JACS: New class of dyes can monitor biological activities in real time

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A new class of dendron-based fluorogenic dyes called "dyedrons," comprised of multiple cyanine donors coupled to a single malachite green acceptor that can be used to monitor biological activities of individual proteins in real-time, has been developed by researchers according to a study published online July 27 in the Journal of the American Chemical Society.

The new fluoromodules are five- to seven-times brighter than enhanced green fluorescent protein, a development that will open new avenues for research, according to Marcel P. Bruchez, associate research professor of chemistry and program director of Molecular Biosensor and Imaging Center (MBIC), Carnegie Mellon University in Pittsburgh.

"By using concepts borrowed from chemistry, the same concepts used in things like quantum dots and light harvesting solar cells, we were able to create a structure that acts like an antenna, intensifying the fluorescence of the entire fluoromodule," said Bruchez.

MBIC's fluoromodules are made up of a dye called a fluorogen and a fluorgen-activating protein (FAP), which is genetically expressed in a cell and linked to a protein of interest, where it remains dark until it comes into contact with its associated fluorogen. When the protein and dye bind, the complex emits a fluorescent glow, allowing researchers to easily track the protein on the cell surface and within living cells.

Fluoromodules are unique in that they do not need to be washed off for specific labeling, they come in a spectrum of colors, and they are more photostable than other fluorescent proteins. To make the fluoromodules brighter, the researchers amplified the signal of one of their existing probes.

Bruchez and colleagues took one of their standard fluorogens, malachite green, and coupled it with another dye called cyanine (Cy3) in a complex the researchers called a "dyedron." Each dyedron is approximately 1-2 nanometers and 3000 g/mol in size. The dyedron is based on a special type of tree-like structure called a dendron, with one malachite green molecule acting as the trunk and several Cy3 molecules acting as the branches.

The two dyes have overlapping emission and absorption spectra — Cy3 typically emits energy at a wavelength where malachite green absorbs energy — and this overlap allows the dyes to efficiently transfer energy between one another. When the Cy3 dye molecules become excited by a light source, such as a laser, they immediately "donate" their excitation energy to malachite green, boosting the signal being emitted by the malachite green, according to Bruchez and colleagues.

The MBIC researchers are currently using fluoromodules to study proteins on the cell surface, and hope to take the technology inside of cells in the near future. Additionally, they will be creating dyedrons for their other existing FAP/dye complexes.

The research was funded by the National Institutes of Health (NIH) as part of the American Reinvestment and Recovery Act. MBIC is one of the NIH's National Technology Centers for Networks and Pathways.