Plant-dependent and pH-responsive Fe₃O₄ nanozymes derived from Teucrium species for colorimetric ascorbic acid...

Nanozymes derived from plant extracts using environmentally friendly methods are garnering increasing attention as stable alternatives to natural enzymes for use in analytical sensing. Here, phytogenic Fe₃O₄ nanoparticles were synthesized via a one-step method using different green precursors (Teucrium chamaedrys and Teucrium polium) to investigate the influence of the phytochemical composition on catalytic activity. All green-synthesized nanoparticles were tested for their catalytic activity as peroxidase-mimetic nanozymes in the oxidation of 3,3'-5,5'-tetramethylbenzidine in the presence of H₂O₂. The results indicated a significant pH-dependent catalytic behaviour, and the nanozymes prepared from the Teucrium chamaedrys extract displayed considerably higher catalytic performance in acidic media than in basic media, outperforming those prepared from Teucrium polium. Kinetic data under steady-state conditions showed high affinity towards the substrate, as indicated by the apparent K _m values of 0.066 mM and 0.12 mM for TMB and H₂O₂, respectively. On the basis of the catalytic system, a colorimetric sensor for ascorbic acid detection was developed, showing a good correlation in the linear range of 5-230 µM with a detection limit of 0.2 µM. This method was successfully applied to ascorbic acid determination in fruit samples, showing good recovery and practical applicability in food analysis.