Design, development and characterization of nanostructured electrochemical sensors

This is a publication-based thesis which focuses on the study of electrochemical microbiosensors for glucose detection. It investigates applications of a series of microfabricated gold electrodes based on several nanostructures in electrochemical biosensing technologies, embracing three major methodologies: direct electro-catalytic detection, enzymatic detection and dual-enzyme cascade detection. The study is described over five main chapters with a sixth providing a summary of the material presented and perspectives for the future. Chapter 1 provides an introduction to the field of the electrochemical biosensors with a specific focus on the chosen nanostructures and miniaturized systems, as well as a brief history of the biosensor. Chapter 2 presents results published in ACS Applied Nanomaterials, 2019, 2, 9, 5878-5889. It demonstrates the enzyme free detection of glucose via a direct electro-catalytic reaction. The miniaturized band array electrodes with specific width, length and inter-electrode-distance were integrated with homogeneously distributed copper foam nano dendrites. Such foam deposits presented for the first time at the micro scale were achieved using the in-situ hydrogen bubble template method. The resulting very high electroactive surface area of the porous foam deposits was one of the major advantages in terms of achieving superior performance from each micro band foam electrode towards glucose detection. Moreover, both sensors also showed a strong resistance to the poisoning effects of chloride ions and displayed excellent stability over a period of three months.Chapter 3 presents the first of t wo sets of results for the enzymatic detection of glucose, results published in Elsevier Electrochimica Acta, 2019, 293, 307-317. Chapter 4 then presents the second set of results on this topic which is published in and Elsevier Electrochimica Acta, 2019, 298, 97-105. The aim of these two chapters is to discuss the effect of miniaturization on the enzymatic biosensor performance which was studied in the presence of a carbon quantum dot (CQD) and gold nanoparticle nanohybrid system. CQDs, are a new class of carbon-based materials and have been used here for the first time as a matrix component integrated onto microfabricated gold electrode surfaces for enzyme immobilization and further miniaturization. The biosensors developed were studied by electrochemistry to investigate the analytical performance of each device. By scaling down the surface area of the biosensor, a 13-times increase in sensitivity was achieved towards glucose. Moreover both sensors-planar, micro disk array- exhibited excellent reproducibility, reusability and operational stability in terms of the performance of biosensors. Chapter 5 presents results published in RSC Analyst, 2020 (DOI: 10.1039/C9AN01664C). It demonstrates the operation of a dual-enzyme cascade which was constructed onto a micro band array electrode based on glucose oxidase and horseradish peroxidase enzymes. To achieve a very high surface area, a porous gold-foam was electrodeposited onto surface and then a second electrodeposition layer of chitosan and multi walled carbon nanotube nano-bio-composite. The micro band cascade scheme developed exhibited the highest sensitivity towards glucose detection in comparison to other systems reported in the literature. Chapter 6 provides an insight into the field of electrochemical biosensing with the support of the achievements presented in this thesis. Thus, by taking advantage of the available system, this chapter discusses the possible future applications of the electrochemical biosensors. The thesis then ends with section 7 which presents some Appendices

Copper-nanostructure-modified laser-scribed electrodes based on graphitic carbon for electrochemical detection of dopamine and glucose

Background: Carbon-based nanostructures have been attracting major interest in many research fields, including chemical and biological sensing, because of their unique structural dimensions and excellent physical, chemical and mechanical properties. A recently developed laser scribing approach allows design and fabrication of flexible, graphitic carbon-based substrates for (bio-)electrochemical applications, as it provides highly robust and low-cost sensing platforms. Results: Here we demonstrate the fabrication of a highly reproducible laser-scribed graphitic electrode (LSE) on a polyimide (Kapton) film using a simple, do-it-yourself laser engraving system equipped with a 405 nm wavelength laser. Copper nanostructures were deposited onto an electrode surface via the electrodeposition process. The developed three-dimensional graphitic electrodes modified by nano copper/copper oxide species (LSE-Cu) were used for the detection of dopamine and glucose. Electrochemical studies of LSE-Cu showed that in the presence of nano-copper there is an apparent shift of the oxidation peaks of dopamine and ascorbic acid, allowing determination of dopamine without an interference effect, with an excellent sensitivity of 1321.54 mu A L mmol(-1) cm(-2). Furthermore, the LSE-Cu sensor exhibited highly satisfying analytical performance towards glucose electro-oxidation, with a reproducibility of 5.47% (RSD %). Conclusion: We have demonstrated a simple design, fabrication and passivation route for the preparation of LSEs performing as biosensors. Such a cost-effective and design-flexible system is highly suitable for developing a biosensing platform towards various target analytes and further miniaturization of the electrode

Cu nanodendrite foams on integrated band array electrodes for the nonenzymatic detection of glucose

We demonstrate the successful electrodeposition of Cu nanodendrite foams (CuFoams) onto a series of lithographically formed gold band array electrodes at negative overpotentials in an acidic environment. The nanodendrite foams were deposited onto two different integrated microelectrode arrays fabricated using standard lithographic techniques. Each electrode consisted of 17 gold band electrodes deposited onto a silicon wafer substrate, labeled BA5 (with a width of 5 μm and a length of 250 μm) and BA10 (with a width of 10 μm and a length of 500 μm). Prior to Cu deposition the gold electrodes were characterized by scanning electron microscopy (SEM) in order to evaluate the morphology of each design and by cyclic voltammetry (CV) in order to investigate their diffusion profiles. After Cu deposition the resulting 3D foam structures were studied using SEM, XPS, and EDX. The CuFoam/Au microelectrodes were then used for the electrocatalytic detection of glucose via oxidation at a potential of +0.45 V vs Ag/AgCl in an alkaline medium. It was found that both types of electrode arrays used showed excellent analytical performance in terms of sensitivity, reproducibility, and stability in comparison with the best performances reported in the literature. In particular, the BA5-CuFoam electrode exhibited an outstanding sensitivity of 10,630 μA mM–1 cm–2 toward glucose with a wide linear range up to 22.55 mM, while the BA10-CuFoam electrode showed a sensitivity of 4,437 μA mM–1 cm–2. The performance of the proposed electrochemical sensor is attributed to a combination of the use of the very high surface area Cu nanodendrite foam and the enhanced radial distribution profile associated with the use of the smaller band microfabricated electrodes. Additionally, both sensors also showed a strong resistance to the poisoning effects of chlorine ions and excellent stability over a period of three months