Study And Application Of Quercetin Aggregation-induced Emission Effect

Sophora japonica buds are the dried flower bud of the leguminous plant Sophora japonica.The main component is rutin,which is a rutin of quercetin.Quercetin is a natural renewable resource,which is non-toxic,cheap and biodegradable.The fluorescence is weak because the?conjugate structure of quercetin is not large enough.As a fluorescent probe,it is limited to be used in fluorescence spectroscopy.Fluorescence nano-materials can be prepared by a simple and green aggregation method to better utilize the fluorescence properties of quercetin.In this paper,quercetin was extracted from Sophora japonica buds by water extraction and acid precipitation.The final product was characterized by High Performance Liquid Chromatography?HPLC?,¹H NMR and FTIR,and its ability to scavenge DPPH free radicals was tested.The purity of quercetin was relatively high.The purity of quercetin was 90.13%?UV-vis?.And the free radical scavenging rate of quercetin was over 90%,it has strong antioxidant activity.In order to improve the fluorescence intensity of quercetin,quercetin was dissolved in THF-H₂O mixed solvent system with different solvent volume ratios,and characterized by Ultraviolet-visible spectroscopy?UV-vis?,fluorescence spectrum?PL?,X-ray photoelectron spectroscopy?XPS?and transmission electron microscopy?TEM?.The results show that in the solvent system of THF-H₂O,the enol emission decrease and the keto emission increase with the increase of the volume fraction of H₂O,keto emission is AIE emission,which is mainly caused by quercetin crystallization.The fluorescence quercetin was strongest when the volume ratio of THF and H₂O was 20:80,the formed aggregations with a large number of hydroxyl groups on the surface were like fibers.The maximum excitation wavelength was 360 nm,and the maximum emission wavelength was 535 nm.Then,the toxicity of quercetin in L929fibroblasts was evaluated,and the cell survival rate was above 80%.Finally,it was used for cytoplasmic imaging of L929 fibroblasts and in vivo imaging of mice.When Al³⁺was present in THF/H₂O?20/80?,the fluorescence of quercetin was enhanced.ppm,the linear equation fitting of the fluorescence intensity of quercetin at 506 nm to ppm.Similarly,when putrescine was present in THF/H₂O?20/80?,the fluorescence of the quercetin also was enhanced.The concentration of putrescine is from 0.6 to 3.0 ppm,the linear equation fitting of the fluorescence intensity of quercetin at 540 nm to concentration of putrescine is y=104x+143?R²=0.99?,and the detection limit of putrescine was about 0.35ppm.Quercetin nanoparticles as fluorescent probe was added to PVA to prepare quercetin AIE composite film.The physical properties of the composite film were tested,and the results showed that the tensile strength of the composite film is 35.28 Mpa,the elongation at break is207.8%,both CO₂ permeability coefficient and water vaper permeability were increased.The light transmittance of the composite film could reach more than 75%in the wavelength range of 425-800 nm.Compared to quercetin solution,fluorescence emission of the composite film was enhanced with AIE property.The antioxidant activity of the composite film was tested by the scavenging ability of DPPH free radicals,and the results showed that the scavenging rate of DPPH free radicals reached over 35%at 8 h.The growth curve method was used to test the antibacterial activity of the composite film.The results showed that it have antibacterial activity against E.coli and B.subtilis.Take bananas and apples as fruit simulators,composite film can use for fruit protection,and extending the shelf life of fruits.Quercetin has good sensitivity to Al³⁺and putrescine.Composite films were used to detect Al³⁺and putrescine.The results showed that the fluorescence of the films was enhanced in the presence of Al³⁺or putrescine.Steamed bread and deep-fried dough sticks as food simulators,Al³⁺in food was detected,and the color of the film changed from dark yellow to light green under UV lamp.Salmon was used to detect biogenic amines released by spoilage,and the color of the film changed from dark yellow to bright yellow under UV lamp.