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Silver nanoparticles are known to have antimicrobial properties. In the present paper, antibacterial activity of biosynthesized silver nanoparticles coated on low density poly ethylene films was evaluated against Escherichia coli as the representative organism. Silver nanoparticles were biosynthesized using banana peel extract as the reducing agent and characterized by means of UV–Visible spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray analyses. Formation of silver nanoparticles was confirmed by the Surface Plasmon Resonance spectrum with absorption maxima at 431 nm. Particles were seen to be highly polydispersed with the average size in the range of 50–390 nm. Presence of elemental silver was confirmed by the Energy dispersive X-ray spectroscopy analysis. Biosynthesized silver nanoparticles showed excellent antibacterial activity against Escherichia coli in the agar well diffusion test, with the zone of inhibition diameter measuring 19 mm. The silver nanoparticle coated low density poly ethylene film was prepared successfully and our antimicrobial studies revealed that the coated films declined the growth profile of bacteria starting from the log phase. Hence biosynthesized silver nanoparticles incorporated low density poly ethylene films can be suggested as an active packaging material for food packaging after further characterization and migration studies.

This study illustrates preparation of well-formed TiO2 and Ag/TiO2 nanoparticles (NPs) by green combustion process using Cucumis melo (Muskmelon) juice as unique fuel. Polycrystalline Ag/TiO2 NPs outline the superior photocatalytic action towards the degradation of methylene blue dye and antioxidant activity through hindrance of free radical scavenging. The PXRD pattern illustrates the existence of Ag in the TiO2 crystal lattice with the average crystallite measure of 9.09 nm and 22.8 nm for TiO2 and Ag/TiO2 respectively. FTIR spectral studies showed a decrease in the intensity upon doping with Ag owing to the arrangement of Ag NPs on the surface of TiO2 NPs. The TEM image of Ag/TiO2 exhibited almost spherical shape with average particle measure of 9.12 nm. Further, HRTEM studies evidence enhancement of the lattice fringe width upon doping and d-spacing values are in conformity with XRD results illustrating successful doping of Ag into TiO2 lattice. PL spectrum of both the NPs exhibited intense peak at 458 nm (2.69 eV) and weak peaks at 486 nm (2.53 eV) and 700 nm (1.76 eV) in the visible region. Ag/TiO2 NPs showed predominant photocatalytic property for the MB dye decomposition compared to TiO2 NPs. This is possibly owing to aid of Ag Surface Plasmon Resonance in expanding the light assimilation of TiO2 NPs from near UV region to visible range driving to better light-absorbing capability and considerably enhances charge separation in TiO2 due to doping. The results manifested that Ag/TiO2 NPs possess conformity surface structure, better photocatalytic property compared to un-doped TiO2. Both the NPs proved to have considerable DPPH free radical scavenging activities.

Membrane fouling is an ongoing challenge in the membrane filtration process. Herein, a photocatalytic membrane comprising a reactive layer was fabricated by engineering partially reduced graphene oxide/Ag nanoparticles/MIL-88A (prGO/Ag/M88A, pGAM) photocatalysts on the PVDF substrate membranes. Benefiting from the high conductivity of prGO and the surface plasmon resonance (SPR) effect of Ag nanoparticles (Ag NPs), the photo-sensitivity of the prGO/Ag/M88A is significantly enhanced. Compared to the membrane in the dark condition, the pGAM membrane displayed an enhanced dye removal efficiency (∼99.7%) and significantly improved permeability (∼189 L·m−2·h−1 bar−1) towards dye contaminants based on the synergistic filtration/photo-Fenton processes. Significantly, the membrane retained high perm-selectivity after 10 cyclic runs (183 L·m−2·h−1 bar−1 of permeability and 98.1% of dye removal), and its nano-channel structure did not collapse under high pressure (0.1–0.4 MPa). The membrane also exhibits antifouling properties with a high water flux recovery of more than 90%. In addition, the pGAM membrane exhibited a high MB degradation efficiency (∼90%) when it is directly used as a photocatalyst in the photo-Fenton system. The mechanism of the self-cleaning is also proposed through quenching experiments. The results of this study demonstrate that this self-cleaning membrane has huge promise for membrane anti-fouling and wastewater remediation.

Surface plasmon resonance (SPR) is used to infer information about a sample that is in contact with an Au-coated glass slide coupled to the SPR prism. Shifts in the angle of the "SPR minimum reflection" can be related to changes in the refractive index (and/or thickness) of the sample that is in contact with the Au film, which can then be used to determine the concentration of an analyte in that sample. Here, we show that by depositing a layer of poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAm-co-AAc)] microgel on the SPR's Au film, with a subsequent layer of Au deposited on top of the microgels, the sensitivity of SPR to changes in solution properties can be enhanced. We investigated the sensitivity of the SPR to changes in the temperature of water in contact with the SPR's Au film as a function of the microgel immobilization density and the thickness of the Au layer deposited on the microgel layer. The data revealed that the SPR's Au film densely coated with microgels, with 5 nm of Au deposited, exhibited the maximal enhancement. The plasmon coupling effect between the additional Au film on the microgels and the SPR's Au film was further confirmed by 3D finite difference time domain simulations.

Electrochemistry exploits local current heterogeneities at various scales ranging from the micrometer to the nanometer. The last decade has witnessed unprecedented progress in the development of a wide range of electroanalytical techniques allowing to reveal and quantify such heterogeneity through multiscale and multifonctionnal operando probing of electrochemical processes. However most of these advanced electrochemical imaging techniques, employing scanning probes, suffer from either low imaging throughput or limited imaging size. In parallel, optical microscopies, which can image a wide field of view in a single snapshot, have made considerable progress in terms of sensitivity, resolution and implementation of detection modes. Optical microscopies are then mature enough to propose, with basic bench equipment, to probe in a non destructive way a wide range of optical (and therefore structural) properties of a material in situ, in real time: under operating conditions. They offer promising alternative strategies for quantitative high-resolution imaging of electrochemistry. The first sections recall the optical properties of materials and how they can be probed optically. They discuss fluorescence, Raman, surface plasmon resonance, scattering or refractive index. Then the different optical microscopes used to image electrochemical processes are examined along with some strategies to extract quantitative electrochemical information from optical images. Finally the last section reviews some examples of in situ imaging, at micro- to nanometer resolution, and quantification of electrochemical processes ranging from solution diffusion to the conversion of molecular interfaces or solids., Comment: 66 pages, 23 figures. To be published in Encyclopedia of Electrochemistry

Model light-confining Tamm plasmon cavities based on gold-coated nanoporous anodic alumina photonic crystals (TMM-NAA-PCs) with spectrally tunable resonance bands were engineered. Laplacian and Lorentzian NAA-PCs produced by a modified Gaussian-like pulse anodization approach showed well-resolved, high-quality photonic stopbands, the position of which was precisely controlled across the visible spectrum by the periodicity in the input anodization profile. These PC structures were used as a platform material to develop highly reflective distributed Bragg mirrors, the top sides of which were coated with a thin gold film. The resulting nanoporous hybrid plasmonic-photonic crystals showed strong light-confining properties attributed to Tamm plasmon resonances at three specific positions of the visible spectrum. These structures achieved high sensitivity to changes in refractive index, with a sensitivity of ∼106 nm RIU-1. The optical sensitivity of TMM-NAA-PCs was assessed in real time, using a model chemically selective binding interaction between thiol-containing molecules and gold. The optical sensitivity was found to rely linearly on the spectral position of the Tamm resonance band, for both Laplacian and Lorentzian TMM-NAA-PCs. The density of self-assembled monolayers of thiol-containing analyte molecules formed on the surface of the metallic film directly contributes to the dependence of sensitivity on TMM resonance position in these optical transducers. Our findings provide opportunities to integrate TMM modes in NAA-based photonic crystal structures, with promising potential for optical technologies and applications requiring high-quality surface plasmon resonance bands.

Photocatalytic nitrogen reduction for the green synthesis of ammonia at ambient conditions has been slowed by the narrow light harvesting range, low activity and high charge recombination of photocatalysts. Plasmonic semiconducting nanomaterials are becoming the promising candidates for nitrogen photofixation because of the broad absorption spectrum, rich defects and hot carriers. In the present study, plasmonic SrMoO4 is developed by regulating the concentration of oxygen vacancies that are accompanied in the reduction process from Mo6+ to Mo5+. The stable and tunable localized surface plasmon resonance (LSPR) absorption in visible and near infrared light range makes the wide bandgap SrMoO4 utilize the solar energy more efficiently. Energetic electrons from both the intrinsic band excitation and the LSPR excitation enable the reduction of dinitrogen molecules thermodynamically in ultrapure water to ammonia. This work provides a unique clue to design efficient photocatalysts for nitrogen fixation.

Nanofunctional photocatalysts are attractive materials in solar energy transformation for environmental protection and green energy source generation. TiO2 nanoparticles are the most prospective photocatalysts due to the high photoactive property. In this paper, Ag nanoparticle-sensitized TiO2 nanotube arrays (Ag/TiO2 NTAs) were constructed as the photoelectrochemical platform for pollutant removal and hydrogen generation. TiO2 NTAs were firstly obtained by the anodization method, and carbon layer was formed by the hydrothermal carbonization of glucose in different concentrations, and then Ag nanoparticles were deposited by carbon reduction of Ag+. Ag/TiO2 NTAs could effectively decompose organic dye molecules and remove toxic heavy metal ions. The samples also could achieve visible light photocurrent and hydrogen generation. The surface plasmon resonance absorption and electron transfer path of Ag nanoparticles benefit photochemical performance improvement of TiO2 NTAs. The construction of multifunctional platform of Ag/TiO2 NTAs would cause extensive response and focus in the synergistic applications of semiconductor photocatalysts.

Increasing the charge separation and the utilization efficiency of sunlight are essential factors in a photocatalytic process. In this study, we prepared crystalline N-CQDs@W18O49 heterostructures, through the in situ growth of W18O49 nanocrystals on nitrogen-doped carbon quantum dots (N-CQDs). N-CQDs@W18O49 nanocomposites showed high activity in the photodegradation of ciprofloxacin (CIP) and methyl orange (MO). The photodegradation activity of the optimized N-CQDs@W18O49-5 sample was four times higher than that of W18O49 under ultraviolet-visible (UV–vis) light irradiation. The photodegradation activity of N-CQDs@W18O49-5 sample was two times higher than that of W18O49 under near-infrared (NIR) light irradiation. The enhanced photosensitivity of the nanocomposites was attributed to the promotion of charge separation by N-CQDs and the local surface plasmon resonance (LSPR) effect of W18O49 under NIR light irradiation. This work provides a promising approach for designing and manufacturing photocatalysts with full-spectral responsiveness and improved charge separation.

Biosensors need to meet the rising food industry demand for sensitive, selective, safe, and fast food safety quality control. Disposable colorimetric sensors based on gold nanoparticles (AuNPs) and localized surface plasmon resonance are low-cost and easy-to-perform devices intended for rapid point-of-need measurements. Recent studies demonstrate various facile and versatile AuNPs-based analytical platforms for the detection of bacteria and their toxins in milk, meat, and other foods. In this review, we introduce the general characteristics and mechanisms of AuNPs calorimetric biosensors, and highlight optimizations needed to strengthen and improve the quality of devices for their application in food matrices.

Surface-enhanced Raman scattering (SERS)-based cancer diagnostics is an important analytical tool in early detection of cancer. Current work in SERS focuses on plasmonic nanomaterials that suffer from coagulation, selectivity, and adverse biocompatibility when used in vitro, limiting this research to stand-alone biomolecule sensing. Here we introduce a label-free, biocompatible, ZnO-based, 3D semiconductor quantum probe as a pathway for in vitro diagnosis of cancer. By reducing size of the probes to quantum scale, we observed a unique phenomenon of exponential increase in the SERS enhancement up to ~106 at nanomolar concentration. The quantum probes are decorated on a nano-dendrite platform functionalized for cell adhesion, proliferation, and label-free application. The quantum probes demonstrate discrimination of cancerous and non-cancerous cells along with biomolecular sensing of DNA, RNA, proteins and lipids in vitro. The limit of detection is up to a single-cell-level detection., Surface enhanced Raman scattering is a bio-analytical tool and the development and optimisation of probes is an active area of investigation. Here, the authors report on the development and testing of biocompatible semiconductor zinc oxide quantum probes on a platform for cell adhesion and analysis.

The generation of surface waveguide modes in telecommunication-grade optical fibers is highly desirable, since it would enable the development of novel all-fiber devices with high performance. Herein, we carry out a comprehensive theoretical investigation on the intrinsic excitation mechanism and sensing performance of fiber-optic surface waveguide modes supported by a tilted fiber grating (TFG) with nanometric-scale gold and $ \operatorname{TiO_{2}}$ films. The results reveal that both P- and S-polarized surface waveguide modes originate from the mode transition tuned by the Au- $ \operatorname{TiO}_{2}$ composite, including inter mode transition associated with two adjacent modes and intra mode transition only related to the mode itself. During the mode transition, the power carried by cladding modes is absorbed by the Au- $ \operatorname{TiO}_{2}$ composite, thereby yielding a strong surface-localized evanescent field that is sensitive to external medium. It is found that for both polarizations the surface waveguide modes induced by the inter/intra mode transition present almost the same refractometric sensitivity, but with the P-polarization ( $ 605.6 \, nm/RIU$ ) being more sensitive than the S-counterpart ( $ 339.2 \, nm/RIU$ ), the state-of-the-art surface plasmon resonance ( $ 539.7 \, nm/RIU$ ), and also the approach enhanced by high-refractive-index film ( $ 7.4 \, nm/RIU$ ). The results attained here represent a breakthrough since they would open new pathways toward single molecular detection.

Al nanoparticles composited with TiO2 (Al-NPs/TiO2) has drawn considerable attention over the years due to the localized surface plasmon resonance (LSPR) effect of Al-NPs can significantly enhance the photocatalytic efficiency of TiO2. However, most of the Al-NPs were obtained on Al substrates which limited its practical application. Herein, the isolated Al-NPs were composited together with the TiO2 by using glutathione (GSH) as linking bridge in aqueous environment. Finite difference time domain (FDTD) simulation was used to reveal the LSPR absorption of Al-NPs. The results show that the LSPR of 70 nm Al-NPs have a strong coupling with the TiO2 band gap. The X-ray diffraction analysis and TEM images show that our sample are pure, and the TiO2 indeed composite on the surface of Al-NPs under the action of GSH ligand bridge as seen in the TEM images. This ligand bridge was further verified by the FTIR and XPS measurements. The EPR experiment indicate the OH signals of Al-NPs/TiO2 are higher than that of pure TiO2 because of enhanced charge separation and transfer. The photodegradation experiment show that Al-NPs/TiO2 can rapidly degrade the concentration of methylene blue (MB) to zero under UV–vis light illumination in 70 min. All the above results indicate that the Al-NPs can significantly enhance the photocatalytic efficiency of TiO2 which due to the LSPR effect of Al.

The ability to detect and characterize drug binding to a target protein is of high priority in drug discovery research. However, there are inherent challenges when the target of interest is an integral membrane protein (IMP). Assuming successful purification of the IMP, traditional approaches for measuring binding such as surface plasmon resonance (SPR) and fluorescence resonance energy transfer (FRET) have been proven valuable. However, the mass dependence of SPR signals may preclude the detection of binding events when the ligand has a significantly smaller mass than the target protein. In FRET-based experiments, protein labeling through modification may inadvertently alter protein dynamics. Graphene Bio-Electronic Sensing Technology (GBEST) aims to overcome these challenges. Label-free characterization takes place in a microfluidic chamber wherein a fluid lipid membrane is reconstituted directly above the GBEST sensor surface. By leveraging the high conductivity, sensitivity, and electrical properties of monolayer graphene, minute changes in electrostatic charges arising from the binding and unbinding of a ligand to a native IMP target can be detected in real time and in a mass-independent manner. Using crude membrane fractions prepared from cells overexpressing monocarboxylate transporter 1 (MCT1), we demonstrate the ability to (1) form a fluid lipid bilayer enriched with MCT1 directly on top of the GBEST sensor and (2) obtain kinetic binding data for an anti-MCT1 antibody. Further development of this novel technology will enable characterization of target engagement by both low- and high-molecular-weight drug candidates to native IMP targets in a physiologically relevant membrane environment.

Gold nanostar (AuNS) particles, characterized by pointed tips emerging from a central core, exhibit localized surface plasmon resonance (LSPR) with strongly amplified electric field upon illumination. Compared to Au nanospheres and nanorods, the absorbance is enhanced with the absorption band extending from 500 to above 1000 nm. However, they are easily reshaped by Ostwald ripening and therefore difficult to use in any application. This study shows that the AuNS particles can be effectively stabilized by encapsulation with TiO2 using a low temperature method. The synthesis parameters and capping solution were optimized to form nanostars. The encapsulated Au nanoparticles promoted the aerobic oxidation of benzyl alcohol to benzaldehyde at ambient temperature under visible light irradiation. AuNS@TiO2 showed significantly higher photocatalytic activity than Au nanospheres, Au nanorods or bulk TiO2 due to its enhanced LSPR. Encapsulation of the colloidal nanoparticles with TiO2 confers robustness to the resulting heterogeneous catalyst with retention of the metal particle size, morphology and associated LSPR properties.

The localized surface plasmon resonance (LSPR) absorption peaks of semiconductor nanocrystals are mainly concentrated in the infrared band, and the absorption characteristics can be controlled by the amount of element doping. The coupling of upconversion nanocrystals (UCNPs) and semiconductor nanocrystals can improve the upconversion luminescence (UCL) of rare-earth ions. Here, the LSPR absorption and morphology of the semiconductor nanocrystalline TiO2: W were adjusted by using ammonium fluoride during synthesis. Significant absorption enhancement of TiO2: W in the near-infrared region was obtained to enhance the UCL of NaYF4: Yb3+, Er3+. The Glass/NaYF4: Yb3+, Er3+/TiO2: W@SiO2 layered structure films were fabricated through spin coating. Compared with Glass/NaYF4: Yb3+, Er3+, the green and red lights of the Glass/NaYF4: Yb3+, Er3+/TiO2: W@SiO2 films were enhanced by 15.9 and 17.8 times, respectively. The UCL enhancement of Glass/NaYF4: Yb3+, Er3+/TiO2: W@SiO2 was derived from the LSPR property of TiO2: W through the enhancement of the excitation. The present work is important for possible applications of these layered structures as biomarkers, photocatalysts, flexible materials, and photoluminescence display panels.

International audience; Adsorption of five different hyperbranched arabinogalactan-protein (AGP) fractions from Acacia senegal gum was thoroughly studied at the solid-liquid interface using a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), and atomic force microscopy (AFM). The impact of the protein/sugar ratio, molecular weight, and aggregation state on the adsorption capacity was investigated by studying AGP fractions with different structural and biochemical features. Adsorption on a solid surface would be primarily driven by the protein moiety of the AGPs through hydrophobic forces and electrostatic interactions. Increasing ionic strength allows the decrease in electrostatic repulsions and, therefore, the formation of high-coverage films with aggregates on the surface. However, the maximum adsorption capacity was not reached by fractions with a higher protein content but by a fraction that contains an average protein quantity and presents a high content of high-molecular-weight AGPs. The results of this thorough study highlighted that the AGP surface adsorption process would depend not only on the protein moiety and high-molecular-weight AGP content but also on other parameters such as the structural accessibility of proteins, the molecular weight distribution, and the AGP flexibility, allowing structural rearrangements on the surface and spreading to form a viscoelastic film

Purpose This paper aims to study the sensitivity enhancement effect of the gold nanorod on fiber surface plasmon resonance (SPR) sensor. It proposes modeling the sensing effects of fiber SPR sensor decorated with metal nanoparticles. By using simulation and experiment, the sensitivity enhancement effect of the gold nanorod was studied and demonstrated. Design/methodology/approach The paper opted for an exploratory study using simulation approach of finite-difference time-domain. Specifically, the effect of ratios and aspect ratios of gold nanorod on sensing performance are investigated theoretically. Based on the mathematical models, the validation experiments by using the gold nanorod with the aspect ratios of 5.1 were done to verify the sensitivity enhancement effect of the gold nanorod. Findings In conclusion, it is evident that with the increases of the aspect ratios, the sensing sensitivity of the refractive index increases first, then gradually stabilizes or decreases. After parameter optimization, the ratios and aspect ratios of gold nanorod are chosen to be 8 nm and 12.5, respectively, which makes the optimal refractive index sensitivity of 4465.53 nm/RIU be realized. In addition, the validation experiments by using the gold nanorod with the aspect ratios of 5.1 verify the sensitivity enhancement effect of the gold nanorods. Originality/value This paper proposes and demonstrates a new method for the sensitivity enhancement of fiber SPR sensor. After parameter optimization, the maximum sensitivity of 4465.53 nm/RIU was achieved by using 8 nm gold nanorods with the aspect ratios of 12.5. To verify the sensitivity enhancement of the gold nanorods, the authors also did the validation experiments. The testing results indicated that after the decoration of the gold nanorods, the sensitivity of the sensing probe increases from 2190.57 nm/RIU to 2693.24 nm/RIU, which demonstrates the sensitivity enhancement effect of the gold nanorods.

One-pot wet chemistry strategy via an ultrasonic hydrothermal in situ procedure has been applied to construct a serial of monoclinic Cu-coupled rugby-shaped hierarchical BiVO4 sosoloids with diverse Cu coupling amount. The SEM and TEM images indicate that the coupled copper content had no effect on the crystalline phase of bismuth vanadate, but it had an important effect on its morphology, which changed from seed shape to rugby shape. As demonstrated by XRD and XPS analysis, it was found parts of Cu2+ doped into the BiVO4 monoclinic lattice to make it self-assemble into a rugby-shaped solid solution and another part of Cu loaded on the surface of BiVO4 sosoloids. Under visible light illumination (>420 nm), as-obtained 1.5% Cu-BiVO4 sosoloid had a degradation rate reached 99% for RhB within 50 min, and its photodegradation activity was 5.6 times higher than that of pure BiVO4. and remained above 96% after 5 cycles. The enhanced photocatalytic efficiency of xCu-BiVO4 sosoloids may be mainly attributed to the superior Cu-coupled rugby-shaped BiVO4 sosoloid microstructures with large specific surface area. During the ultrasonic hydrothermal process, the doping Cu2+ can effectively replace V5+ ions to form a virtual energy level accompanied by V4+, which can become a trapping center and capture the excitation electrons on the conduction band. The surface plasmon resonance (SPR) effect of copper can effectively expand the range of visible light response. On the other hand, d orbital electrons of Cu can quickly transfer to the BiVO4 conduction band according to Fermi energy level, so as to promote the interfacial charge transfer process, thus inhibiting the recombination of photo-generated carriers and improving the photocatalytic activity. Based on the synergetic effects of components in degradation of organic contaminants, this study provides a promising photocatalytic material driven by visible light for environmental remediation and protection.

Background Applied nanomaterials in targeted drug delivery have received increased attention due to tangible advantages, including enhanced cell adhesion and internalization, controlled targeted release, convenient detection in the body, enhanced biodegradation, etc. Furthermore, conjugation of the biologically active ingredients with the drug-containing nanocarriers (nanobioconjugates) has realized impressive opportunities in targeted therapy. Among diverse nanostructures, halloysite nanotubes (NHTs) with a rolled multilayer structure offer great possibilities for drug encapsulation and controlled release. The presence of a strong hydrogen bond network between the rolled HNT layers enables the controlled release of the encapsulated drug molecules through the modulation of hydrogen bonding either in acidic conditions or at higher temperatures. The latter can be conveniently achieved through the photothermal effect via the incorporation of plasmonic nanoparticles. Results The developed nanotherapeutic integrated natural halloysite nanotubes (HNTs) as a carrier; gold nanoparticles (AuNPs) for selective release; docetaxel (DTX) as a cytotoxic anticancer agent; human IgG1 sortilin 2D8-E3 monoclonal antibody (SORT) for selective targeting; and 3-chloropropyltrimethoxysilane as a linker for antibody attachment that also enhances the hydrophobicity of DTX@HNT/Au-SORT and minimizes DTX leaching in body’s internal environment. HNTs efficiently store DTX at room temperature and release it at higher temperatures via disruption of interlayer hydrogen bonding. The role of the physical expansion and disruption of the interlayer hydrogen bonding in HNTs for the controlled DTX release has been studied by dynamic light scattering (DLS), electron microscopy (EM), and differential scanning calorimetry (DSC) at different pH conditions. HNT interlayer bond disruption has been confirmed to take place at a much lower temperature (44 °C) at low pH vs. 88 °C, at neutral pH thus enabling the effective drug release by DTX@HNT/Au-SORT through plasmonic photothermal therapy (PPTT) by light interaction with localized plasmon resonance (LSPR) of AuNPs incorporated into the HNT pores. Conclusions Selective ovarian tumor targeting was accomplished, demonstrating practical efficiency of the designed nanocomposite therapeutic, DTX@HNT/Au-SORT. The antitumor activity of DTX@HNT/Au-SORT (apoptosis of 90 ± 0.3%) was confirmed by in vitro experiments using a caov-4 (ATCC HTB76) cell line (sortilin expression > 70%) that was successfully targeted by the sortilin 2D8-E3 mAb, tagged on the DTX@HNT/Au. Graphic abstract

Steam explosion (SE) was a friendly environmentally pretreatment method. In this study, the effect of steam explosion (SE) pretreatment on structure and α-glucosidase inhibitory activity of Ampelopsis grossedentata polysaccharides was evaluated. Two novel polysaccharides (AGP and AGP-SE) were extracted, isolated, purified and analyzed by NMR, FT-IR and methylation. The results indicated that AGP mainly consisted of Rha, Xyl, Glc, and Ara with a molecular weight of 2.74 × 103 kDa and AGP-SE mainly consisted of Man, Ara, and Gal with a molecular weight of 2.14 × 103 kDa. Furthermore, the backbone of AGP and AGP-SE were mainly composed of 5)-Araf-(1→, -Glcp-(1→, 6)-Glcp-(1→, 6)-Galp-(1→, 3,6)-Manp-(1→, and 2,3,6)-Glcp-(1→. Finally, we demonstrated that all polysaccharides exhibited obviously α-glucosidase inhibition activity and mixed type inhibition. AGP-SE had better α-glucosidase inhibition activity and the binding affinity KD on α-glucosidase by using Surface Plasmon Resonance (SPR) than AGP. Overall, SE pretreatment is an effective method for extracting polysaccharide and provides a new idea into the improvement of biological activity.

Due to its appropriate bandgap (∼2.4 eV) and efficient light absorption, bismuth vanadate (BiVO4) shows promising photocatalysis activity. However, the charge carrier recombination and poor electron transmission often induce poor photocatalytic performance. Herein, we report a new method to in-situ synthesize non-noble metal Bi decorated mulberry-like BiVO4 by a two-step calcination process. Comprehensive characterizations reveal that non-noble metal Bi nanoparticles grown in-situ on BiVO4 result in the red-shift of the absorbance edge, greatly extending the light absorption from the ultraviolet into the near-infrared region. The surface plasmon resonance excitation of Bi nanoparticles and synergetic effects between Bi and BiVO4 effectively improve the photocatalytic efficiency and promote the separation of photoinduced electron-hole pairs in mulberry-like BiVO4. Density functional theory (DFT) calculation results further verify that the electrons are transferred from Bi to BiVO4 and the formation of OH radical in Bi/BiVO4 is attributed to the lower simulated free energy, which supports our experimental outcomes. This work provides a novel strategy to enhance light absorption and promote efficient solar utilization of photocatalysts for practical applications.

A new dissolved oxygen sensor based on optical fiber surface plasmon resonance (SPR) theory and the mechanism of oxygen transporting by hemoglobin was proposed and demonstrated. Gold film was coated on the surface of the optical fiber sensing area, and hemoglobin was modified on the surface of the gold film. The experimental results show that the sensor has good linearity and the limit of detection (LOD) of the sensor is 0.03 mg/L. In addition, in order to enhance the sensitivity of the sensor, the carbon nanotubes were modified on the surface of the gold film of the fiber, and then the hemoglobin was modified in the outermost layer. Through experiments, it was found that the sensitivity of the sensor which modified with carbon nanotubes is 2.8-folds higher than that only modified hemoglobin, the linearity is better, and the LOD is reduced to 0.01 mg/L.

To explore in vivo application of quantum dots (QDs), it is essential to understand the dynamics and energetics of interactions between QDs and proteins. Here, surface plasmon resonance (SPR) and molecular docking were employed to investigate the kinetics and thermodynamics of interactions between human serum albumin (HSA) and CdTe QDs (~3 nm) functionalized with mercaptopropionic acid (MPA) or thioglycolic acid (TGA). Kinetic analysis showed that HSA–QD interactions involved transition-complex formation. Despite the structural similarities between MPA and TGA, the [HSA−CdTe@TGA]‡ formation by association of free HSA and QDs demanded 70% more energy and higher entropic gain (Ea−TGA‡= 65.10 and T∆Sa−TGA‡= 28.62 kJ mol−1) than the formation of [HSA−CdTe@MPA]‡ (Ea−MPA‡ = 38.13 and T∆Sa−MPA‡ = 0.53kJ mol−1). While the [HSA−CdTe@MPA]° dissociation required higher energy and lower entropy loss (Ed−MPA‡ = 49.96 and T∆Sd−MPA‡ = − 32.18kJ mol−1) than the [HSA−CdTe@TGA]° dissociation (Ed−TGA‡= 30.78 and T∆Sd−TGA‡= − 51.12 kJ mol−1). The stability of [HSA−QDs]° was independent of the temperature and functionalizing group. However, the enthalpic and entropic components were highly affected by the substitution of MPA (ΔH° = − 11.83 and TΔS° = 32.72 kJ mol−1) with TGA (ΔH° = 34.31 and TΔS° = 79.73 kJ mol−1). Furthermore, molecular docking results indicated that the metal site on the QDs contributes to the stabilization of [HSA−QDs]°. Therefore, differences in QD functionalization and surface coverage densities can alter the HSA–QD interaction, thus their application.

By placing a single Au nanoparticle on the surface of a cadmium sulfide (CdS) nanowire, we demonstrate strong coupling of localized surface plasmon resonance (LSPR) modes in the nanoparticle and whispering gallery modes (WGMs) in the nanowire. For a 50-nm-diameter Au-nanosphere particle, strong coupling occurs when the nanowire diameter is between 300 and 600 nm, with a mode splitting up to 80 meV. Using a temperature-induced spectral shift of the resonance wavelength, we also observe the anticrossing behavior in the strongly coupled system. In addition, since the Au nanosphere has spherical symmetry, the supported LSPR mode can be selectively coupled with transverse electric (TE) and transverse magnetic (TM) WGMs in the nanowire. The ultracompact strong-coupling system shown here may provide a versatile platform for studying hybrid “photon–plasmon” nanolasers, nonlinear optical devices, and nanosensors.

Refereed/Peer-reviewed A multifunction, high-sensitivity, and temperature-compensated optical fiber DNA hybridization sensor combining surface plasmon resonance (SPR) and Mach–Zehnder interference (MZI) has been designed and implemented. We demonstrate, for the first time to our knowledge, the dual-parameter measurement of temperature and refractive index (RI) by simultaneously using SPR and MZI in a simple single-mode fiber (SMF)–no-core fiber (NCF)–SMF structure. The experimental results show RI sensitivities of 930 and 1899 nm/RIU and temperature sensitivities of 0.4 and −1.4 nm/°C for the MZI and SPR, respectively. We demonstrate a sensitivity matrix used to simultaneously detect both parameters, solving the problem of temperature interference of RI variation-based biosensors. In addition, the sensor can also distinguish biological binding events by detecting the localized RI changes at the fiber’s surface. We realize label-free sensing of DNA hybridization detection by immobilizing probe DNA (pDNA) onto the fiber as the probe to capture complementary DNA (cDNA). The experimental results show that the sensor can qualitatively detect cDNA after temperature compensation, and the limit of detection (LOD) of the sensor reaches 80 nM. The proposed sensor has advantages of high sensitivity, real time, low cost, temperature compensation, and low detection limit and is suitable for in situ monitoring, high-precision sensing of DNA molecules, and other related fields, such as gene diagnosis, kinship judgment, environmental monitoring, and so on.

The production of a high-sensitivity surface Plasmon resonance (SPR) sensor depends on a few main factors, such as metal thin film types and thicknesses, light coupling techniques and acceptable EM wave polarization modes. This work is carried out to investigate the impact on the SPR characteristics of noble metal thicknesses, namely gold and silver, for optical sensor applications. To excite surface Plasmon polaritons (SPP), a Kretschmann prism coupling was used. The thicknesses of noble metal thin films were varied between t=30nm and 60nm. The characteristics of SPR peaks such as Q-factor and FWHM were studied in SPR signal analyses. In comparison with silver, Q-factor results showed an outstanding optical property of gold at t= 40 nm due to its high Q-factor values, which confirms its ability to produce excellent SPP quantities. In conclusion, gold noble metal at t= 40nm is capable of producing optimum SPR. In the development of the highly sensitive SPR sensor, this excellent criterion put gold as a spectacular candidate for optical sensor applications.

Photoelectrochemical (PEC) hydrogen evolution has been acknowledged as a promising "green" technique to convert solar energy into clean chemical fuel. Photoanodes play a key role in determining the performance of PEC systems, spurring numerous efforts to develop advanced materials as well as structures to improve the photoconversion efficiency. In this work, we report the rational design of a plasmonic hierarchical nanorod array, composed of oriented one-dimensional (1D) CdS nanorods decorated with a uniformly wrapped graphite-like carbon (CPDA) layer and Au nanoparticles (Au NPs), as highly efficient photoanode materials. An interfacial in situ reduction-graphitization method has been conducted to prepare the CdS/CPDA/Au nanoarchitecture, where polydopamine (PDA) coating was used as a C source and a reductant. The CdS/CPDA/Au nanoarray photoanode demonstrates superior photoconversion efficiency with a photocurrent density of 8.74 mA/cm2 and an IPCE value (480 nm) of 30.2% (at 1.23 V vs RHE), under simulated sunlight irradiation, which are 12.7 and 13.5 times higher than pristine CdS. The significant enhancement of PEC performance is mainly benefited from the increase of the entire quantum yield and efficiency due to the formation of a Schottky rectifier, localized surface plasmon resonance (LSPR)-enhanced light absorption, and promoted hot-electron injection from interlayered graphene-like carbon. More importantly, thanks to the inhibited charge carrier recombination process and transferred oxidation reaction sites, the fabricated CdS/CPDA/Au photoelectrode exhibits lengthened electron lifetimes and better photostability, illustrating its wonderful potential for future PEC application.

Fluorescence imaging is a major driver of discovery in biology, and an invaluable asset in clinical diagnostics. To overcome quenching limitations of conventional fluorescent dyes and further improve intensity, nanoparticle-based constructs have been the subject of intense investigation, and within this realm, dye-doped silica-coated nanoparticles have garnered significant attention. Despite their growing popularity in research, fluorescent silica nanoparticles suffer from a significant flaw. The degradation of these nanoparticles in biological media by hydrolytic dissolution is underreported, leading to serious misinterpretations, and limiting their applicability for live cell and in vivo imaging. Here, the development of an ultra-stable, dye-embedded, silica-coated metal nanoparticle is reported, and its superior performance in long-term live cell imaging is demonstrated. While conventional dye-doped silica nanoparticles begin to degrade within an hour in aqueous media, by leveraging a modified liquid calcination process, this new construct is shown to be stable for at least 24 h. The stability of this metal-enhanced fluorescent probe in biologically relevant temperatures and media, and its demonstrated utility for cell imaging, paves the way for its future adoption in biomedical research.

In this short communication, we propose a surface plasmon resonance (SPR) sensor based on a ZnO / Au hybrid thin-film material structure and experimentally investigate its sensitivity improvement. The Kretschmann-based SPR sensor utilizes ZnO thin films and nanostructures for performance enhancement. The advancement in SPR technology relies on a low-cost, high-sensitivity, and high-selectivity sensor. Metal oxide (MO) has been incorporated into the SPR sensor to be used for detection of biological and chemical compounds. ZnO as one of the metal oxides is an attractive material due to its unique physical and optical properties. Numerous techniques for fabrication and characterization of ZnO on SPR gold substrate have been studied. The mechanism for gas and biomolecule detection depends on their interaction with the ZnO surface, which is mainly attributed to the high isoelectric point of ZnO. There are several types of ZnO nanostructures which have been employed for SPR application based on the Kretschmann configuration. In the future, the thin film and nanostructures of ZnO could be a potential application for miniature design, robust, high sensitivity, and a low-cost portable type of SPR biosensor to be used for on-site testing in a real-time and label-free manner. The present work includes the application of a developed SPR setup for gas sensing at room temperature using a specially designed gas cell. The change in the optical properties of dielectric layers (ZnO) with adsorption of gases (NO2) in order to develop an optical sensor has been presented. The obtained results emphasize the applications of an SPR setup for the study of interaction of adsorbed gas molecules, with dielectrics and gas sensing.

The growth of surface-attached single-stranded deoxyribonucleic acid (ssDNA) chains is monitored in situ using an evanescent wave optical biosensor that combines surface plasmon resonance (SPR) and optical waveguide spectroscopy (OWS). The "grafting-from" growth of ssDNA chains is facilitated by rolling circle amplification (RCA), and the gradual prolongation of ssDNA chains anchored to a gold sensor surface is optically tracked in time. At a sufficient density of the polymer chains, the ssDNA takes on a brush architecture with a thickness exceeding 10 μm, supporting a spectrum of guided optical waves traveling along the metallic sensor surface. The simultaneous probing of this interface with the confined optical field of surface plasmons and additional more delocalized dielectric optical waveguide modes enables accurate in situ measurement of the ssDNA brush thickness, polymer volume content, and density gradients. We report for the first time on the utilization of the SPR/OWS technique for the measurement of the RCA speed on a solid surface that can be compared to that in bulk solutions. In addition, the control of ssDNA brush properties by changing the grafting density and ionic strength and post-modification via affinity reaction with complementary short ssDNA staples is discussed. These observations may provide important leads for tailoring RCA toward sensitive and rapid assays in affinity-based biosensors.

An ultra-wide detection range refractive-index sensor based on surface plasmon resonance (SPR) with photonic crystal fiber (PCF) is designed and discussed. The central air-hole of the fiber is injected with the analyte. The properties of refractive-index sensor are investigated with different structure parameters. Simulation results show that the proposed sensor has an ultra-wide detection range from 1.29 to 1.49. The refractive index sensitivities of x-polarized and y-polarized core mode are −4156.82 nm/RIU and −3703.64 nm/RIU respectively, and the corresponding linear fitting degrees are 0.99598 and 0.99236. The designed refractive-index sensor with ultra-wide detection range has a great potential in the fields of biology, chemistry, environment and medicine.

The colloidal Langmuir–Blodgett coating process is used to fabricate Au-covered silica sphere monolayer (Au film over silica nanosphere (AuFON)) and study the effects of silica diameter on surface plasmon resonance (SPR) sensing sensitivity. The resulting hexagonal close-packed (HCP) monolayers are prepared with silica sphere diameters of 200, 400, 700, and 1000 nm. In SPR sensing applications, the optical properties of Au-covered silica sphere monolayer are evaluated by measuring normal-incidence reflection spectra and sensing tests. The high sensitivity (nm/RIU) is observed in silica sphere diameter (1000 > 700 > 400 > 200 nm) and plasmon mode (dipole > Fano resonance (FR) > and high order) while the highest sensitivity is 968 nm/RIU (dipole mode, 1000 nm of silica sphere diameter). 3-D Finite Difference Time Domain (FDTD) simulation shows a sensitivity trend similar to the experimental results.

Optical sensors based on surface plasmon resonance (SPR) in the attenuated total reflection (ATR) configuration in layered media have attracted considerable attention over the past decades owing to their ability of label free sensing in biomolecular interaction analysis, and highly sensitive detection of changes in refractive index and thickness, i.e. the optical thickness, of thin film adsorbates (thin film sensing). Furthermore, SPR is highly sensitive to the refractive index of the medium adjacent to the bare metal, and it allows for bulk sensing as well. When deposited at the metal/air interface, an adsorbed layer disturbs the highly localized, i.e. bound, wave at this interface and changes the plasmon resonance to allow for sensing in angular or wavelength interrogation and intensity measurement modes. A high degree of sensitivity is required for precise and efficient sensing, especially for biomolecular interaction analysis for early stage diagnostics; and besides conventional SPR (CSPR), several other configurations have been developed in recent years targeting sensitivity, including long-range SPR (LRSPR) and waveguide-coupled SPR (WGSPR) observed in MIM structures, referred here to by MIM modes, resulting from the coupling of SPRs at I/M interfaces, and Fano-type resonances occurring from broad and sharp modes coupling in layered structures. In our previous research, we demonstrated that MIM is better than CSPR for bulk sensing, and in this paper, we show that CSPR is better than MIM for thin film sensing for thicknesses of the sensing layer (SL) larger than 10 nm. We discuss and compare the sensitivity of CSPR and MIM for thin film sensing by using both experiments and theoretical calculations based on rigorous electromagnetic (EM) theory. We discuss in detail MIM modes coupling and anti-crossing, and we show that when a thin film adsorbate, i.e. a SL), is deposited on top of the outermost-layer of an optimized MIM structure, it modifies the characteristics of the coupled modes of the structure, and it reduces the electric field, both inside the SL and at the SL/air interface, and as a result, it decreases the sensitivity of the MIM versus the CSPR sensor. Our work is of critical importance to plasmonic mode coupling using MIM configurations, as well as to optical bio- and chemical-sensing.

The present work reported synthesis, characterization, and biocompatibility of starch encapsulated silver nanoparticles (St-PF-AgNPs) and their antibacterial activity. The synthesis of St-PF-AgNPs involved in two steps: (i) synthesis of the biogenic silver nanoparticles using the fungal extracts (PF-AgNPs); and, (ii) encapsulation of starch in PF-AgNPs (St-PF-AgNPs). The surface plasmon resonance was found at 420 nm for the PF-AgNPs while it was at 260 and 420 nm for the St-PF-AgNPs. FTIR spectrum demonstrated the capping and encapsulation of the fungal extracts and starch in PF-AgNPs and St-PF-AgNPs. The XRD and TEM-EDS confirmed the crystalline nature, spherical-shaped , and polydispersed- PF-AgNPs and St-PF-AgNPs with strong signals of Ag. The St-PF-AgNPs showed a Z-average size of 115.2 d.nm and zeta potential of -17.8 (mV) as indicated by DLS and zeta potentials. The cytotoxicity results demonstrated higher toxicity of PF-AgNPs than St-PF-AgNPs in HEK293 cells. The antibacterial activity of St-PF-AgNPs were higher than PF-AgNPs in S. aureus. Overall, this work concluded that the starch encapsulation significantly increased the antibacterial activity of PF-AgNPs and this opens a new avenue for the treatment of bacterial infections through the sustained release of PF-AgNPs to target pathogenic bacterial cells.

Graphene oxide (GO) with hydrophilic properties supports the scalable production of highly desirable material graphene. GO nanosheets were prepared with a modified Hummers method, whereas the oxidative cutting technique was used to synthesize graphene quantum dots (GQDs). The surface and structural morphology of both GO and GQDs were examined and compared. In GO, photoluminescence originated mainly due to the conductive electrons present in the sp2 localized sites and the excimer formation. In contrast, in GQDs, PL is increased due to numerous defects present on their surfaces. The pH plays a crucial role in tuning the blue and green PL of GQDs hence the optical properties. The developed GQDs with functional groups act as a solo reducing and stabilizing agent in producing the GQDs-silver nanoparticles (GQDs@AgNPs) hybrid structure, which exhibits strong surface plasmon resonance along with GQDs absorption. Further, GQDs alone support sensing of hydrogen peroxide (H2O2) in an aqueous medium, thus acting as a sensing probe like the GQDs@AgNPs nanohybrids.

A method to enable surface plasmon resonance (SPR) sensors to discriminate between bulk and surface-localized refractive index changes is demonstrated with modified gold-coated tilted fiber Bragg grating SPR sensors (TFBG-SPR). Without this capability, all high-resolution SPR sensors should be using reference channels and strict temperature control to prevent the contamination of the desired detection of surface-localized chemical or binding events by drift of the refractive index of the medium, in which the experiment is carried out. The very fine comb of high-quality-factor resonances of a TFBG-SPR device coupled to the large differential sensitivity of some of the resonances to various perturbations is used to measure unambiguously the refractive index changes within a surface layer thinner than 25 nm from those of the bulk surrounding. The enabling modification of the conventional TFBG-SPR is a reduction of the gold coating from its optimum value near 50-30 nm: at this lower thickness, a surface plasmon wave can still be excited by a limited number of cladding mode resonances, but at the same time, the metal is thin enough to allow modes away from the SPR to tunnel across the metal and probe the bulk RI value. Measurements and simulations of the deposition of a self-assembled monolayer of 1-dodecanethiol in ethanol show that the bulk refractive index changes as small as 0.0004 can be distinguished from the formation of a 1 nm thick coating on the surface of the fiber.

The present study involves the green synthesis of unmodified silver nanoparticles using the aqueous leaf extract of Mimosa diplotricha (AgNP-MD). This work highlights the reliable optical and electrochemical sensing of Hg2+ ion (5–45 μM) by AgNP-MD with high selectivity. Optical sensing was easily identified by the color change of AgNP-MD to colorless upon effective interaction of metal nanoparticles with mercuric ions, which is in accordance with the decrement in surface plasmon resonance (SPR) of nanoparticles. Electrochemical voltammetric sensing was performed using a platinum electrode modified with AgNP-MD (AgNP-MD-Pt). The limit of detection (LOD) of the developed green sensor for mercuric ions was calculated from differential pulse voltammetry (DPV) analysis as 1.46 μM. The applicability of unmodified AgNP-MD towards Hg2+ ions was inspected for the collected real water samples. Ultraviolet–visible (UV–vis) spectrophotometer, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques were used to characterize the synthesized AgNP-MD and AgNP-MD-Hg2+ complexation. Moreover, the catalytic potential of green synthesized AgNP-MD towards the reduction of methyl orange and methylene blue was also evaluated. Both the degradations were fast, completed within few minutes, and followed pseudo-first-order kinetics with good regression coefficients. To the best of our knowledge, this is the first report on the synthesis of AgNP-MD using MD extract and its multifunctional applications including the fields of sensors and catalysis.

[EN] In the current work, an energy-efficient solution combustion route is adopted to synthesize silver-modified ZnO nanomaterials having 1, 3, 5, and 7 mol% of silver content. The samples were characterized by different techniques to uncover the morphology, crystallinity, chemical state, and optical properties. The thermally stable, well-crystalline wurtzite phase of ZnO and cubic phase of silver was obtained in the synthesized samples. It was found that due to the surface plasmon resonance effect of silver there is an enhancement in the light absorption after the introduction of Ag in ZnO. Photocatalytic performances of all samples are analyzed by taking Cibacron Red and Triclopyr as model pollutants. It is observed that due to the surface plasmon resonance effect and formation of oxygen vacancies, Ag¿ZnO nanomaterials containing 7 mol% silver content showed the highest activity for both pollutants under UV illumination. The photoluminescence technique is used to detect the recombination of photoinduced charged species. The samples showed superior activity in the neutral medium as compared to the acidic and basic medium. The synthesized materials are highly beneficial for the energy-efficient removal of pollutants from the environment., Maharshi Dayanand University, Rohtak and University Grant Commission are acknowledged by NK and SY for financial assistance in form of Radha Krishnan Minor Project and Senior Research Fellowship respectively.

The present study explores a facile, non-toxic, and ecofriendly synthesis of biomolecules functionalized copper oxide nanoparticles (CuONPs) using Justicia gendarussa (J.gendarussa) leaf extract for the first time. The leaf extract was used as a potential capping and stabilising agent for the reduction of copper ions to CuONPs.The structure, morphology, elemental composition, and stability of the synthesised CuONPs were characterised using UV, FTIR, FESEM–EDX, TEM, and DLS analyses. The surface plasmon resonance (SPR) of the CuONPs exhibited a strong characteristic band at 340 nm. The capping of biomolecules in the synthesised CuONPs was confirmed by FTIR. The SEM and TEM analyses showed that the synthesised CuONPs were nano flower in shape and the size ranged between 10 and 15 nm. The existence of elements, Cu (56.70) and O (43.30), was confirmed by EDX analysis. The functionalised biomolecules of CuONPs exhibited bactericidal activity against both Gram negative and Gram positive pathogens. The photocatalytic ability of the CuONPs was tested against the textile dye, methylene blue (MB) using natural irradiation method. The results of this study revealed that the synthesised CuONPs proved to be an interesting candidate in wastewater treatment and biomedical applications.

Herein, we report the simultaneously application of surface plasmon resonance (SPR) spectroscopy and electrochemistry (EC) technology for the real-time quantitative investigation of heavy metal ions, with high selectivity and sensitivity. A surface of optical fiber coated over with nanometric gold film and then modified with a dithiol self-assembled monolayer of 1,6-hexanedithiol (HDT) was developed as the dual mode electrochemical-surface plasmon resonance (EC-SPR) optical fiber sensor. The limit of detection of the proposed sensor exposed in Hg2+ ions solution without and with the multiple cyclic voltammetry (CV) scans to activate the HDT monolayer can be improved from 0.47 μM to 0.22 μM. More importantly, the CV scans can activate the redox reaction of Hg2+ ions, and then easily strip the Hg2+ ions from the HDT monolayer to restore the active sites, and endow the designed sensor the characteristics of repeated use. Under simultaneous SPR monitoring, the differential pulse voltammetry (DPV) currents of HDT-functionalized optical fiber can also act as a microelectrode to develop electrochemical sensor platform for monitoring Cu2+, with a limit of detection of 94 nM and a dynamic range up to 90 μM. As a comparison, the EC-SPR sensor still has good analysis performance for both Hg2+ and Cu2+ ions in presence of Ni2+, Fe2+, Co2+, Pb2+, K+, among others. We therefore demonstrated that the proposed fiber-based EC-SPR sensor has the advantages of real-time, miniaturized, and cost-effective sensing, paving the way for environmental monitoring applications for on site inspection.

Toxic aggregates of amyloid-beta (Aβ) have importance in the pathology of Alzheimer's disease, and inhibition of aggregate formation is considered to be a promising strategy for drug development. Here, we report a simple and rapid surface plasmon resonance (SPR) assay method that can identify potential Aβ aggregation inhibitors. Our assay is based on the SPR shifting of the Aβ-gold nanoparticle (Aβ-GNP) aggregates by size under the influence of an Aβ aggregation inhibitor. This user-friendly assay features a short assay time with a low reagent consumption that can be easily adapted as a high-throughput screen. We demonstrated that an effective Aβ aggregation inhibitor induces the blue-shifted SPR peaks of the Aβ-GNP aggregates by hindering the formation of long fibrillar aggregates. Moreover, the blue shifting was correlated to the efficacy and concentrations of an Aβ aggregation inhibitor. Overall, our findings suggest that our simple SPR assay can be a powerful tool to screen small molecules targeting Aβ aggregation.

Abolition of bleaching as a sequential step in functionalization of flax fibers is a quite important issue for diminishing of the treatment steps, saving energy, lowering the chemical consumption and consequently reducing the final cost. Therefore, herein, functionalization of the scoured flax fibers in one-pot process is systematically presented, via straightforward insertion of silver nanoparticles (AgNPs) using two different reduction methods including internal and external reduction. Ag+ was reduced by using the functional groups of flax in the internal reduction, while, trisodium citrate was used as an external reducing agent in the external reduction method. Functionalization was performed to acquire a decorative yellowish color, ultraviolet (UV) protection and antimicrobial properties for flax fibers. The formation of AgNPs within flax fibers was confirmed by absorbance spectra, color data, carboxyl and aldehyde contents. Silver contents onto fibers was ranged in 4.9–11.8 g/kg, depending on the type of flax fibers and reduction method. By insertion of AgNPs, the scoured fibers were acquired reddish-yellow color with color strength of 8.7–10.5 related to the surface plasmon resonance AgNPs. The AgNPs-scoured flax fibers were exhibited by very good UV protection (30 < UPF < 40) and excellent antibacterial activity. The release of Ag from flax fibers was quite low (2.2–15.4 %) confirming that the functionalized fibers had good durability. In one pot step without bleaching, scoured flax fibers were gained concurrent/durable triple functions, which considerably valuable for the economical and environment impact in industrialization of flax.

Here, we compare the electrochemical oxidation potential of 15 nm diameter citrate-stabilized Au NPs aggregated by acid (low pH) to those aggregated by tetrakis(hydroxymethyl) phosphonium chloride (THPC). For acid-induced aggregation, the solution changes to a blue-violet color, the localized surface plasmon resonance (LSPR) band of Au NPs at 520 nm decreases along with an increase in absorbance at higher wavelengths (600-800 nm), and the peak oxidation potential (Ep) in anodic stripping voltammetry (ASV) obtained in bromide has a positive shift by as large as 200 mV. For THPC-induced aggregation (Au/THPC mole ratio = 62.5), the solution changes to a blue color as the LSPR band at 520 nm decreases and a new distinct peak at 700 nm appears, but the Ep does not exhibit a positive shift. Scanning transmission electron microscopy (STEM) images reveal that acid-induced aggregates are three-dimensional with strongly fused Au NP-Au NP contacts, while THPC-induced aggregates are linear or two-dimensional with ∼1 nm separation between Au NPs. The surface area-to-volume ratio (SA/V) decreases for acid-aggregated Au NPs due to strong Au NP-Au NP contacts, which leads to lower surface free energy and a higher Ep. The SA/V does not change for THPC-aggregated Au NPs since space remains between them and their SA is fully accessible. These findings show that metal NP oxidative stability, as determined by ASV, is highly sensitive to the details of the aggregate structure.

Silver nanoparticles (AgNPs) with size of 5 nm to 10 nm have been prepared using Couroupita guianensis flower and characterized using various structural and molecular analysis techniques. We synthesized pure, surface-roughened and coaxial hollow electrospun poly(methyl methacrylate) (PMMA) nanofibers from poly(ethylene oxide)–poly(methyl methacrylate) (PEO–PMMA) blends. Silver nanoparticle-incorporated PMMA nanofibers were prepared by dispersion method. Optical investigation of the silver nanoparticle-incorporated PMMA nanofibers was carried out by photoluminescence (PL) analysis, revealing that their photoluminescent properties depended on the concentration of nanoparticles incorporated. A surface plasmon resonance-enhanced bathochromic shift was observed for all the samples, with the structurally modified PMMA samples showing unique PL properties in terms of intensity and peak shifts depending on their structural modifications. The surface plasmon resonance of silver nanoparticles added with the transparency of PMMA results in enhanced PL properties. Such silver nanoparticle-incorporated PMMA nanofibers could find various applications in optical, nanophotonic devices, etc.

The social impact of virus spread is immeasurable. Vaccine prophylaxes take considerable time to develop because clinical trials are required. The best initial response to an emerging virus is establishing a virus detection technology adapted by simply preparing virus-specific antibodies. A virus detection system that detects two signals from one analyte has been developed to detect the target virus more sensitively and reliably. Plasmon regions on the surface of nanoparticles are effective in enhancing optical and electrochemical signals. Thus, CdSeTeS quantum dots (QDs) have been used as optical and electrochemical signal-generating materials. In contrast, gold nanoparticle-magnetic nanoparticle-carbon nanotube (AuNP-MNP-CNT) nanocomposites are used for the magnetic separation of the virus from interferences and for signal enhancement. In the presence of the target virus, the QDs optically show a virus concentration-dependent fluorescence enhancement effect due to the localized surface plasmon resonance (LSPR) of AuNPs. Regarding the electrochemical signal, Cd ions eluted by acid degradation of the QDs in solution show a virus concentration-dependent increase in the current peak on an electrode whose electrochemical properties are improved by the deposition of these nanocomposites. Both nanomaterials are conjugated with antibodies specific to influenza virus A (IFV/A), binding this target in a sandwich structure. We are successfully detecting the virus from these two signals during actual virus detection, even when the virus particles are in a human serum matrix. The limit of detection is 2.16 fg/mL for optical detection and 13.66 fg/mL for electrochemical detection.

Introduction. Porous silicon (PS) and materials on its basis are of interest for application in nanoelectronics, targeted drug delivery and advanced gas sensors. In addition, PS-based nanostructures are promising as filters in fibre-optic communication systems, since conventional thin-film deposition filters possess sidebands in their operating range thus requiring high vacuum for nanometer-thick coatings.Aim. To develop optical band-stop filter prototypes based on composite magnetic nanoparticles and the effect of localized surface plasmon resonance (LSPR) in an array of silver nanoparticles located on the PS surface. Materials and methods. The development and synthesis of nanostructures for the creation of filter prototypes. The double differentiation method in conjunction with Mie absorption theory was used for processing and analyzing the prototypes attenuation characteristics.Results. Two prototypes were developed. An analysis of the attenuation characteristics of a prototype based on SiO2 matrix functionalized by FemOn indicated that the parameters of the detected absorption bands depend on the size of FemOn nanoparticles. The attenuation characteristics of the LSPR-based prototype contain two absorption bands. The center wavelength value in the band caused by LSPR in the array of silver nanoparticles, close to spherical, is 367.5 nm. Excitation of LSPR in silver quantum clusters, manifested by the appearance of the corresponding band, occurs at a wavelength of 265.5 nm. The suppression in each of the bands can be controlled by changing the parameters of the PS matrix synthesis.Conclusion. Despite the disadvantages, e.g. a relatively low accuracy in setting the center wavelength, as well as certain difficulties concerned with reducing the unevenness in the absorption band, the obtained prototypes surpass existing analogues and are prospective for the development of compact analysis and diagnostics systems in a wide energy range.

Tri-positive lanthanide ion (Eu3+) activated glasses doped with different concentrations of silver (Ag0) nanoparticles obtained using thermal reducing agent were fabricated by applying the method of melt quench. The formation of Ag0 nanoparticles in glasses was revealed by the surface plasmon resonance (SPR) peak in the absorption spectra. Transmission electron microscopic measurements confirmed the presence of spherically shaped Ag0 nanoparticles of different size distribution. The absorption spectra showed a red–shift of the SPR peak with an increase in AgNO3 concentration occurring through Ostwald's ripening process because of the growth of particle size (as evidenced from microscope images). The non-linear optical (NLO) and optical limiting measurements were performed in the near infrared spectral region and femtosecond pulse excitation. The non-linear parameters were found to increase as the AgNO3 concentration increased to 0.6 mol %, however, the parameters subsequently decreased at higher doping level. The optical limiting threshold values demonstrated a reverse trend. The increase in non-linear optical properties regarding Ag nanoparticles concentration attributed to the enhancement of polarizabilities of glasses that occurred through local field stimulated by SPR of Ag nanoparticles when exposed to laser radiation of high energy. The increase in NLO coefficients (particularly the non-linear absorption coefficient) and the decrease in optical limiting threshold values with AgNO3 concentration (up to 0.6 mol %) indicated that these glasses containing 0.6 mol % AgNO3 are useful for the construction of the power optical limiters that function at the infrared region in the femtosecond pulse regime.

Narrowband light absorber with multi-band plasmonic resonances is numerically investigated for high-performance electrical manipulation via introducing the electro-optic (EO) medium in the slit array based grating structure. A maximal absorption efficiency of 99.5% is achieved. The spectral shift sensitivity reaches 0.99 nm/V. Besides, the large spectral intensity change is also obtained due to the use of sharp resonances, which therefore ensures the high signal-to-noise ratio for the manipulation process. It is observed that the strong surface plasmon resonance and the localized optical cavity modes can introduce the differential responses for the multiple modes under the optical adjusting process and also for the EO manipulation process. These features not only contribute to produce the new EO modulator platforms based on the light absorbers but also pave new ways for the cavity-enhanced high-performance EO operation. Moreover, the absorption properties can be well maintained in a wide range of the structural parameters, indicating the high tolerance of the fabrication process. The findings can pave new insights into the high-performance manipulations via the narrowband absorbers with strong electromagnetic field enhancement and hold wide applications in dynamic switching, filtering, displaying, etc.

The present work aimed at synthesizing gold nanoparticles in a biological method employing fruit peel waste dumped in the environment. The peels of Garcinia mangostana (Mangostan), were collected from the nearby tourist spot during the season. The collected fruit peels were washed, dried, powder and extracted by using boiling water and acetone. The precipitated extract was dried and powdered for further use. The dried and powdered peel extract was added to the gold solution and boiled to 80 °C and the color change is observed. The color change indicates the completion of the synthesis of gold nanoparticles. The effect of pH, gold ion concentration, peel extract powder concentration, and the temperature was tested by varying the parameters. The biosynthesized nanoparticles were characterized using the UV–Vis spectrophotometer to identify the surface plasmon resonance peaks corresponding to gold nanoparticles. The bio-moieties responsible for the synthesis of gold nanoparticles were identified using the Fourier Transform Infra-Red Spectroscopy. The crystalline nature was detected by using an X-Ray Diffractometer. Atomic Force Microscope viewed the 3D surface image of the gold nanoparticle. The shape and morphology of the nanoparticle were identified by using a Field Emission Scanning Electron Microscope. The active compounds for gold nanoparticle synthesis were identified using Gas Chromatography-Mass Spectrometry. The gold nanoparticle was synthesized in various colors and used for dyeing cotton fabrics. The dyed cotton materials were exposed to various stress conditions to determine the color fastening.