Low toxic fluorescent nanoprobe applicable for sensing pH changes in biological environment

A novel graphene oxide (GO)-based pH sensor was designed and prepared through covalently attaching a zwitterionic betaine molecule onto a GO surface. This betaine-modified GO (BMGO) exhibited high water solubility and low toxicity. In aqueous media, BMGO displayed increased fluorescence in acidic conditions and decreased fluorescence in basic conditions. BMGO possesses a pH sensing range from 4 to 12 with excellent reversibility, quick response and high stability. With its high sensitivity and robustness, BMGO can be used to monitor the pH of intracellular contents, as demonstrated through cell imaging.