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.     

ESR and NMR studies of poly (amidoamine) dendrimers with ionic surfactants in different media

The electron paramagnetic resonance (EPR) study has been carried out for the micellar solutions of various ionic surfactant solutions as well as various generations of aqueous dendrimer both in their respective presence as well as their absence at 25°C and in different media. From these measurements, the rotation correlation time (τ_B) have been calculated for all the ionic surfactant + PAMAM + water system. A variation in the τ_Bvalue remains mostly constant for the dodecyltrimethyammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) + PAMAM + water ternary mixtures. The τ_Bvalue shows an increase with the increase in the amount of PAMAM for SDS in basic medium and for 12-2-12 in acidic medium. It has been concluded from these results that SDS undergo complexation with all generations of PAMAM in basic medium and 12-2-12 in acidic medium and produce stronger hydrophobic environment. The nuclear magnetic resonance study (NMR) allowed us to evaluate the spin–spin relaxation (T₁) times of SDS in the presence of all generations of PAMAM. The T₁ values for all the tail protons of SDS showed a slight decrease with the increase in the constant amount of PAMAM suggesting the adsorption of PAMAM molecules on the micelle surface.     

Equilibrium glassy phase in a polydisperse hard-sphere system

The phase diagram of a polydisperse hard-sphere system is examined by numerical minimization of a discretized form of the Ramakrishnan-Yussouff free-energy functional. Crystalline and glassy local minima of the free energy are located and the phase diagram in the density-polydispersity plane is mapped out by comparing the free energies of different local minima. The crystalline phase disappears and the glass becomes the equilibrium phase beyond a "terminal" value of the polydispersity. A crystal-to-glass transition is also observed as the density is increased at high polydispersity. The phase diagram obtained in our study is qualitatively similar to that of hard spheres in a quenched random potential.     

Structural and thermal studies on sisal fibre

Mechanical characteristics of sisal fibre, such as UTS and Young's modulus, have been determined. The thermal degradation of sisal fibre has been observed by running its DSC and TG/DTG.

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Zusammenfassung Die mechanischen Kennwerte (UTS, Young's Modul) von Sisalfasern wurden bestimmt. Der thermische Abbau von Sisalfasern wurde mittels DSC und TG/DTG untersucht.

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The authors wish to thank Dr. R. K. Tiwari, Dr. S. V. Prasad and Dr. M. Patel for their useful suggestions.     

Effect of Salicylic Acid on the Activity of PAL and PHB Geranyltransferase and Shikonin Derivatives Production in Cell Suspension Cultures of Arnebia euchroma (Royle) Johnst—a Medicinally Important Plant Species

Cell suspension cultures of Arnebia euchroma were established from the friable callus on liquid Murashige and Skoog medium supplemented with 6-benzylaminopurine (10.0 μM) and indole-3-butyric acid (5.0 μM). Salicylic acid was used to study its effect on the enzymes which participate in shikonin biosynthesis with respect to metabolite (shikonin) content in the cell suspension culture of A. euchroma. In our study, phenylalanine ammonia lyase and PHB geranyltransferase were selected from the entire biosynthetic pathway. Results showed that phenylalanine ammonia lyase is responsible for growth and PHB geranyltransferase for metabolite production. Salicylic acid exhibited an inverse relationship with the metabolite content (shikonin); salicylic acid (100 μM) completely inhibited shikonin biosynthesis. The results presented in the current study can be successfully employed for the metabolic engineering of its biosynthetic pathway for the enhancement of shikonin, which will not only help in meeting its industrial demand but also lead to the conservation of species in its natural habitat.     

Synthesis and single crystal structure of a new polymorph of 5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin,H2TTPCl4: Spectroscopic investigation of aggregation of H2TTPCl4

5, 10, 15, 20-tetrakis-(4-chlorophenyl) porphyrin, H₂TTPCl₄, has been isolated as a new polymorph following the modified Adler’s method and its X-ray crystal structure solved. The new polymorph (I) crystallises in the monoclinic space group, P2₁/n with a?=?10.1574(5) Å, b?=?8.9827(4) Å, c?=?20.9350(8) Å, β?=?102.532(4)°, V?=?1864.62(15) ų, Z?=?2. The previously found polymorph, prepared using Lindsay method was crystallised in monoclinic space group, P2₁/a with a?=?15.776 (13) Å, b?=?8.646 (3) Å, c?=?14.087 (5) Å, β?=?96.05 (5)°, V?=?1910.7 (3) ų, Z?=?2. The main difference between the two polymorphs seems to be the different packing arrangement of molecules in their crystal lattices. The dramatic self aggregation property of new polymorph (I) has also been investigated. The investigation reveals that under certain conditions of solute concentration and pH of the media, the compound exhibits a strong tendency to exist in a prominent self aggregated state in head-to-tail type (j-aggregation) molecular alignment. The self association behaviour of (I) was confirmed by UV-Vis absorption spectra, performed in chloroform by varying concentrations and pH changes and ¹H NMR spectra, performed in deuterated chloroform at varying concentrations and their results have been discussed in detail.     

Fumed silica nanoparticles–chitosan nanobiocomposite for ochratoxin-A detection

Fumed silica nanoparticles (NanoSiO₂) and chitosan (CH) based nanobiocomposite film have been used to co-immobilize rabbit-immunoglobulin antibodies (r-IgGs) and bovine serum albumin (BSA) for ochratoxin-A (OTA) detection. The observed three-dimensional (3D) arrangement of NanoSiO₂ in CH matrix via hydrogen bonding, available NH₂/OH groups and excellent film-forming ability of CH results in increased effective surface area of CH–NanoSiO₂ nanobiocomposite for r-IgGs immobilization. Electrochemical studies suggest that presence of NanoSiO₂ leads to enhanced electrochemical behaviour of CH resulting in increased electron transport between the medium and the electrode. BSA/r-IgGs/CH–NanoSiO₂/ITO immunoelectrode exhibits improved sensing characteristics such as linearity (0.5–6 ng/dL), detection limit (0.3 ng/dL), response time (25 s) and sensitivity (18 μA ng/dL cm⁻²) with correlation coefficient as 0.98.     

Photon transport in thin disordered slabs

We examine using Monte Carlo simulations, photon transport in optically ‘thin’ slabs whose thickness L is only a few times the transport mean free path l*, with particles of different scattering anisotropies. The confined geometry causes an auto-selection of only photons with looping paths to remain within the slab. The results of the Monte Carlo simulations are borne out by our analytical treatment that incorporates directional persistence by the use of the Ornstein-Uhlenbeck process, which interpolates between the short time ballistic and long time diffusive regimes.