Dual-mode sensing strategy for assaying phosphate ions using Fe, N-co-doped carbon dots with peroxidase mimetic activity.

Monitoring phosphate (PF) levels is critically significant because of its environmental, biomedical, and agricultural importance. In the current study, a novel dual-mode sensing platform was developed based on iron-doped nitrogen-rich carbon quantum dots (Fe@N-dCQDs), which exhibit both strong photoluminescence and intrinsic peroxidase mimetic activity. This dual property was the basis of PF determination, where its presence induced a concentration-dependent decrease in both colorimetric absorbance and fluorescence intensity, allowing for label-free and sensitive detection. The Fe@N-dCQDs were prepared using one-step pyrolysis and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR). The developed sensor showed excellent linearity in both detection modes (0.33-23.67 mM for the colorimetric method and 5.0-50.0 mM for the fluorometric method) with low detection limits (0.13 mM and 1.72 mM) and high correlation coefficients (0.9947 and 0.9998). Moreover, the sensor exhibited remarkable selectivity against common interfering ions typically found in environmental matrices, including phosphatic fertilizers. This simple, rapid, and cost-effective sensing strategy provides a promising tool for PF determination in environmental and agricultural samples and establishes Fe@N-dCQDs as a versatile nanomaterial for dual-mode analytical applications.