Investigation of nanocrystalline zinc oxide and zinc oxide/copper oxide composites for use in a continuous flow biosensor

Cao, Lu

Abstract

There are an increasing number of applications for point-of-care biosensing technologies that are able to monitor biochemical levels over a period, rather than as a measurement at a single time point. As with all point-of-care devices, cost and appropriate sensitivity for measurement in the clinical range of the target analyte are very important factors.

In the study described in this thesis, impedimetric, affinity-based non-faradaic biosensors, which incorporate nanoparticles have been investigated to progress towards devices that are suitable for such point-of-care applications. To keep fabrication costs low, a simple colloidal dispersion technique, incorporating sonication was used to create sensor surfaces of zinc oxide (ZnO) and zinc oxide / copper oxide (CuO) nanoparticles. The nanoparticles acted to enhance the signals and thus increase the sensitivity. Using the nanoparticles, two sensor structures were evaluated; the first was formed by dropping the nanoparticle colloidal suspensions on to polyethylene terephthalate (PET) substrates and the second was created by facilitating the absorption of the nanoparticle colloidal suspensions in to nitrocellulose membranes.

Results of the analysis of the sensor structures, performed using scanning electron microscopy, Raman spectroscopy and electrical analysis, are presented. In order to evaluate the biosensing properties, C-Reactive Protein (CRP) was used as a model analyte. The progression from a 2D nanoparticle surface (on PET substrates) to 3D nanoparticle surface (nanoparticle impregnated membranes) resulted in a significant increase in the sensitivity. For example, the limit of detection improved from 0.4 ng/mL for the ZnO/CuO (1:2) nano-surfaces to 16 pg/mL for the ZnO/CuO (1:2) nanoparticle membrane. Altering the ratio of ZnO to CuO within the suspension used to make the sensors structures, also resulted in variation in the sensitivity.

This thesis also reports a flow assay based on ZnO and ZnO/CuO nanoparticle impregnated membranes, using impedance measurement with both planar and interdigitated electrodes. These new paper-based flow systems showed high sensitivity and wide detection ranges over approximately a 2 hour testing period (where samples were added at fixed time intervals).

Using CRP as the analyte, the dynamic range of the biosensor was demonstrated to encompass 10 pg/mL to 366,660 pg/mL on 4 mm gap planar electrode and 1 pg/mL to 3,166 pg/mL on interdigitated electrode , with a calculated limit of detection of < 5 pg/mL for both nano-ZnO and nano-ZnO/CuO membranes. This technique, which combines the benefits of nanoparticle technology, impedimetric measurement and flow immunoassays, offers great potential for the development of real-time, low-cost, point-of-care biosensing devices.

• Thesis Type: Thesis
• Deposit Date: Aug 5, 2019
• Publicly Available Date: Jan 17, 2022
• Public URL: https://uwe-repository.worktribe.com/output/1863268
• Award Date: Jan 17, 2022