Fluorescence anisotropy measurement of green fluorescent protein for nano-environment probing

Fluorescence anisotropy of GFP molecules, suspended in solution and immobilized on a glass substrate, was measured to investigate the application for nano-environment probe. Nano-environment around living cell is of interest in relation with wide range of fields, such as cell interaction in cancer tissue, nerve signal transmission and so on. However, nano-environment is so sensitive to the interference of probe or measurement itself. For example, measurement of neuron potential is performed by inserting electrode to the tissue, or staining with toxic dye. For measurement of nano-environment GFP has some superior characteristics. GFP molecule itself is soluble protein and has little toxicity to the cell. It need no prosthetic group for fluorescent activity, and easily introduced by genetic method. We investigated the fluorescence anisotropy of GFP for probing molecular motion in the nano space. Anisotropy of free molecule in solution was compatible with theoretical value. Immobilized molecule, on the contrary, showed higher anisotropy than theoretically expected. This extraordinary value may come from hydrophobic interaction of GFP with glass surface, that can be utilized for nano-probing.