Dickson Joseph

Surfactant-directed multiple anisotropic gold nanostructures: synthesis and surface-enhanced Raman scattering.

A facile and effective method for the synthesis of gold nanostructures using beta-cyclodextrin in aqueous alkaline medium is reported. The results demonstrate that leaf-like, rugged, dendritic, and tadpole-shaped gold nanostructures are obtained with high yield for the first time under the same experimental conditions by using four different surfactants. To study the effect of surfactant on the shape of the nanoparticles, the experiments were also carried out in the absence of surfactant and in the presence of poly(1-vinyl-2-pyrrolidone). The growth process of the dendritic gold nanostructures formed was investigated by withdrawing samples from the heated solution and examining the intermediate products formed by transmission electron microscopic analysis. The formation mechanism of the anisotropic gold nanostructures is discussed, and it is demonstrated that the cooperative effect of cyclodextrin and the surfactant molecules determines the ultimate morphology of the gold nanostructures obtained. In addition, the effect of the as-prepared nanostructures as an active material in surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol as a probe molecule. Thus, different enhancement signals are obtained for the different nanostructures; the dendritic nanostructures showed the strongest intensity of the SERS signals and smallest for the leaf-like nanostructures.

Synthesis of highly fluorescent gold nanoclusters using egg white proteins.

Gold nanoclusters (AuNCs) have gained interest during the recent years because of their low toxicity and finer size for the bioimaging and biolabeling applications in comparison to the semiconductor quantum dot analogues. Diverse materials such as sulfur compounds, peptides, dendrimers, proteins, etc., are exploited for the preparation of AuNCs. Henceforth, highly fluorescent, water-soluble, and few atom-containing gold nanoclusters are created using a rapid, straightforward, and green method. In this regard for the first time chicken egg white (CEW), one of the most unique materials, is utilized in an aqueous solution under basic conditions at physiological temperature for the preparation of AuNCs. Tyrosine and tryptophan amino acid residues are responsible for the conversion of Au ions to Au(0) under alkaline condtions. CEW contains four major proteins of which the main constituent protein, ovalbumin also leads to the formation of the AuNCs with a higher fluorescence emission compared to the CEW. The ratios between the different reaction partners are very crucial, along with temperature and time for the preparation of AuNCs with high photoluminescence emission. The limited vibrational motion of the proteins under alkaline condition and the bulkiness of the proteins help in the formation of AuNCs.

A direct route towards preparing pH-sensitive graphene nanosheets with anti-cancer activity

Graphene nanosheets were prepared by the direct exfoliation of graphite in an aqueous lysozyme solution using ultrasonication. Atomic force microscopy studies indicated that the nanosheets possessed small lateral dimensions of less than three layers. Raman spectroscopy suggested that defects were introduced by the sonication process. These defects were primarily edge defects, not basal-plane defects. Cytotoxicity studies revealed that the lysozyme-supported nanosheets possessed anticancer activity at certain micromolar concentrations. Three other proteins and gold nanoparticles prepared with those proteins were examined as aids in graphene exfoliation. The overall protein or nanoparticle charge played an important role in the graphite exfoliation to graphene. All of the graphene dispersions were sensitive to pH. Changing the pH reversibly converted the graphene from a highly dispersed state to an aggregated state and vice versa. Although no lateral dimension differences were observed in the nanosheets prepared using the nanoparticles, their cell viability percentages varied depending on the particular protein used.

Double-stranded DNA-graphene hybrid: preparation and anti-proliferative activity.

Herein, we demonstrate a simple method to prepare graphene dispersions in an aqueous solution of DNA by the sonication of bulk graphite. The use of a commercial double-stranded DNA as a stabilizer for graphite exfoliation without any chemical modification is presented. The high energy sound waves cleave a double-stranded DNA into two single-stranded DNAs. UV-vis spectral studies show that the nucleobases in the product are intact. Atomic force microscopy studies reveal that the size of the obtained nanosheets can be enriched into smaller lateral dimensions using centrifugation. Raman spectroscopy suggests that the defects found in the nanosheets induced by the sonication are edge defects, whereas the bodies of the sheets remain relatively defect free. The graphene dispersions are extremely stable over a wide range of pH values, possessing high negative zeta potential values. The anti-proliferative effect observed through in vitro cytotoxicity studies is supported by in vivo studies using the zebrafish human tumor xenograft model. The migration of cancer cells in zebrafish embryos are inhibited by the graphene nanosheet dispersion. The negatively charged nanosheet serves as a platform for the adsorption of gold nanoparticles with positively charged surfaces.

Protein-coated pH-responsive gold nanoparticles: Microwave-assisted synthesis and surface charge-dependent anticancer activity.

Summary The biocompatibility and ease of functionalization of gold nanoparticles underlie significant potential in biotechnology and biomedicine. Eight different proteins were examined in the preparation of gold nanoparticles (AuNPs) in aqueous medium under microwave irradiation. Six of the proteins resulted in the formation of AuNPs. The intrinsic pH of the proteins played an important role in AuNPs with strong surface plasmon bands. The hydrodynamic size of the nanoparticles was larger than the values observed by TEM and ImageJ. The formation of a protein layer on the AuNPs accounts for this difference. The AuNPs exhibited sensitivity towards varying pH conditions, which was confirmed by determining the difference in the isoelectric points studied by using pH-dependent zeta potential titration. Cytotoxicity studies revealed anticancerous effects of the AuNPs at a certain micromolar concentration by constraining the growth of cancer cells with different efficacies due to the use of different proteins as capping agents. The positively charged AuNPs are internalized by the cells to a greater level than the negatively charged AuNPs. These AuNPs synthesized with protein coating holds promise as anticancer agents and would help in providing a new paradigm in area of nanoparticles.

Optical damage threshold and energy deposition in the embedded nanostructures

Results of energy deposition measurement in interaction between an ultra-short laser pulse and nanostructured target are described. As a target we used carbon nanotubes and multilayer graphene deposited on a sapphire wafer surface and embedded in a layer of protein. A 25 fs, p-polarised pulses from a 1 kHz-Ti;sapphire laser of energy up to 3 mJ were focused to give intensity up to 2×1016 W/cm2 on a target positioned within an integrating sphere. The absorption measured showed a level in excess of 80 %, increasing with the intensity. The results suggest that the host material (lysozyme) is responsible for the breakdown while the embedded material contributes dominantly to the absorption.