Ultrasensitive and selective detection of Hg²⁺ using fluorescent phycocyanin in an aqueous system

Hg²⁺ toxicity is one of the most common chemical poisonings that occurs mainly from drinking polluted water. In the current work, Phycocyanin (PC) was exploited as a fluorescent sensor for sensitive and selective detection of Hg²⁺ in an aqueous system. PC-Hg²⁺ interaction was monitored using a spectro-fluorometer under different buffered solutions at pH values of 6,7,8,9, or 10 above the isoelectric point of PC (5.18). A remarkable decrease of PC fluorescence intensity was observed under Tris-buffer at pH 6 upon the addition of increasing Hg²⁺ concentrations (1-120 nM). Under the maintained experimental conditions, the current sensor showed a good linear relationship with R² = 0.9971 and a limit of detection as low as 0.7 nM was achieved. In addition, a notable selectivity of Hg²⁺ over other nine heavy metals (Cu^2+, Zn^2+, Pb²⁺, Mg^2+, Mn⁴⁺, Li⁺, Fe^3+, Co²⁺, and Al³⁺) was achieved in the presence of 120 nM of each metal. Moreover, the current fluorescent detection assay was also tested in real samples of pond water, and recoveries as well as relative standard deviations within the acceptable limits were recorded.