New Red-Emitting Dyes Could Transform Biomedical Imaging
Researchers at MIT have designed a new class of fluorescent molecules based on stabilized borenium ions that glow in the red to near-infrared range. These dyes aim to overcome long-standing challenges in optical imaging, where blue and green dyes often fall short for deep-tissue visualization. The study, published in Nature Chemistry, demonstrates that attaching borenium cations to carefully chosen ligands can yield stable, bright emitters suitable for potential biomedical use, including clearer tumor imaging.
From Lab Curiosities to Practical Dyes
Borenium cations are positively charged boron-containing species that historically behaved like laboratory curiosities—unpredictable and highly reactive, demanding handling in sealed gloveboxes. Over time, MIT chemists showed that binding these ions to ligands could stabilize them, enabling practical study and application. In 2022, they reported that carbon-donor ligands could reduce reactivity, paving the way for open-air experimentation and safer handling. The latest work builds on this progress by using carbodicarbene ligands (CDCs) to further stabilize the borenium ions, generating materials that resist photodegradation and maintain brightness.
Exciton Coupling Powers Red and Near-Infrared Emission
The team discovered that interactions between the CDC-stabilized borenium cations and their accompanying anions trigger exciton coupling. This physical mechanism shifts both emission and absorption toward the red and near-infrared spectrum, which is crucial for tissue imaging. Importantly, the dyes exhibit high quantum yields—up to the thirties percent in the red region—meaning a strong signal for imaging applications. “Not only are we in the correct region, but the efficiency is very suitable,” notes senior author Robert Gilliard, the Novartis Professor of Chemistry at MIT.
Stability, Brightness, and Practical Forms
Traditional red dyes often struggle with stability and brightness, limiting their usefulness in real-world biomedical settings. The borenium approach addresses both issues: the CDC ligands confer robustness against air and light, while exciton coupling tuned by the ionic environment delivers bright, reliable emission. The resulting dyes work as solid crystals, films, powders, or colloidal suspensions, offering versatile formats for various imaging platforms.
How These Dyes Could Be Used
The MIT team envisions several pathways for clinical and research use. One route involves encapsulating the borenium-containing materials in polymers to create injectable imaging agents that can highlight tumors or other structures deep within tissue. The researchers also see potential in applying these materials as temperature-sensitive reporters, which could help verify that pharmaceuticals or vaccines have endured proper storage conditions during transport and storage.
Beyond Imaging: A Wide Range of Smart Materials
In addition to bioimaging, the dyes could serve as components in organic light-emitting diodes (OLEDs) for flexible displays. The combination of near-infrared brightness and environmental stability broadens their appeal to smart materials, sensors, and anticounterfeiting technologies whose performance depends on tunable light emission.
Next Steps and Collaborations
Further work will explore extending emission further into the near-IR by incorporating additional boron atoms while seeking stabilization with new CDC variants. The team plans to collaborate with MIT’s chemistry department and the Broad Institute to test imaging capabilities inside cells, moving from model systems toward real biomedical contexts.
Why It Matters
Red-to-near-infrared dyes are prized for deep-tissue imaging because this light penetrates tissue more effectively and scatters less than blue or green light. Achieving high brightness and stability in this spectral window could yield clearer tumor images, better monitoring of disease progression, and advanced diagnostic tools, all while opening avenues for flexible, robust optoelectronic materials.
