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.
Keywords: C-phycoerythrin; Copper sensing; Cyanobacteria; Fluorescent probe, colorimetric sensing.