A colorimetric sensor for the sensitive and rapid detection of ampicillin based on CS-Cu,Fe/HS nanozyme

A novel copper and iron doped containing chitosan and heparin sodium carbon dots (CS-Cu,Fe/HS) nanozyme was formulated through a single-step microwave digestion method. CS-Cu,Fe/HS exhibits excellent peroxidase (POD)-like activity and positive charge characteristics, and it can oxidize the negatively charged 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) in the presence of H₂O₂ to produce a green compound (ox-ABTS). Furthermore, CS-Cu,Fe/HS enhances electron transfer and provides additional active sites through the valence state transformations of Fe²⁺/Fe³⁺ and Cu²⁺/Cu⁺. Interestingly, the POD-like activity of CS-Cu,Fe/HS is inhibited with the introduction of ampicillin (AMP), which may be because the Cu and Fe ions in CS-Cu,Fe/HS form complexes with AMP, leading to changes in the structure or surface properties of the nanozyme, thereby reducing the number of active sites on the nanozyme. Drawing from this, a straightforward and reliable colorimetric sensor was constructed for AMP detection, featuring a linear range of 0.033 to 110 μg/mL and a detection limit as low as 11.6 ng/mL. The proposed detection method for AMP performed well in real samples, with recoveries ranging from 94.8% to 110.2%.