Covalent immobilization of fluorescent indicators in photo- and electropolymers for the preparation of fibreoptic chemical sensors

摘要

A photo- and an electrochemical method for the immobilization of fluorescein derivatives for the preparation of fibreoptic pH and Ca~(2+) sensors are presented. The methods results in the covalent attachment of the indicator in a polymer matrix. In the electrochemical approach, a fluorescein-derivatized thiophene, thiophene-3-acetylfluoresceinamide (TAF), has been prepared and electrochemically polymerized onto Pt-coated indium tin oxide glass. The fluorescence intensity responses as a function of pH, for TAF and polyTAF, are similar to that of fluorescein in solution. In the photochemical approach, two fluorescein derivatives have been prepared, fluorescein acrylamide (FA) and calcein acrylamide (CA). CA is sensitive to both pH and Ca~(2+). FA and CA have been immobilized covalently within polyacrylamide and polyacrylamide/[(3-methacryoylamino)propyl]-trimethylammonium chloride (MAPTAC) copolymers using photoinitiated radical polymerization directly on the end of a chemically-modified glass surface. The spectroscopic properties of the bound FA and CA are similar to FA and CA in free solution, respectively; however, the cationic properties of the polymers result in a shift in the pK_a of the indicator. The electrochemical and photochemical immobilization of fluorescent indicators within polymer matrices is an ideal arrangement, because it improves the operational lifetime of the chemical sensors.