Colorimetric and fluorometric dual-mode sensing of cefadroxil based on peroxidase-like activity of iron and nitrogen co-doped carbon dots

Herein, new iron and nitrogen co-doped carbon dots (NCDs-Fe) were prepared, exhibiting strong peroxidase-mimetic activity and a photoluminescence quantum yield of 28.76 %. In the presence of NCDs-Fe, an oxidative coupling reaction between 4-aminoantipyrine (4-ANP) and cefadroxil (CFD), a phenolic cephalosporin, was facilitated by H₂O₂, resulting in red-colored product with absorbance at 510 nm. The absorbance of this red-colored product increased proportionally with rising CFD concentrations, serving as the basis for the colorimetric measurement. Additionally, the resultant red color ceased the fluorescence of NCDs-Fe at 460 nm, forming the basis of the fluorometric measurement. The variables affecting the synthesis and detection of CFD were carefully optimized. Under optimized conditions, the absorbance values increased with CFD concentrations in the range of 0.05–400 µM, with LOD value of 0.02 µM. For the fluorometric method, the response ratio increased with rising CFD’s concentrations from 0.01 to 400 µM with LOD of 0.004 µM. The NCDs-Fe was applied to detect CFD in real samples, achieving recovery rates of 96.5 % to 104.0 % with RSD values below 4.12 %.