A natural fluorescent protein for ciprofloxacin sensing and mechanism study using molecular docking and circular dichroism.

Ciprofloxacin (CIP) is one of the common drug pollutants whose residues are often detected in the environment. In the current work, CIP was studied in aqueous environment based on a natural fluorescing compound called phycocyanin (PC). Using, a Spectro fluorophotometer, fluorescence detection of CIP was performed, and absorbance properties were studied using a UV-Visible spectrophotometer. In addition, a circular dichroism (CD) spectrophotometer and molecular docking analysis were implemented for further investigation. As the fluorometric measurement results showed, the fluorescence intensity of PC dropped linearly upon the addition of increasing amounts of CIP ranging from 0 to 120 µmol/L of final concentrations, with the limit of detection reaching down to 95 nM. In addition, the fluorescent sensor was found to be more selective towards CIP when tested against other six antibiotics and six pesticides. In the case of analysis of the PC-CIP interaction using a CD spectrophotometer the α-helix content of PC decreased in the presence of CIP, which is an indication of conformational changes in the secondary structure of PC. Moreover, the molecular docking analysis of the PC-CIP interaction assisted in locating the three sites where CIP binds with CIP, which in turn provided additional instances of the interaction mechanism between PC and CIP.

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 (Cu2+, Zn2+, Pb2+, Mg2+, Mn4+, Li+, Fe3+, 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.