Micelle nanoparticles for FRET-based ratiometric sensing of mercury ions in water, biological fluids and living cells

A fluorescence resonance energy transfer (FRET) based ratiometric sensing system for mercury ions is built in nano-sized core/corona micelles formed by a poly(ethylene oxide)-b-polystyrene diblock copolymer. For this system, a hydrophobic fluorescein derivative (FLS-C12), which serves as the energy transfer donor, is incorporated into the micelle core during the micelle formation; and a spirolactam-rhodamine derivative (RhB-CS) as a probe for mercury ions is located at the micelle core/corona interface. An efficient ring-opening reaction of RhB-CS induced by mercury ions generates the long-wavelength rhodamine B fluorophore which can act as the energy acceptor, affording the micelle nanoparticles the water-dispersible FRET-based ratiometric detection system for mercury ions, with a detection limit of 0.1 μM in water. The donor and the probe fluorophores, with their structure being appropriately modified, can strongly bind (non-covalently) to the specific sites of the micelles and form a stable ratiometric sensor in water and in some biological fluids. In addition, with the water-soluble and biocompatible poly(ethylene oxide) (PEO) as the corona of the micelles, the nano-sized sensing system can readily permeate through cell membrane and detect intracellular Hg(2+) level changes.