An ultra-fast UV-electrochemical sensor based on Cu-MOF for highly sensitive and selective detection of ferric ions

Abstract

A 2D Cu-MOF: {[CuL(H₂O)]}_<i>n</i> (Cu-1, H₂L = 3,4-ethylene dioxythiophene-2,5-dicarboxylic acid) was synthesized using the hydrothermal method. Cu-1 showed excellent solvent stability and was used to fabricate a UV ferric ion sensor. An ultra-low limit of detection (LOD) at 14.5 fM was obtained. Furthermore, <i>N</i>,<i>N</i>-dimethylformamide (DMF) as a 'turn-off' switch was introduced into the Cu-1 framework to construct another 2D Cu-MOF: {[CuL(DMF)]}_<i>n</i> (Cu-2) by a single crystal to single crystal (SCSC) transformation method. Cu-2 lost the ability to recognize ferric ions and the switching effect of Fe³⁺ recognition was realized. Cyclic voltammograms (CVs) were employed to investigate this conversion process and provided a way for explaining the interaction mechanism between Cu-1 and ferric ions. We present an approach for designing and synthesizing MOFs that are suitable for ion sensing.