PH-Sensitive and folate receptor-targeting gold nanorods for fluorescence/photoacoustic imaging and photothermal therapy of tumor

Abstract

A new silica-organic hybrid material with fixed ionic liquid 1-n-propyl-3-methylimidazolium chloride has been synthesized by the sol-gel method. Its specific surface area is 22 m2 g−1, average pore diameter is 8 nm and pore volume is 0.05 cm3 g−1. According to the results of 13C NMR spectroscopy, the fixed 1-n-propyl-3-methylimidazolium cationic group is bound with the siloxane framework via one SiC covalent bond. Properties of the new material were compared with that of its analog, silica with the same modifier covalently grafted at the surface. With the use of the 29Si NMR spectroscopy it was clearly indicated that at the surfaces of both materials silanol groups dominate among all silicon containing groups. The surface polarity was characterized by probing the materials with the solvatochromic Reichardt’s dyes, and the heterogeneous polarity of the near-surface layers has been detected. The values of the normalized Dimroth-Reichardt parameter for three surface regions of different polarities are 0.9–1.0, 0.65 and 0.4. The presence of rather acidic surface silanol groups revealed from probing these materials with solvatochromic dyes was verified with the application of acid-base fluorescent dyes of 2,5-diaryl-1,3-oxazole series having pKa 4.5–4.8 in ethanol/water medium. The fluorescence spectroscopy experiments have proved unambiguously that surface silanol groups predetermine the possibility of coexistence of the conjugated Brønsted basic and acidic forms of the oxazolic dyes in the near-surface layers.