US scientists have developed a molecular shield that stabilizes near-infrared fluorescent dyes and enhances their functionality. Fluorescence bioimaging often uses the near-infrared light region because this radiation can efficiently penetrate human tissue.
Fluorescent dyes designed for this purpose usually have a flat, symmetrical molecular architecture, which favors absorption of near-infrared light, but the dyes also need to be water soluble and carry functional groups for conjugating with targeting biomolecules, for example, antibodies or tumor-binding peptides.
A member of this class of fluorescent dyes, called heptamethine cyanines, or Cy7, is currently under investigation in surgical applications. However, the Cy7 molecules have their drawbacks. Their light-absorbing chromophore is vulnerable to oxygen radicals, which leads to bleaching. In addition, the flat rigid molecules may aggregate and interact nonspecifically with other biomolecules, which slows down their clearance from the body. To tackle these issues, the research group improved the chemical structure of the dye. To protect the heptamethine chromophore from oxygen attack, they introduced a voluminous and smart shield.