Measurements of microproperties of water utilizing charge-transfer dye anilinonaphthalene sulfonate

Abstract

A charge-transfer dye, anilinonaphthalene sulfonate (ANS), shows a drastic change in its fluorescent properties, depending on the change of surrounding microscopic environments. From the characteristic fluorescent features, ANS has often been applied to measurements of solvent microproperties at local environments. Since the fluorescent intensity of ANS drastically increase in hydrophobic environments compared to in water, ANS has been widely used as a hydrophobicity probe for several decades. On the other hand, ANS has also been applied to a micropolarity probe, utilizing its change in fluorescent wavelength, which depends on the solvent polarity. Here, we show a new application of the ANS. Our current study has revealed that the fluorescent lifetime of ANS sensitively reflects the microviscosity. From the results, we proposed a new application of ANS as a microviscosity probe, and applied it to measurements of the microviscosity of water in biologically important systems. The important point is that the microviscosity is probed by the fluorescent lifetime, not by the intensity. Lifetime measurements are free from the difficulty of discriminating of the origin of the intensity change, which is due to both the change in the local properties and localization of the probe molecules. This merit is important for applications of the florescent probe to inhomogeneous systems, such as water in polymer gels, material interfaces, and in living cells. © 2011 The Japan Society for Analytical Chemistry.