Third-order optical autocorrelator for time-domain operation at telecommunication wavelengths

We report on amorphous organic thin films that exhibit efficient third-harmonic generation at telecommunication wavelengths. At 1550 nm, micrometer-thick samples generate up to 17 µW of green light with input power of 250 mW delivered by an optical parametric oscillator. This high conversion efficiency is achieved without phase matching or cascading of quadratic nonlinear effects. With these films, we demonstrate a low-cost, sensitive third-order autocorrelator that can be used in the time-frequency domain

Ultrafast-pulse diagnostic using third-order frequency-resolved optical gating in organic films

We report on the diagnostic of ultrafast pulses by frequency-resolved optical gating (FROG) based on strong third-harmonic generation (THG) in amorphous organic thin films. The high THG conversion efficiency of these films allows for the characterization of sub-nanojoule short pulses emitting at telecommunication wavelengths using a low cost portable fiber spectrometer

Development of a metagenomic DNA extraction procedure and PCR detection of human enteric bacteria in vegetable salad tissues

Outbreaks of illness due to human enteric pathogenic bacteria via fresh vegetables warrant intensive research on changing strategies of these bacteria in alterning their hosts for survival. The systemic infection of human pathogenic bacteria in plants and the plant growth stage at which they establish endophytic relationship is poorly understood. Since cucumber and carrot are major vegetables consumed in the form of unprocessed salads in India, our study aimed at determination of infection abilities of Salmonella enterica sub sp. enterica and Aeromonas hydrophila in carrot and cucumber, respectively based on a  metagenomic detection system. We report an optimized metagenomic DNA isolation procedure from vegetable tissues co-cultivated with bacteria under laboratory conditions. Colonization of bacteria in vegetable tissues was studied by amplification of bacterial 16S rRNA coding region from the metagenome. DNA obtained from carrot vegetable pieces inoculated with Salmonella resulted in expected amplification of 1.2 kb region of bacterial 16S rRNA source sequences. However, the approach failed to detect Aeromonas in cucumber tissues.  We conclude that carrot could be a symptomless alternate host for  Salmonella sp

Biotic activation of abiotic temperature stress tolerance in transgenic BT and wild type cotton

Activation of abiotic temperature stress tolerance in transgenic Bt and non-Bt cotton was studied using Pseudomonas fluorescens as biotic regulator. Seeds germinated at different temperatures after the bacterial treatment exhibited variation at the temperatures of 30°C and 37°C as measured in terms of percent seed germination in both Bt and non-Bt cotton. Pseudomonas treatment enhanced the seed germination in non-Bt cotton at 30°C. Enhancement of seed germination in Bt cotton was significant at 37°C after bacterial treatment. At elevated temperature of 45°C, neither Bt nor non-Bt seeds germinated, irrespective of Pseudomonas treatment. The temperature of 30°C supported better shoot and root growth of seedlings as compared to other temperatures tested. Pseudomonas treatment resulted in enhanced shoot and root length of Bt cotton seedlings at 30°C, whereas at 37° Chad negligible influence. Non-Bt cotton seeds treated with bacteria failed to show significant variation in root and shoot growth compared to untreated control. Activity gelelectrophoresis carried out to study the expression of superoxide dismutase revealed that the SOD activity in both Bt and non-Bt cotton was enhanced due to Pseudomonas seed treatment

Understanding functional group and assembly dynamics in temperature responsive systems leads to design principles for enzyme responsive assemblies

Understanding the molecular rules behind the dynamics of supramolecular assemblies is fundamentally important for the rational design of responsive assemblies with tunable properties. Herein, we report that the dynamics of temperature-sensitive supramolecular assemblies is not only affected by the dehydration of oligoethylene glycol (OEG) motifs, but also by the thermally-promoted molecular motions. These counteracting features set up a dynamics transition point (DTP) that can be modulated with subtle variations in a small hydrophobic patch on the hydrophilic face of the amphiphilic assembly. Understanding the structural factors that control the dynamics of the assemblies leads to rational design of enzyme-responsive assemblies with tunable temperature responsive profiles

Composite supramolecular nanoassemblies with independent stimulus sensitivities

U.S. Army Research Office; National Science Foundation; Chinese National Science Foundation [51173135]; PHaSE Energy Frontier Research Centre; Basic Energy Sciences of the U.S. Department of Energy; NSF-IGERT programNanoscale assemblies with stimuli-sensitive features have attracted significant attention due to implications in a variety of areas ranging from materials to biology. Recently, there have been excellent developments in obtaining nanoscale structures that are concurrently sensitive to multiple stimuli. Such nanostructures are primarily focused on a single nanostructure containing an appropriate combination of functional groups within the nanostructure. In this work, we outline a simple approach to bring together two disparate supramolecular assemblies that exhibit very different stimuli-sensitive characteristics. These composite nanostructures comprise a block copolymer micelle core and nanogel shell, both of which can preserve their respective morphology and stimulus sensitivities. The block copolymer is based on poly(2-(diisopropylamino) ethylmethacrylate-b-2-aminoethylmethacrylate hydrochloride), which contains a pH-sensitive hydrophobic block. Similarly, the redox-sensitive nanogel is derived from a poly(oligoethyleneglycolmonomethylethermethacrylate-co-glycidylmethacrylate-co-pyridyldisulfide ethylmethacrylate) based random copolymer. In addition to the independent pH-response of the micellar core and redox-sensitivity of the nanogel shell in the composite nanostructures, the synergy between the micelles and the nanogels have been demonstrated through a robust charge generation in the nanogels during the disassembly of the micelles. The supramolecular assembly and disassembly have been characterized using transmission electron microscopy, dynamic light scattering, zeta potential measurements, fluorescence spectroscopy and cellular uptake

Mechanisms of light energy harvesting in dendrimers and hyperbranched polymers

Since their earliest synthesis, much interest has arisen in the use of dendritic and structurally allied forms of polymer for light energy harvesting, especially as organic adjuncts for solar energy devices. With the facility to accommodate a proliferation of antenna chromophores, such materials can capture and channel light energy with a high degree of efficiency, each polymer unit potentially delivering the energy of one photon-or more, when optical nonlinearity is involved. To ensure the highest efficiency of operation, it is essential to understand the processes responsible for photon capture and channelling of the resulting electronic excitation. Highlighting the latest theoretical advances, this paper reviews the principal mechanisms, which prove to involve a complex interplay of structural, spectroscopic and electrodynamic properties. Designing materials with the capacity to capture and control light energy facilitates applications that now extend from solar energy to medical photonics. © 2011 by the authors; licensee MDPI, Basel, Switzerland

Genetic divergence is not the same as phenotypic divergence

Far too often, phenotypic divergence has been misinterpreted as genetic divergence, and based on phenotypic divergence, genetic divergence has been indicated. We have attempted to disprove this statement and call for the differentiation of phenotypic and genotypic variation

Characterisation of a dipolar chromophore with third-harmonic generation applications in the near-IR

E-2-Tricyanovinyl-3-n-hexyl-5-[4-{bis(4-n-butylphenyl)amino}-2-methoxystyryl]-thiophene, 1, has previously been used to demonstrate applications relying on frequency tripling of 1.55 μm light. Here we report the synthesis and chemical characterisation of 1, along with quantum-chemical calculations and additional experimental investigations of its third-order nonlinear properties that give more insight into its frequency tripling properties. Although 1 can be processed into amorphous films, crystals can also be grown by slow evaporation of solutions; the crystal structure determined by X-ray diffraction shows evidence of significant contributions from zwitterionic resonance forms to the ground-state structure, and reveals centrosymmetric packing exhibiting π–π and C–H···N≡C interactions. Both solutions and films of 1 exhibit near-infrared two-photon absorption into the low-lying one-photon-allowed state with a peak two-photon cross-section of cɑ. 290 GM (measured using the white-light continuum method with a pump wavelength of 1800 nm) at a transition energy equivalent to degenerate two-photon absorption at cɑ. 1360 nm; two related chromophores are also found to show comparable near-IR two-photon cross-sections. Closed-aperture Z-scan measurements and quantum-chemical calculations indicate that the nonlinear refractive index and third-harmonic generation properties of 1 are strongly dependent on frequency in the telecommunications range, due the aforementioned two-photon resonance