Enhanced Surface Plasmon Resonance Research Articles

Ethanol concentration sensor based on TiO2-ZnO composite film enhanced surface plasmon resonance with a molybdenum disulfide-graphene oxide hybrid nano-sheet

A method of ethanol concentration detection based on surface plasmon resonance is proposed. Therefore, a novel prism coupling structure is designed for the ethanol concentration sensor by use of the unique feature of graphene oxide (GO) to act as a sieve for ethanol in water, and a TiO2-ZnO composite film is chosen to enhance the surface plasmon resonance with a molybdenum disulfide–graphene oxide hybrid nano-sheet. The thickness of each layer of the structure is analyzed by the finite element method to obtain the optimal value in order to improve the sensitivity greatly. The optimal thickness of each layer is given, and the sensitivity of the surface plasmon resonance ethanol concentration sensor can reach as high as 0.089°/% within the detection range of ethanol concentration (0%–80%). The relationship between the surface plasmon resonance angle and the ethanol concentration is obtained within the detection range of ethanol concentration.

Enhanced surface plasmon resonance (SPR) signals based on immobilization of core-shell nanoparticles incorporated boron nitride nanosheets: Development of molecularly imprinted SPR nanosensor for anticancer drug, etoposide

An effective SPR nanosensor based on core-shell nanoparticles (Ag@AuNPs) incorporated hexagonal boron nitride (HBN) nanosheets and molecularly imprinted polymer (MIP) was presented for etoposide (ETO) detection. Scanning electron microscope (SEM), transmission electron microscope (TEM), x-ray diffraction (XRD) method, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) methods were utilized for all characterizations of nanomaterials and polymer surfaces. ETO imprinted SPR nanosensor based on Ag@AuNPs-HBN nanocomposite was developed in the presence of poly(2-hydroxyethyl methacrylate-methacryloylamidoglutamic acid) [p(HEMA-MAGA)]. The results of the study have revealed that 0.001–1.00 ng mL−1 (1.70 × 10–12–1.70 × 10−9 M) and 0.00025 ng mL−1 (4.25 × 10–13 M) were found as the linearity range and the detection limit (LOD). Furthermore, the prepared SPR nanosensor was examined in terms of stability, repeatability and selectivity. Finally, the imprinted SPR nanosensor was applied to the urine samples having high recovery.

Enhancement of localized surface plasmon resonance by inter-band transitions in an Au based nanoshell structure

We present a theoretical study on plasmonic properties of an Au based nanoshell structure in which the localized surface plasmon resonances (LSPRs) and the inter-band electronic transitions (IBTs) are presented. The optical properties of Au nanoshell are depicted by a corrected dielectric function of Drude-Lorentz mode, and Mie theory is applied to calculate the absorption efficiencies. It shows that there are two localized surface plasmon absorption peaks, which are induced from the outside LSPRs and the inside LSPRs, respectively. The positions of these two peaks can shift by changing core radius and shell thickness. By varying the core radius and thickness of the shells, the LSPRs are modulated with the IBTs, leading to the strong interactions between the LSPRs and the IBTs. It is found that the LSPRs and IBTs can couple with each other and the new resonance absorption peaks can be observed. Our results show that the LSPRs are enhanced by the IBTs. This enhancement can be applied to improve biosensor signals and advanced plasmonic applications.

Plasmon-enhanced photocatalysis: Ag/TiO2 nanocomposite for the photochemical reduction of bicarbonate to formic acid

ABSTRACTPlasmonic metallic nanoparticles can significantly enhance the catalytic efficiency of semiconductors via plasmonic photocatalysis. In this study, a hybrid Ag/TiO2 photocatalyst was synthesized and tested for the photochemical reduction of bicarbonate to value-added formic acid. It was found that under solar irradiation, TiO2 is not very efficient, but formate production is significantly increased with the addition of silver nanoparticles. Under 365 nm irradiation, the photocatalytic efficiency of TiO2 is enhanced, but no effect was observed with the addition of silver nanoparticles. Under solar irradiation, Ag/TiO2 reached an apparent quantum efficiency (AQE) of 7.78 ± 0.04%, the highest AQE observed so far. Enhanced photocatalytic activity is attributed to the synergistic effect between UV photon excitation of TiO2 and surface plasmon resonance enhancement. To elucidate the mechanism of plasmon-enhanced photocatalysis, experiments were performed under solar irradiation and 365 nm irradiation. We propose that photo-excited electrons are transferred from above the Fermi level of the metal nanoparticle to the conduction band of the semiconductor through plasmon-induced electron transfer.

Surface plasmon resonance enhancement of photoluminescence intensity and bioimaging application of gold nanorod@CdSe/ZnS quantum dots

Biological applications of core/shell near-infrared quantum dots (QDs) have attracted broad interest due to their unique optical and chemical properties. Additionally, the use of multifunctional nanomaterials with near-infrared QDs and plasmonic functional nanoparticles are promising for applications in electronics, bioimaging, energy, and environmental-related studies. In this work, we experimentally demonstrate how to construct a multifunctional nanoparticle comprised of CdSe/ZnS QDs and gold nanorods (GNRs) where the GNRs were applied to enhance the photoluminescence (PL) of the CdSe/ZnS QDs. In particular, we have obtained the scattering PL spectrum of a single CdSe/ZnS QD and GNR@CdSe/ZnS nanoparticle and comparison results show that the CdSe/ZnS QDs have an apparent PL enhancement of four-times after binding with GNRs. In addition, in vitro experimental results show that the biostability of the GNR@CdSe/ZnS nanoparticles can be improved by using folic acid. A bioimaging study has also been performed where GNR@CdSe/ZnS nanoparticles were used as an optical process for MCF-7 breast cancer cells.

Persea americana seed extract mediated gold nanoparticles for mercury(ii)/iron(iii) sensing, 4-nitrophenol reduction, and organic dye degradation.

In this work, Persea americana (Avocado) seed extract mediated systematically optimized synthesis has been employed for the formation of small sized gold nanoparticles (Av-AuNPs) at different pH values. The size, shape and crystallinity of the as-prepared AuNPs have been studied using transmission electron microscopy and X-ray diffraction. The nanoparticles were found to be selective towards mercury(ii) upon the prior or subsequent addition of iron(iii), revealing a blue shift and an enhancement of the characteristic surface plasmon resonance (at 519 nm). Similar absorbance based selectivity has been observed towards Fe(iii) in the presence of Hg(ii). The high sensitivity and selectivity of Av-AuNPs towards Hg(ii) and Fe(iii) has been attributed to the formation of core–shell structures. From the UV-visible spectroscopic measurements, the limits of detection for Hg(ii) and Fe(iii) are found to be 50 nM and 30 nM (around one order of magnitude less than the Environment Protection Agency limit of 0.7 μM for Fe(iii) in drinking water) respectively, with an excellent linear dependence over a wide range of concentrations. Additionally, as-prepared Av-AuNPs have been demonstrated to be efficient in the reduction of organic pollutant 4-nitrophenol to 4-aminophenol and degradation of some organic dyes, such as Methylene Blue, Direct blue, Rhodamine 6G, Bromophenol blue and methyl orange. The use of the proposed Av-AuNPs for sensing and green catalysis can form the basis of high-performance analytical assays, effective multiplexed intracellular sensors, and sophisticated and sustainable probes/catalysts.

Ethanol concentration sensor based on TiO2-ZnO composite film enhanced surface plasmon resonance with molybdenum disulfide — graphene oxide hybrid nano-sheet

Ethanol concentration sensor based on TiO2-ZnO composite film enhanced surface plasmon resonance with molybdenum disulfide — graphene oxide hybrid nano-sheet

Covalent affixation of histidine-tagged proteins tethered onto Ni-nitrilotriacetic acid sensors for enhanced surface plasmon resonance detection of small molecule drugs and kinetic studies of antibody/antigen interactions.

The Ni2+-histidine (His) chelation yields a more uniform and predicable orientation of immobilized protein molecules than an amine-coupling reaction in surface plasmon resonance (SPR) analyses. However, the gradual dissociation of His-tagged proteins leads to a long and sloped baseline, which adversely affects kinetic studies. Furthermore, as shown in this work for the first time, the strong binding affinity between the histidine-rich Fc domain of immunoglobulin-type antibodies and Ni-nitrilotriacetic acid (NTA) interferes with the kinetic studies of these antibodies and their His-tagged antigens. By performing an amine-coupling reaction immediately after the Ni2+-His chelation, essentially all of the Ni2+-tethered protein molecules can be covalently linked to the carboxyl groups on the underlying carboxymethylated dextran surface. The sequential injections of pH 8.6 phosphate-buffered saline provided additional time to ensure a higher amine coupling efficiency and reverted NHS esters on the protein molecules to carboxyl groups. The application of our method to antibody/antigen interactions is demonstrated with the kinetic analysis of His-tagged t-DARPP protein/anti-t-DARPP interactions. In a separate experiment, the highly efficient immobilization method resulted in a higher immobilization density of His-tagged human carbonic anhydrase (HCA) II, affording accurate kinetic measurements for the binding of 4-carboxybenzenesulfonamide. In addition, the higher HCA II density enhanced the SPR sensitivity, allowing 4-carboxybenzenesulfonamide to be determined with a remarkable detection limit (14 nM).

Self-assembly of Janus Dumbbell Nanocrystals and Their Enhanced Surface Plasmon Resonance.

Self-assembly is a critical process that can greatly expand the existing structures and lead to new functionality of nanoparticle systems. Multicomponent superstructures self-assembled from nanocrystals have shown promise as multifunctional materials for various applications. Despite recent progress in assembly of homogeneous nanocrystals, synthesis and self-assembly of Janus nanocrystals with contrasting surface chemistry remains a significant challenge. Herein, we designed a novel Janus nanocrystal platform to control the self-assembly of nanoparticles in aqueous solutions by balancing the hydrophobic and hydrophilic moieties. A series of superstructures have been assembled by systematically varying the Janus balance and assembly conditions. Janus Au-Fe3O4 dumbbell nanocrystals (<20 nm) were synthesized with the hydrophobic ligands coated on the Au lobe and negatively charged hydrophilic ligands coated on the Fe3O4 lobe. We systematically fine-tune the lobe size ratio, surface coating, external conditions, and even additional growth of Au nanocrystal domains on the Au lobe of dumbbell nanoparticles (Au-Au-Fe3O4) to harvest self-assembly structures including clusters, chains, vesicles, and capsules. It was discovered that in all these assemblies the hydrophobic Au lobes preferred to stay together. In addition, these superstructures clearly demonstrated different levels of enhanced surface plasmon resonance that is directly correlated with the Au coupling in the assembly structure. The strong interparticle plasmonic coupling displayed a red-shift in surface plasmon resonance, with larger structures formed by Au-Au-Fe3O4 assembly extending into the near-infrared region. Self-assembly of Janus dumbbell nanocrystals can also be reversible under different pH values. The biphasic Janus dumbbell nanocrystals offer a platform for studying the novel interparticle coupling and open up opportunities in applications including sensing, disease diagnoses, and therapy.

Phase and Defect Engineering of MoS2 Stabilized in Periodic TiO2 Nanoporous Film for Enhanced Solar Water Splitting

AbstractPhase and defect engineering of the heterostructured MoS2@TiO2 nanoporous film is investigated to achieve a broad solar spectrum light absorption and high solar water splitting efficiency. The phase transition from the semiconducting 2H‐MoS2 to the metallic 1T‐MoS2 is achieved by a hydrothermal exfoliation treatment. Experimental studies elucidate that the solar water splitting activity is greatly improved by forming 1T‐MoS2 along with increasing S‐vacancies because of the significantly enhanced surface plasmon resonance. The mixed‐phase MoS2@TiO2 film shows a high H2 yield rate of 308 µmol h−1 cm−2 and long‐term durability for 30 h, which is superior to the state‐of‐the‐art catalysts for solar water splitting. This study offers a universal and efficient avenue to rationalize the plasmonic catalysts for solar water splitting and other energy and environmental applications.

Plasmonic nickel nanoparticles decorated on to LaFeO3 photocathode for enhanced solar hydrogen generation

Plasmonic Ni nanoparticles were incorporated into LaFeO3 photocathode (LFO-Ni) to excite the surface plasmon resonances (SPR) for enhanced light harvesting for enhancing the photoelectrochemical (PEC) hydrogen evolution reaction. The nanostructured LFO photocathode was prepared by spray pyrolysis method and Ni nanoparticles were incorporated on to the photocathode by spin coating technique. The LFO-Ni photocathode demonstrated strong optical absorption and higher current density where the untreated LFO film exhibited a maximum photocurrent of 0.036 mA/cm2 at 0.6 V vs RHE, and when incorporating 2.84 mmol Ni nanoparticles the photocurrent density reached a maximum of 0.066 mA/cm2 at 0.6 V vs RHE due to the SPR effect. This subsequently led to enhanced hydrogen production, where more than double (2.64 times) the amount of hydrogen was generated compared to the untreated LFO photocathode. Ni nanoparticles were modelled using Finite Difference Time Domain (FDTD) analysis and the results showed optimal particle size in the range of 70–100 nm for Surface Plasmon Resonance (SPR) enhancement.

The Remote Light Emission Modulated by Local Surface Plasmon Resonance for the CdSe NW–Au NP Hybrid Structure

AbstractCdSe nanowire (NW)–Au nanoparticle (NP) compounds are synthesized successfully using the method of physical vapor deposition, and the modulated remote emission is realized in the hybrid structure with strong metal–semiconductor coupling. The well‐crystallized, uniform morphology, smooth surface CdSe NW is attached with an Au NP on the terminal, which forms the integration structure with direct plasmon–exciton coupling of semiconductor–metal hybrid system. When the CdSe terminal or Au NP terminal of the hybrid structure is excited by the laser with wavelength of 633 nm, the remote light emission at another terminal is greatly modulated. To reveal the physical mechanism of energy conviction between plasmon and exciton, finite‐difference time‐domain simulations are performed for the CdSe NW–Au NP hybrid structures. The calculated results confirm that the modulation of remote light emission is attributed to the competing of the quench of photoluminescence and the electric field enhancement of local surface plasmon resonance. These works can provide deeper understanding of physical mechanism of plasmon and exciton coupling, and open up new application for the remote light sensing and detection.

A Paper-Supported Photoelectrochemical Sensing Platform Based on Surface Plasmon Resonance Enhancement for Real-Time H2S Determination

Based on in situ generation of CdS quantum dots (QDs) and surface plasmon resonance (SPR) enhancement between CdS QDs and Ag nanoparticles (NPs), an innovative paper-supported photoelectrochemical (PEC) sensing platform was constructed for real-time intracellular H2S detection. SiO2 shell was coated on the Ag NPs to improve the stability of Ag NPs. H2S was used to trigger the formation of CdS QDs, thereby inducing an improvement of photocurrent response. CdS QDs grown on the Ag@SiO2 core–shell NPs worked efficiently to absorb visible light. The resulting CdS QDs–Ag@SiO2 core–shell NPs exhibit improved PEC behavior, which was attributed to the surface plasmon-resonance effect of Ag NPs. Meanwhile, the separation of cell binding from the photoelectrode would eliminate the commonly existing affection during the biorecognition processes. This novel SPR-enhanced PEC sensing platform not only achieved satisfactory analysis results toward H2S, but also showed excellent sensitivity, selectivity, low cost, and portable features. The strategy of the SPR through the in situ generation of semiconductor nanoparticles on the surface of noble metal semiconductor paves way for the improvements of PEC analytical performance.

Enhancement of a Cu2O/ZnO photodetector via surface plasmon resonance induced by Ag nanoparticles

The localized surface plasmon resonance enhancement of a Cu2O photodetector was realized by Ag nanoparticles (NPs) that were fabricated by electrochemical deposition. A ZnO nanowire was used to accelerate carrier separation. An increase of responsivity was achieved based on the coupling interaction between the surface plasmon resonance in the Ag NPs and the Cu2O film. The photodetector possessed high responsivity (0.27A/W). Compared to the device without Ag NPs, the responsivity was enhanced 20-fold. The excellent comprehensive performance of the Cu2O/ZnO photodetector reveals that localized surface plasmon resonance is an efficient way to improve the performance of Cu2O-based photodetectors.

Flexible Plasmonic Pressure Sensor Based on Layered Two-Dimensional Heterostructures

Ultrathin and tunable pressure sensors are highly desirable for research and engineering applications. This study designed a surface plasmon resonance (SPR) architecture based on a phase modulation method using antimonene/graphene/π-SnSe heterostructures. Atomic layered two-dimensional cubic phase π-SnSe as a pressure detection layer and layered graphene and antimonene to improve sensitivity. Photon absorption efficiency and energy loss in the heterostructures were matched by adjusting Au film thickness and the number of antimonene layers, producing the largest SPR enhancement factor. We obtained a wide pressure detection range from 5 × 104 to 1.5 × 105 kPa, with highest detection sensitivity = 20.8 kPa−1 at the SPR angle. The remarkable detection sensitivity and wide tunable range makes it a promising candidate for applications in wearable devices.

Dual Sensing Arrays for Surface Plasmon Resonance (SPR) and Surface‐Enhanced Raman Scattering (SERS) Based on Nanowire/Nanorod Hybrid Nanostructures

AbstractA multifunctional sensing array with gold nanowire–nanorod hybrid nanostructures for dual detection of surface plasmon resonance (SPR) and surface‐enhanced Raman scattering (SERS) is presented. The cost‐effective and arrayed nanostructures are made simply onto plastic films using hot‐embossing nanoimprint lithography. Five different hybrid nanostructures are studied and compared by measuring SERS enhancement factor and SPR thickness sensitivity. The combination of nanowire and nanorod structures in specific arrangement and quantities of nanorods can not only enhance the SERS effect but also further increase the SPR thickness sensitivity. The area percentage of nanorods of 16.51% can achieve the highest SPR thickness sensitivity and 106 SERS enhancement. On comparison of the nanowire structure, the SERS signal and SPR thickness sensitivity of nanowire/nanorod hybrid nanostructure are increased up to 6 times and 2 times simultaneously. The estimated SERS enhancement factor and SPR thickness sensitivity are 2.82 × 106 and 0.74 (nm/nm), respectively. The enhanced sensitivity is attributed to the increased nanorods contributing to dense hot spots and the reduced SPR evanescent length caused by the localized surface plasmons. These results are verified by finite‐difference time‐domain (FDTD) calculations. Such low‐cost SPR–SERS chips for multifunctional chemical analysis can increase the reliability of biological detection and broaden sensing applications.

Visible light emission from Dy3+ doped tellurite glass: Role of silver and titania nanoparticles co-embedment

We report the influence of silver (Ag) and titania (TiO2) nanoparticles (ATNPs) co-embedment on the photoluminescence (PL) properties of dysprosium ions (Dy3+) doped zinc-magnesium tellurite glass system prepared using conventional melt quenching method. Both up- and down- converted PL spectra of glasses revealed three emission bands located at 482 (blue: 4F9/2 → 6H15/2), 574 (yellow: 4F9/2 → 6H13/2) and 664 nm (weak red: 4F9/2 → 6H11/2), where the band intensities were enhanced with the inclusion of ATNPs. Glasses with 0.2 mol% of ANPs and up to 0.3 mol% of TNPs disclosed highest PL intensity enhancement, which was majorly attributed to the ATNPs mediated localized surface plasmon resonance (LSPR) and large field enhancement (called hot spot) effects in the proximity of Dy3+ ions. Absorption spectra of glasses displayed two plasmon bands characteristics of each type of nanoparticle. It was inferred that the superposition of localized SP modes from ATNPs could generate new hybridized modes (strong local field in the vicinity of Dy3+ ions) shifted with respect to the single type of NPs resonance. HRTEM images showed the existence of both Ag and titania NPs inside the glass matrix. Glasses containing ATNPs exhibited anatase phase with (103) and (112) nanocrystalline lattice plane orientation. Proposed glass system may be useful for the development of solid state laser and photonic devices.

Enhancement of surface plasmon resonances on the nonlinear optical properties in an elliptical quantum dot

In this paper, the nonlinear optical properties in an elliptical semiconductor quantum dot (SQD) have been calculated theoretically. A control laser field is applied to induced dipole moments in a metallic nanoparticle (MNP) and SQD, and they interact with each other through dipole–dipole interaction. By using the effective mass approximation, we can gain the eigenstates and eigenenergies of the MNP and SQD, respectively. And using the compact density matrix method, we can get the analytical expressions of the third-harmonic generation (THG), optical absorption coefficients (OA), and refractive index changes (RICs). It is found that the enhancement of the nonlinear optical properties is distinct when the MNP is close to the SQD. At the same time, these properties are also decreased by changing the radius of the MNP from 1 to 2 nm.

SPR-Enhanced Fluorescence of Solid Organic Dye Films

This paper presents strong fluorescence of spin-coated fluorescent solid organic dye films (SODF) enhanced by surface plasmonic resonance (SPR). In order to manifest the influence of SPR effect on enhancement of organic dye (OD) fluorescence, the organic dye embedded Ag@SiO2 fluorescent films were developed on the glass sheet substrate, in which Ag@SiO2 nanoparticles were embedded in the middle and organic dye was as upper layer. The morphology of the SODFs with and without Ag@SiO2 particles was studied by SEM and EDX, and the tests revealed that the Ag@SiO2 nanoparticles distributed evenly between glass sheet and OD layer. Optical properties were characterized by UV absorption and fluorescence spectroscopy; the lifetime of SODF was tested to discuss the mechanism of SPR enhancement of fluorescence. The results proved that the existence of Ag@SiO2 particles enhanced the fluorescence intensity for 7 times and thus proved the SPR effect for organic dye, especially when the organic dye is the solid films. Therefore, the most important is the creation that the SPR effect of Ag@SiO2 particles works very well under solid organic dye coverage.

Fano Resonance Enhanced Surface Plasmon Resonance Sensors Operating in Near-Infrared

In the phase-sensitivity-based surface plasmon resonance (SPR) sensing scheme, the highest phase jump usually happens at the darkness or quasi-darkness reflection point, which results in low power for detection. To overcome such a limitation, in this paper, a waveguide-coupled SPR configuration is proposed to work at near-infrared. The coupling between surface plasmon polariton (SPP) mode and photonic waveguide (PWG) mode results in electromagnetically induced transparency (EIT) and asymmetric Fano resonance (FR). Near the resonance, the differential phase between p-polarized and s-polarized incident waves experience drastic variation upon change of the surrounding refractive index. More importantly, since the FR occurs at the resonance slope of SPP mode, the corresponding phase change is accompanied with relatively high reflectivity, which is essential for signal-to-noise ratio (SNR) enhancement and power consumption reduction. Phase sensitivity up to 106 deg/RIU order with a minimum SPR reflectivity higher than 20% is achieved. The proposed scheme provides an alternative approach for high-performance sensing applications using FR.