Metal Nanoparticles Involved Chemiluminescence And Their Applications In Liquid Chromatography Detector

In this dissertation, the state of arts in the field of chemiluminescence (CL), the properties and characterization methods of metal nano-materials and their applications in CL were reviewed. Although the theory and the application of CL have been investigated for many years, the study of CL was limited to molecular and ion systems. Recently, metal nanoparticle-involved CL became one of the most attractive developments in these fields, in which metal nanoparticles can participate in CL reactions as catalyst, reductant, naonosized platform and energy acceptor. However, most of the reported nanoparticles-involved CL systems were not of high quantum yield for many applications in analysis. The design of new nanoparticles-involved CL were valuable not only to gain a better understanding the properties of metal nanoparticles and the fundamental studies of CL but also to extend the analytical applications of CL. Meanwhile, the investigation of nanoparticle-controlled CL system has been rarely reported. Therefore, in the present dissertation, the pH-dependent catalysis of Pd-Ag nanoparticles and adsorbate-enhanced reducibility of Ag nanoparticles were employed to design new CL systems. The CL behaviors, rules and mechanisms of these new CL systems were investigated. Moreover, a novel method for simultaneous determination of monoamine neurotransmitters and their metabolites was developed by coupling high-performance liquid chromatography (HPLC) with nanoparticles-involved CL. The main results are as follows:1. Pd-Ag colloid was synthesized by chemical reduction method in a solution. The morphology, chemical composition and structure of the Pd-Ag nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction patterns (XRD). It was found that the acidic Pd-Ag colloid could react with luminol to produce an unusual chemiluminescence, which could be reversibly switchable by modulating the pH of Pd-Ag colloid. When the Pd-Ag colloid was in acidic conditions, the CL was "on"; when the Pd-Ag colloid was in neutral and basic conditions, the CL was "off. Moreover, after the CL reaction, the CL emission could be regenerated by the acidification of the reacted mixture and the repetitious injection of luminol. The CL mechanism was investigated by CL spectra, UV-visible spectra, the effect of N2 and O2 on the CL reaction, and the oxidation reaction between acidic Pd-Ag colloid and 2,2'-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid). It is proposed that acidic Pd-Ag colloid reacted with the dissolved oxygen to yield Pd hydroperoxide, a key intermediate, which oxidized luminol under Ag catalysis to produce light emission. Because H+is necessary for the formation of Pd hydroperoxide, the luminol CL emission could be controlled by the pH of Pd-Ag colloid. pH-switchable chemiluminescence was successfully obtained for the first time by using simple Pd-Ag nanoparticles without coating any smart polymers or functional molecules. Pd-Ag nanoparticles as catalysts in the aerobic oxidation of luminol are very stable and could be reused for at least 30 cycles without obvious losing in their virgin catalytic activity, which is also a promising catalyst for the aerobic oxidation of other organic compounds.2. In the presence of adsorbates (Br-) and Cu2+, Ag nanoparticles could initiate luminol CL. To yield the CL emission, the luminol must be the last reagent added into the system. UV-visible absorption spectra showed that silver nanoparticles in the presence of NaBr could react with CUSO4 before injection of luminol. The X-ray diffraction patterns and X-ray photoelectron spectra demonstrated that Cu (â… ) complex was a key reaction product in AgNPs-NaBr-CUSO4 system. Besides, it was also found that superoxide dismutase could inhibit the CL, revealing that a superoxide anion was involved in the CL reaction. On this basis, it was suggested that the luminol CL induced by silver nanoparticles in the presence of NaBr and Cu2+derived from Cu(I) complex formed via the reduction of CuSO4 by AgNPs by the aid of NaBr, which reacted with the dissolved oxygen to generate the superoxide anion; then the superoxide anion reacted with luminol to produce CL. Br- as an adsorbate was considered to decrease the oxidation potential of silver nanoparticles so that Cu(II) is readily reduced to Cu(I) and to bind to Cu(I) preventing Cu(I) from dismutation in water. As expected, other adsorbates such as Cl-, I-and thiosulfate, which were also efficient to decrease the oxidation potential of AgNPs and bind to Cu (I), could also induce the luminol CL.3. Based on the luminol-AgNO3-Au colloid CL system, a novel method for simultaneous determination of monoamine neurotransmitters and their metabolites was developed by coupling high-performance liquid chromatography with nanoparticle-involved CL reaction. Our previous work showed that gold nanoparticles could trigger chemiluminescence (CL) between luminol and AgNO3. In the present work, the effect of some biologically important reductive compounds, including monoamine neurotransmitters and their metabolites, reductive amino acids, ascorbic acid, uric acid, and glutathione, on the novel CL reaction were investigated for analytical purpose. It was found that all of them could inhibit the CL from the luminol-AgNO3-Au colloid system. Among them, monoamine neurotransmitters and their metabolites exhibited strong inhibition effect. Taking dopamine as a model compound, the CL mechanism was studied by measuring absorption spectra during the CL reaction and the reaction kinetics via stopped-flow technique. The CL inhibition mechanism is proposed to be due to that these tested compounds competed with luminol for AgNO3 to inhibit the formation of luminal radicals and to accelerate deposition of Ag atoms on surface of gold nanoparticles, leading to a decrease in CL intensity. Based on the inhibited CL, a novel method for simultaneous determination of monoamine neurotransmitters and their metabolites was developed by coupling high-performance liquid chromatography with this CL reaction. The new method was successfully applied to determine the compounds in a mouse brain microdialysate. Compared with the reported HPLC-CL methods, the proposed method is simple, fast, and could simultaneously determine catcholamine and indoleamine and their metabolites.4. The electrochemiluminescent (ECL) behavior of luminol on a carbon nanotube (CNT)-modified glass carbon electrode (GCE) during cathodic scanning was investigated. Compared with a bare glass carbon electrode, the CNT-modified GCE promoted a positive shift in ECL potential and an increase in the ECL signal. The effects of CNTs concentration, luminol concentration, and pH on the cathodic ECL of luminol were studied, and the possible cathodic ECL mechanism was proposed. CNTs could catalyze electronic reduction of dissolved oxygen to produce HO2-, which reacted with luminol to give ECL signal.