cis-Silicon phthalocyanine conformation endows J-aggregated nanosphere with unique near-infrared absorbance and fluorescence enhancement: a tumor sensitive phototheranostic agent with deep tissue penetrating ability

Abstract

Organic phototheranostic nanomedicines with an optimized near-infrared (NIR) biological transparent window (700–900 nm) are highly desirable for the diagnosis and treatment of deep-seated tumors in clinic. As excellent organic photosensitizers for photodynamic therapy (PDT) with outstanding photo- and thermo-stability, phthalocyanines (Pcs) have been used as the building blocks of single-component nanomedicines. However, to the best of our knowledge, all the Pc-based single-component self-assemblies reported to date are of an H-aggregate nature. This results in the simultaneous self-quenching of fluorescence emission and photodynamic activity as well as greatly reduced tissue penetration due to blue-shifted absorption. In the present work, intramolecular hydrogen bonding was formed between the two long and flexible axial NH₂-terminated diethylene glycol ligands of the amphiphilic SiPc molecule (SiPc-NH₂) in solution, leading to the employment of a cis-conformation of this molecule according to the ¹H-NMR spectroscopy result, which as a building block then further self-assembled into monodisperse nanospheres (SiPcNano) with a J-aggregation nature on the basis of electronic absorption spectroscopic results. As a result, SiPcNano exhibited significantly enhanced red-shifted absorption in the NIR range of 750–850 nm and fluorescence emission. This in combination with the increased photodynamic effect for SiPcNano triggered by the protonation of amine groups due to the acidic nature of tumors endowed effective synergistic NIR photodynamic and photothermal effects in different cancer cells and thus effective inhibition of tumor growth in A549 tumor-bearing mice on the basis of a series of in vitro and in vivo evaluations. The present result provides a new approach for constructing novel single-component NIR organic nanomedicines for multifunctional cancer therapy.