Carbon Nanodots as a Multifunctional Fluorescent Sensing Platform for Ratiometric Determination of Vitamin B2 and “Turn-Off” Detection of pH

In this work, we synthesized carbon nanodots (CNDs) by a one-pot hydrothermal method to carbonize precursors of dry carnation petals and polyethylenimine. The obtained CNDs possess favorable photostability, good biocompatibility, and excellent water solubility, which can serve as a dual-responsive nanosensor for the determination of vitamin B 2 (VB 2 ) and pH. A unique ratiometric fluorescence resonance energy transfer probe was developed through a strong interaction between VB 2 and surface moieties of CNDs. CNDs emitted at 470 nm; however, in the presence of VB 2, an enhanced emission peak was clearly observed at 532 nm. The value of I 532 / I 470 exhibits a stable response to the VB 2 concentration from 0.35 to 35.9 μM with a detection limit of 37.2 nM, which has been used for VB 2 detection in food and medicine samples and ratiometric imaging of VB 2 in living cells with satisfying performance. In addition, the proposed CNDs also displayed pH-sensitive behavior and can be a turn-off fluorescent sensor to monitor pH. The fluorescent intensity at 470 nm is a good linear response against pH values from 3.6 to 8, affording the capability as a single-emissive nanoprobe for intracellular pH sensing.