Synthesis and Characterization of a Nanozyme-Based MOF (IUST-7): Sacrificial Template for Colorimetric Smartphone-Assisted Hg 2+ Detection

This study introduces a methodological optimization approach to fabricate a sacrificial nanozyme-based metal-organic framework (MOF) capable of detecting and quantifying Hg²⁺ ions in aqueous solutions by using a smartphone. The ([Mn₃(adc)₃(DMF)₄]), IUST-7, compound [adc = azobenzene-4,4-dicarboxylate], crystallizes in the centrosymmetric space group P2₁/n of the monoclinic system in the form of orange-yellow crystals and enables a straightforward visual assessment output without the need for sophisticated analytical instruments. Through its specific interaction with Hg²⁺ ions, the degradation of this structure triggers a color change in the 3,3',5,5'-tetramethylbenzidine (TMB) solution from blue to pale yellow by peroxidase-mimicking nanozyme activity. Our sensor integrates with smartphones, facilitating easy data retrieval and analysis. Furthermore, a portable red, green, and blue (RGB)-based sensor was developed for the immediate and simple quantification of Hg²⁺ ions. DFT calculations were carried out to reveal the interaction of Hg²⁺ with the sensor. Serving as a colorimetric sensor, this distinct structure exhibits high sensitivity to Hg²⁺ ions at low concentrations with an LOD of 0.095 μM (0.025 ppm) and LOQ of 0.319 μM (0.086 ppm) within a linear range of 0.2 to 5 μM and 15 to 345 μM.