Fluorescent pH nanosensor based on carbon nanodots for monitoring minor intracellular pH changes

In this work, fluorescent unmodified carbon nanodots (CDs) were used as a biocompatible, sensitive, selective and reversible intracellular pH nanosensor. This sensor showed a linear response towards pH changes in the physiological pH range of 6.1-7.8 and could resolve pH differences of 0.1 units. The pH of a commercial solution of Roswell Park Memorial Institute medium (RPMI 1640) was determined by using fluorescent pH sensitive CDs. This indicates that the proposed pH nanosensor can monitor pH changes in complex media. An MTT (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide) assay on HeLa and HS-5 cell lines confirmed cell viability and biocompatibility of these unmodified carbon nanomaterials. A distinct fluorescence intensity change in confocal imaging supported the high pH sensitivity of CDs in living cells.