Dipankar Chattopadhyay

Synthesis, characterization and antimicrobial activity of dextran stabilized silver nanoparticles in aqueous medium

A simple one-step rapid synthetic route is described for the preparation of silver nanoparticles by reduction of silver nitrate (AgNO3) using aqueous dextran solution which acts as both reducing and capping agent. The formation of silver nanoparticles is assured by characterization with UV-vis spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The absorbance of the silver nanoparticles is observed at 423 nm. The AFM image clearly shows the surface morphology of the well-dispersed silver nanoparticles with size range of 10-60 nm. TEM images show that the nanoparticles are spherical in shape with ∼5-10 nm dimensions. The crystallinity of Ag nanoparticles is assured by XRD analysis. The antimicrobial activity of as synthesized silver nanoparticles is tested against the bacteria, Bacillus subtilis, Bacillus cereus, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. The bacterial growth is inhibited by gradual reduction of the concentration of the silver nanoparticles.

Anticancer (in vitro) and antimicrobial effect of gold nanoparticles synthesized using Abelmoschus esculentus (L.) pulp extract via a green route

Green synthesis of gold nanoparticles (Au NPs) using Abelmoschus esculentus (L.) pulp extract has been elaborately studied and reported here. The Au NPs have been characterized using several techniques. Optical analysis indicates adequate stability of the synthesized Au NPs, while FTIR analyses the fact that phytochemicals present in the Abelmoschus esculentus (L.) pulp extract play the key role in stabilizing the Au NPs. Morphological study shows that the nanoparticles are mostly spherical in shape with an average particle size of ∼14 nm, and these results are comparable with the particle size obtained from XRD. The selected area electron diffraction pattern indicates the crystalline nature of the Au NPs, which is further confirmed from XRD studies. The present study also demonstrates the in vitro efficacy of Au NPs against Jurkat cells. Results show that the IC50 dose of Au NPs is capable of significantly elevating intracellular reactive oxygen species and diminishing mitochondrial membrane potential, indicating the effective involvement of apoptosis in cell death. Furthermore, the synthesized Au NPs show a sufficient degree of antimicrobial activity against different types of bacteria. These results clearly show that the Abelmoschus esculentus (L.) pulp synthesized Au NPs have excellent medicinal applications.

Studies on methylcellulose/pectin/montmorillonite nanocomposite films and their application possibilities.

Films based on methylcellulose (MC) and pectin (PEC) of different ratios were prepared. MC/PEC (90:10) (MP10) gave the best results in terms of mechanical properties. Sodium montmorillonite (MMT) (1, 3 and 5 wt%) was incorporated in the MP10 matrix. The resulting films were characterized by X-ray diffraction and transmission electron microscopy, and it was found that nanocomposites were intercalated in nature. Mechanical studies established that addition of 3 wt% MMT gave best results in terms of mechanical properties. However, thermo-gravimetric and dynamic mechanical analysis proved that decomposition and glass transition temperature increased with increasing MMT concentration from 1 to 5 wt%. It was also observed that moisture absorption and water vapor permeability studies gave best result in the case of 3 wt% MMT. Optical clarity of the nanocomposite films was not much affected with loading of MMT. In vitro drug release studies showed that MC/PEC/MMT based films can be used for controlled transdermal drug delivery applications.

Effect of xanthan gum and guar gum on in situ gelling ophthalmic drug delivery system based on poloxamer-407

The aim of this investigation was to develop a novel in situ gelling formulation based on poloxamer-407 (PM) for the sustained release of an ophthalmic drug. In an attempt to reduce the concentration of PM without compromising the in situ gelling capability and also to increase the drug release time, xanthan gum (XG) and guar gum (GG) were added into PM to develop different formulations. At concentrations of 18% and above, the PM was able to undergo sol-gel transition below body temperature. It was found that XG and GG at a weight ratio of 3:7 were able to convert PM solution into gel below body temperature at PM concentrations below 18%. Both the in vitro and in vivo studies indicated that the PM with an XG-GG combination had a better ability to retain the drug than PM itself. The results indicated that the developed in situ gelling formulations containing PM with XG-GG may be a better alternative than a conventional eye drop.

Effect of clay concentration on morphology and properties of hydroxypropylmethylcellulose films

Hydroxypropylmethylcellulose (HPMC)/montmorillonite (MMT) nanocomposite films are prepared by solution intercalation method. Mechanical, thermal, moisture absorption, optical clarity and water vapor permeability of HPMC/MMT nanocomposite films are measured. X-ray diffraction (XRD) and transmission electron microscopic (TEM) results establish formation of partially intercalated and partially exfoliated HPMC/MMT nanocomposite films. In presence of MMT, the tensile strength, tensile modulus and elongation at break of HPMC films are improved. The thermal stability of HPMC/MMT nanocomposites is better than pure HPMC. The moisture absorption of HPMC film measured in 75% of constant relative humidity is reduced with loading of MMT. Optical clarity of HPMC film is almost unaffected in presence of MMT. Water vapor permeability of HPMC decreases in presence of nanoclay due to increasing tortuous path for diffusion.

Synthesis of methylcellulose-silver nanocomposite and investigation of mechanical and antimicrobial properties.

In this paper we reported preparation of methylcellulose-silver nanocomposite films by mixing of aqueous solution of methylcellulose with silver nitrate followed by casting. The silver nanoparticles were generated in methylcellulose matrix through reduction and stabilization by methylcellulose. The surface plasmon band at 412 nm indicated the formation of Ag nanoparticles. The MC-Ag nanocomposite films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The X-ray diffraction analysis of synthesized MC-Ag nanocomposite films revealed that metallic silver was present in face centered cubic crystal structure. Average crystallite size of silver nanocrystal was 22.7 nm. The FTIR peaks of as-synthesized MC-Ag nanocomposite fully designated the strong interaction between Ag nanoparticles and MC matrix. Nano-sized silver modified methylcellulose showed enhanced mechanical properties i.e. the introduction of Ag leading to both strengthening and toughening of MC matrix. The methylcellulose-silver nanocomposite films offered excellent antimicrobial activity against various microorganisms.

In situ synthesis of a reduced graphene oxide/cuprous oxide nanocomposite: a reusable catalyst

A reduced graphene oxide/cuprous oxide (RGO/Cu2O) nanocomposite has been successfully synthesized applying a simple in situ reduction method using an aqueous solution of lactulose which is used simultaneously as a reducing and stabilizing agent. Lactulose, a disaccharide, has the ability to reduce both GO and CuSO4 in situ under alkaline conditions. The GO and RGO/Cu2O nanocomposites are characterized using transmission electron microscopy, energy dispersive X-ray spectroscopy, field emission scanning electron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and UV-vis absorption spectroscopy. The surface charge as well as stability is established by analyzing the zeta potential value. The results confirm the synthesis of the RGO/Cu2O nanocomposite and the existence of interactions between Cu2O and RGO. It is also observed that Cu2O nanoparticles with an average size of 5 nm are uniformly dispersed throughout the RGO sheets. The catalytic activity of the RGO/Cu2O nanocomposite is excellent for the ‘click’ reaction and remains the same for six cycles.

Antibacterial activity of Ag-Au alloy NPs and chemical sensor property of Au NPs synthesized by dextran.

Gold and silver-gold alloy nanoparticles with mean diameter of 10nm and narrow size distribution were prepared by reduction of the correspondent metal precursors using aqueous dextran solution which acts as both a reducing and capping agent. The formation of nanoparticles was characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS). The silver and gold nanoparticles exhibited absorption maxima at 425 and 551 nm respectively; while for the bimetallic Ag-Au alloy appeared 520 nm in between them. TEM images showed monodispersed particles in the range of 8-10nm. The crystallinity of the nanoparticles was assured by XRD analysis. DLS data gave particle size distribution. The dextran stabilized Au nanoparticles used as a colorimetric sensor for detection and estimation of pesticide present in water. The dextran stabilized Ag-Au alloy nanoparticles exhibited interesting antimicrobial activity against bacteria at micromolar concentrations.

Synthesis of 2,3-dihydroquinazolinones and quinazolin-4(3H)-ones catalyzed by graphene oxide nanosheets in an aqueous medium: “on-water” synthesis accompanied by carbocatalysis and selective C–C bond cleavage

Graphene oxide (GO) nanosheet catalyzed new and straightforward strategies for the construction of 2,3-dihydroquinazolinones and quinazolin-4(3H)-ones starting from anthranilamide (2-aminobenzamide) and an aldehyde/ketone in aqueous medium at room temperature have been realized. This catalyst is also found to be efficient for the expedient construction of quinazolin-4(3H)-ones starting from anthranilamide and a β-ketoester/1,3-diketone following selective C–C bond cleavage of the β-ketoester/1,3-diketone at an elevated temperature under metal and oxidant free conditions.

Physical and electrochemical characterization of reduced graphene oxide/silver nanocomposites synthesized by adopting a green approach

This study demonstrates the physical and electrochemical characterization of nanocomposites based on reduced graphene oxide (RGO) and silver nanoparticles (Ag NPs) synthesized by adopting a green and low cost approach using lactulose as a reducing and stabilizing agent. The RGO/Ag nanocomposites were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy and transmission electron microscopy (TEM) to obtain clear information about the removal of functional groups and morphology of nanocomposites. XRD results confirmed the formation of a high purity crystal of Ag on RGO. FTIR results established partial reduction of GO to RGO by lactulose. TEM images show that spherical Ag NPs of an average size of 4 nm are uniformly deposited onto RGO sheets and also prevent the restacking of RGO layers. The energy dispersive X-ray spectra (EDX) of RGO/Ag nanocomposites indicate the presence of Ag and graphene. Also, EDX spectra of FESEM show that Ag content increases with the increasing concentration of AgNO3 in RGO/Ag nanocomposites. The surface charge as well as stability of the nanocomposites is examined by measuring the zeta potential while electro-conductivity is measured by potentiostat–galvanostat. The zeta potential and conductivity of RGO/Ag nanocomposites is greatly improved compared to GO and RGO. The electro-conductivity of RGO/Ag nanocomposites indicates that conductivity of RGO/Ag nanocomposite increases with increasing concentration of Ag. The electrochemical result also indicates the presence of a higher amount of ionic functional groups in GO than those in RGO and RGO/Ag nanocomposites. GO indicates the lowest current which gradually increased for RGO and RGO/Ag nanocomposites, respectively.