Living Diatom Microalgae as Robust Bioanodes for Biophotovoltaic Devices

Biophotovoltaic devices are a promising source of renewable energy, given they can generate electrical current from the photosynthetic activity of microalgae, cyanobacteria, or their isolated proteins. Different strategies such as direct electron transfer or, more commonly, the use of soluble mediators allow to directly harvest electrons from the cells of photosynthetic organisms and feed them to a closed circuit to generate current. Green microalgae have been extensively studied for the extraction of photocurrent, yielding promising outputs, mainly thanks to their ease of culture and fast growth. Alternatively, only a few examples are present in literature about the use of Diatom Microalgae for photocurrent extraction. Besides providing significant photocurrent intensities, diatom microalgae exhibit particular resistance to different kinds of stressors such as desiccation, temperature and mechanical pressure, which comes as an advantage when it comes to processing them into living bioandoes. Their sensibility to different contaminants makes them good candidates for the development of electrochemical biosensing devices. Moreover, diatoms hold the unique characteristic of bearing nanostructured biosilica microscopic shells (frustules), that can be functionalized with active molecules or polymers, opening the door to enhancing electron flow through conductive polymers, or to light absorption modulation for example via introduction of external antennae. This work aims to study the photocurrent extraction from different species of diatom microalgae deposited onto ITO, used as working electrode in a photovoltaic cell, evaluate their interaction with the electrode both in the presence and absence of a soluble mediator, and their resistance to the electrochemical process itself. Cyclovoltammetry and chronoamperometry measurements have been performed; optical and fluorescence microscopies, and metabolic assays have been used to study the microalgae's state under the different conditions studied. We have standarized a method that allows to produce bioanodes resistant to dessication from several different species of diatoms, that provide significant levels of power output, and are more resistant to repeated cycles of desiccation/photocurrent than a model green alga.