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.

Extracellular electron transfer features of Gram-positive bacteria

Electroactive microorganisms possess the unique ability to transfer electrons to or from solid phase electron conductors, e.g., electrodes or minerals, through various physiological mechanisms. The processes are commonly known as extracellular electron transfer and broadly harnessed in microbial electrochemical systems, such as microbial biosensors, microbial electrosynthesis, or microbial fuel cells. Apart from a few model microorganisms, the nature of the microbe-electrode conductive interaction is poorly understood for most of the electroactive species. The interaction determines the efficiency and a potential scaling up of bioelectrochemical systems. Gram-positive bacteria generally have a thick electron non-conductive cell wall and are believed to exhibit weak extracellular electron shuttling activity. This review highlights reported research accomplishments on electroactive Gram-positive bacteria. The use of electron-conducting polymers as mediators is considered as one promising strategy to enhance the electron transfer efficiency up to application scale. In view of the recent progress in understanding the molecular aspects of the extracellular electron transfer mechanisms of Enterococcus faecalis, the electron transfer properties of this bacterium are especially focused on. Fundamental knowledge on the nature of microbial extracellular electron transfer and its possibilities can provide insight in interspecies electron transfer and biogeochemical cycling of elements in nature. Additionally, a comprehensive understanding of cell-electrode interactions may help in overcoming insufficient electron transfer and restricted operational performance of various bioelectrochemical systems and facilitate their practical applications.

Protein bioelectronics: a review of what we do and do not know

We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.