New red and near-infrared fluorophores promise sharper deep-tissue imaging
Fluorescent imaging is a staple in biomedical research, helping scientists visualize cellular processes and diagnose diseases. Yet traditional blue and green dyes struggle to penetrate tissue, where scattering and autofluorescence obscure signals. Red and near-infrared (NIR) fluorophores offer a clearer window into deep tissues, tumors, and vascular structures. The challenge has been creating red-emitting dyes that are both bright and stable enough for practical use in living systems. A recent breakthrough from MIT chemists introduces a novel class of red to near-infrared emitters based on a boron-containing, positively charged borenium ion.
Stabilizing borenium ions for practical imaging
Historically, boron-centered emitters faced two major hurdles: instability and non-radiative decay that sapped brightness. The MIT team found a way to stabilize borenium ions by covalently attaching them to a carefully chosen ligand. This stabilization enabled the formation of boron-containing films, powders, and crystals that absorb and emit light in the red to near-infrared range. The approach addresses the intrinsic instability of boron cation chemistry and helps suppress energy losses that would otherwise quench fluorescence.
Exciton coupling shifts emission toward the infrared
A key discovery was the role of exciton coupling. By experimenting with the accompanying anions in CDC-borenium compounds, researchers observed interactions with the borenium cation that shifted both absorption and emission toward longer wavelengths. The result is brighter red-to-NIR emission with a higher quantum yield than usual for boron-based dyes. In fact, the team reports quantum yields climbing into the thirties percent range in the red region, a notable achievement for these materials.
From solid-state materials to potential biomedical probes
Beyond the fundamental science, the researchers demonstrated versatility by converting the materials into various states: crystalline solids, thin films, powders, and colloidal suspensions. Such flexibility is crucial for translating dyes into usable imaging probes. For biomedical applications, the team envisions encapsulating the borenium-containing materials in biocompatible polymers to enable injection into living subjects for deep-tissue visualization. Early collaborations with MIT’s chemistry department and the Broad Institute aim to test imaging capabilities in cells, a foundational step toward in vivo studies.
Broader implications: imaging, sensors, and electronics
The advances extend beyond standard imaging. The temperature responsiveness of these materials suggests potential as molecular thermometers—capable of reporting temperature histories during drug or vaccine transport. In addition, the ability to achieve high, stable red/NIR emission could spur developments in organic light-emitting diodes (OLEDs) and flexible displays, expanding the utility of boron-based fluorophores in optoelectronics. Experts not involved in the study note the strong, tunable near-IR emission and environmental stability as especially promising for a range of biological and technological applications.
Future directions
Looking ahead, researchers plan to push the color emission further into the near-IR by incorporating additional boron atoms. This strategy presents a balance: adding more boron could enhance red-shifted emission but may compromise stability. To counter this, scientists are exploring new carbodicarbene scaffolds to reinforce stability while preserving high quantum yields. The ongoing work aims to deliver even brighter, more stable dyes suitable for complex imaging tasks and potentially smart materials for sensing and anti-counterfeiting technologies.
As the field advances, red-emitting boron dyes could become practical tools for deep-tissue imaging, enabling more explicit views of tumors, neural networks, and organ systems. The combination of higher brightness, better tissue penetration, and broader material versatility marks a meaningful step toward more accurate, noninvasive biomedical imaging.
