Stimuli-responsive Polymer Materials For Optical Sensing Of Alkaline Phosphatase

Alkaline phosphatase（ALP）is an important hydrolytic enzyme,which plays an important role in the normal growth of tissues.At the same time,ALP is also an important biomarker for the diagnosis of many diseases.Therefore,the development of simple and sensitive ALP detection method is of great significance for understanding the physiological and pathological effects of ALP.So far,many different methods for detecting ALP activity have been established.The colorimetric method and fluorescence method are widely concerned because of their advantages of rapidity,simplicity and high sensitivity.But most of them involve complicated instruments and complicated operation process.In addition,these fluorescent probes not only require a time-consuming design and synthesis process,some are even toxic.Alginate（Alg）hydrogel is a hydrophilic system with three-dimensional network structure formed by crosslinking.Due to the wide source of raw material Alg,it has non-toxic and harmless,excellent biocompatibility and degradability,as well as adjustable structure and physicochemical properties.Therefore,it has a great prospect in drug release,biosensors,tissue engineering and other fields.Coordination polymers（CPs）are inorganic-organic hybrid materials with infinite network structure formed by coordination bonds between ions and organic ligands.CPs has the advantages of stable structure,diverse composition and functional flexibility,so it has shown great potential in the fields of sensing and drug release.In this paper,we prepared a responsive Alg hydrogel and a responsive CPs,and established a series of analysis method to detect ALP.The main work is as follows:（1）CDs@Cu/Alg composite hydrogels were synthesized by Cu²⁺as crosslinking agent and positively charged Carbon dots（CDs）as fluorescent indicator.Due to the strong coordination ability of pyrophosphate（PPi）and Cu²⁺,the existence of PPi can competitively combine with Cu²⁺on Cu/Alg,thus destroying the structure of hydrogel and releasing CDs into solution.On this basis,the fluorescence sensor for detection of ALP was further constructed by using the property that ALP can hydrolyze PPi to generate Pi.As a sensor,CDs@Cu/Alg has high detection sensitivity and excellent selectivity,and the detection limit is 0.55 mU/mL.（2）The RhB@Fe³⁺/Alg composite hydrogel based on Rhodamine B（RhB）as the colorimetric indicator was prepared by using Fe³⁺as the cross-linking agent.Compared with Fe³⁺,Fe²⁺has a weak binding ability with Alg,which can hardly support the three-dimensional structure of hydrogel.Therefore,the presence of Ascorbic acid（AA）can destroy the three-dimensional structure of RhB@Fe³⁺/Alg,thereby releasing RhB into an aqueous solution.On this basis,a new colorimetric method for the detection of ALP was constructed by using phospho-2-ascorbic acid as the substrate of ALP,and the detection limit was 0.26 mU/mL.（3）we studied the stimulus response properties of ligand polymers.Firstly,Thioflavin T（ThT）was embedded into the GMP/Eu coordination polymer composed of Eu³⁺and guanosinic acid,and the ThT@GMP/Eu complex with strong fluorescence was prepared.Since ALP can hydrolyze GMP to produce guanosine and phosphate groups,the presence of ALP can damage the structure of GMP/Eu coordination polymer,resulting in the release of ThT,resulting in a greatly reduced ThT fluorescence.Accordingly,a new fluorescence analysis method for the detection of ALP was established.On this basis,the fluorescence immunosensor for the detection of mIgG was further constructed by using ALP as enzyme marker,and the detection limit was 100 ng/mL.