Carbon Nanostructure Functionalization For Antibacterial And Sensing Applications

Carbon dots(CDs),as a new class of fluorescent nanomaterial with a size of<10 nm,possess a series of advantages,e.g.,excellent fluorescence stability,outstanding water solubility,low cell toxicity,favorable biocompatibility and tunable excitation and emission,which facilitate their applications in the field of biological chemistry and analytical chemistry.In this dissertation,we will focus on preparation of economical and eco-friendly carbon dots and the surface functionalization for the detection of bacterial with appropriate carbon sources.Meanwhile,carbon dots doped metallic element with the property of antibiosis can be used as antibacterial.The functionalized carbon dots were prepared by control the concentration of carbon source and modifier,which facilitates their application for sterilization and bacteria sensing with high sensitivity and selectivity.Chapter 1 is a brief introduction of the method for detecting bacteria and sterilization,as well as the preparation methods of carbon dots,the physical and chemical features,and the functionalization strategies.In chapter 2,a simple one-step hydrothermal green approach was reported in the present work for the preparation of carbon dots(CDs)without any further decoration or modification with papaya powder as natural carbon source.In this economical and eco-friendly system,deionized water or 90%ethanol was used as solvent to produce CDs,respectively,termed as W-CDs and E-CDs.The derived W-CDs and E-CDs are nitrogen-doped,oxygen-rich with hydroxyl,carboxyl,amine groups,thus exhibit resistance to photobleaching and excellent photoluminescence stability.Both W-CDs and E-CDs exhibit favorable biocompatibility,and demonstrated to be efficient for HeLa cell imaging.The quantum yield(QY)for W-CDs was 18.98%,while that for E-CDs was 18.39%.The potentials of the prepared carbon dots toward diverse applications were thoroughly investigated.W-CDs and E-CDs provide promising probes for fluorescence detection of Fe3+,offering limits of detection of 0.48 ?mol L-1 and 0.29 ?mol L-1,respectively,which facilitates sensitive fluorescent sensing of hemin in serum and capsule samples.In addition,W-CDs was contained saccharides,i.e.,mannose,which tend to exhibit strong interaction with Escherichia coli 0157:H7 and further demonstrated to be a promising probe for fluorescence sensing of Escherichia coli 0157:H7,along with a limit of detection of 9.5×104 cfu mL-1.In chapter 3,Ag doped carbon dots(Ag-CDs)was prepared by using a simple hydrothermal-assisted multi-amino synthesis approach.Ag-CDs nanoparticles exhibits excellent antibacterial performance towards both Escherichia coli(E.coli O157:H7)and Staphylococcus aureus(S.aureus).E.coli O157:H7 or S.aureus is treated with 2 ?g mL-1 of Ag-CDs nanoparticles under 5 min with a killing rate of 100%.Furthermore,Ag-CDs can be used as simultaneous detection of hemoglobin(Hb)and dichromate(Cr2O72-).A linear response in the presence of Cr2O72-of the relative fluorescent intensity in the range of 0.1-6.0(pmol L-1 with a detection limit of 43.7 nmol L'1 was achieved,and the Ag-CDs nanoparticles was also applied to the detection of Cr2O72-in real water samples.Meanwhile,we can distinguish Cr3+and Cr2O72-under UV light and fluorospectrophotometer.As a novel dichromate-sensitive antibacterial,the Ag-CDs nanoparticles hold great promise to broaden application in the environment pollution and water purification.In chapter 4,a dual functional fluorescent core-shell Ag2S@Carbon nanostructure is prepared via a hydrothermal-assisted multi-amino synthesis approach with folic acid(FA),polyethyleneimine(PEI)and mannoses(Mans)as carbon and nitrogen sources(Ag2S@C).The nanostructure exhibits strong fluorescent emission at ?ex/?em=340/450 nm with a quantum yield of 12.57±0.52%.Strong interaction between Mans in Ag2S@C and FimH proteins on the tip of fimbriae in E.coli 0157:H7 enabled the selective attachment of Ag2S@C onto E.coli O157:H7.Fluorescence emission by the Ag2S@C/E.coli conjugate is closely related to the content of E.coli 0157:H7,and a novel procedure for fluorescence detection of E.coli O157:H7 is thus developed,offering a limit of detection of 330 cfu mL-1.Meanwhile,the Ag2S@C nanostructure exhibits excellent antibacterial performance against E.coli O157:H7.A killing rate of 99.9%can be readily achieved for 106-107 cfu mL'1 of E.coli O157:H7 by using 3.3?g mL-1 or 10 ?g mL-1 of Ag2S@C with an interaction time of 5 min or 0.5 min,respectively.The observations reported herein present a new approach for further designing and developing multifunctional nanostructures for specific applications in biological studies.