Ranjit De

Morphological and SERS Properties of Silver Nanorod Array Films Fabricated by Oblique Thermal Evaporation at Various Substrate Temperatures

Aligned silver nanorod (AgNR) array films were fabricated by oblique thermal evaporation. The substrate temperature during evaporation was varied from 10 to 100 °C using a home-built water cooling system. Deposition angle and substrate temperature were found to be the most important parameters for the morphology of fabricated films. Especially, it was found that there exists a critical temperature at ~90 °C for the formation of the AgNR array. The highest enhancement factor of the surface-enhanced Raman scattering (SERS), observed in the Ag films coated with benzenethiol monolayer, was ~6 × 107. Hot spots, excited in narrow gaps between nanorods, were attributed to the huge enhancement factor by our finite-difference time-domain (FDTD) simulation reflecting the real morphology.

Influence of sodium carboxymethylcellulose on the aggregation behavior of aqueous 1-hexadecyl-3-methylimidazolium chloride solutions.

The influence of sodium carboxymethylcellulose (NaCMC) on the aggregation phenomena of a surface active ionic liquid 1-hexadecyl-3-methylimidazolium chloride (C16MeImCl) was studied in aqueous solutions using electrical conductivity and surface tension measurements. The counterion condensation behavior of NaCMC (aq) and the premicellar ion-association behavior of C16MeImCl (aq) were also investigated. Two characteristic concentrations, namely the critical aggregation concentration and polymer saturation concentration, before free C16MeImCl micelles appear in C16MeImCl-NaCMC solutions have been identified. Effects of temperature, NaCMC concentration, and the charge density parameter of NaCMC on the self-aggregation of the C16MeImCl have been discussed to elucidate C16MeImCl-NaCMC interactions. The thermodynamic parameters for micellization of C16MeImCl were estimated both in absence and in the presence of NaCMC. The observed enthalpy-entropy compensation effect in C16MeImCl and C16MeImCl-NaCMC systems provided important insight as to how micellization processes are governed by the bulk structural property of the solution with respect to that of the water.

Cancer therapeutics with epigallocatechin-3-gallate encapsulated in biopolymeric nanoparticles

With the recent quantum leap in chemoprevention by dietary products, their use as cancer therapeutics is garnering worldwide attention. The concept of effortlessly fighting this deadly disease by gulping cups of green tea or swallowing green tea extract capsules is appreciated universally. Epigallocatechin-3-gallate (EGCG), a major polyphenol in green tea, has generated significant interest in controlling carcinogenesis due to its growth-inhibitory efficacy against a variety of cancers by targeting multiple signaling pathways. However, the success of EGCG in preclinical studies is difficult to translate into clinical trials due to issues of low solubility, bioavailability and an uncertain therapeutic window. The laborious and expensive journey of drugs from the laboratory to commercialization can be improved by utilizing nanoparticles as anti-cancer drug carriers. Exploitation of biopolymeric nanoparticles in recent years has improved EGCGs biodistribution, stability and tumor selectivity, revealing its superior chemopreventive effects. This review briefly summarizes recent developments regarding the targets and side effects of EGCG, complications associated with its low bioavailability and critically analyses the application of biopolymeric nanoparticles encapsulating EGCG as a next generation delivery systems.

Influence of temperature, added electrolyte, and polymer molecular weight on the counterion-condensation phenomenon in aqueous solution of sodium polystyrenesulfonate: a scaling theory approach

Interactions between a polyion and its counterions in aqueous solutions of an anionic polyelectrolyte sodium polystyrenesulfonate in the presence of sodium chloride were investigated using electrical conductivity as the probe. The specific conductivity vs. polyelectrolyte concentration data were analyzed with an equation recently developed by us considering the scaling description for the conformation of a polyion chain. The influences of (a) the molecular weight and the concentration of the polyelectrolyte, (b) the added electrolyte concentration, and (c) the temperature on polyion–counterion interactions were investigated. The extent of counterion condensation was found to be greatly affected by the concentration and molecular weight of the polyelectrolyte, the concentration of the added electrolyte, and the temperature. The polyion equivalent conductivity in conjunction with the derived coefficient of friction between the monomer units and the solvent provided important information concerning the relative importance of the size and charge of the polyions. The overall results have been elucidated taking the medium dielectric constant, the hydration behaviour of the counterions, and the coiling behavior of the polyion chains into account. The present study provides new insight as to how the polyelectrolyte molecular weight influences the counterion condensation behaviour in a polyelectrolyte solution in the presence of an added electrolyte.

Sodium carboxymethylcellulose-induced aggregation of 1-decyl-3-methylimidazolium chloride in aqueous solutions.

Aggregation behavior of a surface active ionic liquid 1-decyl-3-methylimidazolium chloride (C10MeImCl) was studied in aqueous solutions in absence and in presence of sodium carboxymethylcellulose (NaCMC) by electrical conductivity, surface tension, vapor pressure, and fluorescence measurements. Ion-association behavior of C10MeImCl (aq) in the premicellar regime has also been investigated. Two characteristic concentrations, namely the critical aggregation concentration and polymer saturation concentration, before free C10MeImCl micelles appear in C10MeImCl-NaCMC solutions were identified. Effects of temperature, NaCMC concentration, and the bulk solution structural property on the self-aggregation of C10MeImCl have been discussed to elucidate C10MeImCl-NaCMC interactions. Thermodynamics of the micellization processes provided important insight regarding the (a) release of water molecules from the hydration layer around the hydrophilic domain, and from the water cage around the hydrophobic moiety of the SAIL, and (b) transfer of the hydrocarbon chains into the micelle and restoration of the H-bonding structure of the water around the micelle.

Long-Standing Stability of Silver Nanorod Array Substrates Functionalized Using a Series of Thiols for a SERS-Based Sensing Application

Silver nanorod (AgNR) array substrates were fabricated using an oblique angle thermal evaporation technique; their long-term stability, surface uniformity and reproducibility, which are primary requirements for their widespread realistic application and commercialization, were assessed using surface-enhanced Raman scattering (SERS) spectroscopy. The nanorod surfaces were functionalized using a series of organic thiols, which range from hydrophilic to hydrophobic, to mimic various conditions that often arise during detection of hydrophilic/phobic analytes in a realistic application field. A group of these functionalized substrates was stored in ambient laboratory atmosphere; another in light minimized, moisture-free vacuum; while another was stowed carefully and neatly in water to mimic realistic conditions. The effects of these storing conditions were studied. A surfactant was added to the water to maintain consistent surface wetting in the third group. SERS spectra of nanorod substrates prior to functionalization were also recorded to investigate the effect of adventitious carbonaceous contaminants. A meticulous systematic study on the reproducibility of SERS signals was carried out: spot-to-spot, substrate-to-substrate, batch-to-batch, day-to-day. The relative standard deviation (RSD) shown by the SERS signals acquired from various spots of a single substrate was less than 3%, which is very similar to the only account reported so far, in which RSD is reported as 2%. The wetting behavior of these thiol functionalized AgNR substrates are investigated using static contact angle measurements. The functionalized substrates have exhibited excellent long-standing stability over a period of six months when stored appropriately; hence, they are highly suitable for mass production towards realistic application.