Fig. 1.

Overview of approach. 1a) Illustration of the various mechanisms of liposome fluorophore de-quenching. Stable- unchanging low fluorescence of concentrated fluorophore in liposomal core (ex. formulation I). Leaky- gradual increase in fluorescence caused by fluorophore leaking through an intact lipid bilayer, often facilitated by serum proteins (ex. formulation V). Heat Release- an increase in fluorescence due to applied heat at a rate dependent on liposome temperature sensitivity, ranging from complete de-quenching in seconds (formulations III and IV) to minutes (formulations VI and IX). Destruction- immediate increase in fluorescence due to the breakdown of the lipid bilayer, often mediated by lysosomes. 1b) In vitro stability assay of formulations I–IX incubated in mouse serum for 90 minutes at 37°C, fluorophore release profiles shown. 1c) In vitro temperature response assay of formulations I–IX incubated in mouse serum for 90 minutes at 42°C, release profiles shown. 1d) Sample PET and optical images of Formulations I and III immediately post intravenous injection and 60 minutes after injection.