Molecularly imprinted polymer modified g-C₃N₄ integrated into paper-based devices for colorimetric detection of...

To enable rapid, on-site monitoring of amoxicillin and ensure controlled administration, we have developed a paper-based analytical device (PAD) incorporating a molecularly imprinted polymer (MIP) anchored on graphitic carbon nitride (g-C₃N₄) nanosheets. The MIP@g-C₃N₄ composite was synthesized via in situ polymerization of 3-aminopropyl triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS) around amoxicillin templates on g-C₃N₄, yielding highly specific binding cavities upon template removal. The g-C₃N₄ nanozyme's intrinsic peroxidase-like activity catalyzes the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to its blue oxidized form (oxTMB) in the presence of hydrogen peroxide. In the absence of amoxicillin, a vivid blue signal develops, whereas competitive binding of amoxicillin at the MIP sites inhibits nanozyme activity, causing a proportional decrease in color intensity. Analytical characterization demonstrated a linear response over 0-100 µM amoxicillin, with a limit of detection (LOD) of 0.97 µM. The integration with the PAD format permits semi-quantitative visual readout and quantitative determination via a portable smartphone, all within minutes and without the need for complex instrumentation. When applied to spiked milk and tap water, the MIP@g-C₃N₄ sensor achieved recoveries of 92-105% with negligible interference from structurally related antibiotics. The marriage of MIP selectivity, g-C₃N₄ nanozyme catalysis, and low-cost PAD architecture delivers a user-friendly, field-deployable platform for rapid amoxicillin screening, promising significant potential to bolster antibiotic stewardship and mitigate overdose-related health risks across clinical, environmental, and food-safety applications.