Brightness Enhancement of Near-Infrared Semiconducting Polymer Dots for in Vivo Whole-Body Cell Tracking in Deep Organs.

Abstract

In vivo visualization of cell migration and engraftment in small animals provide crucial information in biomedical studies. Semiconducting polymer dots (Pdots) are emerging as superior probes for biological imaging. However, in vivo whole-body fluorescence imaging is largely constrained by the limited brightness of Pdots in near-infrared (NIR) region. Here, we describe the brightness enhancement of NIR fluorescent Pdots for in vivo whole-body cell tracking in deep organs. We first synthesize semiconducting polymers with strong absorption in orange and far-red regions. By molecular doping, the weak broad-band fluorescence of the Pdots was significantly narrowed and enhanced by 1 order of magnitude enhancement, yielding bright narrow-band NIR emission with a quantum yield of ∼0.21. Under an excitation of far-red light (676 nm), a trace amount of Pdots (∼2 μg) in the stomach can be clearly detected in whole-body fluorescence imaging of live mice. The Pdots coated with a cell-penetrating peptide are able to brightly label cancer cells with minimal cytotoxicity. In vivo cell tracking in live mice indicated that the entrapment and migration of the tail-vein-administered cells (∼400 000) were clearly visualized in real time. These Pdots with deep-red excitation and bright NIR emission are promising for in vivo whole-body fluorescence imaging.