Sensing photosynthetic herbicides in an electrochemical flow cell

Specific inhibitory reactions of herbicides with photosynthetic reaction centers bound to working electrodes were monitored in a conventional electrochemical cell and a newly designed microfluidic electrochemical flow cell. In both cases, the bacterial reaction centers were bound to a transparent conductive metal oxide, indium-tin-oxide, electrode through carbon nanotubes. In the conventional cell, photocurrent densities of up to a few mu A/cm(2) could be measured routinely. The photocurrent could be blocked by the photosynthetic inhibitor terbutryn (I (50) = 0.38 +/- 0.14 mu M) and o-phenanthroline (I (50) = 63.9 +/- 12.2 mu M). The microfluidic flow cell device enabled us to reduce the sample volume and to simplify the electrode arrangement. The useful area of the electrodes remained the same (ca. 2 cm(2)), similar to the classical electrochemical cell; however, the size of the cell was reduced considerably. The microfluidic flow control enabled us monitoring in real time the binding/unbinding of the inhibitor and cofactor molecules at the secondary quinone site.