Nano Lettershttp://dx.doi.org/10.1021/nl2018959 (2011)

The light-enhancing effects of plasmonic devices have been widely recognized to be able to boost the performance of solar cells. Mostafa El-Sayed and colleagues now apply this capability to a natural light-harvesting system — the membrane protein bacteriorhodopsin (bR). Used by some bacteria, this protein captures light and uses this energy to create a proton difference across its membrane. This separation of electrical charges has been successfully used to power electrochemical cells, although the observed photocurrents have remained rather low. A problem with the efficiency of the bR photocycle is a bottleneck in the conversion of an intermediate, photoexcited molecular state back to the original state of the protein. This slow conversion can be sped up by the absorption of blue light, but this process hasn't been very efficient. El-Sayed and colleagues now deploy silver nanoparticles in the bR electrochemical cells. The plasmon resonance has been tuned to the blue-light-absorption region of bR so that the large field enhancement close to the nanoparticles accelerates the relaxation of the intermediate state. As a consequence, the photocurrents observed are up to 5,000 times higher than without plasmonic enhancement.