In nature, photosynthetic systems, such as plants, capture the energy from sunlight using moieties called chromophores attached to proteins. Researchers have tried to mimic this process using thin layers of chromophore-functionalised peptides on gold electrode surfaces. When lasers shine on these electrodes, a current is generated. 

Heinz-Bernhard Kraatz, from the University of Saskatchewan, Canada, says that although reports claim that the current is caused by the chromophores capturing the laser light and converting it to electricity, this might not be the case. Kraatz and colleagues performed similar experiments using peptides without attached chromophores. They found that current was still generated, indicating that the chromophores are not responsible its production. Current was even generated when they used a bare gold electrode. 

Kraatz explained: 'A significant consequence of the laser irradiation has been overlooked. The so-called photocurrent phenomenon is probably largely a result of the heating of the electrode.' 

Kraatz hopes to separate and quantify the chromophore-based photocurrent, if any, from the temperature-induced current. This should allow him to learn more about the electron transfer in biomolecular films. However, the work is not expected to be straightforward. 

'The increase temperature of the electrode may also change the structure of the peptides, which may change their electron transfer mechanism. It will be a challenge to isolate the responses due to the individual contributions,' said Kraatz. 

Joanne Thomson