title: Bright, NIR-emitting Au23 from Au25: characterization and applications including biolabeling.
abstract: A novel interfacial route has been developed for the synthesis of a bright-red-emitting new subnanocluster, Au(23), by the core etching of a widely explored and more stable cluster, Au(25)SG(18) (in which SG is glutathione thiolate). A slight modification of this procedure results in the formation of two other known subnanoclusters, Au(22) and Au(33). Whereas Au(22) and Au(23) are water soluble and brightly fluorescent with quantum yields of 2.5 and 1.3 %, respectively, Au(33) is organic soluble and less fluorescent, with a quantum yield of 0.1 %. Au(23) exhibits quenching of fluorescence selectively in the presence of Cu(2+) ions and it can therefore be used as a metal-ion sensor. Aqueous- to organic-phase transfer of Au(23) has been carried out with fluorescence enhancement. Solvent dependency on the fluorescence of Au(23) before and after phase transfer has been studied extensively and the quantum yield of the cluster varies with the solvent used. The temperature response of Au(23) emission has been demonstrated. The inherent fluorescence of Au(23) was used for imaging human hepatoma cells by employing the avidin-biotin interaction.
authors.affiliation: DST Unit on Nanoscience, Department of Chemistry, Sophisticated Analytical Instrument Facility and Indian Institute of Technology Madras, Chennai 600 036, India.
authors.forename: Madathumpady Abubaker Habeeb
authors.initials: MA
authors.lastname: Muhammed
authors.forename: Pramod Kumar
authors.initials: PK
authors.lastname: Verma
authors.forename: Samir Kumar
authors.initials: SK
authors.lastname: Pal
authors.forename: R C Arun
authors.initials: RC
authors.lastname: Kumar
authors.forename: Soumya
authors.initials: S
authors.lastname: Paul
authors.forename: Ramakrishnapillai Vyomakesannair
authors.initials: RV
authors.lastname: Omkumar
authors.forename: Thalappil
authors.initials: T
authors.lastname: Pradeep
mesh_terms: D005453:Fluorescence; D005978:Glutathione / Q000138:chemical synthesis / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D006801:Humans; D053768:Metal Nanoparticles / Q000737:chemistry; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D013438:Sulfhydryl Compounds; D006046:Gold; D005978:Glutathione