Application In Hg²⁺ Ratiometric Detection Of The Polymer Particle-based Fluorescence Resonance Energy Transfer System

In this thesis, according to the principles of Fluorescence Resonance Energy Transfer （FRET）, we choose NBD, FITC as the donors, rhodamine B as the acceptor. Several class of fluorescence resonance energy transfer （FRET） systems based on polymeric nanoparticles were constructed via some facile methods. The presence of Hg²⁺ in the water dispersion of nanoparticles induced the ring-opening reaction of the spirolactam rhodamine moieties and led to the occurrence of the FRET process, affording the nanoparticle system a ratiometric sensor for Hg²⁺. The main contents and the results of this work are as following:The amphiphilic core/shell nanoparticles containing NBD were prepared in aqueous media. For the nanoparticles, the hydrophilic and biocompatible polyethyleneimine （PEI） chain segments serve as the shell and the hydrophobic copolymer of methyl methacrylate （MMA） constitute the core of the nanoparticles. A hydrophobic fluorescent dye spirolactam rhodamine derivative SRHB was introduced into the nanoparticles to form the NBD/SRHB/nanoparticle complexes in water. The presence of Hg²⁺ in the water dispersion of nanoparticles induced the ring-opening reaction of the spirolactam rhodamine moieties and led to the occurrence of the FRET process, affording the nanoparticle system a ratiometric sensor for Hg²⁺. This fluorescence probe for Hg²⁺ has good properties in sensitivity, selectivity and application in a wild pH range.Polymeric nanoparticles prepared by miniemulsion polymerization of methyl methacrylate （MMA） and acrylic acid （AA） were used as the scaffold for the FRET-based sensor. A hydrophobic ?uorescent dye nitrobenzoxadiazolyl derivative （NBD） was embedded in the nanoparticles during the polymerization and used as the donor. A spirolactam rhodamine derivative SRHB-NH2 was synthesized, then covalently linked onto the particle surface and used as an ion-recognition element. The presence of Hg²⁺ in the water dispersion of nanoparticles induced the ring-opening reaction of the spirolactam rhodamine moieties and led to the occurrence of the FRET process, affording the nanoparticle system a ratiometric sensor for Hg²⁺. The nanoparticle sensor can selectively detect the Hg²⁺ in water with the detection limit of 100 nM （ca. 20 ppb）. It has been found that the FRET-based system with smaller nanoparticle as the scaffold exhibited higher energy transfer efficiency and was more preferred for the accurate ratiometric detection. Moreover, the FRET-based sensor was applicable in a relatively wide pH range （pH 4 to 8） in water, thus this approach may provide a new strategy for ratiometric detection of analytes in environmental and biological applicationsA fluorescent dye fluorescein isothiocyanate （FITC, served as the donor） and a spirolactam rhodamine derivative （SRhB, served as mercury ion probe） were covalently attached onto polyethylenimine （PEI） and polyacrylic acid （PAA） respectively; and a ratiometric sensing system was then formed through the deposition of the donor- and probe- containing polyelectrolytes onto the negatively charged polymer particles via the layer-by-layer （LBL） approach. The ratiometric fluorescent signal change of the system is based on the intra-particle fluorescence resonance energy transfer （FRET） process modulated by mercury ions. Under optimized structural and experimental conditions, the particle-based detection system exhibits stable response for Hg²⁺ in aqueous media. More importantly, in this newly developed particle-based detection system formed by the LBL approach, varied numbers of the PAA/PEI layers which served as the spacer could be placed between the donor-containing layer and the probe-containing layer, hence the donor-acceptor distance and energy transfer efficiency could be effectively tuned （from ca 25% to 76%）, this approach has well solved the problem for many particle-based FRET systems that the donor-acceptor distance can not be precisely controlled. Also, it is found that the ratiometric sensor is applicable in a pH range of 4.6 to 7.3 in water. This approach may provide a new strategy for ratiometric detection of analytes in some environmental and biological applications.