Preparation and photophysical behaviors of fluorescent chitosan bearing fluorescein: Potential biomaterial as temperature/pH probes

A novel method for attaching fluorescein (via its epoxy derivative) to water-soluble chitosan, and the temperature /pH-sensitive qualities of fluorescence were investigated. 3-Epoxypropoxy fluorescein (EPF) was firstly synthesized by the reaction between fluorescein and epichlorohydrin, and then water-soluble chitosan bearing fluorescein (CS-EPF) was prepared via ring-opening reaction with EPF. They were characterized by the methods of H-1 NMR, MS, IR, UV-Vis, and luminescence spectra, respectively. The chemiluminescent and photophysical behaviors of EPF and CS-EPF were studied in detail. The results showed that the fluorescent chitosan could still provide temperature and pH sensitivities similar to that of fluorescein, achieving better long-term stability and fast equilibrium response. CS-EPF had an excellent linear response between relative fluorescence intensity and temperature in the range of 0-60 degrees C and two linear relationships between relative fluorescence intensity and pH in 0.0-4.14 and 8.15-13.20, respectively. This investigation may provide a convenient way to prepare low-cost and multifunctional macromolecule biomaterial to probe pH and temperature in biological systems. (C) 2007 Wiley Periodicals, Inc.