Development of a Rhodamine–Rhodanine-Based Fluorescent Mercury Sensor and Its Use to Monitor Real-Time Uptake and Distribution of Inorganic Mercury in Live Zebrafish Larvae

We introduce a new rhodamine–rhodanine-based “turn-on” fluorescent sensor (RR1) and describe its application for detection of mercury, including in solution, in live cells, and in a living vertebrate organism. The sensor RR1, which is a one-pot synthesis from rhodamine B, undergoes a rapid and irreversible 1:1 stoichiometric reaction with Hg²⁺ in aqueous medium. Using fluorescence correlation spectroscopy (FCS), RR1 was shown to detect the presence of as low as a 0.5 pM concentration of Hg²⁺. It may also lend itself to tagging with biomolecules and nanoparticles, leading to the possibility of organelle-specific Hg detection. Results of experiments with mammalian cells and zebrafish show that RR1 is cell and organism permeable and that it responds selectively to mercury ions over other metal ions. In addition, real-time monitoring of inorganic mercury ion uptake by cells and live zebrafish using this chemosensor shows that saturation of mercury ion uptake occurs within 20–30 min in cells and organisms. We also demonstrate the acquisition of high-resolution real-time distribution maps of inorganic mercury (Hg²⁺) in the zebrafish brain by using a simple fluorescence confocal imaging technique