Ferrihydrite Reduction by Photosynthetic Synechocystis sp. PCC 6803 and Its Correlation With Electricity Generation

Microbial extracellular electron transfer (EET) to solid-state electron acceptors such as anodes and metal oxides, which was originally identified in dissimilatory metal-reducing bacteria, is a key process in microbial electricity generation and the biogeochemical cycling of metals. Although it is now known that photosynthetic microorganisms can also generate (photo)currents via EET, which has attracted much interest in the field of biophotovoltaics, little is known about the reduction of metal (hydr)oxides via photosynthetic microbial EET. The present work quantitatively assessed the reduction of ferrihydrite in conjunction with the EET of the photosynthetic microbe Synechocystis sp. PCC 6803. Microbial reduction of ferrihydrite was found to be initiated in response to light but proceeded at higher rates when exogenous glucose was added, even under dark conditions. These results indicate that current generation from Synechocystis cells does not always need light irradiation. The qualitative trends exhibited by the ferrihydrite reduction rates under various conditions showed significant correlation with those of the microbial currents. Notably, the maximum concentration of Fe(II) generated by the cyanobacterial cells under dark conditions in the presence of glucose was comparable to the levels observed in the photic layers of Fe-rich microbial mats.

Charge Transporting Materials Grown by Atomic Layer Deposition in Perovskite Solar Cells

Charge transporting materials (CTMs) in perovskite solar cells (PSCs) have played an important role in improving the stability by replacing the liquid electrolyte with solid state electron or hole conductors and enhancing the photovoltaic efficiency by the efficient electron collection. Many organic and inorganic materials for charge transporting in PSCs have been studied and applied to increase the charge extraction, transport and collection, such as Spiro-OMeTAD for hole transporting material (HTM), TiO2 for electron transporting material (ETM) and MoOX for HTM etc. However, recently inorganic CTMs are used to replace the disadvantages of organic materials in PSCs such as, the long-term operational instability, low charge mobility. Especially, atomic layer deposition (ALD) has many advantages in obtaining the conformal, dense and virtually pinhole-free layers. Here, we review ALD inorganic CTMs and their function in PSCs in view of the stability and contribution to enhancing the efficiency of photovoltaics.

How stable are the collagen and ferritin proteins for application in bioelectronics?

One major obstacle in development of biomolecular electronics is the loss of function of biomolecules upon their surface-integration and storage. Although a number of reports on solid-state electron transport capacity of proteins have been made, no study on whether their functional integrity is preserved upon surface-confinement and storage over a long period of time (few months) has been reported. We have investigated two specific cases—collagen and ferritin proteins, since these proteins exhibit considerable potential as bioelectronic materials as we reported earlier. Since one of the major factors for protein degradation is the proteolytic action of protease, such studies were made under the action of protease, which was either added deliberately or perceived to have entered in the reaction vial from ambient environment. Since no significant change in the structural characteristics of these proteins took place, as observed in the circular dichroism and UV-visible spectrophotometry experiments, and the electron transport capacity was largely retained even upon direct protease exposure as revealed from the current sensing atomic force spectroscopy experiments, we propose that stable films can be formed using the collagen and ferritin proteins. The observed protease-resistance and robust nature of these two proteins support their potential application in bioelectronics.