Development of ultra sensitive nanoscale biosensor devices using carbon nanotube - field effect transistors ( CNT - FETs )

Direct formation of iron phosphate nanoparticles on solid substrates with a narrow size distribution (average diameter = 2.2 nm) has been achieved by a simple spontaneous reaction of ferric chloride and phosphoric acid on hydroxyl-terminated SiO2/Si substrates. Single-walled carbon nanotubes (SWNTs) are grown in high yield from the synthesized iron phosphate nanoparticles by thermal chemical vapor deposition (CVD) method as confirmed by AFM and Raman spectroscopy. Furthermore, three-terminal p-type nanotube network field effect transistor (FET) devices are successfully fabricated with the synthesized SWNTs using a conventional photolithography technique. The reduced solubility of Fe(III) ions when they form iron phosphate salts in aqueous media is the main driving force for the nanoparticle formation. Systematic control experiments have revealed that surface property, concentration and pH of the reaction solution equally play important roles the formation of nanoparticles. As a second part of the projects, ultrasensitive nanotube FET devices have been developed by fabricating the devices using a shadow mask. A substantial increase of the sensitivity by more than five orders of magnitude has been achieved by increasing the area of active sensing region. While the nanotube FET devices fabricated by a conventional photolithography technique show their sensitivities at ~ 100 nM for general proteins, such as Streptavidin (SA) and Protein A (SpA), the devices made by using a shadow mask show typical sensitivities as low as ~ 1 pM. The increase of Schottky contact region formed at wider contact of metal electrodes and carbon nanotubes by a shadow mask metal evaporation as well as internal Schottky junctions of crossing multiple semiconducting and metallic carbon nanotubes are responsible for the increase of sensitivity. I. Development of facile chemical routes for catalyst nanoparticles Catalyst nanoparticles play a critical role for the formation of carbon nanotubes. Especially, size controlled catalyst nanoparticles are necessary in order to produce diameter controlled carbon Report Documentation Page Form Approved