Thin composite films containing cyclo-tetrachromotropylene (Chromol) were deposited onto glass slides by means of polyelectrolyte self-assembly technique. The films obtained were characterised by UV-visible spectral measurements, and a linear dependence of absorbance on the number of deposited layers has been found. It was also found that the shape of UV-visible spectra depends on the presence of ammonia in both gaseous and liquid phases. Other amines, such as il-butylamine, can also affect the spectra. An attempt of urease immobilisation has been done using polyelectrolyte self-assembly. Composite films containing both Chromol and urease demonstrated the possibility of optical registration of enzyme reactions, in particular, decomposition of urea which releases ammonia. After immersion into urea solution, the samples show spectral transformations similar to those observed in the presence of ammonia.