Biocompatible Fluorescent Carbon Dots for Ratiometric Intracellular pH Sensing

We report here carbon dots (CDs) that can be utilized for intracellular pH sensing via fluorescence emission monitoring. The carbon dots are synthesized using a simple procedure from an economical carbon source Agaricus bisporus. Along with the excitation dependent fluorescence emission, typical to carbon dots, these CDs were found to have distinct emission maxima peaks at 450 nm and 550 nm when excited by 365 nm and 500 nm respectively. Interestingly, while the fluorescence emission at 450 nm was unaffected by pH changes in solution, the fluorescence emission intensity at 550 nm increased with decrease in pH, making these CDs a potential probe for pH sensing ratiometrically. Further, the CDs were found to be biocompatible and easily internalized in HeLa cells. We also demonstrated the utility of these CDs in sensing the changes in intracellular pH.