Anumita Paul

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.

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.

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.

Synthesis of Au nanoparticle–conductive polyaniline composite using H2O2 as oxidising as well as reducing agent

We report a new method of synthesis of an Au nanoparticle-conductive polyaniline composite by using H2O2 both for reduction of HAuCl4 and polymerization of aniline in the same aqueous medium: the electrical conductivity of the composite has been measured to be two orders of magnitude higher than the polymer itself.

Modulating enzymatic activity in the presence of gold nanoparticles

The presence of citrate-stabilized gold nanoparticles (cit-Au NPs) significantly enhanced the specific activity of α-amylase, which could also be modulated by varying the concentration of the enzyme, while keeping the NP concentration constant. Also, the lowest concentration (0.175 μg mL−1) at which the Michaelis–Menten behavior of the enzyme could clearly be observed in the presence of NPs was much less than that in their absence. At higher protein concentrations the activity decreased monotonically until it reached nearly the same as that of free enzyme, while exhibiting Michaelis–Menten kinetics at all concentrations. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) based particle size analyses indicated increased agglomeration of the NPs with increased protein concentration. The results have been explained based on a model which considered the presence of enzyme bound to NP and that available for enhanced catalysis, enzyme bound to NP but unavailable due to being buried inside the agglomerate and the free enzyme.

Probing Au nanoparticle uptake by enzyme following the digestion of a starch-Au-nanoparticle composite.

In this letter, we report on the digestion of starch, when present as a composite with Au nanoparticles (NPs), by alpha-amylase. It has been observed that the rate of digestion of free starch and that in the composite were identical. Also, the well-established iodine test could be carried out to investigate the kinetics in the presence of Au NPs. The investigations revealed that following the digestion of starch in the composite the NPs were released and subsequently attached to the enzyme only and not to the degraded products of starch. Also, the enzyme attached to NPs, following digestion, retained its catalytic activity. The particle sizes of the NPs were not affected in the process because no agglomeration was observed. Experimental observations indicated the possibility of oriented attachment of alpha-amylase to the NPs in comparison to amyloglucosidase, another digestive enzyme. Finally, we observed a change in the surface plasmon resonance (SPR) of the NPs following the digestion of starch in the composite, and thus we could demonstrate that the SPR of the NPs could be used as a direct probe for monitoring the digestion of the composite by the enzyme.

Synthesis, characterization and enhanced bactericidal action of a chitosan supported core–shell copper–silver nanoparticle composite

A simple two-step seed-mediated method has been developed to synthesize chitosan (CS)-supported core–shell metal nanoparticles (NPs) in aqueous solution. CS-supported copper NPs (CS–Cu NPs), when treated with silver nitrate (AgNO3) solution, resulted in Ag shells on Cu NP cores in the composite. The Cu@Ag NPs in the CS composite were characterized and found to be spherical in shape with an average particle size of 14.0 ± 3.4 nm. The antibacterial efficacy of the CS–Cu@Ag NP composite was evaluated on Gram-negative Escherichia coli and Gram-positive Bacillus cereus bacteria using turbidity measurement as well as flow-cytometry. Results demonstrated enhanced bactericidal activity of the composite. Analytical techniques, used to elucidate the mode of bactericidal action, revealed that the superior antibacterial activity of the CS–Cu@Ag NP composite was due to synergistic effects of CS and Cu@Ag NPs. The proposed mode of antibacterial action involves the electrostatic binding of CS to the bacterial cell wall and simultaneous interaction of Cu@Ag NPs with membrane proteins leading to perforation of the cell membrane and release of intracellular material.

Catalytic gold nanoparticle driven pH specific chemical locomotion.

Gold nanoparticle (Au NP) catalyzed decomposition of alkaline hydrogen peroxide has been utilized in driving chemical locomotives in a liquid. Au NPs deposited on spherical micron sized polymer resin beads catalyzed the decomposition of H(2)O(2) in the pH range 9.1-10.8. The O(2) gas bubbles produced in the decomposition moved the beads upward with average velocities that depended on the pH of the solution. The measured average velocity of the bead increased with the increase in pH in the range 9.1-10.8. Above this pH, the self-decomposition of H(2)O(2) produced sufficient bubbles in the medium that made the motion haphazard and thus prevented a clear measurement of the velocity. The observed accelerated motion of the locomotive has been explained by considering the time-dependent growth of O(2) gas bubbles on the polymer, while taking into consideration desorption and other factors.