Activity of Horseradish Peroxidase Adsorbed onto Titanate Nanowires

Immobilization of horseradish peroxidase (HRP) onto titanate nanowires (TNWs) was investigated using different strategies. TNWs were synthesized by a hydrothermal method and characterized by scanning electron microscopy, X-ray diffraction, nitrogen physisorption (77K) and Fourier transform infrared spectroscopy. Free HRP was stable and active in a wide range of pH with optimal activity at 7.0. The K-m of HRP with 4-aminoantipyrine and H2O2 as substrate was 0.77 +/- 0.25 mmol l(-1). Immobilization strategies studied were non-specific adsorption and covalent coupling through amine groups. Adsorption isotherms were well fitted by the Langmuir-Freundlich model. The coverage of TNWs containing HRP adsorbed by covalent coupling was 1.56 mg HRP m(-2) and the residual enzymatic activity was approximately 40%. The enzymatic activity of free HRP and immobilized HRP was monitored as a function of storing time. The results confirm that the enzyme is firmly attached to the TNW surface through covalent binding, constituting a very promising platform for a variety of applications such as in biosensing.