| Summary: | Nickel’s durability and catalytic properties make it essential in the aerospace, automotive, electronics, and fuel cell technology industries. Wastewater analysis typically relies on sensitive but costly techniques such as ICP-MS, AAS, and ICP-AES, which require complex equipment and are unsuitable for on-site testing. This study introduces a novel screen-printed electrode array with 16 chemically and, optionally, electrochemically coated Au electrodes. Its electrochemical response to Ni<sup>2+</sup> was tested using Na<sub>2</sub>SO<sub>3</sub> and ChCl-EG deep eutectic solvents as electrolytes. Ni<sup>2+</sup> solutions were prepared from NiCl<sub>2</sub>·6H<sub>2</sub>O, NiSO<sub>4</sub>·6H<sub>2</sub>O, and dry NiCl<sub>2</sub>. In Na<sub>2</sub>SO<sub>3</sub>, the linear detection ranges were 20–196 mM for NiCl<sub>2</sub>·6H<sub>2</sub>O and 89–329 mM for NiSO<sub>4</sub>·6H<sub>2</sub>O. High Ni<sup>2+</sup> concentrations (10–500 mM) were used to simulate industrial conditions. Two linear ranges were observed, likely due to differences in electrochemical behaviour between NiCl<sub>2</sub>·6H<sub>2</sub>O and NiSO<sub>4</sub>·6H<sub>2</sub>O, despite the identical Na<sub>2</sub>SO<sub>3</sub> electrolyte. Anion effects (Cl<sup>−</sup> vs. SO<sub>4</sub><sup>2−</sup>) may influence response via complexation or ion pairing. In ChCl-EG, a linear range of 0.5–10 mM (R<sup>2</sup> = 0.9995) and a detection limit of 1.6 µM were achieved. With a small electrolyte volume (100–200 µL), nickel detection in the nanomole range is possible. A key advantage is the array’s ability to analyze multiple analytes simultaneously via customizable electrode configurations. Future research will focus on nickel detection in industrial wastewater and its potential in the multiplexed analysis of toxic metals. The array also holds promise for medical diagnostics and food safety applications using thiol/Au-based capture molecules.
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