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Schematic illustration for the synthesis of the FITC&PEI polymer and the fluorescence quenching mechanism by FRET.
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Fluorescein isothiocyanate (FITC) conjugated to polyethylenimine (PEI) (FITC&PEI) was synthesized and characterized. The nitrogen-containing organic groups played a key role in sensing nitroaromatic compounds that can bind 2,4,6-trinitrotoluene (TNT) to form TNT anions through an acid–base pairing interaction and FITC dye conjugation. The formation...
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... can couple with dye or anchor at the surface of fluorescent nanomaterials to form multifunctional nanocomposites. For example, mercaptoethylamine (MEA) and l-cysteine (l-cys) can tightly bind at the surface of bare ZnS QDs or Au nanoparticles through the mercapto groups [12,25]. PEI is a polymer molecule containing multi-amine and imino groups (Fig. 1A). When conjugated with a suited signal reporting unit such as fluorescence, Raman and electrochemiluminescence, the resulting polymer molecule would be an excellent sensing platform and features a good capture property ...
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... the present work, the FITC dye was utilized as signal reporting unit because its emission wavelength is close to the peak absorption of TNT anions. The PEI was conjugated with FITC in anhydrous ethanol for 24 h in the dark at room temperature (Step 1 in Fig. 1B). During the course of the reaction, humidity was excluded by the input of dry nitrogen to prevent the hydrolysis of the FITC dye. The resulting FITC&PEI can emit strong fluorescence at 516 nm, indicating that the FITC dye was successfully conjugated with PEI ( Fig. 2A). About 0.45 wt% of fluorophore was loaded to PEI polymer backbone. ...
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... 2B), suggesting the formation of TNT anions. Fig. 2C shows the normalized UV-vis and fluorescence spectra, in which the peak absorption and maximum emission band are located at 512 and 516 nm, respectively. Both bands almost completely overlapped, indicating that TNT can efficiently quench the fluorescence of the FITC&PEI probe by FRET (Step 2 in Fig. 1). Other nitroaromatic compounds except for TNT are all electron-deficient molecules, which also exhibit a response to quench FITC fluorescence with different extents (Dual-recognition selectivity of FITC&PEI probe for TNT section), indicating that the energy transfer (ET) or charge transfer (CT) mode also contributes to the ...
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... previously mentioned, TNT can interact with PEI to form TNT anions and change the color of the PEI aqueous solution from colorless to blood-red (Insets in Fig. 2B). PEI monomer is a structure containing multi-nitrogen atoms with lone-electron pair (Fig. 1A). A majority of the groups containing nitrogen of PEI were maintained after the conjugation with FITC, which made the resulting compound hold almost the same ability with PEI to form TNT anions with TNT (Fig. 1B and C). The TNT concentration-dependent UV-vis spectra of the FITC&PEI aqueous solution exhibited the same characteristic as ...
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... from colorless to blood-red (Insets in Fig. 2B). PEI monomer is a structure containing multi-nitrogen atoms with lone-electron pair (Fig. 1A). A majority of the groups containing nitrogen of PEI were maintained after the conjugation with FITC, which made the resulting compound hold almost the same ability with PEI to form TNT anions with TNT (Fig. 1B and C). The TNT concentration-dependent UV-vis spectra of the FITC&PEI aqueous solution exhibited the same characteristic as that of the PEI aqueous solution. At the beginning, the color of the FITC&PEI aqueous solution appears slightly orange, however, the system color gradually turned red with increasing TNT concentration in the FITC&PEI ...
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Analyte oriented selection of the preparation procedure is essential for improving sensing performance. Herein, we report a one-step approach to synthesize highly fluorescent polymeric nanoparticles through solvothermal method and their application in sensitive detection of TNT in soil samples with fluorescence spectrometric method. The polymeric nanoparticles with bright cyan fluorescence were obtained through polycondensation between melamine and terephthalaldehyde at 180 °C for 3 hrs. The nanoparticles were fully characterized and the effect of the synthesis methods was compared based on the fluorescence intensity and quantum yield (QY). The results indicated that trace amounts of TNT could effectively quench the fluorescence of the polymeric nanoparticles. Effect of the possible co-existing substances was systematically investigated and it was proved that the nanoparticles could be used for selective and robust detection of TNT. Limit of detection of 1.8 nmol/L was achieved. The standard addition recoveries for different soil samples were in a range of 95.3% and 106.4% with relative standard deviations below 5.2%.
