Water Quality Study for Microcystin Detection using Colorimetric Gold Nanoparticles

Mohan, Devesh
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This research study is intended to produce a quantitative and easy-to-use colorimetric assay to monitor cyanobacteria contamination in drinking water, by determining the presence of the microcystin. Cyanobacteria can form blooms in water, and release microcystin toxins which have been confirmed to cause human and animal poisonings with its contamination of drinking water. Microcystin-LR (MCLR) has been identified as the most toxic and common microcystin, which this study aims to detect within its WHO provisional guideline of 1 uM using the properties of gold nanoparticle (AuNP) based assays. The major advantage of AuNP-based assays is that the assay result can be observed by the naked eye, and therefore, no sophisticated instruments are required. A well-dispersed AuNP solution is red in color, whereas aggregated AuNPs appear as a blue (or clear) color. In the presence of a dsDNA and ion buffer solution, AuNPs are readily aggregated showing a blue color, however, in the presence of ssDNA, the AuNP are stabilized showing high resistance to ionic solution. The ssDNA aptamers with high specificity and affinity to the MCLR toxin are selected and incubated with the MCLR. After MCLR interacts with its aptamer, the aptamer would be folded; and then unmodified AuNPs can effectively differentiate between the unfolded and the folded aptamer in the presence of a given high concentration of ionic solution. If MCLR is detected, the solution will aggregate and produce a blue color, otherwise, it will produce a red color. This AuNP and aptamer based assay produces a colorimetric detection of 0.37 nM, far within the WHO guideline. Improved detection is intended to be made available through a smartphone-based readout system.