Excitation Of Surface Plasmon Resonance Research Articles

Visible-NIR surface plasmon resonance sensing technology for high precision refractive index detection.

Molybdenum disulfide (MoS2), as a representative transition metal disulfide material, has contributed significantly to the development of plasmonic technology toward the near-infrared (NIR). In this Letter, the physical mechanism of MoS2 excitation of surface plasmon resonance (SPR) in the NIR is investigated, and it is shown that the MoS2 film can induce the resonance dip to move toward the NIR and demonstrate a sensitivity higher than that in the visible band. A dual-channel SPR sensor capable of operating in the visible and NIR bands for refractive index (RI) detection was also prepared using the cascade method. The simulated and experimental results of the sensor show consistency. The experimental results show that the maximum sensitivity of the NIR detection channel is 14600 nm/RIU in the RI range of 1.333-1.420, which is 37% higher than the sensitivity of the visible channel. However, the visible channel has the advantage of a narrow FWHM. Therefore, the proposed cascaded dual-channel RI sensor combines high sensitivity and narrow FWHM. This dual-channel construction method improves the detection level of RI, promotes the development of SPR sensing technology to the NIR band and significantly improves the narrowband problem existing in the previous multi-channel sensing.

Triple Play of Band Gap, Interband, and Plasmonic Excitations for Enhanced Catalytic Activity in Pd/HxMoO3 Nanoparticles in the Visible Region.

Plasmonic photocatalysis has been limited by the high cost and scalability of plasmonic materials, such as Ag and Au. By focusing on earth-abundant photocatalyst/plasmonic materials (HxMoO3) and Pd as a catalyst, we addressed these challenges by developing a solventless mechanochemical synthesis of Pd/HxMoO3 and optimizing photocatalytic activities in the visible range. We investigated the effect of HxMoO3 band gap excitation (at 427 nm), Pd interband transitions (at 427 nm), and HxMoO3 localized surface plasmon resonance (LSPR) excitation (at 640 nm) over photocatalytic activities toward the hydrogen evolution and phenylacetylene hydrogenation as model reactions. Although both excitation wavelengths led to comparable photoenhancements, a 110% increase was achieved under dual excitation conditions (427 + 640 nm). This was assigned to a synergistic effect of optical excitations that optimized the generation of energetic electrons at the catalytic sites. These results are important for the development of visible-light photocatalysts based on earth-abundant components.

Inglet oxygen generaion via silver nanoparticles UV-photoexcitation

The NIR-luminescence of suspension of silver nanoparticles stabilized in distilled water has been investigated by photoexcitation of surface plasmon resonance (SPR). The observed short-living luminescence with the spectral maximum at 1300 nm is attributed to the singlet oxugen molecules luminescence. The singlet oxygen generation is assumed to pass in two stages as a result of three-photon process. First the one-photon SPR excitation of silver nanoparticle is occurred and leads to superoxide oxygen generation on the nanoparticle surface. Next the superoxide anion absorbs two more photons of the same laser pulse resulting in electron photodetachment with singlet oxygen formation. During a long period of UV-irradiation the studying suspension ceases to be photostable and sedimentation occurs. The sedimentation may be related to disturbance of nanoparticles steric stability resulting in more efficient superoxide anion adsorption on nanoparticles surface with silver oxide formation.

Plasmonic‐assisted Electrocatalysis for CO2 Reduction Reaction

AbstractIntegrating plasmonic features as an emerging strategy for enhancing electrocatalysis for the carbon dioxide reduction reaction (CO2RR). The key parameters responsible for the enhanced electrocatalysis performance are the local heating, the hot carriers, and near‐field enhancement induced by localized surface plasmon resonance (LSPR, that is, plasmonic) excitation. This review provides a concise overview of the fundamental mechanism of CO2RR, detailing the generation and decay of plasmonic and the energy transfer dynamics between plasmonic nanostructures and adsorbates. It further involves recent progress in plasmonic‐assisted electrocatalysis for CO2RR, including experimental and theoretical research to decipher plasmonic mechanisms. Finally, it ends with an insightful discussion of the existing challenges and potential future directions in this field.

Plasmon-induced hot carrier distribution in a composite nanosystem: role of the adsorption site.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. However, gaining insights into HCs at a microscopic level has posed a complex challenge, limiting our ability to create efficient nanoantennas that utilize these energized carriers. In this investigation, we employ real-time time-dependent density functional theory (rt-TDDFT) calculations to examine the creation and distribution of HCs within a model composite system consisting of a silver (Ag) nanodisk and a carbon monoxide (CO) molecule. We find that the creation and distribution of HCs are notably affected by the CO adsorption site. Particularly, when the CO molecule adsorbs onto the hollow site of the Ag nanodisk, it exhibits the highest potential among various composite systems in terms of structural stability, enhanced orbital hybridization, and HC generation and transfer. Utilizing a Gaussian laser pulse adjusted to match the LSPR frequency, we observe a marked buildup of hot electrons and hot holes on the C and O atoms. Conversely, the region encompassing the C-O bond exhibits a depletion of hot electrons and hot holes. We believe that these findings could have significant implications in the field of HC photocatalysis.

The impact of a dopant atom on the distribution of hot electrons and holes in Au-doped Ag nano-clusters.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. In this study, we employ first principles real-time time-dependent density-functional theory (rt-TDDFT) calculations to elucidate the creation and distribution of HCs within Au-doped Ag nanoclusters: Ag11Cl3P7H21, Ag10AucoreCl3P7H21, and Ag10AusurfCl3P7H21 nanoclusters. Our findings indicate that adjustments in HC distribution are achievable through the Au dopant atom, and precise control of HC distribution is possible by manipulating the location of the Au dopant atom. When employing a Gaussian laser pulse tailored to match the LSPR frequency, a substantial accumulation of HCs in the Ag-P bond is observed. This finding suggests a weakening of the Ag-P bonds and, consequently, the initiation of bond stretching. We propose that these findings open up possibilities for tuning HCs in Au-doped chemically functionalized Ag nanoclusters.

Evaluations of ethylene glycol and polyethylene glycol aqueous solutions using a hybrid sensor of surface plasmon resonance and quartz crystal microbalance

A hybrid sensor based on surface plasmon resonance (SPR) and quartz crystal microbalance (QCM) was prepared. One of the electrodes of the QCM sensor had a grating structure to enable SPR excitation. The SPR property was investigated through the transmission of the visible-light spectrum. The theoretical calculation showed that the experimental values almost corresponded to the theoretical ones; this suggests that the transmitted light dips were due to SPR. In order to investigate the usefulness of this hybrid sensor, the characteristics of SPR and the oscillation frequency drops of QCM (ΔF QCM) were investigated for aqueous solutions of ethylene glycol and polyethylene glycols with various degrees of polymerization. The position and slope of the SPR dip wavelength and the ΔF QCM curves depended on the degree of polymerization, suggesting that the sensor can be used to evaluate a solution property and/or discriminate a solute material.

Nano-Impact Single-Entity Electrochemistry Enables Plasmon-Enhanced Electrocatalysis

Plasmon-enhanced electrocatalysis (PEEC), based on a combination of localised surface plasmon resonance excitation and electrochemical bias applied to plasmonic material, can result in improved electrical-to-chemical energy conversion compared to conventional electrocatalysis.1 Here, we demonstrate the advantages of nano-impact single-entity electrochemistry (SEE) over conventional ensemble electrochemical measurements for investigating the intrinsic activity of plasmonic catalysts towards PEEC at the single-particle level using glucose electrooxidation on gold nanoparticles (AuNPs) as a model reaction.First, we performed conventional ensemble measurements using AuNPs coated highly oriented pyrolytic graphite (HOPG) electrodes and AuNPs coated ITO electrodes. Identical photocurrents (Figures A-B,F) were observed at wavelengths where the AuNPs plasmons are active (532 nm) and inactive (650 nm) in an electrolyte consisting of 100 mM NaOH and 30 mM glucose. Controlled experiments demonstrated that in ensemble measurements with working electrodes, where the plasmonic AuNPs are in direct contact with the conductive support, the underlying support material, such as HOPG, is the primary photo-absorber and responsible for the photocurrent. Near-identical photo-absorption of HOPG across the visible region causes consistent temperature increase at different wavelengths. This increased temperature at the electrode-electrolyte interface enhances the charge transfer kinetics and this gets reflected in the identical photocurrent at different wavelengths.2 In ensemble measurements, plasmonic effects have minimal impact on photocurrents. We suggest that this is due to continuous equilibration of the Fermi level (EF) of the AuNPs with the EF of the working electrode, leading to fast neutralisation of hot carriers by the measuring circuit (Figure G). Therefore, the hot carriers generated in plasmonic materials can not participate in catalysing chemical reactions.In SEE, a catalytically inactive carbon ultramicroelectrode (C-UME) is used as the working electrode and AuNPs diffused (~5 pM) in the electrolyte act as the catalyst. When the AuNPs collide with biased C-UME or are at close distances that enable charge tunnelling, electrocatalysis occurs on the AuNPs. This leads to formation of current spikes in the chronoamperograms. Contrary to ensemble measurements, different rate enhancements were detected at different wavelengths, with the charge/spike being higher under 532 nm illumination (1.230±0.058 fC) compared to dark (0.870±0.034 fC) and 650 nm illumination (0.920±0.036 fC) in an electrolyte consisting 10 mM NaOH and 30 mM glucose (Figures C-E,F). This wavelength dependence of photocurrent is in accordance with the absorption properties of AuNPs and therefore confirms that plasmonic effects are contributing to the photocurrents. We suggest that this is due to decoupling of the EF of the dispersed AuNPs and the C-UME. Within the charge transfer distance from the electrode or even at collision, EF level equilibration does not necessarily occur in SEE when the colliding particle does not stick to the electrode.3 The first possibility for current enhancement arises from the injection of hot carriers. When the AuNPs are not in direct contact with the electrode to enable rapid EF equilibration but at a distance sufficient for charge transfer, the hot electrons will be transferred to the C-UME due to the large difference in the energies of the electrode and hot electrons (Figure G). At the same time, the hot holes inside the AuNPs can not be neutralised by electron transfer from the electrode at the same rate as hot electrons are removed to the external circuit as the energies of the holes are either higher than that of the electrons at the electrode or only slightly lower depending on the exact value of EF of the AuNPs and the energy distribution of the hot holes.4 These remaining hot holes participate in charge transfer with glucose molecules. As the hot carrier generation in AuNPs is a wavelength-dependent phenomenon, the participation of hot charge carriers in the catalytic reaction is possible only under 532 nm but not under 650 nm irradiation.5 The second possibility is the facilitation of the catalytic reaction by thermal contribution due to the recombination of charge carriers. As the diffused AuNPs are exposed to laser irradiation, the hot carriers will recombine leading to lattice heating. When a 532 nm laser-irradiated AuNP comes into contact with the working electrode, thereby becoming active for the catalytic reaction, its temperature is already higher compared to the AuNPs in the dark or 650 nm illumination. The interfacial charge transfer will become faster on the heated AuNP leading to enhanced charge/nano-impact.References Chem. Soc. Rev. 2021, 50, 12070-12097 ACS Catal. 2022, 12, 4110–4118 J. Phys. Chem. Lett. 2017, 8, 3564–3575 ACS Nano 2019, 13, 3629–3637 Angew. Chem., Int. Ed. 2023, e202302394, DOI: 10.1002/anie.202302394 Figure 1

Resonant optical trapping of Janus nanoparticles in plasmonic nanoaperture

Controlled trapping of light-absorbing nanoparticles with low-power optical tweezers is crucial for remote manipulation of small objects. This study takes advantage of the synergetic effects of tightly confined local fields of plasmonic nanoaperture, self-induced back-action (SIBA) of nanoparticles, and resonant optical trapping method to demonstrate enhanced manipulation of Janus nanoparticles in metallic nanohole aperture. We theoretically demonstrate that displacement of Au-coated Janus nanoparticles toward plasmonic nanoaperture and proper orientation of the metal coating give rise to enhanced near-field intensity and pronounced optical force. We also explore the effect of resonant optical trapping by employing a dual-laser system, where an on-resonant green laser excites the metal-coated nanoparticle, whereas an off-resonant near-infrared laser plays trapping role. It is found that, at the optimum nanoparticle configuration, the resonant optical trapping technique can result in threefold enhancement of optical force, which is attributed to the excitation of surface plasmon resonance in Janus nanoparticles. The findings of this study might pave the way for low-power optical manipulation of light-absorbing nanoparticles with possible applications in nanorobotics and drug delivery.

An in-fiber sensor for simultaneous measurement of cholesterol concentration and temperature based on SPR and MMI

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are −0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C–46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field.

{111}‐ Faceted Silver Nanoplates: An Automated and Customized Design for Functionality

AbstractSilver nanoparticles (Ag‐NPs) exhibit the highest efficiency of localized surface plasmon resonance (LSPR) excitation that can be tuned to any wave length in the visible spectrum. Its performance depends to a large extent on its physicochemical characteristics such as size and shape; which, in turn, can be modulated by the selective growth of their crystalline facets. We used a simple direct chemical reduction method with a precise manipulation of seed‐mediated growth control through an automated single‐phase continuous flow‐batch system to induce customized geometries on Ag‐NPs. Optimization of the experimental design was carried out from a multivariate analysis, where the height/width ratio of LSPR band was used as response signal. Proposed methodology controls the critical steps in the synthesis of Ag‐NPs that modulate their morphology to attain customized surface plasmon resonance in an interval of 380 nm (spherical‐shaped nanoparticles) to 925 nm ({111}‐ faceted prism‐shaped nanoplates) absorptions, leading to a versatile platform to extend their potential applications. Although the present work focused on silver nanoparticles, we believe that this methodology can be extended to any free‐electron metals.

Thickness measurement of bimetallic film using surface plasmon resonance holographic microscopy.

Bimetallic film with high stability and sensitivity is often used to excite surface plasmon resonance (SPR). The thicknesses of the bimetallic film play an important role in quantitative retrieval of the sample's parameters, and a precise measurement method is not available until now. In this paper, we propose a method for measuring the thicknesses of bimetallic film using surface plasmon resonance holographic microscopy (SPRHM). Considering that the refractive index of the dielectric upon the bimetallic film sensitively modulates the SPR phase response, the two thickness parameters of bimetallic film can be calculated by two phase-contrast SPR images with two different liquid dielectrics. The capability of this method was verified with several Ag-Au film couples by using a compact SPRHM setup. Our work provides a precise characterization method for the parameters of SPR configuration and may find wide applications in the research fields of SPR sensing and imaging.

Mass spectrometric monitoring of ligand-bridged hot electron transfer and anaerobic oxidization on auto renewable droplet-based plasmonic nanoreactors under visible light illumination

The light induced hot-electron on plasmonic nanostructures has been recognized as a breakthrough discovery for photovoltaic and photocatalytic applications. With mass spectrometry, we demonstrate the dynamics of hot electron transfers of anaerobic oxidization reactions on Au decorated TiO2 plasmonic nanoparticles, which were coated on the inner surface of a flask. Those nanoparticles were covered by continuously renewed liquid droplets of solvent and reactants that were transported through a Venturi jet mixer with auto-spray. In addition to intensive mass transfer in such droplet-based nanoreactors, as well as strong adsorption of reactants and rapid desorption of products on materials surfaces, the localized surface plasmon resonance (LSPR) excitation upon visible light illumination, by which accumulated energies of plasmons are transferred to electrons in the conduction band of the material, attributes to the efficient photocatalytic transformation. Mass spectrometric detection of intermediate radical anions and negative ions with stable isotope labeling unambiguously identifies that highly energetic hot electrons can escape from the plasmonic nanostructures, be collected by adsorbed molecules, and initiate bond cleavages. It was demonstrated that losses of two H atoms result in the anaerobic oxidization of each benzyl alcohol molecule to a benzyl aldehyde molecule in the absence of molecular oxygen with more than 90 % yields. The well recyclable plasmonic nanoreactors implicate the injection of transferred electrons eventually back to electronically depleted Au+ positive ions. Bridged by adsorbed molecules, electrons were repeatedly circulated back and forth in plasmonic nanoreactors, where the collected light was eventually converted into chemical energy.

A High-Sensitivity Fiber Biosensor Based on PVDF-Excited Surface Plasmon Resonance in the Terahertz Band

In this paper, a D-type photonic crystal fiber (PCF) with Zeonex material as the substrate and polyvinylidene fluoride (PVDF) material as the surface plasmon resonance (SPR) excitation layer is proposed for biosensing in the terahertz (THz) band. Analyzed with a finite element method, the proposed biosensor has shown excellent sensing properties for analyte refractive indices ranging from 1.32 to 1.45. With a maximum sensor resolution of 8.40 × 10−7 refractive index unit (RIU) and a figure of merit of 39.42 RIU−1, the maximum wavelength sensitivity and amplitude sensitivity can reach 335.00 μm/RIU and −66.01 RIU−1, respectively. A ±2% fabrication tolerance analysis is also performed on the biosensor to prove its practical feasibility. We conclude that our proposed PCF biosensor utilizing PVDF-excited SPR can provide high sensitivity, and thus a compact, label-free, and convenient solution for biomedical liquid sensing in the THz band.

Rapid ultra-sensitive nucleic acid detection using plasmonic fiber-optic spectral combs and gold nanoparticle-tagged targets

Nucleic acid (NA) is a widely-used biomarker for viruses. Accurate quantification of NA can provide a reliable basis for point-of-care diagnosis and treatment. Here, we propose a tilted fiber Bragg grating (TFBG)-based plasmonic fiber-optic spectral comb for fast response and ultralow limit NA detection. The TFBG is coated with a gold film which enables excitation of surface plasmon resonance (SPR), and single-stranded probe NAs with known base sequences are assembled on the gold film. To enhance sensitivity of refractive index (RI) for sensing a chosen combination of probe and target NAs around the TFBG surface, gold nanoparticles (AuNPs) are bonded to the target NA molecules as “RI-labels”. The NA combination-induced aggregation of AuNPs induces significant spectral responses in the TFBG that would be below the detection threshold for the NAs in the absence of the AuNPs. The proposed TFBG-SPR NA sensor shows a fast response time of 30 s and an ultra-wide NA detection range from 1 × 10−18 mol/L to 1 × 10−7 mol/L. In the NA concentration range of 1 × 10−12 mol/L (1 pM) to 105 pM, an ultra-high sensitivity of 1.534 dB/lg(pM) is obtained. The sensor achieves an ultra-low limit of detection down to 1.0 × 10−18 mol/L (1 aM), which is more than an order of magnitude lower than the previous reports. The proposed sensor not only shows potentials in practical applications of NA detection, but also provides a new way for TFBG-SPR biochemical sensors to achieve higher RI sensitivity.

Coherent control of the photonic spin Hall effect by Er3+ ion concentration in an Er3+-doped YAG crystal

We theoretically investigate the effect of doped Er3+ ion concentration on the spin Hall effect (SHE) of light reflected from a Kretschmann-Raether (K-R) structure. In such a structure, an Er3+-doped yttrium aluminum garnet (YAG) crystal acts as the substrate. The excitation of surface plasmon resonance(SPR) leads to the enhancement of the spin splitting of the reflected beam in the resonance reflection dip. Due to the variation of electric dipole moment and energy level lifetime induced by Er3+ ion concentration, the spin-dependent transverse shift is sensitively dependent upon Er3+ ion concentration. Furthermore, under different concentrations of Er3+ ion, the intensity and detuning of the control field have different effects on the magnitude, sign and position of the transverse shift. More importantly, the photonic SHE can be significantly enhanced via choosing the suitable values of the control intensity and detuning at 15% Er3+ ion concentration. Therefore, our scheme may provide a basis for selecting suitable Er3+ ion concentration to enhance the SHE of light in future integrated systems.

Efficiency enhancement of GaAs nanowire array-based solar cell by plasmonic Al nanoparticles

Gallium arsenide (GaAs) nanowire (NW) solar cells (SCs) have piqued the interest of researchers because they exhibit superior light-harvesting and anti-reflection properties along with reduced material consumption compared to their planar counterparts. However, the high surface-to-volume ratio associated with these NWs degrades their performance in practical applications. Light trapping is considered one of the most crucial parameters for producing low-cost high-efficiency NW-SCs. Thus, numerous light-trapping strategies have been explored, among which surface plasmon resonance (SPR) based optical absorption enhancement using metal nanoparticles (NPs) has emerged as a potential method. The role of plasmonic aluminum (Al) NPs in the efficiency enhancement of GaAs NW SC has not yet been explored. Therefore, in this study, a vertically aligned GaAs NW SC structure incorporated with Al NPs has been investigated using the finite-difference time-domain (FDTD) method. The sidewalls of GaAs NWs are embellished with uniformly arranged Al NPs with diameters ranging from 30 to 60 nm. The excitation of localized surface plasmon resonance in metal NPs results in significant light absorption enhancement at the GaAs near-band of the proposed structure. The results demonstrate that even with a low aspect ratio (D/P) of 0.3, optimizing the geometrical parameters of the NPs results in a 41.96 % increase in power conversion efficiency (PCE) and a 45 % increase in absorption efficiency at 800 nm for the proposed structure when compared to the bare structure. Hence, our suggested structure which utilizes the light-trapping mechanism of Al NPs proves to be a cost-effective and promising material combination for high-efficiency nanoscale SCs.

Hot-Electron Dynamics Mediated Medical Diagnosis and Therapy.

Surface plasmon resonance excitation significantly enhances the absorption of light and increases the generation of "hot" electrons, i.e., conducting electrons that are raised from their steady states to excited states. These excited electrons rapidly decay and equilibrate via radiative and nonradiative damping over several hundred femtoseconds. During the hot-electron dynamics, from their generation to the ultimate nonradiative decay, the electromagnetic field enhancement, hot electron density increase, and local heating effect are sequentially induced. Over the past decade, these physical phenomena have attracted considerable attention in the biomedical field, e.g., the rapid and accurate identification of biomolecules, precise synthesis and release of drugs, and elimination of tumors. This review highlights the recent developments in the application of hot-electron dynamics in medical diagnosis and therapy, particularly fully integrated device techniques with good application prospects. In addition, we discuss the latest experimental and theoretical studies of underlying mechanisms. From a practical standpoint, the pioneering modeling analyses and quantitative measurements in the extreme near field are summarized to illustrate the quantification of hot-electron dynamics. Finally, the prospects and remaining challenges associated with biomedical engineering based on hot-electron dynamics are presented.

Excitation of surface plasmon resonance with sodium-based photonic crystal fiber for sensing applications

Surface plasmon resonance (SPR) sensors using precious metal excitation have encountered bottlenecks in performance enhancement. To address this issue, we propose a photonic crystal fiber (PCF) sensor that utilizes a polymer-protected sodium film to excite the SPR effect. The PCF has hexagonally arranged air holes and a polishing plane. The sodium film is deposited on the polished plane and protected with polymethyl methacrylate or polydimethylsiloxane for refractive index sensing or temperature sensing. We analyzed this structure using the finite element method and found that the sodium-based SPR sensor has greater sensitivity, wider detection range, and higher figure of merit (FOM) than the SPR sensor using precious metal excitation. Numerical results showed that the maximum sensitivity was 35,400 nm/RIU, the widest detection range was 1.22–1.42, and the highest FOM was 3550RIU−1 at different sodium film thicknesses. When applied to temperature sensing, its maximum sensitivity is 20.5 nm/°C, and the temperature detection range is 0°C–100°C. In addition, our proposed sodium-based SPR fiber sensor is compatible with a thermo-assisted spin-coating process, so a good guideline scheme is available for the preparation. Therefore, our proposed sensor shows excellent potential in sensing and expands the application range of sodium-based plasma devices.

Photocatalysis of Metallic Nanoparticles: Interband vs Intraband Induced Mechanisms.

Photocatalysis induced by localized surface plasmon resonance of metallic nanoparticles has been studied for more than a decade, but photocatalysis originating from direct interband excitations is still under-explored. The spectral overlap and the coupling of these two optical regimes also complicate the determination of hot carriers' energy states and eventually hinder the accurate assignment of their catalytic role in studied reactions. In this Featured Article, after reviewing previous studies, we suggest classifying the photoexcitation via intra- and interband transitions where the physical states of hot carriers are well-defined. Intraband transitions are featured by creating hot electrons above the Fermi level and suitable for reductive catalytic pathways, whereas interband transitions are featured by generating hot d-band holes below the Fermi level and better for oxidative catalytic pathways. Since the contribution of intra- and interband transitions are different in the spectral regions of localized surface plasmon resonance and direct interband excitations, the wavelength dependence of the photocatalytic activities is very helpful in assigning which transitions and carriers contribute to the observed catalysis.