Strong Localized Surface Plasmon Resonance Research Articles

Metallic Degenerately Doped Free-Electron-Confined Plasmonic Nanocrystal and Infrared Extinction Response

In this paper, synthetically scaled-up degenerately n-type doped indium tin oxide (Sn:In2O3) nanocrystals are described as highly transparent conductive materials possessing both optoelectronic and crystalline properties. With tin dopants serving as n-type semiconductor materials, they can generate free-electron carriers. These free electrons, vibrating in resonance with infrared radiation, induce strong localized surface plasmon resonance (LSPR), resulting in efficient infrared absorption. To commercialize products featuring Sn:In2O3 with localized surface plasmon resonance, a scaled-up synthetic process is essential. To reduce the cost of raw materials during synthesis, we aim to proceed with synthesis in a large reactor using industrial raw materials. Sn:In2O3 can be formulated into ink dispersed in solvents. Infrared-absorbing ink formulations can capitalize on their infrared absorption properties to render opaque in the infrared spectrum while remaining transparent in the visible light spectrum. The ink can serve as a security ink material visible only through infrared cameras and as a paint absorbing infrared light. We verified the transparency and infrared absorption properties of the ink produced in this study, demonstrating consistent characteristics in scaled-up synthesis. Due to potential applications requiring infrared absorption properties, it holds significant promise as a robust platform material in various fields.

Photothermal properties of Cu@polycarbonate composites with strong localized surface plasmon resonances

Photothermal properties of Cu@polycarbonate composites with strong localized surface plasmon resonances

Mesoporous platinum@copper selenide-based NIR-II photothermal agents with photothermal conversion efficiency over 80% for photoacoustic imaging and targeted cancer therapy

Elevating photothermal conversion efficiency (PCE) is the key to enhance curative efficacy during photothermal therapy. Nevertheless, current functionalized or synthetic methods for preparing photothermal agents with high PCE are too complicated, greatly hindering the development of photothermal therapy. In this study, we developed a tumor-targeting flower-like nanocomposite termed mesoporous platinum nanoparticles@Cu2-xSe-AS1411 (MPNPs@Cu2-xSe-AS1411, denoted as MPCSA) with remarkable PCE for high-resolution PA imaging guided photothermal/chemodynamic therapy for tumor ablation. We discovered that MPNPs served as carriers for delivering photoacoustic (PA) contrast agents. Cu2-xSe nanosheets emerged as promising near-infrared-II (NIR-II) PA imaging and photothermal/chemodynamic therapy agents owing to their strong localized surface plasmon resonance property in the NIR-II region. The amine-modified AS1411 aptamer, which is connected to the surface of the flower-like MPNPs@Cu2-xSe can target the nucleolar protein on the surface of 4 T1 cells, achieving the accumulation of MPCSA at the tumor site in mice. Notably, these MPCSA nano-flowers exhibited an excellent PCE up to 82.33 % under 1064 nm laser irradiation, resulting in highly efficient cancer cell ablation and greatly hindering in vivo tumor growth. This study has paved the way for imaging-guided accurate cancer diagnosis and targeted cancer therapy.

Infrared light driven overall water vapor splitting on a plasmonic semiconductor p-n heterojunction photocatalyst

Photocatalytic overall water splitting (OWS) has yet to be realized on plasmonic semiconductor photocatalysts. In this work, we reported a plasmonic heterojunction of p-Cu1.81S/n-CdS with homogeneously distributed p-type and n-type domains in a single nanoparticle. The plasmonic heterojunction displays a strong localized surface plasmon resonance (LSPR) absorption peak at 1480 nm and can drive the OWS into hydrogen and oxygen under infrared light (IR) irradiation. The IR light-induced hot electrons and holes in Cu1.81S nanodisks alone can split water vapor into hydrogen and oxygen, but with poor efficiency. Surprisingly, the plasmonic p-Cu1.81S/n-CdS heterojunction shows significantly improved IR light-driven OWS performance. Under the irradiation of IR light (λ > 800 nm), the hydrogen and oxygen production rates were 0.73 mmol gcat−1 h−1 and 0.33 mmol gcat−1 h−1, respectively. The heterojunction photocatalyst delivered a solar-to-hydrogen conversion efficiency (STH) of 0.02 % under AM 1.5G irradiation. The present study has demonstrated that plasmonic semiconductors are promising photocatalysts for harvesting IR light for green hydrogen generation.

In Situ Construction of Interface with Photothermal and Mutual Catalytic Effect for Efficient Solar-Driven Reversible Hydrogen Storage of MgH2.

Hydrogen storage in MgH2 is an ideal solution for realizing the safe storage of hydrogen. High operating temperature, however, is required for hydrogen storage of MgH2 induced by high thermodynamic stability and kinetic barrier. Herein, flower-like microspheres uniformly constructed by N-doped TiO2 nanosheets coated with TiN nanoparticles are fabricated to integrate the light absorber and thermo-chemical catalysts at a nanometer scale for driving hydrogen storage of MgH2 using solar energy. N-doped TiO2 is in situ transformed into TiNxOy and Ti/TiH2 uniformly distributed inside of TiN matrix during cycling, in which TiN and Ti/TiHx pairs serve as light absorbers that exhibit strong localized surface plasmon resonance effect with full-spectrum light absorbance capability. On the other hand, it is theoretically and experimentally demonstrated that the intimate interface between TiH2 and MgH2 can not only thermodynamically and kinetically promote H2 desorption from MgH2 but also simultaneously weaken Ti─H bonds and hence in turn improve H2 desorption from the combination of weakened Ti─H and Ti─H bonds. The uniform integration of photothermal and catalytic effect leads to the direct action of localized heat generated from TiN on initiating the catalytic effect in realizing hydrogen storage of MgH2 with a capacity of 6.1wt.% under 27 sun.

High-sensitivity refractive index sensor based on strong localized surface plasmon resonance.

This study proposes two types of composite structures based on gold nano circular and nano square rings on a gold thin film for plasmonic refractive index sensing. The finite-difference time-domain method was used for simulation and analysis. The nano square ring composite structure showed superior performance, with five surface plasmon resonance modes, and a peak sensitivity and figure of merit in a liquid environment of 1600nm/RIU and 86R I U -1, respectively. The sensing performances of localized surface plasmon resonance modes of both structures are superior to those of the propagating surface plasmon resonance modes. The proposed composite structures can provide a reference for refractive index sensing and have broad application prospects in bio-chemistry.

Scalable synthesis of Au@CeO2 nanozyme for development of colorimetric lateral flow immunochromatographic assay to sensitively detect heart-type fatty acid binding protein

Nanozymes with core@shell nanostructure are considered promising biolabeling materials for their multifunctional properties. In this work, a simple one-pot strategy has been proposed for scalable synthesis of gold@cerium dioxide core@shell nanoparticles (Au@CeO2 NPs) with strong localized surface plasmon resonance (LSPR) absorption and high peroxidase-like catalytic activity by redox reactions of Ce3+ ions and AuCl4− ions in diluted ammonia solution under room temperature. A colorimetric lateral flow immunochromatographic assay (LFIA) has been successfully fabricated for sensitive detection of heart-type fatty acid binding protein (H-FABP, an early cardiac biomarker) by using the Au@CeO2 NPs as reporters. The as-developed LFIA with Au@CeO2 NP reporter (termed as Au@CeO2-LFIA) exhibits a dynamic range of nearly two orders of magnitude, and a limit of detection (LOD) as low as 0.35 ng mL−1 H-FABP with nanozyme-triggered 3,3′,5,5′-tetramethylbenzidine (TMB) colorimetric amplification. Furthermore, the practicality of Au@CeO2-LFIA has been demonstrated by profiling the concentrations of H-FABP in 156 blood samples of acute myocardial infarction (AMI) patients, and satisfactory results are obtained.

High enhancement, low cost, large area surface enhanced Raman scattering substrates all by atomic layer deposition on porous filter paper

We successfully developed an atomic layer deposition (ALD) method for making Ag noble nanoparticles on cheap, commercial filter paper consisting of three-dimensional porous glass fibers and investigated the evolution of Ag nanostructures with some key process parameters. By tuning Ag particle sizes and controlling the cycle numbers of ALD deposited Ag films, we were able to obtain high-density isolated Ag nanoparticles with average sizes in 3–9 nm without the formation of agglomerates and continuous Ag films. We proved the presence of strong localized surface plasmon resonance peaks near a target wavelength of 632 nm. We further proved the presence of surface enhanced Raman scattering (SERS) signals on the Ag coated filter paper substrates using pyridine as the test analyte. Our results demonstrate that ALD is a very promising technique for a rational design of SERS substrates and, thus, has great potential for the fabrication of large-area, low-cost SERS substrates for future commercial applications, as compared to other existing techniques.

Recent advance on fiber optic SPR/LSPR-based ultra-sensitive biosensors using novel structures and emerging signal amplification strategies

Biomarkers with ultralow concentration in the actual samples play a vital role in the clinical disease diagnosis, infectious disease screening, food security, and environmental monitoring. Fiber optic (FO)-based surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) biosensors attract immense attention for in situ, and rapid detection due to their merits of miniaturized devices, easy integration, and low cost, showing great promising for point of care point-of-caring test. In order to achieve ultrasensitive detection of biomarkers, great effort focused on design of a sensitive FO-based biosensor on the aspect of novel FO probes and signal amplification strategies. Firstly, novel FO probes, including gating and new structure-based, were develop to adjust the light propagation and allow intensely interaction between the light and metal film or nanoparticles, which excites strong SPR or LSPR for sensitive biosensor. Then, nanomaterials on FO surface improved the intensity of electromagnetic fields or provided a good scaffold to modify with more recognition element for signal amplification. Nucleic acid circuits get rid of the limitation of the signal-to-target ratio of 1:1 and exhibited high efficiency to amplify the signal. These efforts have also led to the application of FO-SPR and LSPR sensors for detection of various targets, such as cells, nucleic acids, proteins, and small molecules. In the review, we summarized the important progress of the ultrasensitive FO-based biosensor about emerging FO probes and signal amplification strategies, also discussed its opportunities and challenges for the point-of-caring test. The review aims to promote the application of the FO-SPR and LSPR from experiments to real samples.

Electromechanically reconfigurable plasmonic nanoslits for efficient nano-opto-electro-mechanical tuning

Plasmonic metamaterials with strong localized surface plasmon resonances (LSPRs) have been improved by incorporating a nano-opto-electro-mechanical system (NOEMS) for tunable optical and electrical responses. However, conventional NOEMS devices suffer from the inefficient free-space coupling due to the limited design of reconfigurable antennas and the low optical tunability due to electrostatic pull-in of moving parts. In this paper, we propose efficient mid-infrared plasmonic nanoslits with variable nanometer-sized gaps giving rise to broad optical tunability. Our finite element method (FEM) analysis shows that by applying a voltage bias to asymmetric nanoslits supported on dielectric pillars, the gap width can be increased by more than 60 nm from an initial 1 nm. The large change in gap width results in a significant spectral shift in reflectance, while maintaining strong free-space coupling and a constant full width at half maximum (FWHM). We also analyze the effect of geometrical parameters on the nanometer-sized gap width and optical responses. Our nanoslits with simple geometry resulting in efficient optical coupling show promise for improving active metasurfaces and electromechanically tunable plasmonic devices.

Enhancing Silicon Solar Cell Performance Using a Thin-Film-like Aluminum Nanoparticle Surface Layer.

Solar cells play an increasing role in global electricity production, and it is critical to maximize their conversion efficiency to ensure the highest possible production. The number of photons entering the absorbing layer of the solar cell plays an important role in achieving a high conversion efficiency. Metal nanoparticles supporting localized surface plasmon resonances (LSPRs) have for years been suggested for increasing light in-coupling for solar cell applications. However, most studies have focused on materials exhibiting strong LSPRs, which often come with the drawback of considerable light absorption within the solar spectrum, limiting their applications and widespread use. Recently, aluminum (Al) nanoparticles have gained increasing interest due to their tuneable LSPRs in the ultraviolet and visible regions of the spectrum. In this study, we present an ideal configuration for maximizing light in-coupling into a standard textured crystalline silicon (c-Si) solar cell by determining the optimal Al nanoparticle and anti-reflection coating (ARC) parameters. The best-case parameters increase the number of photons absorbed by up to 3.3%. We give a complete description of the dominating light-matter interaction mechanisms leading to the enhancement and reveal that the increase is due to the nanoparticles optically exhibiting both particle- and thin-film characteristics, which has not been demonstrated in earlier works.

A Three-Dimensional Hydrophobic Surface-Enhanced Raman Scattering Sensor via a Silver-Coated Polytetrafluoroethylene Membrane for the Direct Trace Detection of Molecules in Water.

We report a three-dimensional (3D) SERS substrate consisting of a silver nanoparticle (AgNP) coating on the skeleton-fiber surfaces of a polytetrafluoroethylene (PTFE) membrane. Simple thermal evaporation was employed to deposit Ag onto the PTFE membrane to produce grape-shaped AgNPs. The 3D-distributed AgNPs exhibit not only strong localized surface plasmon resonance (LSPR) but also strong hydrophobic performance. High-density hotspots via silver nano-grape structures and nanogaps, the large 3D interaction volume, and the large total surface area, in combination with the hydrophobic enrichment of the specimen, facilitate high-sensitivity sensing performance of such a SERS substrate for the direct detection of low-concentration molecules in water. An enhancement factor of up to 1.97 × 1010 was achieved in the direct detection of R6G molecules in water with a concentration of 10-13 mol/L. The lowest detection limit of 100 ppt was reached in the detection of melamine in water. Such a SERS sensor may have potential applications in food-safety control, environmental water pollution monitoring, and biomedical analysis.

Highly stable localized surface plasmon resonance of Cu nanoparticles obtained via oxygen plasma irradiation.

Copper nanoparticles (CuNPs) possess strong localized surface plasmon resonance (LSPR) in visible light. However, CuNPs are not chemically stable in air, which has seriously hindered the applications based on the LSPR of CuNPs. We developed an artificial method to passivate CuNPs as Al naturally does in air, preventing the oxidation of CuNPs through swift oxidation of the surface atoms via oxygen plasma irradiation. A hemispheric core-shell structure of CuNPs uniformly covered by a dense CuO shell (CuNPs@d-CuO) was constructed. The 4 nm d-CuO shell can prevent CuNPs from further oxidation. As a result, the LSPR of the CuNPs is stable in air over 180 days.

Hollow cubic CuSe@CdS with tunable size for plasmon-induced Vis-NIR driven photocatalytic properties.

The rational design of the dimension and geometry of a plasmonic semiconductor cocatalyst is vitally important for efficient utilization of near-infrared (NIR) light and superior photocatalytic hydrogen generation. Herein, hollow cubic CuSe@CdS composites with different sizes and strong localized surface plasmon resonance (LSPR) were prepared by selenizing size-tunable Cu2O templates and loading CdS nanoparticles. The size of hollow cubic CuSe can affect the surface area and the conduction band potential through the size effect, regulating the carrier behavior of the CuSe@CdS heterojunction. The CuSe@CdS composites show enhanced and wide absorption in the full spectrum due to the LSPR effect of CuSe. Meanwhile, the composites show excellent photocatalytic hydrogen capacity in the full spectrum in a 0.35 M Na2S/0.25 M Na2SO3 sacrificial reagent solution. The best hydrogen production rate of CSCE2 is 1.518 mmol g-1 h-1 (5.54 times higher than that of CdS) under Vis light (780 > λ > 420 nm) irradiation and 0.28 mmol g-1 h-1 under NIR light (λ > 780 nm) illumination. Interestingly, the photocatalytic activity for H2 under Vis-NIR light (λ > 420 nm) is about 3 times (up to 4.45 mmol g-1 h-1) higher than that without NIR light assistance, due to the photothermal effect. Various analyses and DFT calculations demonstrate that the p-n heterojunction formed in the composites consists of p-type CuSe and n-type CdS, which achieves efficient carrier transfer and separation under the synergistic effect of the size effect and the photothermal effect. In addition, the expansion of the photocatalytic performance to the NIR range is mainly due to the "hot-electron" injection mechanism induced by the LSPR effect of CuSe. The reasonable design coupled with the plasmonic materials offers a new path to achieving the highly efficient conversion of solar energy to hydrogen energy.

Plasmonic silver and gold nanoparticles: shape- and structure-modulated plasmonic functionality for point-of-caring sensing, bio-imaging and medical therapy.

Silver and gold nanoparticles have found extensive biomedical applications due to their strong localized surface plasmon resonance (LSPR) and intriguing plasmonic properties. This review article focuses on the correlation among particle geometry, plasmon properties and biomedical applications. It discusses how particle shape and size are tailored via controllable synthetic approaches, and how plasmonic properties are tuned by particle shape and size, which are embodied by nanospheres, nanorods, nanocubes, nanocages, nanostars and core-shell composites. This article summarizes the design strategies for the use of silver and gold nanoparticles in plasmon-enhanced fluorescence, surface-enhanced Raman scattering (SERS), electroluminescence, and photoelectrochemistry. It especially discusses how to use plasmonic nanoparticles to construct optical probes including colorimetric, SERS and plasmonic fluorescence probes (labels/reporters). It also demonstrates the employment of Ag and Au nanoparticles in polymer- and paper-based microfluidic devices for point-of-care testing (POCT). In addition, this article highlights how to utilize plasmonic nanoparticles for in vitro and in vivo bio-imaging based on SERS, fluorescence, photoacoustic and dark-field models. Finally, this article shows perspectives in plasmon-enhanced photothermal and photodynamic therapy.

Hydrothermal carbonization carbon induced synthesis of flower-like C/Bi/BiOI heterojunction with heightened photocatalytic Cr(VI) reduction

Modification with metallic Bi and formation heterojunction with carbon material are considered as the compelling strategies to address the shortcoming of bismuth oxyhalide in photocatalytic Cr(VI) reduction. However, the simultaneous and in-situ synthesis of metallic Bi and hydrothermal carbonization carbon (HC) on BiOI to fabricate a ternary heterojunction photocatalyst remains a challenge yet, and the synergistic mechanism between the localized surface plasmon resonance (LSPR) effect and HC is still indistinct. Herein, a ternary heterojunction photocatalyst comprising metallic Bi, HC, and flower-like BiOI was designed and synthesized through the in-situ induction of HC. During the solvothermal synthesis, a portion of Bi3+ was reduced to metallic Bi nanoparticles, and simultaneously gauzy HC was formed. In the ternary heterojunction, the metallic Bi nanoparticles displayed strong LSPR effect, and the coated HC was conducive to transferring photogenerated electrons and enriching Cr(VI). Due to the synergistic effect of metallic Bi and HC, multiple channels for photogenerated carrier transfer were constructed. Deriving from the excellent light-harvesting, accelerated transfer/separation, and restrained recombination of photogenerated carriers, the ternary heterojunction of flower-like C/Bi/BiOI showed superior photocatalytic Cr(VI) reduction. The reaction rate constant of photocatalytic Cr(VI) reduction was about 26 times higher than that of BiOI.

Optical Microfiber Coated with WS2‐Supported Gold Nanobipyramids: Ultrasensitive Detecting Prostate Cancer Extracellular Vesicles in Complex Human Samples

AbstractUltrasensitive and rapid detection of single extracellular vesicles (EV) in complex biological samples requires a biosensor that possesses remarkable specificity, cost‐effectiveness, and ease of use; however, this remains a big challenge owing to the small size and high heterogeneity of EV in samples. Although reported biosensors can detect biomarkers in complex biological samples, tedious preprocessing procedures, low sensitivity, and expensive and complicated production hinder their use in early‐stage cancer diagnostics. To address these issues, an optical microfiber modified with WS2‐supported gold nanobipyramid (Au NBPs) nanointerfaces for the ultrasensitive assay of prostate cancer (PC) exosomes is proposed. Owing to the strong localized surface plasmon resonance (LSPR) hotspots of the Au NBPs coupled with the WS2 nanointerface, the sensor could ultrasensitively detect exosomes with an ultralow limit of detection (LODs) of 23.5 particles mL−1 in phosphate‐buffered saline (PBS) solution and 570.6 particles mL−1 in 10% serum. The LOD of 23.5 particles mL−1 is two orders of magnitude lower than those reported for other cutting‐edge techniques. Based on this sensing scheme, the sensor can distinguish PC serum from healthy serum, and successfully diagnose patients’ whole blood by capturing and sizing a single bioparticle. This work presents a novel method for analyzing whole blood with ultrahigh sensitivity.

Cascade amplification of optical absorption on III–V semiconductors via plasmon-coupled graphene

Plasmons in graphene (Gr) show many fascinating characteristics, such as dynamic tunability, strong field confinement of light-matter interaction, and highly responsive, which has been widely exploited for a number of applications, including photodetectors, optical modulators, and sensors. In this paper, graphene plasmons (GPs) were motivated by implanting Au nanoparticles (Au NPs) into Ta2O5 thin layers adjacent to the Gr film, and the strong localized surface plasmon resonance (LSPR) effect has been proposed and demonstrated by placing the GPs structure on a III–V semiconductor quantum well saturable absorber (SA). It has been substantiated that the heightened interaction between light and Gr via LSPR predominantly occurs through the mechanisms of resonant energy transfer and local electromagnetic field enhancement, rather than direct electron transfer. Significant improvement on the nonlinear characteristics of the GPs modulated III–V semiconductor SA has been observed with a 17.1% large modulation depth and obviously improved working stability. A 1550 nm passive mode-locked laser has been successfully constructed with a pulse width down to 523 fs by integrating the SA into the laser cavity. This work lays the foundation for the development of high-performance mode-locked lasers and also demonstrates the substantial enhancement of nonlinear optical properties of various materials not limited to III–V semiconductors provided by this GPs' modulated structure; hence, these findings offer extensive prospects for applications in various photonics and optoelectronic devices.

Ammonia induced strong LSPR effect of chain-like ATO nanocrystals for hyperspectral selective energy-saving window applications

Sb-doped SnO2 (ATO) is a promising multifunctional material with great potentials for practice applications, however, it suffers from poor absorption efficiency of near-infrared (NIR) light due to its relatively weak localized surface plasmon resonance (LSPR) effect. In this study, a series of chain-like ATO nanocrystals (NCs) with high Sb5+/Sb3+ ratio(s) and oxygen defect concentration were precisely prepared by a simple but efficient precipitation-hydrothermal method. The introduction of NH3 served as a double-hero in controlling both the solution pH and the shape of nanocrystals. Both experimental and theoretical calculation results have indicated that our synthesis strategy effectively increases the free carrier concentration and mobility of ATO NCs to improve LSPR effect, and thereby effectively broaden the NIR light absorption region and improve the absorption capacity. Furthermore, the as-prepared ATO hydrosols show great potentials for practical applications in energy-saving building since a flexible application mode as an energy-saving window can be implemented. Both the formation of ATO hydrosol windows by pouring into the laminated glass and spin-coating onto the flat glass to create ATO coatings can result in excellent optical properties and thermal insulation performance. These findings may not only accelerate the commercialization process of ATO but also provide valuable theoretical guidance for developing novel hyperspectral materials.

Fully Discrete VO2 Particulate Film with Ultra‐High Transmittance and Excellent Thermochromic Performance

AbstractVanadium dioxide (VO2) has attracted widespread attention due to its extraordinary thermochromic properties. Visually transparent VO2 films hold great promise for applying in smart windows, smart radiative coolers, solar cells, and microwave absorbing windows. However, it remains a huge challenge to simultaneously achieve ultra‐high luminous transmittance (Tlum) and excellent thermochromic performance due to their contradictory relationship. Here, a fully discrete VO2 particulate (FDVP) film is developed. It shows an ultra‐high Tlum of 92.7% due to the reflectance being significantly reduced. Below the phase transition temperature (Tc, 69.1 °C), it is highly transparent to near‐infrared (NIR) light, while above Tc, it blocks NIR light through the strong localized surface plasmon resonance (LSPR) effect, resulting in an excellent solar energy modulation (ΔTsol) of 10.5% for smart windows. In addition, a 3.5 at.%W‐doped FDVP film exhibits a desired Tc of 25.8 °C, an extremely narrow hysteresis width (ΔT) of 4.6 °C, and good optical properties (Tlum = 92.0%, ΔTsol = 8.2%). The performance represents a new milestone for thermochromic VO2 films. This work will shed light on the structural design for high‐performance VO2 films.