Arun Chattopadhyay

The antibacterial properties of a novel chitosan–Ag-nanoparticle composite

Escherichia coli expressing recombinant green fluorescent protein was used to test the bactericidal efficacy of a newly synthesized chitosan-Ag-nanoparticle composite. The composite was found to have significantly higher antimicrobial activity than its components at their respective concentrations. The one-pot synthesis method led to the formation of small Ag nanoparticles attached to the polymer which can be dispersed in media of pH< or =6.3. The presence of a small percentage (2.15%, w/w) of metal nanoparticles in the composite was enough to significantly enhance inactivation of E. coli as compared with unaltered chitosan. Fluorescence spectroscopy indicated that bacterial growth stopped immediately after exposure of E. coli to the composite, with release of cellular green fluorescent protein into the medium at a faster rate than with chitosan. Fluorescence confocal laser scanning and scanning electron microscopy showed attachment of the bacteria to the composite and their subsequent fragmentation. Native protein gel electrophoresis experiments indicated no effect of the composite on bacterial proteins.

SIGNALING GENE CASCADE IN SILVER NANOPARTICLE INDUCED APOPTOSIS

Nanoscale materials are presently gaining much importance for biological applications especially in the field of medicine. The large numbers of nanomaterial based products that are currently being developed - with projected applications in medicine - have inspired a growing interest in exploring their impact on cellular gene expression. The present study examines the effects of silver nanoparticles (NPs) on genes expression in an endeavor to assess the fundamental mechanisms that contribute to silver NP induced programmed cell death. Here, we have used RT-PCR to study the gene expression, flow cytometry analyses to probe the extent of apoptosis (FACS) and atomic force microscopy (AFM) to follow the cell membrane topology change induced by Ag NPs. The gene expression study revealed that Ag NP induced p53-mediated apoptotic pathway through which most of the chemotherapeutic drugs trigger apoptosis (programmed cell death). The results also suggest that Ag NPs could be attributed as therapeutic agent for biomedical and pharmaceutical applications.

Implications of silver nanoparticle induced cell apoptosis for in vitro gene therapy

The impact of manufactured nanomaterials on human health and the environment is a major concern for commercial use of nanotechnology based products. A judicious choice of selective usage, lower nanomaterial concentration and use in combination with conventional therapeutic materials may provide the best solution. For example, silver nanoparticles (Ag NPs) are known to be bactericidal and also cytotoxic to mammalian cells. Herein, we investigate the molecular mechanism of Ag NP mediated cytotoxicity in both cancer and non-cancer cells and find that optimum particle concentration leads to programmed cell death in vitro. Also, the benefit of the cytotoxic effects of Ag NPs was tested for therapeutic use in conjunction with conventional gene therapy. The synergistic effect of Ag NPs on the uracil phosphoribosyltransferase expression system sensitized the cells more towards treatment with the drug 5-fluorouracil. Induction of the apoptotic pathway makes Ag NPs a representative of a new chemosensitization strategy for future application in gene therapy.

Presence of Amorphous Carbon Nanoparticles in Food Caramels

We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe.

Heightened Reactive Oxygen Species Generation in the Antimicrobial Activity of a Three Component Iodinated Chitosan−Silver Nanoparticle Composite

Herein we report synergy in antimicrobial activity of a chitosan-silver nanoparticle (CS-Ag NP) composite in the presence of molecular iodine. Green fluorescent protein (GFP) expressing recombinant Escherichia coli bacteria have been used to test the efficacy and establish the mechanism of action. Experimental evidence indicate significantly high bactericidal activity of the nanocomposite in the presence of iodine than either due to the composite, chitosan, Ag NP or iodine only. Transmission electron microscopy measurements revealed attachment of bacteria to the composite. In addition, flow cytometry results supported definite occurrence of cell wall damage of the bacteria treated with the composite in the presence of iodine. Further, the nanocomposite and iodine combination was found to exert reactive oxygen species (ROS) generated oxidative stress in the cytoplasm of bacterial cells, leading to cell death. Elucidation of the mechanism of synergy due to three potential antibacterial components suggested that on the surface of Ag NPs molecular iodine possibly generated iodine atom thus contributing toward free radical induced oxidative stress, whereas chitosan and Ag NPs facilitated the process of cell killing and thus collectively enhanced the potency of antimicrobial effect at the lowest concentrations of individual components.

Blue-emitting copper nanoclusters synthesized in the presence of lysozyme as candidates for cell labeling.

Highly fluorescent copper nanoclusters (Cu NCs) have been synthesized using single-step reduction of copper sulfate by hydrazine in the presence of lysozyme. The fluorescence quantum yield was measured to be as high as 18%. The emission was also found to be dependent on the excitation wavelength. Mass spectrometric analyses indicated the presence of species corresponding to Cu2 to Cu9. Transmission electron microscopic analyses indicated the formation of agglomerated particles of average diameter of 2.3 nm, which were constituted of smaller particles of average diameter of 0.96 nm. They were found to be stable between pH 4 and 10 and in addition having excellent chemical and photostability. The noncytotoxic NCs were used to successfully label cervical cancer HeLa cells.

Fabrication of antibacterial silver nanoparticle—sodium alginate–chitosan composite films

A new and simple ecofriendly method for the synthesis of silver nanoparticles (Ag NPs) using a natural biopolymer, sodium alginate as both reducing and stabilizing agent is reported. The synthesized NPs were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction pattern (SAED). The alginate capped NPs (Alg–Ag NPs) were found to be antibacterial. The Alg–Ag NPs were blended with varying amounts of chitosan to form polyelectrolyte complex that was cast into stable films. The films were characterized by field emission scanning electron microscopy (FESEM), optical microscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The water uptake and mechanical properties of the films were also studied. The blended film demonstrated excellent antibacterial activity against both Gram negative and Gram positive bacteria with more activity against Gram positive bacteria. Thus, the developed films have a potential to be used for various antibacterial applications in biotechnology and biomedical fields.

Iodine-stabilized Cu nanoparticle chitosan composite for antibacterial applications.

We report herein the synthesis of a new composite consisting of Cu nanoparticles (NPs) and chitosan (CS), which has been found to be stable in the presence of molecular iodine and has also high antimicrobial activities. The composite could be obtained when aqueous CuSO(4) was treated with hydrazine in the presence of CS. The spherical Cu NPs present in the composite were of average diameters 8±4 nm. The NPs were unstable in atmospheric conditions leading to the formation of oxides of Cu. On the other hand, when molecular iodine was added to the medium following synthesis the NPs were rather stable. Studies of antibacterial property were carried out on Gram-negative green fluorescent expressing Escherichia coli bacteria & Gram-positive Bacillus cereus bacteria. The minimum inhibitory concentration (MIC) of the iodinated composite on Escherichia coli was found to be 130.8 μg/mL, which contained 21.5 μg/mL Cu NPs. This determined value of MIC for Cu NPs was much lower than those reported in the literature. Zeta potential (ζ) measurements supported an attractive interaction between iodinated CS-Cu NP composite and bacteria which was further supported by electron microscopic images. Electron microscopic and flow cytometric studies revealed that the iodinated CS-Cu NP composite was attached to the bacterial cell wall, which caused irreversible damage to the membrane, eventually leading to cell death. Mechanism of bactericidal action of the iodinated composite is discussed in light of our findings.

The pH taxis of an intelligent catalytic microbot.

A Pd nanoparticle-containing polymer microsphere moves with increasing speed across a pH gradient, following differential catalytic decomposition of aqueous hydrogen peroxide. The directional motion is akin to the pH taxis of living microorganisms. The artificial pH taxis exhibits random walk, translation, vertical, hopping, and pulsed motion, when the size of the motor and the imposed pH gradient are modulated.

Gold Nanocluster Embedded Albumin Nanoparticles for Two‐Photon Imaging of Cancer Cells Accompanying Drug Delivery

Gold nanoclusters in albumin nanoparticles (nanovehicles) are used for single-photon and two-photon imaging of cancer cells following the delivery of doxorubicin through the nanovehicle. NIR excitation and emission wavelengths in the biological window (650-900 nm) make the nanovehicle an ideal potential platform for imaging guided drug delivery.