Surface Plasmon Resonance Coupling Research Articles

Highly sensitive biosensor with graphene-MoS2 heterostructure based on photonic spin Hall effect

Abstract We propose a new optical biosensor based on photonic spin Hall effect (PSHE) for detection of DNA hybridization. This device consists of BK7 prism, Ag, SiO2, Au and graphene-MoS2 heterostructure which produces waveguide coupled surface plasmon resonance (WCSPR) effect to enormously enhance PSHE. The adsorption of graphene-MoS2 heterostructure to biomolecules changes the refractive index of the sensing medium, thereby affecting spin-dependent splitting in PSHE. The 2 × 2 transfer matrix method is applied to calculate the generalized Fresnel reflection and we deduce the reflected light shifts in PSHE. We study the correlation between spin-dependent displacements and the refractive index variations of sensed solution to obtain the highest sensitivity in the proposed sensor. However, the PSHE exists in the proposed biosensor is extremely weak, so a signal enhancement technology called weak measurement is adopted to amplify the PSHE shift. Thus, the proposed biosensor can successfully detect the hybridization of probe DNA with target DNA. These results may provide practical applications for PSHE in biological monitoring, medical diagnosis, and food safety.

Direct detection of DNA using 3D surface enhanced Raman scattering hotspot matrix.

Silver nanoparticles (AgNPs) are evaporatively self-assembled into the 3D surface enhanced Raman scattering (SERS) hotspot matrix with the assistant of glycerol to improve the spectral reproducibility in direct DNA detection. AgNPs and DNA in the glycerol-stabilized 3D SERS hotspot matrix are found to form flexible sandwich structures through electrostatic interaction where neighboring AgNPs create uniform and homogeneous localized surface plasmon resonance coupling environments for central DNA. Nearly two orders of magnitude extra SERS enhancement, more stable peak frequency and narrower peak full width at half maximum can therefore be obtained in DNA SERS spectra, which ensures highly stable and reproducible SERS signals in direct detection of both single strand DNA and double strand DNA utilizing the 3D SERS hotspot matrix. By normalizing the SERS spectra using phosphate backbone as internal standard, identification of single base variation in oligonucleotides, determination of DNA hybridization events and recognition of chemical modification on bases (hexanethiol-capped at 5' end) have been demonstrated experimentally. This proposed 3D SERS hotspot matrix opens a novel perspective in manipulating plasmonic nanoparticles to construct SERS platforms and would make the surface enhanced Raman spectroscopy a more practical and reliable tool in direct DNA detection.

Enhanced Quality Factors of Surface Lattice Resonances in Plasmonic Arrays of Nanoparticles

AbstractKey in the application of plasmonics is the realization of low loss or high quality (Q) factor resonances. Nanoparticle arrays are systems capable of sustaining remarkably high Q‐factor resonances through the hybridization of plasmonic and photonic modes, known as surface lattice resonances (SLRs). SLRs result from the coupling of localized surface plasmon resonances (LSPRs) to in‐plane orders of diffraction known as Rayleigh anomalies (RAs). To date, the highest Q‐factors have been achieved with the (±1, 0) diffraction orders. However, these Q‐factors are highly sensitive to the angle of excitation. Here, a strategy is presented to generate high Q‐factor SLRs with low dispersion by coupling LSPRs to the (0, ±1) diffraction orders. 2D arrays of silver nanoparticles are investigated experimentally and numerically, and it is shown that the Q‐factor of SLRs critically depends on the quality of the metal film, the detuning between RAs and LSPRs, and the absorption of adhesive layer used between the substrate and the metallic nanoparticles. These silver nanoparticle arrays can achieve Q‐factors higher than 330 in the visible range. These extraordinarily high Q‐factors could be increased to values above 1500 if no adhesive layer is used, which could significantly improve sensors and enhance nonlinearities in plasmonic systems.

Theoretical and Experimental Investigation of an All-Fiber Waveguide Coupled Surface Plasmon Resonance Sensor With Au–ZnO–Au Sandwich Structure

In this paper, we proposed an all-fiber waveguide coupled surface Plasmon resonance (SPR) sensor which was designed and fabricated with Au-ZnO-Au sandwich multi-layer structure. Based on the transfer matrix method (TMM), the theoretical modeling of the proposed sensor structure was investigated. The influence of the layer thickness on the transmission spectrum of the sensor was studied numerically, in order to optimize each layer thickness, leading to sensitivity enhancement in the infrared spectral range. Meanwhile, an experimental testbed for the refractive index measurement was implemented based on the proposed all-fiber waveguide coupled SPR sensor. Using this waveguide coupled SPR sensor, the refractive index sensing was realized with a sensitivity enhancement of 7%—131% compared with conventional SPR sensors.

Sandwiching analytes with structurally diverse plasmonic nanoparticles on paper substrates for surface enhanced Raman spectroscopy.

This report describes the systematic combination of structurally diverse plasmonic metal nanoparticles (AgNPs, AuNPs, Ag core–Au shell NPs, and anisotropic AuNPs) on flexible paper-based materials to induce signal-enhancing environments for surface enhanced Raman spectroscopy (SERS) applications. The anisotropic AuNP-modified paper exhibits the highest SERS response due to the surface area and the nature of the broad surface plasmon resonance (SPR) neighboring the Raman excitation wavelength. The subsequent addition of a second layer with these four NPs (e.g., sandwich arrangement) leads to the notable increase of the SERS signals by inducing a high probability of electromagnetic field environments associated with the interparticle SPR coupling and hot spots. After examining sixteen total combinations, the highest SERS response is obtained from the second layer with AgNPs on the anisotropic AuNP paper substrate, which allows for a higher calibration sensitivity and wider dynamic range than those of typical AuNP–AuNP arrangement. The variation of the SERS signals is also found to be below 20% based on multiple measurements (both intra-sample and inter-sample). Furthermore, the degree of SERS signal reductions for the sandwiched analytes is notably slow, indicating their increased long-term stability. The optimized combination is then employed in the detection of let-7f microRNA to demonstrate their practicability as SERS substrates. Precisely introducing interparticle coupling and hot spots with readily available plasmonic NPs still allows for the design of inexpensive and practical signal enhancing substrates that are capable of increasing the calibration sensitivity, extending the dynamic range, and lowering the detection limit of various organic and biological molecules.

Cavity-induced hybrid plasmon excitation for perfect infrared absorption.

Photonic microcavity coupling of a subwavelength hole-disk array, a two-element metal/dielectric composite structure with enhanced extraordinary transmission, leads to 100% coupling of incident light to the cavity system and subsequent absorption. This light-funneling process arises from the temporal and spatial coupling of the broadband localized surface plasmon resonance on the coupled hole-disk array and the photonic modes of the optical cavity, which induces spectral narrowing of the perfect absorption of light. A simple nanoimprint lithography-based large-area fabrication process paves the path towards practical implementation of plasmonic cavity-based devices and sensors.

Total Aqueous Synthesis of Au@Cu2-x S Core-Shell Nanoparticles for In Vitro and In Vivo SERS/PA Imaging-Guided Photothermal Cancer Therapy.

Both accurate tumor navigation and nanostructures with high photothermal (PT) conversion efficiency are important but remain challenging to achieve in current biomedical applications. This study reports an anion exchange-based facile and green approach for synthesizing Au@Cu2-x S core-shell nanoparticles (NPs) in an aqueous system. In addition to the PT effect of the suggested NPs, the surface-enhanced Raman scattering (SERS) is also significantly improved due to the tailored localized surface plasmon resonance coupling between the Au metal core and the Cu2-x S semiconductor shell. Using an epitaxial strategy, Au@Cu2 O NPs are first obtained by the in situ reduction of cupric hydroxide on a cresyl violet acetate-coated Au core; then, Au@Cu2-x S NPs are obtained via anion exchange between the S2- and Cu2 O shell. Both the Cu/S atomic ratio and the Cu2-x S shell thickness can be adjusted conveniently. Hence, the ideal integration of the plasmonic Au core and Cu2-x S shell into a single unit is conducive not only to highly efficient PT conversion but also to the construction of a SERS-based navigator. This new type of SERS-guided NP, with enhanced photoacoustic signals, is an important candidate for both accurate tumor navigation and nondestructive PT treatment guided in vivo by two modes of optical imaging.

Reversible Thermoresponsive Plasmonic Core-Satellite Nanostructures That Exhibit Both Expansion and Contraction (UCST and LCST).

The assembly of sophisticated gold nanoparticle constructs where thermoresponsive core-satellite nanostructures are created and the satellites are close enough to the core for strong surface plasmon resonance coupling to occur, has begun to be developed. The linker between the core and the satellites being a thermoresponsive polymer means that a dispersion of these nanostructures will show temperature-dependent optical properties as the distance between the core and the satellites changes. Unlike previous related thermoresponsive core-satellite systems that undergo a single thermoresponsive transition, herein a polymer system with dual thermoresponsive transitions (block copolymer with both lower critical solution temperature and upper critical solution temperature) is employed as a linker that modulates the gap distance between the "core" and "satellites" in response to the temperature. In this way, optical properties of dispersions can be dynamically tuned. The system permits wide and reversible control of the optical properties, which may render them excellent candidates for reversible nanosensors.

Magnetic field and temperature sensor based on D-shaped photonic crystal fiber

We propose and study a magnetic field and temperature sensor based on a D-shaped photonic crystal fiber using surface plasmon resonance and directional resonance coupling methods. Magnetic fluid is deposited on a flat surface of the D-shaped PCF, and used to measure magnetic field. Ethanol is inserted into a defective cavity in the D-shaped PCF, and used to be used to measure temperature. The simulation result showed that a magnetic field measurement at 30 Oe∼270 Oe and a temperature measurement at 5 °C∼65 °C can be measured independently in two different optical wavelength channels. Better linearity can be achieved. A magnetic field sensitivity of about 0.21 nm/Oe and a temperature sensitivity of about −1.25 nm/°C can be exhibited. Such novel sensing structure has potential application in dual parameter measurements.

Influence of Ni, Ti and NiTi alloy nanoparticles on hydrothermally grown ZnO nanowires for photoluminescence enhancement

In this work, surface-plasmon mediated enhanced photoluminescence emission has been investigated on Ni, Ti, and NiTi coated ZnO nanowires (NWs). ZnO NWs have been synthesized using a facile hydrothermal process, where NWs are coated with three different metals (Ni, Ti, and NiTi) using sputter deposition technique. It has been found that there is a significant improvement in near band edge emission (NBE) and passivation in deep level emission (DLE) in such metal embedded ZnO NWs and these emission properties can be tuned as we change the metal. Notably, we have achieved the highest enhancement of ∼6 times in NBE and best suppression of ∼15 times) in DLE by alloying of such metals (Ni and Ti). Such a remarkable DLE suppression is attributed to the presence of defect centers in ZnO NWs. The defect transition energy of ZnO is in resonance with the surface plasmon energy of metal nanoparticles, which leads to the conversion of DLE into NBE. The enhancement of NBE and suppression of DLE are possible due to the surface plasmon resonance coupling between metal nanoparticles (NPs) and ZnO NWs. Therefore, we conclude that earth abundant metals, such as Ni and Ti show significant SPR coupling on ZnO NWs and the alloying (NiTi) of such metals presents further improved SPR compared to the respective individual metals.

Rational Energy Band Alignment and Au Nanoparticles in Surface Plasmon Enhanced Si‐Based Perovskite Quantum Dot Light‐Emitting Diodes

AbstractCombining inorganic perovskite quantum dots (IPQDs) devices with Si platform is an interesting topic since it is helpful for realizing the optoelectronic integration as well as the multiple‐functional electronics in a compact and lightweight format. However, the poor energy band alignment between the IPQDs and Si limits the device performance, such as the emitting efficiency. Here, a light‐emitting diodes (LEDs) structure is proposed by inserting a poly‐TPD (poly[N,N′‐bis(4‐butylphenyl)‐N,N′‐bis(phenyl)‐benzidine]) layer between the n‐type IPQDs and the p‐type Si substrate. The light‐emitting diode based on CsPbI3 quantum dots reaches an output power density of 1.68 mW cm−2 with external quantum efficiency of 0.91%, which is enhanced by 34‐fold compared with the reference device. Similar emission enhancement is also observed in the device based on CsPbBr3 quantum dots but the output power density is only 0.6 mW cm−2. In order to further improve the emission intensity of CsPbBr3 quantum dots devices, Au nanoparticals (Au NPs) are introduced into the hole injection layer, the output power density increases to 1.2 mW cm−2, which is induced by the localized surface plasmon resonance coupling between Au NPs and CsPbBr3 excitons. The results demonstrate that high‐efficiency and stable Si‐based perovskite LEDs can be realized by rational optical and electronic design.

Waveguide coupled surface plasmon resonance based electro optic modulation in SBN thin films

Modulation of light intensity utilizing Waveguide Coupled Surface Plasmon Resonance (WCSPR) technique at low driving voltage has been demonstrated in the present work. The high value of electro optic coefficient of Strontium Barium Niobate Sr0.6Ba0.4Nb2O6(SBN60) makes it a promising material for the SPR based electro optic modulators. Prism coupling technique has been utilized for the excitation of surface plasmons in Strontium Barium Niobate (SBN) thin film in Otto configuration. Modulation of about 36% is observed due to a significant change in the refractive index of SBN60 thin film on application of electric field of 200 kV/cm. The transient response of change in reflectivity of the WCSPR system with electric field indicates the dynamic change of polarization state of SBN thin film.

Improved Surface-Enhanced Raman Spectroscopy Sensitivity on Metallic Tungsten Oxide by the Synergistic Effect of Surface Plasmon Resonance Coupling and Charge Transfer.

Increasing the sensitivity of non-noble metal surface-enhanced Raman spectroscopy (SERS) is an urgent issue that needs to be solved at present. Herein, metallic W18O49 nanowires with a strong localized surface plasmon resonance (LSPR) effect are prepared. Interestingly, the LSPR peaks of these nanowires would undergo a strong blue shift from near-infrared (NIR) to visible light regions as the aggregation degree of the nanowires increases. By narrowing the gap between the LSPR absorption peak and the Raman excitation wavelength (532 nm), the oriented W18O49 bundles with a LSPR peak centered at 561 nm have greatly improved SERS sensitivity compared with that of the dispersed nanowires with a LSPR peak centered at 1025 nm. Enhancement mechanism investigation shows that the high sensitivity can be attributed to the synergistic effect of LSPR coupling among the oriented ultrathin nanowires and oxygen vacancy (Vo)-assisted charge transfer.

Selective Growth Synthesis of Ternary Janus Nanoparticles for Imaging-Guided Synergistic Chemo- and Photothermal Therapy in the Second NIR Window.

Multifunctional therapeutic agents in the second near-infrared (NIR-II) window have attracted wide attention on account of their synergetic properties for effective cancer therapy. Here, we construct a selective growth strategy for the first time to fabricate ternary Janus nanoparticles (JNPs) containing hemispherical MnO2 at one side and Au core covered with CuS shell at opposite side. The obtained ternary JNPs are further modified with poly(ethylene glycol)thiol to enhance the stability and biocompatibility (designated as PEG-CuS-Au-MnO2 ternary JNPs). The MnO2 domain with mesoporous structures can serve as hydrophobic drug carriers and magnetic resonance (MR) imaging contrast agents. Meanwhile, the Au segment is used for X-ray computed tomography (CT) imaging. Moreover, the PEG-CuS-Au-MnO2 ternary JNPs can conduct hyperthermia at 1064 nm in NIR-II window to ablate tumors in deep tissue, which is ascribed to the localized surface plasmon resonance coupling effect of the Au core and CuS domain. All of the results reveal that PEG-CuS-Au-MnO2 ternary JNPs not only exhibit pre-eminent CT/MR imaging capabilities, but also provide high chemo-photothermal antitumor efficacy under the guidance of CT/MR imaging. Taking together, the PEG-CuS-Au-MnO2 ternary JNPs can be regarded as a prospective therapeutic nanoplatform for dual-modal imaging-guided synergistic chemo-photothermal cancer therapy in the NIR-II window.

Ag Nanotwin-Assisted Grain Growth-Induced by Stress in SiO₂/Ag/SiO₂ Nanocap Arrays.

A trilayer SiO2/Ag/SiO2 nanocap array was prepared on a two-dimensional template. When annealed at different temperatures, the curvature of the SiO2/Ag/SiO2 nanocap arrays increased, which led to Ag nanocap shrinkage. The stress provided by the curved SiO2 layer induced the formation of Ag nanotwins. Ag nanotwins assisted the growth of nanoparticles when the neighboring nanotwins changed the local misorientations. Nanocap shrinkage reduced the surface plasmon resonance (SPR) coupling between neighboring nanocaps; concurrently, grain growth decreased the SPR coupling between the particles in each nanocap, which led to a red shift of the localized surface plasmon resonance (LSPR) bands and decreased the surface-enhanced Raman scattering (SERS) signals.

Correction to: Controlling Level Splitting by Strong Coupling of Surface Plasmon Resonances with Rhodamine-6G on a Gold Grating

In addition to his current affilliation declared in the original version, the author would like to add a new affiliation. His correct affiliation is shown in this correction.

Controlling Level Splitting by Strong Coupling of Surface Plasmon Resonances with Rhodamine-6G on a Gold Grating

Strongly coupled system is known to pose challenges, particularly those involving multitude of levels as in molecules. Surface plasmons offer intense and localized electromagnetic fields, wherein molecules placed in such environment exhibit generic features of strongly coupled system. We demonstrate the control over the splitting of surface plasmon polaritons dispersion branches in strong coupling regime within the absorption and fluorescence bands of Rhodamine-6G molecules placed on top of gold grating structures. The enhanced electromagnetic near-fields of surface plasmon polaritons excited on top of gold gratings have been calculated by numerical simulation and various aspects related to the coupling have been captured by modelling the Rhodamine-6G molecule as a theoretical three level Λ–system which support the experimentally observed variation in splitting with varying periods of gratings. The plasmonically enhanced electromagnetic field plays the role of a control field applied across one leg of the Λ–system. Experimentally measured spectral features, including level splitting and dispersions of the strongly coupled system of molecule-gold grating are consistently described by the model for a variety of samples, with different periodicities, different molecule-grating separations obtained through a dielectric spacer layer, and coupling to higher order diffraction modes of the grating.

Surface plasmon resonance sensing with adjustable sensitivity based on a flexible liquid core coupling unit

The signal amplification methods of surface plasmon resonance (SPR) are mainly with sample selectivity. Herein proposed is a liquid core coupling SPR sensing method with adjustable sensitivity and universal applicability. A liquid core coupling unit and based on which a wavelength interrogation SPR sensor have been designed and constructed, in which a conventional chip could be used with an ingenious design and the sensitivity can be adjusted by changing the liquid core refractive index. The experimental data revealed that the sensitivity can be enhanced for 7.8 times by decreasing the liquid core refractive index from 1.5174 to 1.4502. The real applicability was validated by determination of carcinoembryonic antigen (CEA) with the signal intensity of the early stage colon cancer patient clearly up-regulated for nearly 18 folds compared with the healthy. It exhibited an adequate sensitivity, and further considering its simplicity avoiding the troublesome analysis process and/or chip preparing procedure, and extendibility to SPR imaging, the proposed method would be promising for medical diagnostics, food safety, environmental monitoring, and so on.

Surface plasmon resonance extension through two-block metal-conducting polymer nanorods

Research on surface plasmon resonance coupling of metallic nanostructures is an important area in the field of plasmonics because distinctive collective optical properties can be realized that are different from the individual constituents. Here we report the localized surface plasmon resonance of hybrid metal-organic nanorods. Colloidal-dispersed Au-PPy nanorods were synthesized as a representative material using a modified electrochemical method, and the collective oscillation properties were systematically investigated by comparing these materials with pure Au nanorods. We observed the extended surface plasmon resonance of a hybrid system. The presence of doped-PPy segments on Au segments induced an enhanced coherent electric field due to the partial contribution of π-electrons on the PPy segment, which led to a red-shifted plasmon feature. Additionally, we demonstrated that surface plasmon resonance extension can be tuned by dopant anions, which demonstrates a way of tuning a dopant-induced plasmonic system.

Surface-enhanced Raman scattering enhancement due to localized surface plasmon resonance coupling between metallic nanoparticles and substrate

In this study, gold nanostructures (AuNSs) and silver nanoparticles (AgNPs) were integrated with a silver micro-flower-like structure deposited on a screen-printed carbon electrode (AgMF-SPCE) for enhancing surface-enhanced Raman scattering (SERS) by using 4-mercaptobenzoic acid (4-MBA) as a Raman reporter. SERS was enhanced by approximately 3.6–52.1-fold, depending on the frequency of the incident laser, the localized surface plasmon resonance frequency of metallic NPs, and particle–particle aggregation effects. Compared with AgNP/SPCE and AgMF-SPCE substrates, the AgNP/AgMF-SPCE substrate showed high temperature tolerance and long-term durability. Furthermore, the proposed substrates easily obtained hot spots for other Raman reporters such as 4-aminothiophenol, 5,5′-dithiobis-2-nitrobenzoic acid, and 4-chlorothiophenol. A linear relationship was found between the Raman signal and the concentration of Raman reporters in the range 10 nM–100 μM, with the limit of detection in the range of 6.19–77.2 nM at a signal-to-noise ratio of 3.0. These results suggest that the AgNP/AgMF-SPCE substrate will be well suited for quantitative analysis.