Researchers from Carnegie Mellon University's Molecular¹ Biosensor and Imaging Center (MBIC) are turning up the brightness on a group of fluorescent² probes（荧光探针） called fluoromodules that are used to monitor biological activities of individual proteins in real-time. This latest advance enhances their fluormodule technology by causing it to glow an order of magnitude brighter than typical fluorescent proteins. The new fluoromodules are five- to seven-times brighter than enhanced green fluorescent protein (EGFP增强型绿色荧光蛋白), a development that will open new avenues for research. In a paper published online in the Journal of the American Chemical Society, MBIC researchers unveil a new class of dendron（树枝石） -based fluorogenic dyes called "dyedrons," that amplify³ the signal emitted by their fluoromodules.

"By using concepts borrowed from chemistry, the same concepts used in things like quantum dots（量子点） and light harvesting solar cells, we were able to create a structure that acts like an antenna⁴（天线，触角） , intensifying⁵ the fluorescence of the entire fluoromodule," said Marcel Bruchez, associate research professor of chemistry and MBIC program director.

MBIC's fluoromodules are made up of a dye called a fluorogen and a fluorgen-activating protein (FAP). The FAP is genetically⁶ expressed in a cell and linked to a protein of interest, where it remains⁷ dark until it comes into contact with its associated fluorogen. When the protein and dye bind⁸, 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 spectrum⁹ of colors, and they are more photostable（不感光的） than other fluorescent proteins.

To make the fluoromodules brighter, the researchers amplified¹⁰ the signal of one of their existing probes. They took one of their standard fluorogens（荧光团） , malachite green（孔雀绿） , and coupled it with another dye called Cy3 in a complex the researchers called a "dyedron." The dyedron is based on a special type of tree-like structure called a dendron, with one malachite green molecule¹¹ acting¹² as the trunk and several Cy3 molecules¹³ acting as the branches.

The two dyes have overlapping¹⁵ emission¹⁶ and absorption spectra¹⁷（光谱，范围） — Cy3 typically emits energy at a wavelength¹⁸ where malachite green absorbs energy — and this overlap¹⁴ allows the dyes to efficiently¹⁹ 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.

Each dyedron is approximately 1-2 nanometers and 3000 g/mol in size. The very bright, but very small, dye particles allow the researchers to expand their live-cell imaging research. Previously²⁰, when conducting microscopy（显微镜检查） experiments using fluorescent proteins, fluoromodules and fluorescent dyes, if researchers wanted to increase the brightness, they would either increase the intensity²¹ of the laser used to visualize²² the proteins or label the protein being studied with numerous copies of the fluorescent tag. Both methods had the potential to alter the biology of the system being studied, either through the more intense energy coming from the laser or the increased weight caused by the multiple tags added to the protein. The new approach provides a single compact protein tag with signal enhancement provided by only modestly enlarging the targeted dye molecule.

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.