Rational Selection of Nanorod Plasmons: Material, Size, and Shape Dependence Mechanism for Optical Sensors

The localized surface plasmon resonance dependence on surrounding medium refractive index of Ag, Al, Au, and Cu nanoparticles is examined by electrodynamic approach. The refractive index sensitivity and sensing figure of merit (FOM) dependence of selected metal nanoparticles with similar geometry shows that although, sensing relevant parameters are shape (i.e., aspect ratio), and material dependent below the width 20 nm, but above this size these parameters are material independent under similar geometrical conditions. We have concluded that at optimum size, however, Al shows much higher refractive index sensitivity (RIS) in comparison to Au, Cu, and Ag, but FOM is higher for Ag in comparison to other metals. The observed sensing behavior is expected due to parameters like surface scattering, dynamic depolarization, radiation damping, and interband transitions, which may influence the nanorod plasmons.     

Dopamine-Induced Growth of Au and Ag Nanoparticles on ITO Substrate and Their Application in PCPDTBT-Based Polymer Solar Cell

The direct attachment and growth of gold or silver nanoparticles (NPs) on indium tin oxide (ITO) surfaces was demonstrated using a simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method by chemical reduction of the precursor metal salts with dopamine aqueous solution. Ag NPs on ITO substrate were approximately spherical with an average particle size of about 57 nm, but had a wide particle size distribution. Compared with Ag NPs, under the same 10 SILAR cycles, Au NPs have higher density packing and smaller average particle size of about 36 nm. XRD characterization and surface chemistry analysis confirmed the formation of Ag and Au NPs on ITO substrate with small amounts of dopamine-quinone adsorbed on the surface of them. Although Au NPs showed characteristic plasmon absorption, this did not result in performance enhancement in solar cell with the structure of ITO/ZnO/PCPDTBT:[6,6]-phenyl C₇₁/MoO₃/Ag because of the energy level mismatch between ZnO and dopamine molecules adsorbed on the surface of metal NPs.     

Optimization of Surface Plasmon Resonance Biosensor with Ag/Au Multilayer Structure and Fiber-Optic Miniaturization

In this paper, we report a novel wavelength interrogation-based surface plasmon resonance (SPR) system, in which a film of three Ag layers and three Au layers are alternately deposited on a Kretschmann configuration as sensing element. This multilayer film shows higher sensitivity for refractive index (RI) measurement by comparing with single Au layer structure, which is consistent with its theoretical calculation. A sensitivity range of 2056–5893 nm/RIU can be achieved, which is comparable to RI sensitivities of other wavelength-modulated SPR sensors. Compared with Ag film, this Ag/Au multilayer arrangement offers anti-oxidant protection. This SPR biosensor based on a cost-effective Ag/Au multilayer structure is applicable to the real-time detection of specific interactions and dissociation of low protein concentrations. To extend the application of this highly-sensitive metal film device, we integrated this concept on an optical fiber. The range of RI sensitivities with Ag/Au multilayer was 1847–3309 nm/RIU. This miniaturized Ag/Au multilayer-based fiber optic sensor has a broad application in chemical and biological sensing.     

SPR Label-Free Biosensor with Oxide-Metal-Oxide-Coated D-Typed Optical Fiber: a Theoretical Study

In this article, a surface plasmon resonance (SPR) biosensor based on D-typed optical fiber coated by Al₂O₃/Ag/Al₂O₃ film is investigated numerically. Resonance in near infrared with an optimized architecture is achieved. Refractive index sensitivity of 6558 nm/RIU (refractive index unit) and detection limit of 1.5 × 10⁻⁶ RIU, corresponding to 0.4357 nm/μM and detection limit of 23 nM in BSA (bovine serum albumin) concentration sensing, are obtained. The analysis of the performance of the sensor in gaseous sensing indicates that this proposed SPR sensor is much suitable for label-free biosensing in aqueous media.

     

A New Route to Glucose Sensing Based on Surface Plasmon Resonance Using Polyindole

In the present study, we report the first polyindole-modified metal (Au) as a glucose sensor utilizing surface plasmon resonance (SPR) technique. Polyindole (PIn) was deposited by spin coating to modify the surface of the gold disk. Sensor surface was prepared by immobilizing glucose oxidase on the polyindole-modified gold disk. Different concentrations of glucose were taken to analyze the sensor response. A change in refractive index of the film was observed due to the chemical reactions of glucose with glucose oxidase. The response of the sensor is fast and highly sensitive to low concentrations of glucose and the sensitivity increases in the range of 0.075–0.5 μM. The use of Au/polyindole (PIn/Au) substrates for SPR-based study of bio-molecular sensing has been demonstrated.     

A magnetic nanoparticles-zinc oxide/zinc hexacyanoferrate hybrid film for amperometric determination of tyrosine

A method is described for the construction of a highly sensitive amperometric sensor for the detection of tyrosine, employing a magnetic nanoparticles-zinc oxide/zinc hexacyanoferrate (Fe₃O₄NP-ZnO/ZnHCF) hybrid film electrodeposited on the surface of a Pt electrode as working electrode. The sensor is based on electrocatalytic mechanism initiated by electrochemical oxidation of the reduced form of the hybrid film at +0.2 V vs. Ag/AgCl followed by completion of chemical oxidation of tyrosine. The sensor showed optimum response within 2 s at pH 2. The working/linear range of the sensor was 0.02–2.76 mM with a detection limit of 4 μM. The sensor measured tyrosine level in serum, a potential biomarker of phenylketonuria. The working electrode lost only 5 % of its initial activity, when stored at 4 °C, after its regular use over a period of 100 days.     

Effects of Menadione, Hydrogen Peroxide, and Quercetin on Apoptosis and Delayed Luminescence of Human Leukemia Jurkat T-Cells

Menadione (MD) is an effective cytotoxic drug able to produce intracellularly large amounts of superoxide anion. Quercetin (QC), a widely distributed bioflavonoid, can exert both antioxidant and pro-oxidant effects and is known to specifically inhibit cell proliferation and induce apoptosis in different cancer cell types. We have investigated the relation between delayed luminescence (DL) induced by UV-laser excitation and the effects of MD, hydrogen peroxide, and QC on apoptosis and cell cycle in human leukemia Jurkat T-cells. Treatments with 500 μM H₂O₂ and 250 μM MD for 20 min produced 66.0 ± 4.9 and 46.4 ± 8.6% apoptotic cell fractions, respectively. Long-term (24 h) pre-exposure to 5 μM, but not 0.5 μM QC enhanced apoptosis induced by MD, whereas short-term (1 h) pre-incubation with 10 μM QC offered 50% protection against H₂O₂-induced apoptosis, but potentiated apoptosis induced by MD. Since physiological levels of QC in the blood are normally less than 10 μM, these data can provide relevant information regarding the benefits of flavonoid-combined treatments of leukemia. All the three drugs exerted significant effects on DL. Our data are consistent with (1) the involvement of Complex I of the mitochondrial respiratory chain as an important source of delayed light emission on the 10 μs–10 ms scale, (2) the ability of superoxide anions to quench DL on the 100 μs–10 ms scale, probably via inhibition of reverse electron transfer at the Fe/S centers in Complex I, and (3) the relative insensitivity of DL to intracellular OH^? and H₂O₂ levels.     

Tuning the Plasmon of Metallic Nanostructures: From Silver Nanocubes Toward Gold Nanoboxes

One of the most significant advances in nanoscience and nanotechnology was partially driven by plasmonic effect of some noble metal nanostructures with different shapes and sizes. By controlling the geometry of metal nanostructures, their surface plasmon resonance (SPR) peaks could be tuned from the visible to the near-infrared region with various applications in sensors, optoelectronic, nanomedicine, and specifically cancer therapy. In this study, we have prepared gold nanoboxes (NBs) using the galvanic replacement between Ag nanocubes (NCs) and aqueous gold solution. Ultraviolet visible (UVvis) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmitting electron microscopy (TEM) were used to characterize silver NCs and gold NBs. The primary silver NCs were synthesized by conventional polyol method at the presence of sodium sulfide to highly tune the shape and size of the NCs. Optimized cubic silver nanostructures were obtained at 90 μl of sodium sulfide injection into the solution. Moreover, the effect of quality of the cubic structure on the shape and uniformity of gold NBs was investigated. Gold NBs with hollow interior structure and SPR peak ranging from 480 to 800 nm were successfully obtained at different injection volumes of HAuCl₄ into the solution. It was demonstrated that increasing the volume of HAuCl₄ solution to about 3 mL can increase the pore number and size until the primary structure collapses into small pieces. It was also found that the concentration of gold NBs and the corresponding SPR peak intensities decrease due to pore size enhancement and decline of charge density on the surface of metal hollow nanostructures.     

PLANT GROWTH REGULATORS ENHANCE GOLD UPTAKE IN BRASSICA JUNCEA

The use of plant growth regulators is well established and they are used in many fields of plant science for enhancing growth. Brassica juncea plants were treated with 2.5, 5.0 and 7.5 μM auxin indole-3-butyric acid (IBA), which promotes rooting. The IBA-treated plants were also sprayed with 100 μM gibberellic acid (GA₃) and kinetin (Kin) to increase leaf-foliage. Gold (I) chloride (AuCl) was added to the growth medium of plants to achieve required gold concentration. The solubilizing agent ammonium thiocyanate (1 g kg^?1) (commonly used in mining industries to solubilize gold) was added to the nutrient solution after six weeks of growth and, two weeks later, plants were harvested. Plant growth regulators improved shoot and root dry biomass of B. juncea plants. Inductively Coupled Plasma Optical Emission Spectrometry analysis showed the highest Au uptake for plants treated with 5.0 μM IBA. The average recovery of Au with this treatment was significantly greater than the control treatment by 45.8 mg kg^?1 (155.7%). The other IBA concentrations (2.5 and 7.5 μM) also showed a significant increase in Au uptake compared to the control plants by 14.7 mg kg^?1 (50%) and 42.5 mg kg^?1 (144.5%) respectively. A similar trend of Au accumulation was recorded in the roots of B. juncea plants. This study conducted in solution culture suggests that plant growth regulators can play a significant role in improving phytoextraction of Au.     

Optical and Thermal Enhancement of Plasmonic Nanofluid Based on Core/Shell Nanoparticles

The plasmonic effect is introduced in solar thermal areas to enhance light harvest and absorption. The optical properties of plasmonic nanofluid are simulated by finite difference time domain (FDTD) method. Due to the excitation of localized surface plasmon resonance (LSPR) effect, an intensive absorption peak is observed at 0.5 μm. The absorption characteristics are sensitive to particle size and concentration. As the particle size increases, the absorption peak is broadened and shifted to longer wavelength. The absorption of SiO₂/Ag plasmonic nanofluid is improved gradually as the volume concentration increases, especially in the UV region. The absorption edge is shifted from 0.6 to 1.0 μm as the volume concentration increases from 0.001 to 0.01. The thermal simulation of suspended SiO₂/Ag nanoparticle shows a uniform temperature rise of 17.91 K under solar irradiation (AM 1.5), while under the same condition, the temperature rises in Ag nanoparticle and Al nanoparticle are 11.12 and 5.39 K, respectively. The core/shell plasmonic nanofluid exhibits a higher photothermal performance, which has a potential application in photothermal areas. A higher temperature rise can be obtained by improving the incident light intensity or optical absorption properties of nanoparticles.     

Discovery of medium ring thiophosphorus based heterocycles as antiproliferative agents

Hydrogen sulfide (H₂S) has been investigated for its potential in therapy. Recently, we reported novel H₂S donor molecules based on a thiophosphorus core, which slowly release H₂S and have improved anti-proliferative activity in cancer cell lines compared to the most widely studied H₂S donor GYY4137 (1). Herein, we have prepared new thiophosphorus organic H₂S donors with different ring sizes and evaluated them in two solid tumor cell lines and one normal cell line. A seven membered ring compound, 17, was found to be the most potent with sub-micromolar IC_50s in breast (0.76 μM) and ovarian (0.76 μM) cancer cell lines. No significant H₂S release was detected in aqueous solution for this compound. However, confocal imaging showed that H₂S was released from 17 inside cells at a similar level to the widely studied H₂S donor GYY4137, which was shown to release 10 μM H₂S after 12 h at a concentration of 400 μM. Comparison of 17 with its non-sulfur oxygen analogue, 26, provided evidence that the sulfur atom is important for its potency. However, the significant potency observed for 26 (5.94–11.0 μM) indicates that the high potency of 17 is not entirely due to release of H₂S. Additional mechanism(s) appear to be responsible for the observed activity, hence more detailed studies are required to better understand the role of H₂S in cancer with potent thiophosphorus agents.     

[(B3O3H3)nM]+(n = 1, 2;M = Cu, Ag, Au): a new class of metal-cation complexes

A density functional theory (DFT) investigation into the structures and bonding characteristics of [(B₃O₃H₃)_nM]⁺(n?=?1, 2;M?=?Cu, Ag, Au) complexes was performed. DFT calculations and natural bond orbital (NBO) analyses indicate that the ΙB metal complexes of boroxine exhibit intriguing bonding characteristics, different from the typical cation–π interactions between ΙB metal-cations and benzene. The complexes of [B₃O₃H₃M]⁺ and [(B₃O₃H₃)₂?M]⁺ (M?=?Cu, Ag, and Au) favor the conformation of perfectly planar structures with the C_2v and D_2h symmetry along one of the threefold molecular axes of boroxine, respectively. Detailed natural resonance theory (NRT) and canonical molecular orbitals (CMOs) analyses show that interaction between the metal cation and the boroxine in [B₃O₃H₃M]⁺ (M?=?Cu, Ag, and Au) is mainly ionic, while the ΙB metal-cations←π donation effect is responsible for the binding site. In these complexes, boroxine serves as terminals η¹-B₃O₃H₃ with one O atom of the B₃O₃ ring. The infra-red (IR) spectra of [B₃O₃H₃M]⁺ were simulated to facilitate their future experimental characterization. The complexes all give two IR active modes at about 1,300 and 2,700 cm^?1, which are inactive in pure boroxine. Simultaneously, the B–H stretching modes of the complexes are red-shifted due to the interaction between the metal-cation and boroxine. To explore the possibility of the structural pattern developed in this work forming mesoporous materials, complexes [(B₃O₃H₃M)₆]⁶⁺ (M?=?Cu, Ag, and Au) were also studied, which appear to be unique and particular interesting: they are all true minima with D_6h symmetries and pore sizes ranging from 12.04 Å to 13.65 Å.

Tunable Plasmonic Absorber Based on Propagating and Localized Surface Plasmons Using Metal-Dielectric-Metal Structure

We propose a metal-dielectric-metal super absorber based on propagating and localized surface plasmons which exhibits a near perfect absorption in the visible and near-infrared spectrum. The absorber consists of Ag/Al₂O₃/Al triple layers in which the top Al layer is a periodic nano disk array. The absorption spectrum can be easily controlled by adjusting the structure parameters including the period and radius of the nano disk and the maximal absorption can reach 99.62 %. We completely analyze the PSPs and LSPs modes supported by the MDM structure and their relationship with the ultrahigh absorption. Moreover, we propose a novel idea to further enhance the absorption by exciting the PSPs and high-order LSPs modes simultaneously, which is different from the previous works. This kind of absorber using stable inexpensive Al instead of noble metal Au or Ag is an appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensing, and surface-enhanced Raman spectroscopy (SERS).     

Photothermal Switching of SOI Waveguide-Based Mach-Zehnder Interferometer with Integrated Plasmonic Nanoheater

We theoretically and numerically investigated the photothermal switching of a Mach-Zehnder interferometer (MZI) based on two Si waveguides integrated with plasmonic nanoheaters. The nanoheater is a composite nanowire with Au/Al₂O₃/Au three-layer structure, which is designed to have a highly efficient optical absorption peak at wavelength of 1,064 nm. Based on this finding, we further analyze a MZI built with two 40-μm-long symmetric waveguide branches, each integrated with a 20-μm-long nanoheater. The optical switching power of the MZI device is 190 mW (280 mW) for the capped (buried) channel waveguide, when pumped by a circular Gaussian beam with a waist of 10 μm. Alternatively, the switching power can be reduced to 38 mW (56 mW) by using an astigmatic Gaussian beam, with a semi-major axis of 10 μm and an aspect ratio of 5. The switching response time of the MZI is 0.7 μs (1.0 μs) for capped (buried) channel waveguide design. Our design opens a new route for optically driven non-contact optical on-off switching with sub-microsecond time response.     

Investigating the Effect of Ag and Au Nanostructures with Spherical and Rod Shapes on the Emission Wavelength of OLED

Noble metals, especially Ag and Au nanostructures, have unique and adjustable optical attributes in terms of surface plasmon resonance. In this research, the effect of Ag and Au nanoparticles with spherical and rod shapes on the light extraction efficiency and the FWHM of OLED structures was investigated using the finite difference time domain (FDTD) method. The simulation results displayed that by changing the shape and size of Ag and Au nanostructures, the emission wavelength can be adjusted, and the FWHM can be reduced. The presence of Ag and Au nanoparticles in the OLEDs showed a blue and red shift of the emission wavelength, respectively. Also, the Ag and Au nanorods caused a significant reduction in the FWHM and a shift to the longer wavelengths in the structures. The structures containing Ag nanorods showed the narrowest FWHM and longer emission wavelength than the other structures.

     

Electronic, magnetic and optical properties of Cu, Ag, Au-doped Si clusters

The structural, optical and magnetic properties of Cu, Ag, Au-doped Si₇ Clusters have been systematically investigated using density functional theory calculations. The global optimized structures of Cu, Ag, Au-doped Si clusters are predicted to have a lower HOMO–LUMO gap and higher magnetic moment. M-doping (M?=?Cu, Ag, Au) in Si cluster widens a range of adsorption wavelength, especially Au-doping. The characteristics in electronic density of states (DOSs) show that C_5v-Si₆Cu has a big asymmetrical spin-up and spin-down. The average atomic moment is 0.428 mμ_B per atom for the Si₆Cu cluster with C_5v symmetry, while the average paramagnetic moment is 0.143 mμ_B per atom for other M-doped (M?=?Cu, Ag, Au) Si₇ clusters.     

Voltammetric detection of anti-HIV replication drug based on novel nanocomposite gold-nanoparticle–CaCO<Subscript>3</Subscript> hybrid material

A novel bionanocomposite, horse radish peroxidase- gold-nanoparticle–Calcium carbonate (HRP-AuNPs-CaCO₃), hybrid material was encapsulated by silica sol on a glassy carbon electrode (GCE). The fabricated modified electrode was used as a novel voltammetric sensor for electrochemical sensing of anti-HIV replication drug i.e. deferiprone. The surface morphology of the modified electrode was characterized by scanning electron microscopy (SEM). Results obtained from the voltammetric measurements show that HRP-AuNPs-CaCO₃ modified GCE offers a selective and sensitive electrochemical sensor for the determination of deferiprone. Under experimental conditions, the proposed voltammetric sensor has a linear response range from 0.01 to 10,000 μM with a detection limit of 0.01 μM. Furthermore, the fabricated sensor was successfully applied to determine deferiprone level in spiked urine and serum samples.     

Silver-decorated orthorhombic nanotubes of lithium vanadium oxide: an impeder of bacterial growth and biofilm

Reoccurrence of infectious diseases and ability of pathogens to resist antibacterial action has raised enormous challenges which may possibly be confronted by nanotechnology routes. In the present study, uniformly embedded silver nanoparticles in orthorhombic nanotubes of lithium vanadium oxide (LiV₂O_5/Ag) were explored as an impeder of bacterial growth and biofilm. The LiV₂O₅/Ag nanocomposites have impeded growth of Gram-positive Bacillus subtilis NCIM 2063 and Gram-negative Escherichia coli NCIM 2931 at 60 to 120 μg/mL. It also impeded the biofilm in Pseudomonas aeruginosa NCIM 2948 at 12.5 to 25 μg/mL. Impedance in the growth and biofilm occurs primarily by direct action of the nanocomposites on the cell surfaces of test organisms as revealed by surface perturbation in scanning electron microscopy. As the metabolic growth and biofilm formation phenomena of pathogens play a central role in progression of pathogenesis, LiV₂O₅/Ag nanocomposite-based approach is likely to curb the menace of reoccurrence of infectious diseases. Thus, LiV₂O₅/Ag nanocomposites can be viewed as a promising candidate in biofabrication of biomedical materials.     

Recognition of silver nanoparticles surface‐adsorbed citrate anions by macrocyclic polyammonium cations: a spectrophotometric approach to study aggregation kinetics and evaluation of association constant

In this report, we have studied the recognition of citrate anions adsorbed on the surface of silver nanoparticles (cit‐Ag‐NPs), by macrocyclic polyammonium cations (MCPACs): Me₆[14]ane‐N₄H₈⁴⁺ (Tet‐A/Tet‐B cations) and [32]ane‐N₈H₁₆⁸⁺, which are well reputed anion recognizers and are treated as to mimic of biological polyamines. The study was monitored on ultraviolet–visible spectroscopy by performing a titration of the aqueous dispersion of the cit‐Ag‐NPs by the aqueous solution of MCPACs. The ultraviolet–visible time‐scan plots over the reduction of the absorption band of surface plasmon resonance of cit‐Ag‐NPs at 390 nm are well fitted with fourth‐order polynomial equation and are employed to determine the initial aggregation rate constants. It has been stated that the aggregation is the result in electrostatic attraction followed by H‐bond formation between the surface‐adsorbed citrate anions and added MCPACs. The atomic force microscopy results have evidenced aggregation of cit‐Ag‐NPs in presence of MCPACs. The evaluated H‐bonded association constant (K_asso) using Benesi–Hildebrand method reveals that [32]ane‐N₈H₁₆⁸⁺ cations form stronger association complex, as expected, with the citrate anions than the Me₆[14]ane‐N₄H₈⁴⁺ cations. The study would thus provide the insight of molecular interactions involved in nanoparticle surface‐adsorbed anions with biological polyamines. Copyright © 2016 John Wiley & Sons, Ltd.     

GIS-facilitated ex situ conservation of the rare Greek endemic Campanula incurva Aucher: Seed germination requirements and effect of growth regulators on in vitro proliferation and rooting

In order to develop conservation protocols for Campanula incurva, the geographical information systems (GIS) were used to unveil its ecological requirements; this facilitated the selection of substrates and of appropriate temperatures for cultivation and guided propagation experiments and acclimatization. Seed germination was tested under (i) dark, (ii) 16-h photoperiod, (iii) immersion in 400 ppm gibberellic acid (GA₃) followed by incubation at dark, and (iv) immersion in 400 ppm GA₃ followed by incubation at 16-h photoperiod (all at 21 ± 1°C). Dormancy was not detected. Germination exceeded 85% in 10 days. Shoot tips were established in vitro in Murashige and Skoog (MS) medium with 1 μM 6-benzyladenine (BA) and 0.1 μM indole-3-butyric acid (IBA). The effect of 1–8 μM BA and 1–8 μM kinetin on shoot proliferation was studied. Moreover, 8 μM BA was combined with 0, 1, 5, and 10 μM IBA to investigate effects of cytokinin/auxin. The highest number of microshoots/explant (4.03) was obtained with 8 μM BA. Microshoots were transferred to half strength MS and full strength MS media with 0, 0.5, 1, 5, and 10 μM IBA to evaluate their root induction ability. Half strength MS medium with 5 μM IBA resulted in 100% rooting (16.80 average number of roots/microshoot). Plantlets produced were successfully acclimatized.