Bioinspired single-atom copper nanozyme enables dual-mode colorimetric detection of ciprofloxacin and D-penicillamine

The occurrence of pharmaceutical residues, including antibiotic ciprofloxacin (CIP) and the chelating drug D-penicillamine (D-PA), in food and environmental samples has raised increasing concerns regarding food safety and public health. Herein, a bioinspired single-atom copper nanozyme was synthesized via a template-guided strategy by encapsulating sodium copper chlorophyllin (SCC) within zeolitic imidazolate framework-8 (ZIF-8). SCC served as a biomimetic precursor, mimicking the active sites of natural oxidase enzymes. Upon pyrolysis, it guided the in-situ formation of atomically dispersed Cu–N x sites. The resulting nanozyme efficiently catalyzed 3,3′,5,5′-tetramethylbenzidine oxidation and enabled dual colorimetric detection of CIP and D-PA. CIP produced a signal-enhancement response by coordinating with the Cu centers, which facilitated interfacial electron transfer and accelerated the oxidase-like catalytic reaction. In contrast, D-PA induced a signal-suppression response by competitively occupying the Cu active sites through its thiol and amino groups and by reducing oxidized TMB (oxTMB) to its colorless form. Linear detection ranges were 1–7 μg/mL for both analytes, limits of detection of 0.097 μg/mL for CIP and 0.108 μg/mL for D-PA. Recoveries ranged from 94.38% to 103.71% in milk and from 97.73% to 105.18% in river water samples, demonstrating reliable performance in real samples. This work provides a straightforward approach for multi-target colorimetric sensing using Cu single-atom nanozymes, with promising applications in food safety and environmental analysis.