Smartphone-integrated bifunctional sensing platform for visual detection of ampicillin and tetracycline in animal...

Antibiotic residues in environmental matrices pose escalating threats to ecosystems and human health, creating demand for rapid detection. Here, we present a portable smartphone-integrated bifunctional sensor based on Fe-CDs that enables sequential colorimetric and fluorescent detection of ampicillin (Amp) and tetracycline (TC). The Fe-CDs, synthesized via a one-pot hydrothermal process, exhibit stable fluorescence and intrinsic peroxidase-mimicking activity. Ampicillin inhibits the Fe-CDs nanozyme-catalyzed TMB/H₂O₂ chromogenic reaction via •OH consumption, allowing visual colorimetric quantification. Meanwhile, tetracycline strongly quenches the fluorescent signal of Fe-CDs through an inner filter effect, enabling a sensitive fluorescence readout. This bifunctional assay achieves high sensitivity (LOD as low as ∼0.012 μg/mL for Amp and 0.005 μg/mL for TC). By incorporating Fe-CDs onto paper test strips and analyzing with smartphone cameras, the platform allows real-time, rapid quantification of antibiotics in complex matrices. In manure samples, the sensor's results (recoveries ∼94.4-104.8%) agree well with LC-MS/MS measurements, underscoring its accuracy and robustness. Overall, the portable bifunctional Fe-CDs sensor provides a sensitive, field-deployable tool for environmental antibiotic surveillance.