Waste-derived chlorogenic-acid Ag nanozyme for nanomolar dopamine sensing in pharmaceutical formulations

Biosynthesized nanozymes are attractive for low-cost dopamine (DA) sensing, yet most reported systems rely either on synthetic nanomaterials or poorly defined "green" extracts, which limits sustainability, reproducibility, and translational relevance. Here, we establish a waste-to-nanozyme platform that converts Musa balbisiana wine-processing residues into chlorogenic-acid-capped silver nanoparticles (BK-AgNPs) using an HPLC-isolated CGA (chlorogenic acid) fraction as a chemically defined bioreductant and stabilizer. The resulting BK-AgNPs display a plasmon band at 443 nm, a TEM core size of ∼28 nm and a face-centred cubic Ag lattice with high elemental purity. Engineered as peroxidase-mimetic nanozymes, they efficiently catalyse H₂O₂-driven oxidation of TMB under mildly acidic conditions (pH 4.0, 35 °C), with steady-state kinetics indicating strong affinity for both TMB and H₂O₂. Exploiting DA-induced inhibition of this peroxidase-like activity, we developed a simple colorimetric assay that affords a linear response from 20-200 nM and a detection limit of 42.51 nM, outperforming several recent nanozyme-based DA platforms that operate in the 0.072-2.31 µM range. Zeta potential and DLS measurements reveal that DA adsorption neutralizes the CGA-capped surface (-8.0 → -1.4 mV) and reorganizes aggregates (≈5.4 → 3.3 µm), directly linking signal suppression to surface charge modulation and colloidal restructuring. Validation using a commercial dopamine hydrochloride injection demonstrates nanomolar-level sensing in a realistic pharmaceutical matrix, while explicitly quantifying matrix-induced attenuation. Overall, this work introduces a chemically defined, wine-waste-derived nanozyme platform that couples green synthesis with mechanistically understood, pharmaceutically relevant DA detection.