Development of solid-state nanodevices for studying proteins

Abstract

In both lab-on-a-chip applications and biocomputation, being able to easily track a molecule passing a particular point along a channel is heavily desirable. This thesis has centred on electrical detection of passing filaments in an actomyosin in vitro motility assay (IVMA). This would enable tracking large numbers of agents at once, an important advance in scaling up parallel processing biocomputers. We built a custom CVD furnace for growing CNTs that safely handled a variety of input gases with precise flow rate and temperature control. Ethanol vapour was found to be a superior feedstock gas to methane, and EBL-defined Fe islands more reliably catalysed CNTs of the appropriate density than solution deposited FeMoC or alumina nanoparticles. The definition of Fe islands was improved by the design and optimisation of a photolithography process that allowed batch-fabrication of many samples in parallel. CNFET contacts made from Cr, Ti, and Pd were compared and Pd was found to be the most reliable for high quality CNFETs that lasted more than 3 weeks with little degradation. The best performing devices had on-state conductances of up to 2 µS and subthreshold swings as low as 0.3 V/dec for liquid gated measurements although leakage currents through our EBL resist encapsulation between the liquid gate and the source-drain contacts were present. These leakage currents could be removed by ensuring a particle-free surface or doubling the thickness of the encapsulating resist. A Faraday cage was integrated with a fluorescence microscope to assist with electrical detection of a passing actin filament by simultaneous electrical and optical measurement. We developed a method to raise CNFETs up to the actin travelling height and combine them with the required nanostructures for actomyosin motility on the same substrate. We demonstrate the potential for a thin layer of parylene to coat the CNFET, preventing myosin binding without adversely affecting electrical detection or filament crossing. A novel EBL process was developed to fabricate thin strips of Nafion with resolution around 1 µm This process was used to create Nafion wrap-gate InAs transistor, an ionic transducer, which was characterised in several measurement ranges and atmospheric conditions.