Study On Some New Materials For Electrochemiluminescence

Electrochemiluminescence （ECL） analysis is a new analytical method, which isdeveloped based on the combination of electrochemisty （EC） withChemiluminescence （CL）. This method has many advantages of electrochemistry andchemiluminescence, such as high sensitivity, high selectivity, low background signal,wide linear response range, and easy control. In this dissertation, studies were focusedon finding new materials （e.g. ionic liquids, quantum dot luminophores, nanomaterialcoreactants） for ECL, revealing possible new ECL mechanisms, and applyingsensitive, selective and environmentally benign ECL systems in chemosensing andbiosensing.This dissertation consists of four parts, or six chapters. Chapter1is also the firstpart. In this chapter, the general introduction, the mechanisms of ECL, the historicalperspective and classificationss of ECL, developing direction of ECL and the pruposeand signification of this disserataion were described based on the investigation ofliteratures in the field of ECL.The second part is chapter2. In this part, the ECL behaviors of Ru（bpy）₃²⁺/TEA in1-butyl-3-methylimidazolium hexafluorophosphate （BMIPF6） ionic liquid wereinvestigated and compared with those in aqueous solution （pH7.0PBS） at a goldelectrode. The electrochemical and ECL behaviors of Ru（bpy）₃²⁺/TEA were muchdifferent with those in aqueous solution. It was found that the Ru（bpy）₃²⁺/TEA systemgave rise to one small and one large peak ECL peak at anodic process and thecatalytic current of Ru（bpy）₃²⁺/TEA system was disappeared in ionic liquid. Theeffects of viscosity and ionic strength of ionic liquid on diffusion coefficients,catalytic efficiency, and ECL intensity were investigated and discussed to reveal theECL mechanism of Ru（bpy）₃²⁺/TEA system in the ionic liquid of BMIPF6.The third part is chapter3. In this part, a simple and effective method for preparingwater-soluble carbon nanocrystals （CNCs） with ECL activity by applying a scanningpotential at graphite rods were reported, and the ECL behaviors of the as-preparedCNCs were observed and studied in detail. The cathodic ECL intensity increased withthe number of potential cycles before reaching a constant value after30cycles. With increasing the electrolysis time, the color of the electrolyte solution changed fromcolorless to yellow and finally dark brown. A colorless CNC solution was obtained byultrafiltering the dark brown solution with10k Da molecular weight cutoff （MWCO）membrane. High-resolution transmission electron microscopy （HRTEM） indicatedthat the obtained CNCs were monodispersed, spherical-shaped particles with averagesize of2.0nm. The maximum PL emission wavelength of CNCs is455nm. Bothanodic and cathodic ECL emission of the CNCs werer observed when the potentialwas cycled between+1.8and-1.5V. Additionally, in the presence of peroxydisulfate（S2O82-）, the ECL intensity of CNCs in the presence of S2O82-was greatly enhanced.The maximum ECL emission wavelength （535nm） was substantially red-shifted fromPL maximum. The ECL emission of CNCs was attributed to the formation of excitedstate CNCs （R*） via electron transfer between negatively charged CNCs （R·-） andpositively charged CNCs （R·+） or SO·-4.The fourth part includes chapters4-6. In this part, some new efficient coreactants ofRu（bpy）₃²⁺were found, and their ECL behaviors and ECL reaction were stuied indetail. In chapter4, O2was found to act as a new coreactant for Ru（bpy）₃²⁺ECL inNafion film, resulting in a strong ECL light emission. ECL experiments were carriedout at a Ru（bpy）₃²⁺/Nafion film-modified glassy carbon electrode （GCE） immersing inair-saturated phosphate buffer solution （pH7.4）. Scanning in the potential range of+1.5to-1.0V resulted in three luminescent processes, including twopotential-dependent luminescence peaks （ECL-1and ECL-2）, and onepotential-independent persistent luminescence emission （CL-P）. Therein, ECL-2occurring at potential less than-0.5V was demonstrated to be a newchemiluminescent reactions between O2and Ru（bpy）₃²⁺. In ECL-2, Nafion film playsimportant roles in stabilizing Ru（bpy）33+and O2-radical essentially for producing thenew ECL. Unlike previously reported ECL processes, ECL-2peak potential wasdependent on the reduction potential of the coreactant （i.e., O2） rather than the redoxpotentials of the luminopore, Ru（bpy）₃²⁺, which would provide a useful way to probeO2, O2-radical, and their stabilities in electrochemical reactions.In chapter5, we found that stannous chloride could significantly enhance theelectrochemiluminescence （ECL） of tris （2,2’-bipyridyl） ruthenium （II）(Ru（bpy）₃²⁺)in aqueous solution. An obvious electrocatalytic oxidation current of Sn²⁺byRu（bpy）₃²⁺was observed. Sn²⁺was the first reported metal ion that could serve as anexcellent ECL coreactant of Ru（bpy）₃²⁺. ECL properties of Sn²⁺were evaluated by comparison with a common ECL coreactant, tripropylamine （TPrA）. TheRu（bpy）₃²⁺-Sn²⁺ECL coreactant system produces stronger and more stable ECLsignals, can keep its excellent ECL activity in a wider pH range and have morechoices in using electrode materials than Ru（bpy）₃²⁺/TPrA ECL coreactant system.Moreover, the coreactant ECL mechanism between Ru（bpy）₃²⁺and Sn²⁺was alsostudied in detail. This study would be very useful for finding and understaning othermetal ion-based coreatants for Ru（bpy）₃²⁺ECL.In chapter6，the SnO nanoparticles deposited multiwall carbon nanotubes （SnONPs@MCNTs） were synthesised in aqueous solution by hydrolyzing Sn²⁺and usingMCNTs as carriers. The XRD pattern and HRTEM images indicated that SnO NPswith an average size of ca.4.0nm were well coated at MWCNTs. In the experiment, aGC electrode was coated with SnONPs@MCNTs composites, and inserted into anECL cell containing Ru（bpy）₃²⁺solution （pH7.4）. A very strong ECL signal wasobserved when the electrode was applied a potential higher than+1.0V. This strongECL signals indicate there is a highly effective electron transfer process between SnOnanoparticles and Ru（bpy）33+. The high ECL sensitivity, easy labeling, convenientassembly at the electrode and low toxicity, suggest promising application of the nanocoreactant-Ru（bpy）₃²⁺system in sening, and electron transfer probing fornanomaterials.