Iron-Porphyrin-Based Covalent Assembly With Peroxidase-Like Activity For Colorimetric Sensing

Due to their well-defined macromolecular structure and unique morphology advantages,such as large specific surface area and multiple catalytic sites,polymer vesicles have attracted extensive attention.Covalent self-assembly is an effective method discovered in recent years to construct polymer vesicles based on covalent interactions,with high efficiency and high stability.Polymer vesicles formed by covalent self-assembly method have robust structure and persistent morphology,showing great application potential in the fields of photocatalysis,analytical sensing,drug delivery,and cancer therapy.The active site of native horseradish peroxidase（HRP）consists of heme and histidine residues（His-170）.Heme is a kind of iron porphyrin derivative with excellent stability and unique enzyme-like activity.Based on their performance characteristics,a variety of iron porphyrin-based nanozymes have been researched.In particular,the polymer nanozyme directly assembled by self-assembly method with iron porphyrin has super stability,excellent substrate specificity and selectivity,and has shown great promise in the fields of biocatalysis and biosensing.Based on the above background,this paper constructed a new type of covalent self-assembly iron porphyrin-based polymer vesicles（CAIPs）,which has stable structure,uniform size and excellent enzymatic properties.The shape and size of the assembly can be regulated by adjusting assembly ratio and flexible chain length.In addition,through flexible chain design,it is proved that molecules with certain rigidity can also be used as cross-linking agents for the construction of polymer vesicles.Particularly,by covalently modifying the flexible chain,we successfully introduced histidine-imidazole groups on the surface of the vesicles to construct imidazole-iron porphyrin-based polymer vesicles（IMZ-CAIPs）.IMZ-CAIPs fully mimiced the active site of HRP and improved the enzymatic properties of vesicles.Finally,based on the excellent structures and properties of the two enzyme models,a colorimetric detection platform for Cr（Ⅵ）and ascorbic acid（AA）was developed,showing great linear range,sensitivity and selectivity.The details are as follows:1.Construction of iron-porphyrin-based peroxidase based on covalent self-assembly for colorimetric detection of Cr（Ⅵ）.5,10,15,20-tetra-（4-hydroxy-phenyl）iron porphyrin（FeThpp）was synthesized as a building block,3,3’-dithiodipropionic acid（DTDPA）was used as the initial flexible chain,and flexible chain molecules with different chain lengths were designed and synthesized.Based on this,using the covalent self-assembly method,three novel iron porphyrin-based polymer vesicles（CAIPs）were successfully constructed.The three groups of CAIPs models all exhibited spherical structures with uniform size and good dispersion,and their size increased with the increase of chain length,showing a certain regularity.Next,the enzymatic properties of CAIPs were systematically researched.In the presence of H₂O₂,CAIPs could rapidly catalyze TMB oxidation to produce a blue reaction,exhibiting excellent peroxidase activity and substrate specificity.Furthermore,using the CAIPs enzyme model as sensor,a colorimetric detection method for Cr（Ⅵ）was established.8-hydroxyquinoline（8-HQ）was used as a color inhibitor,based on its electron-donating reaction with the blue product oxTMB and its strong coordination with Cr（Ⅵ）,Cr（Ⅵ）was realized by UV-vis spectroscopy or directly visual recognition.Finally,the colorimetric detection method was successfully applied to the Cr（Ⅵ）content detection in tap water and lake water.2.Construction of imidazole-iron-porphyrin-based peroxidase based on covalent self-assembly for AA colorimetric detection.5-hydroxyisophthalic acid（IPA-OH）was used as the initial flexible chain,and it was modified to introduce histidine-imidazole groups.Three kinds of crosslinkers were synthesized by adjusting the distance between the imidazole groups and the main chain.Taking Fe Thpp as the building block,based on the covalent self-assembly method,imidazole-iron-porphyrin-based polymer vesicles（IMZ-CAIPs）was successfully constructed.The imidazole groups distributed at different distances around the vesicles can coordinate with the active center,adsorb H₂O₂ directionally,activate the O-O bond,thus improving the stability and catalytic activity of IMZ-CAIPs vesicles,and showing more excellent substrate affinity and catalytic efficiency.Based on this,a colorimetric detection method for ascorbic acid（AA）was established using the IMZ-CAIPs enzyme model.As a molecule with certain reducibility,AA can reduce the catalytic product oxTMB reaction to make the blue color of the system lighter and the absorbance decrease.Based on this principle,AA can be detected by UV-vis spectroscopy and identified by naked eyes,thus realizing the comparison of AA in real samples.Color analysis detection.