Search Results (95)

Tea, a worldwide prevalent beverage, is continually contaminated by pesticide residues and heavy metals, presenting considerable health concerns to consumers. Nonetheless, effective monitoring is limited by conventional detection techniques—such as gas chromatography (GC) and inductively coupled plasma mass spectrometry (ICP-MS)—which, despite their high precision, necessitate intricate pretreatment, incur substantial operational expenses, and are inadequate for swift on-site analysis. Biosensors have emerged as a viable option, addressing this gap with their exceptional sensitivity, rapid response, and ease of operation.This review rigorously evaluates recent advancements in biosensing technologies for the detection of pesticide residues and heavy metals in tea, emphasizing the mechanisms, analytical performance, and practical applicability of prominent platforms such as fluorescence, surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), colorimetric, and electrochemical biosensors. Electrochemical and fluorescent biosensors provide the highest promise for portable, on-site use owing to their enhanced sensitivity, cost-effectiveness, and flexibility to intricate tea matrices. The paper further emphasizes upcoming techniques such multi-component detection, microfluidic integration, and AI-enhanced data processing. Biosensors provide significant potential to revolutionize tea safety monitoring, with future advancements dependent on the synergistic incorporation of sophisticated nanomaterials, intelligent microdevices, and real-time analytics across the whole “tea garden-to-cup” supply chain. Full article

This study develops an optical surface plasmon resonance (SPR) biosensing platform for non-invasive glucose detection directly in urine and examines how two-dimensional (2D) nanomaterials modulate sensing performance. Angular interrogation at 633 nm is modeled using a transfer-matrix framework for Au/Si₃N₄ stacks capped with graphene, semiconducting single-walled carbon nanotubes (s-SWCNTs), graphene oxide (GO), or reduced graphene oxide (rGO). Urine–glucose (UGLU) refractive indices spanning clinically relevant concentrations are used to evaluate resonance angle shifts and line-shape evolution. Sensor metrics—sensitivity, detection accuracy, figure of merit, quality factor, and limit of detection—are computed to compare architectures and identify thickness windows. Across all designs, increasing glucose concentration produces monotonic angle shifts, while the 2D overlayer governs dip depth and full width at half maximum. Graphene- and s-SWCNT-capped stacks yield the lowest limits of detection and the most favorable figures of merit, particularly at higher concentrations where narrowing improves the quality factor. rGO exhibits a thin, low-loss regime that provides large shifts with acceptable broadening, whereas thicker films degrade detectability; GO offers stable line shapes suited to metrological robustness. These results indicate that nanoscale optical engineering of 2D overlayers can meet practical detectability targets in urine without biochemical amplification, supporting compact, label-free platforms for routine glucose monitoring. Full article

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

Single-molecule detection (SMD) has reformed analytical science by enabling the direct observation of individual molecular events, thus overcoming the limitations of ensemble-averaged measurements. This review presents a comprehensive analysis of the principles, devices, and emerging materials that have shaped the current landscape of SMD. We explore a wide range of sensing mechanisms, including surface plasmon resonance, mechanochemical transduction, transistor-based sensing, optical microfiber platforms, fluorescence-based techniques, Raman scattering, and recognition tunneling, which offer distinct advantages in terms of label-free operation, ultrasensitivity, and real-time responsiveness. Each technique is critically examined through representative case studies, revealing how innovations in device architecture and signal amplification strategies have collectively pushed the detection limits into the femtomolar to attomolar range. Beyond the sensing principles, this review highlights the transformative role of advanced nanomaterials such as graphene, carbon nanotubes, quantum dots, MnO₂ nanosheets, upconversion nanocrystals, and magnetic nanoparticles. These materials enable new transduction pathways and augment the signal strength, specificity, and integration into compact and wearable biosensing platforms. We also detail the multifaceted applications of SMD across biomedical diagnostics, environmental monitoring, food safety, neuroscience, materials science, and quantum technologies, underscoring its relevance to global health, safety, and sustainability. Despite significant progress, the field faces several critical challenges, including signal reproducibility, biocompatibility, fabrication scalability, and data interpretation complexity. To address these barriers, we propose future research directions involving multimodal transduction, AI-assisted signal analytics, surface passivation techniques, and modular system design for field-deployable diagnostics. By providing a cross-disciplinary synthesis of device physics, materials science, and real-world applications, this review offers a comprehensive roadmap for the next generation of SMD technologies, poised to impact both fundamental research and translational healthcare. Full article

We propose a dual-groove few-mode fiber surface plasmon resonance sensor that exploits the LP₁₁ mode for enhanced plasmonic sensing. The device incorporates two physically separated grooves with distinct metallic coatings, enabling dual-channel operation via wavelength-division multiplexing. Finite element method simulations show that the optimized design achieves a maximum sensitivity of 14,800 nm/RIU within the RI range of 1.33–1.40. The introduction of a TiO₂–Au bilayer enhances mode coupling and ensures complete spectral separation, thereby improving stability and reducing environmental interference. Biosensing simulations at 37 °C further confirm the practicality of the proposed architecture. Channel 1, filled with ethanol as a temperature-sensitive medium, provides temperature monitoring, while Channel 2 successfully distinguishes between normal and tumor cells, reaching a sensitivity of up to 9428.57 nm/RIU for Jurkat cells. Overall, the TiO₂-enhanced dual-channel FMF-SPR sensor combines ultra-high sensitivity, spectral independence, and biosensing capability, demonstrating strong potential for next-generation fiber-optic sensing and biomedical applications. Full article

Graphene, a two-dimensional carbon material with a hexagonal lattice structure, possesses remarkable properties. Exceptional electrical conductivity, mechanical strength, and high surface area that make it a powerful platform for biosensing applications. Its sp²-hybridised network facilitates efficient electron mobility and enables diverse surface functionalisation through bio-interfacing. This review highlights the core detection mechanisms in graphene-based biosensors. Optical sensing techniques, such as surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS), benefit significantly from graphene’s strong light–matter interaction, which enhances signal sensitivity. Although graphene itself lacks intrinsic piezoelectricity, its integration with piezoelectric substrates can augment the performance of piezoelectric biosensors. In electrochemical sensing, graphene-based electrodes support rapid electron transfer, enabling fast response times across a range of techniques, including impedance spectroscopy, amperometry, and voltammetry. Graphene field-effect transistors (GFETs), which leverage graphene’s high carrier mobility, offer real-time, label-free, and highly sensitive detection of biomolecules. In addition, the review also explores multiplexed detection strategies vital for point-of-care diagnostics. Graphene’s nanoscale dimensions and tunable surface chemistry facilitate both array-based configurations and the simultaneous detection of multiple biomarkers. This adaptability makes graphene an ideal material for compact, scalable, and accurate biosensor platforms. Continued advancements in graphene biofunctionalisation, sensing modalities, and integrated multiplexing are driving the development of next-generation biosensors with superior sensitivity, selectivity, and diagnostic reliability. Full article

This review summarizes the recent advances in the application of nanomaterial coatings in optical fiber sensors, with a particular focus on deposition techniques and the research progress over the past five years in humidity sensing, gas detection, and biosensing. Benefiting from the high specific surface area, abundant surface active sites, and quantum confinement effects of nanomaterials, advanced thin-film fabrication techniques—including spin coating, dip coating, self-assembly, physical/chemical vapor deposition, atomic layer deposition (ALD), electrochemical deposition (ECD), electron beam evaporation (E-beam evaporation), pulsed laser deposition (PLD) and electrospinning, and other techniques—have been widely employed in the construction of functional layers for optical fiber sensors, significantly enhancing their sensitivity, response speed, and environmental stability. Studies have demonstrated that nanocoatings can achieve high-sensitivity detection of targets such as humidity, volatile organic compounds (VOCs), and biomarkers by enhancing evanescent field coupling and enabling optical effects such as surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), and lossy mode resonance (LMR). This paper first analyzes the principles and optimization strategies of nanocoating fabrication techniques, then explores the mechanisms by which nanomaterials enhance sensor performance across various application domains, and finally presents future research directions in material performance optimization, cost control, and the development of novel nanocomposites. These insights provide a theoretical foundation for the functional design and practical implementation of nanomaterial-based optical fiber sensors. Full article

This study proposes a dual-parameter photonic crystal fiber-based surface plasmon resonance (SPR) sensor for simultaneous refractive index and temperature detection. The sensor architecture incorporates an asymmetric air hole lattice, featuring elliptical inner holes (aspect ratio: 1.5) to enhance birefringence and axially aligned outer circular holes to optimize surface plasmon coupling. Horizontally, symmetrically deposited silver films and silicon nitride layers constitute the RI-sensing channel, while a vertically machined PDMS-coated silver–nitride structure enables temperature responsivity. The temperature-sensing channel delivers a sensitivity of 20 nm/°C within 0–100 °C, while the RI channel achieves a peak sensitivity of 18,600 nm/RIU across n_a = 1.33–1.41 with a resolution of 5.38 × 10⁻⁶ RIU. Notably, cross-sensitivity between the two channels remains below 5%, underscoring the sensor’s capability for independent dual-parameter analysis. This low-interference, high-sensitivity platform holds significant promise for advanced biosensing applications requiring real-time multiparametric monitoring. Full article

This article presents a comprehensive overview of recent advancements in photonic crystal fiber (PCF)-based sensors, with a particular focus on the surface plasmon resonance (SPR) phenomenon for biosensing. With their ability to modify core and cladding structures, PCFs offer exceptional control over light guidance, dispersion management, and light confinement, making them highly suitable for applications in refractive index (RI) sensing, biomedical imaging, and nonlinear optical phenomena such as fiber tapering and supercontinuum generation. SPR is a highly sensitive optical phenomenon, which is widely integrated with PCFs to enhance detection performance through strong plasmonic interactions at metal–dielectric interfaces. The combination of PCF and SPR technologies has led to the development of innovative sensor geometries, including D-shaped fibers, slotted-air-hole structures, and internal external metal coatings, each optimized for specific sensing goals. These PCF-SPR-based sensors have shown promising results in detecting biomolecular targets such as excess cholesterol, glucose, cancer cells, DNA, and proteins. Furthermore, this review provides an in-depth analysis of key design parameters, plasmonic materials, and sensor models used in PCF-SPR configurations, highlighting their comparative performance metrics and application prospects in medical diagnostics, environmental monitoring, and chemical analysis. Thus, an exhaustive analysis of various sensing parameters, plasmonic materials, and sensor models used in PCF-SPR sensors is presented and explored in this article. Full article

The integration of two-dimensional graphene with gold nanostructures has significantly advanced surface plasmon resonance (SPR)-based optical biosensors, due to graphene’s exceptional optical, electronic, and surface properties. This review examines recent developments in graphene-based hybrid nanomaterials designed to enhance SPR sensor performance. The synergistic combination of graphene and other functional materials enables superior plasmonic sensitivity, improves biomolecular interaction, and enhances signal transduction. Key focus areas include the fundamental principle of graphene-enhanced SPR, the functional advantages of graphene hybrid platforms, and their recent applications in detecting biomolecules, disease biomarkers, and pathogens. Finally, current limitations and potential future perspectives are discussed, highlighting the transformative potential of these hybrid nanomaterials in next-generation optical biosensing Full article

Diagnosing Alzheimer’s disease (AD) remains a significant challenge due to its multifactorial nature and the limitations of traditional diagnostic methods, such as clinical assessments and neuroimaging, which often lack the specificity and sensitivity required for early detection. The urgent need for innovative diagnostic tools is further underscored by the potential of early intervention to improve treatment outcomes and slow disease progression. Recent advancements in biosensing technologies offer promising solutions for precise and non-invasive AD detection. Electrochemical and optical biosensors, in particular, provide high sensitivity, specificity, and real-time detection capabilities, making them valuable for identifying key biomarkers, including amyloid-β (Aβ) peptides and tau proteins. Additionally, integrating these biosensors with nanomaterials enhances their performance, stability, and detection limits, enabling improved diagnostic accuracy. Beyond nanomaterial-based sensors, emerging innovations in microfluidics, surface plasmon resonance (SPR), and artificial intelligence-assisted biosensing further contribute to the development of next-generation AD diagnostics. This review provides a comprehensive analysis of the latest advancements in biosensing technologies for AD, highlighting their mechanisms, advantages, and future perspectives in detecting biomarkers from biological fluids. Full article

Accurate detection of biomolecular interactions is essential in many areas, from the detection of the presence of biomarkers in the clinic to the development of therapeutic drugs and biologics in biopharma to the understanding of various biological processes in basic research. Traditional endpoint approaches can suffer from false-negative results for biomolecular interactions with fast kinetics. By contrast, real-time detection techniques like surface plasmon resonance (SPR) monitor interactions as they form and disassemble, reducing the risk of false-negative results. By leveraging cell-free expressed proteins captured on either glass or SPR biosensors and using two different commercial antibodies with variable off-rates that both target HaloTag antigens as a model, we compare and contrast results from a fluorescence endpoint assay versus real-time sensor-integrated proteome on chip (SPOC^®) SPR-based detection. In this study, we illustrate the limitations of the representative immunofluorescent endpoint assay when investigating transient interactions characterized by fast dissociation rates. We highlight the importance of choosing reagents well suited to the selected assay, as well as the importance of considering binding kinetics and protein ligand conformational states when interpreting results from binding assays, especially for applications as critical as the off-target screening of therapeutics. Full article

The rapid and precise identification of multiple pathogens is critical for ensuring food safety, controlling epidemics, diagnosing diseases, and monitoring the environment. However, traditional detection methods are hindered by complex workflows, the need for skilled operators, and reliance on sophisticated equipment, making them unsuitable for rapid, on-site testing. Optical biosensors, known for their rapid analysis, portability, high sensitivity, and multiplexing capabilities, offer a promising solution for simultaneous multi-pathogenic identification. This paper explores recent advancements in the utilization of optical biosensors for multiple pathogenic detection. First, it provides an overview of key sensing principles, focusing on colorimetric, fluorescence-based, surface-enhanced Raman scattering (SERS), and surface plasmon resonance (SPR) techniques, as well as their applications in pathogenic detection. Then, the research progress and practical applications of optical biosensors for multiplex pathogenic detection are discussed in detail from three perspectives: microfluidic devices, nucleic acid amplification technology (NAAT), and nanomaterials. Finally, the challenges presented by optical biosensing technologies in multi-pathogen detection are discussed, along with future prospects and potential innovations in the field. Full article

This study presents a black phosphorus-based surface plasmon resonance (SPR) biosensor for malaria detection, integrating silicon nitride (Si₃N₄) and single-stranded DNA (ssDNA) to enhance sensitivity and molecular recognition. The biosensor configurations were optimized through numerical simulations, evaluating metal thickness, dielectric layer thickness, and the number of black phosphorus layers to achieve maximum performance. The optimized system (Opt-Sys₄) exhibited high sensitivity (464.4°/RIU for early-stage malaria) and improved detection accuracy, outperforming conventional SPR sensors. Performance was assessed across malaria progression stages, demonstrating a clear resonance shift, increased attenuation, and enhanced biomolecular interactions. Key metrics, including the figure of merit, limit of detection, and comprehensive sensitivity factor, confirmed the sensor’s superior performance. Comparative analysis against state-of-the-art SPR biosensors further validated their capability for highly sensitive and specific malaria detection. These findings establish a promising plasmonic biosensing platform for early malaria diagnosis, potentially improving disease management in resource-limited settings. Full article

We present an experimental study of a sensitivity-enhanced surface plasmon resonance (SPR) sensor utilizing a cladding etched multimode polymer optical fiber (POF) coated with a layer of gold followed by an indium tin oxide (ITO) layer. Our findings indicate that POF SPR sensors with an ITO overlayer exhibit higher sensitivity compared to those coated solely with gold. Additionally, increasing the thickness of the ITO layer increases the sensitivity of the sensor at the expense of a broader SPR spectrum. We determined that the optimal ITO thickness for maximizing sensitivity is 25 nm. The sensor coated with 40 nm gold and 25 nm ITO demonstrated a refractive index sensitivity of 2258 nm per refractive index unit (nm/RIU) with a figure of merit and resolution of 10.13 ${\mathrm{R}\mathrm{I}\mathrm{U}}^{-1}$ and $2.74\times {10}^{-4} \mathrm{R}\mathrm{I}\mathrm{U}$, respectively, within the range of 1.33 to 1.37 RIU. Notably, this sensitivity is 70% greater than that of a POF SPR sensor coated only with 40 nm gold. Long-term stability tests conducted in a hydrated environment confirmed that the ITO layer remains unaffected over time and that the maximum SPR wavelength drift was only 1.2 nm. The standard deviation of the three-round measurements also revealed that the sensor has good repeatability. We believe that this sensor offers a simple structure and a relatively easy fabrication process, eliminating the need for side polishing while providing a large interaction area, making it a promising candidate for high-sensitivity biosensing applications. Full article