Nature’s chemical computer: Herbal residue-derived carbon dots build logic gates for H2O2 tracking and ecological antimicrobials

In this work, we report the use of logic platforms and iron-doped carbon dots (Fe-CDs) as a promising peroxidase-like analogue for the qualitative quantification of hydrogen peroxide (H₂O₂). The synthesised Fe-CDs exhibited excellent peroxidase-like (POD-like) activity compared to carbon dots (CDs), which catalyzed the formation of blue oxidation product (ox-TMB) with maximum absorption at 652 nm from the chromogenic substrate 3,3', 5,5' - tetramethylbenzidine (TMB). Steady state kinetic analysis shows that Fe-CDs have strong POD-like activity. Using the POD-like activity of Fe-CDs, H₂O₂ can be specifically detected colorimetrically. Based on this, we constructed a logic platform for H₂O₂ colourimetric sensing using Fe-CDs and H₂O₂ as inputs and the colorimetric signal as output. The H₂O₂ concentration and absorbance values showed good linearity in the range of 60-800 μM (R² = 0.9887) with a limit of detection (LOD) of 7.25 μM, and the current method was successfully applied to the detection in mouthwash samples and laboratory tap water with recoveries in the range of 96.39 %-104.01 %. Fe-CDs catalyse the production of reactive oxygen species from H₂O₂, which can kill both Gram-positive and Gram-negative bacteria, and Fe-CDs have a highly efficient antimicrobial effect compared to CDs. Fe-CDs can be as high as 99.89 % antibacterial against <i>E. coli</i> and 97 % against <i>S. aureus</i>. In conclusion, we used herbal dregs to prepare Fe-CDs antimicrobial agent, and by recycling herbal dregs, the resources were maximised, and the nanozymes can not only construct the logical platform for H₂O₂ colorimetric sensing, but also show good application prospects in antimicrobials.