Thick film urea sensor based on nanostructured zinc oxide

Flower-like structures of ZnO was synthesised by solution method using zinc acetate dihydrate and sodium hydroxide. Hydroxylamine hydrochloride (0.4M and 0.8M) was used as a structure directing agent. Structural morphology significantly changed with precursor concentration from a flower-like structure to sea-urchin like structure. Thick films of this powder were prepared on Al-sheet, by conventional doctor blade method using organic additives and used for urea sensing. Urease was attached with zinc oxide (by soaking in urease solution containing 100 units for three hours). In general, film conductivity increases after urease immobilisation. Urease immobilised films were found sensitive to urea concentration from 1 mM to 100 mM. Flowery structure resulted in higher urea sensitivity. The sensor responses are reproducible, reliable, reversible and selective, with a response time of 6S.