Efficient Electrochemical Lead Detection by a Histidine-Grafted Metal-Organic Framework MOF-808 Electrode Material

As the excessive presence of heavy metals in the environment significantly affects human health, it becomes necessary to develop efficient, selective, and sensitive methods for their detection. In this study, a novel electrochemical sensor for the detection of Pb²⁺ ions is described. The proposed sensor is based on a glassy carbon electrode (GCE) modified by a thin film of histidine-grafted metal-organic framework (MOF-808-His). The MOF-808 was obtained solvothermally, and then postsynthetically modified by substituting the coordinated acetate with histidinate. By electrochemistry, the MOF-808-His-modified GCE demonstrated high charge selectivity, while electrochemical impedance spectroscopy (EIS) and kinetic studies gave a lower charge transfer resistance (4196 Ω) and a better standard heterogeneous electron transfer rate constant (1.80 × 10^-5 cm s^-1) on MOF-808-modified GCE. These results indicated a swift and direct electron transfer rate from [Fe(CN)₆]^3-/4- to the electrode surface. Using square wave anodic stripping voltammetry (SWASV), the rapid and highly sensitive determination of Pb²⁺ was achieved on MOF-808-His-modified GCE. By optimizing the accumulation-detection parameters including pH of the detection medium, deposition time and potential, and concentration, a remarkable limit of detection (LoD, based on a signal-to-noise ratio of 3) of (1.12 × 10^-10 ± 0.10 × 10^-10) mol L^-1 was obtained, with a sensitivity of (9.6 ± 0.1) μA L μmol^-1. After interference and stability studies, the MOF-808-His-modified GCE was applied to the detection of Pb²⁺ in a tap water sample with a concentration of 10 μmol L^-1 Pb²⁺.