A Sensitive Water-Soluble Reversible Optical Probe for Hg²⁺ Detection

Area of Science:

• Chemical Sensing
• Environmental Science
• Biomedical Optics

Background:

• Development of fluorescent sensors for heavy metal detection is crucial for environmental monitoring.
• Photoinduced electron transfer (PET)-based sensors are common for metal ion detection.
• Previous work focused on manganese probes using pentaaza macrocycles.

Purpose of the Study:

• To report the serendipitous discovery and characterization of a novel optical mercury sensor.
• To investigate the sensing mechanism and applicability of the developed probe.
• To evaluate the sensor's performance in complex biological and environmental samples.

Main Methods:

• Synthesis of a hemicyanine dye conjugated to a pentaaza macrocycle (qHCM).
• Spectroscopic analysis (absorption, fluorescence) for mercury ion (Hg2+) detection.
• In vitro and in vivo imaging in living cells and zebrafish larvae using confocal microscopy.
• Computational studies including Density Functional Theory (DFT) and 1H NMR.

Main Results:

• qHCM exhibits reversible color change and fluorescence quenching upon Hg2+ binding.
• Achieved a low detection limit of 10 ppb for Hg2+ with high selectivity.
• Demonstrated successful Hg2+ detection in living cells and zebrafish larvae.
• DFT and NMR studies revealed Hg2+ coordination to oxygen donors, not PET.

Conclusions:

• qHCM is a highly water-soluble, selective, and sensitive fluorescent sensor for Hg2+.
• The sensor is effective for real-time Hg2+ detection in biological systems and environmental samples.
• The sensing mechanism involves direct coordination rather than a PET pathway.