C-Phycoerythrin as a Colorimetric and Fluorometric Probe for the Sensitive, Selective and Quantitative Detection of Cu 2+ in Aqueous Samples.

C-phycoerythrin (CPE) was investigated as a colorimetric and fluorometric quantitative sensor for Cu2+ ions in an aqueous medium. UV - visible studies with 50 μM concentration of different metals were carried out with only Cu and Ag showing changes in the absorption spectra. Fluorescence emission studies showed similar results. UV - visible titration of CPE with different [Cu] resulted in a linear relationship within 10 μM Cu and a 'naked eye' visible difference in colour, most likely due to the formation of a CPE - Cu complex. Fluorescence emission of CPE was quenched rapidly within 5 min of mixing. Fluorescence emission titration studies revealed gradually decreasing CPE emission with increasing [Cu] with a Stern - Volmer constant of 2.5 × 104  M-1 and a detection limit of 5 μM.. CPE was selective for Cu even in the presence of different metals which were 5 times the concentration of Cu; it was also effective in aqueous samples spiked with Cu. FTIR studies showed considerable changes in the amide III, indicating side chain interactions, even as the protein backbone remained largely unaffected.