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The optoelectronic application of gold nanoparticles is majorly influenced by certain unique features they exhibit, like surface plasmon resonance, ready functionalization and ease of conjugation with bio-analytes etc. Production of gold nanoparticles through laser ablation is the simplest method with the advantage of obtaining high purity particles. In this work, the saturation and reverse saturation behaviour during ultrafast absorption in laser ablated gold nanoparticles is studied using the Z-scan technique. The Z-scan experiment is conducted using 800 nm, 84 MHz and 120 fs intense laser pulses at different excitation intensities from 6.23 GW/cm2 to 23.37 GW/cm2. The open aperture Z-scan measurements show distinct positive region till an excitation of 17 GW/cm2 after which there is a clear cross-over into negative trend. The strength of this negative wing increases with the excitation intensity, which is featured by the nonlinear absorption due to the two-photon and three-photon absorption contributions with their respective coefficients in the range of 10-3. The optical limiting nature of these gold nanoparticles is demonstrated. An understanding of these nonlinear optical properties provides better insight in their application towards biomedical diagnostics and optical switching and limiting.

The present work exhibits a novel design of surface plasmon resonance (SPR) biosensor, which comprises CaF2 prism, TiO2, metal (Ag/Au), PtSe2, 2D materials (graphene/ transition metal dichalcogenides (MoS2/WS2)) and sensing medium, for point-of-care detection of various stages of malaria diseases. The transfer matrix method (TMM) is employed to examine the angular reflectivity of the proposed structure after judiciously optimizing the layer thicknesses and layer numbers. Phase interrogation technique is utilised to validate the position of occurrence of resonance angles. Additionally, the proposed SPR structure is designed using COMSOL Multiphysics, to assay the electric field intensity and electric field enhancement factor near the edge of 2D material-sensing layer interface. Simulation upshots revealed that the use of new class of 2D materials catapult the sensor performance to a new height compared to the traditional SPR configuration. A maximum sensitivity of 240.10°/RIU, quality factor of 78.46 RIU-1 and detection accuracy of 1.99 is attained for Ag-based SPR configuration with bilayer of WS2. Sensing parameters are compared with previously reported works to prove the superiority of the present research. Moreover, the real-time and label-free detection of malaria diseases makes the suggested sensor worth to fabricate as a SPR chip with the recent nanofabrication technologies.

The semiconductor-based photocatalysts with local surface plasmon resonance (LSPR) effect can extend light response to near-infrared region (NIR), as well as promote charge-carriers transfer, which provide a novel insight into designing light-driven photocatalyst with excellent photocatalytic performance. Here, we designed cost-effective wide-spectrum Zn2In2S5/W18O49 composite with enhanced photocatalytic performance based on a dual-channel charge transfer pathway. Benefiting from the synergistic effect of Z-scheme heterostructure and unique LSPR effect, the interfacial charge-carriers transfer rate and light-absorbing ability of Zn2In2S5/W18O49 were enhanced significantly under visible and NIR (vis-NIR) light irradiation. More reactive oxygen species (ROS) were formed by efficient molecular oxygen activation, which were the critical factors for both Escherichia coli (E. coli) photoinactivation and tetracycline (TC) photodegradation. The enhancement of molecular oxygen activation (MOA) ability was verified via quantitative analyses, which evaluated the amount of ROS through degrading nitrotetrazolium blue chloride (NBT) and p-phthalic acid (TA). By combining theoretical calculations with diverse experimental results, we proposed a credible photocatalytic reaction mechanism for antibiotic degradation and bacteria inactivation. This study develops a new insight into constructing promising photocatalysts with efficient photocatalytic activity in practical wastewater treatment.

A plasmonic Cu6Sn5/polyaniline (Cu6Sn5/PANI) nanocomposite was synthesized by chemical reduction and hydrothermal methods. The best photocatalytic overall water splitting performance was achieved by the Cu6Sn5/PANI3wt% composite, which contains 3 wt% PANI, which is approximately three times more than that of pure Cu6Sn5. Meanwhile, Cu6Sn5/PANI3wt% exhibited excellent photocatalytic stability for water splitting during the stability investigation. The dramatic promotion of the photocatalytic activity performance can be ascribed to the cocatalyst PANI. The existence of PANI can remarkably promote the separation and transfer efficiency of the photoinduced electron-hole pairs, and therefore enhance the photocatalytic activity. Our results also verify that the photogenerated charge comes from plasmonic Cu6Sn5 with the surface plasmon resonance (SPR) effect, which is different from traditional semiconductor-based photocatalysts. This work sheds some light on plasmonic photocatalyst development and provides an alternative pathway for photocatalytic reactions.

Localized surface plasmon resonance (LSPR) enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts. In the past decades, noble metal nanoparticles (Au and Ag) with LSPR feature have found wide applications in solar energy conversion. Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures. However, high cost and scarce reserve of noble metals largely limit their further practical use, which drives the focus gradually shift to low-cost and abundant nonmetallic nanostructures. Recently, various heavily doped semiconductors (such as WO3-x, MoO3-x, Cu2–xS, TiN) have emerged as potential alternatives to costly noble metals for efficient photocatalysis due to their strong LSPR property in visible-near infrared region. This review starts with a brief introduction to LSPR property and LSPR-enhanced photocatalysis, the following highlights recent advances of plasmonic photocatalysts from noble metal to semiconductor-based plasmonic nanostructures. Their synthesis methods and promising applicability in plasmon-driven photocatalytic reactions such as water splitting, CO2 reduction and pollution decomposition are also summarized in details. This review is expected to give guidelines for exploring more efficient plasmonic systems and provide a perspective on development of plasmonic photocatalysis.

We report on an extrinsic surface plasmon-enhancedrefractometer based on cladding mode resonance excitation in a photonic crystal fiber (PCF) equipped with a straight fiber Bragggrating (FBG). First, we show that the lattice pitch and the air hole diameter of the PCF microstructure define the spectral locationof the excited cladding mode resonances. Second, we demonstrate that if the PCF parameters are properly selected, those resonancesare sensitive to increases in steps of 1×10−4 refractive index units(RIU) of the refractive index value close to that of water. To thebest of our knowledge, this is the first time that the sensitivity of PCF cladding mode resonances to refractive index changesin water-based solutions is reported. We achieved experimental values of 40.3 nm/RIU in terms of wavelength sensitivity and −801dB/RIU in terms of amplitude sensitivity. The performance of our sensor is therefore comparable to that of tilted FBGs in step-indexfibers used for water refractometry, which indicates the potential ofour PCF sensor for biosensing. In addition, the sensor fabricationdoes not require any post-processing such as etching or polishing,which allows preserving the integrity of the fiber probe. Finally, thenarrowspectrum within which the PCF operates, allows envisagingmulti-target detection with a single fiber probe by using cascadedwavelength-multiplexed gratings.

Optical tunneling is an effect extremely sensitive to wavelength changes. In this article, we use this effect to design a new type of biosensor. The tunneling effect is excited by long range surface plasmon resonance, the energy is concentrated in the sensing medium in the form of standing waves, which lead a very high wavelength sensitivity and quality factor. By using COMSOL for finite element analysis, for the sensor structure of BK7/Cytop /Al2O3/Ag/Al2O3/sensing media/air, a quality factor of 10296 RIU-1 is achieved under angle modulation, a sensitivity of 170,000 nm/ RIU and a quality factor of 11333 RIU-1 are obtained under wavelength modulation. At the same time, the advantage of this structure is that there is no excessive requirement on the refractive index of the material, and a good sensing effect can be achieved even if the material is cheap and easy to prepare. After optimization, this structure is suitable for sensing media with a refractive index of 1.335-1.375, which can be applied to most liquid solutions.

The sun provides a plentiful and inexpensive source of carbon-neutral energy that has yet to be fully utilized. This is a major driving force behind the development of organic photovoltaic (OPV) materials and devices, which are expected to offer benefits such as low cost, flexibility, and widespread availability. For the photovoltaic performance enhancement of the inverted ZnO-nanorods (NR)/organic hybrid solar cells with poly(3-exylthiophene):(6,6)-phenyl-C61-butyric-acid-methylester (P3HT:PCBM) and poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) active layers, gold nanoparticles (Au-NPs) were introduced into the interface between indium-thin-oxide cathode layer and ZnO cathode buffer layer, and the efficiency improvement was observed. It's worth noting that adding Au NPs had both a positive and negative impact on device performance. Au NPs were shown to be advantageous to localized surface plasmon resonance (LSPs) in the coupling of dispersed light from ZnO NRs in order to extend the light's path length in the absorbing medium. Although the light absorption in the active layer could be enhanced, Au NPs might also act as recombination centers within the active layer. To avoid this adverse effect, Au NPs are covered by the ZnO seeded layer to prevent Au NPs from direct contact with the active layer. The dominant surface plasmonic effect of Au NPs increased the photoelectric conversion efficiency from 2.4% to 3.8%.

Extremely high sensitivity is the long-time pursing goal for the surface plasmon resonance (SPR) sensor, which means the capability to detect analytes with lower concentrations or interactions for smaller biomolecules. It was suggested that a flat dispersion for the plasmon material enables to enhance the sensitivity dramatically. However, the regulation ability of inherent dispersion in natural materials is limited. With the appearance of hyperbolic metamaterials (HMMs), the management of the plasmon materials dispersion becomes possible. In this paper, the HMMs with metal/dielectric multilayer structure are proposed to construct the SPR sensors. Through numerical simulations and theoretical analysis, we find that the flat dispersion in the HMM structure could significantly benefit the sensitivity improvement for HMM-SPR sensors. As a result, the proposed HMM-SPR sensor obtains an ultrahigh sensitivity of 34.00 m/RIU in the experiment, which is one order higher in magnitude than that of the conventional monolayer metallic SPR sensors. Thus, this research shows insight into understanding the dependence of the HMM-SPR sensitivity on dispersion management and provides a practical methodology to develop extremely high-sensitivity SPR sensors based on artificial plasmon materials.

In this work, we firstly used a new two-dimensional (2D) semiconductor material Bi2O2Se for optical-fiber SPR sensor sensitization, proposed and validated a U-shaped optical-fiber SPR sensor with Au film- Bi2O2Se Sandwich structure. The finite element simulation results illustrate that the electric field strength on the surface is 2.08 times higher than that of the pure Au film, which excites a stronger SPR phenomenon thus leading to a high sensitivity of the sensor. The effect of the Radius on the sensor performance was investigated, and the optimal structural parameters were derived to fabricate the sensing probes. The RI sensitivity of the presented sensor is 6827.41 nm/RIU, 1.98 times superior to that of the pure Au film U-shaped optical SPR sensor. The sensor is insensitive to temperature fluctuations and has good repetitive and environmental stability. The proposed sensor has good potential for future applications in biomass detection, which also indicates that Bi2O2Se has good prospects for future applications in optoelectronic devices.

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

Designing and constructing advanced heterojunction architectures are desirable for boosting CO2 photoreduction performance of semiconductor photocatalysts. Herein, we have prepared hierarchical ZnS@ZnIn2S4 core-shell cages with controlled particle sizes using sequential synthesis of Zeolitic imidazolate (ZIF-8) polyhedrons, ZnS cages, and ZnIn2S4 nanosheets on the ZnS polyhedron cages. ZIF-8 polyhedrons are firstly synthesized by a liquid-phase approach. The subsequent sulfidation of the ZIF-8 polyhedrons results in the formation of ZnS polyhedron cages, which act as substrates for fabricating ZnS@ZnIn2S4 core-shell cages by growing ZnIn2S4 nanosheets. The size of ZnS cages can be tuned to optimize CO2 photoreduction performance of hierarchical ZnS@ZnIn2S4 core-shell cages. The synergy of the unique hierarchical core-shell cage-like structure and heterojunction composition endows the hybrid catalyst high incident light utilization, abundant active sites, and effective separation of photoexcited charge carriers. Benefiting from these advantages, the optimized hierarchical ZnS@ZnIn2S4 core-shell cages exhibit enhanced performance for CO2 photoreduction with the CO yield of 87.43 μmol h−1g−1 and 84.3% selectivity, which are much superior to those of single ZnIn2S4 or ZnS. Upon Au decoration, the CO2 photoreduction performance of ZnS@ZnIn2S4 core-shell cages is further enhanced because of the Schottky junctions and surface plasmon resonance effect.

Transition metal dichalcogenide (TMD) monolayers, such as MoS2, possess a direct optical bandgap and are useful for emerging ultrathin optoelectronics in the visible light range, whereas their thickness limits light absorption and emission properties. To address this drawback, one promising approach is to hybridize plasmonic nanostructures with monolayer TMDs to utilize local field enhancement effects owing to localized surface plasmon resonance (LSPR). Herein, we propose a strong enhancement of the local light–matter interaction in MoS2 monolayers on naturally generated nanoscale grooves. The nanogrooves are formed at grain boundaries (GBs) of template-stripped metal film substrates that are fabricated by mechanically stripping Ag films deposited on an ultra-flat Si substrate, wherein the nanogroove densities are systematically modulated by the Ag film thickness. We observe an effective photoluminescence enhancement factor of 758 and a Raman spectroscopy intensity enhancement of approximately 5 times in MoS2 on the subwavelength-scale nanogrooves, compared with that on grain planes, which is attributed to a strong local field enhancement of the LSPR effect. Moreover, this plasmonic enhancement effect is elucidated by dark-field scattering spectroscopy and optical simulations. Our results can facilitate the utilization of density-controllable plasmonic nanogrooves synthesized without nanopatterning techniques for plasmonic hybrids on 2D semiconductors.

A coupling enhanced surface plasmon resonance (SPR) sensor based on coreless fiber is proposed. Compared with the common fiber, the coreless fiber is easier to perceive the changes of the external medium environment. As one-dimensional material with superior performance, the Au nano biconical particles are used to improve the sensor performance. Based on the finite element method (FEM), the electric field enhancement effect of the coupling between the SPR of the gold film and the Localized surface plasmon resonance (LSPR) of the Au nano biconical particles on the surface of the coreless fiber is analyzed, and the experimental results show that the Au nano biconical particles can improve the sensitivity. The sensitivity of the improved Au nano biconical particle sensor is 3514 nm/RIU, which is 64% higher than that of the traditional gold film SPR sensor, and the quality factor is increased by 24%. The new sensor based on Au nano biconical particles and gold film has a good application prospect in biosensor and chemical measurement.

The interfacial charge transfer (CT) that plays an important role in enhancing the photoelectric conversion efficiency of dye-sensitized solar cells (DSSCs) has not always been fully explored. Here, TiO2@N719@Ag DSSCs system was constructed, and the CT processes have been monitored by surface-enhanced Raman scattering (SERS) spectra. Meanwhile, it is well known that as one of the most common external stimulis, high pressure can increase the free carrier density of TiO2 NPs and cause the band gap to narrow. In the high pressure SERS experiment, we observed a significant enhancement of N719 dye in the TiO2@N719@Ag system up to 2.48 GPa, which is consistent with the variation trend of charge transfer degree (ρCT). It is indicated that band gap changes will strongly affect the CT process, further influence the SERS signal intensity (or ρCT), and thus increase the CT probability of DSSCs. Futhermore, the decoration of Ag NPs in the TiO2@N719@Ag DSSCs system can introduce localized surface plasmon resonance (LSPR), enhance the light trapping ability and offer additional CT pathways. Importantly, it is possible to improve the photoelectric conversion performance of DSSCs via high pressure method and the introducing of Ag NPs. Finally, in order to observe the CT process of DSSCs more clearly, the models describing the CT mechanism have been proposed. SERS spectroscopy is expected to be a promising technique for the exploration of the interfacial CT behavior in DSSCs devices, which may further broaden the thoughts of improvement of efficiency of cells.

CsxWO3 nanocrystals which exhibit localized surface plasmon resonance (LSPR) and small polaron transfer in wavelength of the near-infrared radiation have attracted great attention to fabricate the spectrally selective coating. Enhancing the LSPR and small polaron transfer of CsxWO3 nanocrystals is effectively achieved by introducing aliovalent dopant into its empty trigonal tunnels of the crystal lattice, but the lack of controllable synthesis process reserves some essential issues unanswered with respect to the effects of the dopant concentration on absorption coefficient, free carrier density and carrier mobility. Herein, Li-doped CsxWO3 nanocrystals were successfully prepared with the highest reported absorption coefficient, which demonstrated stronger absorption performance than the CsxWO3 nanocrystals without Li doping. The introduction of lithium into the crystal structure as a cation dopant can enhance the free carrier density of the nanocrystals, which leads to a higher absorption coefficient. The absorption coefficient variation of LSPR and small polaron transfer of Li-doped CsxWO3 nanocrystals was explained by the free carrier density and carrier mobility. This doping strategy allows CsxWO3 nanocrystals to become spectrally tunable within the wavelength of near-infrared radiation. When the Li/W molar ratio was 0.4, the free carrier density reached 10.22 × 1014 cm−3. The spectrally selective coating prepared by Li-doped CsxWO3 nanocrystals displayed excellent spectral selectivity with TVis, TNIR, Tlum, and Tsol of 68.79 %, 9.17 %, 72.61 % and 47.95 %, respectively. This doping strategy provides a promising potential to improve the spectral tunability of CsxWO3 nanocrystals for the practical application of energy-saving windows.

Metal oxide-based plasmonics is an emergent field for which indium tin oxide (ITO) is a promising material. Improving the performance of ITO-based surface plasmon resonance (SPR) sensors requires a deeper knowledge of their optical and electrical properties. The effects of microstructural parameters and defects on mobility, which strongly influences SPR in the near-IR regime was explored. The proposed model incorporates different scattering mechanisms and non-parabolic conduction bands to obtain realistic values of mobility. The results show that larger grain sizes and higher carrier concentrations in ITO thin films improve SPR performance at near-IR wavelengths as low as 1300 nm

In this work, we propose a simple yet highly sensitive multi-channel hexagonal photonic crystal fiber (PCF) based surface plasmon resonance (SPR) refractive index (RI) sensor for detecting multiple analytes. The target analytes and the plasmonic materials, such as, gold (Au), Au with Tantalum Pentoxide (Ta2O5) and Au with Titanium Dioxide (TiO2) are employed around the exterior of the sensor for the feasibility of the operation. Twelve circular air-holes in two layers constitute the fiber structure which makes the fabrication process easy and realizable. Numerical investigations are carried out employing a full-vector finite element method (FEM) to obtain the sensing performance of the PCF-SPR structure. After optimizing the structural parameters, the sensor achieves maximum wavelength sensitivity (WS) of 38100 and 21600 nm/RIU, for channels-1 and -2, respectively. For channel-3, the sensor achieves a maximum WS of 45800 nm/RIU. To the best of our knowledge, the proposed sensor achieves better performance in terms of wavelength sensitivity, wavelength resolution, amplitude sensitivity, amplitude resolution, figure of merit, etc., compared to the existing literature. In the case of cancerous cell detection, the proposed sensor achieves maximum WS and amplitude sensitivity of 12000 nm/RIU and -2440.30 RIU-1, respectively, for HeLa cells. We envisage that the proposed sensor has a high potential to detect unknown RI for different chemical and biomedical applications due to its superior performance, simple design, and multi-analyte detection ability.

One of the key elements for early diagnosis of acute and severe diseases is the development of ultra-sensitive detection methods, which are required to analyze the pathological state of the human body from trace amounts of substances in blood or urine. Surface plasmon resonance (SPR) optical fiber biosensors, particularly those based on tilted fiber Bragg gratings (TFBG), have emerged in recent years as a novel solution for in-situ biomedical detection. TFBGs can sensitively detect the physical and chemical interactions between biomolecules in real-time by sensing minute changes in refractive index, even in vivo. The TFBG-based SPR method can achieve rapid and accurate analysis of biological samples by demodulating the wavelength, intensity, phase and polarization state of the optical spectrum. In addition, TFBG-based SPR fiber optic sensors are capable of simultaneously detecting the absolute or relative values of multiple parameters. This effectively eliminates the interference from the ambient environment and ensures the stability and reliability of the sensor.

Surface plasmon resonance (SPR) is used to infer information about a sample that is in contact with an Au-coated glass slide coupled to the SPR prism. Shifts in the angle of the "SPR minimum reflection" can be related to changes in the refractive index (and/or thickness) of the sample that is in contact with the Au film, which can then be used to determine the concentration of an analyte in that sample. Here, we show that by depositing a layer of poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAm-co-AAc)] microgel on the SPR's Au film, with a subsequent layer of Au deposited on top of the microgels, the sensitivity of SPR to changes in solution properties can be enhanced. We investigated the sensitivity of the SPR to changes in the temperature of water in contact with the SPR's Au film as a function of the microgel immobilization density and the thickness of the Au layer deposited on the microgel layer. The data revealed that the SPR's Au film densely coated with microgels, with 5 nm of Au deposited, exhibited the maximal enhancement. The plasmon coupling effect between the additional Au film on the microgels and the SPR's Au film was further confirmed by 3D finite difference time domain simulations.

Surface-enhanced Raman scattering (SERS)-based cancer diagnostics is an important analytical tool in early detection of cancer. Current work in SERS focuses on plasmonic nanomaterials that suffer from coagulation, selectivity, and adverse biocompatibility when used in vitro, limiting this research to stand-alone biomolecule sensing. Here we introduce a label-free, biocompatible, ZnO-based, 3D semiconductor quantum probe as a pathway for in vitro diagnosis of cancer. By reducing size of the probes to quantum scale, we observed a unique phenomenon of exponential increase in the SERS enhancement up to ~106 at nanomolar concentration. The quantum probes are decorated on a nano-dendrite platform functionalized for cell adhesion, proliferation, and label-free application. The quantum probes demonstrate discrimination of cancerous and non-cancerous cells along with biomolecular sensing of DNA, RNA, proteins and lipids in vitro. The limit of detection is up to a single-cell-level detection., Surface enhanced Raman scattering is a bio-analytical tool and the development and optimisation of probes is an active area of investigation. Here, the authors report on the development and testing of biocompatible semiconductor zinc oxide quantum probes on a platform for cell adhesion and analysis.

This paper reports on gas sensing based on near-infrared (NIR) reconstructive spectroscopy using a surface plasmon resonance (SPR) photodetector. The reconstructive spectrometer consists of an Au g...

A highly sensitive quadrature cluster-based surface plasmon resonance photonic crystal fiber (QC-SPR-PCF) sensor has been stated in this manuscript for detecting unspecified analytes within the RI span of 1.32 to 1.43. Tactical placement of air holes in the cladding region and the external sensing approach has been chosen to ameliorate sensing performance. This fiber shows the highest amplitude sensitivity of 5274 RIU−1 with ultra-high wavelength sensitivity of 75,000 nm/RIU at optimum conditions. It has achieved an ultra-high figure of merit (FOM) of 4230.42 RIU−1 which is the highest till now to the best of our knowledge, with an amplitude resolution of 1.90 × 10–6 RIU and a wavelength resolution of 1.33 × 10–6 RIU. Furthermore, the temperature sensitivity of 1 nm/°C and a magnetic field sensitivity of 160 pm/Oe achieved during the numerical investigation introduce the possibility of a multipurpose sensor. Fabrication tolerance for ± 10% variation in diameter of air holes has also been analyzed. So, it is believed that this study can contribute a lot to pharmaceutical researches and biomedical engineering because of the proposed fiber’s versatile features.

Although pyroelectric photodetectors have been intensively studied, the transient temperature change rate of pyroelectric materials is a main restrictive factor for improving the performance. In this work, we fabricate an ultrafast response self-powered near-infrared (NIR) photodetector (PD) based on Au nanoparticles (NPs) coated an n-ZnO nanowires (NWs)/p-Si heterojunction. The local surface plasmon resonance (LSPR) effect generated at the local contacts of Au NPs/ZnO NWs can significantly enhance the transient temperature change rate of the ZnO material to improve the photoresponse performances of the NIR PD. Compared with that in the pristine ZnO-based PD, the response time of the Au-coated NIR PD is decreased from 113 to 50 μs at the rising edge and 200 to 70 μs at the falling edge. Optical responsivity and detectivity of the Au-coated ZnO-based PD are increased by 212 and 266%, respectively. The pyroelectric current gain is produced by injecting hot electrons from the LSPR effect of Au NPs into the ZnO material and the thermal energy transfer caused by the photothermal effect of plasmonic Au nanostructure. This work provides an in-depth understanding of plasmonic effect-enhanced pyroelectric effect and presents a unique strategy for developing high-performance NIR photodetectors.

In this work we study the luminescence properties of europium-doped titanium dioxide and tellurium oxide thin films enhanced by gold plasmonic nanostructures. We propose a new type of plasmon structure with an ultrathin dielectric film between plasmonic platform and luminescent material. Plasmonic platforms were manufactured through thermal annealing of the gold thin film. Thermal dewetting of gold film results in spherical gold nanostructures with average dimensions of 50 nm. Both, luminescent TiO2:Eu and TeO2:Eu films were deposited by RF magnetron sputtering from mosaic targets. The morphology of the gold nanostructures was investigated by SEM and TEM, while the composition of oxides film was analyzed by XPS. Luminescence properties were studied on the basis of excitation and emission spectra. The experiments show that the additional dielectric layer enhances the luminescence intensity. Such structures could be potential candidates as phosphors in white LEDs.

This work focused on the construction of a nanomaterial-patterned structure for high-resolved ECL signal modulation. Due to the surface coupling effect, the different shapes and distribution states of surface plasmonic nanomaterials not only affect the luminescence intensity enhancement but also decide the electrochemiluminescence (ECL) polarization characteristics. Herein, tin disulfide quantum dots were synthesized via a solvothermal method as ECL emitters. Compared with other nanostructures, Au nanotriangle (Au NT) displayed both the localized surface plasmon resonance electromagnetic enhancement effect and the tip amplification effect, which had significant hot spot regions at three sharp tips. Therefore, self-assembled Au NT-based patterned structures with high density and uniform hot spots were constructed as ideal surface plasmonic materials. More importantly, the distribution states of the hot spots affect the polarization characteristics of ECL, resulting in directional ECL emission at different angles. As a result, a polarization-resolved ECL biosensor was designed to detect miRNA 221. Moreover, this polarization-resolved biosensor achieved good quantitative detection in the linear range of 1 fM to 1 nM and showed satisfactory results in the analysis of the triple-negative breast cancer patients' serum.

A surface plasmon resonance-based biosensor is investigated theoretically and mathematically. The proposed sensor is a multilayered structure of titanium disilicide and graphene along with Ag metal. These layers are stacked over a BK7 prism. The thickness of the metal, titanium disilicide, and graphene layers is 45 nm, 2 nm, and 1.7 nm, respectively. Titanium disilicide is an air-stable two-dimensional (2D) material. The performance of the biosensor is analyzed using the attenuated total reflection (ATR) method. The proposed configuration exhibits a maximum sensitivity of 183.4°/RIU, being 47.45% higher than that of the conventional sensor. The designed sensor has wide applications in chemical, medical, and biological analyte sensing.

Objectives The aim of this study was to evaluate the serum RE1 silencing transcription factor (REST) level in Alzheimer's disease (AD), mild cognitive impairment (MCI), and elderly controls by using surface plasmon resonance (SPR) technology. Materials and Methods In this case–control study of 133 subjects, 49 patients with AD, 49 patients with MCI, and 35 elderly controls were recruited. The REST protein concentrations were evaluated by SPR. The resonance unit for each sample was recorded and the concentration of serum REST of study group was derived from the standard curve. All the experiments were done in triplicates. Statistical analysis was done and p-value of < 0.05 was considered as statistically significant. Results A significant difference was observed in the Montreal Cognitive Assessment score, Hindi Mental State Examination scale (HMSE) score education, disease duration, and gender among the groups. A significant (p>0.0001) difference in the duration of disease between AD and MCI was observed. It was observed that the mean concentration of serum REST was not significantly (p = 0.266) different among the groups. Conclusion This study first time evaluated the serum levels of REST in AD, MCI and age-matched elderly controls. The rest levels were similar in all groups; however, it can provide a new direction to future blood-based biomarker studies of REST.

Label-free biosensors, and especially those based on optical transducers like plasmonic or silicon photonic systems, have positioned themselves as potential alternatives for rapid and highly sensitive clinical diagnostics, on-site environmental monitoring, and for quality control in foods or other industrial applications, among others. However, most of the biosensor technology has not yet been transferred and implemented in commercial products. Among the several causes behind that, a major challenge is the lack of standardized protocols for sensor biofunctionalization. In this review, we summarize the most common methodologies for sensor surface chemical modification and bioreceptor immobilization, discussing their advantages and limitations in terms of analytical sensitivity and selectivity, reproducibility, and versatility. Special focus is placed on the suggestions of innovative strategies towards antifouling and biomimetic functional coatings to boost the applicability and reliability of optical biosensors in clinics and biomedicine. Finally, a brief overview of research directions in the area of device integration, automation, and multiplexing will give a glimpse of the future perspectives for label-free optical biosensors., Financial support is acknowledged from the SensCELL project (Ref. No. PGC-2018–099870), funded by the Spanish Ministry of Science and Innovation, the Spanish Research Agency (AEI), and the European Regional Development Fund (ERDF). The ICN2 is funded by the CERCA program/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centers of Excellence program, funded by AEI (Grant No. SEV-2017–0706).

Au nanoparticles (NPs) were drop-casted onto germanium (Ge) devices to investigate the influence of Au NPs on the electronic transport and photodetection properties of Ge metal–semiconductor–metal photodetectors. A significant hysteresis behavior was observed in the current–voltage curves of the Au NP-decorated Ge photodetector, which was ascribed to the energy band bending below the Au NPs and the electrostatic effect of image charges in the Au NPs. More interestingly, at the optical communication wavelength of $1.55~\mu \text{m}$ , the introduction of Au NPs effectively improved the responsivity of the device from 0.18 to 0.92 A/W. Rather than the localized surface plasmon resonance effect, the increase of responsivity in the Au NP-decorated Ge photodetector was caused by a type-II liked energy band alignment, which enhanced the spatial electron–hole separation effect. These results provide inspiration for the development of novel optoelectronic devices.

The spatial and angular Goos-Hanchen and Imbert-Fedorov shifts occur simultaneously for the light beam reflected from a lossy surface (e.g., metal surface). The mixture of spatial and angular Goos-Hanchen (Imbert-Fedorov) shifts, referred to as composited Goos-Hanchen (Imbert-Fedorov) shift, has been experimentally confirmed in recent years. The temperature-dependent composite Goos-Hanchen and Imbert-Fedorov shifts for a light beam reflected from the prism-gold interface in the Kretschmann-Raether configuration are theoretically investigated. The spatial and angular Goos-Hanchen and Imbert-Fedorov shitfs of $p$ -polarized incident light are significantly enhanced around the resonant angle with the generation of surface plasmon resonance. The ultrahigh temperature sensitivities of 0.79 cm/K and 188 $\mu$ m/K are obtained with the composite Goos-Hanchen and Imbert-Fedorov shift, respectively, which are about 5 orders higher than those obtained with a bare gold surface. The ultrahigh temperature sensitivity is mostly contributed by the angular shift effect. Our results demonstrated the importance of angular shift effect in achieving an ultrahigh sensitivity. This work can serve as a guidance for the design of temperature sensor, chemical sensor and biosensor based on composite Goos-Hanchen and Imbert-Fedorov shifts.

In the present study, a novel heterostructure of surface plasmon resonance (SPR) sensors has been proposed based on two-dimensional (2D) materials. 2D materials have attracted a huge response in the area of SPR biosensors, for the sensor performance analysis sensitivity and figure of merit (FOM) are the important parameters. Recently, SPR sensors are getting significant research interest due to their variety of applications. Fluorinated graphene (fluorographene) and MXene 2D materials have been theoretically investigated in this work, and also discussed about the detection accuracy (DA), sensitivity, FOM, and Full width half maximum (FWHM) for the proposed SPR sensors. It is investigated that the FOM found very high i.e., (347 RIU−1) in this proposed sensor which is ten times greater as per the conventional Au thin film (50 nm) in the visible range SPR sensors at wavelength of 1550 nm. Our study using the novel proposed heterostructure can be developed into a new Surface Plasmon Polarization technique (SPP) SPR sensor material.

In a wide range of applications such as healthcare treatment, environmental monitoring, food processing and storage, and semiconductor chip manufacturing, relative humidity (RH) sensing is required. However, traditional fiber-optic humidity sensors face the challenges of miniaturization and indirectly obtaining humidity values. Here, we propose and demonstrate an optical barcode technique by cooperating with RH meta-tip, which can predict the humidity values directly. Such RH meta-tip is composed of fiber-optic sensor based on surface plasmon resonance (SPR) effect and graphene oxide film as humidity sensitizer. While SPR sensor is composed of multimode fiber (MMF) integrated with metallic metasurface. Dynamic time warping (DTW) algorithm is used to obtain the warp path distance (WPD) sequence between the measured reflection spectrum and the spectra of the precalibrated database. The distance sequence is transformed into a pseudo-color barcode, and the humidity value is corresponded to the lowest distance, which can be read by human eyes. The RH measurement depends on the collective changes of the reflection spectrum rather than tracking a single specific resonance peak/dip. This work can open up new doors to the development of a humidity sensor with direct RH recognition by human eyes.

This study used photochemical reduction to successfully synthesize triangular silver nanoplates (TAgNPs) and silver nanodecahedrons (AgNDs) with higher light-absorption and higher light-scattering properties, respectively, for the same wavelength. To analyze the contribution of light-absorption and light-scattering of silver nanoparticles to the localized surface plasmon resonance (LSPR) effect, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate was doped with TAgNPs or AgNDs at the same concentration (1.17 μg/cm2) and made into polymer light-emitting diodes (PLEDs). According to the current density-voltageluminance characteristics and electroluminescence (EL) spectra, the enhancement factors for current efficiency and EL intensity for AgND-containing PLEDs were found to be higher than those for PLED with TAgNPs by 24.9% and 138%, respectively. This shows that the metal nanoparticles with higher light-scattering property can induce a relatively strong LSPR effect, which possibly gives a hint to design plasmonic photovoltaic in future.

The transmission of SARS-CoV-2, the novel severe acute respiratory syndrome corona virus have caused the corona virus disease (Covid-19) worldwide pandemic. Overcoming this pandemic requires identifying patients to avoid further spread of the disease. Real-time, sensitive, and cost-efficient methods for detecting the COVID-19 virus are crucial. Optical sensors provide one such means to achieve this, especially using surface plasmon resonance due to its advantages such as high sensitivity and excellent detection limits. In this paper, we propose a sensor for COVID-19 detection which is based on a simple Kretschmann configuration with gold layers and thiol-tethered DNA for the ligand layer. Angle interrogation was used to obtain the sensitivity of this structure using Matlab numerical analysis. The performance of the sensor was investigated with two types of prisms, SF10 and SF11, while varying the gold layer thickness between 45 - 60 nm. This information was then used to determine which combination of prism and gold thickness are ideal for detecting COVID-19 using thiol-tethered DNA. Thiol-tethered DNA layer sensor showed the highest sensitivity of 137 degree/RIU when a SF10 prism was used with a 50 - 60 nm gold layer and thiol tethered DNA layer.

A high sensitivity surface plasmon resonance (SPR) based temperature and magnetic field sensor in a dual-core D-shaped photonic crystal fiber (PCF) with two types of holes is reported. The flat sur...

Model light-confining Tamm plasmon cavities based on gold-coated nanoporous anodic alumina photonic crystals (TMM-NAA-PCs) with spectrally tunable resonance bands were engineered. Laplacian and Lorentzian NAA-PCs produced by a modified Gaussian-like pulse anodization approach showed well-resolved, high-quality photonic stopbands, the position of which was precisely controlled across the visible spectrum by the periodicity in the input anodization profile. These PC structures were used as a platform material to develop highly reflective distributed Bragg mirrors, the top sides of which were coated with a thin gold film. The resulting nanoporous hybrid plasmonic-photonic crystals showed strong light-confining properties attributed to Tamm plasmon resonances at three specific positions of the visible spectrum. These structures achieved high sensitivity to changes in refractive index, with a sensitivity of ∼106 nm RIU-1. The optical sensitivity of TMM-NAA-PCs was assessed in real time, using a model chemically selective binding interaction between thiol-containing molecules and gold. The optical sensitivity was found to rely linearly on the spectral position of the Tamm resonance band, for both Laplacian and Lorentzian TMM-NAA-PCs. The density of self-assembled monolayers of thiol-containing analyte molecules formed on the surface of the metallic film directly contributes to the dependence of sensitivity on TMM resonance position in these optical transducers. Our findings provide opportunities to integrate TMM modes in NAA-based photonic crystal structures, with promising potential for optical technologies and applications requiring high-quality surface plasmon resonance bands.

We theoretically propose a surface plasmon resonance (SPR)-based fiber optic refractive index (RI) sensor. A surface plasmon exciting metallic grating formed with the alternation of indium tin oxide (ITO) and silver (Ag) stripes is considered on the core of the fiber. A thin film of silicon is used as an overlay. Silicon film not only protects the metallic grating from oxidation but also enhances the field to improve the device sensitivity. The sensor is characterized in terms of sensitivity, detection accuracy (DA), figure of merit (FoM), and quality factor (QF). The maximum sensitivity in the RI range 1.33 to 1.38 refractive index unit (RIU) is reported to be ~25 µm/RIU in infra-red region of investigation.

We report a simple route to design highly sensitive triangular silver nanoplates (TSNPs)-based SERS substrate for the trace-level detection of explosive molecules. The size-dependent localized surface plasmon resonance (LSPR) tunability for the synthesis of TSNPs is achieved by controlling reaction kinetics and seed volume in a modified seed-mediated approach. The computed extinction spectra of TSNP, using the finite-difference time-domain (FDTD) method, are in excellent agreement with the experimental results, therefore assisting further in the investigation of the plasmonic properties of TSNP. The higher electric field enhancement offered by TSNP is systematically investigated by performing the FDTD simulations for various sizes and corner rounding of TSNP. The FDTD results show that the dipolar plasmon resonance wavelength, size, and corner rounding of TSNP are the principal contributing factors for designing the high-performance SERS substrate. Herein, we have used a portable Raman system for the SERS-based detection of three important explosive molecules: picric acid (PA), ammonium nitrate (AN), and 2, 4-dinitrotoluene (DNT). The TSNP-based SERS substrates display excellent intensity enhancement factors of ~ 107 for rhodamine 6G (R6G) and PA and ~ 105 for AN. The high sensitivity of SERS substrate with limit-of-detection (LOD) of value 2.3 × 10−11 M for PA and 3.1 × 10−8 M for AN and effective batch-to-batch reproducibility for DNT, thus offering its potentials for field detection of explosive molecules at trace-level.

Copper sulfide (CuxS) as a plasmonic solar photothermal semiconductor material that expands the light collection range by altering localized surface plasmon resonance (LSPR) to the near- to mid- infrared (IR) spectral region. The versatile synthesis strategies of CuxS nanostructure offer its variability of morphology and provide additional freedom in tuning the optical property. Particularly, nanocage (or nanoshell) has hybridized plasmon resonances as a result of super-positioned nanosphere and nanocavity, which extends its receiving range of solar spectrum and increases light-to-heat conversion rate. Here, we offer novel “nanoink” and “nanofilm” developed from colloidal Cu27S24 nanocages with excellent solar photothermal response. Via combining experimental measurement and theoretical calculation, we estimated the optical properties of covellite Cu27S24. And based on obtained dielectric functions, we then calculated its solar photothermal performance, which was further validated by our experimental measurement. The simulation results showed that hollow Cu27S24 nanocages have excellent solar photothermal performance, and exhibit much higher solar photothermal conversion efficiency than solid Cu27S24 nanospheres.

A highly sensitive surface plasmon resonance (SPR) sensor comprising a dual-core photonic crystal fiber (PCF) is designed to detect minute changes in analyte refractive indices (RIs) between 1.33 and 1.42. In order to simplify the fabrication process and analytical protocol, a gold film is deposited on the external surface of the fiber to excite surface plasmon polaritons (SPPs). The larger diameter air holes are used in the photonic crystal fiber (PCF) cladding, which not only simplifies the actual production, but also makes the energy of the core more concentrated, and can more fully generate surface plasmon resonance with surface plasmon polaritons (SPPs). The dual-core PCF-SPR sensor is analyzed by the finite-element method (FEM), and the various structural parameters are investigated systematically and optimized. The optimized PCF-SPR sensor shows a maximum wavelength sensitivity of 29,500 nm/RIU and resolution of 3.39 × 10−6 RIU.

We report an extraordinary transmission (EOT) of gold-capped silica microsphere monolayers in the mid-infrared range of 5–25 μm. The observed transmittance is significantly greater than that of a flat gold film with the same thickness, although the surface of the microsphere monolayer appeared to be completely covered with gold when observing from above. The calculations based on the finite difference time domain method indicate that light passes through the openings between the gold coating on the substrate and that on the microspheres. The EOT-type studied here occurs over the mid-infrared wavelength range, thus indicating that it is not attributable to the resonance of the surface plasmons. This type of EOT is absent in the visible and near infrared wavelength range, where gold does not function as an ideal metal. In addition, spectral modification originating from localized phonon polariton resonance (LPhPR) in silica microsphere is observed. LPhPR can be interpreted based on the analogy of the localized surface plasmon resonance in metallic nanospheres, in the visible or ultraviolet wavelength range.