Electrifying the Encapsulin—Charge Transport Studies across Protein Nanocages

Charge transport across biomolecules, such as proteins, DNA, and peptides, has been demonstrated to be efficient over long distances. This is called long-range tunnelling which is ubiquitous in nature in several biological systems. This phenomenon is very interesting for development of next generation bio-molecular electronic devices. However, it is unknown that under which conditions the long-range tunnelling regime can be accessed in the solid-state. Further, Encapsulin protein nanocages represent self-assembled compartments with adjustable number of monomers, and subsequently, the nanocompartment size. These nanocompartments can be used to load different types and amounts of cargoes with different properties. Recently, these nanocages have been shown as useful candidates for bioengineering in targeted drug delivery. However, the effect of these electronic properties has only been investigated for encapsulins in solution. Due to such tunable properties of Encapsulin nanocages, they present an interesting platform for biomolecular electronics.<br/><br/>In this project, we demonstrate a first investigation of self-assembled Encapsulin protein nanocages in the solid-state, either empty or containing different cargoes. We show that these encapsulin protein nanocages can be made stable in solution and on surface without any aggregation using dynamic light scattering, transmission electron microscopy, and atomic force microscopy. We investigated the electronic properties by measuring the current density over different voltage ranges using a conical top electrode of eutectic Gallium-Indium alloy. We determined that the encapsulated cargo has a significant effect on the electronic properties. Higher current densities and rectification ratios were measured in case of a redox active protein as a cargo, such as the ferritin-like protein, compared to a redox-neutral self-folding green fluorescent protein or without any cargo. This project presents a new platform for development of biomolecular electronic devices where the properties can be controlled via an active guest inside the protein host.