Red fluorescence in two steps | 9/14/2017 | Staff
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Scientists have identified the mechanism that allows fluorescent proteins to switch colour in two phases. They are thereby laying the groundwork for new applications in microscopy and functional analyses in biological research.

It all started out with an observation that ETH scientists made about two years ago with a special fluorescent protein isolated from corals, Dendra 2, which fluoresces green. Light can be used to change its molecular structure so that it switches its colour to red. The researchers discovered a new way to induce this colour switch: First, it is briefly excited with a pulse of blue laser light and then illuminated immediately with near-infrared light. Applications for this two-phase colour switch include fluorescence microscopy.

Team - Researchers - Periklis - Pantazis - Department

An international team of researchers led by Periklis Pantazis, of the Department of Biosystems Science and Engineering (D-BSSE) at ETH Zurich in Basel, has now explained this two-phase colour switch mechanism. The scientists refer to this as "primed conversion." The new knowledge allows the researchers to modify other light-sensitive proteins so that they can also be excited in two phases.

The researchers from ETH Zurich, the Karlsruhe Institute of Technology, and the Janelia Research Campus in Ashburn, Virginia, closely examined the proteins activated with blue light and succeeded in showing that these proteins enter an excited state lasting several milliseconds. "That's relatively long," explains Pantazis. "Other fluorescence phenomena are much shorter."

Scientists - State - Case - Phenomenon - Quantum

The scientists also demonstrated that this state is a case of a phenomenon known from quantum chemistry—a "triplet state." After about five milliseconds, the fluorescent protein Dendra 2 returns to its ground state. Primed conversion happens only if the second phase—illumination with near-infrared light—occurs within the triplet time window.

The duration of the triplet state depends greatly on the stability of the fluorescent protein. This, in turn, depends on the exact sequence of protein building blocks (amino acids),...
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