Detection of Zn2+ ions using a high-affinity low-molecular-weight fluorescence probe in two freshwater organisms.

Objective: The objective of this study was to determine the uptake and distribution of zinc ions (Zn²⁺) in two freshwater organisms, Moina macrocopa and Rheocricotopus larvae using a high-affinity low-molecular-weight Zn²⁺-ion-selective fluorescence probe. Methods: M. macrocopa and Rheocricotopus larvae were exposed separately to dissolved Zn²⁺ (0.1 and 1 mg/L) for 12, 24, and 48 h in three replicates along with a control. Later, the organisms were incubated with the fluorescence probe in six-well plates in the dark at room temperature. At the end of the incubation period, the organisms were washed with a phosphate buffer solution (0.01 M). The live organisms were then imaged using a fluorescence microscope and the fluorescence intensities of the images were determined. Results: The results revealed that the Zn²⁺ ions are uptaken and internalized into the bodies of the organisms exposed to Zn²⁺ ion concentrations, as indicated by a significant increase in the fluorescence intensities of the fluorescence images of the organisms. According to the fluorescence images, the Zn²⁺ ions were mainly localized in the lower gut region of M. macrocopa at the end of 48 h. However, in Rheocricotopus larvae, the Zn²⁺ ions were detected in the midgut region of the digestory tube after 48 h of exposure. Therefore, this was dependent upon both the Zn²⁺ concentration in the exposure media and the exposure duration. Conclusion: Taken together, the distribution of Zn²⁺ ions in different aquatic species is species-specific. Furthermore, the present study provides insight into the potential use of high-affinity low-molecular-weight Zn²⁺-ion-selective fluorescence probes to detect labile Zn²⁺ in aquatic organisms and the toxicological implications of zinc pollution in aquatic environments. [ABSTRACT FROM AUTHOR]