Zwitterionic carbon dot-encapsulating pH-responsive mesoporous silica nanoparticles for NIR light-triggered photothermal therapy through pH-controllable release.

Here, we designed a pH-responsive Indocyanine Green (ICG)-loaded zwitterion fluorescent carbon dot (CD)-encapsulating mesoporous silica nanoparticle (MSN) for pH-tunable image-guided photothermal therapy. ICG was loaded into MSN(CD) via hydrophobic and electrostatic interactions between zwitterionic CDs and ICG to achieve a controlled photothermal temperature with a fluorescent "off/on" system. The porosity of the MSNs was altered after ICG loading because of intermolecular interactions between the CDs and ICG inside the MSN shell and core, which blocked the MSN pore. The acidic environment pH affected the fluorescent signals of the ICG-MSN(CD), reflecting the "off-on" characteristics of the synthesized MSN, which then induced the release of ICG from the matrices. Moreover, the photothermal conversion of ICG-MSN(CD) showed sufficient heat generation to kill cancer cells at an acidic pH with low-temperature elevation at physiological pH. ICG-MSN(CD) demonstrated good cell viability of MDA-MB-231 cells without irradiation; however, high necrosis was observed when the environment was adjusted to acidic pH and after near-infrared irradiation. These pH-responsive photothermal mesoporous silica nanoparticles may have applications in biomedicine, particularly for cancer treatment.