Preparation And Sensing Properties Of Chitosan Based Intelligent Fluorescent Polymer Materials

Intelligent fluorescent polymer materials are widely used in many emerging fields such as biosensing,chemical substance detection,and optical imaging because of their luminescent properties can be adjusted according to external stimuli.In this thesis,we prepared solution-type and hydrogel-type fluorescent polymer materials using chitosan as matrix and 1,8-naphthylimide as fluorescent unit.The details are as follows:(1)Chitosan-based highly selective formaldehyde fluorescent chemical sensor: A functionalized fluorescent polymer material is prepared by bonding a hydrazino-naphthalimide fluorophore to a chitosan molecular chain by a post-modification reaction.The fluorescent polymer material has stimulating responsiveness when exposed to formaldehyde.It can achieve high selectivity,high sensitivity and quantitative detection of formaldehyde,and has the advantages of good luminescent stability and simple preparation.In addition,we demonstrate the practical application value of the probe by detecting formaldehyde in water and food.(2)Intelligent fluorescent polymer hydrogel containing chitosan: a fluorescent hydrogel CS/PAAm-DEAN(Chitosan/polyacrylamide-4-(N,N-dimethylaminoethylene)amino-N-allyl-1,8-naphthalimide)was prepared by one-pot copolymerization of chitosan,acrylamide and fluorescent monomer(naphthalimide derivative)mixed solution.Under acidic conditions,the protonation of the tertiary amine causes electrostatic repulsion between the naphthalene imide fluorophores,thereby attenuating the aggregation-induced quenching(ACQ)effect of the fluorophore,while the protonation of the tertiary amine also inhibits intramolecular photoinduced electron transfer(PET)so that the gel emits intense yellow-green fluorescence.Under alkaline conditions,the tertiary amine will deprotonate and the ACQ and PET processes will work again to induce fluorescence quenching.Therefore,the fluorescent hydrogel CS/PAAm-DEAN has a good pH stimuli responsiveness.Further,the luminescence properties of the hydrogel are locally regulated by the pH response characteristic of the hydrogel,and the gel-emitting performance is precisely controlled by the paper-based ion-printing "diffusion-reaction" method,which is expected to be used in information storage and encryption application.(3)Robotic fish integrated with fluorescent polymer hydrogel: The robotic fish for detection was prepared by adhering fluorescent hydrogel CS/PAAm-DEAN to the surface of a mechanical fish that can swim underwater by itself.The luminescence of the fluorescent hydrogel CS/PAAm-DEAN changes as the pH of the environment changes.Therefore,we can judge the pH change in a complex environment by the change of fluorescence intensity which is visible to the naked eye.