Effect of neutral red incorporation on Al-doped ZnO thin films and its bio-electrochemical interaction with NAD + /NADP + dependent enzymes.

A new approach to deposition of electroactive ZnO thin films have been carried out, by one-pot chemical bath deposition with Al dopant and incorporation of neutral red as organic mediator. The morphological, structural and functional characterization of the neutral red incorporated, Al-doped ZnO (NR-AZO) film was carried out using electron microscopy, FTIR, XRD and EIS respectively. The incorporated neutral red was found to induce strain in the crystal of AZO proportional to the concentration used in depositing solution which further affected the charge transfer resistance of the films in solution. One mM neutral red was found to be the optimum concentration for both conductivity and response to NADH/NADPH. The response of the films was further validated by immobilizing NAD+ dependent alcohol dehydrogenase (ADH) and NADP+ dependent glucose dehydrogenase (GDH) independently. The ADH/NR-AZO showed a sensitivity of 3.2 μA cm-2  mM-1 with a LoD of 1.7 μM of ethanol in the range 5.6 μM-7 mM, whereas GDH/NR-AZO showed a sensitivity of 4.33 μA cm-2  mM-1 with a LoD of 27 μM of glucose in the range 90 μM-4 mM. This method serves as a simple alternative to immobilize the organic redox dyes into the inorganic thin films in a single step making it electroactive towards specific biomolecules.