Ultra-high Sensitivity Plasmonic Nanosensor Based on Multiple Fano Resonance in the MDM Side-Coupled Cavities

We propose a compact plasmonic structure comprising a metal-dielectric-metal (MDM) waveguide coupled with a side cavity and groove resonators. The proposed system is investigated by the finite element method. Simulation results show that the side-coupled cavity supports a local discrete state and the groove provides a continuous spectrum, the interaction between them, gives rise to the Fano resonance. The asymmetrical line shape and the resonant wavelength can be easily tuned by changing the geometrical parameters of the structure. Moreover, we can extend this plasmonic structure by the double side-coupled cavities to gain the multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of ～1900 nm/RIU and a figure of merit of about ～3.8?×?10⁴, which can find wide applications for nanosensors.     

Ultra-High Sensitivity Nanosensor Based on Multiple Fano Resonance in the MIM Coupled Plasmonic Resonator

This paper proposes a compact plasmonic structure that is composed of a metal-insulator-metal (MIM) waveguide coupled with a groove and stub resonators, and then investigates it by utilizing the finite element method (FEM). Simulation results show that the interaction between the local discrete state caused by the stub resonator and the continuous spectrum caused by the groove resonator gives rise to one of the two Fano resonances, while the generation of the other resonance relies only on the groove. Meanwhile, the asymmetrical linear shape and the resonant wavelength can be easily tuned by changing the parameters of the structure. By adding stubs on the groove, we excited multiple Fano resonances. The proposed structure can serve as an excellent plasmonic sensor with a sensitivity of 2000 nm/RIU and a figure of merit of about 3.04?×?10³, which can find extensive applications for nanosensors.     

Tunable Multi-Fano Resonances in MDM-Based Side-Coupled Resonator System and its Application in Nanosensor

In this paper, two Fano resonances are achieved in the proposed plasmonic system. Theoretical analysis and simulation results show that two discrete states coupled with a continua lead to these Fano resonances. The discrete states are provided by the side-coupled square cavity, and a baffle plate placed in metal-dielectric-metal waveguide is used to produce a continuous transmission spectrum. The resonant wavelengths and the linewidth of these Fano resonances can be easily tuned by adjusting the parameters of system. This system exhibits high sensitivities as high as 850 and 1120 nm/RIU corresponding to two Fano resonances, and the figure of merit can reach to 1.7 × 10⁵ by optimizing the system. By introducing another square cavity, four Fano resonances are obtained which originate from four discrete states coupled with continua, and they can be tuned independently. The flexible multi-Fano resonances system has significant application bio-nanosensor, nonlinear, and slow light devices.     

Ultrasmall Plasmonic Cavity for Chemical Sensing

We propose an ultrasmall plasmonic cavity based on the channel waveguides for chemical sensing. The plasmonic mode gap due to cutoff angular frequency enables strong optical confinement in a subwavelength volume and suppression of radiation loss. Due to strong field overlap of the surface plasmon polariton mode with environmental material, large sensitivity (1,100 nm/refractive index unit) and a high figure of merit (330) are achieved in the plasmonic cavity with a small physical size of 600?×?800?×?2,500 nm having a telecommunication resonant wavelength. This plasmonic cavity can introduce a broad range of applications including biochemical sensing and strong light–matter interactions.     

Coupling of Whispering-Gallery Modes in the Graphene Nanodisk Plasmonic Dimers

In this paper, we proposed plasmonic dimers consisted of two evanescent field coupled graphene monolayer nanodisks. The electromagnetic properties including the split modes with non-degenerate wavelengths, enhancement of the quality factors (Q factors) and mode areas, and the coupling between the fundamental and the first-order whispering-gallery modes are numerically predicted and analyzed systematically. Compared with the single graphene nanodisk, the Q factor of TM_4,1 reaches 356 in a dimer with a radius of 5 nm of each nanodisk and an inter-disk gap of 0.4 nm, where the corresponding mode area is as small as 6.88?×?10^‐?5(λ ₀)². In addition, the enhanced performances of size-mismatched coupled graphene plasmonic dimers are investigated. This graphene monolayer plasmonic dimer could be one of the fundamental components in the future ultra-high density plasmonic circuit technique, on-chip plasmonic interconnect, and transformation plasmonics. It also could be used as the test-beds for added explorations of cavity quantum electrodynamic experiments.     

Highly Sensitive Plasmonic Sensor Based on Fano Resonance from Silver Nanoparticle Heterodimer Array on a Thin Silver Film

We investigate the optical spectrum of a multilayer metallic slab using multiple-scattering formalism. A thin silver film is attached to a periodic array of heterodimers consisting of two vertically spaced silver nanoparticles of different radii. Depending on the radius of nanoparticles, heterodimer array presents a simple nanoscale geometry which gives rise to remarkable plasmonic properties of multipolar resonances. Due to the coherent interference of the localized nanoparticle plasmons (discrete mode) and surface plasmon polaritons of metallic film (continuous mode), the reflection spectrum represents a sharp asymmetric Fano resonance dip, which is strongly sensitive to the refractive index of the surrounding embedded dielectric host. The physical features contribute to a highly efficient plasmonic sensor for refractive index sensing with sensitivity of ～1.5?×?10^?3 RIU/nm.     

Highly Sensitive Side-Polished Birefringent PCF-Based SPR Sensor in near IR

We propose a highly sensitive side-polished birefringent photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR). The polished surface of the proposed structure is coated with indium tin oxide (ITO) to excite plasmon and the analytes can be placed on the flat surface easily instead of filling the voids. The birefringent nature of the structure helps in coupling more fields to the ITO-dielectric interface. With the optimum thickness of 110 nm of ITO, the structure shows a maximum wavelength sensitivity of 17000 nm/RIU with a resolution of 5.8?×?10^?6 RIU. Further this also showed an amplitude sensitivity of 74 RIU^?1 along with a resolution of 1.35?×?10^?5 RIU. Moreover, the effect of bending on this low loss structure is also analyzed.     

Understanding nucleosomal histone and DNA interactions: a biophysical study

Histones are associated with DNA to form nucleosome essential for chromatin structure and major nuclear processes like gene regulation and expression. Histones consist of H1, H2A, H2B and H3, H4 type proteins. In the present study, combined histones from calf thymus were complexed with ct DNA and their binding affinities were measured fluorimetrically. All the five histones were resolved on SDS page and their binding with DNA was visualized. The values of biding affinities varied with pH and salt concentration. Highest affinity (4.0?×?10⁵ M^?1) was recorded at pH 6.5 in 50 mM phosphate buffer and 1.5?×?10⁴ M^?1 in 2 M NaCl at pH 7.0. The CD spectra support the highest binding affinity with maximum conformational changes at pH 7.0. The time-resolved fluorescence data recorded two life times for histone tyrosine residues at 300 nm emission in phosphate buffer pH 6.5. These life times did not show much change upon binding with DNA in buffer as well as in 2 M NaCl. The isothermal calorimetric studies yielded thermodynamic parameters ΔG, ΔH and ΔS as ?1.6?×?10⁵ cal/mol, ?1.13?×?10³ cal/mol and ?3.80 cal/mol/deg, respectively, evidencing a spontaneous exothermic reaction. The dominant binding forces in building the nucleosome are electrostatic interactions.     

Analysis of a Surface Plasmon Resonance Probe Based on Photonic Crystal Fibers for Low Refractive Index Detection

A photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) probe with gold nanowires as the plasmonic material is proposed in this work. The coupling characteristics and sensing properties of the probe are numerically investigated by the finite element method. The probe is designed to detect low refractive indices between 1.27 and 1.36. The maximum spectral sensitivity and amplitude sensitivity are 6 × 10³ nm/RIU and 600 RIU^?1, respectively, corresponding to a resolution of 2.8 × 10^?5 RIU for the overall refractive index range. Our analysis shows that the PCF-SPR probe can be used for lower refractive index detection.     

Review of Carbon Fixation in Bamboo Forests in China

Bamboo is widespread in the subtropics and tropics of Asia, Africa, and Latin America. The total area of bamboo forests of various species is 22.0?×?10⁶ ha, accounting for about 1.0% of the total global area of forest. Although the total forest areas in many countries have decreased drastically, bamboo forests have increased at a rate of 3% annually. China has the richest resources of bamboo in the world, with over 500 species in 39 genera. Carbon storage of vegetation, soils, and litter in bamboo forest system in China was 0.2511?×?10¹⁵, 0.8516?×?10¹⁵, and 0.0361?×?10¹⁵ g C, respectively, giving a total of 1.1388?×?10¹⁵ g C. This paper reviews carbon storage of vegetation, soils, and litter in bamboo forest system and compares the carbon fixation abilities of bamboo forest ecosystems with those of other tree species in subtropical China.     

Fano Resonance of Nanocrescent for the Detection of Single Molecules and Single Nanoparticles

This paper reports a theoretical study on the Fano resonance of a 3D nanocrescent and its application in single molecular detection. The resonance wavelength changes with the crescent radius, gap width and thickness. The Fano resonance is attributed to the interference between the quadrupolar mode supported by the horizontal crescent and the quadrupolar mode supported by the nanotip oscillating along the height direction. The Fano resonance is highly sensitive to a nanoparticle trapped by the nanocrescent. The wavelength shift is larger than 0.5 nm when a single protein nanoparticle with radius only of 1.25 nm is trapped. For a protein with radius of 0.3 nm, the wavelength shift is still larger than 0.03 nm, over the detection limit (10^?5 nm) by 3 orders in the magnitude, which indicates that the nanocrescent can be used to detect small molecule with several atoms.     

Enhancing Diamond Fluorescence via Optimized Nanorod Dimer Configurations

Light extraction from silicon (SiV) and nitrogen (NV) vacancy diamond color centers coupled to plasmonic silver and gold nanorod dimers was numerically improved. Numerical optimization of the coupled dipolar emitter—plasmonic nanorod dimer configurations was realized to attain the highest possible fluorescence enhancement by simultaneously improving the color centers excitation and emission through antenna resonances. Conditional optimization was performed by setting a criterion regarding the minimum quantum efficiency of the coupled system (cQE) to minimize losses. By comparing restricted symmetric and allowed asymmetric dimers, the advantages of larger degrees of freedom achievable in asymmetric configurations was proven. The highest 2.59?×?10⁸ fluorescence enhancement was achieved with 46.08% cQE via NV color center coupled to an asymmetric silver dimer. This is 3.17-times larger than the 8.19?×?10⁷ enhancement in corresponding symmetric silver dimer configuration, which has larger 68.52% cQE. Among coupled SiV color centers the highest 1.04?×?10⁸ fluorescence enhancement was achieved via asymmetric silver dimer with 37.83% cQE. This is 1.06-times larger than the 9.83?×?10⁷ enhancement in corresponding symmetric silver dimer configuration, which has larger 57.46% cQE. Among gold nanorod coupled configurations the highest fluorescence enhancement of 4.75?×?10⁴ was shown for SiV color center coupled to an asymmetric dimer with 21.8% cQE. The attained enhancement is 8.48- (92.42-) times larger than the 5.6?×?10³ (5.14?×?10²) fluorescence enhancement achievable via symmetric (asymmetric) gold nanorod dimer coupled to SiV (NV) color center, which is accompanied by 16.01% (7.66%) cQE.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.     

<Emphasis Type="Italic">Bacillus amyloliquefaciens</Emphasis> Spore Production Under Solid-State Fermentation of Lignocellulosic Residues

This study was conducted to elucidate cultivation conditions determining Bacillus amyloliquefaciens B-1895 growth and enhanced spore formation during the solid-state fermentation (SSF) of agro-industrial lignocellulosic biomasses. Among the tested growth substrates, corncobs provided the highest yield of spores (47?×?10¹⁰ spores g^?1 biomass) while the mushroom spent substrate and sunflower oil mill appeared to be poor growth substrates for spore formation. Maximum spore yield (82?×?10¹⁰ spores g^?1 biomass) was achieved when 15 g corncobs were moistened with 60 ml of the optimized nutrient medium containing 10 g peptone, 2 g KH₂PO₄, 1 g MgSO₄·7H₂O, and 1 g NaCl per 1 l of distilled water. The cheese whey usage for wetting of lignocellulosic substrate instead water promoted spore formation and increased the spore number to 105?×?10¹⁰ spores g^?1. Addition to the cheese whey of optimized medium components favored sporulation process. The feasibility of developed medium and strategy was shown in scaled up SSF of corncobs in polypropylene bags since yield of 10?×?10¹¹ spores per gram of dry biomass was achieved. In the SSF of lignocellulose, B. amyloliquefaciens B-1895 secreted comparatively high cellulase and xylanase activities to ensure good growth of the bacterial culture.     

Growth characteristics and reproductive capability of green tide algae in Rudong coast, China

Since 2007, green tides have occurred along the coast of the Yellow Sea, China. The green tide extended to 50,000 km² (floating area) within 2–3 months and the calculated covering area was about 400 km² in 2010. These facts implied that the growth and reproduction of the dominant species Ulva prolifera were stimulated. We observed that 1 cm² blades (single layer) released 2.84–6.62?×?10⁶ spores or 1.14–2.65?×?10⁷ gametes and that 91.6–96.4 % of them germinated into younger seedlings. This means that, in theory, 1 g (fresh weight) of blades was able to produce about 2.8?×?10⁸–2.7?×?10⁹ new younger seedlings. From 2009 to 2011, the growth rate of green tide algae was measured in situ in enclosure experiments in Rudong coast, Jiangsu Province and the growth curve of the algae was divided into four phases: lag phase, accelerated phase, stationary phase, and decline phase. Usually, the average daily specific relative growth rate was about 23.2–23.6 % d^?1 for a whole growth period, and it reached up to 56.2 % d^?1 in the accelerated phase. Correspondingly, the morphology of green tide algae in enclosures also showed periodic variation as follows: blades presented new filamentous branches from old thallus in the lag phase, longer filamentous branches in the accelerated phase, tubular and cystic blades in the stationary phase, and folded blades in the decline stage. Those studies may be useful for understanding the green tide blooming mechanism.     

Boosting and Localizing Near-Field in Plasmonic Mirror-Image Nanoepsilon

A novel plasmonic mirror-image nanoepsilon (MINE) structure is studied to achieve significantly enhanced and localized near-field. It is well-known that the nanorod dimer is able to gain a high local field at the center of the structure by adjusting its rod width, rod length, and gap distance. When adopting an auxiliary nanoring structure electron reservoirs surrounding the nanorod-dimer to form the MINE structure, the local field can be further enhanced owing to a large amount of charges into sharp dimer structure which can confine the accumulation of charges to apexes. Thus, better synergistic interaction of gap effect and lightning-rod effect can be achieved for high field enhancement around nanoscale gap. The symmetric mode in the MINE structure enables strong near-field with a concentrated distribution around the gap. The influences of rod-tip angle and gap distance on the optical properties of plasmonic MINE structures are numerically investigated. With reducing the rod-tip angle and gap distance, considerable enhancements on the field intensities at the rod tips and the gap center can be attributed to the improved lightning-rod and gap effects. The near-field intensities at the rod tip and gap center are dramatically enlarged ~1.94 × 10⁴ and ~1.41 × 10⁴ times with the rod-tip angle of 41° and gap distance of 10 nm, and the near-field is localized within an extremely small range. These features are very beneficial for various plasmonic applications.     

The mechanism of (+) taxifolin’s protective antioxidant effect for •OH-treated bone marrow-derived mesenchymal stem cells

The natural dihydroflavonol (+) taxifolin was investigated for its protective effect on Fenton reagent-treated bone marrow-derived mesenchymal stem cells (bmMSCs). Various antioxidant assays were used to determine the possible mechanism. These included ?OH-scavenging, 2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide radical-scavenging (PTIO?-scavenging), 1, 1-diphenyl-2-picryl-hydrazl radical-scavenging (DPPH?-scavenging), 2, 2′-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid) radical-scavenging (ABTS⁺?-scavenging), Fe³⁺-reducing, and Cu²⁺-reducing assays. The Fe²⁺-binding reaction was also investigated using UV-Vis spectra. The results revealed that cell viability was fully restored, even increasing to 142.9?±?9.3% after treatment with (+) taxifolin. In the antioxidant assays, (+) taxifolin was observed to efficiently scavenge ?OH, DPPH? and ABTS⁺? radicals, and to increase the relative Cu²⁺- and Fe³⁺-reducing levels. In the PTIO?-scavenging assay, its IC₅₀ values varied with pH. In the Fe²⁺-binding reaction, (+) taxifolin was found to yield a green solution with two UV-Vis absorbance peaks: λ_max =?433 nm (ε =5.2?×?10² L mol^?1 cm ^?1) and λ_max =?721 nm (ε?=?5.1?×?10² L mol^?1 cm ^?1). These results indicate that (+) taxifolin can act as an effective ?OH-scavenger, protecting bmMSCs from ?OH-induced damage. Its ?OH-scavenging action consists of direct and indirect antioxidant effects. Direct antioxidation occurs via multiple pathways, including ET, PCET or HAT. Indirect antioxidation involves binding to Fe²⁺.     

Optical Properties of Noncontinuous Gold Shell Engineered on Silica Mesosphere

The optical properties of individual noncontinuous shells with different gold coverage are investigated by the single-particle dark field scattering measurements and single-particle surface-enhanced Raman scattering (SERS) measurements at different excitation wavelengths. By controlling the growth of gold seeds, multi-metallic nanogaps/crevices with different optical responses are assembled on silica mesospheres forming noncontinuous shells that can be confirmed through the transmission electron microscope images. We find the surface plasmon resonance of single shell red-shifts from 510 to 680 nm with the increase of gold coverage. At the excitation of 532 and 785 nm, the best enhancements about 2.0?×?10⁵ and 1.1?×?10⁷ are obtained on spheres with ～60 and 83 % gold coverage, respectively. The weak polarization-dependent SERS indicates that the enhancement is from the multi-gaps on single noncontinuous shell. This optical tunable and SERS active noncontinuous gold shell can be applied in biosensing, ultra trace detection, and molecule analysis needing multi-wavelengths excitation.     

Simulation of carbon nanotube welding through Ar bombardment

Single-walled carbon nanotubes show promise as nanoscale transistors for nanocomputing applications. This use will require appropriate methods for creating electrical connections between distinct nanotubes, analogous to welding of metallic wires at larger length scales, but methods for performing nanoscale chemical welding are not yet sufficiently understood. This study examines the effect of Ar bombardment on the junction of two crossed single-walled carbon nanotubes, to understand the value and limitations of this method for generating connections between nanotubes. A geometric criterion was used to assess the quality of the junctions formed, with the goal of identifying the most productive conditions for experimental ion bombardment. In particular, the effects of nanotube chirality, Ar impact kinetic energy, impact particle flux and fluence, and annealing temperature were considered. The most productive bombardment conditions, leading to the most crosslinking of the tubes with the smallest loss of graphitic (i.e., conductive) character, were found to be at relatively mild impact energies (100 eV), with low flux and high-temperature (3000 K) annealing. Particularly noteworthy for experimental application, a high junction quality is maintained for a relatively broad range of fluences, from 3?×?10¹⁹ m^?2 to at least 1?×?10²⁰ m^?2.     

Speckled SiO2@Au Core–Shell Particles as Surface Enhanced Raman Scattering Probes

Silica particles of ~800 nm size were functionalized using 3-amino propyl triethoxysilane molecules on which gold particles (~20 nm size) were deposited. The resulting particles appeared to form speckled SiO₂@Au core–shell particles. The surface roughness, along with hot spots, due to nanogaps between the gold nanoparticles was responsible for the enhancement of the Raman signal of crystal violet molecules by ~3.2?×?10⁷ and by ~1.42?×?10⁸ of single-wall carbon nanotubes. It has also been observed that the electromagnetic excitation near surface plasmon resonance (SPR) of core–shell particles is more effective than off resonance SPR excitation.