Silicon Nanowires for Biosensing

Over the past 20 years, nanomaterials, such as quantum dots, nanoparticles, nanowires(NWs), nanotubes, and graphene, have received enormous attention due to their suitable properties for designing novel nanoscale biosensors. Nanomaterials are very small structures with at least one of their dimensions in the nanoscale (10 nm range).The size of these nanostructures is comparable to those of biomolecular and chemical pecies and thus provides a perfect feature to study most biological entities, such as nucleic acids, proteins, viruses, and cells.In addition, the high surface-to-volume ratio for nanomaterials allows a huge proportion of the constituent atoms in the material to be located at, or close to, the surface. As a consequence, surface atoms play an extremely important role in determining the physical, chemical, and electrical properties of nanomaterials, making them very sensitive devices capable of low concentration and even single-molecule detection. Among nanomaterials, NWs have become significant candidates for nanoscale-sensing applications. NWs are extremely small wires with cross section in the nanoscale size. Thanks to their size, NWs have distinct and diverse electrical, physical, and mechanical properties that are not shared by the corresponding bulk material. NWs can be made from metallic (Ni, Pt, Au), dielectric (ZiO,TiO2), composite, or semiconductor (Si,GaN,InP) materials. For the purpose of bio-or chemical sensing, semiconductor materials are typically used, due to the electronic property of semiconductors that can be easily tuned via doping and applied gate voltages, providing also a way for affecting the sensitivity capabilities. Within the subclass of semiconducting NWs, silicon NWs (SiNWs) are often used for the fabrication of biosensors. Indeed, SiNWs can benefit from existing and mature silicon industry processing and be easily integrated with well-developed field effect transistor (FET) technology. Moreover, SiNW surfaces can be readily modified thanks to well-established silicon and silicon oxide functionalization techniques, thus making SiNW-FETs particularly attractive for the label-free detection of biological species.