Photo-thermoresponsive polypyrrole-crosslinked single-chain nanoparticles for photothermal therapy.

Irradiating a chromophore allows cancer diagnostics by photoacoustic (PA) imaging, but also causes transformation of light into thermal energy and so enables therapy by photothermal effects. Useful chromophores for photothermal therapy (PTT), such as nanoconfined oligomers and polymers, should not only display an excellent light-to-heat efficiency, but in addition must display biocompatibility and good water-solubility. We in this study have designed water-dispersible, nanocaged polypyrroles (PPy), embedded into single-chain nanoparticles (SCNP, sized 6.8 - 8.9 nm) displaying thermoresponsivity, so reaching largely increased PTT-effects. Such encaged PPy-SCNPs allow an efficient photothermal heat conversion reaching temperatures up to 85°C. In a parallelized 96-well-plate-design the PPy-SCNPs can effect an almost complete death of illuminated (cancer) cells at already low concentrations (0.001 mg/mL) with low radiant fluxes. The thermoresponsivity of the SCNPs, surrounding the PPy-chains, then responds to the photothermal heat, so creating a unique self-amplifying effect for photothermal therapy and photoacoustic imaging.