Design Of Ratiometric Sensor And Its Visualization Of Small Molecules For Environmental Pollutants

Fluorescent sensors,because of their simple design,convenient synthesis,low cost,the ability for fast,selective,sensitive and in-situ detection of target analyte,have been widely applied in such as life sciences,material sciences,environmental monitoring,biochemical sensing,biological imaging,immunoassay,medical diagnosis and other research fields.Ratiometric fluorescent sensors can achieve visualization of the analyte by regulating the value of two or more fluorescence intensity ratios.Compared to the single wavelength fluorescent sensors,ratiometric sensors has interior label which can eliminate a variety of interference factors,such as probe concentration,temperature,excitation intensity,and environment pH,and can provide more precise measurement.Therefore many probes based on ratiometric method have been developed for various species sensing,including metal ions,reactive oxygen/sulfide species,and small biological molecules.In this dissertation,our goal is to design and construct optical sensors based on ratiometric method for the detection of nitrogen dioxide(NO2),hydrogen sulfide(H2S),and mercury ions(Hg(II)):1.A novel nanohybrid ratiometric fluorescence probe for on-site and visual determination of nitrogen dioxide(NO2)has been designed.The hybrid probe comprises blue-colored fluorescence carbon nanodots(CDs)and red-colored emission CdTe quantum dots(QDs).Such hybridized probe exhibits dual emission bands centered at 460 and 665 nm,respectively.The blue fluorescence of CDs is insensitive to the analyte,whereas the red emission of QDs is specifically quenched by the analyte,resulting in a distinguishable color change from orange-red to blue upon exposure to NO2.The limit of detection for nitrogen dioxide is estimated to be 19 nM in aqueous solution.More importantly,the nanohybrid probe has been successfully applied in visual detection of gaseous NO2 with a detection limit of 1 ppm by the fabricating indicating vials,suggesting its potential application for real time monitoring NO2 gas.2.We present a fluorescence probe for hydrogen sulfide which was prepared by firstly encapsulating inorganic cadmium telluride(CdTe)QDs in silica nanospheres,and subsequently engineering the silica surface with functional molecules azidocoumarin-4-acetic acid Cy-N3,which can be reduced by H2S to Cy-NH2 and greatly enhances the fluorescence of the coumarin fluorophore.The red fluorescence of QDs is stable against H2S,while the blue fluorescence is specifically sensitive to H2S.Thus,the probe showed a distinct fluorescence color evolution from light-magenta to blue upon exposure to different amounts of H2S,while other relative species have no significant effect on the hybrid probe,showing the probe’excellent selectivity for H2S and a detection limit of 7.0 nM was estimated in aqueous solution.We further applied the nanohybrid probe for visual detection of gaseous H2S with a low concentration of 0.5 ppm using glass indicating plate,Such an efficient on-site visual determination of gaseous H2S is highly demanded in on-site environmental monitoring and protection.3.In this work,we also designed another ratiometric probe for the sulfide ions detection by fabricating GSH-functionalized silver nanoclusters with blue fluorescence and decorated them onto the surface of QDs wrapped in silica nanospheres through covalent S-Ag bonding.The two emission peaks of the nanohybrid locate at 446 and 626 nm,in which the red-colored fluorescence of CdTe@SiO2 is inert to S2-,while the blue-colored fluorescence of Ag NCs is specifically responsive to sulfide.The different responses of the two fluorescence results in a distinct fluorescence color variation from violet blue to red.Therefore,such nanohybrid with two components can be used to detect sulfide ion,and exhibited its good selectivity and sensitivity for gaseous hydrogen sulfide(H2S).4.Here,we also report a sensitive and selective fluorescent sensor for the detection of mercury ion Hg(II),by hybridizing carbon nanodots(C-dots)and gold nanoclusters(Au NCs)through intrinsic interactions of the two components.The design was inspired by the fact:the specific high affinity metallophilic Hg2+-Au+interactions which can greatly quench the red fluorescence of Au NCs,thus the Au NCs act as the reporter;while the blue fluorescence of C-dots is stable against Hg(II)and severs as the reference signal,the two different responses leads to distinct ratiometric fluorescence changes when exposed to Hg(II).The ratiometric sensor has a high selectivity,sensitivity,stability and good solubility and a limit of detection(LOD)of 28 nM for Hg(II)in aqueous solution was estimated.Then we applied the sensor for the detection of Hg(II)in real water samples,including tap water,lake water and mineral water samples with good results.We further demonstrated that a visual chemical sensor could be manufactured by immobilizing the nanohybrid probe on a cellulose acetate circular filter paper.The paper-based sensor immediately showed a distinct fluorescence color evolution from pink to blue after exposure to a drop of Hg(Ⅱ)solution,suggesting its potential application for Hg(Ⅱ)sensing.