Herein we report on a new chemo sensor based on ligand induced plasmon band shift of gold nanoparticles [F. Goettmann, A. Moores, C. Boissiere, P. Le Floch and C. Sanchez, Small (2005) 636. [1]]. Phosphininine stabilized gold nanoparticles were hosted in periodically organized mesoporous silica thin films. These layers feature a strong absorption in the UV-visible spectrum caused by the nanoparticles plasmon band. The position of the latter is unusual, due to the electronic properties of the phosphinine (the phosphorus analog of pyridine). This user-friendly system proved to be remarkably efficient in UV-visible detection of thiols and small phosphines. The sensor is sensitive, selective and reusable. Exchange processes at gold nanoparticles surface in solution or hosted were also discussed in regard of the plasmon band position. (c) 2005 Elsevier B.V. All rights reserved.