Noble Metal Nanoparticles Involved Chemiluminescence

In this dissertation, the recent developments in the field of chemiluminescence (CL), the preparation and properties of nano-materials, and their applications in CL analysis were reviewed. Though CL has been investigated for many years, study of CL was limited to molecular system. Recently, attentions about CL studies have been paid to nanoparticle systems, in which nanoparticles can participate in CL reactions as catalyst, reductant, luminophor, and energy accepter. Up to date, nanoparticles as catalyst were only used to take the place of catalyst of traditional CL reactions, and only one system in which nanoparticles were used as reductant was reported. In the present work, gold, silver and platinum nanoparticles are utilized as catalyst and reductant to design new CL systems. The behavior, rule, mechanism, and the potential in analytical applications of these new nanopaticles involved CL reactions were invetigated. The main results are as follows:1. Ag colloid was found to enhance intensely the CL from the reaction between luminol and hydrogen peroxide. Ag nanoparticles exhibited the better CL catalytic activity than gold and platinum nanoparticles. The superoxide anion scavenger nitro blue tetrazolium and superoxide dismutase was added to the hydrogen peroxide-Ag colloid and the luminol-hydrogen peroxide-Ag colloid systems, respectively, showing that the decomposition of hydrogen peroxide by catalysis of silver nanoparticles formed superoxide anion and superoxide anion was involved in luminol-hydrogen peroxide-Ag colloid CL reaction. The Ag nanoparticle-enhanced CL was ascribed to that Ag nanoparticles could catalyze the decomposition of H₂O₂ to produce some reactive intermediates such as hydroxyl radical, superoxide anion. Hydroxyl radical reacted with luminol to form luminol radical and diazaquinone, followed by the reaction with superoxide anion or monodissociated hydrogen peroxide, giving rising to light emission. Halide ions (X^- ) were found to quench the CL in the following order: I^- > Br^- > Cl^-, due to the formation of AgX shell on Ag nanoparticles surface which poisoned the Ag catalyst. An obvious turning point was observed in the curve of CL intensity versus iodine ion concentration, which corresponded to the I" concentration needed for mono-layer saturation adsorption on the Ag nanoparticles. A chemical adsorption model for iodine ions on the surface of Ag colloids has been proposed. Among 20 natural amino acids, cysteine, histidine, methionine, tyrosine and tryptophan were found to inhibit the CL due to their adsorption on the Ag nanoparticles and their competitive consumption for the reactive intermediates. The most intense inhibition of cysteine may be of potential for selective determination of cysteine.2. It was found that luminol could react with AgNO₃ in the presence of gold colloid to generate CL at 425 nm. UV-Visible spectra and X-ray photoelectron spectra showed that AgNO₃ was reduced by luminol to Ag that covered on the surface of gold nanoparticles to form Au/Ag core/shell nanoparticles by virtue of the catalysis of gold nanoparticles in the CL reaction. The luminophor was identified by the CL spectrum as 3-aminophthalate. The CL mechanism has been proposed to be due to that luminol radical formed by the oxidation of luminol reacted with the dissolved oxygen. Kinetic curve revealed that the CL reaction was fast and completed in 2 seconds. The catalytic effect of Au/Ag core/shell nanoparticles with various compositions on luminol-AgNO₃ system was also studied. It was found that the formed core/shell nanoparticles could also catalyze this CL reaction, but their catalytic ability was much weaker than that of gold nanoparticles. On this basis, a model for the catalytic process has been proposed that when Au colloid was injected into the mixture of luminol and AgNO₃, AgNO₃ was rapidly reduced by luminol to Ag, accompanying by a strong CL; then, with instant deposition of Ag atoms on the surface of Au particles, the catalytic activity declined, leading to a sharp decrease in CL intensity and a slow growth of core/shell nanoparticles.3. It was found that noble metal nanoparticles including Ag, Au and Pt nanoparticles in the presence of adsorbates such as iodide ion, cysteine, mercaptoacetic acid, mercaptopropionic acid, and thiourea could reduce lucigenin (bis-N-methylacridinium) to produce CL. Lucigenin-Ag-KI system was chosen as a model to study the CL process. Absorption spectra and X-ray photoelectron spectra showed that when Ag colloid was mixed with KI, Ag nanoparticles were covered by adsorbed iodide ions. X-ray diffraction patterns and fluorescence spectra indicated that Ag nanoparticles were oxidized to AgI and lucigenin was converted to N-methylacridone in the CL reaction. According to Nernst's equation, the presence of iodide ions decreased the oxidation potential of Ag nanoparticles. As a result, lucigenin was rapidly reduced by Ag nanoparticle-KI to monocation radical, which reacted with oxygen to generate superoxide anion; then superoxide anion reacted with the monocation radical to produce CL. Other adsorbates such as cysteine, mercaptoacetic acid, mercaptopropionic acid, and thiourea that could decrease the oxidation potential of Ag nanoparticles could also induce the CL reaction.4. The electrogenerated chemiluminescence (ECL) behavior of lucigenin at a glassy carbon electrode in the presence of platinum nanoparticles dispersed in alkaline aqueous solutions was studied under conventional cyclic voltammetry (CV). Two ECL peaks were observed at -0.65 and -2.0 V (vs SCE), respectively. ECL-1 was a conventional ECL peak of lucigenin also observed in the absence of platinum nanoparticles. ECL-2 was a new ECL peak appearing in the hydrogen evolution potential region. It was found that ECL-1 decreased and ECL-2 increased with an increase in the concentration of platinum nanoparticles. The ECL properties under various conditions were studied. It has been proposed that ECL-2 is likely due to that reductive intermediate H_adsPt⁰ formed during the hydrogen evolution process reduced lucigenin cation (Luc²⁺) to mono-cation radial (Luc^·+); Luc^·+ and H_adsPt⁰ reacted with dissolved oxygen to generate O₂^·-, which interacted with Luc^·+ to produce the excited state N-methylacridone (NMA), giving rise to light emission at 495 nm. Pt nanoparticles synthesized in various methods showed different catalysis abilities for ECL-2. Furthermore, palladium particles similar to platinum particles can also catalyze the generation of ECL-2 while gold particles can not.