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Plasma and Plasmonics || 7 Advanced Topics in Plasmonics
摘要： As the name suggests, NIMs are materials which have a negative index of refraction and were first proposed by V. G. Veselago in 1968 [24]. These materials are not naturally occurring but are artificially constructed using ideas similar to that used in the generation of spoof surface plasmon (SSP) waves discussed in Chapter 6. The refractive index of a material is given by n = √(?rμr), where ?r is the relative permittivity and μr is the relative permeability of the material. For naturally occurring materials, ?r and μr are usually positive for most frequencies. However, as was discussed in Chapter 2, the permittivity of metals can become negative for some range of frequency near the visible spectrum. As shown in Chapter 6, we can mimic this negative permittivity behavior at much lower frequencies by drilling holes in the metal surface with an appropriate hole size and array size. In these cases, the permeability of the material is still positive, and hence the refractive index is imaginary. Due to this regular electromagnetic waves cannot travel inside the medium and all we have are surface plasmon waves. However, if we could make both the permittivity and permeability negative for the same frequency range, the product ?rμr will again be positive and hence the refractive index will be a real quantity. Such materials are also called double negative metamaterials (DNGs). In this case, we choose the negative sign for n to distinguish it from the usual case when ?r and μr are positive. When the refractive index is real, we again have regular electromagnetic waves traveling through the medium but some of the properties of wave propagation in NIMs are very intriguing and very different from the case of Positive Index Materials (PIMs). NIMs have several applications, the primary among them being the superlens which can allow imaging beyond the diffraction limit. Other applications include metamaterial antennas which can help in miniaturization of transmitting devices, optical nanolithography and nanotechnology circuitry.
关键词： Plasmonics,NIMs,SERS,Negative Index Metamaterials,Surface-Enhanced Raman Scattering,Particle Traps
更新于2025-09-16 10:30:52
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Plasmonic Nanoassemblies: Tentacles Beat Satellites for Boosting Broadband NIR Plasmon Coupling Providing a Novel Candidate for SERS and Photothermal Therapy
摘要： Optical theranostic applications demand near-infrared (NIR) localized surface plasmon resonance (LSPR) and maximized electric field at nano-surfaces and nanojunctions, aiding diagnosis via Raman or optoacoustic imaging, and photothermal-based therapies. To this end, multiple permutations and combinations of plasmonic nanostructures and molecular “glues” or linkers are employed to obtain nanoassemblies, such as nano-branches and core–satellite morphologies. An advanced nanoassembly morphology comprising multiple linear tentacles anchored onto a spherical core is reported here. Importantly, this core-multi-tentacle-nanoassembly (CMT) benefits from numerous plasmonic interactions between multiple 5 nm gold nanoparticles (NPs) forming each tentacle as well as tentacle to core (15 nm) coupling. This results in an intense LSPR across the “biological optical window” of 650?1100 nm. It is shown that the combined interactions are responsible for the broadband LSPR and the intense electric field, otherwise not achievable with core–satellite morphologies. Further the sub 80 nm CMTs boosted NIR-surface-enhanced Raman scattering (SERS), with detection of SERS labels at 47 × 10-9 m, as well as lower toxicity to noncancerous cell lines (human fibroblast Wi38) than observed for cancerous cell lines (human breast cancer MCF7), presents itself as an attractive candidate for use as biomedical theranostics agents.
关键词： branched polymers,core–satellites,surface-enhanced Raman scattering (SERS),plasmonic nanoassemblies,broadband NIR absorbance,cell toxicity
更新于2025-09-16 10:30:52
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A review of 2D and 3D plasmonic nanostructure array patterns: fabrication, light management and sensing applications
摘要： This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a material’s plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (light-matter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whispering-gallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surface-enhanced Raman scattering (SERS) sensors.
关键词： sensor,lithography,nanofabrication,nano-array,plasmon,surface-enhanced Raman scattering (SERS),nanostructures
更新于2025-09-16 10:30:52
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Chemical Nanoplasmonics: Emerging Interdisciplinary Research Field at Crossroads between Nanoscale Chemistry and Plasmonics
摘要： Plasmonics research deals with understanding and manipulating the interaction between light and matter at a scale that is significantly smaller than the wavelength of light (e.g., metal nanoparticles). Such an interaction can be correlated with various forms of energy and signals such as thermal energy and optical spectra. Research efforts in plasmonics range from rationally designing and precisely synthesizing nanostructures that allow for unraveling and reliably tuning novel and useful plasmonic properties (e.g., surface-enhanced spectroscopies and photothermal effects) to ultimately obtaining and utilizing plasmonic functionalities for applications, for example, in the biomedical field. With enormous potential and versatility in terms of plasmonic materials and devices, the principles of plasmonics are expected to provide new or improved solutions to many important challenges in various subfields of chemistry, including nanoparticle chemistry, catalytic reactions, surface-enhanced Raman scattering, photovoltaics, sensing, biochemistry, and therapeutics. Additionally, many hurdles and issues related to the advances and applications of plasmonics can be addressed by material- or property-based chemistry at the nanoscale (i.e., nanochemistry), while chemical principles and methods can offer new research directions in plasmonics. Nanochemistry allows scientists to develop exquisitely accurate methods for the synthesis of nanostructures with high precision and provides tools for functionalizing and analyzing complex plasmonic nanostructures (e.g., heterostructured-nanoparticles). Therefore, recent advancements in nanochemistry with plasmonic materials have made a great impact on the proper use and real applications of plasmonics, and plasmonics offers in turn new pathways and tools for chemical processes. The field of chemical nanoplasmonics includes the study of nanoscale chemistry for the advancement of plasmonics and the use of plasmonics to address key issues and challenges in chemistry. Newly emerging principles, methods, and materials in plasmonics can be useful in various fields of chemistry, including optical and chemical hot spots, typically based on strong electromagnetic fields formed within plasmonic nanostructures, as well as single-molecule and 3D SERS with plasmonic hot-spot platforms. Plasmonic multimers (e.g., gold nanoparticle dimers), plasmonic supercrystals, plasmonic nanoparticle lattices, gold nanobipyramids, virus-sized gold nanorods, spherical nucleic acids, plasmonic metamaterials, and chiral plasmonic structures are some of the key nanostructures for materials chemistry-based plasmonics. Hot charge carriers and plasmon-driven catalysis have been identified as important directions for many subfields of chemistry including physical chemistry, materials chemistry, and catalysis. Further, newly emerging platforms such as plasmonic nanoparticle-interfaced cell membranes, DNA origami-based plasmonics, and graphene-based nonlinear plasmonics have emerged as next-generation platforms that can provide new ways of forming functional materials and devices, including optical and computing devices.
关键词： photovoltaics,plasmonics,nanochemistry,biochemistry,nanoplasmonics,sensing,surface-enhanced Raman scattering,therapeutics
更新于2025-09-12 10:27:22
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Development of Highly Reliable SERS‐active Photonic Crystal Fiber Probe and its Application in the Detection of Ovarian Cancer Biomarker in Cyst Fluid
摘要： Conventionally Surface enhanced Raman spectroscopy (SERS) is realized by adsorbing analytes onto nano-roughened planar substrate coated with noble metals (silver or gold) or their colloidal nanoparticles (NPs). Nano scale irregularities in such substrates/NPs could lead to SERS sensors with poor reproducibility and repeatability. Herein, we demonstrate a suspended core photonic crystal fiber (PCF) based SERS sensor with extremely high reproducibility and repeatability in measurement with a relative standard deviation of only 1.5% and 4.6% respectively, which makes it more reliable than any existing SERS sensor platforms. In addition, our platform could improve the detection sensitivity owing to the increased interaction area between the guided light and the analyte, which is incorporated into the holes that runs along the length of the PCF. Numerical calculation established the significance of the interplay between light coupling efficiency and evanescent field distribution, which could eventually determine the sensitivity and reliability of the developed SERS active-PCF sensor. As a proof of concept, using this sensor, we demonstrated the detection of haptoglobin, a biomarker for ovarian cancer, contained within the ovarian cyst fluid, which facilitated in differentiating the stages of the cancer. We envision that with necessary refinements, this platform could potentially be translated as a next generation highly sensitive SERS-active opto-fluidic biopsy needle for the detection of biomarkers in body fluids.
关键词： reproducibility and repeatability in measurement,Surface enhanced Raman scattering,photonic crystal fiber,biopsy needle,protein sensing,ovarian cancer
更新于2025-09-12 10:27:22
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Direct Laser Annealing of Surface‐Enhanced Raman Scattering Substrates
摘要： A laser-annealing technique for the fabrication of surface-enhanced Raman scattering (SERS) substrates consisting of closely packed gold nanoparticles (AuNPs) with high densities and small separation distances is reported. Laser annealing enables strongly localized interaction between the laser spot and the colloidal AuNPs within the irradiation area. Multiple stages of the alternative spin-coating of colloidal AuNPs and laser-annealing processes enable filling of the gaps between the AuNPs by newly produced ones in the subsequent stages. Thus, both the fill factor and the distribution density of the AuNPs are increased largely with increasing the number of fabrication stages, which favors the improvement of the SERS performance. In contrast, the conventional furnace or hot-plate annealing heats the substrate and the colloidal film simultaneously, and the melted AuNPs tend to aggregate to form larger ones with large separation distance. Thus, compared with the SERS effective by furnace-annealed substrates, laser-annealed substrates supply a further enhancement factor larger than 3.7. Thus, laser annealing is proved as a more effective approach for the fabrication of SERS substrates through annealing colloidal AuNPs.
关键词： direct laser annealing,furnace annealing,gap widths,surface-enhanced Raman scattering substrates,fill factors,closely packed gold nanoparticles
更新于2025-09-12 10:27:22
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Dual-Enhanced Raman Scattering-Based Characterization of Stem Cell Differentiation Using Graphene-Plasmonic Hybrid Nanoarray
摘要： Surface-enhanced Raman scattering (SERS) has demonstrated great potential to analyze a variety of bio/chemical molecular interactions within cells in a highly sensitive and selective manner. Despite significant advancements, it remains a critical challenge to ensure high sensitivity and selectivity, while achieving uniform signal enhancement and high reproducibility for quantitative detection of targeted biomarkers within a complex stem cell microenvironment. Herein, we demonstrate an innovative sensing platform, using graphene-coated homogeneous plasmonic metal (Au) nanoarrays, which synergize both electromagnetic mechanism (EM)- and chemical mechanism (CM)-based enhancement. Through the homogeneous plasmonic nanostructures, generated by laser interference lithography (LIL), highly reproducible enhancement of Raman signals could be obtained via a strong and uniform EM. Additionally, the graphene-functionalized surface simultaneously amplifies the Raman signals by an optimized CM, which aligns the energy level of the graphene oxide with the target molecule by tuning its oxidation levels, consequently increasing the sensitivity and accuracy of our sensing system. Using the dual-enhanced Raman scattering from both EM from the homogeneous plasmonic Au nanoarray and CM from the graphene surface, our graphene?Au hybrid nanoarray was successfully utilized to detect as well as quantify a specific biomarker (TuJ1) gene expression levels to characterize neuronal differentiation of human neural stem cells (hNSCs). Collectively, we believe our unique graphene?plasmonic hybrid nanoarray can be extended to a wide range of applications in the development of simple, rapid, and accurate sensing platforms for screening various bio/chemical molecules.
关键词： DNA detection,Surface-enhanced Raman scattering,biosensing,stem cell differentiation,2D nanomaterials
更新于2025-09-12 10:27:22
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Large-scale highly ordered periodic Au nano-discs/graphene and graphene/Au nanoholes plasmonic substrates for surface-enhanced Raman scattering
摘要： In this paper, the study of using masks to directly generate large area, highly ordered and periodical nanostructure has been exhibited. Periodic Au nano-discs(NDs) arrays have been fabricated on top of graphene by using holey Si3N4 mask which is directly fixed on top of graphene and Au metal is deposited through the holes in mask by thermal evaporation method under vacuum condition. This fabrication method provides an easy, fast and cost efficiency way to generate periodical nanostructure. Also, Au nanoholes(NHs) structure has been studied by using holey Si3N4 as a template. The surface-enhanced Raman scattering (SERS) sensitivities of periodical Au NDs/graphene and graphene/Au NHs hybrid structures have been systematically studied. The internal mechanisms could be explained by chemical mechanism effect of graphene and electromagnetic mechanism effect of metallic nano-structures. The enhancement factors have been systematically investigated by varying the diameter and the thickness of Au discs and Au NHs. Raman mappings of Au NDs with 2.5 μm diameter illustrate that the larger SERS enhancements exist in the rim of NDs which has good agreement with the electric field simulation result. The SERE enhancement factors of fluorescein obtained from Au NDs/graphene substrates shows an improvement factor of 500% in comparison of graphene substrate. The calculated SERS enhancement factors of graphene/Au NHs achieve 1,200% in comparison of graphene/planar Au film substrate.
关键词： graphene,surface-enhanced Raman scattering (SERS),periodic,Au nano-discs (NDs),Au nanoholes (NHs)
更新于2025-09-12 10:27:22
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One-Step Controlled Synthesis of Size-Tunable Toroidal Gold Particles for Biochemical Sensing
摘要： Controlling the size and shape of nanoparticles is a major goal in materials science. Here we show the fast, 30-minute, controlled one-step synthesis of gold particles (tAUPs) with sizes tunable from 350 nm to 1.7 microns by using a mixture of surfactant scaffolds made from sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). The as-synthesized tAUPs have nanospikes that protrude either inwards or outwards from the ring cavity. The number of nanospikes can be tuned by a two-step temperature change process to create so-called rough tAUPs. The toroidal gold particle structures exhibit surface plasmon extinction peaks in the near infrared-region and demonstrate a high surface-enhanced Raman scattering (SERS) sensitivity for the detection of 4-mercaptobenzoic acid (4-MBA) molecules. The protruding nanospikes significantly enhance the electromagnetic field oscillating inside the ring cavity. This is confirmed through sensitive detection of 4-MBA molecules as well as by simulation. Rough tAUP structures generate the highest sensitivity with an estimated total enhancement (TE) factor of 3.33 ×106, which is two orders of magnitude greater than reported by gold nanostars. A variety of different gold structures such as gold nanodendrites, nanowires, and nanochains can be obtained by changing the SDS to CTAB concentration ratios. The unique structures and plasmonic properties of tAUPs hold promise for ultrasensitive biochemical sensing.
关键词： toroidal gold particles (tAUPs),binary capping,surface-enhanced Raman scattering,mild reduction,surfactant template
更新于2025-09-11 14:15:04
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Controlling the Morphologies of Silver Aggregates by Laser-Induced Synthesis for Optimal SERS Detection
摘要： Controlling the synthesis of metallic nanostructures for high quality surface-enhanced Raman scattering (SERS) materials has long been a central task of nanoscience and nanotechnology. In this work, silver aggregates with different surface morphologies were controllably synthesized on a glass–solution interface via a facile laser-induced reduction method. By correlating the surface morphologies with their SERS abilities, optimal parameters (laser power and irradiation time) for SERS aggregates synthesis were obtained. Importantly, the characteristics for largest near-field enhancement were identified, which are closely packed nanorice and flake structures with abundant surface roughness. These can generate numerous hot spots with huge enhancement in nanogaps and rough surface. These results provide an understanding of the correlation between morphologies and SERS performance, and could be helpful for developing optimal and applicable SERS materials.
关键词： laser-induced synthesis,silver aggregates,surface-enhanced Raman scattering,hot spots
更新于2025-09-11 14:15:04