Self-assembly of magnetically recoverable ratiometric Cu2+ fluorescent sensor and adsorbent

Abstract

A mesoporous shell containing a fluorescence resonance energy transfer (FRET) type of ratiometric Cu²⁺ fluorescent sensor was coated around a cetyltrimethylammonium bromide (CTAB) stabilized Fe₃O₄@SiO₂ core. All of the units comprising the sensor composite, including the Cu²⁺ ligand, signal reference and reporter units, are independent of each other and without a direct covalent linkage between them, and are site-selectively self-assembled into the pore framework or channel of the mesoporous silica matrix through the electrostatic interaction between CTAB porogen and silicates. The coordination of Cu²⁺ and its ligand leads to the variation of fluorescence energy transfer efficiency between neighboring FRET pairs benefiting from the nanosized pore system of the mesoporous matrix, which finally results in the ratiometric detection of Cu²⁺. Investigation of Cu²⁺ adsorption performance indicated rapid removal efficiency, with a maximum adsorption capacity of 17.86 mg g⁻¹. Fe₃O₄ nanoparticles were introduced as a core to make the sensor system magnetically recyclable after sensing and adsorption. Finally, the disassembly and reassembly of the Cu²⁺ sensor were achieved by extracting and reintroducing the units in CTAB micelles, making the sensing system reproducible.