May 2, 2013
Electronic connection to biomolecular fibre established
Electronic components are only useful when they are connected, which applies to biological matter – for example, metallo-proteins – as well as conventional electronics. Indeed, connecting biological samples to conventional electronics is a big challenge due to the difficulty in interfacing electrochemicals with solid-state structures. In a recent study, researchers led by Paul Barker and Colm Durkan from the University of Cambridge have used STM in vacuo to connect up a large protein fibre displaying a helical array of haem molecules (cofactors). The fibre diameter of 5 nm is a very long way for electrons to tunnel so the team used the cofactors as a bridge between the tip and the gold substrate, to reveal the cofactor location in the insulating fibres.
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.”
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.
About the author
The team consists of Dr Paul Barker's group in the Chemistry Department at the University of Cambridge who study protein engineering with medical and bioelectronic applications. Dr Chris Forman, a postdoc in chemistry supported by the ERC, made the fibres using protein synthesized by Dr Adrian Nickson. The particularly challenging STM analysis was performed using in-house low-noise machines in UHV, which are hosted by the probe microscopy group at the Nanoscience Centre in Cambridge run by Dr Colm Durkan. Much of the STM and ncAFM was conducted by Dr Nan Wang. Also Dr Zhi-Yong Yang, now an associate professor at the Chinese Academy of Science, performed some of the STM work. Additional electron transfer protein for control experiments was provided by Dr Chris Mowat at the University of Edinburgh. Supporting AFM studies were also conducted in conjunction with Prof. Suiz Jarvis at University College Dublin.