Uniform, monodisperse gold nanocrystals have been adsorbed and chemically bound to Merino wool fibres, providing a permanent colouration through the interaction of visible light with the plasmon resonant modes of the nanocrystals. Surface analysis by X-ray photoelectron spectroscopy confirmed that the nanocrystalline gold was bound through the nitrogen of the amino groups on the surface of the gold to the keratin of the fibres. No shift in the absorptions attributed to the plasmon resonance modes of the nanocrystals were observed. (C) 2007 Elsevier Inc. All rights reserved.