Plasmonic Materials Research Articles

Gold-coated D-shaped photonic crystal fiber refractive index sensor with a wide detection range and large manufacturing tolerance

A D-shaped photonic crystal fiber refractive index (RI) sensor is designed, and its performance is analyzed using the finite element method (FEM). A gold film is coated on the D-shaped surface of the fiber as a plasmonic material for surface plasmon resonance sensing. The U-shaped arrangement of holes of the same size in the fiber structure enhances the coupling resonance between the core mode and the surface plasmon polariton mode. Numerical results show that the RI range of the sensor is 1.20–1.40, the maximum wavelength sensitivity is 16008.98 nm/RIU, and the detection width is up to 0.2 RIU. In addition, this study analyzes the manufacturing tolerance for the sizes of the air holes. The results show that the manufacturing tolerance for the three types of air holes is as high as 25%, 11.1%, and 10.2% when h is 40µm. These findings lay the foundation for the mass production of sensors. The above results indicate that the sensor has remarkable advantages such as enhanced sensitivity, wide measurement range, and exceptional manufacturing stability, and has promising applications in the fields of bio-detection, drug supply detection, and water pollution control.

Advances in Plasmonic Photonic Crystal Fiber Biosensors: Exploring Innovative Materials for Bioimaging and Environmental Monitoring

AbstractThis review paper comprehensively analyzes recent advancements in optical fiber‐based biosensors, focusing on conventional fiber and photonic crystal structures. This paper overviews the significant applications of optical fiber biosensors, including bioimaging, quality analysis, food safety, and field environment monitoring, setting the stage for subsequent discussions. The primary objective of the review is to systematically evaluate recent literature concerning optical fiber‐based biosensors, emphasizing their sensitivities and resolutions. The second section explores integrating plasmonic materials such as graphene, TDMC, germanium, black phosphorus, and silicon within optical fiber biosensors, elucidating their roles in enhancing sensitivity and resolution in biosensing applications. A detailed examination of photonic crystal fibers (PCF) follows, categorizing them into internally and externally metal film‐coated biosensors, highlighting their distinct advantages and limitations. Comparative analyses in two tables delineate the performance and sensitivity of optical fiber‐based biosensors, mainly focusing on different coating strategies. The final section of the review discusses emerging trends and applications in optical fiber biosensing technologies, underscoring their potential to transform biomedical and environmental monitoring fields. By synthesizing recent developments and challenges, this review aims to offer researchers and practitioners a comprehensive understanding of optical fiber‐based biosensors, facilitating informed decision‐making and driving further advancements in the field.

Enantioselective Surface-Enhanced Raman Scattering by Chiral Au Nanocrystals with Finely Modulated Chiral Fields and Internal Standards.

The chiral discrimination of enantiomers is crucial for drug screening and agricultural production. Surface-enhanced Raman scattering (SERS) is proposed for discriminating enantiomers benefiting from chiral plasmonic materials. However, the mechanism of enantioselective SERS is unclear, and fluctuating SERS intensities may result in errors. Herein, this work demonstrates a reliable SERS substrate using chiral Au nanocrystals with finely modulated chiral fields and internal standards. Chiral electromagnetic fields are enhanced after modulation, which is conducive to increasing the difference in the enantiomeric SERS intensity, as evidenced by the experimental and simulation results. Furthermore, the SERS stability is improved by the corrective effect of the internal standards, and the relative standard deviation is significantly reduced. Using finely modulated chiral fields and internal standards, L- and D-phenylalanine exhibit a stable six times difference in SERS ratio. Theoretical simulations reveal that linearly polarized light can also excite the chiral fields of chiral Au nanocrystals, indicating non-chiral far-field light is converted into chiral near-field sources by chiral Au nanocrystals. Thus, the mechanism of enantioselective SERS can be elucidated by the scattering difference of chiral molecules in chiral near fields. This study will pave the way for the development of enantioselective SERS and related chiroptical technologies.

Plasmonic trimers designed as SERS-active chemical traps for subtyping of lung tumors

Plasmonic materials can generate strong electromagnetic fields to boost the Raman scattering of surrounding molecules, known as surface-enhanced Raman scattering. However, these electromagnetic fields are heterogeneous, with only molecules located at the ‘hotspots’, which account for ≈ 1% of the surface area, experiencing efficient enhancement. Herein, we propose patterned plasmonic trimers, consisting of a pair of plasmonic dimers at the bilateral sides and a trap particle positioned in between, to address this challenge. The trimer configuration selectively directs probe molecules to the central traps where ‘hotspots’ are located through chemical affinity, ensuring a precise spatial overlap between the probes and the location of maximum field enhancement. We investigate the Raman enhancement of the Au@Al2O3-Au-Au@Al2O3 trimers, achieving a detection limit of 10−14 M of 4-methylbenzenethiol, 4-mercaptopyridine, and 4-aminothiophenol. Moreover, single-molecule SERS sensitivity is demonstrated by a bi-analyte method. Benefiting from this sensitivity, our approach is employed for the early detection of lung tumors using fresh tissues. Our findings suggest that this approach is sensitive to adenocarcinoma but not to squamous carcinoma or benign cases, offering insights into the differentiation between lung tumor subtypes.

Engineering Epsilon‐Near‐Zero Media with Waveguides

AbstractEpsilon‐Near‐Zero (ENZ) media have attracted widespread interest due to their unique electromagnetic properties, which have brought distinctive characteristics and phenomena, such as spatiotemporal decoupling, supercoupling and tunneling, constant phase transmission, near‐field enhancement, and so on. However, these ENZ characteristics are existed in natural plasmonic materials at their intrinsic plasma frequencies and accompanied by significant losses, thus limiting their applications in engineering. Different from the effect ENZ media with artificially periodic structures, the waveguide ENZ media offers a promising platform with non‐periodic architectures. Unlike the natural plasmonic materials and the periodic‐structured ENZ media, the waveguide ENZ media utilizes waveguide dispersion to achieve effective ENZ characteristics and phenomena with lower loss and smaller dimensions. This review begins with an exploration of the fundamental properties of the waveguide ENZ media and then introduces the design principles of different ENZ‐based electromagnetic devices. Finally, the review concludes with the challenges and potential development directions encountered by the ENZ media in the realm of electromagnetic applications.

Highly sensitive surface plasmon resonance sensor based on the anti-resonant fiber with six nested tubes

On the heels of the continuous development of optical fiber sensing technology, optical fiber sensors based on surface plasmon resonance (SPR) have attracted widespread attention. Herein, an SPR sensor based on the six nested anti-resonant fiber (ARF) is designed and analyzed by the finite element method (FEM). All the structural parameters are optimized to achieve high-sensitivity liquid refractive index detection. Filling the anti-resonant tube with plasmonic materials to excite SPR can further reduce the manufacturing complexity. The optimal ARF-SPR sensor has excellent characteristics, including an average wavelength sensitivity of 42,000 nm/RIU, maximum sensor length of 0.08 cm, and resolution of 1.61×10−6RIU. The ARF-SPR sensor has great potential in chemical analysis, biomedicine, and other fields.

Stable and Efficient Perovskite Solar Cells by Controlling the Crystal Growth via Introduction of Plasmonic TiN Nanoparticles

AbstractIncorporating noble‐metal plasmonic nanoparticles (NPs) enhances the optoelectronic properties of perovskite solar cells (PSCs) but at a higher cost. In this work, the overlooked potential of refractory plasmonic materials is highlighted as a cost‐effective alternative additive in PSC research. This investigation aims to stimulate interest in this area by showcasing the theoretical and practical impacts of TiN plasmonic NPs when integrated into PSCs. TiN plasmonic NPs present a cost‐effective yet underexplored option. This study explores the impact of TiN NPs on PSCs through theoretical and experimental approaches. Finite‐difference time‐domain (FDTD) optical simulations and empirical data indicate that TiN NPs increase absorption and reduce reflectance in PSCs, driven by surface plasmon resonance and the significant growth of perovskite grains from 450 to 1400 nm. These NPs also regulate the perovskite crystallization rate by adsorbing DMF/DMSO, fostering larger grain formation. Improved band alignment and decreased trap states enhance charge transport and diminish non‐radiative recombination losses. As a result, PSC efficiency with optimal TiN NP concentration increased from 19.07% to 21.37%. Additionally, TiN‐enhanced PSCs display better stability, retaining 98.1% of their original PCE after 31 days under ambient conditions.

Gold nanowire-infused square-clad SPR-PCF biosensor for detection of various cancer cells

This research work introduces a Surface Plasmon Resonance (SPR) based Photonic Crystal Fiber (PCF) sensor using gold nanowires as plasmonic material designed for the detection of various cancer cells, boasting remarkable sensitivity and ease of fabrication. The sensor's structure was devised and analyzed using the Finite Element Method (FEM) of COMSOL v5.5, with a focus on exploring the impact of varying geometric parameters on its overall performance. The simulation utilized extremely fine mesh elements to ensure the utmost accuracy. Excitation between the core and plasmonic modes is achieved using Gold (Au) nanowires. The determination of the sensor's wavelength sensitivity involves assessing the resonance wavelength shift between samples of normal and cancerous cells. Simultaneously, the measurement of amplitude sensitivity is accomplished through a comparison of the amplitudes associated with their respective confinement losses. Various parameters of the PCF were varied during the experimentation, leading to the achievement of exceptionally high Amplitude Sensitivity (AS) of −273.16 RIU−1, −286.58 RIU−1, −455.59 RIU−1, −698.76 RIU−1, −1172.72 RIU−1 and −1971.30 RIU−1 for Skin Cancer, Cervical Cancer, Blood Cancer, Adrenal Gland Cancer, Breast Type-1 Cancer and Breast Type-2 Cancer respectively. Additionally, the Wavelength Sensitivity (WS) values were found to be 6500 nm/RIU, 14583.33 nm/RIU, 16428.57 nm/RIU, 25714.28 nm/RIU, 32857.14 nm/RIU, and 35714.28 nm/RIU for the same cancer types, respectively. The achieved resolutions for wavelength sensitivity are 1.54×10−5 RIU, 6.86×10−6 RIU, 6.09×10−6 RIU, 3.89×10−6 RIU, 3.04×10−6 RIU and 2.80×10−6 RIU, while the resolutions for amplitude sensitivity are 7.32×10−5 RIU, 8.37×10−5 RIU, 3.07×10−5 RIU, 2.00×10−5 RIU, 1.19×10−5 RIU and 7.10×10−6 RIU for the respective cancer types mentioned above. The design of the presented biosensor is notably uncomplicated and can be readily manufactured using contemporary fabrication techniques. In summary, the remarkable sensitivity exhibited by the proposed SPR-based PCF (SPR-PCF) biosensor, shows significant potential for enhancing the detection of cancer cells.

High-performance plasmonics nanostructures in gas sensing: a comprehensive review.

Plasmonic nanostructures have emerged as indispensable components in the construction of high-performance gas sensors, playing a pivotal role across diverse applications, including industrial safety, medical diagnostics, and environmental monitoring. This review paper critically examines seminal research that underscores the remarkable efficacy of plasmonic materials in achieving superior attributes such as heightened sensitivity, selectivity, and rapid response times in gas detection. Offering a synthesis of pivotal studies, this review aims to furnish a comprehensive discourse on the contemporary advancements within the burgeoning domain of plasmonic gas sensing. The featured investigations meticulously scrutinize various plasmonic structures and their applications in detecting gases like carbon monoxide, carbon dioxide, hydrogen and nitrogen dioxide. The discussed frameworks encompass cutting-edge approaches, spanning ideal absorbers, surface plasmon resonance sensors, and nanostructured materials, thereby elucidating the diverse strategies employed for advancing plasmonic gas sensing technologies.

Plasmonic Cross-Reactive Sensing Noses and Tongues.

The advancements in the capabilities of artificial sensory technologies, such as electronic/optical noses and tongues, have significantly enhanced their ability to identify complex mixtures of analytes. These improvements are rooted in the evolving manufacturing processes of cross-reactive sensor arrays (CRSAs) and the development of innovative computational methods. The potential applications in early diagnosis, food quality control, environmental monitoring, and more, position CRSAs as an exciting area of research for scientists from diverse backgrounds. Among these, plasmonic CRSAs are particularly noteworthy because they offer enhanced capabilities for remote, fast, and even real-time monitoring, in addition to better portability of instrumentation. Specifically, the synergy between the localized surface plasmon resonance (LSPR) of metallic nanoparticles (NPs) and CRSAs introduces advanced techniques such as LSPR, metal-enhanced fluorescence (MEF), surface-enhanced infrared absorption (SEIRA), surface-enhanced Raman scattering (SERS), and surface-enhanced resonance Raman scattering (SERRS) spectroscopies. This review delves into the importance and versatility of optical-CRSAs, especially those based on plasmonic materials, discussing recent applications and potential new research directions.

A unique wheel-shaped exposed core LSPR-PCF sensor for dual-peak sensing: Applications in the optical communication bands, M-IR region and biosensing

Photonic Crystal Fibers (PCF) effectiveness in practice decreases if the fabrication of the sensor becomes too complex. Keeping this in mind, we propose a one-of-a-kind wheel shaped PCF sensor with an exposed core containing only three air holes with exceptional sensing features. The sensor is equipped with dual plasmonic layers, Indium Tin Oxide (ITO, 10 % wt) and silver (Ag) with a coating of TiO2 to enhance the sensing capabilities and provide protection against oxidation. The sensor's distinctive configuration enables it to exhibit two distinct peaks within a range of refractive index from 1.32 to 1.38 for y-polarization and from 1.35 to 1.38 for x-polarization. The sensor specifications have been optimized to achieve the maximum levels of wavelength sensitivity (WS) and double peak shift sensitivity (DPSS). The sensor portrays a WS of 50,652 nm/RIU and the highest DPSS ever recorded, measuring 50,000 nm/RIU. Additionally, the sensor exhibits a significantly high scale of amplitude sensitivity (AS) of 1668.34 RIU−1 which is a very remarkable value considering silver as plasmonic material along with an outstanding figure of merit (FOM) of 1017.11 RIU−1. In addition, our sensor is able to manifest resolutions in the order of 10−6, demonstrating a resolution of 5.94 × 10−6 RIU with the deployment of amplitude interrogation method and 1.97 × 10−6 RIU with the wavelength interrogation method. The design spans an extensive spectrum, covering ultraviolet to mid-infrared wavelengths, enabling detection of biomolecules and biochemicals, along with operation in the optical communication band.

Amplified linear and nonlinear chiral sensing assisted by anapole modes in hybrid metasurfaces

The interaction between chiral molecules and circularly polarized light is largely influenced by the local optical chirality density. This interaction prompts substantial demand of the design of nanophotonic platforms capable of enhancing such effects across large and accessible volumes. Such a magnification requires nanostructures that provide strong electric and magnetic field enhancements while preserving the phase relation of circular light. Dielectric nanostructures, particularly those able to support resonances, are ideal candidates for this task due to their capacity for high electric and magnetic field enhancements. On the other hand, efficient third harmonic generation requires strong electric field resonances within dielectric materials, a feature often boosted by incorporating plasmonic materials into hybrid systems. In this work, we numerically propose a coupled silicon disk-gold ring system that can exploit the anapole-induced field confinement to provide a broadband magnified circular dichroism under realistic conditions, reaching values up to a 230-fold enhancement. We also demonstrate that this structure can be employed as an efficient third harmonic generator, which, when integrated with chiral media, enables an 800-fold enhancement in circular dichroism. Furthermore, we show that pulsed illumination at intensities up to 10 GW/cm2 does not induce temperature increments that could potentially damage the samples. These findings suggest that this system can be a promising and versatile approach toward ultrasensitive chiral sensing.

How Depletion Layers Govern the Dynamic Plasmonic Response of In-Doped CdO Nanocrystals.

Doped metal oxide nanocrystals exhibit a localized surface plasmon resonance that is widely tunable across the mid- to near-infrared region, making them useful for applications in optoelectronics, sensing, and photocatalysis. Surface states pin the Fermi level and induce a surface depletion layer that hinders conductivity and refractive index sensing but can be advantageous for optical modulation. Several strategies have been developed to both synthetically and postsynthetically tailor the depletion layer toward particular applications; however, this understanding has primarily been advanced in Sn-doped In2O3 (ITO) nanocrystals, leaving open questions about generalizing to other doped metal oxides. Here, we quantitatively analyze the depletion layer in In-doped CdO (ICO) nanocrystals, which is shown to have an intrinsically wide depletion layer that leads to broad plasmonic modulation via postsynthetic chemical reduction and ligand exchange. Leveraging these insights, we applied depletion layer tuning to enhance the inherently weak plasmonic coupling in ICO nanocrystal superlattices. Our results demonstrate how an electronic band structure dictates the radial distribution of electrons and governs the response to postsynthetic modulation, enabling the design of tunable and responsive plasmonic materials.

Ultralow Catalytic Loading for Optimised Electrocatalytic Performance of AuPt Nanoparticles to Produce Hydrogen and Ammonia

AbstractThe hydrogen evolution and nitrite reduction reactions are key to producing green hydrogen and ammonia. Antenna–reactor nanoparticles hold promise to improve the performances of these transformations under visible‐light excitation, by combining plasmonic and catalytic materials. However, current materials involve compromising either on the catalytic activity or the plasmonic enhancement and also lack control of reaction selectivity. Here, we demonstrate that ultralow loadings and non‐uniform surface segregation of the catalytic component optimize catalytic activity and selectivity under visible‐light irradiation. Taking Pt−Au as an example we find that fine‐tuning the Pt content produces a 6‐fold increase in the hydrogen evolution compared to commercial Pt/C as well as a 6.5‐fold increase in the nitrite reduction and a 2.5‐fold increase in the selectivity for producing ammonia under visible light excitation relative to dark conditions. Density functional theory suggests that the catalytic reactions are accelerated by the intimate contact between nanoscale Pt‐rich and Au‐rich regions at the surface, which facilitates the formation of electron‐rich hot‐carrier puddles associated with the Pt‐based active sites. The results provide exciting opportunities to design new materials with improved photocatalytic performance for sustainable energy applications.

Ultralow Catalytic Loading for Optimised Electrocatalytic Performance of AuPt Nanoparticles to Produce Hydrogen and Ammonia.

The hydrogen evolution and nitrite reduction reactions are key to producing green hydrogen and ammonia. Antenna-reactor nanoparticles hold promise to improve the performances of these transformations under visible-light excitation, by combining plasmonic and catalytic materials. However, current materials involve compromising either on the catalytic activity or the plasmonic enhancement and also lack control of reaction selectivity. Here, we demonstrate that ultralow loadings and non-uniform surface segregation of the catalytic component optimize catalytic activity and selectivity under visible-light irradiation. Taking Pt-Au as an example we find that fine-tuning the Pt content produces a 6-fold increase in the hydrogen evolution compared to commercial Pt/C as well as a 6.5-fold increase in the nitrite reduction and a 2.5-fold increase in the selectivity for producing ammonia under visible light excitation relative to dark conditions. Density functional theory suggests that the catalytic reactions are accelerated by the intimate contact between nanoscale Pt-rich and Au-rich regions at the surface, which facilitates the formation of electron-rich hot-carrier puddles associated with the Pt-based active sites. The results provide exciting opportunities to design new materials with improved photocatalytic performance for sustainable energy applications.

High sensitivity and wide detection range temperature and refractive index photonic crystal fiber sensor

A D-shaped surface plasmon resonance temperature and refractive index (RI) sensor based on photonic crystal fiber is proposed. The fiber core is composed of five air holes arranged in a pentagonal shape, which effectively improves the sensitivity. The gold film is used as a plasmonic material, and the mixture of ethanol and chloroform is used as a temperature sensitive liquid. A finite element method with higher accuracy and stronger applicability is used to study the performance of the sensor. The results indicate that when filling the mixture, the temperature sensor can detect the temperature in the range of 0 °C–60 °C. A maximum temperature sensitivity of 11.0 nm °C−1 is obtained by filling the mixture. The RI sensor can detect RI in the range of 1.13–1.40, with the wavelength range of 1.2–2.4 μm, and the maximum wavelength sensitivity reaches up to 21 000 nm RIU−1. The sensor can be used in biomedicine, environmental monitoring, food detection, temperature detection and other related fields, and has certain competitiveness and commercial value.

Molten Salt‐Assisted Synthesis of Titanium Nitride

AbstractTitanium nitride is an exciting plasmonic material, with optical properties similar to gold. However, synthesizing TiN nanocrystals is highly challenging and typically requires solid‐state reactions at very high temperatures (800–1000°C). Here, the synthesis of TiN nanocrystals is achieved at temperatures as low as 350°C, in just 1 h. The strategy comprises molten salt, Mg as reductant and Ca3N2 as nitride source. This brings TiN from the realm of solid‐state chemistry into the field of solution‐based synthesis in regular, borosilicate glassware.

Optical Switchers to Manipulate Intracellular Pathways and Boost Tissue Regeneration

AbstractThe possibility to remotely manipulate intracellular pathways in single cells is among the current goals of regenerative medicine, demanding new strategies to enhance tissue repair and reprogram stem cell activity. Plasmonic nanomaterials are addressing this need, due to improvements in the controlled synthesis allowing convenient regulation and precise thermal positioning. Leveraging on the thermal properties of gold nanoprisms (AuNPs) and on the unparalleled regenerating capabilities of the small invertebrate Hydra vulgaris, here the possibility to activate the molecular machinery underlying the animal regeneration by using AuNPs and applying regular pulses of near infrared irradiation (NIR) is shown. The efficiency of the head regeneration, reproductive capability, and stem cell proliferation rate are boosted by the AuNP photostimulation, indicating NIR triggered hyperthermia as new tool to enhance tissue regeneration. By transcriptional profiling of key developmental genes in animals exposed to external heat or irradiated an estimation of the heat developed in vivo by intracellular nanoheaters is obtained, revealing Hydra as a living thermometer to test performance of plasmonic materials. These results shed light on a novel function of heat emitting nanoparticles to control cell stemness through the activation of molecular pathways that can be targeted for regenerative medicine or wound healing strategies.

Noble Metal Plasmon-Molecular Catalyst Hybrids for Renewable Energy Relevant Small Molecule Activation.

Significant endeavors have been dedicated to the advancement of materials for artificial photosynthesis, aimed at efficiently harvesting light and catalyzing reactions such as hydrogen production and CO2 conversion. The application of plasmonic nanomaterials emerges as a promising option for this purpose, owing to their excellent light absorption properties and ability to confine solar energy at the nanoscale. In this regard, coupling plasmonic particles with molecular catalysts offers a pathway to create high-performance hybrid catalysts. In this review, we discuss the plasmonic-molecular complex hybrid catalysts where the plasmonic nanoparticles serve as the light-harvesting unit and promote interfacial charge transfer in tandem with the molecular catalyst which drives chemical transformation. In the initial section, we provide a concise overview of plasmonic nanomaterials and their photophysical properties. We then explore recent breakthroughs, highlighting examples from literature reports involving plasmonic-molecular complex hybrids in various catalytic processes. The utilization of plasmonic materials in conjunction with molecular catalysts represents a relatively unexplored area with substantial potential yet to be realized. This review sets a strong basis and motivation to explore the plasmon-induced hot-electron mediated photelectrochemical small molecule activation reactions. Utilizing in situ spectroscopic investigations and ultrafast transient absorption spectroscopy, it presents a comprehensive template for scalable and sustainable antenna-reactor systems.

Trends in surface plasmon resonance biosensing: materials, methods, and machine learning.

Surface plasmon resonance (SPR) proves to be one of the most effective methods of label-free detection and has been integral for the study of biomolecular interactions and the development of biosensors. This trend delves into the latest SPR research and progress built upon the Kretschmann configuration, a pivotal platform, and highlights three key developments that have enhanced the capabilities of the technique. We will first cover a range of explorations of novel plasmonic materials that have shaped SPR performance. Innovative signal transduction and collection, which leverages traditional materials and emerging alternatives, will then be discussed. Finally, the evolving landscape of data analysis, including the integration of machine learning algorithms to navigate complex SPR datasets, will be reviewed. We will also discuss the implementation of these improvements that have enabled new biosensing functions. These advancements not only pave the way for enhanced biosensing in general but also open new avenues for the technique to play a more significant role in research concerning human health.