title: Synthesis and capping of water-dispersed gold nanoparticles by an amino acid: bioconjugation and binding studies.
abstract: We report a novel strategy for the synthesis of aqueous stable, carboxylated gold nanoparticles (GNPs) by using glutamic acid as the reducing agent. The ratio of chloroaurate ions, AuCl(-)(4) to glutamic acid was optimized in the reaction medium to obtain monodispersed GNPs. Glutamic acid reduced gold nanoparticles were characterized by UV-visible, FTIR, dynamic light scattering and transmission electron microscopy, which demonstrated high stability in aqueous solution over a period of time indicating stabilization via surface-bound amino acid. Functionalized nanoparticles were conjugated with protein molecules through electrostatic attraction between the surface-terminated negatively charged carboxylate groups (COO(-)) of glutamic acid and the positively charged amino groups (NH(+)(3)) of the protein. The conjugation efficiency of the GNP:protein conjugates was confirmed qualitatively and quantitatively through gel electrophoresis and critical flocculation concentration analysis. The interaction between functionalized GNPs with protein molecules was investigated using fluorescence spectroscopy showing the fluorescence quenching of the tryptophan residues of protein molecules after conjugation. Circular dichroism (CD) studies of the conjugates confirmed that the protein undergoes a more flexible conformational state on the boundary surface of GNPs after conjugation. There was substantial conformational transition from alpha-helix to beta-sheet structure after conjugation of protein to GNPs.
authors.affiliation: Institute of Microbial Technology, Sector 39-A, Chandigarh 160014, India.
authors.forename: Nishima
authors.initials: N
authors.lastname: Wangoo
authors.forename: K K
authors.initials: KK
authors.lastname: Bhasin
authors.forename: S K
authors.initials: SK
authors.lastname: Mehta
authors.forename: C Raman
authors.initials: CR
authors.lastname: Suri
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D002942:Circular Dichroism; D004587:Electrophoresis, Agar Gel; D018698:Glutamic Acid / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D017612:Gold Compounds / Q000737:chemistry; D008027:Light; D053768:Metal Nanoparticles / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology / Q000379:methods; D012542:Scattering, Radiation; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: D000596:Amino Acids; D002264:Carboxylic Acids; D002712:Chlorides; D017612:Gold Compounds; D018698:Glutamic Acid; D006046:Gold; C024568:gold tetrachloride, acid