Viscosity of Sucrose Aqueous Solutions Measured by Using Fluorescence Correlation Spectroscopy

Fluorescence correlation spectroscopy (FCS) is a technique for investigating diffusion phenomena from fluorescence fluctuation in a small volume. As the diffusion coefficient; of fluorescent; dye is governed by the properties of surrounding liquids, essential properties, such as the viscosity can be measured by using FCS, provided enough care is taken to account for subtle changes in the experimental conditions. We characterized the performance of FCS as a micro-viscometer by monitoring the diffusional motion of dye molecules in aqueous sucrose solutions. The viscosity values of the sucrose solutions determined by using the Stokes-Einstein relations were reliable, and their variations under different experimental conditions, such as excitation beam power and data acquisition scheme, could be clarified, demonstrating that FCS is an suitable tool for determining the viscosity of liquid systems.