Fabrication of novel sensors from nanomaterials

Small, William Richard

Abstract

This thesis describes the fabrication and characterisation of novel sensors from nanomaterials. These are materials that have at least one length scale in the nanometre region, and in many cases they exhibit fascinating electrical, mechanical or optical properties due to their small size. While their small size makes them candidates for miniaturising macro-scale technologies, many researchers are concerned with exploiting their unique properties in larger scale applications. These might include strong, lightweight building materials based on their mechanical properties, or visual displays based on their electrical and/or optical properties. To achieve transfer of the properties from the nano-scale to the macro-scale however is not straight forward, and there are a number of obstacles that must be overcome. One obstacle is that of processing the nanomaterials, ensuring that their properties do not become lost when they are incorporated into bulk materials or composites due to aggregation or poor interactions with their host matrix. This obstacle will also be addressed in the thesis, as we fabricate and characterise composites incorporating nanomaterials, and develop methods to process these materials into novel sensors.

The synthesis and characterisation of a number of different composites has been achieved, incorporating either carbon nanotubes or silver nanowires as the nanomaterials of interest. These have been fabricated using either mixing or in situ polymerisation routes, with surfactants, polysaccharides or conducting polymers as the dispersant. The composites are all soluble in either water or organic solvents to give stable dispersions, and show interesting properties including optical activity, high loading fractions of the nanomaterials and electrochromic behaviour.

The methods that we have developed for processing the dispersions are drop deposition, inkjet printing and dielectrophoretic assembly. Drop deposition has been performed as it forms the basis of numerous solution-based processing techniques, and we have investigated specifically the effects of substrate hydrophobicity and the effect of aggregates in the dispersion on the resulting composite films that are formed. We have reported for the first time the inkjet printing of single wall carbon nanotubes, and have printed composite films that show good transparency and high conductivity. A novel method for arresting the structures formed through dielectrophoretic assembly within a gel solution has also been developed. This has led to the fabrication of electrically anisotropic gels, and free-standing 'strings' of yeast cells. Novel sensors have been fabricated through two of our processing methods.

Thin films containing carbon nanotubes have been inkjet printed, and show sensitivity to water vapour (with gellan gum as the composite material) and alcohol vapour (with a water soluble conducting polymer as the composite material). A sensor based on biotin-functionalised silver nanowires assembled into a microwire and encapsulated within agarose gel has also been fabricated. This sensor showed sensitivity to streptavidin when the response was measured parallel to the formed microwire, but gave a much lower signal when the response was measured perpendicular to the microwire. This provides a proof of concept that a whole range of biosensors based on assembled silver nanowires into an anisotropic gel can be produced by employing an antigen-antibody strategy, similar to the one shown for biotin-streptavidin.

Citation

Small, W. R. (2009). Fabrication of novel sensors from nanomaterials. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4208993

• Thesis Type: Thesis
• Deposit Date: Aug 15, 2011
• Publicly Available Date: Feb 22, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4208993
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Jan 1, 2009