Bio-sourced Fe-doped carbon dots for dual-mode fluorescence and colorimetric sensing of 4-nitrophenol

The rapid and on-site detection of 4-nitrophenol (4-NP), a refractory and highly toxic environmental pollutant, remains a significant challenge. In this study, iron-doped carbon dots (Fe-CDs) were synthesized via a facile one-pot hydrothermal method using a natural herbal precursor, Citri Reticulatae Pericarpium, as the carbon source. Comprehensive characterization revealed that the Fe-CDs are uniform quasi-spherical nanoparticles with hydrophilic surfaces rich in functional groups such as hydroxyl and carboxyl. This structure endows them with dual functionality: strong intrinsic fluorescence and excellent peroxidase-like activity at neutral pH. Leveraging these properties, we constructed a dual-mode (fluorescence/colorimetric) sensing platform integrated with smartphone-based colorimetric analysis for the rapid, on-site detection of 4-NP. The platform exhibited high sensitivity with a detection limit of 0.17 μM, excellent selectivity against common interferents, and reliable performance in real water samples with satisfactory recovery rates (95.45–107.38 %). Furthermore, the intrinsic Fenton-like activity of the Fe-CDs enabled the oxidative degradation of 4-NP This work presents a sustainable and efficient strategy for environmental monitoring and remediation, highlighting the great potential of herb-derived carbon-based nanozymes in portable sensing applications.