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Considering that the plasmonic properties of metallic nanoparticles (NPs) are strongly influenced by their dielectric environment, comprehension and manipulation of this interplay are crucial for the design and optimization of functional plasmonic systems. In this study, the plasmonic behavior of silver nanoparticles encapsulated in diverse copolymer dielectric environments was investigated, focusing on the analysis of the emerging localized surface plasmon resonances (LSPRs) through both experimental and theoretical approaches. Specifically, two series of nanostructured silver ultrathin films were deposited via magnetron sputtering on heated Corning Glass substrates at 330 °C and 420 °C, respectively, resulting in the formation of self-assembled NPs of various sizes and distributions. Subsequently, three different polymeric layers were spin-coated on top of the silver NPs. Optical and structural characterization were carried out by means of UV–Vis spectroscopy and atomic force microscopy, respectively. Rigorous Coupled Wave Analysis (RCWA) was employed to study the LSPRs theoretically. The polymeric environment consistently induced a red shift as well as various alterations in the LSPR amplitude, suggesting the potential tunability of the system.

Oxygen vacancies (OV) in nonmetallic plasmonic photocatalysts can decrease the energy barrier for CO2 reduction, boosting C1 intermediate production for potential C2 formation. However, their susceptibility to oxidation weakens C1 intermediate adsorption. Herein we proposed a "photoelectron injection" strategy to safeguard OV in W18O49 by creating a W18O49/ZIS (W/Z) plasmonic photocatalyst. Moreover, photoelectrons contribute to the local multi‐electron environment of W18O49, enhancing the intrinsic excitation of its hot electrons with extended lifetimes, as confirmed by in situ XPS and femtosecond transient absorption analysis. Density functional theory calculations revealed that W/Z with OV enhances CO2 adsorption, activating *CO production, while reducing the energy barrier for *COH production (0.054 eV) and subsequent *CO−*COH coupling (0.574 eV). Successive hydrogenation revealed that the free energy for *CH2CH2 hydrogenation (0.108 eV) was lower than that for *CH2CH2 desorption for C2H4 production (0.277 eV), favouring C2H6 production. Consequently, W/Z achieves an efficient C2H6 activity of 653.6 μmol g−1 h−1 under visible light, with an exceptionally high selectivity of 90.6 %. This work offers a new strategy for the rational design of plasmonic photocatalysts with high selectivity for C2+ products. [ABSTRACT FROM AUTHOR]

MOFs are known for their absorption properties and widely used for accumulation, filtering, sensorics, photothermal, catalytical and other applications. Their combination with plasmonic metal nanoparticles leads to hybrid structures that profit from the stabilizing effect and high porosity of the MOF as well as the optical and electronic properties of the nanoparticles. The growth of MOFs on plasmonic nanoparticles can be monitored in‐situ using LSPR spectroscopy, simultaneously applying microfluidic reaction conditions for the fabrication of NP@MOF structures. Here, a systematic study is conducted using LSPR spectroscopy for the monitoring of the Layer‐by‐Layer deposition of twelve different MOFs, determining the suitability of LSPR spectroscopy for this purpose. In addition to some well‐investigated materials like HKUST‐1, other MOFs such as MIL‐53, MIL‐88 A and Cu‐BDC are deposited successfully. For some MOFs such as Zn‐Fum, the LSPR experiment indicates that no deposition had taken place. The results are confirmed with AFM, SEM and XPS measurements. This work shows that LSPR spectroscopy is suitable for the in‐situ monitoring of LbL MOF growth and the microfluidic setup is a very promising method for the controlled manufacturing of NP@MOF hybrid structures. Further studies may include the optimization of the synthesis process or the transfer to other materials. [ABSTRACT FROM AUTHOR]

Optical materials with a tunable localized surface plasmon resonance (LSPR) are of great interest for applications in photonics and optoelectronics. In the present study, we explored the potential of generating an LSPR band with an ultra-broad range of over 1000 nm in gold nanoparticles (NPs), precipitated through a thermal treatment in ZnO-Al2O3-SiO2 glass. Using optical absorption spectroscopy, we demonstrated that the LSPR band's position and shape can be finely controlled by varying the thermal treatment route. Comprehensive methods including Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy were used to study the glass structure, while computational approaches were used for the theoretical description of the absorption spectra. The obtained results allowed us to suggest a scenario responsible for an abnormal LSPR band broadening that includes a possible interparticle plasmonic coupling effect taking place during the liquid–liquid phase separation of the heat-treated glass. The formation of gold NPs with an ultra-broad LSPR band in glasses holds promise for sensitizing rare earth ion luminescence for new photonics devices. [ABSTRACT FROM AUTHOR]

Considering that the plasmonic properties of metallic nanoparticles (NPs) are strongly influenced by their dielectric environment, comprehension and manipulation of this interplay are crucial for the design and optimization of functional plasmonic systems. In this study, the plasmonic behavior of silver nanoparticles encapsulated in diverse copolymer dielectric environments was investigated, focusing on the analysis of the emerging localized surface plasmon resonances (LSPRs) through both experimental and theoretical approaches. Specifically, two series of nanostructured silver ultrathin films were deposited via magnetron sputtering on heated Corning Glass substrates at 330 °C and 420 °C, respectively, resulting in the formation of self-assembled NPs of various sizes and distributions. Subsequently, three different polymeric layers were spin-coated on top of the silver NPs. Optical and structural characterization were carried out by means of UV–Vis spectroscopy and atomic force microscopy, respectively. Rigorous Coupled Wave Analysis (RCWA) was employed to study the LSPRs theoretically. The polymeric environment consistently induced a red shift as well as various alterations in the LSPR amplitude, suggesting the potential tunability of the system. [ABSTRACT FROM AUTHOR]

Optical materials with a tunable localized surface plasmon resonance (LSPR) are of great interest for applications in photonics and optoelectronics. In the present study, we explored the potential of generating an LSPR band with an ultra-broad range of over 1000 nm in gold nanoparticles (NPs), precipitated through a thermal treatment in ZnO-Al2O3-SiO2 glass. Using optical absorption spectroscopy, we demonstrated that the LSPR band’s position and shape can be finely controlled by varying the thermal treatment route. Comprehensive methods including Raman spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy were used to study the glass structure, while computational approaches were used for the theoretical description of the absorption spectra. The obtained results allowed us to suggest a scenario responsible for an abnormal LSPR band broadening that includes a possible interparticle plasmonic coupling effect taking place during the liquid–liquid phase separation of the heat-treated glass. The formation of gold NPs with an ultra-broad LSPR band in glasses holds promise for sensitizing rare earth ion luminescence for new photonics devices.

The utilization of plasmonic nanomaterials in catalytic technologies is an emerging research field with foreseeable applications in energy-catalytic technologies. On this front, the coupling of plasmonic nanomaterials with molecular catalysts is a newly approached, thus far unexploited field, that we discuss herein. In the present mini review, we contrast the case where the plasmonic particle itself is the catalytic center against the case where the plasmonic particle acts as a co-catalyst for an operational catalytic system. In the first part, we present an outline of the key phenomena in nanoplasmonics, and their potential implications in catalytic processes. The concepts of hot electrons, hot holes, and the dynamics of their generation and transfer are reviewed, as are the contribution of near-field and photothermal effects to catalytic processes. All these plasmonic-phenomena are then discussed in conjunction with representative catalytic systems from the literature. [ABSTRACT FROM AUTHOR]

The increasing demand for rapid, cost-effective, and reliable diagnostic tools in personalized and point-of-care medicine is driving scientists to enhance existing technology platforms and develop new methods for detecting and measuring clinically significant biomarkers. Humanity is confronted with growing risks from emerging and recurring infectious diseases, including the influenza virus, dengue virus (DENV), human immunodeficiency virus (HIV), Ebola virus, tuberculosis, cholera, and, most notably, SARS coronavirus-2 (SARS-CoV-2; COVID-19), among others. Timely diagnosis of infections and effective disease control have always been of paramount importance. Plasmonic-based biosensing holds the potential to address the threat posed by infectious diseases by enabling prompt disease monitoring. In recent years, numerous plasmonic platforms have risen to the challenge of offering on-site strategies to complement traditional diagnostic methods like polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA). Disease detection can be accomplished through the utilization of diverse plasmonic phenomena, such as propagating surface plasmon resonance (SPR), localized SPR (LSPR), surface-enhanced Raman scattering (SERS), surface-enhanced fluorescence (SEF), surface-enhanced infrared absorption spectroscopy, and plasmonic fluorescence sensors. This review focuses on diagnostic methods employing plasmonic fluorescence sensors, highlighting their pivotal role in swift disease detection with remarkable sensitivity. It underscores the necessity for continued research to expand the scope and capabilities of plasmonic fluorescence sensors in the field of diagnostics. [ABSTRACT FROM AUTHOR]

Plasmonic heterostructures refer to the class of hybrid nanostructures where two or more nanocrystals (NCs) are chemically bonded, at least one of which is plasmonic. The light concentration property of plasmons is used to manipulate the light–matter interaction in the resulting heterostructures for applications in the fields of nanoscience, photonics, catalysis, and biology among many others. With the advancement of colloidal synthesis, plasmonic heterostructures have a versatile landscape of their own in the last couple of decades. In particular, after the discovery of semiconductor plasmonic NCs (In2O3, CdO, Cu2–xS, etc.) and halide perovskite NCs (CsPbX3, X: Cl, Br, I), the possibility of heterostructures expanded multifold. Nevertheless, challenges remain in successfully synthesizing phase pure structures, optimizing the right geometry and composition for applications, or more fundamentally, observing plasmonic properties despite the formation of heterostructures. In this Review, we briefly review the progress of the colloidal plasmonic heterostructures in terms of synthesis, optical properties, and applications. We discuss these aspects in the traditional noble metal nanoparticle-based compounds, followed by semiconductor plasmonic and halide perovskite heterostructures. We specifically focus on the current challenges faced by the research community in the field of plasmonic halide perovskites and how fundamental design principles can bypass the current limitations. [ABSTRACT FROM AUTHOR]

This work explores the utilization of plasmonic resonance (PR) in silver nanowires to enhance the performance of organic solar cells. We investigate the simultaneous effect of localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), and waveguide plasmonic mode on silver nanowires, which have not been thoroughly explored before. By employing finite-difference time-domain (FDTD) simulations, we analyze the plasmonic resonance behavior of a ZnO/Silver nanowires/ZnO (ZAZ) electrode structure. Our investigations demonstrate the dominance of LSPR, leading to intense electric fields inside the nanowire and their propagation into the surrounding medium. Additionally, we observe the synergistic effects of SPP and waveguide plasmonic mode, contributing to enhanced light absorption within the active layer of the organic solar cell. This leads to an improvement in photovoltaic performance, as demonstrated by our previous work, showing an approximate 20% increase in photocurrent and overall power conversion efficiency of the organic solar cell. The incorporation of metallic nanostructures exhibiting these multiple plasmonic modes opens up new opportunities for improving light absorption and overall device efficiency. Our study highlights the potential of these combined plasmonic effects for the design and optimization of organic solar cells. [ABSTRACT FROM AUTHOR]

The increasing demand for rapid, cost-effective, and reliable diagnostic tools in personalized and point-of-care medicine is driving scientists to enhance existing technology platforms and develop new methods for detecting and measuring clinically significant biomarkers. Humanity is confronted with growing risks from emerging and recurring infectious diseases, including the influenza virus, dengue virus (DENV), human immunodeficiency virus (HIV), Ebola virus, tuberculosis, cholera, and, most notably, SARS coronavirus-2 (SARS-CoV-2; COVID-19), among others. Timely diagnosis of infections and effective disease control have always been of paramount importance. Plasmonic-based biosensing holds the potential to address the threat posed by infectious diseases by enabling prompt disease monitoring. In recent years, numerous plasmonic platforms have risen to the challenge of offering on-site strategies to complement traditional diagnostic methods like polymerase chain reaction (PCR) and enzyme-linked immunosorbent assays (ELISA). Disease detection can be accomplished through the utilization of diverse plasmonic phenomena, such as propagating surface plasmon resonance (SPR), localized SPR (LSPR), surface-enhanced Raman scattering (SERS), surface-enhanced fluorescence (SEF), surface-enhanced infrared absorption spectroscopy, and plasmonic fluorescence sensors. This review focuses on diagnostic methods employing plasmonic fluorescence sensors, highlighting their pivotal role in swift disease detection with remarkable sensitivity. It underscores the necessity for continued research to expand the scope and capabilities of plasmonic fluorescence sensors in the field of diagnostics.

Plasmonic effect-enhanced Z-type heterojunction photocatalysts comprise a promising solution to the two fundamental problems of current TiO2-based photocatalysis concerning low-charge carrier separation efficiency and low utilization of solar illumination. A plasmonic effect-enhanced TiN@anatase-TiO2/rutile-TiO2 Z-type heterojunction photocatalyst with the strong interface of the N–O chemical bond was synthesized by hydrothermal oxidation of TiN. The prepared photocatalyst shows desirable visible light absorption and good visible-light-photocatalytic activity. The enhancement in photocatalytic activities contribute to the plasma resonance effect of TiN, the N–O bond-connected charge transfer channel at the TiO2/TiN heterointerface, and the synergistically Z-type charge transfer pathway between the anatase TiO2 (A-TiO2) and rutile TiO2 (R-TiO2). The optimization study shows that the catalyst with a weight ratio of A-TiO2/R-TiO2/TiN of approximately 15:1:1 achieved the best visible light photodegradation activity. This work demonstrates the effectiveness of fabricating plasmonic effect-enhanced Z-type heterostructure semiconductor photocatalysts with enhanced visible-light-photocatalytic activities. [ABSTRACT FROM AUTHOR]

Localized surface plasmonic resonance (LSPR) provides a unique scheme for light management and has been demonstrated across a large variety of metallic nanostructures. More recently, non-metallic nanostructures of two-dimensional atomic materials and heterostructures have emerged as a promising, low-cost alternative in order to generate strong LSPR. In this paper, a review of the recent progress made on non-metallic LSPR nanostructures will be provided in comparison with their metallic counterparts. A few applications in optoelectronics and sensors will be highlighted. In addition, the remaining challenges and future perspectives will be discussed. [ABSTRACT FROM AUTHOR]

Plasmonic nanomaterials have attracted great attention in the field of catalysis and sensing for their outstanding electrical and optical properties. Here, a representative type of nonstoichiometric Cu2−xSe nanoparticles with typical near-infrared (NIR) localized surface plasma resonance (LSPR) properties originating from their copper deficiency was applied to catalyze the oxidation of colorless TMB into their blue product in the presence of H2O2, indicating they had good peroxidase-like activity. However, glutathione (GSH) inhibited the catalytic oxidation of TMB, as it can consume the reactive oxygen species. Meanwhile, it can induce the reduction of Cu(II) in Cu2−xSe, resulting in a decrease in the degree of copper deficiency, which can lead to a reduction in the LSPR. Therefore, the catalytic ability and photothermal responses of Cu2−xSe were decreased. Thus, in our work, a colorimetric/photothermal dual-readout array was developed for the detection of GSH. The linear calibration for GSH concentration was in the range of 1–50 μM with the LOD as 0.13 μM and 50–800 μM with the LOD as 39.27 μM. To evaluate the practicability of the assay, tomatoes and cucumbers were selected as real samples, and good recoveries indicated that the developed assay had great potential in real applications. [ABSTRACT FROM AUTHOR]

Chiral plasmonic nanostructures have emerged as promising objects for numerous applications in nanophotonics, optoelectronics, biosensing, chemistry, and pharmacy. Here, we propose a novel method to induce strong chirality in achiral ensembles of gold nanoparticles via irradiation with circularly-polarized light of a picosecond Nd:YAG laser. Embedding of gold nanoparticles into a nanoporous silicate matrix leads to the formation of a racemic mixture of metal nanoparticles of different chirality that is enhanced by highly asymmetric dielectric environment of the nanoporous matrix. Then, illumination with intense circularly-polarized light selectively modifies the particles with the chirality defined by the handedness of the laser light, while their "enantiomers" survive the laser action almost unaffected. This novel modification of the spectral hole burning technique leads to the formation of an ensemble of plasmonic metal nanoparticles that demonstrates circular dichroism up to 100 mdeg. An unforeseen peculiarity of the chiral nanostructures obtained in this way is that 2D and 3D nanostructures contribute almost equally to the observed circular dichroism signals. Thus, the circular dichroism is neither even nor odd under reversal of direction of light propagation. These findings will help guide the development of a passive optical modulator and nanoplatform for enhanced chiral sensing and catalysis. [ABSTRACT FROM AUTHOR]

Plasmonic materials currently have a plethora of applications. How would a dielectric matrix, such as diblock copolymers, tune plasmonic properties? In this work, self-assembled gold nanoparticles were fabricated in medium vacuum conditions on heated Corning glass substrates (kept at 440 °C) under the coexistence of argon and air by means of DC magnetron sputtering. These samples were compared structurally and optically to samples deposited at room temperature and post annealed. Subsequently, the better of the two preparations, those deposited on heated glass, were covered with three different polymers, namely: Polystyrene-block-polybutadiene-block-polystyrene (PS-b-PBD-b-PS); Polystyrene-co-methyl methacrylate (PS-co-PMMA); and Polystyrene-block-polyisoprene-block-polystyrene (PS-b-PI-b-PS), by means of spin coating. Localized surface plasmon resonances were recorded and analyzed, respectively, for polymer-covered gold nanoparticles, with the width, intensity, and position of the resonances changing according to multiple factors, such as the nanoparticles size and the refractive index of each polymer. Lastly, for purposes of justification and comparison with the experimental results, rigorous theoretical calculations have been carried out. [ABSTRACT FROM AUTHOR]

Gold nanostars (NS) are emerging as a versatile tool in surface-enhanced Raman scattering (SERS) applications because of their wide localized surface plasmon resonance (LSPR) tunability, simple synthesis procedure, and high SERS enhancement. These particles are commonly used in solutions with a stabilizing coating shell (e.g., thiolated molecules or silver shell). However, coatings cannot be used for the fabrication of SERS substrates as the NS have to interact with the substrate planar surface. Without coating, NS have been observed to change over time, leading to a hypochromic shift of the LSPR. To understand this shift, we synthesized surfactant-free gold NS with different spike morphologies and investigated their reshaping morphology and kinetics. Using TEM, the NS sharp spike features were observed to reshape over time. The kinetics of this process were analyzed and determined by monitoring the LSPR, which was observed to follow an exponential decay over time. We used an empirical fit for the LSPR-shift data as a function of time, which permits to predict the LSPR at a specific time based only on the initial LSPR (independently of the initial spike morphology). We show the effect of the LSPR on the SERS signal for the NS and how the SERS signal correlated to our prediction. Finally, we evaluated our approach by fabricating SERS substrates with immobilized NS and collecting the reflectance spectra. We were able to predict the substrate LSPR and aim for an optimal LSPR with an average 3% deviation. These new insights on NS reshaping can permit the fabrication of NS-based substrates with desirable optical/plasmonic properties. Graphical Abstract [ABSTRACT FROM AUTHOR]

Metallic nanoparticles have been extensively used to adsorb biomolecules and improve their stability under broader conditions. This study focuses on the interaction of Cytochrome C (CytC) and gold nanoparticles (AuNP), CytC@AuNP. Circular dichroism (CD) and Raman show significant differences in secondary structure, mainly in α‐helix. CD ramp temperatures revealed enhanced thermal stability of CytC@AuNP, as evidenced by a refolding of the α‐helix conformation of CytC and a delay in denaturation temperature by approximately 15 °C. Catalytic oxidation performed with CytC@AuNP showed a hyperbolic profile up to 104 % higher yields compared to CytC, which exhibited a linear profile and 30 % loss of activity after thermal treatment. The same reaction performed upon plasmon stimulus comparatively increased the catalytic yield of CytC@AuNP in 12 %, although it had no effect on free CytC. This study highlights the advantages of adsorbing biomolecules on nanoparticles and is a glimpse at plasmon‐driven nanobiocatalysis. [ABSTRACT FROM AUTHOR]

Biochemical–chemical sensing with plasmonic sensors is widely performed by tracking the responses of surface plasmonic resonance peaks to changes in the medium. Interestingly, consistent sensitivity and resolution improvements have been demonstrated for gold nanoparticles by analyzing other spectral features, such as spectral inflection points or peak curvatures. Nevertheless, such studies were only conducted on planar platforms and were restricted to gold nanoparticles. In this work, such methodologies are explored and expanded to plasmonic optical fibers. Thus, we study—experimentally and theoretically—the optical responses of optical fiber-doped gold or silver nanospheres and optical fibers coated with continuous gold or silver thin films. Both experimental and numerical results are analyzed with differentiation methods, using total variation regularization to effectively minimize noise amplification propagation. Consistent resolution improvements of up to 2.2× for both types of plasmonic fibers are found, demonstrating that deploying such analysis with any plasmonic optical fiber sensors can lead to sensing resolution improvements. [ABSTRACT FROM AUTHOR]

In this work, the plasmonic properties of magnetic and liquid nanoparticles coated with aluminium are studied for egg-like/multilayer structures. The optical spectra of multilayers nanoparticles under core–shell or bi-layer (Fe/FeO/Fe2O3/Fe3O4@Al, Cs/Cs2O@Al) and egg-like or multilayer (Fe/FeO/Fe2O3/Fe3O4@Cs/Cs2O@Al) nanostructures are theoretically investigated. Variations in materials types and size parameters including inner core, shell, and outer shell have shown their significant influence on enhancement in LSPR peak position, intensity, and broadening. It is observed that the LSPR peak position effectively increased with pure materials and the peak's intensity along with line-width or broadening increased with oxide materials in core–shell configuration. In an egg-like/multilayer configuration, varying sizes of oxide materials in the core, as well as shell, have their direct impact on line-width as well as the intensity of peaks. It is found that the LSPR peaks get red-shifted with increasing core size and blue-shifted with increasing shell thickness and enhanced spectra are seen for Fe2O3-core with varying Al-shell thickness. The plasmonic LSPR peaks at λmax are revealed in the range of 221–1004 nm wavelengths and tuned in the deep UV–visible-NIR region of core–shell and visible region of egg-like (multilayer) nanostructures. Such response of core–shell and egg-like/multilayer nanostructures for optical-absorption properties opens new potential in stretchable plasmonic devices, solar cells, and therapeutic as well as appropriate light absorption-based applications. [ABSTRACT FROM AUTHOR]

Surface enhanced infrared absorption (SEIRA) is an experimental method where trace amount of a compound can be detected with high sensibility. This high detection sensibility is the result of the interaction of the molecules with a localized plasmon, usually from a metallic nanoparticle. In this study we numerically investigate by discrete dipole approximation the origin of the Fano-like response of the system, including the induced transparency when the plasmon resonance and the molecular vibrational mode coincide. The detailed analysis of the localization of the absorption shows that the modification of the absorption cross-section when the molecule is present comes from a change of the plasmonic resonance, not from the direct molecular response which is negligible. This sheds a new light on the SEIRA mechanism. In particular, it demonstrates that the sensibility is associated with the influence of the molecule on the plasmon resonance rather than with the local field enhancement itself.

Gallium based alloy nanoparticles are of great concern in the field of liquid plasmonics. The study focuses on optical properties of gallium alloy nanoparticles in sphere and spheroidal shapes. The absorption spectra are tuned for different sizes and aspect ratios. Herein, we observe core–shell nanoparticles for different core (GaAg, GaAl, GaHg and GaIn) and same Ag shell, to study the dominance of core and shell on localized surface plasmon resonance (LSPR) induced properties. This work is solely dedicated for analyzing shape effects on LSPR of Ga based alloys other than Gallinstan and EGaIn etc. The effect of fixed aspect ratio and variable effective radius on the optical efficiencies of spheroidal (prolate) nanoparticles is analyzed in comparison to spherical and oblate nanoparticles for corresponding effective radius. Mie theory and discrete dipole approximation (DDA) methods are used for analyzing the optical behavior of Ga based alloys for different size and shapes. The spectra are observed within near UV and Visible region of electromagnetic spectrum. Gallium alloys: GaAg and GaAl show good plasmonic behavior as an alternative material to popular GaIn and can serve as an application in various plasmonics process based energy storage devices and soft electronics. [ABSTRACT FROM AUTHOR]

In this work, an Si–SiO2–ZnO–Au nanoparticles (NPs) structure based plasmonic multilayer FET design is studied for sensing application. Here, Si is used as a substrate, ZnO is used as an active layer, and Au NPs are used to introduce the plasmonic enhancement effect in the proposed FET design. The simulation and analysis are carried out in the visible spectral range. The effect of design parameters such as the diameter of Au NPs, obliqueness of light incidence, and spacing between Au NPs is studied on the sensor's sensitivity. Further, the effect of incorporating 3-mercapto propionic acid (3-MPA) with Au NPs has been studied while targeting an increase in sensitivity of the proposed device. The results indicate that the size of NPs and angle of light incidence have a coupled effect on the sensitivity. Further, at normal incidence, the larger size of Au NPs can be helpful in achieving greater sensitivity (finer limit of detection) and larger figure of merit. Also, smaller spacing between the NPs leads to enhanced absorption behaviour. Furthermore, the incorporation of 3-MPA has the capability to increase the sensitivity, particularly for the detection of low refractive index (RI) media (e.g., gaseous ones). The proposed device design can be helpful in gaseous and RI sensing along with biosensing (with 3-MPA) in the visible spectral range. [ABSTRACT FROM AUTHOR]

With the growing need for portable, compact, low-cost, and efficient biosensors, plasmonic materials hold the promise to meet this need owing to their label-free sensitivity and deep light–matter interaction that can go beyond the diffraction limit of light. In this review, we shed light on the main physical aspects of plasmonic interactions, highlight mainstream and future plasmonic materials including their merits and shortcomings, describe the backbone substrates for building plasmonic biosensors, and conclude with a brief discussion of the factors affecting plasmonic biosensing mechanisms. To do so, we first observe that 2D materials such as graphene and transition metal dichalcogenides play a major role in enhancing the sensitivity of nanoparticle-based plasmonic biosensors. Then, we identify that titanium nitride is a promising candidate for integrated applications with performance comparable to that of gold. Our study highlights the emerging role of polymer substrates in the design of future wearable and point-of-care devices. Finally, we summarize some technical and economic challenges that should be addressed for the mass adoption of plasmonic biosensors. We believe this review will be a guide in advancing the implementation of plasmonics-based integrated biosensors. [ABSTRACT FROM AUTHOR]

Complex shapes of gold nanostars (GNS) have been the major obstacle to the comprehensive understanding of the rich plasmonic phenomena of GNS. We conducted extensive, systematic numerical study of far-field and near-field spectral responses of GNS for varying geometrical parameters (e.g., number of spikes, spike tip angle, and spike-to-core ratio) to elucidate the relationship between the optical property and the geometry of GNS. We found that symmetric configurations of GNS spikes generated both dipole and quadrupole localized surface plasmon (LSP) modes, their hybridization resulted in the final near-field intensity at the spike tips, and there existed a specific GNS geometry that optimized the hybridization and thus the E-field intensity for any given wavelength. From these results, we further identified the shapes of GNS that generated the strongest Surface Enhanced Raman Scattering (SERS) enhancement factors in the visible and NIR spectral range. Hence, our results provide guiding principles in determining the optimal geometry of GNS for SERS applications with any choice of excitation wavelength. [ABSTRACT FROM AUTHOR]

In the field of plasmonics, the nanogap effect is often related to one aspect like the far-field resonance shift or near-field enhancement. In this study, we present a details analysis of the nanogap effect on plasmonic behaviours of the magneto-plasmonic dimer Ni–Ag and Ni–Au nanoparticles by taking the full advantages of DDA simulation. The sets of non-spherical dimer nanostructure viz. edge-to-edge (EE) and face-to-face (FF) and spherical dimer nanoparticles for plasmonic properties like LSPR peak position's tunability as well as peak intensity at the maximum wavelength (λmax.) and near-field enhancement in Ni–Ag and Ni–Au heterodimer nanoparticles is studied. It is observed that the emerging spectra are found between the UV–visible regions (357–586 nm) for spherical dimer nanostructure while prolate dimers are in the UV–visible-Near Infrared region (345–817 nm) under both EE and FF configurations. The emergent wavelength-dependent spectra with varying nanogap between the dimer are red-shifted. The maximum plasmonic field enhancement is observed for Ni–Ag as compared to Ni–Au dimer nanoparticles under spherical and prolate geometry. It is found that the FF configuration of Ni–Ag and Ni–Au dimers nanoparticles has maximum field enhancement in comparison to the EE configuration. These results could have a big impact on how surface-enhanced spectroscopies and related plasmonic instruments based on E-field hot spots or intensity are being utilized. [ABSTRACT FROM AUTHOR]

A hybrid plasmonic transducer made of a Poly‐(ethylene glycol) diacrylate (PEGDA) hydrogel and citrate gold nanoparticles detects the biotin‐streptavidin interaction at picomolar (× 10−12m) concentrations. The all‐solution fabrication strategy, herein proposed, is large‐scale, easily tunable, and low‐cost; nevertheless, this innovative device is highly reproducible and optically stable, and it can be used in dual‐optical mode. Indeed, both metal‐enhanced fluorescence and localized surface plasmon resonance signals can be exploited to quantify the biorecognition process in a 3D architecture. The large swelling capability of high molecular weight PEGDA is used to investigate the plasmon absorption variations resulting from the exposure to biological solutions containing high molecular weight molecules within the 3D network. The proposed transducer represents a low‐cost, flexible, and easy‐to‐use platform for sensing applications in biomedical or environmental diagnostics. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the fabrication of LSPR sensor chips consisting of crystalline gold nanoparticles (AuNPs) over a large area. These crystalline AuNPs were grown on a heated silica substrate via thermal evaporation in a simple single-step fabrication process. To the best of our knowledge, the fabrication of LSPR sensor chips via the growth of crystalline AuNPs has not been demonstrated earlier. We present a process of AuNP growth wherein nanoparticles have been successfully formed for deposition thicknesses up to 40 nm at comparatively lower temperatures than what has been demonstrated earlier. The crystalline AuNPs are formed during the evaporation process, without the requirement of any additional annealing time. The growth of crystalline AuNPs, as proposed in this paper, enables the formation of AuNPs for larger values of equivalent QCM film thicknesses, going up to 40 nm, and possibly even higher. The AuNPs from different values of film thicknesses also allow the tuning of LSPR peak wavelength over a wider range of the visible spectrum. Increased crystallinity was also obtained in the nanoparticles grown at high temperatures and for larger thicknesses. The evaluation of the LSPR sensor chips containing these crystalline AuNPs showed that high surface sensitivity of 28.89 nm/nm was obtained for a conformal thin film layer of Al2O3 over the AuNPs, which is higher than what has been demonstrated earlier. These sensor chips containing crystalline AuNPs also show higher bulk sensitivity than what has been reported previously for AuNPs nanoparticles formed by template-free methods and annealing. [ABSTRACT FROM AUTHOR]

Doping plasmonic nanoparticles in aerogel to achieve optical selectivity can significantly extend its applicable prospect. An optical selectivity aerogel by doping with gold/silver nanoparticles is introduced in this work. The radiative properties of optical selectivity aerogels were predicted by the combination of T-matrix and Monte Carlo method. The effects of morphology, aspect ratio, size, and doping concentration of nanoparticles on the spectral selectivity of the hybrid aerogels were discussed. The results show that the aspect ratio of the plasmonic particle affects the multispectral conversion of solar radiation significantly. The aerogel containing silver nanocylinders of AR = 0.2 and ITO nanospheres achieves the highest solar energy absorption. Even with an extremely low doping concentration (f v,ITO = 0.01% and f v,p = 0.001%), the absorption to solar radiation can be increased by over 75% for a 1 cm thick aerogel, which can be employed for efficient solar desalination. In addition, by doping with silver nanocylinders (AR = 0.15), the hybrid aerogel is penetrable to the visible light but absorbs infrared solar radiation for the application of anti-fogging/deicing. The silver nanospheroids (AR = 0.3)-based hybrid aerogel can serve as a greenhouse envelope for augmented photosynthesis to absorb the green light while allowing most of the other wavelengths of solar radiation to pass through. • An optical selectivity aerogel is proposed by doping plasmonic nanoparticles. • The radiative properties of the aerogel are investigated theoretically. • The aerogels are optimal designed for multispectral conversion of solar radiation. [ABSTRACT FROM AUTHOR]

The activation of Au–Ag plasmonic bimetallic nanocatalyst can make the nanocatalyst exhibit superior visible-light (VL) photocatalytic activity. An efficient activation of Au–Ag nanocatalyst by cold plasma requires the restructuring of Au and Ag species over catalyst surface to form Au–Ag alloy nanoparticles while suppressing agglomeration of the nanoparticles. We here report that the loading sequence of Au and Ag components on titanium dioxide (TiO2) support during catalyst preparation and discharge atmosphere play important roles in the plasma activation. Preparation of AuAg/TiO2 nanocatalyst by depositing Ag and Au in sequence could avoid the undesired loss of Ag component, and ensure an effective restructuring of Au and Ag species in O2 plasma activation. Compared with the reductive (H2) and inert (Ar and N2) plasmas, discharge in oxidative O2 establishes Coulomb field with the negatively charged species over catalyst surface and enable the restructuring and intimate interaction of Au and Ag species. The catalyst characterization and density functional theory calculations suggest that O2 plasma endows AuAg/TiO2 nanocatalyst with large numbers of Au–Ag alloy nanoparticles, small size of plasmonic nanoparticles, high density of coordinatively unsaturated sites, and high content of surface oxygen species in the activation, which facilitates the adsorption and activation of O2, and thus CO oxidation reaction under VL irradiation. [ABSTRACT FROM AUTHOR]

Biochemical–chemical sensing with plasmonic sensors is widely performed by tracking the responses of surface plasmonic resonance peaks to changes in the medium. Interestingly, consistent sensitivity and resolution improvements have been demonstrated for gold nanoparticles by analyzing other spectral features, such as spectral inflection points or peak curvatures. Nevertheless, such studies were only conducted on planar platforms and were restricted to gold nanoparticles. In this work, such methodologies are explored and expanded to plasmonic optical fibers. Thus, we study—experimentally and theoretically—the optical responses of optical fiber-doped gold or silver nanospheres and optical fibers coated with continuous gold or silver thin films. Both experimental and numerical results are analyzed with differentiation methods, using total variation regularization to effectively minimize noise amplification propagation. Consistent resolution improvements of up to 2.2× for both types of plasmonic fibers are found, demonstrating that deploying such analysis with any plasmonic optical fiber sensors can lead to sensing resolution improvements.

We report radiatively coupled arrayed gold nanodisks on invisible substrate (AGNIS) as a cost-effective, high-performance platform for nanoplasmonic biosensing. By substrate undercut, the electric field distribution around the nanodisks has been restored to as if the nanodisks were surrounded by a single medium, thereby provides analyte accessibility to otherwise buried enhanced electric field. The AGNIS substrate has been fabricated by wafer-scale nanosphere lithography without the need for costly lithography. The LSPR blue-shifting behavior synergistically contributed by radiative coupling and substrate undercut have been investigated for the first time, which culminates in a remarkable refractive index sensitivity increase from 207 nm/RIU to 578 nm/RIU. The synergy also improves surface sensitivity to monolayer neutravidin-biotin binding from 7.4 nm to 20.3 nm with the limit of detection (LOD) of neutravidin at 50 fM, which is among the best label-free results reported to date on this specific surface binding reaction. As a potential cancer diagnostic application, extracellular vesicles such as exosomes excreted by cancer and normal cells were measured with a LOD within 112–600 (exosomes/ $\mu \text{L}$), which would be sufficient in many clinical applications. Using CD9, CD63, and CD81 antibodies, label-free profiling has shown increased expression of all three surface antigens in cancer-derived exosomes. This work demonstrates, for the first time, strong synergy of arrayed radiative coupling and substrate undercut can enable economical, ultrasensitive biosensing in the visible light spectrum where high-quality, low-cost silicon detectors are readily available for point-of-care applications. [ABSTRACT FROM AUTHOR]

The review summarizes numerical technique employed simulations of optical fiber plasmonic sensors (OFPS) based on fiber types, probe geometry, metal-dielectric film, and nanostructures. The recent progress in nano-optics has developed susceptible and label-free optical devices by using SPR/LSPR techniques of the thin metal film and nanostructures. The survey focuses on the contribution of numerical analysis based on highly reliant OFPS, incorporating metal layers, strips, nanoparticles, nanowires, metamaterials, along with other new materials and components. Subsequently, the article compares the sensing performance of various sensing structures and analyses the result with applications, which have been published in the last few years. Finally, we examined some conclusions and perspectives and hoped this review might provide adequate directives to researchers/students willing to take up these areas for their future endeavours. [ABSTRACT FROM AUTHOR]

[Display omitted] • Systematic comparison between FDTD calculations and experimental LSPR results. • FDTD to predict nanosensors that give the best LSPR experimental signals. • FDTD to design sensors that are fine-tuned for optimal performance. • FDTD confirms that LSPR peak shift follows Campbell's model even at sub-ML coverage. Finite-Difference Time-Domain (FDTD) calculations are widely used to interpret experimental Localized Surface Plasmon Resonance (LSPR) spectra. With FDTD it is possible to predict the physical parameters of the nanostructures that will theoretically give the best experimental LSPR signals. This information is crucial for optimizing sample fabrication and saving significant time. FDTD is also essential to control and calibrate various parameters of the nanostructures and to understand effects such as a Cr adhesion layer and LSPR sensor size distribution. Finally, for water adsorption sensing, FDTD confirms that the LSPR peak shift strictly follows Campbell's model, even at submonolayer coverage. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) and localized SPR (LSPR) effects have been shown as the principles of some highlysensitive sensors in recent decades. Due to the advances in nano-fabrication technology, the plasmon nano-array sensors based on SPR and LSPR phenomena have been widely used in chemical and bioloical analysis. Sensing with surface-enhanced field and sensing for refractive index changes are able to identify the analytes quantitatively and qualitatively. With the newly developed ultrasensitive plasmonic biosensors, platforms with excellent performance have been built for various biomedical applications, including point-of-care diagnosis and personalized medicine. In addition, flexible integration of plasmonics nano-arrays and combining them with electrochemical sensing have significantly enlarged the application scenarios of the plasmonic nano-array sensors, as well as improved the sensing accuracy.

We propose the tunable optical properties of plasmonic nanoparticle (NP)-plane antenna. In order to choose proper configurations to obtain sensitive and reproducible platform for electromagnetic enhancement in the sub-nanometer junction, the plasmonic resonance of the nanostructure shifts with NP size, gap distance and gap refractive index was simulated. The tunable optical properties of NP-plane antenna make it a good optical sensor in the visible optical range. Then we changed the NP size, gap distance and gap refractive index by fabricating the nanostructure. The experiment and simulation results match with each other. Each plasmon mode in localized surface plasmon resonance was recognized through simulation and also the polarization components in the experiment. [ABSTRACT FROM AUTHOR]

Plasmonic nanoperiodic Ag nanoparticle arrays with hexagonal close-packed structures and different symmetries were synthesized by localized surface plasmon resonance (LSPR) induced chemical growth. When the plasmonic nanostructure was excited by a laser, the neighboring silver nanoparticles generated high local electric field enhancement for surface-enhanced Raman spectroscopy (SERS), which was used to show the relationship between the axisymmetry of the plasmonic nanostructure and the SERS polarization effect. The experimental results indicate that the optimal axisymmetric structure (six-axis symmetric) exhibited the strongest SERS polarization-dependence, whereas the disordered structure with an arbitrary axis exhibited a relatively weak SERS polarization dependence. To clarify the root cause of SERS polarization dependence, the electric field enhancement distribution for the plasmonic nanostructures was numerically simulated based on S- and P-polarization excitation. Most importantly, the fundamental reasons for the polarization dependence of SERS were obtained by the quantitative numerical simulation of the hotspot distribution for the plasmonic nanostructures. Unlabelled Image • The plasmonic arrays of different axisymmetry were grown by LSPR-induced chemical reaction. • The effect of the axisymmetry on SERS polarization signals was revealed. • SERS polarization dependent mechanism was proven by experimental data and numerical simulation. [ABSTRACT FROM AUTHOR]

The study of optical and plasmonic properties of structures is an important step in the development of substrates for surface-enhanced Raman scattering (SERS) applications. In this work, structures based on a disordered array of hemispherical silver nanoparticles (AgNPs) on a single-crystal silicon (c-Si) substrate are studied. A simple and reproducible method is proposed in which an Ag island film obtained by chemical reduction of AgNO 3 is transformed after annealing at 350 °C into an array of hemispherical AgNPs on a thin SiO 2 layer. The average radii of AgNPs range from 30 to 130 nm, which can be varied due to the concentration of AgNO 3 in the initial deposition solution. Numerical calculations of the scattering, absorption, and extinction cross-sections are used to determine the positions of the localized surface plasmon resonance (LSPR) multipoles depending on the hemispherical AgNP size. The splitting of the LSPR dipole is found in the reflection spectra at oblique angles of incidence for p-polarization of light, which indicates the prolate shape of the hemispherical AgNPs. Finally, SERS shows reliable detection of 10−7 M (crystal violet) with the enhanced factor ∼ 6.2 × 10 5 and the relative standard deviation of signal ∼ 10 %. These studies suggest that hemispherical AgNPs on a SiO 2 @c-Si are promising candidates for detecting triphenylmethane dyes. [Display omitted] • SERS substrates based on hemispherical AgNPs on SiO 2 @c-Si have been fabricated. • FDTD calculations were used to determine LSPR multipoles as a function of AgNP size. • Splitting of the LSPR in the reflection spectra of p-polarized light was found. • Prolate shape of the AgNPs were confirmed by SEM method and optical investigations. • SERS substrates showed reliable CV detection of 10−7 M with EF ∼ 6.2 × 10 5 and RSD ∼ 10 %. [ABSTRACT FROM AUTHOR]

Designing a sensor to rapidly and simply detect iodine (I 2) in liquid and gaseous phase with excellent sensitivity, high stability, and low cost at room temperature is highly desirable. Herein, a two-dimensional Au@Ag nanoparticle ordered array was prepared by template method combined with chemical reduction for detecting I 2 at room temperature. Due to the ordered structure, a plasmonic surface lattice resonances (PSLR) peak appeared in extinction spectrum of the Au@Ag nanoparticle ordered array. When the ordered array exposed to I 2 , the Ag shell would react with I 2 to form AgI, thus leading to a change in the dielectric medium surrounding the Au nanoparticles. This change would cause a variation of color and a shift of PSLR peak, realizing multi-mode detection of liquid and gaseous I 2 at room temperature without any sophisticated instrument. With the increase of I 2 concentration, the color of the Au@Ag nanoparticle array changed from red to yellow-green. Meantime, the PSLR peak displayed highly sensitive redshift with a larger offset (about 156 nm) and intense signal strength. Moreover, due to the ordered array structure, the PSLR peak possessed good uniformity and stability. Therefore, the PSLR peak was more suitable for detecting I 2 in a large concentration region. Furthermore, the practical application of the present prepared Au@Ag nanoparticle array was explored by detecting gaseous I 2 at room temperature. It was found that the Au@Ag nanoparticle array possessed high sensitivity to gaseous I 2 with a detection limit reaching to trace level (1 ppb), suggesting tremendous potential for real-world application. • Rapid and simple detection of I 2 at room temperature was realized through color change and PSLR peak shift. • The PSLR peak displayed highly sensitive redshift with a larger offset and intense signal strength. • The PSLR-based sensor exhibited excellent selectivity, good repeatability and stability. • Such PSLR-based sensor displayed a very low detection limit (1 ppb) to gaseous I 2 in air at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen-deficient Na y WO 3−x nanosheet array on tungsten foil was facilely synthesized. • The Na y WO 3−x nanosheet array demonstrated a localized surface plasmon resonance band at 620 nm. • The array substrate showed sensitive SERS detection of pollutants. Nonmetal plasmonic semiconductors have attracted increasing research interests for the low cost and promising surface plasmon properties. Here, oxygen-deficient sodium tungsten bronze Na y WO 3 - x microstructures on tungsten foil has been facilely fabricated, showing nonmetal plasmonic behavior and surface-enhanced Raman scattering (SERS) detection potential. The Na y WO 3 was firstly grown on tungsten sheets with Na doping in the solvothermal processing. Then, the oxygen vacancies have been introduced with thermal treatment in a hydrogen-containing atmosphere, resulting in Na y WO 3-x microstructures which revealed a localized surface plasmon resonance band at 620 nm. The Na y WO 3-x microstructures was used as SERS substrate for detecting methylene blue of 10-7 M, showing application potentials of plasmonic nonmetal materials. [ABSTRACT FROM AUTHOR]

Localized surface plasmon resonance applied in catalytic and optical field has attracted more attentions in recent years. Plasmonic MoO 3-x nanosheets with tunable oxygen vacancies were constructed via facile solvothermal method. The as-prepared MoO 3-x nanosheets were found to have LSPR absorption band centered at 680 nm, and exhibited excellent photocatalytic performance in photodegradation of organic dyes and tetracycline under visible light irradiation. X-ray photoelectron spectroscopy showed the higher content of surface oxygen vacancies in MoO 3-x (88 mmol). Photocurrent, electrochemical impedance spectroscopy and photoluminescence results demonstrated that MoO 3-x (88 mmol) exhibits the best photo-induced electron hole separation efficiency and the highest charge transfer efficiency. Taken together, oxygen vacancies are not only responsible for the light harvesting in the visible and near-infrared region via LSPR, but also play a key role in greatly suppressing the recombination of photoexcited carriers. Moreover, electron paramagnetic resonance revealed that photoinduced h+ and ·OH radicals act as the main reactive species participating in the photoxidation process. Unlabelled Image • Plasmonic MoO 3-x nanosheets with tunable oxygen vacancies were obtained. • LSPR effect results in MoO 3-x nanosheets with light adsorption in visible and near-infrared region. • MoO 3-x nanosheets show superior photodegradation efficiency on organic dyes and tetracycline. • Oxygen vacancies play a key role in greatly suppressing the recombination of photoexcited carriers. • OH radicals act as the main reactive species participating in the photoxidation process. [ABSTRACT FROM AUTHOR]

Abstract In this work, we experimentally investigate the photoconductance behavior of gold nano-island film due to the plasmonic effect. The current-voltage measurements are performed under continuous wave (CW) low laser irradiance at the wavelength properly matching the localized surface plasmon resonance (LSPR), λ = 532 nm. We measure the photoconductance of the nanostructured film as a function of laser irradiance. An enhancement of the film´s current is observed by increasing the applied voltage and the laser irradiance. Furthermore, our results show that the photoconductance is attributed to an additional voltage induced by the strong confined plasmonic electric field on the nano-islands' surface. The experimental results are in good agreement with the Simmons' model of electron tunneling. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to improve the sensitivity and the performance of nano-sensors by using the simulation, which was done by finite element method in 2D plasmonic nanostructures. Meanwhile, the effects of geometric parameters of a hexagonal gold nanostructure, and the influence of two dielectrics Si 3 N 4 and SiO x were treated. In order to have better sensitivity, the nature and the thickness of a deposed dielectric were controlled. Whenever we change the geometric parameters of the metallic nanostructure, we see changes in nanoparticle's plasmonic response. Adjusting the theoretical curve to experimental LSPR curve allowed the geometry of the plasmonic interface to be fixed and evaluation of the change in the wavelength at resonance ( λ R ) as a function of the SiO x overlayers thickness. The theoretical data were compared with experimental results obtained on glass/Au nanowires/SiO x and glass/Au Nanowires/Si 3 N 4 interfaces. Highlights • We propose a new design structure with gold nanoparticles. • The effect of geometrical nanowires in the structure and evolution of plasmon resonance are studied. • The theoretical data were compared with experimental results obtained. • The LSPR parameters are optimized to improve the sensitivity and the performance of nano-sensors. [ABSTRACT FROM AUTHOR]