Functionalized Titania Nanosheet Dispersions of Peroxidase Activity

Nanocomposites of titania nanosheets (TNS), horseradish peroxidase (HRP), and poly­(diallyldimethylammonium chloride) (PDADMAC) were prepared, and their colloidal and functional stabilities were assessed. HRP quantitatively adsorbed on bare TNS, and the adsorption process did not affect the charging and aggregation behavior of the colloidal system. The obtained TNS–HRP composite was functionalized by PDADMAC to stabilize the enzyme on the surface and to maintain good colloidal stability. Depending on the PDADMAC dose applied, its adsorption on TNS–HRP led to charge reversal of the particles from negative to positive. The formation of a saturated polyelectrolyte layer on the TNS–HRP (TNS–HRP–PDADMAC) gave rise to highly stable colloids, and especially the resistance against salt-induced aggregation was excellent. The enzymatic activity of different systems was investigated as a function of the pH of the medium and over time. The results indicated that HRP remained enzymatically active upon immobilization, and in addition, the pH range of application broadened compared to its native form. The developed TNS–HRP–PDADMAC system can thus be used in a wider pH range and possesses the advantages of a heterogeneous catalyst compared to the bare enzyme.