December 2007

New Squaraine Rotaxane Dyes

MTTI has started selling an emerging series of fluorescent dyes known as Squaraine Rotaxanes under the brand name SRfluor. Currently there are two different SRfluor dyes available for biological studies: (i) SRfluor-680 Phenyl which accumulates at lipophilic sites within live cells such as the endoplasmic reticulum and/or lipid droplets (see movie on the right), and (ii) SRfluor-680 carboxylate which can be coupled to peptides, proteins, antibodies and other biomolecules to provide extremely bright fluorescent conjugates.

These compounds were discovered by a team led by Professor Bradley D Smith at the University of Notre Dame, Indiana. They found that by wrapping a squaraine dye in a molecular cloak, the reactive dye compound was shielded from nucleophiles and became more stable, thereby increasing its viability as a near-infrared fluorescent-imaging probe for cellular and other biological studies (J. Am. Chem. Soc. 2005, 127, 3288). Furthermore, the Notre Dame team has found that the squaraine rotaxane complex readily self-assembles within the complicated molecular environment of a living cell (J. Am. Chem. Soc. 2007, 129, 15054). This work was also recently highlighted in an article titled “Two-Piece Imaging Probes” in the December 10, 2007 edition of Chemical Engineering News.