Fluorescent/phosphorescent dual-emissive conjugated polymer dots for hypoxia bioimaging

A kind of fluorescent/phosphorescent dual-emissive conjugated polyelectrolyte has been prepared by introducing phosphorescent platinum(ii) porphyrin (O(2)-sensitive) into a fluorene-based conjugated polyelectrolyte (O(2)-insensitive), which can form ultrasmall conjugated polymer dots (FP-Pdots) in the phosphate buffer solution (PBS) via self-assembly caused by their amphiphilic structures with hydrophobic backbones and hydrophilic side chains. These FP-Pdots can exhibit an excellent ratiometric luminescence response to O(2) content with high reliability and full reversibility for measuring oxygen levels, and the excellent intracellular ratiometric O(2) sensing properties of the FP-Pdots nanoprobe have also been confirmed by the evident change in the I (red)/I (blue) ratio values in living cells cultured at different O(2) concentrations. To confirm the reliability of the O(2) sensing measurements of the FP-Pdots nanoprobe, O(2) quenching experiments based on lifetime measurements of phosphorescence from Pt(ii) porphyrin moieties have also been carried out. Utilizing the sensitivity of the long phosphorescence lifetime from Pt(ii) porphyrins to oxygen, the FP-Pdots have been successfully applied in time-resolved luminescence imaging of intracellular O(2) levels, including photoluminescence lifetime imaging and time-gated luminescence imaging, which will evidently improve the sensing sensitivity and reliability. Finally, in vivo oxygen sensing experiments were successfully performed by luminescence imaging of tumor hypoxia in nude mice.