Polyethyleneimine Assisted Synthesis Of Fluorescent Gold/Silver Nanomaterials And Their Applications

Fluorescent noble metal nanomaterials, in particular, fluorescent gold and silvernanomaterials because of their unique optical properties and excellent biocompatibility havereceived intensively attention in many fields, including chemosensing, bioimaging andbiomedicine. Their optical properties are closely relative to the shape, size, atom density andsurface ligand of nanomaterials, which are widely investigated in materials engineering,chemo/bio sensing and biomedical imaging. Synthesizing fluorescent gold and silvernanomaterials with fast and simple methods gather researcher’s interests. Polyethyleneimine(PEI) is a kind of polyamine polymer, and it can stabilize metal ions well. This thesis focusedon the synthesis, properties and application investigations of fluorescent gold and silvernanomaterials based on the stabilizing power of PEI, and summarized as follows:(1) In chapter2, we synthesized blue emissive gold nanoclusters by etching PEIstabilized nanometer sized gold nanoparticles with the assistance of hydrogen peroxide. Wecharacterized these gold nanoclusters with UV-visible spectra, fluorescence spectra and massspectra, and ascertained that these nanoclusters consist of eight gold atoms (Au8). Furtherexperiments indicate the synthesis of Au8could be affected by several factors, such astemperature, amount of hydrogen peroxide and amount of PEI. We constructed a turn-offsensor with these Au8, which is highly sensitive and selective towards Fe3+.(2) In chapter3, we synthesized gold nanoclusters with the assistance of thiolates, andenhanced the yield the nanoclusters. Blue emissive Au8can be prepared with use of seventypes of thiolates, indicating the good universality of this method. We constructed a proteinsensing array with these Au8on the basis of fingerprinting technique, and we tested sixdifferent proteins.(3) With use the method described in chapter3, when introduce11-mercaptoundecanoicacid into the system, blue emissive Au8and red emissive Au(I)-MUA complexesnanoparticles appeared simultaneously. These two components can be completely separatedwith centrifugation under acid condition. The yields of these two components were related tothe concentration of PEI: under high concentration, only red component appeared; whileunder low concentration, both of them appeared and Au8had a high yield. PEI can quench thefluorescence of Au, thus decease the pH of solution would weak the interaction between PEIand Au8, resulting in the increase of fluorescence intensity. Based on this property, weconstructed a ratiometric fluorescent pH sensor. This pH sensor would emit purplish lightunder high pH condition, and emit blue light under low pH condition. (4) Au(I)-thiolate complexes also show fluorescent properties because of theAu(I)…Au(I) aurophilic interactions. These Au(I)-thiolate complexes have long lifetime andlarge Stokes shift. However, because of the existence of inter-and inter-molecular aurophilicinteractions, most Au(I)-thiolate complexes are insoluble or not stable in aqueous solution.We synthesized strongly red emissive and water soluble Au(I)-MUA complexes with one-pot,two steps method under high PEI concentration condition (chapter5). Gold atom can reactwith cyanide and form a stable AuI(CN)－2coordinates, based on this, we constructed aturn-off cyanide sensor with red emissive Au(I)-MUA complexes. This cyanide sensor showshigh sensitivity and distinguishs cyanide from other anions with excellent anti-jammingcapacity.(5) The Au(I)-MUA complexes have been applied in fast photodegradation of organicdyes (chapter6). Other gold nanomaterials have no such a photodegradation ability. Westudied the effect of mixing time and light to photodegradation reaction. According to thespectral variety of dye under light illumination, we confirm that reactive oxygen is producedduring the photodegradation processes. On the basis of photoreaction results of reactiveoxygen indicator and photodegradation results of organic molecule with only UV absorption,we presumed the mechanism and process of the production of reactive oxygen.(6) In chapter7, we synthesized bluish green silver nanoclusters with PEI template,through directly reduce silver ions. We investigated the stability of silver nanoclusers underextreme pH, high ionic strength solution and various temperature conditions. Since copperions can quench the fluorescence of silver nanoclusters, we constructed a turn-off copper ionssensor with PEI stabilized silver nanoclusters. And the quenching mechanism has beenstudied. We also studied the selectivity and sensitivity of this sensor towards copper ions.