Ag-decorated, tryptophan-functionalised MOF-808 as a potential electrode material for the Cd2+ electrochemical sensing

This study aimed to develop a sensitive electrochemical sensor for Cd2+ using direct Differential pulse voltammetry (DPV). A nano-porous material was synthesised two step post-modification of MOF-808. First, formate ligand exchange with tryptophan. The infrared spectrum of MOF-808-Trp exhibited characteristic peaks of tryptophan, while 1H NMR evidenced the exchange of tryptophan with formate ligands within the MOF-808 framework. Second, Ag particles were incorporated into MOF frameworks via the adsorption and reduction of Ag+ ions. Powder X-ray diffraction and energy dispersive X-ray confirmed the incorporation of Ag particles and the consistency of the MOF framework after modification. Ag/MOF-808-Trp was then used to create a modified glassy carbon electrode (GCE) for the electrochemical sensing of Cd2+ ions. Cyclic voltammetry of the Ag/MOF-808-Trp modified electrode demonstrated significantly enhanced performance compared to the bare GCE, owing to the synergistic effect of Ag particles and tryptophan functional groups. Differential pulse voltammetry confirmed improved sensitivity towards Cd2+ through effective surface complexation and facilitated charge transfer. Under optimised conditions, the sensor exhibited a linear response in the concentration range of 2–9 µM with a limit of detection of 0.24 µM for Cd2+.