The Preparation Of Cellulose-Modified Polymer Dots And Studying Of Their Sensing Properties

As a new emerging class of carbon points（CDs）,carbon polymer dots（CPDs）consist of organic polymer chains and carbon skeletons with unique polymer/carbon hybrid structures and properties.Compared with conventional CDs,CPDs not only exhibit superior optical properties but also retain the properties of polymers,thus attracting increasing attention for the design of fluorescent materials due to their advantages,such as simple preparation,excellent optical properties and good biocompatibility.However,the major polymer materials used for the synthesis of CPDs are mainly polyethyleneimine,polydopamine,polyfluorene,or poly（ether amide）;therefore,it is of great significance to expand the available materials for the synthesis of CPDs,especially those based on renewable natural materials,in a facile and environmentally friendly manner.In this paper,functional CPDs were synthesized through a“synthesis-modification integration”route by regulating carboxymethylcellulose（CMC）as the precursor,and their applications,including the recognition of lysine chirality and the detection of silver ions and glucose,were explored through fluorescent analytical methods.The main research works are as follows:（1）Fluorescein-functionalized fluorescent polymer dots（F-PDs）were prepared by a facile one-pot method by magnetic stirring under mild conditions based on CMC and fluorescein as the precursors.The obtained F-PDs exhibited a nanoscale size of 3.2±1.1 nm,excellent water solubility and bright yellow fluorescence emission with a fluorescence quantum yield of 12.0%.The above fluorescent probe displays rapid and sensitive chiral discrimination for lysine focused on the different complexation abilities between lysine enantiomers and Cu²⁺.The concentration of L-lysine ranging from 4 to 14 m M（R²=0.997）could be measured by fluorescence intensity ratio(I₅₁₃/I₄₂₉)analytical methods atλ_ex=365 nm,and its detection limit（LOD）was calculated to be 0.28 m M（3σ/slope）.Moreover,this sensor could accurately predict the enantiomeric excess（ee）of lysine enantiomers at the designed concentration(lysine:20 m M,Cu²⁺:10 m M)ranges.Meanwhile,the proposed sensor was successfully applied to analyze L-lys（recovery:95.8-101%,RSD:0.465-3.34%）and ee values（recovery:98.5-102%,RSD:2.61-3.21%）in human urine samples by the standard addition method.（2）Citric acid-functionalized fluorescent polymer dots（C-PDs）were synthesized by an amidation reaction under mild conditions based on CMC and citric acid monohydrate（CA）as the precursors.The C-PDs displayed a uniform nanoscale size distribution,excellent water solubility,photostability and bright fluorescence emission with a fluorescence quantum yield of11.41%under mild conditions.Importantly,these C-PDs can be used as an excellent fluorescent probe to detect Ag⁺in aqueous solutions.The fluorescence at 473 nm can be quenched by Ag⁺.The concentration of Ag⁺ranging from 100 to 350μM（R²=0.994）could be measured by the fluorescence intensity at 460 nm analytical methods atλ_exi=382 nm,and its LOD was calculated to be 6.4μM（3σ/slope）.Meanwhile,the proposed sensor was successfully applied to analyze Ag⁺（recovery:95.7-102%,RSD:1.64-3.81%）in human urine samples by the standard addition method.（3）Phenylboronic acid-functionalized fluorescent polymer dots（B-PDs）were synthesized by a“synthesis-modification integration”route under mild conditions based on CMC and phenylboronic acid as precursors.The B-PDs displayed a uniform nanoscale size distribution,excellent water solubility,photostability and bright fluorescence emission with a fluorescence quantum yield of 21.6%under mild conditions.B-PDs have a reversible fluorescence response in acidic solution（blue emission）and alkaline solution（green emission）.When the p H values ranged from 1 to 14,the fluorescence emission of B-PD showed an obvious redshift.Importantly,these B-PDs can be used as an excellent fluorescent probe to detect glucose in aqueous solutions.The fluorescence atλ_exi=388 nm can be increased by glucose,which can assemble on the surface of B-PDs due to the reversible reaction between boronic acid and cis-diols through the aggregation-induced enhancement effect.Glucose concentrations ranging from 0.0001 to 1.2mol/L（R²=0.998）could be measured by the fluorescence intensity at 455 nm analytical method atλ_exi=388 nm,and its LOD was calculated to be 52μM（3σ/slope）.The fluorescent sensor exhibits excellent selectivity and high sensitivity toward glucose detection.Meanwhile,the proposed sensor was successfully applied to analyze glucose（recovery:97.2-104%,RSD:1.53-3.85%）in human urine samples by the standard addition method.