Glutathione-Induced Aggregation of Gold Nanoparticles: Electromagnetic Interactions in a Closely Packed Assembly
Gold nanoparticles of variable sizes have been prepared by reducing HAuCl4 with trisodium citrate by Frens' method. The synthesized gold particles show intense surface plasmon band in the visible region. The optical resonances in the visible are due to the surface plasmon oscillation, which is a function of geometry of the particles. The work reported here describes the interaction between nanoscale gold particles and a biomolecule, glutathione at low pH. Glutathione, which is a major cellular antioxidant and consists of amino acids glutamic acid, cysteine, and glycine, has been used as a molecular linker between the gold nanoparticles. In glutathione, the reactivity of the α-amines (adjacent to –COOH) is found to be pH-dependent. Linking via the α-amines are activated at low pH but suppressed at high pH due to electrostatic repulsive forces between the gold surfaces and the charged carboxylate groups. In colloidal solutions, the colour of gold nanoparticles may range from red to purple to blue, depending on the degree of aggregation as well as orientation of the individual particles within the aggregates. The citrate-functionalized gold nanoparticles with glutathione in variable acidic pH condition produce different but well-ordered aggregates. It is observed that a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position depending on the particle size, concentration of glutathione, and pH of the solution. The aggregates have been characterized by UV/Vis, FTIR, XRD, and TEM. On the basis of the first appearance of a clearly defined new peak at longer wavelength, a higher sensitivity of glutathione detection has been achieved with gold nanoparticles of larger dimension.
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Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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