Synthesis, Characterizations And Properties Of Functionalized Gold Nanomaterials And Their Applications In Chemiluminescence Sensors

In this dissertation,the state of arts in the field of chemiluminescence(CL) and the synthesis and properties of nano-materials and their applications in the fabrications of sensors were reviewed.Recently,nanoparticle-involved CL became one of the most attractive and valuable aspects in these fields.However,most reports focused on the CL reactions initiated by unmodified nano-materials.There were few reports about the CL systems involved by functionalized nanomaterials.Therefore,the present dissertation was engaged in the synthesis and optical properties of functionalized gold nanomaterials,which were of CL activity or could initiate CL reactions through a controllable way,and their applications in CL sensors.The main results are as follows:1.It was found that chloroauric acid(HAuCl₄) could be directly reduced by luminescent reagent luminol in aqueous solution to form gold nanoparticles(AuNPs) and the size of AuNPs depended on the amount of luminol.The morphology and surface state of as-prepared AuNPs were characterized by transmission electron microscopy,UV-visible spectroscopy,X-ray photoelectron spectroscopy,and thermal gravimetric analysis.All results indicated that residual luminol and its oxidation product 3-aminophthalate(AP^2-) coexisted on the surface of AuNPs through the weak covalent interaction between gold and nitrogen atoms in their amino groups. Subsequently,a luminol-capped gold nanoparticle(lumAuNPs) modified electrode was fabricated via the immobilization of AuNPs on a gold electrode by virtue of cysteine molecules and then immersion in luminol solution.The modified electrode was characterized by cyclic voltammetry,electrochemical impedance spectroscopy and scanning electron microscopy.The as-prepared modified electrode exhibited an electrochemiluminescence(ECL) response in alkaline aqueous solution under a double-step potential.H₂O₂ was found to enhance the ECL intensity.On this basis,an ECL sensor for the detection of H₂O₂ was developed.The method is simple,fast and reagentless.It is applicable for the determination of hydrogen peroxide in the range of 3×10^-7 mol/L～1×10^-3 mol/L with the detection limit of 1×10^-7 mol/L(S/N=3).2.Fluorescent(FL) and ECL properties of functionalized lumAuNPs synthesized above were investigated.It was observed that the FL intensity of a single gold nanoparticle was 70 times as bright as that of one free APA molecule,even though 91%FL emission of APA molecules on the surface of AuNPs were inhibited by gold cores through both intra- and interparticle quenching effects.Moreover,the photobleaching of surface-bound APA molecules was found to be dramatically inhibited compared with that of free ones in carbonate buffer.The improvement of photostability was attributed to the reactive AuNPs which acted as radical scavengers to protect the surface-bound APA molecules from oxidation by carbonate radicals. Furthermore,as-prepared lumAuNPs could react with cysteine to produce strong ECL, which was enhanced by 20 fold compared with that in the absence of cysteine.The experimental results suggested that luminol and cysteine were co-adsorbed on the gold nanoparticle platform via Au-N and Au-S interactions,respectively.The shorter distance between reactant molecules by overcoming the electrostatic repulsion,i.e., platform effect,was proposed to be responsible for the ECL enhancement.Combined with the biocompatibility of gold cores,the brighter FL emission,enhanced photostability and stronger ECL intensity may make as-prepared lumAuNPs promising FL and ECL biomarkers for their applications in biosensors and bio-imaging.3.By reducing HAuCl₄ with CL reagent luminol in the presence of hydrophilic polymer chitosan,three-dimensional(3-D) flower-like gold nanostructures(AuNFs) were synthesized via a convenient one-pot method.As-prepared stable and monodisperse AuNFs were consisted of smaller-sized nanodots according to subsequent characterizations by high-resolution transmission electron microscopy, scanning electron microscopy and powder X-ray diffraction.The size and morphology of AuNFs could be tailored by varying the amount of luminol or chitosan,which further influenced their SPR properties in both visible and near-infrared regions. Based on the characterizations,a chitosan-assisted second-growth mechanism was proposed to explain their formations and morphology evolutions with the amount of reactants.Moreover,an electromagnetic simulation method,discrete dipole approximation,was introduced to calculate the morphology-dependent extinction spectra of geometrically irregular AuNFs.The simulations were well consistent with the experimental results.Finally,because luminol was attached on the surface of AuNFs,as-prepared AuNFs could react with H₂O₂ to generate CL.The functionalized AuNFs were immobilized on the solid supports by virtue of the film-forming property of chitosan solution to fabricate a reagent-free CL sensor for the determination of H₂O₂.Due to their shape-dependent SPR properties and specific surface structures, these AuNFs might also have great potential for the applications in biosensors and surface enhanced Raman scattering.4.A facile method is proposed for the room-temperature synthesis of flower-like AuNFs with the size of 50～115nm by reducing HAuCl₄ with ascorbic acid(AA) in the presence of chitosan.It was found that the concentration of chitosan controlled the size,while that of AA influenced the morphology of as-prepared AuNFs.With higher concentration of AA,flower-like nanostructures were produced,whereas,with lower concentration of AA,quasi-spherical nanoparticles were formed.Time-dependent surface plasmon resonance(SPR) absorption spectroscopy and resonance Rayleigh scattering(RRS) technique were used to monitor the growth processes.According to the temporal evolutions of SPR maximum absorption wavelength and RRS intensity,a second-growth mechanism is proposed to explain the effect of AA concentration on the morphology and the effect of chitosan concentration on the size of obtained gold nanostructures.In order to determine whether or not the present method is suitable for the synthesis of flower-like gold nanostructures by use of other reductants in the presence of chitosan,four other conventional reductants,including gallic acid,oxalate acid,tartaric acid and sodium citrate,instead of AA were examined.The intrinsic reason for the different performances of these reductants was further investigated,and the results also supported the proposed second-growth mechanism.5.It was found that the catalytic activity of aptamer-functionalized AuNPs could be improved after the target-binding to surface-bound aptamers in the presence of specific targets.When AuNP-catalyzed CL reaction between luminol and AgNO₃ was used as an indicator,the change in the catalytic activity of AuNPs induced by specific target could be quantitatively investigated by CL intensity.By taking anti-K⁺ aptamer as a model system,the proposed homogeneous method could determine K⁺ ion with the concentration as low as 0.7 mM in the presence of high concentration Na⁺,Mg²⁺ and Ca²⁺ ions.Moreover,unmodified aptamers were used in the present strategy to avoid complex and expensive terminal modifications of aptamers.6.The curves of ECL intensity(I_ECL) versus potential(E)(I_ECL-E curves) were obtained when the ECL of luminol was induced by cyclic voltammetry(CV).In the I_ECL-E curves,if there was an ECL peak during initial scan,a corresponding ECL peak called as a counter-peak was usually observed around the similar potential during the reversal scan.In the present work,a couple of strong and well-resolved ECL peaks were found in a model luminol ECL system.The effects of various factors on this couple of ECL peaks,including electrolyte,buffer solution,electrode material,pH, N₂/O₂/air atmosphere,scan rate,and electrochemical technique,were studied.On this basis,a continuous electron transfer coupled with a competitive chemical reaction (E-E/C) mechanism involved in an accumulation and consumption model has been proposed for the formation of the ECL counter peak.Electrochemical digital simulation method was used to simulate the formation of the ECL counter-peak according to the proposed E-E/C mechanism.The results also supported the mechanism.Subsequently,it was further validated that ECL peak width,reversal potential and coexisted electro-active species were three important factors affecting the emergence and intensity of the ECL counter-peak.The proposed E-E/C mechanism is considered to be the general explanation of usual counter-peak phenomenon in the luminol ECL under CV conditions since the mechanism is involved in most pathways of the luminol ECL.