Research On Fluorescence Spectrometric Property Of Bio-resourced Carbon Quantum Dots And The Efficacy Of Fast Detection Of Water Pollution

17β-estradiol（E2）is a kind of natural steroid estrogen with high biological activity,which is an important endocrine disruptor（EDCs）.Even at low concentration,it can have adverse effects on normal endocrine function of human and animal,so it has attracted extensive attention.Therefore,in order to protect the environment and public health,it is necessary to establish sensitive and rapid estradiol detection methods in natural systems.Metal ions are one of the most persistent environmental pollutants,with long-term,severe toxicity and irreversibility.Excess metal ions will accumulate in the water and accumulate in the organism through the food chain,resulting in serious toxic effects on the organism.Therefore,it is of great significance to realize rapid and accurate detection of heavy metal ions.Carbon quantum dots（CQDs）are a new type of fluorescent nanomaterials with good water dispersion,biocompatibility,excellent photostability,easy synthesis and surface functionalization.A growing number of researchers are optimizing synthesis methods to improve their optical and photoelectrical properties,and are expanding the applications of carbon quantum dots in selective sensing,target-specific biological imaging,environmental remediation,photocatalysis,and drug delivery.Aptamer is an oligonucleotide sequence that can be folded into a precise tertiary conformation and binds to the target molecule with high affinity and high specificity through spatial complementarity.In nanomaterial-based aptamer sensors,aptamers as recognition elements and nanomaterials as signal transduction and amplification media result in significantly improved performance of biosensors,as well as improved sensitivity,selectivity and analysis time.Different from the previous single-path synthesis methods,our work use a combination of‘top-down’and‘bottom-up’methods were used to prepare bagasse biochar derived carbon quantum dots and explore the fluorescence characteristics of carbon quantum dots.The advantage of this method is that the quantum dots have uniform particle size distribution and strong fluorescence emission.Then,the quenching characteristics of 15 heavy metal ions such as Cu²⁺,Co²⁺,Pb²⁺,Cr³⁺,Fe³⁺and Fe²⁺on quantum dots were investigated.The detection effect and quenching mechanism of quantum dots were analyzed.After analyzing the optical properties of quantum dots,aptamer functionalized carbon quantum dots fluorescent probe was successfully constructed using aptamer as recognition element to detect E2.We studied the construction mechanism of the fluorescent probe.At the same time,we also studied the detection selectivity of the method and the detection response to actual environmental water samples.This study will provide theoretical basis and technical support for revealing the detection mechanism of pollutants in water and the highly sensitive and specific detection of trace pollutants based on aptamer modified carbon quantum dot fluorescent probe.We draw the following main conclusions:（1）Fluorescent carbon quantum dots（SBB-CQDs）were prepared by acidification and hydrothermal synthesis method using agricultural waste bagasse biochar as raw material.Combined with transmission electron microscopy and atomic force microscopy analysis,the size of the SBB-CQDs was 2-5 nm.The surface structure of SBB-CQDs was analyzed by FTIR and X-ray photoelectron spectroscopy.It was found that there were carboxyl and hydroxyl groups on the surface.Through a series of optical analysis,it is found that SBB-CQDs has strong fluorescence characteristics,excitation wavelength dependence,photobleaching resistance,good stability and so on.（2）The prepared SBB-CQDs can be used for the detection of a variety of heavy metal ions.The results show that Cu²⁺,Cr³⁺,Co²⁺,Pb²⁺,Fe²⁺,Mn²⁺and Fe³⁺can quench the fluorescence of SBB-CQDs in different degrees when the concentration range is 0-50μM.The quenching effect of SBB-CQDs on heavy metal ions under different p H was studied.It was found that SBB-CQDs has a good quenching effect on heavy metal ions under neutral and weak acid conditions.The fluorescence quenching of SBB-CQDs by heavy metal ions is static quenching.When the concentration of Cu²⁺is in the range of 0.1-2μM,the detection limit is 10.69 n M.（3）Fluorescent probes of aptamer functionalized carbon quantum dots were constructed by chemical bond cross-linking method and used to detect E2.The optimal concentration of SBB-CQDs and E2-Apt was 200μg/m L and 1μM,respectively.The optimal detection temperature of E2 was 25℃and the optimal detection time was 30min.（4）It was found that the fluorescence probe had obvious fluorescence attenuation when E2 concentration was in the range of 0-20 ng/m L,and the detection limit was 0.42ng/m L.In addition,this probe can achieve the specific detection of E2 in the presence of other interferences,and the E2 detection method is reliable by calculating the recovery rate of actual water samples.Therefore,fluorescent biosensors based on aptamer-functionalized biological carbon nanoparticles proved to be a promising method for the detection of environmental pollutants efficiently.