Solution-based functionalization of gallium nitride nanowires for protein sensor development

article A solution-based functionalization method for the specific and selective attachment of the streptavidin (SA) pro- tein to gallium nitride (GaN) nanowires (NWs) is presented. By exploiting streptavidin's strong affinity for its li- gand biotin, SA immobilization on GaN NWs was achieved by exposing the GaN NW surface to a 3- aminopropyltriethoxysilane (APTES) solution followed by reaction with biotin. Functionalization of the NWs with APTES was facilitated by the presence of an ≈1 nm thick surface oxide layer, which formed on the NWs after exposure to air and oxygen plasma. Biotinylation was accomplished by reacting the APTES-functionalized NWs with sulfo-N-hydroxysuccinimide-biotin at slightly alkaline pH. It was determined that the biotinylated GaN NW surface was specific towards the binding of SA and demonstrated no affinity towards a control protein, bovine serum albumin (BSA). There was however, evidence of non-specific, electrostatic binding of both the SA protein and the BSA protein to the APTES-coated NWs, revealing the importance of the biotinylation step. Suc- cessful SA immobilization on the biotinylated GaN NW surface was verified using fluorescence microscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The functionalized GaN NWs demonstrate potential as bio- sensing platforms for the selective detection of proteins. Published by Elsevier B.V.