Tailoring diacid carbon chains of precursors to boost the peroxidase activity of carbon dot nanozymes for dual-mode glyphosate detection

Background: carbon dot nanozymes (CDszymes) hold significant promise for sensing applications due to their excellent water solubility and intrinsic fluorescence. However, conventional approaches for synthesizing CDszymes with high peroxidase-like (POD) activity remain largely empirical, relying on trial-and-error precursor screening, which limits rational design and optimization. Results: carbon dot nanoenzymes (CDszymes) demonstrate potential applications in nanoenzymatic sensing due to their excellent solubility and intrinsic fluorescence. However, conventional methods for synthesizing CDszymes with high peroxidase (POD) activity rely on empirical precursor screening. In this study, CDszymes with optimal POD activity were rationally designed by regulating the carbon chain length of dicarboxylic acids. Among the six synthesized CDszymes, ethanedioic acid-derived CDszymes-2 exhibited the highest POD activity, which catalyzes the oxidation of TMB by H2O2 to produce blue oxidized TMB (oxTMB), alongside fluorescence quenching via an inner filter effect. Utilizing glyphosate's (GLY) inhibition of acetylcholinesterase (AChE), a dual-mode colorimetric/fluorescent sensing platform was established, attaining detection limits of 13 ng mL−1 (colorimetric) and 7 ng mL−1 (fluorescent). Dual-mode sensing was successfully applied to detect GLY in fruit and vegetable samples, demonstrating potential for ultrasensitive trace-level pesticide detection in agricultural products.