Smartphone-Based colorimetric platform for reversible detection of essential metal ions (Cu2+, Ni2+, Zn2+)

The accurate detection of essential trace metals, such as copper (Cu-2(+)), nickel (Ni-2(+)), and zinc (Zn-2(+)), in food is critical due to their significant impact on human health and nutrition. This study uses N'-((6-methyl-4-oxo-4H-chromen-3-yl)methylene)thiophene-2-carbohydrazide (MMT) ligand to introduce a smartphone-based colorimetric platform for reversibly detecting essential metal ions (Cu2+, Ni2+, Zn2+). The Benesi-Hildebrand equation was employed to determine association constants, yielding values of 1.11 x 10(5) M-1 for Cu2+, 1.00 x 10(6) M-1 for Ni2+, and 1.294 x 10(5) M-1 for Zn2+. Limits of Detection (LOD) and Quantitation (LOQ) for Cu2+, Ni2+, and Zn2+ were calculated as 1.271 x 10(-7) M, 1.081 x 10(-7) M, 8.557 x 10(-8) M, and 4.238 x 10(-7) M, 3.604 x 10(-7) M, 2.852 x 10(-7) M, respectively. MMT-functionalized paper, cotton, mask, fingerprint stamp, and silica gel were developed for visible, portable detection, demonstrating distinct color changes upon metal ion binding. UV-Vis spectroscopy revealed bathochromic and hypochromic shifts indicative of metal-ligand complexation, with 1:1 stoichiometry confirmed via Job's plots. The pH stability of the complexes was optimal at 7-8, with reversible binding demonstrated using Na(2)EDTA. Real sample analysis showed high recovery rates for spiked metal ions in tap water. A smartphone application quantified the RGB values of Cu2+, Ni2+, and Zn2+, providing a portable and low-cost detection solution with strong correlation coefficients (r > 0.97). This sensor system offers significant potential for environmental monitoring, food safety, and biomedical applications, combining high sensitivity, reproducibility, and user-friendliness.