A chemical sensor for detecting an analyte in a fluid, useful for the production of an apparatus for the analysis of odours (an electronic nose), comprises a film of composite material formed by a matrix of a non-conductive polymer constituted by a polyamidoamine and a conductive filler, e.g. carbon black. In preferred embodiments, the polyamidoamine is formed as the adduct of bisacrylamidoacetic (BAC) and N, N′-dimethylethylenediamide (DMEDA) else N, N′-ethlenediaminoaceticacid (EDDA), and can include copper or cobalt ions as complexes.