Charge Extraction in Photosynthetic Systems

Due to the growing demand for new energy resources, the capture and conversion of bio-energy in the photosynthetic organisms have received a lot of new attention. This dissertation investigates and studies the methods of the charge extraction from the natural electron transport chain in photosynthesis systems to an outside circuit. This dissertation specifically focuses on two major methods. The first approach is to extract photocurrent directly from an intact algae cell. Ultra sharp microelectrodes are manufactured using self-designed dynamic feedback electrochemical etching system to insert the membrane of chloroplast of alga to extract the photocurrent. Pico-amp level photocurrent could be collected when the algae cell membrane and chloroplast membrane were both being successfully penetrated. The second approach is to investigate the photocurrent from the isolated thylakoids. Several tests have been applied to verify the photocurrent measured is indeed from the photosynthesis on the thylakoid membranes. Various electron mediators are used to facilitate the charge transfer from the thylakoid's charge transport chain to the outside medium. Peak dependence in the photocurrent as a function of concentration of the electron mediators is observed for all mediators used. The photocurrent collected varies substantially with the types of artificial electron mediators used. A semi-quantitative explanation is discussed.