New metal-free molecules glow deep red in water and boost MRI contrast in test images

Bioimaging technologies, such as fluorescence imaging (FI) and magnetic resonance imaging (MRI), excel in their respective domains, yet they carry limitations. FI excels in visualizing biological processes at high resolution but lacks depth, while MRI can pierce deep into the body but falls short in single-cell resolution. Moreover, MRI contrast agents often contain metals like gadolinium, which may lead to adverse side effects.

In this study, a research team from Kyushu University introduces a novel solution - a water-soluble, metal-free molecule with dual functionality for both FI and MRI. The team, led by associate professor Ken Albrecht, aimed to overcome the challenges associated with merging the distinct mechanisms of these two imaging techniques. They focused on luminescent organic radicals, a promising class of molecules capable of producing fluorescence and functioning as MRI contrast agents.

However, these radicals were hydrophobic, limiting their use in biological systems. The team optimized a molecule called tris(2,4,6-trichlorophenyl) methyl (TTM), which displayed good MRI activity but weak fluorescence. After multiple iterations, two water-soluble molecules, TTM-trisTP3B and TTM-trisTP9B, were developed. Both exhibited deep-red fluorescence in water and significantly enhanced the contrast of MRI phantom images by 2.5 to 4.5 times compared to previously reported water-soluble TTM radicals.

The deep-red fluorescence made these molecules suitable for imaging in living cells, with TTM-trisTP3B retaining its fluorescence for at least 24 hours. While further animal studies are required to validate the long-term viability of these molecules, this research represents a significant step towards developing safer, multifunctional, and less toxic imaging agents with potential applications in basic research and medical diagnostics.