Monitoring the Biodegradation of Dendritic Near-Infrared Nanoprobes by <i>in Vivo</i> Fluorescence Imaging

Synthetic polymers and dendrimers have been widely used by the medical community to overcome biological barriers and enhance in vivo biomedical applications. Despite the widespread use of biomaterials it has been generally extremely difficult to monitor noninvasively their fate in vivo. Here we report multilayered nanoprobes, consisting of a near-infrared core, nanoencapsulated in a biodegradable dendrimer, and surrounded by a shell of polyethylene oxide. Covalent encapsulation of the near-infrared fluorophores in the dendritic scaffold conferred enhanced stability to the nanoprobe with added resistance to enzymatic oxidation and prolonged blood residence time. Insight into the time course of biodegradation of the dendritic aliphatic polyester nanoprobe was gained using noninvasive whole body in vivo fluorescence lifetime imaging. As the dendritic shell biodegrades the NIR probe becomes exposed, enabling monitoring of fluorescence lifetime changes in vivo.