J. Phys. Chem. B 2005, 109, 8701-8706
8701
Enhanced Luminescence of Phenyl-phenanthridine Dye on Aggregated Small Silver Nanoparticles Jian Zhang and Joseph R. Lakowicz* Center for Fluorescence Spectroscopy, UniVersity of Maryland School of Medicine, Department of Biochemistry, 725 West Lombard Street, Baltimore, Maryland 21201 ReceiVed: September 3, 2004; In Final Form: January 21, 2005
Tiopronin-coated silver particles (average diameters of core ) 1.6 nm) were prepared by a modified Brust method, and the ligands on the metal core were partially displaced by (2-mercapto-propionylamino) acetic acid-2,5-dioxo-pyrrolidin-1-ylester through ligand exchanges. The particles were bound on amine-pendent polymer backbones by condensation to generate compact aggregates of particles. The aggregated particles displayed a plasmon absorbance rising at 440 nm. Luminescence was enhanced to about 2 times with increasing the plasmon rising by the particle aggregation upon excitation at 400 nm when the polymer was labeled by 3,8-diamino-6-phenyl-phenanthridine.
Introduction Luminescence spectroscopy can be enhanced when the dye is localized near a metal particle.1,2 This phenomena, defined as surface enhanced fluorescence (SEF), can be used to develop next-generation biological and chemical sensors.3-8 The SEF is suggested to occur only when the dye is localized at a certain distance from the metal surface to overcome competitive quenching.2c-e An electromagnetic field is believed to exist near the metal core to bring up the SEF.9 When several particles approach closely, the electromagnetic fields from them are expected to be overlapped to result in a stronger field that leads to a stronger SEF. Meanwhile, the SEF is suggested to be dependent on the core size of the particle. The small particle (diameter
