Intracellular pH-propelled assembly of smart carbon nanodots and selective photothermal therapy for cancer cells

ABSTRACT A kind of smart carbon nanodots (CNDs) with pH response feature was prepared by one-pot hydrothermal treatment of citric acid and dicyandiamide, which was used for differentiation of cancer/normal cells and selective photothermal therapy (PTT) of cancer cells. When they were cultured with cells, they were highly internalized in the lysosomes of cells. Since the small-sized CNDs (about 5 nm) tends to form aggregation (as large as about 20 nm or even over) under the an acid condition (pH = 4.7) due to the electrostatic attraction produced by surface protonation, relatively severer aggregation of the CNDs were observed in liver cancer cells (HepG2 cells) relative to normal ones (LO2 cells) due to a relative lower pH in the lysosomes of HepG2 cells, which endows them a new strong absorption band at longer wavelengths (450-900 nm) and a higher photothermal conversion efficiency (42.13 %), benefiting to differentiated PTT. The flow cytometric data indicates strong photothermal ablation (8 min, 509.6 mW/cm2) for cancer cells with assistance of these smart CNDs achieves 82 % death rate of cancer cells, while much less damageis observed on the normal cells (6.35 %). To the best of our knowledge, this is the first report about CNDs for selective PTT owing to their intrinsic property without assistance of any other targeting ligands. This smart CNDs is also available for other acid-responsive sensing systems and this study inspires us in the synthesis of near-infrared featured carbon materials.