Near-infrared and highly photostable squaraine-based nanoparticles for photoacoustic imaging guided photothermal therapy

Effective photothermal agents (PTAs) are of particular importance for anticancer phototherapy. Nevertheless, conventional PTAs are frequently plagued by inadequate photostability, short-wavelength absorption, and low photothermal conversion efficiency (PCE). Herein, we designed and synthesized a near-infrared squaraine dye (SQ) with the maximum absorption wavelength at ∼710 nm. The squaraine dye demonstrates much enhanced photostability compared with indocyanine green (ICG), a commercial PTA. To improve the tumor targeting capacity, SQ was encapsulated into polymeric nanoparticles (SQ-NPs), which show a high photothermal conversion of 52.8% with strong photoacoustic signals upon 760 nm NIR laser irradiation. Through intravenous injection into tumor-bearing mice, SQ-NPs accumulate at the tumor site and efficiently inhibit the growth of tumor under photoacoustic image-guided photothermal therapy.