Enhancing the Stokes' shift of BODIPY dyes via through-bond energy transfer and its application for Fe3+-detection in live cell imaging

The world of organic luminophores has been confined for a long time to fairly standard biological labeling applications and to certain analytical tests. Recently, however, the field has undergone a major change of direction, driven by the dual needs to develop novel organic electronic materials and to fuel the rapidly emerging nanotechnologies. Among the many diverse fluorescent molecules, the Bodipy family, first developed as luminescent tags and laser dyes, has become a cornerstone for these new applications. The near future looks extremely bright for "porphyrin's little sister".

Fluorescence targeted imaging in vivo has proven useful in tumor recognition and drug delivery. In the process of in vivo imaging, however, a high autofluorescence background could mask the signals from the fluorescent probes. Herein, a high contrast upconversion luminescence (UCL) imaging protocol was developed for targeted imaging of tumors based on RGD-labeled upconversion nanophosphors (UCNPs) as luminescent labels. Confocal Z-scan imaging of tissue slices revealed that UCL imaging showed no autofluorescence signal even at high penetration depth (approximately 600 microm). More importantly, region of interest (ROI) analysis of the UCL signal in vivo showed that UCL imaging achieved a high signal-to-noise ratio (approximately 24) between the tumor and the background. These results demonstrate that the UCL imaging technique appears particularly suited for applications in tracking and labeling components of complex biological systems.