Nanostructured and Bulk III-Nitride Semiconductors in Electrochemical Sensors and Biosensors
N. Sofikiti, J. Grandal, M. Utrera, M. Sanchez-Garcia, E. Calleja, G. Tsiakatouras, E. Iliopoulos, D. Ajagunna, A. Georgakilas, N. Chaniotakis
University of Crete, GR
Keywords: III-Nitrides, bio-sensors, electrochemistry, nanocolumns
Abstract:In this presentation, we will show very recent results from our efforts to utilize nanostructured GaN & InN as sensing elements and transducers, and provide pertinent methodologies and data on how these materials can be successfully employed for the development of novel chemical sensors and biosensors. More specifically, our results indicate that these two materials (c-plane GaN & InN, Ga and In face respectively) show similar pH and anionic (Cl-) potentiometric response when they are in bulk form. Interestingly, though, both of these materials lose a big part of their anionic sensitivity when in nanostructured (nanocolumns) form, while on the contrary they maintain their pH sensitivity almost intact. These results indicate that the anionic potentiometric response of these materials is closely related with the crystal orientation, as has been previously shown for GaN, since the observed sensitivity is due to the direct interaction of the Lewis basic anions with the Lewis acidic gallium or indium atoms of the surface which act as the fixed sites for the specific and reversible anion coordination. This actually seems to be the main reason for this intense reduction of the anionic sensitivity of these materials when they are in nanostructured form, because in this form the crystal orientation homogeneity of the materialís surface is intensively disturbed. On the contrary, our results indicate that the pH sensitivity of these materials is almost completely irrelevant with the crystal orientation of the material, since the pH sensitivity seems to be due to, not only the direct and specific interaction of the Lewis basic hydroxide anions of the solution with the Lewis acidic gallium or indium atoms of the surface, but also due to hydrogen ion interaction with the generated hydroxide sites on the native surface, as has been previously shown in the case of GaN. Based on these results, we thought to investigate the possible use of these materials (in both bulk and nanostructured form), as sensing elements and transducers for the development of novel urea potentiometric biosensors. The development of these urea biosensors was based on the following enzymatic reaction: NH2CONH2 + 3H2O → NH4+ + HCO3- + OH- The Urease enzyme was physically adsorbed on the GaN and InN surfaces and the urea detection was accomplished by exploiting the pH sensitivity of these surfaces. The obtained results show that both GaN & InN surfaces can be utilized for the development of such potentiometric biosensors, but only when they are in nanostructured form they maintain their enzymatic activity for a significant period of time (a week or so). This fact indicates that the extended total surface area of the nanostructured form is of great importance for the enzyme stabilization and thus for the lifetime of the biosensor.