C-Phycocyanin as a potential biosensor for heavy metals like Hg2+ in aquatic systems

The purpose of this study is to exploit the fluorescence quenching ability of C-phycocyanin (CPC) with heavy metals, establishing it as a biosensor specifically for the detection of Hg2+ even in lower concentrations (mM) in polluted water containing various metals. In this work, we have compared the fluorescence quenching of C-phycocyanin upon binding with 12 different metal ions (Cr3+, Zn2+, Fe2+, Mg2+, Ni2+, Pb2+, Cu2+, Hg2+, Co2+, Ca2+, Ag+ and Li+). The binding efficiency and intensity of fluorescent quenching were investigated using fluorescent spectral studies. Fluorescence quenching data clearly demonstrate that the fluorescence quenching effect with different metals on the C-phycocyanin are in the order Hg2+ > Cu2+ > Ag+ > Pb2+ > Cr3+. The decrease of fluorescence intensity is proportional to the concentration of Hg2+, which is further confirmed by spectral analysis using FT-IR spectroscopy. FT-IR analysis revealed that C-PC-Hg2+ interactions resulted in conformational changes in CPC. Changes in the secondary structure of CPC were confirmed by CD spectral analysis. The ITC results also corroborate the higher binding of Hg2+ with CPC shown from the higher Gibbs free energy value among the metal ions studied. Thus, CPC could be further utilized as a selective and sensitive biosensor for the detection of perilous Hg2+ in the environment.