Subhra Jana

Interaction of DNA bases with silver nanoparticles: Assembly quantified through SPRS and SERS

Colloidal silver nanoparticles were prepared by reducing silver nitrate with sodium borohydride. The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported here describes the interaction between nanoscale silver particles and various DNA bases (adenine, guanine, cytosine, and thymine), which are used as molecular linkers because of their biological significance. In colloidal solutions, the color of silver nanoparticles may range from red to purple to orange to blue, depending on the degree of aggregation as well as the orientation of the individual particles within the aggregates. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and absorption spectroscopy were used to characterize the assemblies. DNA base-induced differential silver nanoparticle aggregation was quantified from the peak separation (relates to color) of surface plasmon resonance spectroscopy (SPRS) and the signal intensity of surface-enhanced Raman scattering (SERS), which rationalize the extent of silver-nucleobase interactions.

Ligand-stabilized metal nanoparticles in organic solvent

This critical review reports the fundamental behavior of metal nanoparticles in different organic solvents, i.e., metal organosol. An overview on metal organosol and then their smart synthetic approaches, characterization, and potential applications in the fields of catalysis and spectroscopy with special emphasis on SERS are embodied. Aspects of organosol fabrication, stabilization, morphology control, growth mechanisms, and physical properties as mono- and bimetallic nanoparticles are discussed. The article inspires the repetitive usage of metal nanoparticles as stable deliverable organic and molecular compounds.

Cysteine functionalized copper organosol: synthesis, characterization and catalytic application

We herein report a facile one-pot synthesis, stabilization, redispersion and Cu–S interaction of L-cysteine and dodecanethiol (DDT) protected copper organosol in toluene from precursor copper stearate using sodium borohydride in toluene under a nitrogen atmosphere. Surface modification of the synthesized copper organosol with an amino acid L-cysteine and an alkanethiol (dodecanethiol, DDT) is accomplished by a thiolate bond between the used ligands and nanoparticle surface. The cysteine molecule binds the copper surface via a thiolate and amine linkage but not through electrostatic interaction with the carboxylate group due to the solvent polarity and dielectric medium. Fourier transform infrared (FTIR) analysis was performed to confirm the surface functionalization of the amino acid and DDT to the copper surface. Copper organosol has been characterized by optical spectroscopy (UV/vis), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The as-synthesized particles are spherical in shape and exhibit a Mie scattering profile with an absorption maxima in the visible range. Copper nanoparticles capped by cysteine and/or DDT in non-aqueous media are found to represent an interesting catalytic approach for the synthesis of octylphenyl ether.

New hydrothermal process for hierarchical TiO2nanostructures

Hydrothermolysis of inorganic Ti(IV) compounds (peroxo or sulfate) yields hierarchical titania nanocrystals of controlled morphologies on either a glass or resin surface.

Dipole-dipole plasmon interactions in self-assembly of gold organosol induced by glutathione

Assemblies of gold nanoparticles in an organic medium have been synthesized to study the plasmon–plasmon interactions amongst the gold nanoparticles. A pH-sensitive biomolecule, glutathione (GSH), has been introduced as a molecular linker of the ‘parent’ gold nanoparticles to obtain small nanoparticle aggregates. The optical spectra of gold nanoparticles shifted to the red region indicate dipole–dipole interactions in the gold particle assembly. The aggregates have been characterized by UV-Vis, FTIR, HRTEM and XRD techniques. A controlled method of aggregating gold nanoparticles in organic solvents has been achieved successfully under controlled pH conditions with different concentrations of the molecular linker, GSH. The pH dependent anchoring of GSH onto gold surfaces has been proved beyond doubt to bring about nanoparticle aggregation.

Effect of concentration of methanol for the control of particle size and size-dependent SERS studies.

In this paper the effect of concentration of cosolvent (methanol) for the formulation of particles size has been discussed briefly. The binary solvent system has been used which is prepared by simple mixing of two solvents. The morphology of the particles was controlled by varying the amount of cosolvent, keeping the concentration of the stabilizer and reducing agent constant. The polarity of the solvent, transport of the Au(III) ions, and coordinating ability of the solvent play vital roles for nucleus formation and the growth process, which subsequently form different size particles. The particles formed in methanol at lower composition are angular. At higher concentrations of methanol they are spherical. In all the cases the particle size increases as the concentration of the cosolvent decreases. In the methanol system, particles form multiple twined structures and the twining of the particles increase with the decrease of methanol content. The particles have been characterized by XRD analysis, UV-visible spectroscopy, and transmission electron microscopic (TEM) studies. The variable size of the particles, obtained in a water methanol system, was employed for SERS measurement. A Raman probe, Rhodamine 6G (Rh 6G), has been found to be suited for the surface modification of the gold particles and it has also been demonstrated that the larger particles show better SERS signal than the corresponding smaller ones.