Stability of new optical pH sensing material based on cross-linked poly(vinyl alcohol) copolymer

Cross-linked poly(vinyl alcohol) (PVA)-silica gel copolymer has been employed as a optical pH sensor substrate for immobilisation of fluorescein. Cross-linking was carried out by the sol-gel process incorporating PVA in initial sol-gel solution of tetra-methoxysilane (TMOS) under acidic conditions. Three dimensional network formation could be achieved using compositions of PVA/TMOS = 80-90/20-10 vol.% to result in crack-free films. The fluorescent sensor layers were prepared by dip-coating of gel solution onto glass slides. The dynamic fluorescence response towards different pH values was investigated in terms of the influence of sample ionic strength, membrane composition as well as age of sol-gel layers. Depending on the composition of the matrix pK sub a values of 6.50, 6.68 and 7.06 were found 18 days after continues storage in buffer.