Strong Surface Plasmon Resonance Effect Research Articles

Plasmon-enhanced photoelectrochemical-SERS simultaneous dual-read-out determination of enrofloxacin based on bifunctional Bi2S3 quantum dots/triangular Ag nanoparticles/Ti3C2 MXene heterojunction

The exploration of high-efficiency detection technologies of antibiotic residues plays vital roles for the evaluation of food quality and environmental safety risks owing to the adverse effects of antibiotics, which could accelerate the emergence of antibiotic-resistant genes. Herein, an integrated complementary dual-mode sensor was developed based on Bi2S3 quantum dots/triangular silver nanoparticles/Ti3C2 MXene (Bi2S3 QDs/T-Ag NPs/Ti3C2) heterojunction by in-situ coupling photoelectrochemical (PEC) analysis with surface-enhanced Raman spectroscopy (SERS) method. The bifunctional heterojunction could enhance light absorption, boost the generation of the electron-hole pairs, and facilitate the light-matter interactions, resulting in increased photoelectric conversion efficiency and enhanced Raman scattering for sensing applications. Moreover, the unique triangular shape and strong surface plasmon resonance effect of T-Ag NPs were conducted to further enhance the output signals of the dual-mode sensing platform. Such as-fabricated PEC/SERS detection system offered good complementarity and achieved mutually check via the combination of the inherent characteristics of two individual modes, which provided more accurate measurement results and more convincing information. Further, aptamer was adopted to recognize enrofloxacin molecules, which could achieve selective and sensitive detection of target. The detection limit of PEC and SERS was calculated as 0.61 fM (S/N = 3) and 0.21 fM (S/N = 3), respectively. Besides, the dual-mode aptasensor exhibited excellent stability and reproducibility, showing a promising prospect to detect enrofloxacin in real samples.

Highly sensitive SPR based PCF sensor for broader analyte detection range including blood compositions detection

In this manuscript, a photonic crystal fiber (PCF) based sensor working on surface plasmon resonance (SPR) concept, which is polished at both the sides and consisting of semi-circular grooves is presented for the detection of a broad range of analytes with refractive index (RI) from 1.17 to 1.40. Also, the analysis is carried out for the diagnosis of different blood compositions such as water, plasma, white blood cells (WBCs), hemoglobin (HB) and red blood cells (RBCs). Plasmonic material gold is coated in the semi-circular grooves, which causes the strong SPR effect due to reduced distance between core and analyte resulting in excellent detection of the analytes. Thus, the optimum wavelength sensitivity and resolution in the case of broad analyte range detection with RI from 1.17 to 1.40 is obtained as 13000 nm/RIU and 7.7×10−6 RIU respectively. Also, blood composition detection using the proposed sensor results in excellent sensing performance with the maximum wavelength sensitivity for hemoglobin-RBCs as 11,500 nm/RIU with finer resolution of 8.69×10−6 RIU.

Surface Plasmon Resonance Enhanced Photoelectrochemical Sensing of Cysteine Based on Au Nanoparticle-Decorated ZnO@graphene Quantum Dots.

In this work, Au nanoparticle-decorated ZnO@graphene core-shell quantum dots (Au-ZnO@graphene QDs) were successfully prepared and firstly used to modify an ITO electrode for the construction of a novel photoelectrochemical biosensor (Au-ZnO@graphene QDs/ITO). Characterization of the prepared nanomaterials was conducted using transmission electron microscopy, steady-state fluorescence spectroscopy and the X-ray diffraction method. The results indicated that the synthesized ternary nanomaterials displayed excellent photoelectrochemical performance, which was much better than that of ZnO@graphene QDs and pristine ZnO quantum dots. The graphene and ZnO quantum dots formed an effective interfacial electric field, enhancing photogenerated electron-hole pairs separation and leading to a remarkable improvement in the photoelectrochemical performance of ZnO@graphene QDs. The strong surface plasmon resonance effect achieved by directly attaching Au nanoparticles to ZnO@graphene QDs led to a notable increase in the photocurrent response through electrochemical field effect amplification. Based on the specifical recognition between cysteine and Au-ZnO@graphene QDs/ITO through the specificity of Au-S bonds, a light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine with an extremely low detection limit of 8.9 nM and excellent selectivity. Hence, the Au-ZnO@graphene QDs is a promising candidate as a novel advanced photosensitive material in the field of photoelectrochemical biosensing.

SERS and machine learning based effective feature extraction for detection and identification of amphetamine analogs

Surface-enhanced Raman spectroscopy (SERS) is extensively researched in diverse disciplines due to its sensitivity and non-destructive nature. It is particularly considered a potential and promising technology for rapid on-site screening in drug detection. In this investigation, a technique was developed for fabricating nanocrystals of Ag@Au SNCs. Ag@Au SNCs, as the basic material of SERS, can detect amphetamine at concentrations as low as 1 μg/mL. The Ag@Au SNCs exhibits a strong surface plasmon resonance effect, which amplifies molecular signals. The SERS spectra of ten substances, including amphetamine and its analogs, showed a strong peak signal. To establish a qualitative distinction, we examined the Raman spectra and conducted density functional theory (DFT) calculations on the ten aforementioned species. The DFT calculation enabled us to determine the vibrational frequency and assign normal modes, thereby facilitating the qualitative differentiation of amphetamines and its analogs. Furthermore, the SERS spectrum of the ten mentioned substances was analysed using the support vector machine learning algorithm, which yielded a discrimination accuracy of 98.0 %.

Highly efficient near-infrared electrochemiluminescence resonance energy transfer system for biosensing: Nonmetallic plasmon Mediated well-matched energy donor-acceptor pair

Herein, a well-matched energy donor-acceptor pair strategy was designed to construct highly efficient NIR ECL-RET system. In detail, an ECL amplification system consisting of SnS2 quantum dots decorated Ti3C2 MXene nanocomposites (SnS2 QDs-Ti3C2) as the energy donor were developed via a one-pot method, and the nanocomposites exhibited highly efficient NIR ECL emission due to the surface-defect effect generated by the oxygen-containing functional groups in MXene. Nonmetallic plasmon hydrated defective tungsten oxide nanosheets (dWO3•H2O) were utilized as energy acceptors because of its strong surface plasmon resonance effect in Vis-NIR absorption range. Compared with non-defective tungsten oxide hydrate nanosheets (WO3•H2O), the overlapping area between ECL spectrum of SnS2 QDs-Ti3C2 and UV–vis spectrum of dWO3•H2O was increased by 2.1 times, and the results showed that more efficient quenching effect was obtained. As a proof of concept, tetracycline (TCN) aptamer and its complementary chain were served as a bridge to connect the energy donor and acceptor, achieving the successful construction of NIR ECL-RET aptasensor. The as-fabricated ECL sensing platform exhibited a low detection limit of 6.2 fM (S/N = 3) within a wide linear range from 10 fM to 10 μM. Besides, the NIR ECL-RET aptasensor also showed excellent stability, reproducibility and selectivity, providing a promising tool to detect TCN in real samples. This strategy offered a universal and effective method in constructing highly efficient NIR ECL-RET system for developing rapid, sensitive and accurate biological detection platform.

Atomic layer deposition assisted fabrication of large-scale metal nanogaps for surface enhanced Raman scattering

Metal nanogaps can confine electromagnetic field into extremely small volumes, exhibiting strong surface plasmon resonance effect. Therefore, metal nanogaps show great prospects in enhancing light–matter interaction. However, it is still challenging to fabricate large-scale (centimeter scale) nanogaps with precise control of gap size at nanoscale, limiting the practical applications of metal nanogaps. In this work, we proposed a facile and economic strategy to fabricate large-scale sub-10 nm Ag nanogaps by the combination of atomic layer deposition (ALD) and mechanical rolling. The plasmonic nanogaps can be formed in the compacted Ag film by the sacrificial Al2O3 deposited via ALD. The size of nanogaps are determined by the twice thickness of Al2O3 with nanometric control. Raman results show that SERS activity depends closely on the nanogap size, and 4 nm Ag nanogaps exhibit the best SERS activity. By combining with other porous metal substrates, various sub-10 nm metal nanogaps can be fabricated over large scale. Therefore, this strategy will have significant implications for the preparation of nanogaps and enhanced spectroscopy.

Advances in the Application of Exosomes Identification Using Surface-Enhanced Raman Spectroscopy for the Early Detection of Cancers

Exosomes are small nanoscale vesicles with a double-layered lipid membrane structure secreted by cells, and almost all types of cells can secrete exosomes. Exosomes carry a variety of biologically active contents such as nucleic acids and proteins, and play an important role not only in intercellular information exchange and signal transduction, but also in various pathophysiological processes in the human body. Surface-enhanced Raman Spectroscopy (SERS) uses light to interact with nanostructured materials such as gold and silver to produce a strong surface plasmon resonance effect, which can significantly enhance the Raman signal of molecules adsorbed on the surface of nanostructures to obtain a rich fingerprint of the sample itself or Raman probe molecules with ultra-sensitivity. The unique advantages of SERS, such as non-invasive and high sensitivity, good selectivity, fast analysis speed, and low water interference, make it a promising technology for life science and clinical testing applications. In this paper, we briefly introduce exosomes and the current main detection methods. We also describe the basic principles of SERS and the progress of the application of unlabeled and labeled SERS in exosome detection. This paper also summarizes the value of SERS-based exosome assays for early tumor diagnosis.

Surface plasmon-enhanced solution-processed phosphorescent organic light-emitting diodes by incorporating gold nanoparticles

Organic light-emitting diodes (OLEDs) have attracted increasing attention due to their superiority as high quality displays and energy-saving lighting. However, improving the efficiency of solution-processed devices especially based on blue emitter remains a challenge. Excitation of surface plasmons on metallic nanoparticles has potential for increasing the absorption and emission from optoelectronic devices. We demonstrate here that the incorporation of gold nano particles (GNPs) in the hole injection layer of poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid with an appropriate size and doping concentration can greatly enhance the efficiency OLED device especially at higher voltage. Apparently, the spectral of the multiple plasmon resonances of the GNPs and the luminescence of the emitting materials significantly overlap with each other. At 1000 cd m−2 for example, the power efficiency of a studied green device is increased from 29.0 to 36.2 lm W−1, an increment of 24.8%, and the maximum brightness improved from 21 550 to 27 810 cd m−2, an increment of 29.1%, as 2 wt% of a 12 nm GNP is incorporated. Remarkably, designed blue OLED also exhibited an increment of 50% and 35% in power efficacy at 100 and 1000 cd m−2, respectively, for same device structure. The reason why the enhancement is marked may be attributed to a strong absorption of the short-wavelength emission from the device by the gold nano particles, which in turn initiates a strong surface plasmon resonance effect, leading to a high device efficiency.

Exploring recent advances in silver halides and graphitic carbon nitride-based photocatalyst for energy and environmental applications

Engineering visible light active photocatalytic systems for renewable energy production and environmental remediation has always been a promising technology to counter overall energy demands and pollution challenges. As a fascinating conjugated polymer graphitic carbon nitride (g-C3N4) has been developed as a hotspot in the research field as a metal-free semiconducting material with the appealing band gap of 2.7 eV. Recently, g-C3N4 has gained tremendous interest in photocatalytic wastewater abatement as well as for hydrogen (H2) generation, carbon dioxide (CO2) reduction, and pollutant degradation, under exposure to visible light. Plasmonic silver halides (AgX) such as AgCl, AgBr, and AgI as plasmonic photocatalyst have received immense research interest owing to their escalating photocatalytic efficacy and strong surface plasmon resonance effect (SPR). AgX is the photosensitive, broad bandgap semiconducting materials with effectual antimicrobial properties. This review summarizes the heterostructure of carbonaceous g-C3N4 with plasmonic AgX, to reduce the recombination of photo-generated charge carriers, thus enhancing the natural light absorption. g-C3N4 grafted AgX nanoarchitectures can be utilized for several potential applications, for instance, overall water splitting (OWS), CO2 conversion to hydrocarbon fuels, pollutant exclusion, and antibacterial disinfection. This review focuses on the evolution of g-C3N4 as well as AgX, facile, and synthetic routes for fabrication of g-C3N4 tailored AgX, construction of nano-junctions (AgX/g-C3N4) with various photocatalytic applications. Finally, we provided a viewpoint of current hassles and some perceptions of novel trends in this exciting as well as developing research arena.

Recent advances in surface-enhanced Raman spectroscopy for the detection of tumor markers

Sensitive and accurate detection of tumor markers is critically essential for the early clinical diagnosis, treatment and prognosis of cancers. Surface-enhanced Raman spectroscopy (SERS) utilizes plasmonic nanomaterials to generate a strong surface plasmon resonance (SPR) effect in the visible to near-infrared region, such as silver and gold nanostructures. The SPR effect can significantly enhance the Raman signals of adsorbed molecules on the surface of nanostructures, allowing to gain the sensitive fingerprint information for the analyte itself or the Raman reporter. Benefitted from the superior properties of high sensitivity, good selectivity, fast and noninvasive analysis, SERS has attracted increasing interest and become a very promising technique for biological analysis. In comparison with other bioanalytical techniques, such as enzyme-linked immunosorbent assay, fluorescence and electrochemical methods, SERS possesses the following advantages: (1) SERS has an ultrahigh sensitivity, even down to single molecule level; (2) SERS can provide the intrinsic molecular fingerprint information, and the bandwidths of SERS peaks are usually very narrow; (3) SERS is suitable for long-term monitoring, because of the resistance of photobleaching and photodegradation; (4) non-invasive detection can be achieved with a low amount of sample and no preparation; (5) the interference of water is very weak, so biological samples can conveniently be detected in aqueous solutions; (6) various SERS-active nanostructures can be designed for multiplex detection. In this review, we provide an overview of recent advances in SERS technology for the detection of different tumor markers, including proteins, enzymes, nucleic acids, cells, tissues, gases and others. Great successes have been achieved by utilizing SERS, which can facilitate the fabrication of assays for tumor biomarkers. However, SERS has not been widely applied in clinical bioanalysis and biodiagnosis in the past over 40 years. SERS-based bioassay involves complex interactions between light, surface plasmon nanomaterials, and bioassay systems. It is difficult to obtain reproducible and reliable Raman spectroscopy data, which is one of the main bottlenecks in SERS bioassay, resulting in the deficiency of clinical and standardized applications. Therefore, there are still many efforts to be done to control the potential factors: (1) It is necessary to prepare a SERS substrate with high uniformity, high enhancement, clean, or/and to properly modify its surface; (2) the suitable Raman reporters and tags are selected to improve the biocompatibility and avoid unspecific adsorption, which can trap analytes in the “hot spots”; (3) biological samples are retained in their native state during the storage and pretreatment procedure to avoid irreversible degradation; (4) appropriate SERS detection conditions are performed, such as excitation wavelength, exposure time, and laser power, to obtain real detection information; (5) accurate biomolecule database are established for spectral assignments. By further improving these challenges, we anticipate the more widespread application of SERS-based assay in biomedicine and bioanalysis fields.

Elliptical-hole PCF structure with selective Y-axis gold coating for tunable single-polarization band-stop filtering

An elliptical-hole photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) is proposed, which can work as a tunable single-polarization band-stop filter (BSF). Theoretical results show that the proposed structure is very sensitive to the polarization of the guided modes, due to its high birefringence coefficient and strong SPR effect. It can achieve single-polarization single-mode (SPSM) filtering without liquid filled in the gold coated air holes. At resonant wavelength, the loss of the y polarization fundamental mode reaches 792.16 dB cm−1, but the loss of the x polarization fundamental mode is only 0.52 dB cm−1, causing that the extinction ratio is as high as 688 dB and the bandwidth is larger than 520 nm with the PCF length of 1 mm. When liquids with the refractive index (RI) ranging from 1.44 to 1.48 are filled in the gold coated air holes, the PCF could be used as a BSF to filter the x polarization fundamental mode selectively on the premise of SPSM filtering. And the center wavelength of the BSF is extremely sensitive to the liquid RI with a high sensitivity of 16 820 nm/RIU, which indicates a potential application in RI sensing. The proposed PCF realizing the integration of SPSM filter and BSF is available for compact optical communication systems.

Asymmetrical photonic crystal fiber based plasmonic sensor using the lower birefringence peak method

An asymmetrical configuration of hexagonal lattice photonic crystal fiber (PCF) based surface plasmon resonance (SPR) refractive index sensor is proposed. Instead of the typical confinement loss method, the lower birefringence peak method is considered to explore the sensing performance. The asymmetry in the core region induces birefringence that enhances the coupling efficiency between the core and surface plasmon polariton (SPP) mode. To form the strong SPR effect, both the gold layer and analyte layer are deposited on the external surface of the PCF. The proposed birefringent sensor exhibits the maximum wavelength sensitivity of 22,000 nm/RIU within broad analyte refractive index (RI) from 1.33 to 1.42. The sensing characteristics are carried out with the variation of several PCF structural parameters. Owing to enhanced sensitivity, the proposed sensor can be a potential candidate for biological and biomolecular analyte detection.

Composition-Tunable Hollow Au/Ag SERS Nanoprobes Coupled with Target-Catalyzed Hairpin Assembly for Triple-Amplification Detection of miRNA.

Detecting disease-related biomarkers is of great significance for disease diagnosis and therapy. In this work, we develop an ultrasensitive surface-enhanced Raman scattering (SERS) biosensor for the detection of an acute myocardial infarction-related miRNA (miR-133a) using composition-adjustable hollow Ag/Au nanosphere-based SERS probes coupled with the target-catalyzed hairpin assembly (CHA) strategy. Bimetallic probes displaying high stability and a strong surface plasmon resonance effect were synthesized with a controllable ratio of silver and gold by a galvanic replacement method and then captured by a duplex linker produced in the CHA process to accomplish signal amplification. In this way, the target miR-133a can be detected in a wide linear range with a detection limit of 0.306 fM and high selectivity over other miRNAs expressed in human hearts. Practical applications in human blood samples reveal the strong anti-interference ability and ideal sensitivity of our developed sensing platform in physiological environments, benefiting its potential biomedical applications.

Selective methane production from visible-light-driven photocatalytic carbon dioxide reduction using the surface plasmon resonance effect of superfine silver nanoparticles anchored on lithium titanium dioxide nanocubes (Ag@LixTiO2)

This study focused on the results of applying the strong surface plasmon resonance (SPR) effect of silver (Ag) particles anchored on cubic phase LixTiO2 to the carbon dioxide (CO2) photoreduction reaction. The study demonstrated the importance of three aspects: First, the cubic TiO2, which activated the [101] facet, was successfully produced. Secondly, Li+ ions were introduced as Frenkel defects in some lattices to create oxygen defects. These vacancies increased the adsorption of carbon dioxide and sped up the rate-determining step in the CO2 reduction reaction. In other words, they induced the easy conversion of CO2 to CO, which is the first reduction product. Finally, the loading of Ag nanoparticles onto the LixTiO2 cubic surface the improved photocatalytic activity through SPR effects, and in particular led to selective conversion of CO2 to methane (CH4). Quantitatively, the yield of CH4 from CO2 using the Ag@Li0.075TiO2 particles was 49 μmol/g after 10 h of reaction, which was 8.2 and 1.5 times higher than that of cubic TiO2 (6 μmol/g) and Li0.075TiO2 (33 μmol/g) under UV-light. Additionally, its activity did not decrease under visible lights of 420 and 620 nm with the similar CH4 yields of 42 and 34 μmol/g after 10 h, respectively. In particular, the production ratio of CH4 and CO using cubic TiO2 and LixTiO2 were about 1:1, with no selectivity for either product. However, after metallic Ag nanoparticles were loaded, the product selectivity shifted towards CH4, and the product ratio of CH4 to CO was about 3:1. Furthermore, the Ag@Li0.075TiO2 particles exhibited a strong SPR effect (in particular, direct electron transfer), which contributed to maintaining the charge separation and the lifetime of the catalyst over a long period. Catalytic deactivation was not observed during five cycles of recycling tests.

Gold nanobipyramid@cuprous oxide jujube-like nanostructures for plasmon-enhanced photocatalytic performance

Nobel metal/semiconductor composites is a kind of alluring photocatalysts based on their broad light absorption and high photocatalytic efficiency. In this work, we reported a novel jujube-like gold nanobipyramid core/cuprous oxide shell (Au NBP@Cu2O) composite photocatalyst, with adjustable aspect ratio of Au NBP core and thickness of Cu2O shell. The Au NBP@Cu2O products possess tunable light absorption from visible to near-infrared region and all of them exhibit excellent photocatalytic performances compared with pure Cu2O. The optimal Au NBP@Cu2O sample achieves nearly 100% degradation of methyl orange in 60 min compared with 2.45% for pure Cu2O under illumination (λ > 400 nm), and 47.5% degradation of methyl orange in 60 min compared with 1.23% for pure Cu2O under illumination (λ > 700 nm). The enhanced photocatalytic behaviors are attributed to the efficient charge separation driven by Schottky junction in Au NBP@Cu2O, as well as the strong surface plasmon resonance effect from Au NBPs which not only extends the light response for Cu2O but also enhances the photodegradation by generating hot electrons to inject into Cu2O. Furthermore, it is worth mentioning that the Au NBP@Cu2O composites exhibit significantly enhanced stability because the Au NBP core can draw holes from Cu2O. This work may provide guidance to the fabrication of plasmon-enhanced photocatalysts based on Au NBPs and other semiconductors along with the exploration of wider applications for them in the future work.

One-dimensional Au/SiC heterojunction nanocomposites with enhanced photocatalytic and photoelectrochemical performances: Kinetics and mechanism insights

In this work, highly dispersed Au nanoparticles (NPs) decorated SiC nanowires (NWs) hybrids were firstly synthesized by a facile deposition-precipitation method. The as-prepared Au/SiC samples were characterized using various instrumental methods such as XRD, TEM, EDS, UV–vis DRS, BET, FTIR, XPS, PL, TRPL, and photoelectronchemical measurements. The solar H2 production performances were investigated by using Na2S as sacrificial reagents in water under simulated sunlight illumination produced from a 300 W xenon lamp. Results showed that a significantly enhanced photoactivity for H2 evolution (1495.8 μmol h−1·g−1) with apparent quantum efficiency (AQE) of 2.12% was achieved over the compostion-optimized Au/SiC composite (with 0.5 wt% Au), which was much higher than those of pure SiC NWs, Pt NPs deposited SiC NWs sample as well as the previously reported SiC-based catalysts. In cyclic tests, the AS0.5 showed acceptable photocatalytic stability and good structural stability. PL, TRPL and photoelectrochemical measurements disclosed that improved charge separation and retarded charge recombination were realized. However, the Au-loaded SiC products with strong surface plasmon resonance (SPR) absorption showed no activity for visible light photocatalytic H2 production (λ ≥ 400 nm). Based on band-gap structures, the critical factors for SPR effect of Au NPs in activating or enhancing the visible-light photoactivities of semiconductors were proposed. This work can pave the avenue to the development of plasmonic metal decorated other narrow band gap semiconductors with plasmon-enhanced visible-light photoactivity for solar water splitting and related applications.

Stimuli-disassembling gold nanoclusters for diagnosis of early stage oral cancer by optical coherence tomography

A key design consideration in developing contrast agents is obtaining distinct, multiple signal changes in diseased tissue. Plasmonic gold nanoparticles (Au NPs) have been developed as contrast agents due to their strong surface plasmon resonance (SPR). This study aims to demonstrate that stimuli-responsive plasmonic Au nanoclusters (Au NCs) can be used as a contrast agent for optical coherence tomography (OCT) in detecting early-stage cancer. Au NPs were clustered via acid-cleavable linkers to synthesize Au NCs that disassemble under mildly acidic conditions into individual Au NPs, simultaneously diminishing SPR effect (quantified by scattering intensity) and increasing Brownian motion (quantified by Doppler variance). The acid-triggered morphological and accompanying optico-physical property changes of the acid-disassembling Au NCs were confirmed by TEM, DLS, UV/Vis, and OCT. Stimuli-responsive Au NCs were applied in a hamster check pouch model carrying early-stage squamous carcinoma tissue. The tissue was visualized by OCT imaging, which showed reduced scattering intensity and increased Doppler variance in the dysplastic tissue. This study demonstrates the promise of diagnosing early-stage cancer using molecularly programmable, inorganic nanomaterial-based contrast agents that are capable of generating multiple, stimuli-triggered diagnostic signals in early-stage cancer.

A Novel In-Situ Synthesis and Enhanced Photocatalytic Performance of Z-Scheme Ag/AgI/AgBr/Sulfonated Polystyrene Heterostructure Photocatalyst

Novel Z-scheme Ag/AgI/AgBr/sulfonated polystyrene composite is prepared via ion-exchange followed by light reduction. The photocatalytic activities of as-synthesized samples are evaluated through the degradation of methyl orange (RhB) under visible light irradiation. The Z-scheme Ag/AgI/AgBr/SPs photocatalysts display excellent photocatalytic activity and stability compared with Ag/AgI and Ag/AgBr. The improved photocatalytic activity is mainly due to the combined effects of the Z-scheme structure of Ag/AgI/AgBr/SPs and the strong surface plasmon resonance effect of Ag0 nanoparticles. Moreover, after four successive cycles, the Ag/AgI/AgBr/SPs photocatalysts have no obvious loss of activity for the degradation of RhB, illustrating that the Z-scheme Ag/AgI/AgBr/SPs photocatalysts are rather stable under visible-light irradiation.

Effects of Ag on the photocatalytic activity of multiple layer TiO2 films

This work reports effective activated multiple layers Ag-TiO2 films and Ag-TiO2/Ag films via a solgel and direct coating approach. Scanning electron microscopy and transmission electronic microscope are performed to characterize the morphology. The roles of metallic Ag on TiO2 films for photodegradation stearic acid are explained by UV–vis spectroscopy and photoluminescence spectroscopy. The photocatalytic activity of Ag-TiO2 films for stearic acid decomposition is 5 times higher than that of pure TiO2 films. Different Ag-TiO2/Ag films have almost the same activity of photodegradation stearic acid. The strong surface plasmon resonance effect of Ag makes TiO2 absorb more visible light. The separation effect of photogenerated electron–hole pairs could be increased by doping a small amount of Ag. For more Ag amount in Ag film, there will likely be an equilibrium between the separation of electron–hole pairs and the recombination of them.

Highly sensitive D-shaped photonic crystal fiber biological sensors based on surface plasmon resonance

A D-shaped photonic crystal fiber (D-PCF) with square-lattice and nanoscale gold film is proposed and analyzed by the finite element method. Based on the strong surface plasmon resonance effect between fiber core modes and surface plasmon polariton modes, the designed D-PCF is sensitive to the refractive index variation of analyte and can be found application in biological sensors. The structure parameters of the proposed D-PCF are investigated in order to optimize the sensing performance. The sensitivity can reach to 12,450 nm/RIU as refractive index of analyte ranging from 1.345 to 1.410. The simulation results also show that the sensing performance has high linearity which is necessary in application.