Two dye-immobilization techniques on optodes are comparated ; first : adsorption of dyes on a cross-linked styrene-divinylbenzene resin ; second : ionic and adsorption binding on a hydrophilic charged polymer layer. This layer is based upon quaternized poly N-(vinylimidazole) grafted on silica fiber. The kinetics of dyes desorption, the shift of pK'a, the reproducibility of disposal probes are analyzed. A new technique of dyes coimmobilization is also explored.