Selective Functionalization of Silicon Micro/Nanowire Sensors via Localized Joule Heating

A novel approach to achieve localized surface functionalization of silicon-based micro and nanoscale linear structures (e.g., silicon nanowire sensors) is proposed in this paper. This method is based upon the protection of silicon surface by hydrophobic polymer layers such as polytetrafluoroethylene (PTFE). These layers are used as a protective, patterning barrier against surface functionalization of silicon or silicon oxide surface. Subsequently, these polymer layers undergo selective thermal ablation along the silicon micro / nanowire sensors by localized Joule heating. This local ablation is then followed by a brief low power O₂ plasma for activating the surface of silicon oxide with more hydroxyl (-OH) groups for further surface functionalization. Next, organosilane groups including amino-propyltriethoxysilane (APTES) and 3-mercaptopropyltri-methoxysilane (3-MPTMS) are used as a chemical linker between silicon oxide surface and protein or DNA molecules. We first present a finite element analysis (FEA) of localized Joule heating of silicon nanowires and experimental results of localized ablation of the protective polymer by Joule heating. We also verify localized surface modification of ablated surface of silicon with 3-MPTMS by selective binding of gold nanoparticles on the thiolized silicon surface. This localized functionalization is expected to have great advantages such as increasing the sensitivity and lowering the detection limit of silicon micro/nanowire-based sensors.