The team, which includes members of University College Dublin and Edinburgh University, measured 10 nm of separation between cofactors along the fibre, which is too large for longitudinal current flow. Although the vast majority of cases were insulating, which is desirable if the haem network is to eventually manage current flow, around 1 in 150 fibres showed signs of conductance regardless of haem. The scientists are confident that fully controlled conducting fibres are possible because certain bacteria can harvest electrons from solid-state fuel sources several centimetres away using similar natural protein fibres.

“Locating the cofactors within the fibre is critical to understand how they affect the fibre shape and, in turn, knowledge of the shape is necessary to control the cofactor arrangement,” said Forman. “There are many possibilities for what could be displayed on the fibre. We think of cofactors as the ultimate quantum dots and, just like solid-state quantum dots, the colour is easily controlled. For example, chlorophyll is green and haem makes your blood red.”

Helical path

Although the experiments assess transverse tunnelling across the fibres, the helicity of the fibres may allow longitudinal conductance too because the tip-to-fibre connection could be some lateral distance from the fibre-to-substrate connection, requiring longitudinal tunnelling through the haem network.

These results will help to design the next generation of fibre, which is the brain-child of Dr Paul Barker. If the structure and conductive properties of the new fibres can be controlled, they could act as an interface between conventional solid-state electronics and aqueous biochemistry.

Potential applications may include computer interfaced biosensing and biochemical actuation, perhaps yielding software control over catalytic events in a 3D reaction volume such as a battery, fuel cell, solar cell, biological cell, synthetic tissue or arbitrary material.

More information can be found in the journal Nanotechnology.