Alkali treatment of dye-doped sol–gel glass films for rapid optical pH sensing

Alkaline post-fabrication treatment of dye-impregnated pH sensitive sol–gel films has been demonstrated as a means of overcoming the problem of extended response times associated with the use of such films in optical sensor systems. Hydrogen bonded silanol groups and water molecules present on the surface and within the bulk of the glass structure have been shown to be of great influence on the sensing characteristics. These may be modified in such a way as to dramatically improve response times without incurring the penalty of leaching of the sensitive dye. This procedure was demonstrated by producing bromocresol green doped glass films displaying response times of the order of a few seconds.