Long-lifetime based pH micro-optodes without oxygen interference

The first decay time-based fiber optic pH mi crosensors are presented which are without cross-sensitivity to molecular oxygen. They are based on radiationless energy transfer from the donor ruthenium(TI)-tris(1,10-phenanthroline) to a pH-sensitive sulfonephthalein acceptor dye. The microsensors have decay times in the microsecond range, a fact that makes them compatible with existing devices designed for optical oxygen microsensing. The sensor tips have diameters of 20 to 30 mu m. Outstanding features are the excellent mechanical stability and the inertness to quenching by oxygen. The dynamic range depends on the pK(a) of the selected pH indicator. The sensors were characterized with respect to the dynamic range, response, storage stability and photostability. A high resolution pH measurement in a marine sediment core serves as an example for its utility.