A new insight of a pH-dependent fluorescence switching mechanism and the novel radical scavenging ability of nitrogen-doped citric acid-based carbon dots

Abstract

In this report, nitrogen-doped citric acid-based carbon dots (N-CAdots) were synthesized, and their apparent pK_a values as well as a fluorescence switching pK_a were systematically determined, providing new insight into the pH-dependent fluorescence switching mechanism of these materials. In addition, the N-CAdots presented as an efficient radical scavenger in mildly alkaline medium, exhibiting high reactivity toward the peroxymonocarbonate radical (CO₃˙⁻) compared with N,N-dimethylaniline. This property enables their application as a fluorescence sensor for hydrogen peroxide (H₂O₂). Based on a simple reaction system involving N-CAdots, H₂O₂, HCO₃⁻, and Co²⁺, the sensor demonstrates high sensitivity toward H₂O₂ at low, biologically relevant concentration levels in serum matrices. Furthermore, a novel modified glucose oxidase method was successfully developed by coupling enzymatic H₂O₂ generation with N-CAdots as the fluorescence probe, enabling glucose determination in serum. This versatile sensing platform offers a promising alternative strategy for the detection of H₂O₂ and H₂O₂-generating analytes by exploiting the radical scavenging properties of N-CAdots. These sensors highlight sustainable analytical approaches that support global efforts to reduce the carbon footprint of chemical measurements.