Eric Ackerman, Chenghong Lei and Dehong Hu from the Pacific Northwest National Laboratory in Richland, have successfully coupled state-of-art single-molecule fluorescence spectroscopy with a conventional electrochemical method to study chemical and biological single molecule electron transfer dynamics. 

The team used cresyl violet, which is fluorescent when oxidized under high electrical potential and non-fluorescent when reduced under low electrical potential, to demonstrate the powerful new tool. 'Fluorescent reactions are particularly attractive because they can be detected with great sensitivity in dilute solutions, even at the level of single molecules' says Ackerman. 

Using traditional, non-single molecule methods they showed that it was possible to turn the fluorescence of a concentrated solution of cresyl violet fluorescence on and off, by changing the electrical potential. The team then diluted the solution by several orders of magnitude and connected the same electrochemical cell to a single-molecule fluorescence microscope. Examination of individual dye molecules (that randomly diffused past the focus area of the microscope) revealed a tremendous heterogeneity for the same dye molecules. An average of many of the single-molecule measurements provided the same results as the concentrated solution, but at any given time some molecules that should have been oxidized or reduced by the applied electrochemical potential were not. Ackerman commented that they are still investigating the reasons for this dynamic variation, but that this demonstrates that the approach can work. 

The team plans to explore more complicated, biological electron transfer processes involving redox proteins, especially those related to the production of bioenergy. They also hope to learn far more about the molecular machines found in cells, particularly those involved in energy production. Ackerman point out that 'without expensive metals or other components, cellular molecular machines generate the energy necessary to sustain life and electrochemistry plays a very important role in these reactions.' 

Rachel Cooper