STRATEGIES TO INCREASE THE CELL-TO-ELECTRODE ELECTRON TRANSFER OF BIOANODES FOR THEIR APPLICATION IN CELLULAR-BASED BIOPHOTOVOLTAICS
The aim of this Thesis is to explore strategies for the improvement of cell-to-electrode electron transfer in bioanodes for their application in cellular-based biophotovoltaic (BPV) devices. The first strategy was focused on designing electrode surfaces with boronic acid derivatives to improve the intimate contact with the cell and consequently the electron transfer process. 3-aminophenylboronic acid (3-APBA) modified electrodes, either in the form of conducting polymers or as single molecules embedded in redox hydrogels, outperformed bare electrodes in terms of photocurrent generation from C. vulgaris. Furthermore, the photocurrent performance of C. vulgaris was also assessed with electrodes modified with other conducting polymers synthesised from monomers structurally related to 3-APBA. The electronic and structural properties of these polymers were also evaluated. Photocurrent generation from C. vulgaris was only obtained with polyaniline (PANI) and polymers with electron withdrawing substituents. The polymer of 3-APBA exceeded all polymers tested in photocurrent generation from C. vulgaris. The second strategy was aimed at improving the exoelectrogenesis of C. vulgaris by subduing the alga to nutrient starvation or desiccation stress. The photocurrent generation, the photosynthetic efficiency and the stress induced to the cells immobilized on electrodes under these conditions were analysed by simultaneously combining electrochemistry and fluorometry. Photocurrent was only obtained when cells were desiccated. However, fluorometry and transmission electron microscopy (TEM) performed on C. vulgaris revealed that desiccation compromised the integrity of the cell. Overall, this Thesis contributes to expanding the knowledge of the cell-to-electrode electron transfer processes and exposes boronic acid derivatives as promising materials to construct bioanodes for cellular-based BPVs.
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