Preparation Of Gold Clusters And Doped Carbon Dots And Their Applications In Cell Imaging And In Fluorescence Sensing

Nanomaterals have attracted much more attentions due to their novel chemical properties and physical properties such as optical,electrical and magnetic.They have many particular characterizations such as surface effect and quantum size effect and play a unique role in biomedical,electronic devices,sensors,industrial catalysis and other fields.Among them,the fluorescent nanomaterials because of their excellent optical properties,have been the third“eyes”for researcher to study on the fields of biomedicine,sensors and so on.The synthesis of the fluorescent nanomaterials becomes one of the key factors to promote the development of these fields.At present,the fluorescent nanomaterials includ quantum dots,polymer dots,noble metal nanoclusters,fluorescent carbon dots,rare earth upconversion nanomaterials.And owing to their excellent biocompatibility,low toxicity,good fluorescence properties and stability,gold nanoclusters and fluorescent carbon dots receive considerable research interest.In this dissertation,we focus on the synthesis of gold nanoclusters and fluorescent carbon dots and their applications in bioimaging and sensing with the combination of nanotechnology,material science,analytical technology and so on.The main contents are listed below.1.BackgroundThis part describes properties,synthesis methods and application of gold nanoclusters and fluorescent carbon dots in detail and reviews recent study of them in recent years.2.Simple and rapid preparation of orange-yellow fluorescent gold nanoclusters using DL-homocysteine as a reducing/stabilizing reagent and their application in cancer cell imagingA simple,convenient and fast preparation for successful fabrication of water-soluble DL-homocysteine capped Au nanoclusters?Hcy-AuNCs?was demonstrated.This preparation allowed the generation of water-soluble Au NCs within a short time of 15 min.The resulting Hcy-AuNCs were characterized by photoluminescence,UV-Vis absorption,X-ray photoelectron spectroscopy,and transmission electron microscopy?TEM?.The mean diameter of Hcy-Au NCs was found to be 1.6±0.2 nm.The Hcy-AuNCs exhibited an orange-yellow fluorescence emission at 560 nm with a large Stokes shift of 120 nm,a quantum yield of 3.01%and a good stability over the physiologically relevant pH range and ionic strength.Furthermore,cytotoxicity studies showed that the Hcy-AuNCs exhibited negligible effects in altering cell proliferation or triggering apoptosis.Cancer cell imaging of HeLa cell lines indicated that the obtained Hcy-AuNCs could serve as a promising fluorescent bioprobe for bioimaging.This strategy,based on the one-step preparation using DL-homocysteine as a reducing/stabilizing reagent,may offer a novel approach to fabricate otherwater-soluble metal nanoclusters for application in biolabelling and bioimaging3.Preparation of orange-red fluorescent gold nanoclusters using denatured casein as a reductant and stabilizing agent,and their application to imaging of HeLa cells and for the quantitationof mercury?II?We describe a method for the preparation of water-soluble gold nanoclusters?Au NCs?from chloroauric acid using denatured-casein as both a reducing and stabilizing agent.The resulting Au NCs were characterized by photoluminescence,UV–vis absorption,and X-ray photoelectron spectroscopies,and by transmission electron microscopy.The Au NCs have an average diameter of 1.7±0.2 nm and exhibit orange-red fluorescence emission peaking at 600 nm?with a Stokes'shift as large as 237 nm?,a quantum yield of 4.3%,and good stability over the physiologically relevant range of pH values and ionic strength.Cytotoxicity studies showed the the Au NCs displayed negligible effects in terms of altering cell proliferation or triggering apoptosis.Fluorescence imaging of He La cancer cells was accomplished by loading such cells with the Au NCs.The fluorescence of the Au NCs was found to be strongly quenched by Hg?II?ions,and thus the Au NCs could be used for detecting and,possibly,imaging of Hg?II?.4.Green preparation of nitrogen-doped carbon dots?NCDs?from triethanolamine for bioimagingA one-step pyrolysis method for synthesizing nitrogen-doped carbon dots?NCDs?from organic carbon sources is presented in this paper.There is intense blue emission under ultraviolet illumination with a quantum yield of 16.8%and excitation-independent photoluminescence behavior when the NCDs are in aqueous solution.The as-prepared NCDs show good aqueous solubility,small particle sizes,good stability in a wide range of pH values?pH 4–9?,high tolerance of salt concentration,strong resistibility to photobleaching,holding great promise for biological applications.The biocompatibility evaluation and in vitro imaging study reveals that the synthesized NCDs can be used as effective fluorescent probes in bioimaging without noticeable cytotoxicity.These findings suggest that as-prepared NCDs from triethanolamine can find potential applications in cellular imaging.5.Preparation of water-soluble nitrogen and sulfur co-doped carbon dots using casein as a precursor and their applications in cell imaging and fluorescence sensingIn this work,fluorescent nitrogen and sulfur co-doped carbon dots?NSCDs?were synthesized by a one-step pyrolysis strategy using casein as carbon,nitrogen and sulfur sources,and characterized by UVevis spectrum,fluorescent spectrum,X-ray photoelectron spectroscopy?XPS?and FT-IR,etc.The synthesized NSCDs displayed a blue emission under ultraviolet illumination with a quantum yield of 31.8%,and a good aqueous solubility,photostability and biocompatibility.It was found that the fluorescence intensity of NSCDs could be selectively quenched by Hg²⁺,so NSCDs was used as an effective probe for the detection of Hg²⁺.The linear range and the limit of detection?LOD?of the fluorescent sensor based on NSCDs for the detection of Hg²⁺were 0.01-0.25 mM and 6.5nM,respectively.Spiked water samples were detected by the sensor with the recovery of95.4-106.3%and relative standard deviation?RSD?of 3.6-8.6%.It was also observed that the quenched NSCDs-Hg²⁺system could be restored by the addition of biothiols such as L-cysteine?Lcy?,homocysteine?Hcy?and glutathione?GSH?,thus NSCDs-Hg²⁺system was employed as a fluorescent sensor for the detection of biothiols.The linear range and LOD of the NSCDs-Hg²⁺system were 1-10 mM and 23.6 nM for Lcy,0.2-2.5 mM and12.3 nM for Hcy,and 0.1-2.0 m M and 16.8 nM for GSH,respectively.The NSCDs-Hg²⁺system was applied for the detection of biothiols in serum samples with satisfied results.In addition,the study in vitro imaging HeLa cells revealed that the synthesized NSCDs could be used as effective fluorescent probes in cellular imaging without noticeable cytotoxicity.