"An Italian research team has developed an optical control method that alters the structure of green fluorescent protein (GFP), which allows the fabrication of single-biomolecule optical toggle switches, offering the possibility of biological memory devices."

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    http://www.edtneurope.com/printableArticle?doc_id=OEG20011114S0030

Abstract: "A single-biomolecule optical toggle switch is demonstrated based on a mutated green fluorescent protein (GFP). We have exploited molecular biology techniques to tailor the GFP molecular structure and photophysical properties and to give it optically controlled bistability between two distinct states. We present optical control of the fluorescence dynamics with two laser beams at 476 and 350 nm down to the ultimate limit of single molecules. These results indicate that GFP-class fluorophores are promising candidates for the realization of biomolecular devices such as volumetric optical memories and optical switches"