Nanoparticle Sizing and Potential Quality Control of Sols Using a Unique Fluorescence Anisotropy Probe and 3D Contour...

Spectroscopic properties of the particle sizing fluorophore Dipole Blue are reported. The probe is cationic in nature, highly water-soluble, and strongly adheres to anionic silica surfaces by electrostatic interactions, as is demonstrated here by Ludox SM 30. The probe has a distinct absorbance band centered at 320 nm, and the fluorescence emission band is Stokes-shifted 100 nm with a peak centered at 426 nm. From time-correlated single-photon counting experiments, the fluorescence lifetime was found to be adequately described by a three-exponential decay model with an intensity-averaged lifetime of 15.6 ns. Perrin graph analysis of steady-state anisotropy shows the presence of silica particles with a radius of (5.44 ± 0.16) nm, which, considering the distribution of particle sizes, is in reasonable agreement with 3.5 nm found from dynamic light scattering experiments.