Ultrasound-boosted laccase-like activity of Cu-MOF@PDA for Cr sensing

In this study, a colorimetric detection system for Cr(III) was established by leveraging the laccase-mimicking activity of two-dimensional Cu-based metal-organic frameworks (Cu-MOFs) modified with polydopamine (PDA) nanomaterials (Cu-MOF@PDA), through which Cr(III) specifically inhibits the catalytic performance. The Cu-MOF@PDA composite exhibited significant laccase-mimicking activity, enabling the oxidation of 2,4-dichlorophenol (2,4-DP) and 4-aminoantipyrine (4-AP), leading to the generation of a red-colored compound. Notably, the laccase-like activity of Cu-MOF@PDA was substantially enhanced under ultrasonic (US) stimulation. Free-radical trapping experiments revealed that the levels of singlet oxygen (¹O₂) and hydroxyl radicals (OH) were markedly increased, while the electron transfer rate was accelerated, thereby boosting catalytic efficiency under US exposure. The research confirmed that Cr(III) binds to Cu-MOF@PDA, leading to the suppression of its catalytic activity. A strong linear correlation (R² = 0.995) was observed between the absorbance at 505 nm and Cr(III) concentrations ranging from 0.67 to 54.17 μg/L, with a low detection limit (LOD) of 0.26 μg/L (S/N = 3). The developed approach was effectively utilized for the analysis of Cr(III) and total Cr in cigarette tipping paper samples, yielding highly satisfactory results.