Dye doped fluorescent polypyrrole nanotherapeutic probes as a versatile platform for ratiometric pH sensing-guided and self-monitored photothermal therapy of tumors

A multifunctional fluorescence polypyrrole nanotherapeutic probe (denoted as PPy@RhB-PAA-FITC) was constructed for pH sensing-guided photothermal therapy (PTT) of cancer and self-monitoring temperature variations during PTT. By using photothermal therapy materials polypyrrole (PPy) nanoparticles as a matrix, the temperature-responsive rhodamine B (RhB) and pH-sensitive fluorescein isothiocyanate (FITC) fluorescent dye were linked to the nanoparticles through encapsulation and electrostatic interaction, respectively. The fluorescent intensity of FITC increased dramatically with enhanced pH and little variation appeared in emission intensity of RhB, which was responsible for ratio fluorescent pH sensing performance. For pH detection, the nanoprobes exhibited a linearity in pH range from 4.54 to 6.4 with an acid dissociation constant (pKa) value of 5.80. PPy nanoparticles were in charge of PTT that endowed this nanotherapeutic system with 36.24% photothermal conversion efficiency. Meanwhile, the fluorescent intensity of RhB was decreased due to the increase of heat-induced temperature, which enabled to satisfy the need of self-monitoring temperature during PTT. The thermal sensitivity of 1.4%/°C were harvested in temperature-sensing assays. Moreover, by the combination of the ratio fluorescent pH imaging, the photothermal conversion and self-detection temperature, the PPy@RhB-PAA-FITC was successfully applied for pH-mediated tumor diagnosis and self-monitored treatment. The proposed PPy@RhB-PAA-FITC broadens the PPy-based nanomaterials applications in ratiometric fluorescent pH imaging and self-feedback temperature changes guided photothermal therapy.