Application Of Optical Probe Based On Cyclodextrin Polymer And Carbon Nitride Nanoenzyme

β-Cyclodextrin polymer（β-CDP）is a kind of functional polymer with great application potential,which not only keeps the recognition ability of cyclodextrin monomer and the host-guest interaction,but also has good mechanical strength,good stability and chemical adjustability.Based on the host-guest interaction and fluorescence enhancement of cyclodextrin polymer,a simple and sensitive sensing was constructed for the detection of isocarbophos（ICP）and severe acute respiratory syndrome corona virus 2（SARS-Co V-2）,which further expanded the application of cyclodextrin polymer in biochemical analysis.In addition,we also studied carbon nitride nanoenzyme,which was used to detect fluoride ions in tea.The main research contents and conclusions are as follows:（1）The extensive use of organophosphorus pesticides in agriculture poses a high risk to human health and has boosted the demands for developing sensitive monitoring methods.Herein,we developed a facile and sensitive method for ICP detection based on the remarkable fluorescence enhancement of pyrene during host-guest interaction ofβ-CDP and pyrene.The 3′-pyrene-labeled ICP aptamer could be cleaved by exonuclease I to obtain free pyrene that was tagged on mononucleotides,which could enter the hydrophobic cavity ofβ-CDP,resulting in a prominent fluorescence enhancement.While the target ICP was added,aptamer could undergo a conformational change into a hairpin complex,which prevented the cleavage and host-guest interaction because of the steric hindrance,leading to a weak fluorescence.The ICP has been sensitively and selectively analyzed by detecting the system fluorescence intensity with a detection limit as low as 1.2μg/L.In addition,we have verifified the ability of our proposed method in real sample detection from fruit extract.The construction of this method offers a new choice for highly sensitive and selective organophosphorus pesticide detection and has great application potential in the field of food safety inspection（2）Nucleocapsid protein（N protein）is an appropriate target for early determination of viral antigen-based SARS-Co V-2.Herein,we developed a sensitive and selective N protein sensing method that combined the high recognition of aptamer with host-guest interaction fluorescence enhancement strategy.The DNA aptamer of N protein modified with pyrene at its 3′terminal was designed as the sensing probe.The added exonuclease I（Exo I）could digest the probe and the obtained free pyrene as guest could easily enter into the hydrophobic cavity of hostβ-cyclodextrin polymer（β-CDP）,thus inducing luminescent enhancement.The probe could combine with N protein to form a complex owing to its high affinity,which prevented the digestion of Exo I.The steric hindrance of complex prevented pyrene to enter the cavity ofβ-CDP,resulted in tiny fluorescence change.N protein has been selectively analyzed with a low detection limit（11.27 n M）through detection of the fluorescence intensity.And the sensing of spiked target from human serum and throat swabs samples of three volunteers has been achieved.These results indicated that our proposed method has broad application prospect for early diagnosis of corona virus disease 2019.（3）Nanoenzymes could overcome the disadvantages of natural enzymes,such as high cost,low stability and difficult storage in biosensor applications.By simulating the structure of natural enzymes,iron-loaded graphite-phase carbon nitride nanosheets with peroxidase-like activity were synthesized by reducing iron（Ⅲ）ion onto graphite-phase carbon nitride（Fe/g-C₃N₄）nanosheets.The results show that Fe/g-C₃N₄ nanosheets could catalyze the decomposition of hydrogen peroxide to generate hydroxyl radical and accelerate and the oxidation of 3,3’,5,5’-tetramethylbenzidine（TMB）to blue oxide.According to the excellent peroxidase-like activity of Fe/g-C₃N₄ nanosheets,a colorimetric detection method with high sensitivity and good selectivity was developed.The quantitative detection of F^-was realized in the range of 20 n M～1 m M（R²=0.9922）,and the detection limit was as low as 2.0 n M.Furthermore,we verified the ability of the colorimetric sensing platform based on Fe/g-C₃N₄nanosheets to detect fluoride ions in tea.The average recovery rate was 102.4%～112.4%,and the relative standard deviation（RSD）was 1.8%～6.7%.These results showed that the colorimetric method based on Fe/g-C₃N₄ nanosheets has a broad application prospect in ion detection.