Enhanced Surface Plasmon Resonance Research Articles

Enhanced Surface Plasmon Resonance (SPR) Fiber Optic Sensor for Environmental Monitoring: A Coreless Fiber–Based Design

Enhanced Surface Plasmon Resonance (SPR) Fiber Optic Sensor for Environmental Monitoring: A Coreless Fiber–Based Design

Interface interaction mediated surface plasmon resonance enhancement promoted visible-light-driven CO2 reduction with water

The conversion of carbon dioxide (CO2) into fuel using solar energy holds significant promise. However, the inefficient use of light and poor production activity have hindered its development. Here, we propose a simple in situ annealing oxidation method by coating a layer of TiO2 outside TiN, a material with a favorable price and localized surface plasmon resonance (LSPR) effect, to create an L-TiNO composite. The yield of CO over L-TiNO (50.8 μmol g−1 h−1) is 56.4 times that over TiO2 (0.9 μmol g−1 h−1) under visible light irradiation in pure aqueous environment, with a selectivity of 95.98%. In-situ Fourier transform infrared (FTIR) measurements reflect the CO2-COOH*-CO conversion route happening on L-TiNO. Characterizations like the Kelvin probe force microscopy (KPFM) technique confirm the generation of built-in electric field, which facilitates efficient carrier separation and migration. Density functional theory (DFT) calculations support that L-TiNO with LSPR effect alters the shape of absorbed CO2 to facilitate generation COOH* via forming hydroxyl end group (Ti-OH) and promotes CO* desorption to CO(g). This work provides valuable insights into the coupling of plasmonic materials with semiconductors to achieve efficient solar energy utilization.

Optimizing bimetallic plasmonic structures for enhanced surface plasmon resonance sensing through golden ratio design

Optimizing bimetallic plasmonic structures for enhanced surface plasmon resonance sensing through golden ratio design

Unique gap-related SERS behaviors of p-aminothiophenol molecules absorbed on TiO2 surface in periodic TiO2/Ni nanopillar arrays

We observed a unique interpillar gap-related surface-enhanced Raman scattering (SERS) behavior of p-aminothiophenol (PATP) molecules from periodic TiO2 nanopillar arrays with three gap sizes of 191, 297 and 401 nm, which is completely different from that on Ag and Ni nanopillar arrays. Especially, the gap-size-dependent charge-transfer (CT) resonance enhancement from TiO2/Ni has been indicated through comparisons of variation trend of SERS intensities with inter-pillar gap size between TiO2/Ni and Ag/TiO2/Ni as well as Ni nanoarrays, and been confirmed by spectra of ultraviolet–visible absorption and photoluminescence. Results demonstrate that the CT resonance enhancement is more susceptible to the change of the gap size compared with the surface plasmon resonance (SPR) enhancement in TiO2/Ni nanoarrays. Hence, SPR and CT enhancement showing different variation trend and rate with the gap size that leads to a different relative contribution of CT resonance to the overall SERS enhancement as gap size changes, and consequently results in a unique gap-related SERS behavior for TiO2/Ni nanoarrays. The present study is not only helpful for investigating SERS mechanism for semiconductors but also providing a method to design and optimize periodic metal/semiconductor SERS substrates in a controllable way.

Flexible Antibacterial Respiratory Monitoring Sensor Based on Controllable Au-Modified Surface of Highly {001} Preferred Anatase Titanium Dioxide Thin Film.

Respiratory signals are critical clinical diagnostic criteria for respiratory diseases and health conditions, and respiratory sensors play a crucial role in achieving the desired respiratory monitoring effect. High sensitivity to a single factor can improve the reliability of respiratory monitoring, and maintaining the hygiene of the sensors is also important for daily health monitoring. Herein, we propose a flexible Au-modified anatase titanium dioxide resistive respiratory sensor, which can be mechanically compliantly attached to curved surfaces for respiratory monitoring in different modalities (i.e., respiratory intensity, frequency, and rate). The uniform and preferentially oriented anatase titanium dioxide films gained by the polymer-assisted deposition technique can be fabricated on flexible substrates through a liquid-assisted transferring process. The Au modification can enhance surface plasmon resonance to facilitate the photocatalytic activity of titanium dioxide, and the optimized distribution of Au on the surface of titanium dioxide film made the sensor have an excellent antibacterial effect. The uniquely designed encapsulation can effectively control the contact between the surface of titanium dioxide films and electrodes, allowing the flexible sensor to exhibit fast response time (0.71 s) and recovery time (1.06 s) to respiratory as well as insensitivity or low sensitivity to other factors (i.e., gas composition, humidity, temperature, stress, and strain). This work provided an effective strategy for flexible wearable respiratory sensors and has great potential in daily respiratory monitoring for health management and pandemic control.

Enhanced photocatalytic degradation of Rhodamine B using gold nanoparticles decorated on BaTiO3 with surface plasmon resonance enhancement.

This study focused on synthesizing and applying gold nanoparticle (Au NP) decorated barium titanate (BaTiO3) nanoparticles for photocatalytic purposes. BaTiO3 NPs were synthesized using a facile hydrothermal method. Various techniques were employed to characterize the structure and morphological characteristics of the prepared materials. The photocatalytic degradation of Rhodamine B over the Au NPs-modified BaTiO3 photocatalysts was studied. Trapping experiments were conducted using different scavengers to elucidate the degradation mechanism and the involvement of photogenerated species. The incorporation of an appropriate amount of Au NPs into the composites resulted in a significant improvement in photocatalytic activity, attributed to the combined effect of Schottky junction at the interface and the surface plasmon resonance of Au NPs.

Advanced quasi-2D amorphous TiOx-Au photocatalyst: Harnessing defects and carriers transport to boost visible-light organic pollutants degradation

Amorphous materials have recently garnered significant interest due to their low-cost fabrication methods, extensive surface area and plentiful surface defects, which offer numerous active sites for catalytic reactions. However, carriers self-trapping and recombination caused by bulk defects limit the employment of amorphous materials as photocatalysts. As such, it is essential to adjust the structure and defects to improve carriers utilization for creating high-performance amorphous photocatalysts. In this study, we developed a novel and facile strategy to fabricate a quasi-2D amorphous crepe-like TiOx-Au (cTiOx-Au) photocatalyst, in which the cTiOx was synthesized simply through one-step hydrolysis method at room temperature by constructing discrete reaction system with mass-confinement of the precursor to guide the morphology of the cTiOx. The removal efficiencies of the cTiOx-Au to antibiotic tetracycline (TC) and gaseous pollutant formaldehyde (HCHO) under visible light were 84.43 % and 95.92 %, respectively, which greatly surpassed those of its counterparts, normal amorphous TiOx (amTiOx)-Au (54.32 % and 73.67 %) and crystalline catalyst TiO2-P25-Au (49.29 % and 54.03 %). The remarkable visible-light photocatalytic capacity of cTiOx-Au can be attributed to the unique quasi-2D morphology of cTiOx. The ultrathin nanostructure not only maximizes surface defects and minimizes bulk defects, but also effectively shortens the carriers transport time and reduces recombination probability, on the other hand, it provides ample adsorption sites and accessible binding sites for plasmonic Au nanoparticles to amplify the effect of surface plasmon resonance enhancement. The excellent photocatalytic performances of cTiOx-Au for removing both aqueous and atmospheric pollutants endow it great potential in real environmental remediation applications.

Controllable synthesis of multi-tip spatial gold nanostructures to facilitate SPR enhancement for exosomal PD-L1 assay

A surface plasmon resonance (SPR) biosensor was developed utilizing gold nanoflowers with multi-tip tiny petals (Au@Au mNFs) and multifunctional peptides for the selective detection of exosomal programmed cell death 1 ligand 1 (ExoPD-L1). In the presence of different salt concentrations, DNA-functionalized gold seeds underwent in situ gold growth, resulting in Au@Au NFs with varying numbers of petals or Au@Au nanospheres (Au@Au NSs). The growth orientation of the gold shells was influenced by the “upright”, “tilted” or “lying” state of the DNA on the gold core surface, depending on the salt concentration solution. The finally prepared Au@Au mNFs exhibited a multi-tip spatial structure, which served as a highly efficient SPR sensitized layer with abundant hot spots on the gold film surface. The enhanced SPR sensitivity was attributed to the substantial electromagnetic field enhancement generated at the tips of the mNFs. By achieving suitable surface coverage of the multifunctional peptide at the sensing interface constructed by Au@Au mNFs, efficient capture of ExoPD-L1 was ensured. The analysis results demonstrated that the developed SPR sensor successfully detected ExoPD-L1 within a concentration range of 10–107 particles/mL, with a detection limit of 4.95 particles/mL. This work highlights the significant improvement in SPR sensing and detection performance achieved by utilizing Au@Au mNFs with multi-tip spatial nanostructures, providing a straightforward approach for achieving ultra-sensitive detection of target substances through SPR.

Subtractive Nanopore Engineered MXene Photonic Nanomedicine with Enhanced Capability of Photothermia and Drug Delivery for Synergistic Treatment of Osteosarcoma.

Two-dimensional (2D) nanomaterials as drug carriers and photosensitizers have emerged as a promising antitumor strategy. However, our understanding of 2D antitumor nanomaterials is limited to intrinsic properties or additive modification of different materials. Subtractive structural engineering of 2D nanomaterials for better antitumor efficacy is largely overlooked. Here, subtractively engineered 2D MXenes with uniformly distributed nanopores are synthesized. The nanoporous defects endowed MXene with enhanced surface plasmon resonance effect for better optical absorbance performance and strong exciton-phonon coupling for higher photothermal conversion efficiency. In addition, porous structure improves the binding ability between drug and unsaturated bonds, thus promoting drug-loading capacity and reducing uncontrolled drug release. Furthermore, the porous structure provides adhesion sites for filopodia, thereby promoting the cellular internalization of the drug. Clinically, osteosarcoma is the most common bone malignancy routinely treated with doxorubicin-based chemotherapy. There have been no significant treatment advances in the past decade. As a proof-of-concept, nanoporous MXene loaded with doxorubicin is developed for treating human osteosarcoma cells. The porous MXene platform results in a higher amount of doxorubicin-loading, faster near-infrared (NIR)-controlled doxorubicin release, higher photothermal efficacy under NIR irradiation, and increased cell adhesion and internalization. This facile method pioneers a new paradigm for enhancing 2D material functions and is attractive for tumor treatment.

Guided Mode Induced Surface Phase Mutation for Enhanced SPR Biosensor with Dual‐Parameters Interrogation

AbstractOngoing research on the sensitivity and integration of refractive index‐based biosensors has resulted in significant advancements. Here, the study presents an enhanced surface plasmon resonance biosensor that integrates imaging technology and features dual‐parameter interrogation (intensity and phase) with guided mode coupling. By depositing a silica‐waveguide‐layer on a metal‐layer, two‐mode coupling is established to generate a high Q resonance and induce a phase mutation. The sensing performance experiment demonstrated a phase sensing sensitivity of 1.1 × 105 degree RIU−1, Q‐value of the resonant peak up to 314, and figure of merit of 300 RIU−1, superior to most standard plasmonic sensors. An in‐line phase‐polarization modulation scheme combined with imaging technology is proposed to extract the resonant phase carrying refractive index information. Additionally, a pair‐prism module is designed to optimize the sensing system configuration. Meanwhile, dual‐parameters interrogation including the intensity and phase are demonstrated, which offers potential for complementary and multi‐sensing fusion applications. The intensity interrogation also shows a considerable sensitivity of 7.2 × 104 a.u. RIU−1. Furthermore, it is combined with microfluidic chip to detect of alpha‐synuclein protein closely related to Parkinson's disease, and the limit of detection can reach 300 pg mL−1 level, which indicated a considerable potential for high‐throughput diagnosis application.

Synthesis of Pt/FeVO4: A novel heterostructure for efficient photocatalysis

In this work, a unique platinum-loaded iron vanadate (Pt/FeVO4) composite for escalating the photocatalytic performance via the facile sonicated assisted hydrothermal method was synthesized. Morphological results revealed that the FeVO4 and well-dispersed Pt/FeVO4 particle is in the range of 150–200 nm size, which developed transportation of the photogenerated electrons into FeVO4, resulting in efficient separation of the photogenerated carriers in coupled Pt/FeVO4 nanocomposite heterostructure. The multi-characterizations results indicate an excellent adsorption ability and enhanced surface plasmon resonance (SPR) of Pt/FeVO4 composites as these composites are strongly associated with Pt loading. The induced impedance spectroscopy and photoluminance results demonstrated that Pt enhances separation efficiency as well as transferring rates for photogenerated charges. The ESR data suggests that the reactive oxygen species (OH•) was the most reactive specie agent with h+, •O2¯ having a minor role in methylene blue (MB) degradation.

Bilayer Magnetoplasmonic Grating for Enhancement of the Transverse Magneto-Optical Kerr Effect and Dual Sensing Performance by Surface Plasmon Resonance

Magnetoplasmonic nanostructures with magnetic and metallic compositions have received considerable attention because they can greatly enhance the transverse magneto-optical Kerr effect (T-MOKE) due to surface plasmon resonance (SPR) excitations, which can be used to realize extremely high detection performance. Here, a bilayer heterogeneous grating is proposed that comprises gold and cerium-substituted yttrium iron garnet layers on a gold film for remarkable SPR enhancement of the T-MOKE. Numerical simulations via the finite element method indicated that the proposed structure substantially improves the sensing performance of the incident angle and wavelength with high detection sensitivity and a figure of merit that is an order of magnitude better than previously reported results. Moreover, the proposed structure can be used to fabricate devices for sensing gaseous media.

Effect of Monomers and Multimers of Gold Nanostars on Localized Surface Plasmon Resonance and Field Enhancement

Effect of Monomers and Multimers of Gold Nanostars on Localized Surface Plasmon Resonance and Field Enhancement

The Influence of Surface Processing on the Surface Plasmonic Enhancement of an Al-Nanoparticles-Enhanced ZnO UV Photodectector.

Surface Plasmonic Resonance (SPR) induced by metallic nanoparticles can be exploited to enhance the response of photodetectors (PD) to a large degree. Since the interface between metallic nanoparticles and semiconductors plays an important role in SPR, the magnitude of the enhancement is highly dependent on the morphology and roughness of the surface where the nanoparticles are distributed. In this work, we used mechanical polishing to produce different surface roughnesses for the ZnO film. Then, we exploited sputtering to fabricate Al nanoparticles on the ZnO film. The size and spacing of the Al nanoparticles were adjusted by sputtering power and time. Finally, we made a comparison among the PD with surface processing only, the Al-nanoparticles-enhanced PD, and the Al-nanoparticles-enhanced PD with surface processing. The results showed that increasing the surface roughness could enhance the photo response due to the augmentation of light scattering. More interestingly, the SPR induced by the Al nanoparticles could be strengthened by increasing the roughness. The responsivity could be enlarged by three orders of magnitude after we introduced surface roughness to boost the SPR. This work revealed the mechanism behind how surface roughness influences SPR enhancement. This provides new means for improving the photo responses of SPR-enhanced photodetectors.

Tunable Au@SiO2/Au Film Metasurface as Surface Plasmon Resonance Enhancer for Direct and Ultrasensitive Detection of Exosomes.

Surface plasmon resonance (SPR) spectroscopy with non-labelling, sensitive, and real-time properties is critical for clinical diagnosis applications. However, conventional SPR sensors face the challenge of lower sensitivity and selectivity for trace exosomes assay in complex serum. We proposed a core-shell Au@SiO2-Au film (Au@SiO2-Au film) metasurface to enhance SPR signal based on systematic study on the relationship between gap modes and SPR enhancement. The self-assembled multifunctional peptide was designed as recognition layer with antifouling properties for ultrasensitive and selective detection of PD-L1+ exosomes in serum. The tuning electromagnetic (EM) field model by manipulating the gap was established to guide the preparation of Au@SiO2-Au film metasurface. The in-plane and out-of-plane coupling of Au@SiO2 nanoparticles (NPs) could greatly enlarge and enhance three-dimensional EM field to meet the size of exosomes located in the evanescent field. At the structural level, we achieved high sensitivity (0.16 particles/mL) and a broad response range (10-5 × 103 particles/mL) through optimizing the thickness of SiO2 and surface coverage of Au@SiO2. Furthermore, clinical sample assay achieved the optimal diagnostic accuracy (AUC = 0.97) for differentiating cancer patients from healthy controls. This work provides an opportunity for the construction of a tunable gap mode as SPR enhancer in a total internal reflection architecture. The systematic study on the relationship between gap modes and SPR sensitivity provides a broad scope for promoting direct, efficient, highly selective, and sensitive detection of SPR sensors for clinical application.

Prism SPR Glucose Sensor Based on Gold Nanoparticle/Gold Film Coupling Enhanced SPR

A novel glucose sensor based on gold nanoparticles (AuNPs) enhanced surface plasmon resonance (SPR) is proposed for the accurate detection of glucose concentration. The coupling enhancement effect of localized surface plasmon resonance (LSPR) of AuNPs and SPR of gold film can improve the refractive index sensitivity of the sensor. The specific reaction between glucose and glucose oxidase (GOD) causes a change in the refractive index of the glucose solution microenvironment and eventually leads to a drift in the resonance angle. Field emission scanning electron microscopy (SEM) was used to characterize the GOD before and after immobilization, and the effect of different concentrations of GOD on the detection of glucose by the sensor was investigated. The experimental results showed that the proposed sensor surface out excellent performance in terms of sensitivity (0.8633 degree/(mg/ml)).

Design of an efficient ultra-thin film Cu(In,Ga)Se2 solar cell, using plasmonic cluster back reflectors

In this paper, an ultra-thin film CIGS solar cell using a cluster back reflector is discussed to improve optical parameters. This cluster nanostructure includes four silver nanoparticles embedded in the back surface of the active layer. By optimizing the effective parameters of the plasmonic phenomenon, such as length, width, height, and distances between the nanoparticles, among the studied cases, the cylindrical nanostructure, is selected as the most efficient back reflector. To achieve these results, it is mainly focused on short-circuit current density analysis. Besides, power conversion efficiency, absorption spectrum and transmission of light are also studied. As a result, due to the localized surface plasmon resonance enhancement, short-circuit current density and power conversion efficiency reach 27.2 mA/cm2 and 15.7 %, respectively. These values for the bare state were 19 mA/cm2 and 10.7 %.

Plasmon Tunability and Field Enhancement of Gold Nanostar

Objective: The localized surface plasmon resonance (LSPR) and field enhancement of Gold nanosphere and nanostar were evaluated. Method: FDTD solutions, a product of Lumerical solutions Inc., Vancouver, Canada [17], was used to perform the electromagnetic simulations in this work. The impact of particle size and spike number on peak wavelength was studied quantitatively. Result: By altering the particle size and amount of spikes, we were able to detect a hot zone around nanostar. For Au nanostar, the peak wavelength for nanostar varies from visible to near-infrared. When compared to a nanosphere of the same dimension, the shift seen in nanostar is substantially higher, making it more suitable for biosensing applications. When the refractive index of the surrounding medium is increased, a red shift in peak wavelength is noticed, forming the basis for a plasmonic refractive index sensor. Aside from having a higher sensitivity, nanostar has a twofold hot spot system due to their unique surfaces. There is no evidence of spike aggregation in the near field pattern. As a result, it is thought to be a better nanostructure for biosensing applications. Conclusion: The LSPR and field enhancement for Au nanosphere and Nanostar were investigated using the FDTD method. The nanosphere's peak wavelength is in visible region, whereas the nanostar's range extends from visible to near-infrared, depending on the size and number of spikes. At 517 nm, the enhancement factor for a nanosphere was 102, but at 1282 nm, the enhancement factor for a nanostar with six spikes was 108.

Highly sensitive plasmonic biosensor enhanced by perovskite-graphene hybrid configuration

This study theoretically proposes a highly sensitive plasmonic biosensor comprising a silver film, perovskite nanosheets, bi-layer silicon nanosheets, and a graphene overlayer. The introduction of perovskite-graphene hybrid structure can reduce the optical reflectivity of the proposed biosensor configuration so that photons are converted into energy to support surface plasmon resonance (SPR) enhancement. Unlike conventional angular modulation, our proposed biosensor configuration is designed using phase modulation, offering sensitivity enhancements as high as 3 orders of magnitude. Excellent biosensing performances have been examined by optimizing the silver film thickness and the number of perovskite nanosheets. Considering a tiny refractive index change of 0.0012 refractive index unit (RIU) caused by biomolecules adsorption behavior, the optimal plasmonic biosensor configuration of 46-nm silver film–5.7-nm silicon interlayer-1-layer CH3NH3PbI3 perovskite film–0.7-nm silicon interlayer-1-layer graphene can produce the highest detection sensitivity of 1.2314 × 105 degree/RIU. In addition, an excellent linear response in the differential phase can be obtained, as the refractive index variation of the sensing interface can be as low as 10−6 RIU, showing great potential in performing ultrasensitive biosensing.

In Operando Photoswitching of Cu Oxidation States in Cu-Based Plasmonic Heterogeneous Photocatalysis for Efficient H2 Evolution.

Metal nanoparticles (NP) supported on TiO2 are known to be efficient photocatalysts for solar-to-chemical energy conversion. While TiO2 decorated with copper NPs has the potential to become an attractive system, the poor oxidative stability of Cu severely limits its applicability. In this work, we demonstrate that, when Cu NPs supported on TiO2 nanobelts (NBs) are engaged in the photocatalytic generation of H2 from water under light illumination, Cu is not only oxidized in CuO but also dissolved under the form of Cu+/Cu2+ ions, leading to a continuous reconstruction of nanoparticles via Ostwald ripening. By nanoencapsulating the CuOx (Cu/CuO/Cu2O) NPs by a few layers of carbon supported on TiO2 (TC@C), Ostwald ripening can be suppressed. Simultaneously, the resulting CuOx@C NPs are photoreduced under light illumination to generate Cu@C NPs. This photoswitching strategy allows the preparation of a Cu plasmonic photocatalyst with enhanced activity for H2 production. Remarkably, the photocatalyst is even active when illuminated with visible light, indicating a clear plasmonic enhancement of photocatalytic activity from the surface plasmonic resonance (SPR) effect of Cu NPs. Three-dimensional electromagnetic wave-frequency domain (3D-EWFD) simulations were conducted to confirm the SPR enhancement. This advance bodes for the development of scalable multifunctional Cu-based plasmonic photocatalysts for solar energy transfer.