2004 Volume 25 Issue 1 Pages 34-41
Single molecular photocurrent generation was investigated using a novel light-illumination scanning tunneling microscope (LI-STM) equipped with an optical fiber probe. For this study, self-assembled monolayers (SAMs) of biological photosynthesis mimicking chimera proteins composed of cytochrome b562 mutant proteins fused with a green fluorescent protein (GFP) were prepared. With light illumination, the GFP was excited, resulting in photocurrent generation due to the energy transfer to the cytochrome part instead of a typical fluorescence. Two different types of measurements were carried out employing a conventional LI-STM with a metallic probe and far-field optics, and another LI-STM in which the metallic probe was replaced with a laboratory-built doubly metal-coated optical fiber probe and thus a local near-field illumination was possible. Comparison of these two techniques indicated that the new technique was superior in sensitivity to the conventional one. Evidence of the intramolecular energy transfer at a single molecular level was shown.
