Ratiometric Sensor for Hg2+ Ions Based on Thermo. responsive Organic/Inorganic Hybrid Nanoparticles

A ratiometric fluorescent probe for Hg2+ ions in aqueous media based on organic/inorganic hybrid nanoparticles was prepared. Amphiphilic diblock copolymer, poly( 3-( trimethoxysilyl) propyl methacrylate-co-NBDAE )-b-poly( N-isopropylacrylamide-co-RhBHA ), abbreviated as P( MPS-co-NBDAE)-b-P(NIPAM-co-RhBHA ), was firstly synthesized via consecutive reversible addition. fragmentation chain transfer (RAFT) polymerization of MPS and NIPAM monomer together with NBDAE and RhBHA respectively, where NBDAE and RhBHA were 7-nitro-2,1,3-benzoxadiazole( NBDAE ). based acrylic derivative monomer and Hg2+. reactive rhodamine B ( RhB )-based acrylamide derivative monomer, respectively. Upon exposure to aqueous media, the amphiphilic diblock copolymer of P( MPS-co-NBDAE )-b-P( NIPAM-co-RhBHA ) underwent self. assembly to form spherical nanoparticles with NBD-labeled PMPS cores and thermos-responsive PNIPAM coronas co-labeled with RhBHA moieties. Then a sol-to-gel process was conducted via addition of trimethylamine ( TEA ) into the micellar solution as the catalyst, resulting in core-crosslinked organic/inorganic hybrid nanoparticels. In the absence of Hg2+ ions, the micellar solution of the hybrid nanoparticles was solely green emissive under UV irradiation, which was originated from the NBD moieties trapped in the crosslinked PMPS micellar cores. However, upon addition of Hg2+ ions into the aqueous solution, Hg2+ induced ring. opening of the lactam ring in RhBHA moieties and thus generated RhB residues capable of fluorescence emission. Due to the fluorescence resonance energy transfer ( FRET ) between NBD and RhB moieties that were located in the micellar cores and coronas and acted as FRET donors and acceptors respectively, when the aqueous micellar solution was exposed to UV irradiation, a drastically green-to-orange emission transition was facilely discerned by both naked eye and fluorescence spectrometry, thus allowing for probing Hg2+ ions in a ratiometric manner. Moreover, because of the thermos-responsiveness of PNIPAM blocks, the collapse of PNIPAM coronas was induced by increasing the solution temperature, and the spatial distance between NBD and RhB moieties was therefore shortened, leading to an enhanced probing sensitivity. As a result, the organic/inorganic nanoparticle-based fluorescent probe could be employed as a highly selective ratiometric fluorescent sensor for Hg2+ in aqueous solution.