Naked eye detection of mercury (II) ion using horseradish peroxidase inhibitive assay

Urbanization and industrialization process have caused the elevation of heavy metals in the environment including mercury. The current determination of the heavy metal ions primarily depends on sophisticated instruments such as atomic absorption spectrometry, inductively coupled plasma mass spectrometry, anodic stripping voltammetry, x-ray fluorescence spectrometry, and microprobes. The techniques used in determining the level of heavy metals are accurate but the process involved is time-consuming, expensive, and require highly trained personnel to operate. Therefore, it is necessary to develop simple and rapid detection for monitoring the heavy metal ions through the naked eye detection in an inhibitive horseradish peroxidase enzyme assay. In this study, 4-aminoantipyrine and phenol are the chromogens used. When they react with hydrogen peroxide, in the presence of horseradish peroxidase, it will form a red coloured product which is visible by our naked eye. A colourless product on the other hand will be formed indicating the presence of heavy metals. This naked eye detection shows good selectivity for mercury (II) ions (Hg2+) over other metal ions as the distinctive colour of Hg2+ can be observed at as low as 0.5 ppm. IC50 of Hg2+ shows the lowest value which is 0.290 ppm compared to the other metal ions tested. This study also investigated the mechanism of Hg2+ inhibition towards HRP by using dynamic light scattering and molecular dynamic simulation. The naked eye detection can also qualitatively be determined by using application downloaded via the smartphone namely Color Assist which shows that the naked eye detection does not require expensive instruments to run through. Thus, this naked eye detection is projected to be applied to the environmental for its low cost, easier preparation, and rapid.

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