Study On Property And Application Of Optical Sensors Based On Polyethyleneimine

Polyethyleneimine(PEI) is a commercially available, water-soluble cationic polymer, which is widely used in the field of polymer dye, gene transfection, catalysis, and so on. The molecular weight distribution of PEI is broad. According to their molecular structure, PEI can be divided into branched PEI(bPEI) and linear PEI(lPEI). PEI shows high positive charge density, and has the "proton sponge" effect, so it is still one of the most popular polycationic non-viral gene vectors. lPEI only contains primary amine, while bPEI contains amount of primary, secondary, and tertiary amino groups, and could react with many substances. Due to the lone pair of electrons on nitrogen and the hydrogen bond interaction, PEI exhibits outstanding adsorption capacity for different substances. Compared to lPEI, bPEI is more reactive, and has three-dimensional network. Therefore, bPEI has been chosen for further study.With the above advantages, we can combine the fluorescence and resonance Rayleigh scattering, establish optical sensors, study the properties of these sensors, and apply them to the detection of environmental pollutants and biomolecules. 1. Enhanced Emission of Polyethyleneimine-Coated Copper Nanoclusters and Their Solvent EffectThe solvent-dependent properties of PEI-capped Cu nanoclusters are discussed in this study. The PEI-encapsulated Cu nanoclusters were dispersed in 12 polar organic solvents, and in water and alcohols, the nanoclusters display similar properties and could be stable in the dark. Moreover, Cu nanoclusters exhibit blue shift of the emission peak in tetrahydrofuran(THF) and 1,4-dioxane, and the absorption spectra change dramatically. Furthermore, in THF the fluorescence intensity increases significantly over time. Besides, the absorption spectra also display a significant change in acetonitrile, dimethyl sulfoxide, and ethylene glycol monomethyl ether, while the emission bands show no obvious shift. In acetonitrile, THF, and 1,4-dioxane, the solvents look milky under bright light, and the fluorescence colors look more blue under a UV lamp. The solvent effect on the fluorescence and absorption spectra of the PEI-capped Cu nanoclusters in water–THF mixtures at different solvent ratios is discussed. Additionally, it should be noticed that the solvent effect of PEI-capped Cu nanoclusters described in this paper is different from the reported solvatofluorochromic properties of PEI-capped Ag nanoclusters. Furthermore, a possible mechanism was explored to explain the solvent-dependent properties of PEI-Cu nanolusters. An increase in n will decrease the Stokes shift, whereas an increase in ε results in a larger Stokes shift. Nevertheless, the influence of refractive index and dielectric constant partially explains the solvent effect but does not account for other effects such as hydrogen bonding or internal charge transfer. THF and 1,4-dioxane have stronger ability to form hydrogen bonds relative to water, and the larger energy gaps between singlet excited state and ground state in THF and 1,4-dioxane result in the blue shift of the emission. Thus, the ground state of PEI-Cu nanoclusters could form hydrogen bonds in THF and 1,4-dioxane. Furthermore, because of the solubility of the Cu nanoclusters and the insolubility of PEI in THF, the branches of PEI will collapse in THF and swell in water. The conformational changes of PEI in THF cause aggregationinduced emission enhancement effect, which can directly enhance thefluorescence intensity. 2. Rapid Fluorescence Assay for Sudan Dyes Using Polyethyleneimine-Coated Copper NanoclustersWe report that the blue fluorescence emission of copper nanoclusters coated with PEI is strongly reduced in the presence of the food dyestuffs Sudan I-IV. This finding was exploited in a label-free fluorescence assay for these Sudan dyes both in ethanol and aqueous solutions. The PEI-capped nanoclusters have an average diameter of 1.8 nm and are displaying, under 355 nm excitation, a blue emission at 480 nm that matches the absorption bands of the Sudan dyes. The fact that temperature has little effect on the fluorescence decrease further suggested that the fluorescence of PEI-Cu nanoclusters should be mainly decreased by the inner filter effect rather than other possible processes. This conclusion could be confirmed from the marginally small change of fluorescence decay time before and after addition of Sudan I, which is not much more than the experimental error. In addition, the shape of the emission spectrum of PEI-capped Cu nanoclusters changed by adding enough Sudan dyes. This phenomenon can be ascribed to the inner filter effects. The clusters are stable in solution for at least one month. Under optimum conditions, this assay can be applied to the quantification of the dyes Sudan I, II, III, and IV, respectively, in the 0.1- 30, 0.1- 30, 0.1- 25, and 0.1- 25 μM concentration ranges, and the detection limits(3σ/slope) are 65, 70, 45, and 50 nM, respectively. The capability of reducing the fluorescence of the PEI-capped copper nanoclusters is directly related to the number of the functional groups in that Sudan III and IV give lower detection limits. This analytical scheme exhibits a remarkably high selectivity for the Sudan dyes over potentially interfering substances. The method was successfully applied to determine Sudan I, II, III, and IV in hot chili powder. 3. Fluorescent Detection of Hydrogen Peroxide and Glucose with Polyethyleneimine-Templated Cu NanoclustersAn interesting, simple, and label-free strategy for the detection of hydrogen peroxide and glucose has been developed with PEI-capped copper nanoclusters as a fluorescence probe in aqueous solution. The PEI-templated Cu nanoclusters which we have synthesized have an average diameter of 1.8 nm and show a blue emission at 480 nm. In the presence of hydrogen peroxide, the fluorescence of the Cu nanoclusters is quenched. Similarly, glucose oxidase catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide, so we can also use this probe to detect glucose. Because of the high zymolyte specificity of glucose oxidase, the detection of glucose has good selectivity. Under the optimized experimental conditions, the linear ranges for hydrogen peroxide and glucose are 0.5- 10 ?M and 10- 100 ?M, respectively. And the detection limits for hydrogen peroxide and glucose are 0.4 and 8 ?M, respectively. Furthermore, we discussed the mechanism of fluorescence quenching which is caused by the interaction between hydrogen peroxide and Cu nanoclusters. This sensing system has been applied successfully to the detection of glucose in human serum samples. 4. Multidimensional Optical Sensing Platform for Detection of Heparin and Reversible Molecular Logic Gate Operation Based on the Phloxine B/Polyethyleneimine SystemA multidimensional optical sensing platform which combines the advantages of resonance Rayleigh scattering(RRS), fluorescence, and colorimetry has been designed for detection of heparin. Phloxine B, a fluorescein derivative showing the special RRS spectrum in the long wavelength region was selected to develop an easy-to-get system which can achieve switch-on sensing to obtain high sensitivity. The noise level of RRS in the long wavelength region is much weaker and the reproducibility is much better, in this way the sensitivity and selectivity can be improved. In the absence of heparin, the phloxine B and PEI form a complex through electrostatic interaction, thus the RRS signal at 554 nm is low, the phloxine B fluorescence is quenched, and the absorption signal is low. In the presence of heparin, competitive binding occurred between phloxine B and heparin toward PEI, then phloxine B is gradually released from the phloxine B /PEI complex, causing obvious enhancement of the RRS, fluorescence and absorption signals. Besides, the desorption of phloxine B is less effective for the heparin analogues, such as hyaluronic acid and chondroitin sulfate. In addition, the system presents a low detection limit of heparin to 5.0 × 10-4 U m L-1, and can also be applied to the detection of heparin in heparin sodium injection and 50% human serum samples with satisfactory results. Finally, the potential application of this method in reversible on-off molecular logic gate fabrication was discussed using the triple-channel optical signals as outputs. 5. Diverse States and Properties of Polymer Nanoparticles and Gel Formed by Polyethyleneimine and Aldehydes and Analytical ApplicationsMulticolor polymer nanoparticles(or dots) were prepared via the reaction between hyperbranched PEI and aldehydes, and when the concentration of aldehydes was lower, the final mixture displayed gelation behavior. This phenomenon can be applied to visual detection of aldehydes. Moreover, the colors of the polymer dots and gel are varied by using different kinds of aldehydes, which can be utilized for visual discrimination of aldehydes. For simplicity, we focus our attention on the interaction between PEI and formaldehyde. The nanoparticles show an average diameter of 42 nm, emit bright cyan fluorescence with high quantum yield, and exhibit high water dispersibility and excellent photostability. Due to the advantages, our polymer nanoparticles(PNPs) are utilized as a fluorescent probe for imaging in living SK-N-SH cells. Furthermore, valuable explorations have been carried out on the fundamental properties of PNPs, such as concentration-dependent fluorescence, p H-dependent fluorescence, and solvent effect.