The biochemical functionalization of AlGaN and GaN surfaces by silanization and subsequent immobilization of biomolecules has recently been demonstrated and the adequacy of AlGaN/GaN field-effect transistors (FETs) for the realization of pH-based enzymatic sensors has been shown [1,2]. The reliability of enzyme-modified FETs sensitively depends on the functionality of the employed enzymes after immobilization on the gate area. In the present work we have applied a photometric method [3] to characterize the activity of penicillinase after covalent immobilization on silanized GaN surfaces. The enzymatic constants have been extracted from recorded absorption transients by advanced modeling using Michaelis Menten kinetics. We have compared the characteristics of covalently immobilized and physisorbed enzymes on GaN to those of free enzymes to assess the impact of the immobilization process. We demonstrate the functionality of covalently immobilized penicillinase over several weeks.

[1]    B. Baur, G. Steinhoff, J. Hernando, O. Purrucker, M., Tanaka, B. Nickel, M. Stutzmann, and M. Eickhoff,  Appl. Phys. Lett. 87, (2005) 263901.

[2]      B. Baur, J. Howgate, H.-G von Ribbeck, Y. Gawlina, V. Bandalo, G. Steinhoff, M. Stutzmann and M. Eickhoff,  Appl. Phys. Lett. 89, (2006) 183901.

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