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 B2 (VB2) and pH. A unique ratiometric fluorescence resonance energy transfer probe was developed through a strong interaction between VB2 and surface moieties of CNDs. CNDs emitted at 470 nm; however, in the presence of VB2, an enhanced emission peak was clearly observed at 532 nm. The value of I532/I470 exhibits a stable response to the VB2 concentration from 0.35 to 35.9 μM with a detection limit of 37.2 nM, which has been used for VB2 detection in food and medicine samples and ratiometric imaging of VB2 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.