Enhanced Surface Plasmon Research Articles

Plasmonic sensor design: Cu-SiO₂-Ni-black phosphorus for enhanced surface plasmon resonance in visible regime.

Anovel surface plasmon resonance (SPR) sensor is presentedutilizing a BK7 prism, copper (Cu), silicon dioxide (SiO2), nickel (Ni), and black phosphorus (BP) for enhanced biomolecule sensing in the refractive index (RI) range of 1.33 - 1.335. The combination of Cu and Ni offers strong plasmonic properties, while BP tunable bandgap and superior light-matter interactions significantly improve sensitivity. SiO2 enhances chemical stability and enables surface functionalization, making the sensor robust for real-world applications. The high sensitivity of 417.11°/RIU is attained with a remarkable quality factor (QF) of 102.19/RIU at minimum reflectance (Rmin), outperforming existing SPR sensors in terms of both sensitivity and reliability. The maximum sensitivity of 479.10°/RIU is achieved. The proposed design addresses key challenges in SPR sensing, including environmental stability, layer optimization, and sensitivity enhancement, positioning it as a promising platform for advanced biomolecular detection.

Regulating Charge Separation Via Periodic Array Nanostructures for Plasmon-Enhanced Water Oxidation.

Plasmonic resonance intensity in metallic nanostructures plays a crucial role in charge generation and separation, directly affecting plasmon-induced photocatalytic activity. Engineering strategies to enhance plasmonic effects involve designing specific nanostructures, such as triangular nanoplates with sharp corners or dimer nanostructures with hot spots. However, these approaches often lead to a trade-off between enhanced plasmonic intensity and resonance energy, which ultimately determines local charge density and photocatalytic performance. Here, inspired by theoretical predications, it is shown that a flexibly controlled plasmonic photocatalyst, consisting of an ordered array of Au nanoparticles on a SrTiO3 surface, exhibits an enhanced surface plasmon resonance (SPR) intensity while maintaining a constant SPR resonant energy, due to the presence of surface lattice resonance. This trade-off results in improved charge separation efficiency and an increase in local charge density at catalytically active sites, as verified by theoretical simulations, surface photovoltage microscopy, and ultrafast transient absorption spectroscopy. Moreover, the optimized periodic photocatalyst shows a 7-fold increase in water oxidation activity over disordered nanostructures. This work provides a novel approach for balancing the intensity and energy of SPR, which will contribute to optimizing photocatalytic activity on plasmonic platforms.

Enhanced Surface Plasmon Resonance Sensing via Kramers-Kronig Phase Extraction.

This study introduces a novel approach to enhance surface plasmon resonance (SPR) sensing using Kramers-Kronig (K-K) relations for phase extraction from reflection spectra. By applying the K-K relations, a phase shift sensitivity of 3400°/RIU is achieved improving SPR detection limits to 9 × 10-6 RIU, which is four times more sensitive than conventional methods for determining SPR peak shifts. This advancement enables more precise detection of refractive index changes in aqueous solutions, making it valuable for biosensing and environmental monitoring with spectrometers.

Prominence of copper in AuCu alloy towards enhance surface plasmon resonance-driven water oxidation

To fully harness the potential of surface plasmon resonance (SPR) in augmenting photocatalytic water oxidation, a comprehensive exploration of structure-activity relationship of metal nanoparticles is essential. This work presents a wrap-bake-peel (WBP) strategy designed to stabilize AuCu/TiO2 nanostructures while preserving SPR absorption and refining the metal-semiconductor interfaces. Through strategically incorporating trace Cu into Au (Cu/Au = 0.06), we achieved a 2.6-fold enhancement of SPR-induced oxygen evolution reaction (OER) performance compared to pristine Au/TiO2. This enhancement is due to the synergistic effect of SPR and a well-defined Schottky barrier, which improves plasmonic hot carrier charge separation, as verified by detailed spectroscopic analyses. The incorporation of copper plays a critical role, acting as an electron shuttle that facilitates the transfer of hot electrons from photoexcited gold to the AuCu NP surface, thereby reducing recombination. This process, driven by SPR-induced hot electrons from Au, also extends electron-phonon (τ0e-ph), interactions by 138 %, significantly prolonging hot carrier lifetimes. Mechanistic insights reveal that d-band onset potentials (Ed-AuCu∼-0.9 V/ Ed-Au∼-1.2 V) and increased hot hole d-band occupancy in AuCu further enhance the overall SPR-induced water oxidation performance. Simulated electron distributions and quantum confinement in AuCu vs. Au critically dictate SPR characteristics, enabling precise modulation of plasmonic responses. These findings underscore the crucial role of Cu in fine-tuning the properties of plasmonic photocatalysts, demonstrating a significant advancement in the rational design of efficient solar-to-fuel conversion systems.

(Invited) Development of Bipolar Electrochemical Microscopy for High-Speed and High-Resolution Monitoring of Biochemical Phenomena

Closed bipolar electrochemistry (cBPE) involves simultaneous oxidation and reduction at opposite poles of a conductor in two separated solutions. (Figure left). The unique property of cBPE to be operated without direct connection to an external power source is expected to lead to higher resolution in electrochemical imaging than the conventional microelectrode array type imaging platforms. We have applied cBPE to an electrochemical microscopy (BEM) (Figure right) for high-resolution biochemical imaging.1- 7 The operation principle of BEM has been successfully verified,1 then the current focus is on fabrication method of cBPE array. Previously, we filled Au into pores of a polyethylene terephthalate track-etched membrane having D=8 µm pores by electroless plating using 50 mM HAuCl4 aqueous solution and 50 mM NaBH4 EtOH solution.2 Using this cBPE array, an image of oxygen concentration distribution around cell spheroids was successfully obtained, but this method has a problem of the inability to completely fill the pores with gold, resulting in large ionic currents. In this study, we use conductive pastes for fabrication of vertical closed bipolar electrode array to completely fill the pores with conductive materials.Epoxy-based carbon paste (ECP) was prepared by mixing acetylene carbon black (ACB; particle size=42 nm; Strem Chemicals) and epoxy resin (mixture of Epok 812 (62 mL), DDSA (100 mL), and DMP-30 (1.5%); Okenshoji). Oil-based carbon paste (OCP) was prepared by mixing the ACB and the liquid paraffin. For Au paste (AuP), commercially available AURoFUSE (particle size (D50) 0.2–0.4 µm; Tanaka Kikinzoku Kogyo) was used as is. Vertical cBPE arrays using the carbon paste filled in pores of a glass capillary plate was fabricated by filling ECP (ACB: epoxy resin=1:4 in weight ratio) cured at 60°C for 15 h. After cooling, the surface was coated by OCP (ACB: liquid paraffin=1:1 in weight ratio) to fill the dented parts shrank by heat curing. For [Fe(CN)6]3 − imaging, a sample side of the array was modified with reduced graphene oxide (RGO) by coating OCP containing 5 wt.% RGO (RGO-OCP). For H2O2 imaging, a sample side of the array was modified with Prussian blue (PB) by coating commercially available PB containing carbon paste (Carbon Mediator Paste, C2070424P2; SunChemical Gwent). The BEM system was constructed using two solution chambers (detection/sample chambers), BPE array, and driving electrodes. The detection chamber located at the bottom side of the BPE array was filled with 10 mM [Ru(bpy)3] Cl2/20 mM tripropylamine (TPA) solution containing phosphate buffered saline (PBS). The sample chamber located at the bottom side was filled with the sample solution for each measurement. A platinum driving electrode inserted into the detection chamber, another platinum driving electrode and a Ag/AgCl reference electrode inserted into the sample chamber were connected WE, CE and RE connector of a potentiostat, respectively. The entire system was mounted on an inverted microscope with a high sensitivity CCD camera to observe the electrochemiluminescence (ECL) generated at the underside of the BPEs.By using RGO and PB modified carbon paste (PC) cBPE array for BEM element, we successfully obtained an image of 5 mM [Fe(CN)6]3− and H2O2 inflow, respectively.5 These results show that cBPE arrays for BEM can be fabricated by filling micropores with carbon paste taking advantage of the flexibility and ease of modification of the paste electrode. We are now investigating the use of AuP as an electrode material of cBPE array. We have obtained the result that ECL can be enhanced by using AuP as an electrode material.7 This may be due to the surface plasmon enhancement effect by the Au particles contained in the AuP. The establishment of a simple method for fabricating vertical cBPE arrays without ion leakage is expected to further accelerate the research and development of BEM.

MoS2-mediated gap-mode surface plasmon enhancement: Construction of SPR biosensor for direct detection of LECT2

Serum levels of leukocyte cell-derived chemotaxin-2 (LECT2) have emerged as promising diagnostic biomarker for liver fibrosis. Targeting the LECT2/Tie1 signaling pathway holds potential for innovative treatment approaches to this condition. Despite this, the development of highly sensitive assays for serum LECT2 remains limited. Surface plasmon resonance (SPR), a label-free technique for detecting biomolecular interactions via refractive index (RI) changes, has demonstrated notable sensitivity for biomarker assays, though improving its sensitivity for direct LECT2 detection faces certain challenges. In this study, we present an innovative enhanced SPR biosensor designed to overcome current limitations in LECT2 detection. By incorporating molybdenum disulfide (MoS2) nanosheets as nano-spacer between the gold film and cyclodextrin functionalized-gold nanoparticles (CD-AuNPs), this gap-mode design significantly enhances the electric field intensity near the gold film surface, which effectively improves the detection sensitivity of the RI changes. Compared to traditional gold-film-only SPR sensors, our sensor achieves a remarkable sensitivity increase from 73.1 to 133.3 deg/RIU, with a commendable quality factor and detection accuracy. By further modifying the specific peptide of the terminal label phenylalanine (TFF) through the host-guest recognition effect of the CD hydrophobic cavity, we achieved a broad linear range and a low limit of detection (LOD = 0.6206 ng/mL) for the detection of the liver fibrosis marker LECT2. Our proposed enhanced SPR sensing platform demonstrates significant potential for clinical applications in LECT2 detection.

Surface plasmon resonance (SPR)-enhanced photocatalytic degradation by periodically ordered δ-MnO2 arrays with alkali metals doping

Periodically ordered δ-MnO2 arrays of different periods have been fabricated by using polystyrene (PS) nanosphere lithography (NSL) combined with following hydrothermal growth. By choosing different precursors, δ-MnO2 arrays with different alkali metals doping were obtained. It was observed that the K-doped δ-MnO2 array of 500 nm period exhibited superior photocatalytic degradation performance of methylene blue (MB) under visible light irradiation relative to those of Na- or Mg-doped δ-MnO2 arrays of 500 nm period, as well as K-doped δ-MnO2 array of 800 nm period. The best performance of K-doped δ-MnO2 array of 500 nm period can be firstly attributed to enhanced surface plasmon resonance (SPR) effect caused by alkali metal doping, where K-doped MnO2 could provide more free electrons than those of Na- or Mg- doped MnO2. Furthermore, for the nanomaterials with SPR effect the surface plasmon polaritons (SPP) can change the propagation path of incident light to vertical direction after scattering on them. Since the MnO2 array of 500 nm period possessed the distance between neighbor unites smaller than the wavelength of irradiation light, and thus the scattered light interfered with each other after the incident light was scattered by the MnO2 unites. Then the electric field (E-field) intensities generated by SPR effect near each MnO2 unit were elevated due to the interference effect. Therefore, our finding may provide a peculiar way to improve SPR-mediated photocatalytic performance of non-metallic materials by combination of doping and arrays fabrication of particular periods.

Surface plasmon enhancement of 1D Ag nanowires modified electro-treated BiVO4 photoanode with abundant oxygen vacancies for solar water oxidation

The high carrier complexation rate is still one of the main obstacles for bismuth vanadate (BiVO4) to be used in photoelectrochemical (PEC) water oxidation. In this work, we used a simple method for dropping one dimension (1D) silver nanowires (Ag NWs) on the surface of electro-treated BiVO4 (Ag NWs/E-BiVO4). The photocurrent of Ag NWs/E-BiVO4 under AM 1.5 G illumination reaches to 3.12 mA/cm2 which is about 6.2 times than the pure BiVO4 photoelectrode. Meanwhile, the photogenerated charges injection efficiency of Ag NWs/E-BiVO4 photoelectrodes increasing from 12.7 % to 77.5 % than the pure BiVO4 photoelectrode. This is because the surface plasmon resonance (SPR) effect of 1D Ag nanowires enhanced the visible light absorption and provide more Ag active sites. Furthermore, the density functional theory (DFT) calculations show that the Ag NWs/E-BiVO4 have the best adsorption capacity for OH– and the electro-treated BiVO4 with rich oxygen vacancies greatly improves the electron transport efficiency which is benefit for improving the PEC catalytic performance. Thus, this work provides a simple method to enhance the PEC water splitting performance of BiVO4.

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

Derivative-synchronous fluorescence spectroscopy enhanced surface plasmon coupled emission for sensitive detection of tannic acid

In this study, we developed a new derivative-synchronous fluorescence spectroscopy enhanced surface plasmon coupled emission (DS-SPCE) technique for the detection of tannic acid (TA). DS-SPCE generates greatly amplified directional fluorescence signal, approaching nearly a 20-fold enhancement. The property of a gradual fluorescence quenching of the monolayer Rhodamine B isothiocyanate (RBITC) with increasing TA concentration was used for the quantitative detection of TA. The method achieved an ultra-low limit of detection (LOD) of 15.3 pM. It exhibited high selectivity for TA detection, even in the presence of common interferences such as glucose, catechin, and ascorbic acid at concentrations exceeding 100-fold. DS-SPCE method demonstrated robust performance in analyzing TA in tea samples, yielding good average recoveries of TA. Consequently, DS-SPCE emerges as a straightforward fluorescence enhancement approach, providing valuable insights for its practical application.

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

Effects of thermal treatment on sea-urchin-like platinum nanoparticlese

The size and shape of metallic nanoparticles significantly influence the focus of light illumination and affect the plasmonic energy transformation process in plasmonic photocatalytic reactions. This study examined the effects of thermal treatment on the surface shape and plasmonic enhancement of Pt nanoparticles. SEM and XRD results indicate that the nanosized protruding thrusts on the surfaces of Pt sea urchin particles have a lower chemical potential and higher activity. They can be melted and reshaped at 600℃, which is much lower than their melting point of over 1700 ℃. The XPS results suggest that thermal treatment at 600℃ does not cause additional oxidation of the Pt nanocrystals. The samples not subjected to high-temperature treatment exhibited notable photocatalytic degradation of methylene blue in water under UV illumination. These results demonstrate that the surface features of Pt sea urchin nanoparticles play an essential role in the photocatalytic degradation of methylene blue under UV light. Larger particles treated at high temperatures exhibited reduced photocatalytic processing efficiency, whereas smaller particles treated at a lower temperature exhibited increased efficiency, indicating that the protruding sharp cones enhance plasmonic effects in photocatalytic reactions.

Quantitative Assessment of Fungal Biomarkers in Clinical Samples via an Interface-Modulated Optical Fiber Biosensor.

Invasive fungal infections pose a significant public health threat. The lack of precise and timely diagnosis is a primary factor contributing to the significant increase in patient mortality rates. Here, an interface-modulated biosensor utilizing an optical fiber for quantitative analysis of fungal biomarkers at the early stage of point-of-care testing (POCT), is reported. By integrating surface refractive index (RI) modulation and plasmon enhancement, the sensor to achieve high sensitivity in a directional response to the target analytes, is successfully optimized. As a result, a compact fiber-optic sensor with rapid response time, cost-effectiveness, exceptional sensitivity, stability, and specificity, is developed. This sensor can successfully identify the biomarkers of specific pathogens from blood or other tissue specimens in animal models. It quantifies clinical blood samples with precision and effectively discriminates between negative and positive cases, thereby providing timely alerts to potential patients. It significantly reduces the detection time of fungal infection to only 30 min. Additionally, this approach exhibits remarkable stability and achieves a limit of detection (LOD) three orders of magnitude lower than existing methods. It overcomes the limitations of existing detection methods, including a high rate of misdiagnosis, prolonged detection time, elevated costs, and the requirement for stringent laboratory conditions.

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.

Surface plasmon enhancement in silver nanowires and bilayer two-dimensional materials.

In order to improve the low light absorption of two-dimensional (2D) transition metal dichalcogenides (TMDCs), surface plasmon (SP) nanostructures have been widely studied. However, the impact of interlayer twist on such nanostructures has rarely been studied. Here, we construct two different composite structures of silver nanowires (Ag NWs) and pristine bilayer MoS2 (pBLM) or twisted bilayer MoS2 (tBLM). The interlayer twist can further promote the light utilization of MoS2, resulting in an ∼4-fold higher spectral enhancement in Ag/tBLM than that in Ag/pBLM. In addition, the photocurrent and detectivity of the phototransistor based on the Ag/tBLM composite structure were improved by 7-fold and ∼100-fold, respectively, compared to those of the Ag/pBLM phototransistor. Theoretical simulations show that the enhancement of photocurrent can be attributed to the enhancement of the local electric field at the interface between Ag NWs and the tBLM film, which is called the 'hot spot'. These results provide a reference for understanding the modulation mechanism of SPs and interlayer twist on the optoelectronic properties of 2D materials.

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.

Efficiently accelerated free electrons by metallic laser accelerator

Strong electron-photon interactions occurring in a dielectric laser accelerator provide the potential for development of a compact electron accelerator. Theoretically, metallic materials exhibiting notable surface plasmon-field enhancements can possibly generate a high electron acceleration capability. Here, we present a design for metallic material-based on-chip laser-driven accelerators that show a remarkable electron acceleration capability, as demonstrated in ultrafast electron microscopy investigations. Under phase-matching conditions, efficient and continuous acceleration of free electrons on a periodic nanostructure can be achieved. Importantly, an asymmetric spectral structure in which the vast majority of the electrons are in the energy-gain states has been obtained by means of a periodic bowtie-structure accelerator. Due to the presence of surface plasmon enhancement and nonlinear optical effects, the maximum acceleration gradient can reach as high as 0.335 GeV/m. This demonstrates that metallic laser accelerator could provide a way to develop compact accelerators on chip.

Paper electrophoretic enrichment-assisted ultrasensitive SERS detection

To achieve sensitive detection of trace substances in fluids by surface-enhanced Raman spectroscopy (SERS), effective enrichment of molecules at subwavelength regions (hot spots) with a large enhancement is adopted. In this work, a glass fibre paper with Ag nanoparticles (AgNPs) is employed for electrodynamic enrichment of analytes in fluids by paper electrophoresis integrated with field amplification sample stacking (FASS) and capillary effects to obtain both Raman and SERS convenient and sensitive detection. With the help of electrophoretic enrichment on the glass fibre paper and surface plasmon enhancement on the AgNPs, this paper electrophoretic enrichment could improve the detection limit of Raman and SERS detection by more than an order of magnitude, even achieving a SERS detection limit of 10−17 M for Nile Blue A. Furthermore, this flexible SERS detection method can also detect trace organic contaminants at the ppt level in aquaculture and food applications.

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.