Protein-graphene system for bio-organic photovoltaics

The goal of this project was to expand the knowledge of hybrid, protein-graphene systems by assembling a team of computational chemists and physicists. We focused on the theoretical study of a new hybrid protein-graphene system, as a candidate for bio-electronic devices, such as biosensors and bio-organic photovoltaic cells (bio-OPV).

Silvio Osella

The considered protein is the reaction centre (RC) of the photosystem I (PS-I) protein, responsible for absorption of light and conversion into energy in bacteria, while graphene (SLG) is a monolayer of carbon atoms bonded together in a two dimensional honeycomb structure. The study focused on the interaction between these two fragments as conducting and charge carrier material. The way the protein and SLG interact is crucial to ensure the efficiency of the final device and thus the investigation of the nature of the interface is essential. A more complex interface presents the addition of a monolayer of molecules forming a Self-Assembled Monolayer (SAM), such as pyrene derivatives, in between SLG and the RC, which improve the stability of the system, direct charge transport mechanism and at the same time suppress the recombination of charges at the interface.

In this project, we resorted to a multiscale computational approach for the description of chemical and physical properties of the systems of interest. Due to the huge size of the PS-I, a smaller model system was considered, namely the Cytochrome C533 (Cyt), with the same characteristic of PS-I but at a feasible computational cost. First, we modelled the time-evolution of Cyt and SLG with a classical molecular dynamic method, which consists in considering the atoms bonded together in a spring-like way, without explicitly considering the electronic attractive forces. This allowed us to consider realistic model systems (thousands of atoms) and physically meaningful time-scales (hundreds of nanoseconds), for the investigation of the time-evolution of the Cyt/SLG interaction with and without SAM.

In the second step of the project we focused on a smaller portion of the system (the haem group of Cyt/SLG or SAM/ SLG interaction) using more accurate ab initio methods that account explicitly for the electrons, to describe and understand the electron transfer mechanism occurring in between the Cyt-SLG, Cyt-SAM and SAM-SLG interfaces. Here, we analysed the electronic wavefunction and the change in electronic properties of the interface, by means of energy level alignment (for the charge transport mechanism) and bandgap opening (for electronic properties).

Our project offered a rational design for novel complex systems composed of proteins and organic surfaces, with the possible use of such interfaces in the future as bio-organic photovoltaic cells and transistors, which may solve the problem of rapidly growing world energy consumption.

The project contributed to a better understanding of the impact of graphene on the stability and physical and chemical properties of the light harvesting protein and vice versa, and it offered answers to pressing questions such as how to avoid the recombination of charges at the interface, which is the most common problem observed in working devices.

As part of the project, I arranged an intersectoral study visit to a small company based in Warsaw, whose team members are experts in nuclear magnetic resonance (NMR) data acquisition and processing, with years of experience in developing new methods for better description of molecular systems. The main achievement from the visit was gaining a practical knowledge of how a small company is run on both the administrative and legal level. Moreover, they recently started to produce end-user products, and their strategy and process was of valuable importance since it gave me ideas on possible commercialization of our own research. I believe that the research conducted within the POLONEZ project is at a stage that is too early to be commercialized. Yet, the continuing collaborations and the development of novel methodologies are closing the gap between pure basic research and I envision possible commercialization of our findings in the near future.

Dr Silvio Osella received his PhD in Science at the University of Mons (Belgium) in 2014. He is currently an assistant professor at the Centre of New Technologies, University of Warsaw. His research focuses on the computational study of the opto-electronical properties of graphene and its derivatives (i.e. Nanoribbons, Nanoclusters) and of photoswitchable and fluorophore molecules when (but not limited to) inserted into biological environments. Two main research lines are followed. The first concerns the study of fluorophores embedded in lipid membranes and proteins, while the second is on the formation and study of hybrid organic-biological materials of interest for bio-organic electronics.