Rose Bengal-derived pH-sensitive carbon quantum dots for the detection of urea and urease activity

In this work, rose Bengal-derived carbon quantum dots (S-CQDs) were prepared by a one-step solvothermal method in ethanol using rose Bengal and 2-aminothiophenol as raw materials. The morphological properties, surface functional group information, elemental composition and optical properties of S-CQDs were carefully characterized by TEM, FTIR spectroscopy, XPS and fluorescence spectroscopy. The as-prepared S-CQDs dispersed well in water with a particle size of 1.74 ± 0.06 nm and exhibited excitation-independent yellow-green fluorescence emission (529 nm) with a high quantum yield (55.4%) and excellent salt tolerance and photostability. Importantly, S-CQDs were sensitive to pH and displayed significant fluorescence enhancement with increased pH values from 4.0 to 6.0. Based on this, a fluorescent strategy for the detection of urea and urease activity was developed with linear ranges of 0-4.0 mM and 0-100 mU mL^-1 and detection limits (LODs) of 0.0566 mM and 2.46 mU mL^-1, respectively. Furthermore, S-CQDs were successfully applied for the detection of urea and urease activity in actual samples with satisfactory recoveries and acceptable relative standard deviations. These results indicate that S-CQDs are promising probes for use in biological analysis.