Smartphone-assisted Colorimetric/Fluorescent Collaborative Sensing Platform Based on Laccase-like Activity Fluorescent Nanozyme for Visual Monitoring of <italic>β</italic>-Lactam Antibiotics

β-Lactam antibiotics (BLs) are widely used for preventing and treating bacterial infections in poultry and livestock. However, their abuse and irrational use have led to excessive residues in animal-derived foods, posing a significant threat to consumer health and safety. Thus, there is an urgent need to develop rapid, sensitive, and reliable on-site detection methods for BLs. In this study, a copper metal-organic framework (Cu-MOF) with both laccase-like activity and fluorescent properties was synthesized via a solvothermal method. Cu-MOF could catalyze the oxidation of colorless o-phenylenediamine (OPD) to yellow 2,3-diaminophenazine (DAP) using O2 as the oxidant, resulting in a characteristic absorption peak at 418 nm. Under excitation at 365 nm, DAP emitted yellow fluorescence at 550 nm, which could quench the blue fluorescence of Cu-MOF at 425 nm through the inner-filter effect (IFE). BLs could competitively inhibit the oxidation of OPD to DAP, leading to a decrease in the absorbance of DAP at 418 nm and the intensity of its yellow fluorescence at 550 nm, accompanied by the recovery of the blue fluorescence of Cu-MOF at 425 nm. This dual response generated both colorimetric signals and ratiometric fluorescent signals (F425/F550). Based on the colorimetric/ratiometric fluorescent dual-mode response of the sensing system to BLs, a portable on-site analytical method for BL concentration detection was established by combining the image acquisition function of a smartphone with the RGB information extraction capability of ImageJ software. The linear response ranges of the colorimetric and fluorescent modes were 0.56–30 μmol/L and 0.40–5 μmol/L, with limits of detection (LOD=3σ/k) of 0.19 μmol/L and 0.13 μmol/L, respectively. This method was successfully applied to detection of BLs residues in pork and beef, providing a novel strategy for rapid on-site screening and quantitative analysis of antibiotic residues in foods.