Composite polyelectrolyte self-assembled films for optical bio-sensors

The main idea of the present work is to combine in the same film different enzymes and pH sensitive organic dyes in order to form an optical transducer. Decomposition of substrate molecules, catalyzed by enzymes, usually accompanied by pH changes in local surrounding, which can be registered by spectral transformations of indicator molecules. This idea was realized by using cyclo-tetrachromotropylene (Chromol) as an indicator and an enzyme, such as Urease. These two negatively charged molecules were deposited by alternation with polycation poly(alylamine chloride) (PAA). As a result, composite self-assembled multilayered films of (Chromol/PAA)(n)(Urease/PAA)(m) were produced and characterized by ellipsometry, SPR and UV-visible optical spectroscopy. As has been shown previously, absorption spectra of these films are sensitive to the presence of ammonia. It was found here that ammonia released by decomposition of urea, the reaction which is catalyzed by Urease, causes similar spectral transformations. Effect of urea concentration and time of exposure were studied as well as the effect of the presence of heavy metal salts. The results of the present study are encouraging and indicate the potential of using composite polyelectrolyte films, containing both enzymes and indicator molecules, as active membranes for optical bio-sensors and sensor arrays.