Selective and sensitive colorimetric detection of copper(II) using methylthiazole-quinolinol based sensor:...

A novel methylthiazole-quinolinol-based sensor (MTAMQ) named (E)-2-methyl-5-((4-methylthiazol-2-yl)diazenyl)quinolin-8-ol was synthesized. In the presence of copper(II) ions (Cu²⁺), the MTAMQ sensor exhibits a stable color change from yellow to red. The MTAMQ sensor displayed a linear response toward Cu²⁺ ions over the concentration range of 0.10 to 55 µM (0.006 to 3.5 mg L^-1), with a detection limit of 103.93 nM (6.60 µg L^-1). The binding constant of the MTAMQ-Cu²⁺ complex was 1.41 × 10⁴ M^-1, and the stoichiometric ratio of complex formation was 1 : 1. Using EDTA, the MTAMQ sensor can be recycled and reused up to 4 times. Density functional theory (DFT) calculations were conducted for the MTAMQ sensor and the MTAMQ-Cu²⁺ complex. The MTAMQ sensor was successfully used to detect and quantify Cu²⁺ ions in various foodstuff and water samples, and the results were very close to those of the atomic absorption spectroscopy (AAS) method. To enable the detection of Cu²⁺ ions without the need for a complex device, paper test strips were prepared using the MTAMQ sensor and offered successful results. The unique features of the MTAMQ sensor, including naked-eye detection of copper ions in environmental samples without the need for specialized equipment, real-time analysis, cost-effectiveness, simple operation, rapid response, high stability under different conditions, and excellent selectivity and sensitivity, make it a promising alternative to previously reported colorimetric sensors.