Study of Epithelial Cells on Polypyrrole based Conducting Polymers using Electrochemical Impedance Spectroscopy

PhDPolypyrrole (PPy) is a conjugated polymer that displays special electronic properties including conductivity. It may be electrogenerated with the incorporation of any anionic species including negatively charged biological molecules such as proteins and polysaccharides. For this thesis, variously loaded-PPy films were prepared on gold sputter-coated coverslips. The growth and characteristics of epithelial cells, namely keratinocytes, were studied on these films by microscopy, biochemical assay, immunocytochemistry and electrochemical impedance spectroscopy. Keratinocyte viability was found to be PPy-load dependent. For chloride, polyvinyl sulphate, dermatan sulphate and collagen-loaded PPy films, polycarbonate and gold, keratinocyte viability, as assessed by the AlamarBlueTM assay, was respectively 47%, 60%, 88% and 23%, 75% and 61% of tissue culture polystyrene controls after 5 days. This was found to require a previously unreported polymer washing step prior to cell seeding due to the observed toxicity of untreated films. Keratinocytes stained positive for proliferation (PCNA), suprabasal differentiation (K10) and hyperproliferation (K16) markers although cell morphology was poor for organotypical cultures on dermatanloaded PPy compared with de-epidermalised dermis. Cell-induced impedance changes were detected in a three-electrode format over PPy modified electrodes. Results obtained showed the effects of cell density, cell type and monitoring frequencies. In particular, it was seen that lower cell densities could be detected on PPy compared to unmodified gold electrodes. Keratinocyte confluence as determined by impedimetric analysis was reached more rapidly on PPy than bare gold in agreement with AlamarBlueTM measurements. Electrical equivalent circuit analysis using parameters whose contributions may be directly mapped to intracellular and intercellular spaces, and membrane components suggested that the technique can be extended to cell morphology discrimination. This work shows that PPy biocomposites are attractive candidates for tissue engineering applications since they may incorporate biomolecules and are electrically addressable with the potential to both direct and report on cell activities

Fabrication of 3-Dimensional Polymeric Drug Delivery Systems

Development of new polymer structures for local drug delivery to the brain is an exciting research area. The main aim of this study is to develop biocompatible controlled drug delivery systems, using biodegradable or conducting polymers, for the treatment of central nervous system disorders such as epilepsy

Application of impedance spectroscopy to the study of dithiocarbamate species on Au surfaces: Effects of aqueous Cu²⁺ and Mg²⁺ ions

Self-assembled monolayers (SAM) of dithiocarbamate ligands were formed on the Au surface of an interdigitated electrode (IDE) array by reaction of amines with CS2 in H2O/CH3OH solutions. Impedance spectroscopy was used to probe for the presence of each SAM as they were individually applied to the surface of the IDE by examining differences in collected impedance data after each step of the chemical application sequence. The impedance behavior of the SAM’s were then studied in the presence of aqueous Cu2+ and Mg2+ ions. A treated IDE array would, in theory, be able to preferentially detect lower concentrations of Cu2+(aq) by complexing with that specific ion, thus concentrating it within the capacitance field. Cupric ion chelating groups anchored to the gold surface by the dithiocarbamate group included morpholine or 5-amino-1,10-phenanthroline. A sensitive determination of the amount of Cu2+ leaching from anti-fouling marine hull coatings into water would be a useful example of practical applications of impedance-based sensors for heavy metal ions. Results of this work indicate that the SAM-treated IDE arrays differed in their impedance behavior relative to untreated IDE arrays. The SAM-treated IDE arrays detected 1.00 μM Cu2+ concentrations with confidence, while untreated IDE arrays only detected as low as 50.0 μM Cu2+ with confidence. i

NANOPILLAR BASED ELECTROCHEMICAL BIOSENSOR FOR MONITORING MICROFLUIDIC BASED CELL CULTURE

In-vitro assays using cultured cells have been widely performed for studying many aspects of cell biology and cell physiology. These assays also form the basis of cell based sensing. Presently, analysis procedures on cell cultures are done using techniques that are not integrated with the cell culture system. This approach makes continuous and real-time in-vitro measurements difficult. It is well known that the availability of continuous online measurements for extended periods of time will help provide a better understanding and will give better insight into cell physiological events. With this motivation we developed a highly sensitive, selective and stable microfluidic electrochemical glucose biosensor to make continuous glucose measurements in cell culture media. The performance of the microfluidic biosensor was enhanced by adding 3D nanopillars to the electrode surfaces. The microfluidic glucose biosensor consisted of three electrodes - Enzyme electrode, Working electrode, and Counter electrode. All these electrodes were enhanced with nanopillars and were optimized in their respective own ways to obtain an effective and stable biosensing device in cell culture media. For example, the `Enzyme electrode\u27 was optimized for enzyme immobilization via either a polypyrrole-based or a self-assembled-monolayer-based immobilization method, and the `Working electrode\u27 was modified with Prussian Blue or electropolymerized Neutral Red to reduce the working potential and also the interference from other interacting electro-active species. The complete microfluidic biosensor was tested for its ability to monitor glucose concentration changes in cell culture media. The significance of this work is multifold. First, the developed device may find applications in continuous and real-time measurements of glucose concentrations in in-vitro cell cultures. Second, the development of a microfluidic biosensor will bring technical know-how toward constructing continuous glucose monitoring devices. Third, the methods used to develop 3D electrodes incorporated with nanopillars can be used for other applications such as neural probes, fuel cells, solar cells etc., and finally, the knowledge obtained from the immobilization of enzymes onto nanostructures sheds some new insight into nanomaterial/biomolecule interactions

Hybrid Electrochemical Capacitors: Materials, Optimization, and Miniaturization

With the ever-advancing technology, there is an incessant need for reliable electrochemical energy storage (EES) components that can provide desired energy and power. At the forefront of EES systems are electrochemical capacitors (ECs), also known as supercapacitors that typically have higher power and superior cycle longevity but lower energy densities than their battery counterparts. One of the routes to achieve higher energy density for ECs is using the hybrid EC configuration, which typically utilizes a redox electrode coupled with a counter double-layer type electrode. In this dissertation, both scale-up (coin-cell type) as well as scale-down (on-chip miniaturized) hybrid ECs were designed, constructed and evaluated. The first part of the dissertation comprised material identification, syntheses, and electrochemical analyses. Lithium titanate-anatase titanium oxide (Li4Ti5O12-TiO2) composites were synthesized via electrostatic spray deposition (ESD) and characterized in both half-cell and full-cell assembly against lithium and nanostructured carbon based counter electrodes, respectively. The second redox type material studied for hybrid electrochemical capacitors was ESD derived manganese oxide (MnOx). The MnOx electrodes exhibited a high gravimetric capacitance of 225F g-1 in aqueous media. Further improvement in the rate handling of the MnOx electrodes was achieved by using CNT additives. The MnOx-CNT composites were tested in full-cell assembly against activated carbon counter electrodes and tested for different anode and cathode mass ratios in order to achieve the best energy-power tradeoff, which was the second major goal of the dissertation. The optimized hybrid capacitor was able to deliver a high specific energy density of 30.3 Wh kg-1 and a maximal power density of 4kW kg-1. The last part of the dissertation focused on a scale-down miniaturized hybrid microsupercapacitor; an interdigitated electrode design was adopted in order to shorten the ion-transport pathway, and MnOx and reduced graphene oxide (rGO) were chosen as the redox and double layer components, respectively. The hybrid microsupercapacitor was able to deliver a high stack energy density of 1.02 mWh cm-3 and a maximal stack power density of 3.44 W cm-3, both of which are comparable with thin-film batteries and commercial supercapacitor in terms of volumetric energy and power densities

Improvement of a pesticide immunosensor performance using site-directed antibody immobilisation and carbon nanotubes

The potential toxicity of pesticide residues in drinking water has meant a rigid regulation for the appearance of these pollutants. Thus, in this work, we developed a new immunosensor for atrazine detection. We focused on the optimisation of the antibody immobilisation method on sensor surface for the enhancement of the biosensor sensitivity. First, with site-directed immobilisation of rabbit anti-atrazine antibodies using goat anti-rabbit immunoglobulin, a detection limit of 0.5 ng/mL was obtained. This value is 20 times lower than the detection limit obtained with non-oriented antibodies. The second way to improve immunosensor sensitivity consisted of the addition of carbon nanotubes (CNT). As result of using these CNT, detection limit has been improved again from 0.5 ng/mL to 100 pg/mL.This work was financially supported by the PCI cooperation project between Spain and Tunisia.Marrakchi, M.; Helali, S.; Soto Camino, J.; González Martínez, MÁ.; Abdelghani, A.; Hamdi, M. (2013). Improvement of a pesticide immunosensor performance using site-directed antibody immobilisation and carbon nanotubes. International Journal of Nanotechnology. 10:496-507. doi:10.1504/IJNT.2013.053519S4965071