Ratiometric Sensing of Intracellular pH Based on Dual Emissive Carbon Dots

Accurate monitoring of intracellular pH in living cells is critical for developing a better understanding of cellular activities. In the current study, label-free carbon dots ( p- CDs), which were fabricated using a straightforward one-pot solvothermal treatment of p -phenylenediamine and urea, were employed to create a new ratiometric pH nanosensor. Under single-wavelength excitation (λ ex  = 500 nm), the p -CDs gave dual emission bands at 525 and 623 nm. The fluorescent intensity ratio ( I 525 / I 623 ) was linearly related to pH over the range 4.0 to 8.8 in buffer solutions, indicating that the ratiometric fluorescence nanoprobe may be useful for pH sensing. In pH measurements, the p -CDs also demonstrated outstanding selectivity, reversibility, and photostability. Owing to the advantages outlined above, the nanoprobe was used to monitor the pH of HeLa cells effectively. The label-free CD-based ratiometric nanoprobe features comparatively easy manufacturing and longer excitation and emission wavelengths than the majority of previously reported CD-based ratiometric pH sensors, which is ultimately beneficial for applications in biological imaging. Graphical Abstract