Mn3O4 with multiple enzyme-like activity for differential detection of lead and copper ions

Mn 3 O 4 with dual-enzyme-like activity is synthesized via a simple and green method. • Pb(II) & Cu(II) boost OXD-like activity of Mn 3 O 4 via promoting the generation of O • – 2 . • Pb(II) inhibits the LAC-like activity of Mn 3 O 4 via uncompetitive inhibition. • Fluorescent & colorimetric methods realize differential Pb(II) & Cu(II) detection. Pb(II) can cause irreversible developmental and neurological damage, Cu(II) is an essential trace element but exhibits significant toxicity at excessive concentrations. Therefore, development of reliable detection methods for Pb(II) and Cu(II) is crucially important. In this work, Mn 3 O 4 nanomaterial with both oxidase (OXD)-like and laccase (LAC)-like activities was synthesized using a green and mild approach. Based on the enhancing effect on OXD-like activity of Mn 3 O 4 by Pb(II) and Cu(II), simple and sensitive fluorescent sensing methods for detecting Pb(II) and Cu(II) were developed, with the limits of detection of 0.073 μM and 0.391 μM, respectively. The developed methods were successfully applied to analyze Pb(II) and Cu(II) in various real samples. Furthermore, given that Pb(II) can inhibit the LAC-like activity of Mn 3 O 4 , a colorimetric method for Pb(II) detection with an ultra-wide linear range (1–7 μM and 7–2000 μM) was developed. By combining the fluorescence and colorimetric detection results, the differential detection of Pb(II) and Cu(II) can be realized. In addition, the substrate-dependent regulation of enzyme-like activity of Mn 3 O 4 by Pb(II) was elucidated. Specifically, when 2,4-DP was used as the substrate, Pb(II) inhibited product formation through stabilizing the Mn 3 O 4 –2,4-DP complex. In contrast, when OPD was used as the substrate, Pb(II) promoted the generation of free radicals on the material's surface, enhancing the catalytic reaction. The findings of this study provide a reference for the discriminatory detection of different metals based on multiple enzyme-like activity of nanomaterials. Download: Download high-res image (344KB) Download: Download full-size image