The GraftFast® process is a simple ant quick method to covalently graft a chemical on a substrate, provided that the chemical has an aromatic primary amine. Thus, this method is studied for an application in pH measurement via an optode. The aim of this PhD work, which started in October 2012, is to covalently graft a dye sensible to pH variations on an optical fiber, so as to be able to solve the stability issues encountered with other techniques used to assemble the dye and the optical fiber – like physical entrapment or electrostatic interactions. The work presented here explains the concept of an optode and the GraftFast® process. The first results obtained show the two dyes that will be studied, and that one ot those potential dyes, the neutral red, can be quite efficiently grafted on a gold substrate.