Photostable far-red emitting pluronic silicate nanoparticles: perfect blood pool fluorophores for biphotonic in vivo imaging of the leaky tumour vasculature

Abstract

For correct analysis of anti-angiogenic therapies, we need new fluorescent probes that do not diffuse across the leaky tumour vascular endothelium before any treatment. The latter makes estimations of the functional blood volume and changes in vascular permeability uncertain after treatment. Therefore, we present here a new non diffusible fluorescent probe for two photon microscopy, which is composed of a hydrophobic push–pull dye (1) encapsulated in the apolar core of Pluronic F127–silica nanoparticles (1@F127–SiO₂, d = 22 nm). In apolar media, (1) has intense emission in the red (Φ_f = 39% at 650 nm) and two-photon absorption properties in the NIR. The NP probe was successfully tested in vivo on mice bearing tumours without diffusion across the tumour vascular endothelium. The two photon excitation wavelength at 1000 nm is optimum for deep tissue excitation.