Polyaniline (PAni) is a conducting polymer which switches between distinct states exhibiting dramatically different properties. The colour, conductivity and redox state of PAni all depend on the local chemical environment of the material. Consequently PAni has great potential for sensing applications. The nanostructured form of PAni is particularly interesting as it provides a very large surface-to-volume ratio that can lead to dramatic enhancement of sensor sensitivity and response time. In this work, we focus on derivatising polyaniline nanofibres. Using the technique described, carboxylate terminated side-chains can be covalently bound to solution based fibres.