Rh(III)-Catalyzed One-Step Synthesis of ortho-Alkynylated Perylene Imide Dyes: Optical and Electrochemical Properties of New Derivatives

A one-step Rh-catalyzed site-selective ortho-C−H alkynylation of perylene as well as naphthalene mono- and diimides is reported. A single step regioselective access to ortho-C−H alkynylated derivatives of these ryleneimides not only increases the step economy of the ortho-functionalization on these dyes but also provides a quick access route towards highly functionalized dyes that have potential optoelectronic applications. Increased solubility of tetra(triisopropylsilyl)acetylenyl PDIs in organic solvents greatly enhances their utility for further derivatization.     

DNA-Origami-Based Assembly of Au@Ag Nanostar Dimer Nanoantennas for Label-Free Sensing of Pyocyanin

Early-stage detection of diseases caused by pathogens is a prerequisite for expedient patient care. Due to the limited signal-to-noise ratio, molecular diagnostics needs molecular signal amplification after recognition of the target molecule. In this present study, we demonstrate the design of plasmonically coupled bimetallic Ag coated Au nanostar dimers with controlled nanogap using rectangular DNA origami. We further report the utility of the designed nanostar dimer structures as efficient SERS substrate for the ultrasensitive and label-free detection of the pyocyanin molecule, which is a biomarker of the opportunistic pathogenic bacteria, Pseudomonas aeruginosa. The experimental results showed that the detection limit of pyocyanin with such nanoantenna based biosensor was 335 pM, which is much lower than the clinical range of detection. Thus, fast, sensitive and label-free detection of pyocyanin at ultralow concentration in an infected human body can pave a facile route for early stage warning for severe bacterial infections.     

Chemically imaging the interaction of acetylated nanocrystalline cellulose (NCC) with a polylactic acid (PLA) polymer matrix

The non-covalent interaction of acetylated nanocrystalline cellulose (AC-NCC) with polylactic acid (PLA) in a composite blend has been studied at the micron scale by synchrotron Fourier transform infrared (FTIR) microspectroscopy. Microtomed sections of AC-NCC in PLA showed strong, localized carbonyl stretching (νC=O) absorbance characteristic of the cellulose acetylation, and this was observed on the surface of larger aggregated AC-NCC particles. A shift in the νC=O IR absorption peak of AC-NCC in PLA, relative to unblended AC-NCC was observed, which is indicative of an intermolecular interaction between AC-NCC and PLA matrix. Acetylation can therefore potentially improve the performance of the composite by enabling linkages between carbonyl groups, helping to establish a good stress transfer between the fiber and the matrix. This could in turn lead to a material with high yield elastic modulus. This is the first reported chemical imaging of acetylated nanocrystalline cellulose-based composite materials using synchrotron FTIR microspectroscopy.     

Design of Silica@Au Hybrid Nanostars for Enhanced SERS and Photothermal Effect

Core-shell nanostructures of silicon oxide@noble metal have drawn a lot of interest due to their distinctive characteristics and minimal toxicity with remarkable biocompatibility. Due to the unique property of localized surface plasmon resonance (LSPR), plasmonic nanoparticles are being used as surface-enhanced Raman scattering (SERS) based detection of pollutants and photothermal (PT) agents in cancer therapy. Herein, we demonstrate the synthesis of multifunctional silica core – Au nanostars shell (SiO₂@Au NSs) nanostructures using surfactant free aqueous phase method. The SERS performance of the as-synthesized anisotropic core-shell NSs was examined using Rhodamine B (RhB) dye as a Raman probe and resulted in strong enhancement factor of 1.37×10⁶. Furthermore, SiO₂@Au NSs were also employed for PT killing of breast cancer cells and they exhibited a concentration-dependent increase in the photothermal effect. The SiO₂@Au NSs show remarkable photothermal conversion efficiency of up to 72 % which is unprecedented. As an outcome, our synthesized NIR active SiO₂@Au NSs are of pivotal importance to have their dual applications in SERS enhancement and PT effect.     

Synthesis and Characterisation of Polyvinyl alcohol (PVA)/Silica Hybrid Composites Derived Through the Sol-Gel Method in Aqueous Medium: Effect of Acid Content,Silica Content and Viscosity of PVA on the Dispersion Characteristics of Silica and the Physical Properties of the Composites

A cheap and environment friendly route towards the synthesis of Polyvinyl alcohol/silica hybrid composites is presented. Polyvinyl alcohol/silicate hybrid materials were synthesised in aqueous medium by the sol-gel method using dil HCl (0.5 N) as catalyst and a cost-effective silica source sodium silicate. The synthesis method was aimed at enhancing the rate of co-condensation of silica within the polyvinyl alcohol matrix. Transparent and flexible hybrid films of homogenous thickness were obtained after gelation at 45°C for 24 h and extended drying for another 48 h. The hybrid composites were characterised by fourier transform infrared spectroscopy (FTIR), scanning electron microscopoy (SEM), thermogravimeric analysis (TGA), tensile strength, elongation at break and water uptake measurements. SEM micrographs revealed that silica was dispersed in the PVA matrix without the large aggregation of particles for a molar composition of 0.0004 PVA:0.048 Sodium silicate: 0.004 HCl.     

Spectroscopic Investigations on the H-Type Aggregation of Coumarin 153 Dye Molecules: Role of Au Nanoparticles and γ- Cyclodextrin

Here, we study the formation of H-type aggregation of coumarin 153 (C153) dye molecule in presence of Au nanoparticles and the removal of dye aggregation in presence of γ- cyclodextrin (CD) due to confinement of dye molecules inside the nanocavity of γ- cyclodextrin (CD) using steady state and time resolved spectroscopy. Blue shifting of absorption band, photoluminescence (PL) band and the enhancement of decay time of C153 dye confirm the formation of H-aggregation. It is found that the concentrations of γ-CD and Au nanoparticles play an important role on H-type aggregation of dye. The rotational relaxation time of free C153 is 0.113 ns and the average relaxation time of C153 dye are 0.275 ns and 0.425 ns for 2 mM and 5 mM γ-CD confined systems, respectively, indicating the anisotropy increases due to confinement of dye. An associated type anisotropy decay of C153 dye is found at 20 mM concentration of CD may be due to formation of nanotubular aggregates of γ-CD.     

Harvesting of a prey–predator fishery in the presence of toxicity

In this model we discuss the bioeconomic harvesting of a prey–predator fishery in which both the species are infected by some toxicants released by some other species. Here both the species are harvested where we use the usual catch-per-unit-effort hypothesis. The dynamical behaviour of the exploited system is examined. The possibility of existence of a bionomic equilibrium is considered. The optimal harvesting policy is studied by using Pontryagin’s maximal principle. Some numerical examples and the corresponding solution curves are studied to illustrate the results of the model. Finally, the existence of limit cycle is discussed.     

Photophysical Properties of Au‐CdTe Hybrid Nanostructures of Varying Sizes and Shapes

We design well‐defined metal‐semiconductor nanostructures using thiol‐functionalized CdTe quantum dots (QDs)/quantum rods (QRs) with bovine serum albumin (BSA) protein‐conjugated Au nanoparticles (NPs)/nanorods (NRs) in aqueous solution. The main focus of this article is to address the impacts of size and shape on the photophysical properties, including radiative and nonradiative decay processes and energy transfers, of Au‐CdTe hybrid nanostructures. The red shifting of the plasmonic band and the strong photoluminescence (PL) quenching reveal a strong interaction between plasmons and excitons in these Au‐CdTe hybrid nanostructures. The PL quenching of CdTe QDs varies from 40 to 86 % by changing the size and shape of the Au NPs. The radiative as well as the nonradiative decay rates of the CdTe QDs/QRs are found to be affected in the presence of both Au NPs and NRs. A significant change in the nonradiative decay rate from 4.72×10⁶ to 3.92×10¹⁰ s^?1 is obtained for Au NR‐conjugated CdTe QDs. It is seen that the sizes and shapes of the Au NPs have a pronounced effect on the distance‐dependent energy transfer. Such metal‐semiconductor hybrid nanostructures should have great potentials for nonlinear optical properties, photovoltaic devices, and chemical sensors.