title: Functionalized gold nanoparticles as phosphorescent nanomaterials and sensors.
abstract: Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'-dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of approximately 340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands ( approximately 5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with Eu(III)/Tb(III) ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between Eu(III)/Tb(III) ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:Eu(III) complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:Tb(III) complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:Eu(III) complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca(2+), Mg(2+)) and transition metal ions (Cu(2+), Zn(2+), Ni(2+)), resulting from an isomorphous substitution of Eu(III) ions, whereas the luminescence intensity was not influenced by the addition of Na(+) and K(+) ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu(2+) ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles.
authors.affiliation: Photosciences and Photonics, Regional Research Laboratory (CSIR), Trivandrum 695 019, India.
authors.forename: Binil Itty
authors.initials: BI
authors.lastname: Ipe
authors.forename: Karuvath
authors.initials: K
authors.lastname: Yoosaf
authors.forename: Kakkudiyil George
authors.initials: KG
authors.lastname: Thomas
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry; D015374:Biosensing Techniques; D005063:Europium / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D049449:Luminescence; D049408:Luminescent Agents / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry*; D013725:Terbium / Q000737:chemistry
chemical_list: D049408:Luminescent Agents; D013725:Terbium; D005063:Europium; D015082:2,2'-Dipyridyl; D006046:Gold