This work presents several significant novelties in the field of histamine detection and biosensing through the development of nitrogen and iron co-doped carbon dots (N, Fe@CDs) with intrinsic peroxidase-like activity. The dual-mode sensing mechanism is particularly innovative, simultaneously exploiting both the colorimetric conversion of 2,3,5-triphenyl-2 H-tetrazolium chloride (TTC) to formazan and the fluorescence enhancement of the carbon dots N, Fe@CDs. This approach cleverly integrates enzymatic specificity through porcine diamine oxidase (DAO) with nanozyme catalysis. The ability to achieve both visual detection and fluorometric analysis for precise measurements. The developed dual-mode sensing platform demonstrates excellent analytical performance with both colorimetric and fluorometric detection modes showing linear detection ranges of 1.0–60.0 µM and 0.1–13.0 µM, achieving limits of detection of 0.28 µM and 0.034 µM respectively, with strong linearity (R² >0.9959). The method was successfully applied to determine histamine levels in different fish products, demonstrating excellent accuracy with percentage recovery values ranging from 97.11 to 102.0%. The successful application to diverse fish products demonstrates the practical versatility of this sensing strategy, overcoming matrix interference challenges. This multifunctional nanomaterial-based approach represents a significant advancement in developing cost-effective, user-friendly analytical tools for food quality control and safety assessment.

Carbendazim, a widely used benzimidazole fungicide, poses significant environmental and health risks, necessitating sensitive analytical methods for its determination in food and environmental samples. A novel dual-emission iron and nitrogen co-doped carbon dots nanozyme with fluorescent bands at 440 nm and 522 nm was developed, functioning simultaneously as both ratiometric probe and peroxidase mimic. The nanozyme catalyzes 3,3’,5,5’-tetramethylbenzidine oxidation in hydrogen peroxide presence, generating blue oxidized 3,3’,5,5’-tetramethylbenzidine that quenches the 522 nm emission while 440 nm serves as internal reference. Carbendazim scavenges reactive oxygen species, suppressing oxidized 3,3’,5,5’-tetramethylbenzidine formation and restoring 522 nm fluorescence, producing a self-calibrating fluorescence ratio immune to environmental variations. Additionally, the reduction of oxidized 3,3’,5,5’-tetramethylbenzidine color upon carbendazim addition enables colorimetric detection. Kinetic studies revealed excellent peroxidase-like activity with Michaelis-Menten parameters. The dual-mode sensing platform achieved linear responses of 3.0–18.0 ng/mL (colorimetric, limit of detection = 1.25 ng/mL) and 1.0–38.0 ng/mL (fluorometric, limit of detection = 0.64 ng/mL) for carbendazim detection. Successful application to fruit and water samples demonstrated excellent accuracy with recovery rates of 96.89–102.00%, representing the first integration of carbon dots-based peroxidase mimicry with ratiometric fluorescence detection for carbendazim analysis.