Enzyme/indicator optrodes for detection of heavy metal ions and pesticides

Composite films containing enzyme and indicator molecules were produced by means of polyelectrolyte self-assembly. These membranes provide two functions: (i) molecular recognition of the substratum by respective enzyme, and (ii) optrode transducing, when the products of the substratum decomposition affect optical spectra of indicator molecules. Apart from direct registration of enzyme reactions, inhibition reactions can also be monitored with this method. Particularly, heavy metal salts and phosphororganic pesticides acting as inhibitors for Urease and Cholinesterase, respectively, were registered. Composite PESA films were deposited onto glass slides and consisted of several layers of poly(alylamine) hydrochloride (PAA) alternated with indicator molecules, either Cyclo-tetra-chromotropylene or Thymol Blue, both containing SO3- Na+ groups. Then a few layers of PAA/enzyme (either Urease or Cholinesterase) were deposited on top. A typical structure of the samples was (PAA/Indicator)(n)/ (PAA/Enzyme)(m)/PAA with n = 10-30 and m = 1-5. The obtained films were characterised with W-visible absorption spectroscopy. The effect of the substrata decomposition on the UV-vis spectra of respective indicator molecules was studied. The inhibition of enzymes Urease and Cholinesterase by heavy metal ions (for instance, Cd2+) and phosphorogranic pesticide (PVDP), respectively was found. The results obtained show the prospects towards development of optical enzyme sensor arrays.