Since their discovery in 1977, intrinsically conducting polymers have been studies for applications such as electronic devices, sensors and actuators[1-3]. Polyaniline (PAni) is an example of a stable conducting polymer and can be classified as an ‘adaptive material’ in that it can be switched between two or more forms (each with their own distinct characteristics) using an external stimulus. In contrast to a classical metallic conductor or a polymeric insulator, PAni can be switched reversibly between an insulating emeraldine base form and a conducting emeraldine salt. More recently, interest has developed in the area of nanostructured polyaniline[4-6]. These one-dimensional objects combine the advantages of an organic conductor and a high surface area material, thus making them suitable for a diverse range of applications such as chemical sensors, flash memory and electro-optic devices[7-9]. Here we present how polyaniline nanofibres can be successfully functionalised with both amine and carboxylate groups. The modified nanofibres maintain their ability to switch between diffferent forms displaying distinctly different optical properties (as shown by Raman and UV-vis spectroscopy), thus making them suitable for adaptive sensing applications. The attachment of functional groups to polyaniline nanofibres provides a route for manipulating the surface chemistry of nanofibres. While interesting materials in themselves, these functionalised nanofibres are also attractive as molecular scaffolds for building yet more innovative derivatives that nonetheless retain the basic underlying nanostructure and intrinsic characteristics of PAni. That we have demonstrated the ability to regulate the extent of side-chain attachment to one-dimensional objects, in a safe and simple manner, represents a step forward in the area of adaptive nano-structured materials. Functionalisation can be controlled using a simple, scalable and inexpensive technique[10-11]. [1] C. O. Baker, B. Shedd, P. C. Innis, P. G. Whitten, G. M. Spinks, G. G. Wallace, R. B. Kaner, Adv Mater 20 (2008) 155-+. [2] W. R. Small, F. Masdarolomoor, G. G. Wallace, M. Panhuis, J Mater Chem 17 (2007) 4359-4361. [3] J. G. Roh, H. R. Hwang, J. B. Yu, J. O. Lim, J. S. Huh, Journal of Macromolecular Science-Pure and Applied Chemistry A39 (2002) 1095-1105. [4] J. X. Huang, R. B. Kaner, Chemical Communications (2006) 367-376. [5] N. R. Chiou, C. M. Lui, J. J. Guan, L. J. Lee, A. J. Epstein, Nat. Nanotechnol. 2 (2007) 354-357. [6] F. Masdarolomoor, P. C. Innis, S. Ashraf, R. B. Kaner, G. G. Wallace, Macromol. Rapid Commun. 27 (2006) 1995-2000. [7] S. Virji, J. X. Huang, R. B. Kaner, B. H. Weiller, Nano Lett. 4 (2004) 491-496. [8] S. Virji, R. B. Kaner, B. H. Weiller, J. Phys. Chem. B 110 (2006) 22266-22270. [9] S. Virji, R. B. Kaner, B. H. Weiller, Chemistry of Materials 17 (2005) 1256-1260. [10] E. Lahiff, T. Woods, W. Blau, G.G. Wallace, D. Diamond, Synth. Metals, accepted. [11] E. Lahiff, S. Bell, D. Diamond, Mat. Res. Soc. Symp. Proc., Vol. 1054, FF-05-05, 2008