Feedback-regulated dual enzyme–like activity in Ce-MOFs: enabling colorimetric/fluorescence dual-mode detection of tetracycline in water and milk

This study introduces a dual-mode sensing platform based on a cerium-based metal-organic framework (UIO-66-NH 2 (Ce)) that exhibits dual-enzyme-like activity for the sensitive and selective detection of tetracycline (TC) in water and milk. It employs feedback-regulated dual-enzyme cascades along with Ce 3+ /Ce 4+ redox-mediated ligand-to-metal charge transfer (LMCT) to achieve signal inversion in both colorimetric and fluorescence outputs. The phosphatase-like activity of UIO-66-NH 2 (Ce) hydrolyzes L-ascorbyl-2-phosphate (AAP), resulting in the generation of ascorbic acid (AA), which subsequently reduces Ce 4+ to Ce 3+ within UIO-66-NH 2 (Ce). This reduction suppresses its oxidase-like activity while enhancing fluorescence through LMCT inhibition. In the presence of TC, the phosphatase-like activity is selectively inhibited, thereby restoring Ce 4+ -driven oxidase activity and quenching fluorescence. The platform offers broad detection ranges, low limits (5.95 nM fluorescence, 17.54 nM colorimetry), high selectivity, and real sample applicability, with smartphone-based analysis via RGB signals for rapid, on-site testing, aiding environmental and food safety monitoring.