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Localized surface plasmon interaction of colloidal gold nanoparticles and the resultant changes in the linewidth of plasmon bands are reported. The evolution of the plasmon band in colloids is investigated by increasing the number of particles per unit volume. The volume of the solvent is reduced from 15 to 3 ml by the simple evaporation method. It is observed that the linewidth of the plasmon band varies in a non-uniform manner, which is attributed to the interaction of plasmons from the surface of gold nanoparticles rather than aggregation effects. Indication of aggregation effects such as a progressive redshift in plasmon peak and continuous broadening of linewidth were absent. Gold nanoparticles are prepared using laser ablation of the gold target with nanosecond laser pulses using pure water as a solvent. Change in the linewidth of plasmon bands on colloidal gold nanoparticles with minimized size distribution prepared using laser fluences viz. 5.09, 10.19, 15.28, 20.38 and 25.48 J/cm2 are explored.

Ag loaded Ga2O3 photocatalysts are well known to be highly active for the CO2 reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. To examine the chemical state change during the photocatalytic CO2 reduction, we have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga2O3 by monitoring UV–vis reflectance spectra under the atmosphere simulating the photocatalytic CO2 reduction. In UV–vis spectra, two characteristic absorptions appeared at around 450 nm and 600 nm corresponding to resonance absorptions of localized surface plasmon (LSPR) of Ag nanoparticles (Ag-NPs) and Ag in metallic state. The LSPR absorption appeared as light irradiation started and grew with the time. It was revealed that Ag on Ga2O3 was initially in the oxidized state and reduced by the light irradiation to be Ag-NPs. Further light irradiation enlarged the size of Ag-NPs to be the metallic state especially under atmosphere with water. Under CO2 atmosphere, Ag-NPs remained small after further light irradiation. These results suggest that Ag initially loaded on Ga2O3 in the oxidized state was reduced to be dissolved as Ag+ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such reduction process depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while CO2 suppressed the formation Ag-NPs.

CuS materials exhibit excellent near infrared (NIR) photoabsorption and photothermal effect, but they are lack of magnetic resonance imaging (MRI) ability. Fe-based nanomaterials possess MRI capacity, but they usually exhibit poor NIR photoabsorption. In order to solve the above problems, we synthesize three kinds of CuxFeySz samples, including FeS2, CuFeS2 and Cu5FeS4 nanomaterials. With the Cu/Fe ratios increase from 0/1.0 to 1.0/1.0 and 5.0/1.0, the localized surface plasmon resonances (LSPRs) characteristic peaks shift to longer wavelength, and the photothermal transduction efficiencies go up from 24.4% to 36.6% and 45.9%. Thus, Cu5FeS4 is found to be the most excellent sample. Especially, Cu5FeS4 exhibits photothermal-enhanced Fenton effect, which can produce hydroxyl radical (·OH) under a wide pH range (e.g., pH = 5.4–7.4) to realize the chemodynamic effect. In addition, Cu5FeS4 can be employed as an efficient MRI contrast agent. When Cu5FeS4 dispersion is intravenously injected into the mouse, the tumor can be detected by MRI as well as thermal imaging, and eliminated through photothermal-enhanced chemodynamic effect. Therefore, Cu5FeS4 can be used as an efficient “one-for-all” type agent for MRI-guided photothermal-enhanced chemodynamic therapy of tumor.

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e−/h+ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.

The hot electron transition of noble materials to catalysis accelerated by localized surface plasmon resonances (LSPRs) was detected by in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) in this article. This paper synthesized an Ag Nanowire (AgNW) @ WS2 core-shell structure, with an ultra-thin shell of WS2 (3 ∼ 7 nm), and characterized its photocatalytic properties. The AgNW@WS2 core-shell structure exhibited different surface-enhanced Raman spectroscopy (SERS) effects by changing shell thickness, indicating that the effect of AgNW could be controlled by WS2 shell. Furthermore, the hydrogen production of AgNW@WS2 could reach to 356% of that of pure WS2. The hot electrons arising from the LSPRs effect broke through the Schottky barrier between WS2 and AgNW and transferred to the WS2 shell, whose photocatalytic effect was thus enhanced. In addition, when the LSPRs effect was intensified by reducing the shell thickness, the hot electron transition of noble materials to catalysis was accelerated.

The plasmonics of two–dimensional materials, such as graphene, has become an important field over the past decade. The active tunability of graphene via electrical gating or chemical doping has generated a great deal of excitement among engineers seeking sensing devices. Consequently there is significant demand for robust and highly accurate computational capabilities which can simulate such materials. The class of High–Order Perturbation of Surfaces methods have proven to be particularly appropriate for this purpose. In this contribution we describe our recent efforts to utilize both Dirichlet–Neumann Operators and Impedance–Impedance Operators in these schemes. In addition, we present detailed numerical results which not only validate our simulations using the Method of Manufactured Solutions, but we also describe Localized Surface Plasmon Resonances in graphene nanotubes enclosing rod–shaped dielectric materials.

Exotic electronic excitations beyond normal selection rules would open novel possibilities for photoenergy conversion. The large intensity gradient of electromagnetic fields resulting from the confinement of localized surface plasmons at the molecular scale could exceed the limit of light–matter interactions via modification of electronic excitation selection rules. We discuss the possible application of surface-enhanced Raman scattering as a probe for exotic electronic excitations by reviewing studies on small numbers of molecules at the surface of plasmonic metal nanostructures. Future innovative photo-functionalization is also discussed by considering the excited states produced by the exotic electronic excitations.

The photocatalytic reduction of CO2 with H2O to fuels and chemicals using solar energy is one of the most attractive but highly difficult routes. Thus far, only a very limited number of photocatalysts has been reported to be capable of catalyzing the photocatalytic reduction of CO2 under visible light. The utilization of the localized surface plasmon resonance (LSPR) phenomenon is an attractive strategy for developing visible-light photocatalysts. Herein, we have succeeded in synthesizing plasmonic MoO3−x-TiO2 nanocomposites with tunable LSPR by a simple solvothermal method. The well-structured nanocomposite containing two-dimensional (2D) molybdenum oxide (MoO3−x) nanosheets and one-dimensional (1D) titanium oxide nanotubes (TiO2-NT) showed LSPR absorption band in the visible-light region, and the incorporation of TiO2-NT significantly enhanced the LSPR absorption band. The MoO3−x-TiO2-NT nanocomposite is promising for application in the photocatalytic reduction of CO2 with H2O under visible light irradiation.

Hot carriers (electrons and holes) generated from the decay of localized surface plasmon resonances can take a major role in catalytic reactions on metal nanoparticles. By obtaining surface enhanced Raman scattering (SERS) spectra of p-aminothiophenol as product of the reduction of p-nitrothiophenol by hot electrons, different catalytic activity is revealed here for nanoparticles of silver, gold, and copper. As a main finding, a series of different ligands, comprising halide and non-halide species, are found to enhance product formation in the reduction reaction on nanoparticles of all three metals. A comparison with the standard electrode potentials of the metals with and without the ligands and SERS data obtained at different electrode potential indicate that the higher catalytic activity can be associated with a higher Fermi level, thereby resulting in an improved efficiency of hot carrier generation. The concept of such a ligand-enhanced hot electron reduction provides a way to make light-to-chemical energy conversion more efficient due to improved electron harvesting.

We propose a plasmon induced tunable metasurface for multiband superabsorption and terahertz sensing. It consists of a graphene sheet that facilitates perfect absorption where the graphene pattern at the top layer creates an enhanced evanescent wave that facilitates the metasurface to work as a sensor. The modelling and numerical analysis are carried out using Finite Element Method (FEM) based software, CST microwave studio where a genetic algorithm (GA) is used to optimize the geometric parameters, and metasurface tunability is achieved via an external gate voltage on the graphene. By exploiting graphene’s tunable properties we demonstrate a multiband superabsorption spectra having a maximum absorption of 99.7% in a frequency range of 0.1–2.0 THz that also maintain unique optical performance over a wide incidence angle. Further results show how the superabsorber can be used as a sensor, where the resonance frequency shifts with the refractive index of the surrounding environment.

The optical properties of a two-dimensional gold nanoparticle-over-nanosheet (2D-AuNP/NS) have been studied using Finite-Difference Time-Domain (FDTD) method. 2D-AuNP/NS hybrid structure exhibits three typical localized surface plasmon (LSP) resonances, which occur in nanogaps between NP-NP, NP-NS and coupled upper and lower surface of NS respectively. Thus, the influence of AuNP-size, surface AuNP-coverage, NP-NP-spacing and NS-thickness on the localized electric field was analyzed in details. The LSP resonance between NP-NS has been predicted to be the most important effect on SERS, which is dominant, stable and can maintain the SERS intensity even at a relatively low NP-coverage. If a slight deviation of AuNPs away from their original periodic positions was permitted, a disordered model was then constructed which would more closely approximate the real AuNP/NS hybrid structure and was able to calculate the influence of disorder on LSP resonance. A blue shift (rather than red shift) of the resonance peak was observed and its peak intensity would increase first and decrease then with the increase of NP-NP-spacing. FDTD simulations have finally illustrated that NP-coverage should be controlled ranging from 80.0 % to 87.0% or just equal to 100%, if both AuNP-size and NP-thickness is controlled to 10 nm. The FDTD simulation results are qualitative agreement with the existing experimental data and are very useful in the future materials designs for AuNS-based nanocomposite.

Plasmonic nanofluids has been reported beneficial for enhancing absorption of the solar energy in a direct-absorption solar collector (DASC). In order to overcome the shortage of narrow absorption band associated with the localized surface plasmon, two strategies can be adopted. One is to blend nanoparticles with different absorption peaks, and the other is to develop nanoparticles capable of exhibiting multiple absorption peaks at different wavelengths. In this study, the latter strategy is explored systematically by investigating the absorption efficiency of metallic nanoparticles with sharp edges. The results show that the Ag nanoparticles with sharp edges can induce multiple absorption peaks due to both localized surface plasmon resonance and lightning rod effect. We also show that the sharper edges (i.e., with either smaller radius of curvature or smaller edge angle) can greatly enhance the lightning rod effect. In addition, the study of SiO2-core/Ag-shell suggests that the core/shell configuration is beneficial for further broadening the absorption band compared to the Ag nanoparticle. Further investigation shows that the solar-weighted absorption coefficient of a DASC using the four-edge nanoparticle is 35% and 20% point higher than the nanosphere and the nanorod respectively with a fixed volume fraction of 10 − 6 .

White light-emitting diodes (LEDs) are great candidates for general lighting. Phosphors have commonly been used for the color conversion layers of white LEDs; however, they backscatter more than half of the down-converted light, which is lost within the device, thus degrading the overall performance. In this study, we propose and demonstrate white LEDs with improved efficiency enabled by the intimate integration of Ag@SiO2-supported blue InGaN/GaN nanorod LEDs together with green- and red-emitting perovskite nanocrystal (PNC) films as color conversion layers. The photoluminescence (PL) intensity of the blue LEDs (BLEDs) was significantly enhanced owing to the localized surface plasmon (LSP) effect of Ag@SiO2 nanoparticles. In addition, the perovskite PL intensity was improved by the high-power BLED backlight. The resulting PL intensity of the Ag@SiO2 nanoparticle-embedded nanorod white LED was 62% greater than that of a planar white LED.

Localized surface plasmon-enhanced diamond UV photodetectors with different Ir nanoisland arrays had been successfully fabricated. Three different Ir nanoisland arrays with the diameters of 20(D20), 30(D30) and 40(D40) nm were deposited on the diamond surface, respectively, and their height was 10 nm. Ti/Au metal electrodes were patterned on Ir nanoisland arrays area and bare diamond surface to form UV photodetectors. According to photoelectric performance test results, the responsivities of diamond photodetectors with Ir nanoislands were far greater than that of diamond photodetector, and the D40 showed the highest photocurrent and responsivity at 210 nm, and the D20 indicated the highest UV/vis rejection ratio. The results of simulated extinction spectra exhibited three resonance peaks at UV and visible region for each sample, indicating that D20 had the highest ratio of UV/vis, which was coincide with experiment results.

In this paper, single silver nanocube dimer with nanometer-sized gap is designed and numerically simulated. We demonstrate that the electric fields can be highly confined in the gap of nanocube dimer, leading to ultrasmall mode volume of ≈2 × 10-7 μm3. Furthermore, the strong plasmon-exciton coupling in single nanocube dimer coupled with J-aggregate molecules is investigated using coupled oscillator model and we show that the strong plasmon-exciton coupling can be tuned by changing the background refractive index and the concentration of J-aggregate molecules. The tuning of dual strong plasmon-exciton couplings between single rounded silver nanocube dimer and J-aggregate molecules is also investigated, and dual strong couplings can be achieved closely approaching the quantum optics limit benefiting from the ultrasmall mode volume of the proposed system. The proposed systems can be easily prepared and have high experimental feasibility, which has potential applications in integrated nanophotonics such as sensing and all-optical switches.

Localized surface plasmon resonances (LSPR) are widely employed for improving the upconversion luminescence (UCL) and photocatalysis. Here, we prepare a nano-semiconductor heterostructure (NSH) consisting of Er-Yb:TiO2 nanosheets (NTs) integrated with plasmonic MoO3-x NTs in a two-step solvothermal processes. The LSPR of MoO3-x amplifies and transfers the near-infrared (NIR) energy to the neighboring Er-Yb:TiO2 UC system, leading to a 182-fold increase in green emissions. Moreover, the LSPR effect extends the absorption range of the Er-Yb:TiO2/MoO3-x NSH from the visible to the NIR region. The interface of the Er-Yb:TiO2/MoO3-x NSH acts as a charge carrier channel to separate the plasmon-induced electrons and holes effectively. We perform H2 production experiments of Er-Yb:TiO2/MoO3-x NSH from ammonia borane (BH3NH3). Upon the excitation of a 980 nm laser, the H2 production of the Er-Yb:TiO2/MoO3-x NSH is 1.5 times and 61 times higher than that of the MoO3-x NTs and BH3NH3. In addition, the H2 yield is 2.5 times and 52 times higher than that of the MoO3-x NTs and BH3NH3 under the irradiation of simulated sunlight (AM 1.5), demonstrating the superior photocatalytic properties of the Er-Yb:TiO2/MoO3-x NSH.

In this paper, a dynamic plasmonic subtractive color filter is investigated. The proposed filter consists of aluminum disks immersed in nematic liquid crystal. The performance of the structure is based on the interaction between liquid crystal and localized surface plasmons, which the transmittance colors are electrically controlled by the applied voltage. The optical efficiency and the full-width at half-maximum (FWHM) of the filter are attained to be about 80 percent and 40–45 nm, respectively. Moreover, the suggested color filter is polarization-insensitive due to its symmetric geometry.

Fiber-based photonic nanostructures with potential employment in nano/microscale optical devices are attracting a growing interest. In this work, we report on the emission features of polymer fibers made of 4(dicyanomethy-lene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) doped polyvinyl pyrrolidone (PVP) with diameters in the range of 1.5–2 μm, realized by electrospinning method. In the fibers, silver nanoparticles (Ag NPs) are introduced as scatters, where multimode random lasing action is achieved. Experiments indicate that strengthened lasing shot has been triumphantly realized in the existence of metal Ag NPs. By optimizing the ratio of Ag NPs to DCJTB during the process of the preparation, random lasing emission has been realized with much cut down thresholds to 0.55 mW cm−2. The microscopic resonators may be shaped both by randomly oriented polymeric fibers and multiple scattering of Ag NPs which offer special opportunities to design multiple light scattering and random laser. Besides, the localized surface-plasmon resonance (LSPR) of Ag NPs is excited, which couples with output emission of DCJTB to improve the lasing efficiency. This system is a promising candidate for the coming growth of all-plastic, micro- to macroscale optical tables for signal transmission and processing.

A highly selective, sensitive, and rapid colorimetric sensor for the determination of dopamine (DA) was developed using the color change of S-doped carbon dots functionalized gold nanoparticles (S-CDs@Au NPs). The base of the method is the formation of a complex between the amine groups of dopamine with carboxylic groups of S-CDs@Au NPs followed by their aggregation with Fe3+ ions which acts as the linkers causing a red shift from 520 to 670 nm in the localized surface plasmon peak of S-CDs@Au NPs. The ratio of absorbance intensity at 670 nm to 520 nm was monitored as the analytical signal for determination of dopamine. The parameters affecting the analytical signal including reaction time, solution pH, the concentration of Au NPs and concentration of Fe3+ were optimized. At optimized conditions, the calibration curve was linear in the concentration range of 0.81–16.80 μM of dopamine. The detection and quantification limits were 0.23 μM and 0.77 μM, respectively. The intra-day and inter-day relative standard deviation (RSDs) at 5.0 μM of DA were 3.9% and 5.6%, respectively (n = 5). The applicability of the method for determination of DA in dopamine ampoule, urine and serum human samples was investigated.

The controllable catalytic reaction plays a pivotal role in heterogeneous catalysis. Surface-enhanced Raman scattering (SERS) and tip enhanced Raman spectroscopy (TERS) are considered promising techniques for the study of catalytic reactions due to the highly localized sensitivity of SERS and the nanoscale spatial resolution of TERS. Herein, Ag/Au composite films were employed as catalyst for in situ monitoring of the catalytic reaction of 4‑nitrobenzenethiol (4NBT) to p, p'‑dimercaptoazobenzene (DMAB). The catalytic reaction of 4NBT adsorbed on Au film can be manipulated at the nanoscale using TERS by controlling the height between the tip-apex and the sample surface in Ag tip-Au substrate geometry. According to finite difference time domain (FDTD) simulations, the 'hot electron' induced by the localized surface plasmon is sufficient for promoting the catalytic reaction. These findings provide a novel way for controllable graph drawing of molecules at the nanoscale level.

Tungsten disulfide (WS2) has been demonstrated for optoelectronic devices due to its favorable semiconducting band gaps, high stability and higher carrier mobility than other transition metal dichalcogenides (TMDs). However, the photoresponsivity of WS2-based photodetector is low due to the poor optical absorbance, which limits its application in high-performance photodetection. Here, we show an easy realized method to improve the responsivity of WS2 detectors by Au nanospheres (NPs). The Au NPs concentrate free space electromagnetic wave efficiently by localized surface plasmon resonances (LSPR), strongly enhance the electric field on WS2 films. As a result, more carriers are excited with the assistant of LSPR. With optimized design, the detector exhibited several times to ten folds enhancement from near infrared to visible spectrum region, and reach an excellent high responsivity of 1050 A/W at the wavelength of 590 nm. Furthermore, the photodetector showed an excellent temperature stability after annealing at 300 °C on air environment. The work provides a new way for high-performance and stable photodetector for extreme and harsh environment.

The surface enhanced-Raman spectroscopy (SERS) of the graphene was measured using Au nanodimers prepared by angle-resolved nanosphere lithography and 785 nm laser with increasing power. It is found that the ratio between D band and 2D band changes with laser power. The change is attributed to the effect of localized surface plasmon (LSP), which causes the restructuring of Au nanodimers and oxidation of graphene. We established the method to characterize the formation of the defects in graphene using SERS.

We report on the enhancement effect of metal nanotriangles (NTs) on the photoluminescence and its time-resolved dynamics of tris(8-quinolinolato) aluminum (Alq3). Regularly arranged Al NTs arrays were fabricated on the quartz substrate by means of nanosphere lithography. The absorption peaks corresponded to the localized surface plasmon (LSP) resonance of Al NTs were observed within a visible light region, and it was significantly shifted towards longer wavelength as increasing refractive index of the covering medium. The typical resonance wavelength of LSP of Alq3/Al NTs fabricated with 350 nm-PSt beads was 600 nm. From the PL measurement 2.6-fold PL enhancement was observed in Alq3 with Al NTs at room temperature, whereas the 4.4-fold PL enhancement was observed for Ag NTs with same size. According to the time-resolved PL data, the coupling of LSP with the excitation light field mainly contribute to the observed emission enhancement for the Al NTs, whereas the emission enhancement by Ag NTs can be originated from the direct coupling of LSP and emission which was suggested from the large contribution of short lifetime component.

A fascinating strategy of molybdenum ions supporting was utilized to enhance green upconversion (UC) emissions of Er-Yb:TiO2 prepared by sol-gel method. Er-Yb:TiO2 nanoparticles exhibited irregular sizes approximately 100–350 nm, which showed stronger red emission and weaker green emissions under the irradiation of near-infrared (NIR). After molybdenum ions supporting, Er-Yb:TiO2 nanoparticles were turned into uniformly dispersed eight prism structure and average particle size reached about 800 nm. Also, the green UC luminescence integrated intensity of Mo/Er-Yb:TiO2 was about 46 times improved than that of Er-Yb:TiO2. Furthermore, a novel photocatalyst of Mo/Er-Yb:TiO2@W18O49 quasi-core/shell heterostructure was designed based on the localized surface plasmon resonances (LSPR) effect of W18O49 through solvothermal process. With the excitation of NIR, the photocatalytic property of Mo/Er-Yb:TiO2@W18O49 for H2 producing from ammonia borane (BH3NH3) was researched. H2 production was about 2-fold enhancement compared with that of W18O49. Besides, the application of natural sunlight for H2 producing was provided. About 3 times H2 yield was obtained in contrast to that of W18O49. This work provided an effective way to enhance UC luminescence intensity and H2 production efficiency for solving energy deficiency problems.

Using Transfer Matrix method combined with Effective Medium Approximation as well as Finite-Difference Time-Domain calculations we have determined the light absorption in organic solar cells with silver nanoparticles embedded in the active layer. In calculations, we introduced additional terms in permittivity of the nanoparticles due to their finite size. Our results show, that the optimal nanoparticle concentration in such a system is about 30% greater than when assuming that the permittivity of the Ag nanoparticles equates that of a continuous silver layer. We have found, that although the absorption curves for both models (with and without the finite size contribution) are similar, the dominant mechanism of absorption enhancement is different. When assuming that the permittivity of silver nanoparticles is that of a continuous Ag layer, the light scattering on the surface of the nanoparticles seems to dominate over localized surface plasmon (LSP) excitation, while when considering the finite sizes of the nanoparticles the opposite is true.

Current presumptive tests for illicit drugs can suffer from false positive results and poor selectivity, and consequentially there is a need to develop new colour spot tests specifically designed to circumvent these existing challenges. In this work, we report on a new fluorescent hybrid nanozyme peroxidase-like catalytic colorimetric sensor and demonstrate proof of concept of this novel colorimetric-specific presumptive test for cocaine. A novel peroxidase-mimic hybrid nanozyme was developed based on the localized surface plasmon resonance-enhanced fluorescence interaction between multi-shaped cationic cetyltrimethylammonium bromide (CTAB)-functionalized gold nanoparticles (AuNPs) and anionic non-cadmium fluorescent-emitting L-cysteine-capped ZnSeS alloyed quantum dots (QDs). The affinity-based interaction of cocaine with the QDs-CTAB-AuNP surface was induced by its distinct structural conformation and this forms the basis for the selective recognition. Thus, the hybrid nanozyme could function both as a catalytic affinity-based receptor and as an optical signal transducer based on the catalysed oxidation of 3,5,5-tetramethylbenzidine by H2O2. A positive bluish-green colour, specific to cocaine recognition, was colorimetrically obtained under optimum catalytic conditions. The optimized assay system detected cocaine within two minutes with unique specificity and distinct colour reaction. Under the optimum cocaine reaction conditions, the analysis of other substances and drugs on the colorimetric response of the QDs-CTAB-AuNP hybrid nanozyme revealed no colour interference, thus demonstrating that the developed probe could be utilized as a presumptive colour spot test for cocaine.

Metallic nanoparticles exhibit localized surface plasmon resonances resulting from the coherent oscillation of free electrons in response to electric field from incident electromagnetic radiation. In this work, the dependence of peak surface plasmon resonance of gold nanoparticles on the particle size using UV–Vis spectra is shown. Small-sized gold nanoparticles (10–15 nm) were prepared through citrate reduction method. From theoretical modelling based on their resonance peaks and full wave at half maximum, the gold nanoparticles were found to have a narrow size distribution of ∼12 nm optimized over 1.0–1.10 mL of the citrate. A comparison of the experimental data and data from multiple scattering theory revealed that the plasmon resonances were centered at wavelengths between 520 and 518 nm for all samples under citrate volume range from 0.85 to 1.15 mL. Further analysis indicated that, small sized AuNPs exhibited multiple resonances, which could be attributed to the radiative interband recombination between the sp- and d-bands.

Ferroelectric ceramics possess great application potential in optoelectronic and solar energy devices. However, ferroelectric ceramics normally have large band gaps, strongly inhibiting their photovoltaic performances. In this work, we use a strategy to enhance the visible light absorption of ferroelectric ceramics by incorporating Au nanoparticles into the ferroelectric BaTiO3(BT) matrix. The BT-Au nanohybrids are preliminarily synthesized as the “building blocks”, which are assembled and then sintered as the 0–3 type composite ceramic. We find that the UV–vis absorption of composite ceramic is improved by localized surface plasmon resonances (LSPRs). While the ferroelectric property of the 0–3 type BT-Au ceramic remains robust. As a result, the composite ceramics show excellent ferroelectric photovoltaic effect with a photocurrent being approximately seven times as that in pure BT ceramics and an open-circuit voltage of 6 V. These findings suggest that interfacial control of ceramic composites may act an effective approach to optimize the photovoltaic responses in ferroelectric ceramics.

We report a one-pot seedless green method for the synthesis of gold-silver (AuAg) spiky branched nanostars, with gold (90%) being the major component. Here, the zwitterionic surfactant lauryl sulfobetaine (LSB) is employed in the synthesis of bimetallic nanostars. The concentration of LSB plays an important role in determining the shape of nano-objects. A minimum LSB concentration of 50 mM is required for the formation of spiky branched nanostars, the size of which is controlled by increasing the LSB concentration. Two distinct intense localized surface plasmon resonances in the near-infrared (NIR) and short-wavelength infrared ranges are observed. The molecular structure of LSB causes LSB molecules to assemble into spherical micelles that act as a soft template for the growth of the nano-objects. An analysis of the mechanisms behind the formation of the nanostars suggests that there is a rapid growth of spikes followed by the formation of a spherical core at the center. AuAg nanostars with evenly spaced spikes and low branching demonstrate great potential as efficient nanocatalysts, surface-enhanced Raman scattering-active substrates and for photothermal therapy, active in both the visible and NIR regions.

The enhancement of surface plasmon-coupled emission (SPCE) by the synergistic effect of silver nanocubes (AgNCs) and graphene oxide (GO) on gold film has been observed with the enhancement factor over 30. The enhancement mechanisms were investigated through simulating the electromagnetic (EM) field patterns of near field and testing different concentration of AgNCs and thickness of dye layer. The enhancement was mainly triggered by the high electromagnetic field of AgNCs, the interaction between localized surface plasmons (LSP) and propagating surface plasmons (PSP) and the assistance of GO. This synergistic enhancement strategy provides a simple way to increase SPCE signal and enable develop a new fluorescence-based detection system.

Magnesium nanostructures have recently emerged as an outstanding material with new and intriguing plasmonic properties. Here we investigate the optical properties of pristine and pyridine adsorbed magnesium nanodisks having diameter spanning in the range of 0.50 nm–2.0 nm. We base our calculations on computationally efficient time-dependent density-functional theory calculations. Our results demonstrate that pristine magnesium nanodisks possess localized surface plasmon resonances. The adsorption of a dipole-carrying molecule significantly alters their plasmonic response due to the strong plasmon splitting, leading to new features in their optical response. We believe that magnesium nanodisks provide a versatile platform for sensing and in the design of novel ultra-sensitive plasmonic devices.

The localized surface plasmon enhanced luminescence behaviors of a radiating dipole in an all-inorganic perovskite light-emitting diode (PeLED) by incorporating a gold (Au)-silver (Ag) alloy nanoparticle (NP) in the electronic transport layer are demonstrated. The analyses of finite difference time domain (FDTD) show that the localized surface plasmon resonance (LSPR) wavelength mainly depends on the size and the material composition of NP. An increase of 25% of the luminescence efficiency can be achieved by selecting the proper size and the Au molar fraction of the alloy NP. This result can be attributed to the match between the LSPR wavelength of NP and emission peak of PeLED. And the luminous performance of PeLED can be improved by optimizing the thickness of functional layers. This finding indicates great potential of Au-Ag alloy nanoparticle in developing the efficiency of PeLEDs and provides a new method for the future improvement of PeLEDs.

Localized surface plasmons at nanostructured surfaces are played a key role in a wide range of industrial applications. Here, hexagonal arrays of uniformly distributed Pt nanocylinders were fabricated on the top surface of nanoporous anodic alumina (PAA) membrane using low-cost sputter coating technique under low vacuum. Set of PAA membranes were synthesized at the same conditions and coated with Pt for different periods of time. The implemented growth mechanism allowed the vertical accumulation of Pt nanoparticles to form Pt nanocylinders on the active dots of PAA. SEM images showed nanocylinders of heights ranged from 10.0 ± 0.7 nm to 32.0 ± 2.1 nm based on sputtering time. The nanocylinders rate of growth is 1.22 ± 0.09 nm/min. According to SEM images, the uniformity of the nanocylinders decreased as the porosity of the PAA membrane increased. The optical properties of Pt nanocylinders/PAA membranes were investigated and showed strong transverse, longitudinal, and higher longitudinal surface plasmon modes. Relative to the previously reported SPRs for other Pt nanostructures, our Pt/PAA nanostructures showed stronger SPRs at longer wavelengths due to the using of PAA as a host material, the strong electromagnetic coupling between the very close Pt nanocylinders, and the strong coupling between SPRs and interfernce fringes. Moreover, the effects of sputtering time and membrane porosity on the SPR position, oscillation strength, and bandwidth were studied.

A composite structure based on a Kretschmann structure loaded with silver nano-cube is proposed. A 442-nm laser was used to excite surface plasmons in the composite structure, and the electric field enhancement was numerically simulated using the finite element method. The excitation angles of surface plasmons under conditions of different thicknesses of a PMMA film were obtained by studying the reflection spectrum of the Kretschmann structure. By examining the extinction spectra of silver nano-cubes of different sizes, its optimal size was selected, which is 70 nm. The electric field enhancement factors of the composite structure and the composite PMMA-spaced silver nano-cube and silver film structure were compared in detail. The results show that the coupling of localized surface plasmons and propagating surface plasmons produced by the proposed composite structure mean that its electric field enhancement factor is significantly greater. Moreover, the electric field enhancement factor can be further improved by adding another laser to irradiate the composite structure symmetrically. The high electric field enhancement generated by the composite structure indicates that it has considerable application prospects in surface-enhanced Raman scattering. Keywords: Surface plasmons, Silver nano-cube, Electric field enhancement factor

Surface-enhanced Raman scattering (SERS) is a powerful tool for studying nanoscale molecule-metal interfaces across a range of electrochemical applications. SERS combines molecular-level information with a high degree of surface specificity, making it an ideal tool for understanding interfacial processes, from understanding how analytes and electrolytes organize near metal surfaces to following surface-mediated reactions in real time. However, because SERS relies on the excitation of localized surface plasmons, additional effects such as the production of hot charge carriers and photothermal heating can impact electrochemical SERS signals. These effects must also be considered when using SERS for quantitative electrochemical studies.

Discovery of tunable localized surface plasmon resonances (LSPRs) in boron (B) and phosphorous (P) doped silicon (Si) nanocrystals has opened exciting possibilities for Si-based plasmonics. Here, using computationally efficient time-dependent density-functional theory calculations, we investigate the optical response modulations of B- and P-doped Si NPs as a function of dopant locations (incorporated in the bulk, sub-surface, and surface regions) and nanoparticle size. More specifically, we show that the optical features of doped Si NPs are critically depend on the location of the dopant atom and a maximal spectral intensity enhancement can be achieved via surface doping. We believe that our theoretical findings would help in the emerging field of doped Si-based plasmonics.

Aggregates of plasmonic nanoparticles (NPs) are known to show greater electric field amplification, multiple resonant peaks, and precisely controlled spectral tuning compared to their isolated counterpart. The ability of localized surface plasmon mediated electric field amplification is an important criterion for a plasmonic system to act as an efficient Surface Enhanced Raman Scattering (SERS) substrate. Conventional coinage metals like gold (Au), silver (Ag) and copper (Cu) are most widely used SERS substrates, mainly due to their well established synthesis process and large Raman signal amplification. However, there is a pressing need to expand the list of plasmonic materials feasible for SERS substrates to match the exponential growth in SERS research. Identification of new plasmonic substrates will reduce the dependence on conventional plasmonic materials and SERS applications will extend into unexplored spectral regions. Moreover, one can circumvent the limitations arising due to the intrinsic nature of conventional plasmonic materials. Refractory Transition Metal Nitrides (RTMN) such as zirconium nitride (ZrN) and titanium nitride (TiN) has emerged as viable alternatives to coinage metals due mainly to, high electron conductivity, suitability for high temperature applications, optical response in Vis–NIR region, flexible spectral fine-tuning, and bio/CMOS compatibility. To the best of our knowledge, this article presents first-ever theoretical assessment of ZrN and TiN nanoparticle dimers for their suitability in enhancing electric field. Moreover, the role of nanoparticle size, embedding medium and inter-particle separation is quantified through fitting relations whose usefulness is demonstrated by designing nitrides based SERS substrates for selected wavelengths. The present work will provide handy tools to the designers and manufacturers.

Localized surface plasmons are highly confined modes at the subwavelength surfaces. The modes provide enhanced electric field intensity sites in close proximity to the surface which display potential applications in the form of optical-sensing devices. Intriguingly, at nanoscale, the modes can also increase the optical transmission through the aperture. In this work, we analyze the light transmission through a pyramid-shaped slit based on numerical simulations. We demonstrate the phenomenon by studying the behavior of Poynting vectors in the near surroundings of the slit. Furthermore, near and far transmitted optical intensities are calculated which show the supremacy of pyramid-shaped slit over the rectangular-shaped slit. The near and far field intensity through the pyramid slit is ∼2.25-times stronger than that of the rectangular slit. To see the influence of the shape of the slit on optical transmission, a reverse case, wherein pyramid-shaped slit is rotated by 180°, is also investigated. Based on our analysis, it is shown that enhancement of the output field emanates due to the excitation of the LSP modes while directionality of the field by a single slit depends on the shape of the slit. The study could be useful for the enhancement of fluorescent and Raman emissions from the molecules that are located eminently close to the slit.

This work studies the effect of different diameter sizes of Au nanodisc on the plasmonic surface plasmon resonance simulated using FDTD method. The extinction efficiency and the local field intensity enhancement have been observed via manipulating diameter sizes of the Au nanodisc whilst fixing its thickness to 5 nm. This plasmonic effect tailoring steps can provide for many potential applications for design and fabrication of plasmonic devices. Both the extinction efficiency and electric field intensity at the center of the Au nanodisc show significant enhancement with the increase of diameter sizes. This observation of localized surface plasmon effect on the different size of the Au nanodisc are expected to provide understanding on the design of plasmonic hot carrier generation.

This study presents the fabrication and characterization of imine-functionalized Au nanoparticle (Au NP) film using Poly (ethyleneimine) (PEI) as a reducing and surface stabilizing reagent. The PEI-capped Au NPs can be self-assembled at the water-hexane interface by adding alcohol containing alkanethiol. Furthermore, large-area film made from PEI and alkanethiol-capped Au NPs is produced on a glass substrate with varying interparticle distances that can be controlled by the alkyl chain lengths, ranging from C2 (ethanethiol), C4 (1-butnaethiol), C6 (1-hexanethiol), C8 (1-octanethiol), to C10 (1-decanethiol) at the water-hexane interface. These 2D films show strong collective localized surface plasmon resonance (LSPR) extinction bands that are tunable via near-field coupling of adjacent Au NPs. Pronounced chain-length-dependent red shifts of the SPR bands have been observed for the PEI-capped Au films. The obtained PEI-capped Au films exhibit distinct interparticle-distance-dependent SERS characteristics.

Substoichiometric tungsten oxide (WO3-x) has become one of the interesting candidates for localized surface plasmon resonance (LSPR) hosts because of its fascinating properties. Herein, we report that substoichiometric WO3-x can be fabricated via a facile solid phase reduction method, and at the same time it exhibits a strong LSPR in the near infrared region. Tunable plasmon resonances can be observed in a wide range by changing their stoichiometry. In the bovine serum albumin (BSA) based optical bio-sensing system, the plasmonic WO3-x displays superior sensitivity. Moreover, the hybrid nanocomposites combining the plasmonic WO3-x and plasmonic Ag can be also obtained, which show great potentials in heterogeneous catalysis. Specially, the WO3-x prepared at the reduction temperature of 350 °C (WO3-350) exerts improved photocatalytic performance toward methylene blue degradation, which is due to the synergistic effect of the strong plasmonic effect of WO3-350 and Ag nanoparticles.

The optical properties of Cu island films, in particular their plasmonic behaviour, are investigated. The films are fabricated by electron beam evaporation using different deposition parameters (deposited mass thickness and substrate temperature). The optical response can be tuned from a metal-like behaviour to well-defined localized surface plasmon resonances and is well correlated with the structural and morphological properties of the samples. Significant changes of optical properties take place with sample aging, including quenching and non-monotonic frequency shift of the plasmon resonance. These changes are interpreted in terms of Cu oxidization process, that appears to strongly depend on the initial morphology of samples. Theoretical calculations in the framework of effective medium theories qualitatively explain the experimental observations. Overall, the results give a detailed insight on the morphology dependence and time evolution of the optical response of Cu island films that may provide useful guidelines for applying these nanostructures in plasmonic applications.

The aim of this paper is to present a new efficient and accurate semi-implicit finite-difference time-domain (FDTD) method for modeling thin plasmonic metamaterials supporting spoof surface plasmons. The presented method is formulated by combining Yu–Mittra's conformal FDTD technique for dielectrics, the simplified conformal finite integration technique for perfectly electric conductors (PECs) and the Newmark-Beta method. The resultant scheme is magnetically implicit, has a more relaxed stability condition than that of Yee's FDTD scheme, and allows for accurate modeling of both PEC and dielectric curved surfaces. Energy conservation and stability of the presented scheme is theoretically proved with the energy inequality method. Its formulation can be generalized to a class of magnetically implicit FDTD schemes with weakly conditional and unconditional stability in a unified manner. The presented scheme is used to simulate thin structures supporting spoof surface plasmon polaritons and spoof localized surface plasmons, and also applied to recent plasmonic devices such as planar frequency splitter, ultrathin rainbow trapping device and compact planar metadisk with split-ring resonators. The accuracy and efficiency of the presented scheme are assessed in comparison with the conventional explicit and implicit FDTD methods, and their conformal variants.

The optical transmission properties of a novel bi-layer plasmonic nanostructure array (BPNA), consisting of an array of gold nanoholes, glass and an array of gold nanodisks, was investigated by the finite element method. A well-defined localized surface plasmon (LSP) resonance peak appeared in the transmission spectra due to the coupling between the LSP of the metal nanoholes and the LSP of the nanodisks. The position and the intensity of the coupled LSP resonance peak depended strongly on the distance between the nanohole and the nanodisk arrays, the diameters of the arrays and the thickness of the nanohole or nanodisk arrays. The coupled LSP resonance peak exhibited a higher figure of merit compared to that for either the nanohole array or the nanodisk array. Results indicated that the bi-layer nanodevice was a highly sensitive detector for tunable plasmas, and should aid in better understanding of the mechanisms for extraordinary optical transmission phenomena.

A new method of label free sensing approach with superior selectivity and sensitivity towards virlabel-freeon is presented here, employing the localized surface plasmon resonance (LSPR) behavior of gold nanoparticles (AuNPs) and fluorescent CdSeTeS quantum dots (QDs). Inorganic quaternary alloyed CdSeTeS QDs were capped with L -cysteine via a ligand exchange reaction. Alternatively, citrate stabilized AuNPs were functionalized with 11-mercaptoundecanoic acid to generate carboxylic group on the gold surface. The carboxylic group on the AuNPs was subjected to bind covalently with the amine group of L -cysteine capped CdSeTeS QDs to form CdSeTeS QDs/AuNPs nanocomposites. The fluorescence of CdSeTeS QDs/AuNPs nanocomposite shows quenched spectrum of CdSeTeS QDs at 640 nm due to the close interaction with AuNPs. However, after successive addition of norovirus-like particles (NoV-LPs), steric hindrance-induced LSPR signal from the adjacent AuNPs triggered the fluorescence enhancement of QDs in proportion to the concentration of the target NoV-LPs. A linear range of 10−14 to 10−9 g mL−1 NoV-LPs with a detection limit of 12.1 × 10−15 g mL−1 was obtained. This method was further applied on clinically isolated norovirus detection, in the range of 102–105 copies mL−1 with a detection limit of 95.0 copies mL−1, which is 100-fold higher than commercial ELISA kit. The superiority of the proposed sensor over other conventional sensors is found in its ultrasensitive detectability at low virus concentration even in clinically isolated samples. This proposed detection method can pave an avenue for the development of high performance and robust sensing probes for detection of virus in biomedical applications.

We review our recent studies of photochemistry and plasmon chemistry of dimethyl disulfide, (CH 3 S) 2 , molecules adsorbed on metal surfaces using a scanning tunneling microscope (STM). The STM has been used not only for the observation of surface structures at atomic spatial resolution but also for local spectroscopies. The STM combined with optical excitation by light can be employed to investigate chemical reactions of single molecules induced by photons and localized surface plasmons. This technique allows us to gain insights into reaction mechanisms at a single molecule level. The experimental procedures to examine the chemical reactions using the STM are briefly described. The mechanism for the photodissociation reaction of (CH 3 S) 2 molecules adsorbed on metal surfaces is discussed based on both the experimental results obtained with the STM and the electronic structures calculated by density functional theory. The dissociation reaction of the (CH 3 S) 2 molecule induced by the optically excited plasmon in the STM junction between a Ag tip and metal substrate is also described. The reaction mechanism and pathway of this plasmon-induced chemical reaction are discussed by comparison with those proposed in plasmon chemistry.

A comprehensive study on the factors affecting the surface enhanced Raman scattering capability of copper nanoparticles for furanoflavonoid, karanjin is reported. The copper nanoparticles have been synthesized by pulsed laser ablation of a copper target immersed in distilled water. An interesting trend of increase followed by a decrease in the Raman enhancement with the decrease in concentration of copper nanoparticles is observed. This variation is attributed to the count of number of nanoparticles present around karanjin. The optimum concentration of copper nanoparticles for maximum SERS intensity of nanoparticle treated karanjin is found to be approximately 0.291 mg/mL. This optimum concentration corresponds to the sample having an average particle size of ∼11 nm. There is a fall in the enhancement for smaller nanoparticles of average size ∼7 nm as well as larger nanoparticles of ∼20 nm. The observations have been explained on the basis of the electromagnetic enhancement due to the localized surface plasmons of the copper nanoparticles. The role of aggregation amongst the nanoparticles and also the degree of oxidation of the nanoparticles in controlling the SERS intensity is discussed.

In this study, localized surface plasmon-enhanced electrochemiluminescence (LSP-ECL) biosensor, a new ECL enhancement way for S2O82−/O2 system, was constructed based on urchin-like Au and Ag nanoparticles (AgNPs) for fast, one-step, and label-free detection of broad-spectrum bacteria. We found plasmonic metals with small diameters contributed to the ECL enhancement. Moreover, relying entirely on the physical puncture of urchin-like Au, the bacteria could be captured to the electrode surface without the need for target recognition agents. The single-step LSP-ECL biosensor exhibited high sensitivity in the range of 102-108 CFU/mL bacteria with the detection limit as low as 52 CFU/mL, meanwhile possessing a short detection time of 30 min. What’s more, the LSP-ECL biosensing strategy achieved detection of S.aureus present in plasma samples without involving bacterial culture and nucleic acid extraction. Considering the merits of label-free, short assay time, and one-step operation, the developed LSP-ECL strategy provides a versatile and culture-free platform for pathogenic bacteria detection.

The remote excitation of a localized surface plasmons (LSP) by the propagating plasmonic excitations, i.e., propagating surface plasmons (PSP), receives increasing attention in recent years. Here, we study the local near-field optical response of the gold nanohole, which support LSP, remotely excited by the PSP (PSP-LSP) and the results show that this optical response of the gold nanohole relates to the excitation field, the local near-field optical spectra show a redshift phenomenon, but the intrinsic frequency of LSP remains invariant. We attribute this spectral redshift phenomenon of the PSP-LSP to the dominating effects of the PSP. A weak dependence of the resonant wavelength peak on the size of a nanostructure has been observed. Moreover, it is found that the dephasing time of the PSP-LSP is longer than the case directly excited by the laser field, and it presents a decreased trend with the increasing distance from the PSP launching location. The results in this work can be used to improve the efficiency of remote excitations and provide a new path to prolong the dephasing time of the enhanced resonant field.

In this paper, a hybrid photonic-plasmonic resonator, which comprises an electrospun polymer fiber with a micrometer diameter and a core/shell nanostructure with a gold nanoparticle core, is constructed to investigate the dynamics of the coupled spontaneous emission of CdS/CdSe quantum dots (QDs). The gold nanoparticle core; covered with a silica shell, anchored with individual CdS/CdSe QDs, is placed inside a hollow cylindrical nanocavity formed on the surface of the microfiber to enable integration of the optical mode with the plasmonic effect, which is induced by the localized surface plasmons of the metal nanoparticle being present in the vicinity of the dipoles. The spontaneous emission rate of the QDs, coupled into the hybrid photonic-plasmonic mode, is measured to enhance by a factor of 23 via a time-resolved experimental technique. This result suggests that the regeneration of the optical mode-field inside the photonic-plasmonic resonator through the interaction of the dipoles with the localized surface plasmons of a metal nanoparticle strongly enhances the density of the electromagnetic states of the quantum emitters to facilitate an enhanced spontaneous emission within the host medium of the proposed polymer based-photonic structure.