1. University of Wisconsin MRSEC on Nanostructured Interfaces Juan J. De Pablo, DMR-0520527 Gallium Nitride is a very promising material for interfacing microelectronics with wet-chemical environments, such as those relevant for chemical and biological sensing. Historically the development of direct bio-electronic interfaces has been hindered by the relatively poor stability of many materials in wet- chemical environments. Ideally such an interface would use covalent linkages to provide a high degree of chemical stability. The relatively poor stability of commonly used materials such as silicon and gold has lead researchers to investigate numerous other materials. Gallium Nitride (GaN) has emerged as a high-quality semiconducting material that can be grown as single-crystal epitaxial films. Because the surface states of GaN lie near the band edges, this material is likely to be tolerant of defects and therefore provide an exceptionally good material for interfaces into wet-chemical environments. “Biomolecular Functionalization of GaN Surfaces ” Heesuk Kim, Beth Nichols, Bin Sun, John Uhlrich, Thomas F. Kuech, and Robert J. Hamers Figure: Schematic illustration of the functionalization of GaN with DNA and the subsequent hybridization with fluorescently labeled complementary (matched) DNA. The data at upper right right show the stability to repeated hybridization and denaturation cycles; the data at lower right demonstrate the selectivity of recognition. However, its surface chemistry is not well understood and methods for providing GaN surfaces with specific chemical and biomolecular recognition properties have not been developed previously. In work currently being prepared for publication, researchers at UW-Madison have grown high- quality single-crystal GaN thin films and have developed a method to functionalize the surfaces with DNA and other biomolecules in manner that provides excellent biomolecular recognition properties and excellent stability. The new method uses metallorganic chemical vapor deposition (MOCVD) to grow the high-quality GaN epitaxially on sapphire substrates. After passivating the surfaces in a hydrogen plasma, the researchers used a photochemical reaction with organic molecules bearing an olefin (C=C) group and a protected amine group. The amine-modified GaN surfaces were then further modified using more conventional chemical reaction steps to tether DNA oligonucleotides to the surface. The biomolecular recognition properties were tested by exposing the DNA-modified surfaces to complementary and non-complementary DNA and using fluorescence methods. The new functionalization method provides a direct covalent link between biomolecules and the GaN substrate. The development of this method is significant because it is readily extendable to tether a variety of related molecules that can confer other specialized properties, such as the ability to resist nonspecific binding of proteins and/or acting as well-defined attachment sites for proteins, antibodies, and other molecular and/or biomolecular systems. The stability demonstrated in these experiments highlights the potential practical application of GaN in a variety of wet environments. GaN-based sensing systems are of interest for applications such as real-time environmental sampling systems that can provide continuous monitoring for biological pathogens.