Tailoring local density of optical states to control emission intensity and anisotropy of quantum dots in hybrid photonic-plasmonic templates

We report results of controlled tuning of the local density of states (LDOS) in versatile, flexible, and hierarchical self assembled plasmonic templates. Using 5 nm diameter gold (Au) spherical nanoantenna within a polymer template randomly dispersed with quantum dots, we show how the photoluminescence intensity and lifetime anisotropy of these dots can be significantly enhanced through LDOS tuning. Finite difference time domain simulations corroborate the experimental observations and extend the regime of enhancement to a wider range of geometric and spectral parameters bringing out the versatility of these functional plasmonic templates. It is also demonstrated how the templates act as plasmonic resonators for effectively engineer giant enhancement of the scattering efficiency of these nano antenna embedded in the templates. Our work provides an alternative method to achieve spontaneous emission intensity and anisotropy enhancement with true nanoscale plasmon resonators. (C) 2015 AIP Publishing LLC.

Phenomenology and control of buckling dynamics in multicomponent colloidal droplets

Self-assembly of nano sized particles during natural drying causes agglomeration and shell formation at the surface of micron sized droplets. The shell undergoes sol-gel transition leading to buckling at the weakest point on the surface and produces different types of structures. Manipulation of the buckling rate with inclusion of surfactant (sodium dodecyl sulphate, SDS) and salt (anilinium hydrochloride, AHC) to the nano-sized particle dispersion (nanosilica) is reported here in an acoustically levitated single droplet. Buckling in levitated droplets is a cumulative, complicated function of acoustic streaming, chemistry, agglomeration rate, porosity, radius of curvature, and elastic energy of shell. We put forward our hypothesis on how buckling occurs and can be suppressed during natural drying of the droplets. Global precipitation of aggregates due to slow drying of surfactant-added droplets (no added salts) enhances the rigidity of the shell formed and hence reduces the buckling probability of the shell. On the contrary, adsorption of SDS aggregates on salt ions facilitates the buckling phenomenon with an addition of minute concentration of the aniline salt to the dispersion. Variation in the concentration of the added particles (SDS/AHC) also leads to starkly different morphologies and transient behaviour of buckling (buckling modes like paraboloid, ellipsoid, and buckling rates). Tuning of the buckling rate causes a transition in the final morphology from ring and bowl shapes to cocoon type of structure. (C) 2015 AIP Publishing LLC.

Design and morphology control of a thiophene derivative through electrospraying using various solvents

In the present work, electrospraying of an organic molecule is carried out using various solvents, obtaining fibril structures along with a range of distinct morphologies. Solvent characteristics play a major role in determining the morphology of the organic material. A thiophene derivative (7,9-di(thiophen-2-yl)-8H-cyclopentaa]acenaphthylen-8-one) (DTCPA) of donor-acceptor-donor (DAD) architecture is used to study this solvent effect. Seven solvents with decreasing vapour pressure are selected for experiments. Electrospraying is conducted at a solution concentration of 1.5 wt% and a constant applied voltage of 15 kV. Gradual transformation in morphology of the electrospun product from spiked-spheres to only spikes is observed. A mechanism describing this transformation is proposed based on electron micrograph analysis and XRD analysis. These data indicate that the morphological change is due to the synergistic effect of both vapour pressure and dielectric constant of the solvents. Through a reasonable control of the crystallite size and morphology along with the proposal of the transformation mechanism, this study elucidates electrospraying as a prospective method for designing architectures in organic electronics.

Instrumentation and control of a two-stage 4-bed silica gel plus water adsorption cooling cum desalination system

This paper presents the instrumentation and control architecture for a laboratory based two-stage 4-bed silica gel + water adsorption system. The system consists of primarily two fluids: refrigerant (water vapour) and heat transfer fluid (water) flowing through various components. Heat input to the system is simulated using multiple heaters and ambient air is used as the heat sink. The laboratory setup incorporates a real time National Instruments (NI) controller to control several digital and analog valves, heaters, pumps and fans along with simultaneous data acquisition from various flow, pressure and temperature sensors. The paper also presents in detail the various automated and manual tasks required for successful operation of the system. Finally the system pressure and temperature dynamics are reported and its performance evaluated for various cycle times. (C) 2015 Elsevier Ltd. All rights reserved.

Mitochondrial selectivity and remarkable photocytotoxicity of a ferrocenyl neodymium(III) complex of terpyridine and curcumin in cancer cells

A series of four novel neodymium(III) complexes of the formulation Nd(R-tpy)(O-O)(NO3)(2)] (1-4), where R-tpy is 4'-phenyl-2,2': 6', 2''-terpyridine (Ph-tpy; 1, 2) and 4'-ferrocenyl-2,2': 6', 2''-terpyridine (Fc-tpy; 3, 4); O-O is the conjugate base of acetylacetone (Hacac; 1, 3) or curcumin (Hcurc; 2, 4), are synthesized and characterized. The single crystal structure of 1 shows that the complex is a discrete mononuclear species with the Nd(III) centre in a nine coordinate environment provided by a set of O6N3 donor atoms. Complexes 1 and 3 having the simple acac ligand are prepared as control compounds. Complex 4, possessing an appended ferrocenyl (Fc) and the curcumin moiety, is remarkably photocytotoxic to HeLa and MCF-7 cancer cells in visible light giving respective IC50 values of 0.7 mu M and 2.1 mu M while being significantly less toxic to MCF-10A normal cells (IC50 = 34 mu M) and in the dark (IC50 > 50 mu M). The phenyl appended complex 2, lacking a ferrocenyl moiety, is significantly less toxic to both the cell lines when compared with 4. Complexes 1 and 3, lacking the photoactive curcumin moiety, do not show any apparent toxicity both in light and in the dark. The cell death is apoptotic in nature and is mediated by the light-induced formation of reactive oxygen species (ROS). Fluorescence imaging experiment with HeLa cells reveals mitochondrial accumulation of complex 4 within 4 h of incubation. The complexes bind to calf thymus (ct) DNA with moderate affinity giving K-b values in the range of 10(4)-10(5) M-1. The curcumin complexes 2 and 4 cleave plasmid supercoiled DNA to its nicked circular form in visible light via O-1(2) and (OH)-O-center dot pathways. The presence of the ferrocenyl moiety is likely to be responsible for the enhanced cellular uptake and photocytotoxicity of complex 4. Thus, the mitochondria targeting complex 4, being remarkably cytotoxic in light but non-toxic in the dark and to normal cells, is a potential candidate for photochemotherapeutic applications.