Fabrication of FeNi@PDA Nanozyme-Driven Dual-Mode Platform for Visual and On-Site Monitoring of Ampicillin

The widespread accumulation of ampicillin (AMP) poses significant ecological and health risks, demanding rapid and portable monitoring tools. Herein, a Fe-Ni bimetallic-doped polydopamine (FeNi@PDA) nanozyme with exceptional peroxidase-like activity was synthesized for the visual and on-site monitoring of AMP. Optimized through bimetallic electronic coupling, FeNi@PDA exhibited enhanced catalytic efficiency (KM = 0.051 mmol/L for H2O2 and 0.049 mmol/L for 3,3′,5,5′-tetramethylbenzidine) and generated 1O2 and ·O2− via H2O2 activation. Leveraging the competitive consumption of reactive oxygen species (ROS) by electron-rich AMP, a colorimetry detection mode was developed where AMP concentration inversely correlated with oxidized 3,3′,5,5′-tetramethylbenzidine (oxTMB) formation. This strategy achieved a good linear relationship of between 0.05 to 100 μg/mL, with a limit of detection (LOD) of 10.38 ng/mL. Furthermore, a smartphone-integrated paper-based detection mode was fabricated by immobilizing FeNi@PDA on filter paper. The color gradient of test papers, analyzed via smartphone imaging, enabled on-site AMP quantification with a LOD of 340 ng/mL. This work not only developed a novel Fe-Ni bimetallic nanozyme with enhanced peroxidase-like activity and established a competitive ROS-consumption sensing mechanism but also pioneered a dual-mode detection platform for low-cost, user-friendly ampicillin monitoring in environmental samples.