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

A solution-based functionalization method for the specific and selective attachment of the streptavidin (SA) protein to gallium nitride (GaN) nanowires (NWs) is presented. By exploiting streptavidin's strong affinity for its ligand 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 AFTES was facilitated by the presence of an approximate to 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 NI/Vs 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 NWs, revealing the importance of the biotinylation step. Successful 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 biosensing platforms for the selective detection of proteins.