Preparation And Application Of New Fluorescent Nanosensors Based On Fluorescence Resonance Energy Transfer (FRET)

Fluorescence is the output signal of fluorescent chemical sensor. The fluorescentchemical sensor was widely used in analysis, analytical science, life science and otherfield due to its good selectivity, high sensitivity and simple means o f detection. Ourwork is focused on design and synthesis of fluorescent nanosensor based onFluorescence Resonance Energy Transfer （FRET）, and carried out the following work.1. We choose mesoporous silica as the host material, incorporatedpoly（p-phenylenevinylene）（PPV） into the channels of mesoporous silicananoparticles by in situ formation and in situ polymerization method （PPV as anenergy donor）, and get the organic-inorganic fluorescent hybrid nanoparticles（PPV@MSN）. The amino groups were modified on the inner wall of PPV@MSNsthrough―post-grafting‖to form PPV@MSN-NH2. Amine can be used as theidentification and adsorption groups of TNT because of the forming Meisenheimercomplex （TNT-amine complexes） between of them. TNT-amine complexes canstrongly suppress the fuorescence emission of the chosen PPV through FRET inmesoporous channels. We can carry out fluorescent detection of TNT according thequenching degree of PPV. In ethanol solution, The TNT quenching fluorescencetoward PPV@MSN-NH2had a distinct linearly reduce in the concentration range of0-15μM with a detection limit of200nM.2. We used8-hydroxyquinoline （HQ） as the organic small molecule ligands, andsynthesized the surface-functionalized ZnS nanoparticles with amine-capping layer byHQ （ZnS-NH2-Q NPs） through a ligand-exchange process. ZnS-NH2-Q NPs havestrongly fluorescence emission at503nm. This novel surface-functionalized ZnS NPsexhibit excellent optical properties, high fluorescence quantum yield （36%, QYs） andthe impact of solvent on the optical properties is small. The amino groups on thesurface of ZnS NPs can be used as the identification and adsorption groups of TNT,and quench the flurescence of ZnS-NH2-Q NPs through FRET. The amine wasintroduced one-off in the synthetic process of nanoparticles, which can avoid theimpact on the fluorescence properties by post-grafting. The detection limit of thisnovel fluorescent sensor for TNT is down to10nM.3. We synthesized a kind of new fluorescent sensing material based on fuorescein5（6）-isothiocyanate （FITC） modified-cyclodextrin （β-CD）, and its chemical structure and optical properties were characterized. Through controlling the molarratio （1:1） of FITC and per-6-amino--CD, we can endow the-CD with fluorescenceproperties, and also make it reserve a mumber of identification groups of analytes.The remaining amino groups of per-6-amino--CD can identify and adsorp TNTmolecular, and form Meisenheimer complex with TNT. The absorption spectra ofMeisenheimer complex has a spectral overlapping with the emission of FITC in water,so the fluorescence quenching of FITC will be observed on-CD because of theFRET between energy donor and acceptor. The fluorescent sensor for TNT can becarried out according to the quenching degree of FITC, and the detection limit canreach20nM.4. We designed and synthesized a kind of Hg²⁺organic-inorganic fluorescenthybrid nanosensing material denoted as PPV@MSN@SRhB. We choose PPV@MSNNPs as the fluorescent donor, spirolactam rhodamine amine （SRhB） was introducedinto the channel of mesoporous silica as energy acceptor. In ethanol/water （8:2, V/V）solution, a green PL emission （at502nm） of PPV can be observed in the absence ofHg²⁺. However, upon addition of Hg²⁺, the spirolactam ring of SRhB was opened andlead to a turn-on fuorescence change （emission at585nm）; at the same time, thefluorescence of PPV was quenched due to the FRET from PPV to ring-openingrhodamine B. We can perform ratiometric fluorescence detection of Hg²⁺by thefluorescent change （I585/I502） of energy acceptor and donor of PPV@MSN@SRhB.The PPV@MSN@SRhB sensor has excellent selectivity and anti-interference abilityin Hg²⁺detection, and the detection limit is20nM （about4ppb）.