Method for producing an ionic sensor

The present invention provides processes for the preparation of ionic sensors that include a matrix material, such as ion-permeable cellulose, having a sensing component included therein, such as a fluorescent dye, and an opaque overcoat material. For example, the present invention provides a method of making an ionic sensor comprising: contacting a water-swellable ion-permeable matrix material with an aqueous-based bath of a sensing component, or precursor thereof, under conditions effective to covalently attach the sensing component, or precursor thereof, to the water-swellable ion-permeable matrix material; wherein the aqueous-based bath comprises water and an organic solvent in an amount effective to solubilize the sensing component, or precursor thereof; contacting the water-swellable ion-permeable matrix material having covalently attached sensing component, or precursor thereof, with an aqueous solution having a pH of at least about 10 and an ionic strength of at least about that of a 5% aqueous sodium chloride solution to form a sensing element; and covering the sensing element with an opaque overcoat material. Also provided is a method of making a precursor to a preferred sensing component, i.e., acetoxypyrenetris(sulfonyl)chloride, which is made using a thionyl chloride method. If the sensing component is attached to the matrix material using amine groups, any unreacted amine groups can be capped by contacting them with a solution comprising an acetylating agent, an organic amine, and an ethereal solvent.