Ferrocene-functionalized Ni(II)-based metal-organic framework as electrochemical sensing interface for ratiometric analysis of Cu2+, Pb2+ and Cd2+

The development of selective electrochemical response materials and new detection strategies are the research focus in the field of heavy metal ion (HMI) electroanalysis. Herein, a Ni(II)-based metal-organic framework (NH 2 -Ni-MOF) was synthesized and functionalized by electrochemically active molecule of ferrocene (Fc) via post-synthesis modification. Based on the Fc-functionalized NH 2 -Ni-MOF (Fc-NH 2 -Ni-MOF), a novel electrochemical ratiometric sensing platform was developed and applied for the simultaneous determination of various HMIs. The prepared NH 2 -Ni-MOF exhibits nanoplate structure, which is conducive to increase accessible electrode area and expose more active sites, thus promoting the adsorption and pre-concentration of HMIs. The modification of Fc on MOF not only enhances the electrical conductivity of the MOF material, but also provides an internal reference signal for the ratiometric analysis. Due to the excellent characteristics of the Fc-NH 2 -Ni-MOF, the as-prepared ratiometric electrochemical sensing platform exhibits wide linear ranges (0.001 μM to 2.0 μM for lead ions (Pb 2+ ), and 0.01 μM to 2.0 μM for copper ions (Cu 2+ ) as well as cadmium ions (Cd 2+ )) and high sensitivity (the detection limit toward Cu 2+ , Pb 2+ and Cd 2+ is 6.3 nM, 0.2 nM and 7.1 nM, respectively). In addition, compared with the non-ratiometric strategy, the reproducibility of ratiometric analysis is significantly improved. The developed electrochemical method with high sensitivity, selectivity and reliability exhibits bright application prospects in the detection of real samples. Moreover, the electrochemical application of MOF materials has been effectively expanded.