Entrapment of phenol red pH indicator into a sol–gel matrix

Entrapment of phenol red pH indicator into transparent monolithic silica matrices, was made by the acid catalyzed sol–gel reaction of tetraethylorthosilicate and the phenol red indicator. The immobilized phenol red shows similar behavior as its solution counterpart. It retains its structure during the sol–gel reactions in terms of response to pH. The polarized light microscopy has indicated that the phenol red molecules are strongly interacted within the host silica network. The successful encapsulation of phenol red results in using it as solid indicator.