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Green synthesis of CuO/CQD nanocomposites for printed electrochemical glucose sensor
Author(s)
Atson, Ryal
Date Issued
2026
Type
master thesis
Publisher
Cape Peninsula University of Technology
Abstract
Enzymatic electrochemical glucose sensors are widely used to monitor glucose levels and effectively manage diabetes. However, these sensors suffer from poor environmental stability and complex enzyme immobilisation procedures. Additionally, many traditional nanomaterial synthesis routes used in the development of electrochemical glucose sensors rely on toxic reagents and harsh reaction conditions, raising concerns about sustainability. To address this, non-enzymatic glucose (NEG) sensors can be realised through plant-mediated green synthesis. In this approach, plant phytochemicals drive the formation of nanomaterials that function as the active sensing elements, avoiding enzyme-related issues and providing a more sustainable alternative to conventional methods. Among candidate nanomaterials, CuO offers strong catalytic activity toward glucose oxidation, and its performance can be enhanced by integrating conductive carbon quantum dots (CQDs) into a hybrid nanocomposite. For this, plant extracts can serve as both reducing agents for synthesising CuO nanoparticles and carbon sources for synthesising CQDs. However, despite its phytochemical abundance, Aloe arborescens has not previously been explored for the green synthesis of a NEG sensor. The strategy used to deposit these nanomaterials onto sensor substrates also plays a decisive role in shaping sensor performance. Yet, the influence that microplotting (a digitally controlled printing technique) has on the electrochemical performance of green-synthesised glucose sensors has not been systematically investigated previously. To this end, this study aimed to synthesise CuO/CQD nanocomposites via a green hydrothermal route using A. arborescens extract as a reducing agent and carbon source, and to evaluate their performance as an electrochemical NEG sensor. A secondary aim was to assess the effect of microplotting deposition on the overall sensing performance of the fabricated sensor electrodes. Optimisation of the A. arborescens phytochemical extraction temperature and time maximised the phenolic content, and optimisation of the hydrothermal synthesis conditions (i.e., temperature, time, pH, precursor concentration, and extract concentration) ensured the reproducible formation of CuO/CQD nanocomposites. Structural characterisation (SEM, EDS, FT-IR, Raman, XRD, TGA/DTA) confirmed the formation of quasi-spherical CuO nanostructures decorated with CQDs. Electrochemical characterisation of pristine CuO and CuO/CQD films drop-cast on fluorine-doped tin oxide (FTO) glass revealed that the CuO/CQD/FTO platform improved charge-transfer kinetics, electroactive surface area, and catalytic efficiency. Drop-casting was employed as a benchmark method before the development of microplotted sensors. A comparative study of deposition techniques demonstrated that microplotting yields CuO/CQD electrodes with more application-relevant electrochemical behaviour than dropcasting. Accordingly, CuO/CQD ink was microplotted onto screen-printed gold electrodes (SPGEs) and evaluated for glucose detection in 0.1 M NaOH. The resulting CuO/CQD/SPGE platform exhibited a wide linear range of 0.9–17.1 mM (R2 ≥ 0.995), a detection limit of 0.33 mM, and sensitivities of 0.131–0.0826 mA·mM-1·cm-2, with a rapid steady-state response (<6 s). The wide linear range spans hypoglycemic, normoglycemic, and hyperglycemic states, confirming its clinical relevance. The CuO/CQD sensor also demonstrated excellent repeatability, reproducibility, stability, and selectivity under the influence of common interferents, chelating agents, and physiologically relevant chloride concentrations. Comparative benchmarking against state-of-the-art CuO-based NEG sensors highlights the role of electrode geometry, deposition precision, and material compatibility in extending the linear range. Proof-of-concept testing in serum showed <6% deviation from a commercial glucose meter, affirming the clinical potential of the CuO/CQD/SPGE platform. These findings illustrate how green-synthesised nanomaterials and precision microfabrication can enable sustainable, high-performance glucose sensing platforms for clinical and point-of-care applications.
Additional information
Thesis (Master of Engineering in Chemical Engineering )--Cape Peninsula University of Technology, 2026
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