In this work we report the use of the localized surface plasmon resonance dumping to achieve the detection of different organic molecules in liquid and in vapor phase. The all-optical sensor has been obtained by the development of noble metal nanoparticle/polymer nanocomposites. An interesting property of these nanocomposites is that their polymeric matrix is based on a photosensitive compound which allows ultra-violet (UV) lithography and hence they can be patterned with a resolution determined by the host. Positive and negative tone nanocomposites, containing silver or gold nanoparticles (NPs), have been developed. This fabrication technique is a fast, simple and non-expensive approach to the formation of extended polymer patterns with embedded silver nanoparticles. Moreover, the material constitutes a mechanism to position nanoscale particles in the range 5-40 nm with resolution limited by the UV lithography, which represents a useful tool for nanoscience. By using this nanostructured plasmonic material, the detection of amines and 2- mercaptoethanol molecules has been achieved, both in dilution in water and in vapor phase. The sensing mechanism is based on the plasmon signal dumping related to the binding of the organic molecules at the surface of the nanoparticles, which produces a color change that can be appreciated with the naked eye. This nanocomposite constitutes a platform for the fabrication of colorimetric arrays of bio/chemical sensors.