Electrosensing Applications by Using Titania as a Support for Bio(inspired) Molecules
25 May 2018
Campus Groenenborger, U.241 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Chemistry
Karolien De Wael & Vera Meynen
PhD defence Vanousheh Rahemi − Faculty of Science, Department of Chemistry
In my thesis, new strategies were developed for the detection of phenolic compounds by using titania and horseradish peroxidase (HRP). HRP is a heme-containing enzyme that utilises hydrogen peroxide to oxidise a wide variety of organic and inorganic compounds. However, the application of free enzymes is often hampered by a lack of long-term operational stability and difficult recovery and re-use of the enzyme. These drawbacks can generally be overcome by immobilisation/incorporation of the enzyme in a support. As a first step, HRP was incorporated in titania. An adhesive conducting electrode material containing graphite, biocompatible ion exchange polymer nafion and commercial mesoporous TiO2 impregnated with horseradish peroxidase (HRP) was prepared. The role of mesoporous titania is to protect the incorporated enzyme from denaturation and increases the operational stability of the enzyme. HRP exhibits affinity for phenolic compounds, the detection can only occur in the presence of hydrogen peroxide (H2O2) which creates a reactive HRP-H2O2 complex (strong oxidant initiating the further reaction).
However, the addition of H2O2 complicates the detection strategy as time is needed for background stabilization. Therefore, different strategies were developed to tackle this drawback. In the second step, a new strategy was described how to avoid the presence of hydrogen peroxide during HRP sensing. In the third step, the special features of titania were used to construct a highly efficient electrochemical enzyme based biosensor in order to detect phenolic compounds in flow systems without the need of the addition of supplementary reagent. These features are related to the presence of reactive oxygen species (ROS) at the surface of titania upon irradiation in day light. This ROS worked as the necessary oxidant for phenolic detection. Flow cells make it possible to achieve high sensitivity using very small amounts of sample with distinctive properties: (i) aqueous flow is generally laminar, not turbulent; (ii) diffusion is an efficient process for mixing the dissolved content of two or more fluids.
Enzyme-based electrochemical biosensors were an inspiration for the development of (bio)analytical techniques. However, the instability and reproducibility of the reactivity of enzymes, combined with the need for chemical reagents for sensing remain challenging for the construction of devices. In order to overcomes the drawbacks of current enzymatic sensors the photosensitizer, a bioinspired perfluorinated Zn phthalocyanine was explored that generates singlet-oxygen from air under visible light illumination and oxidizes analytes, yielding electrochemically-detectable products while resisting the oxidizing species it produces.