Red fluorescent dyes might sharpen biomedical imaging

Most fluorescent imaging depends on dyes that emit blue or inexperienced mild. These imaging brokers work nicely in cells, however they’re much less helpful in tissue as a result of the low ranges of blue and inexperienced fluorescence produced by the physique intervene with the sign. Blue and inexperienced mild additionally scatter in tissue, limiting their potential to penetrate deeply.

Red-emitting dyes provide extra express pictures for deep-tissue imaging, however they’ve lengthy been hindered by poor brightness and instability. Most pink dyes have low quantum yields; solely about 1% of the absorbed mild is re-emitted as fluorescence, making them dim and unreliable.

Achieving environment friendly pink and near-infrared (NIR) emission in boron cation-based emitters stays difficult owing to their intrinsic instability, robust electrophilicity of the boron centre, and pronounced non-radiative decay ruled by the vitality hole regulation.

Now, MIT chemists have designed a brand new sort of fluorescent molecule based mostly on a borenium ion, a positively charged type of boron that may emit mild within the pink to near-infrared vary. Until just lately, these ions have been too unstable for use for imaging or different biomedical purposes.

In a research showing in the present day in Nature Chemistry, the researchers confirmed that they may stabilize borenium ions by attaching them to a ligand. This method enabled them to create boron-containing movies, powders, and crystals, all of which emit and take up mild within the pink and near-infrared ranges.

That is essential as a result of near-IR mild is less complicated to see when imaging constructions deep inside tissues, which might enable for extra express pictures of tumors and different constructions within the physique.

In the brand new research, researchers started experimenting with the anions (negatively charged ions) which are part of the CDC-borenium compounds. Interactions between these anions and the borenium cation generate a phenomenon referred to as exciton coupling, the researchers found. This coupling, they discovered, shifted the molecules’ emission and absorption properties towards the infrared finish of the colour spectrum. These molecules additionally exhibited a excessive quantum yield, enabling them to emit mild extra effectively.

“Not only are we in the correct region, but the efficiency of the molecules is also very suitable,” Gilliard says. “We’re up to percentages in the thirties for the quantum yields in the red region, which is considered to be high for that region of the electromagnetic spectrum.”

The researchers additionally demonstrated that they may convert their borenium-containing compounds into numerous states, together with stable crystals, movies, powders, and colloidal suspensions.

For biomedical imaging, Gilliard envisions that these borenium-containing supplies could possibly be encapsulated in polymers, permitting them to be injected into the physique to make use of as an imaging dye. As a primary step, his lab plans to work with researchers within the chemistry division at MIT and on the Broad Institute of MIT and Harvard to discover the potential of imaging these supplies inside cells.

Because of their temperature responsiveness, these supplies may be deployed as temperature sensors, for instance, to observe whether or not medicine or vaccines have been uncovered to temperatures which are too excessive or too low throughout delivery.

“For any type of application where temperature tracking is important, these types of ‘molecular thermometers’ can be beneficial,” Gilliard says.

“If incorporated into thin films, these molecules could also be useful as organic light-emitting diodes (OLEDs), particularly in new types of materials such as flexible screens,” Gilliard says.

“The very high quantum yields achieved in the near-IR, combined with the excellent environmental stability, make this class of compounds extremely interesting for biological applications,” says Frieder Jaekle, a professor of chemistry at Rutgers University, who was not concerned within the research.

“Besides the obvious utility in bioimaging, the strong and tunable near-IR emission also makes these new fluorophores very appealing as smart materials for anticounterfeiting, sensors, switches, and advanced optoelectronic devices.”

In addition to exploring potential purposes for these dyes, the researchers at the moment are engaged on extending their colour emission additional into the near-infrared area, which they hope to realize by incorporating further boron atoms. Those further boron atoms might make the molecules much less steady, so the researchers are additionally engaged on new sorts of carbodicarbenes to assist stabilize them.

Journal Reference:

1. Deng, CL., Tra, B.Y.E., Zhang, X. et al. Unlocking red-to-near-infrared luminescence by way of ion-pair meeting in carbodicarbene borenium ions. Nat. Chem. (2025). DOI: 10.1038/s41557-025-01941-6