Jonathan Lloyd

UV photodecomposition of zinc acetate for the growth of ZnO nanowires

The thermal annealing of zinc precursors to form suitable seed layers for the growth of ZnO nanowires is common. However, the process is relatively long and involves high temperatures which limit substrate choice. In this study the use of a low temperature, ultra-violet (UV) exposure is demonstrated for photodecomposition of zinc acetate precursors to form suitable seed layers. Comparisons are made between ZnO nanowire growth performed on seed layers produced through thermal annealing and exposure to UV. The dependence of growth density and nanowire diameter on UV exposure time is investigated. Growth quality is confirmed with energy dispersive x-ray (EDX) and x-ray diffraction analyses. The chemical composition of the exposed layers is investigated with EDX and x-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) is utilized to investigate morphological changes with respect to UV exposure. The diameter and density of the resultant growth was found to be strongly dependent on the UV exposure time. UV exposure times of only 25-30 s led to maximum density of growth and minimum diameter, significantly faster than thermal annealing. EDX, XPS and AFM analyses of the seed layers confirmed decomposition of the zinc precursor and morphological changes which influenced the growth.

Uniform sensing layer of immiscible enzyme-mediator compounds developed via a spray aerosol mixing technique towards low cost minimally invasive microneedle continuous glucose monitoring devices

In this study, a uniformly mixed sensing layer of typically immiscible compounds, such as tetrathiafulvalene (TTF) mediator and glucose oxidase (GOx) enzyme, was developed using a simultaneous spray deposition technique ideal for mass production of glucose sensors at low cost while exhibiting enhanced amperometric response. For comparison, the sensors were fabricated via three different methods: conventional drop-cast of TTF and GOx compounds in subsequent layers (DL), spray deposition of the compounds in subsequent layers (SL), and spray mixing of the compounds as one uniform layer (SM). Uniformity of the sensing layers was investigated via Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) techniques demonstrating an even distribution of the TTF and GOx throughout the sensing layer for the SM sensors. The amperometric studies showed a significantly larger maximum current response, Imax and sensitivity for the SM sensors as compared to the SL and DL sensors. The significantly better performance of the SM sensors correlated well with the even distribution of TTF and GOx throughout the sensing layer, resulting in enhanced electron transfer and redox reaction between GOx and TTF. The SM spray technique was then applied to deposit a uniformly mixed sensing layer on to 3D microneedle arrays to provide minimally invasive continuous glucose monitoring (CGM). In-vivo studies showed amperometric response from the microneedle CGM device was compatible to changes in blood glucose levels measured via the standard finger prick tests. Importantly, the deposition technique is suitable for mass production of the microneedle CGM at very low cost.