Simultaneous and Interference-Free Electrochemical Monitoring of Cd ^{2 <b>+</b>} , Cu ^{2 <b>+</b>} , and Hg ^{2 <b>+</b>} using a CoFe ₂ O ₄ @Fe-Pda MOF Composite

There is a high risk of heavy metal contamination to both the environment and the population; hence, special care and selective, trustworthy detection technology is required. This paper describes the preparation and use of a CoFe₂O₄@Fe-Pda metal-organic framework (MOF)-based electrochemical sensor to concurrently detect Cd²⁺, Cu²⁺, and Hg²⁺ ions. The sensor exhibits a strong electrochemical response, characterized by well-resolved peak potentials for each target ion and a linear current response as the target ion concentration varies. Measurement of differential pulse voltammetry (DPV) provides a limit of detection (LOD) of 9.6 ppb Cd²⁺ (10-55 ppb), 13.5 ppb Cu²⁺ (5-55 ppb) and 12.0 ppb Hg²⁺ (3-55 ppb) in individual analysis and 15 ppb, 8.45 ppb, and 11 ppb for simultaneous detection of Cd²⁺, Cu²⁺, and Hg²⁺ ions, respectively. It is interesting to note that the presence of one metal ion does not affect the detection of the others, even at lower concentrations, which supports the sensor's high selectivity and minimal cross-reactivity. The increased sensing power can be ascribed to the synergistic effects between the magnetic CoFe₂O₄ nanoparticles and the Fe-Pda MOF, which together enable rapid electron transfer, a high surface area, and the potential for specific molecular interactions. These results demonstrate the promise of the CoFe₂O₄@Fe-Pda MOF as a robust electrochemical sensing platform for tracking toxic heavy metals in real time under complex aqueous conditions.