A ratiometric electrochemical sensor for simultaneous detection of multiple heavy metal ions based on ferrocene-functionalized metal-organic framework

• trGNO/Fc-NH 2 -UiO-66 with excellent electrochemical property and stability was prepared. • A ratiometric electrochemical detection strategy was proposed based on this composite. • The functionalized NH 2 -UiO-66 has been used as both electrochemical sensing interface and internal reference probe. • The ratiometric method has significantly improved reproducibility and reliability. • Sensitive, reliable and simultaneous detection of Cd 2+ , Pb 2+ and Cu 2+ was realized. It is a significant and challenging task to simultaneously detection of multiple heavy metal ions with convenience, sensitivity and reliability. Herein, a novel ratiometric electrochemical sensing method was established for the simultaneously detection of three main heavy metal ion pollutants (Cd 2+ , Pb 2+ and Cu 2+ ). The sensing platform was constructed by a composite of ferrocenecarboxylic acid functionalized metal-organic framework (MOF), Fc-NH 2 -UiO-66, and thermally reduced graphene oxide (trGNO), which was designated as trGNO/Fc-NH 2 -UiO-66. NH 2 -UiO-66 has porous structure and large specific surface area, which is beneficial to the adsorption and preconcentration of heavy metal ions. The introduction of trGNO and Fc improves the conductivity and electrochemical activity of the MOF material. Moreover, the signal of Fc can be used as internal reference to develop ratiometric detection, which greatly improves the reproducibility and reliability of electrochemical detection. Based on this ratiometric electrochemical sensing platform, the simultaneous, sensitive and reliable detection of Cd 2+ , Pb 2+ and Cu 2+ was realized. This work provides a new sensing platform for simultaneous detection of multiple heavy metal ions and greatly expands the application of UiO-66-type MOFs in electrochemical field.