating enhanced signal intensity in closely spaced configurations. These results confirm that geometric field concentration and plasmonic coupling are the dominant mechanisms responsible for SERS enhancement in these systems. This work provides a strategic framework for optimizing the geometry of plasmonic substrates to improve the sensitivity and reliability of SERS-based sensing platforms. Full article

Nanoplasmonic structures have emerged as a promising approach to address light trapping limitations in thin-film optoelectronic devices. This study investigates the integration of metallic nanoparticle arrays onto nanocrystalline silicon (nc-Si:H) thin films to enhance optical absorption through plasmonic effects. Using finite-difference time-domain (FDTD) simulations, we systematically optimize key design parameters, including nanoparticle geometry, spacing, metal type (Ag and Al), dielectric spacer material, and absorber layer thickness. The results show that localized surface plasmon resonances (LSPRs) significantly amplify near-field intensities, improve forward scattering, and facilitate coupling into waveguide modes within the active layer. These effects lead to a measurable increase in integrated quantum efficiency, with absorption improvements reaching up to 30% compared to bare nc-Si:H films. The findings establish a reliable design framework for engineering nanoplasmonic architectures that can be applied to enhance performance in photovoltaic devices, photodetectors, and other optoelectronic systems. Full article

Nanoporous metals have garnered significant attention in catalysis due to their unique three-dimensional interconnected network structure and pronounced localized surface plasmon resonance (LSPR) properties. In this study, nanoporous Au–Ag shells with varying pore sizes (8, 10, 12, and 18 nm) were synthesized, and their catalytic efficiencies were systematically evaluated. The conversion of p-nitrothiophenol (PNTP) to dimercapto-azobenzene (DMAB) was used to investigate the influence of pore size on the reaction kinetics and surface-enhanced Raman scattering (SERS) effects. Experimental results reveal that the nanoporous Au–Ag shells with a 12 nm pore size exhibit relatively high catalytic efficiency. Furthermore, tuning the pore size enables the modulation of LSPR in the near-infrared region. These findings highlight the critical role of pore size modulation in determining the photocatalytic performance of nanoporous metallic materials and provide valuable insights for the design and optimization of highly efficient photocatalysts. Full article

Functionalized plasmonic nanostructure platforms are widely used for developing optical biosensors and SERS assays. In this work, we present a low-cost and scalable surface-enhanced Raman scattering (SERS) system based on an innovative optical transducer comprising gold nanoparticles (AuNPs) embedded in nano-fibrillated bacterial cellulose (BC). The AuNPs@BC composite leverages the unique nanofibrillar architecture of bacterial cellulose, which provides a high surface area, flexibility, and uniform nanoparticle distribution, enabling the formation of numerous electromagnetic “hot spots”. This structure excites localized surface plasmon resonance (LSPR), as demonstrated by a bulk sensitivity of 72 nm/RIU, and supports enhanced Raman signal amplification. The eco-friendly and disposable AuNPs@BC platform was tested for agrifood applications, focusing on the detection of thiram pesticide. The system achieved a detection limit of 0.24 ppm (1 µM), meeting the sensitivity requirements for regulatory compliance in food safety. A strong linear correlation (R² ≈ 0.99) was observed between the SERS peak intensity at 1370 cm⁻¹ and thiram concentrations, underscoring its potential for quantitative analysis. The combination of high sensitivity, reproducibility, and environmental sustainability makes the AuNPs@BC platform a promising solution for developing cost-effective, flexible, and portable sensors for pesticide monitoring and other biosensing applications. Full article

Gold nanoparticles (NPs) have demonstrated significance in several important fields, including drug delivery and anticancer research, due to their unique properties. Gold NPs possess significant optical characteristics that enhance their application in biosensor development for diagnosis, in photothermal and photodynamic therapies for anticancer treatment, and in targeted drug delivery and bioimaging. The broad surface modification possibilities of gold NPs have been utilized in the delivery of various molecules, including nucleic acids, drugs, and proteins. Moreover, gold NPs possess strong localized surface plasmon resonance (LSPR) properties, facilitating their use in surface-enhanced Raman scattering for precise and efficient biomolecule detection. These optical properties are extensively utilized in anticancer research. Both photothermal and photodynamic therapies show significant results in anticancer treatments using gold NPs. Additionally, the properties of gold NPs demonstrate potential in other biological areas, particularly in antimicrobial activity. In addition to delivering antigens, peptides, and antibiotics to enhance antimicrobial activity, gold NPs can penetrate cell membranes and induce apoptosis through various intracellular mechanisms. Among other types of metal NPs, gold NPs show more tolerable toxicity capacity, supporting their application in wide-ranging areas. Gold NPs hold a special position in nanomaterial research, offering limited toxicity and unique properties. This review aims to address recently highlighted applications and the current status of gold NP research and to discuss their future in nanomedicine. Full article