Fluorescence spectra were used to measure the quenching effect of small thiolated nanoparticle, Au25(S(CH2)2Ph)18. The study of quenching effect was achieved by analysis of fluorescence spectra where the concentrations of Au25 were varied in the presence of laser dye, 2-(4-Biphenylyl)-6-phenylbenzoxazole (PBBO). The quenching constant of Au25(S(CH2)2Ph)18 (simply Au25) was determined to be 1.578x107 M-1s-1 for PBBO dissolved in dichloromethane by the correlation of the Stern-Volmer kinetic relationship. We measured quenching constant in various solvents and the effect of a solvent polarity on the quenching constant displays an increasing effect on the quenching constant of Au25 nanoparticles with increase of solvent polarity. The protecting ligands that surround the gold center act as a solvent shell with properties that dictates the dynamics of energy transfer. The investigation of the effects of ligands size on the quenching was accomplished by changing the length of the carbon chain during ligand exchange reaction. . It was observed that the longer carbon chain length of the ligands decreased the quenching constant of the Au25 nanoparticle. However the decreasing effect on the quenching constant due to the carbon chain length do not agree with FRET theory.

Fluorescence quenching by various Au<sub>25 </sub>?nanoparticles: Effect of surface-protecting-ligand length and solvent polarity

245th National Meeting (2013)

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Fluorescence quenching by various Au25 ?nanoparticles: Effect of surface-protecting-ligand length and solvent polarity

Fluorescence quenching by various Au₂₅?nanoparticles: Effect of surface-protecting-ligand length and solvent polarity