title: Biomolecule induced nanoparticle aggregation: effect of particle size on interparticle coupling.
abstract: Gold nanoparticles of variable sizes have been prepared by reducing HAuCl(4) with trisodium citrate by Frens' method. It has been found that the gold particles under consideration produce well-ordered aggregates upon interaction with a biomolecule, glutathione in variable acidic pH condition and exhibit pronounced changes in their optical properties arising due to electromagnetic interaction in the close-packed assembly. The effect of nanoparticle size on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects amongst the gold particles have been investigated. The optical properties of the gold aggregates have been accounted in the light of Maxwell-Garnett effective medium theory considering the changes in the filling factor in different aggregates produced by variable sizes of gold colloids. The aggregates have been characterized by UV-vis spectroscopy, FTIR, Raman, XRD and TEM studies. It has been observed that a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position depends on the particle size, concentration of glutathione and pH of the solution. 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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India.
authors.forename: Soumen
authors.initials: S
authors.lastname: Basu
authors.forename: Sujit Kumar
authors.initials: SK
authors.lastname: Ghosh
authors.forename: Subrata
authors.initials: S
authors.lastname: Kundu
authors.forename: Sudipa
authors.initials: S
authors.lastname: Panigrahi
authors.forename: Snigdhamayee
authors.initials: S
authors.lastname: Praharaj
authors.forename: Surojit
authors.initials: S
authors.lastname: Pande
authors.forename: Subhra
authors.initials: S
authors.lastname: Jana
authors.forename: Tarasankar
authors.initials: T
authors.lastname: Pal
mesh_terms: D002712:Chlorides / Q000737:chemistry*; D055590:Electromagnetic Phenomena; D005978:Glutathione / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D017612:Gold Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D010316:Particle Size; D013057:Spectrum Analysis
chemical_list: D002712:Chlorides; D017612:Gold Compounds; D006046:Gold; C024568:gold tetrachloride, acid; D005978:Glutathione