The Preparation And Application Of Polydopamine-based Magnetic Nanoparticles

Endocrine disrupting chemicals?EDCs?have been found in environment and the endocrine disruption has become an increasingly important problem nowadays.It is shown that EDCs could interfere with the normal functions of endocrine systems as well as alter the normal growth and reproduction of both humans and wildlife.Widespread use of steroid hormone drugs for the treatment of endocrine disorders during female menopause and infertility could influence the normal level of natural steroid hormones that are vital messenger molecules.The proper level of these steroid sexual hormones in the body determines not only reproductive performance but also normal physiological functions of the organism.Therefore,the determination of the levels of sexual hormones in biological fluids,such as plasma and urine,is very important.Furthermore,with regard to animal husbandry,it's well-known that some natural or anabolic steroids have been forbidden to promote growth and to increase muscle size of animals in both Europe Union and Asia because of their potential toxic and carcinogenic effects on public health.Meanwhile,the estrogenic and progestational chemicals excreted by humans and animals become one of the main sources of steroid hormones in aquatic environments,which may do harm to the normal secretion of endocrine system as well as aggravate the public health hazard.Consequently,sensitive and rapid analytical methods should be developed to accurately monitor the residue content of steroid hormones in edible products and drinking water.So far,there are mainly two categories of methods generally used for the determination of steroids hormones in various samples,including immunoassays as well as chromatographic methods.Although immunoassays are sensitive,the cross reactivity and lot-to-lot variation of antibodies often lead to the decrease of specificity and accuracy of the methods.In comparison with gas chromatographic methodologies,high performance liquid chromatography?HPLC?is widely accepted as a superior technique to monitor steroid hormones in aqueous matrices,which is more rugged and versatile without the need of derivatization step.To achieve higher detection sensitivity,it is crucial to perform rough separation of steroids from complicated matrices through some online or offline sample enrichment?or clean up?steps prior to chromatographic analysis.Magnetic solid-phase extraction?MSPE?,as a kind of sample pretreatment technique,has been widely applied in different areas,exhibiting some obvious advantages,such as easy manipulation,low cost and remarkable enrichment effect.Fe₃O₄ nanoparticles often have a high surface area-to-volume as well as good dispersibility,which help to obtain much greater extraction capacity and higher efficiency.Furthermore,Fe₃O₄ nanoparticles can be easily modified by various materials to achieve selective extraction from complex matrices.During the past few years,numerous studies have been focused on dopamine?DA?because of the formation of polydopmine?PDA?film on almost all types of organic or inorganic substrates,through the self-polymerization of DA in mild and simple reaction conditions.Recently,PDA layer has also been exploited as both the reductant and stabilizer for the synthesis of high dispersion of metallic nanoparticles via the reducibility and metal-binding ability of catechol and nitrogen-containing groups.As one of the mostly widely used metallic nanoparticles,Au NPs possess a variety of excellent physical and chemical properties such as catalysis,long-term stability and easiness in chemical modification,which enables them to be extensively utilized in catalysis chemistry,chemiluminiscence,immunodetection and separation science.In this study,we used polydopamine?PDA?as the binding agent to connect Fe₃O₄ NPs with Au NPs.There are mainly three parts in this dissertation.In chapter 1,the developments of solid-phase extraction,especially magnetic solid-phase extraction,were introduced.Different functionalized magnetic nanoparticle materials used in MSPE and the applications of PDA coating in chromatographic analysis were reviewed.In chapter 2,a simple,facile and sensitive magnetic solid-phase extraction method for the extraction and enrichment of three representative steroid hormones prior to HPLC analysis was developed.Gold modified Fe₃O₄ nanoparticles,as novel magnetic adsorbents,were prepared by a rapid and environmentally friendly procedure in which polydopamine served as the reductant as well as the stabilizer for gold nanoparticles,thus successfully avoiding the use of some toxic reagents.Fe₃O₄@PDA@Au NPs were characterized by transmission electron microscopy?TEM?,X-ray diffraction?XRD?and Zeta potential analysis.To obtain maximum extraction efficiency,several significant factors affecting the preconcentration steps mainly including the amount of adsorbent,extraction time,pH of the sample solution and the desorption conditions,were optimized by a comprehensive study and the enrichment factors for three steroids were all higher than 97.The validity of the established MSPE-HPLC method was evaluated and good analytical characteristics were obtained.Wide linearity range(0.8⁵00?g L^-1 for all the analytes)was attained with good correlation?R²?0.991?.The low LODs were found to be0.20⁰.25?g L^-1 and RSDs ranged from 0.83 to 4.63%,demonstrating the good precision.The proposed method was also successfully applied to the extraction and analysis of steroids in urine,milk and water samples with satisfactory results,which showed its reliability and feasibility in real sample analysis.In chapter 3,in order to deposit more gold nanoparticles on the surface of magnetic nanoparticles,branched polyethyleneimine molecules were utilized to reduce and stabilize Au NPs on the surface of the PDA layer.This preparation process is also simple,mild and environmentally friendly.The synthesized products were characterized by TEM,XRD and magnetic properties test system.The as-formed Fe₃O₄@PDA@PEI@Au NPs have a promising application in chromatographic separation and enrichment.