| This thesis focuses on the sensitization of electrochemiluminescence by nanoparticles and related development of flow-injection analysis system with electrochemiluminescent detection. It consists of the following sections.1 Sensitization of Electrochemiluminescence by Nanoparticles（1） Sensitization of Luminol’s ECL by Pt-Au Bimetallic Nanoparticles Modified ElectrodeThe platinum-gold bimetallic nanoparticles with different component ratio and size were prepared by chemical reduction. The methods such as UV-Vis spectra, TEM and XRD were applied to characterize the properties of the nanoparticles. The information from these methods revealed that the prepared bimetallic nanoparticles were truly of alloy structure and absolutely not the mixture of two kinds of metallic nanoparticles. The component of the nanoparticles could be regulated for a series of Pt/Au ratio and the diameter of nanoparticles, which were determined by Laser-granulometer, could be regulated from 4.03-92.33nm by the method or controlled condition. In alkaline medium of pH=12.0, the bimetallic Pt-Au nanoparticle modified electrode, which was modified on a Pt disk electrode by electrodeposition, sensitized the electrochemiluminescence of luminol. With the variation in the composition and size of the bimetallic nanoparticles, the sensitization efficiency varied as well, with a highest at a Pt/Au ratio of 6:1 and diameter of 4.03nm, at which the electrochemiluminescence intensity was an order of magnitude better than that obtained from unmodified electrode.The atom distribution in the cell of Pt-Au bimetallic nanoparticles was studied. Then found that the crystalline structure is face--centered cubic. A cell contains 10 Pt atoms and 4 Au atoms, The 4 Au atoms hold the 4 corners that are in the two diagonals, and they substitute Pt atoms in two steps. The paper also studied the interaction between bimetallic Pt-Au nanoparticle and luminol. Adsorption occurred between them, and energy transfers from one to the other, thereby Pt-Au bimetallic nanoparticles enhance the intensity of luminol. There are two reasons for sensitization for electrochemiluminescence of luminol from Platinum-Gold bimetallic nanoparticles modified electrode. One is as nanoparticle, the Pt-Au bimetallic nanoparticle has catalysis such as size effect, surface effect and etc. It prolongs the interaction time of OH. and luminol-.,thereby enhances the intensity of luminol. The other reason is when Pt and Au were alloyed; the d band cavity in Pt was increased. The cavity became the adsorption of radicals in the solution. So the electrode surface adsorped more OH. and Luminol-. , thereby enhances the intensity of luminol.（2） Sensitization of Luminol ECL by Metallic Oxide Nanoparticles on Pt ElectrodeIn this work, the sensitization of luminol electrochemiluminescence by metallic oxide nanoparticles, as ZnO, MnO2 and TiO2, under alkaline condition was reported and the related mechanism was studied. It was found that all three types of nanoparticles exhibited similar enhancement toward the electrochemiluminescence reaction. Furthermore a sol-gel method was taken for the immobilization of the metallic oxide nanoparticles onto platinum electrodes. The so-obtained modified electrodes also showed enhanced electrochemiluminescence and better signal/noise ratio, and the stability of the signal was improved as well. Luminol together with the nanoparticles were directly immobilized onto the electrode surface and the performance of the sensors greatly improved. Also good linear response was obtained toward hydrogen peroxide. It was found that the developed modified ECL electrodes provided responses to H2O2. For the TiO2 modified one, a linear response was obtained with the range 1.0×10-71.0×10-5mol/L. This could be used to measure the concentration of H2O2 and the detection limit was low to 1×10-8mol/L. This ECL electrode was applied to test the antioxidant capacity of grapes. The result was that the antioxidant capacity of the grape seed was much better than grape meat. Cyclic voltammetry and UV-visible absorption methods were taken for the study of the mechanism. It was proposed that the nanoparticles could enhance the production of reactive oxygen species, as well as the adsorption of luminescent reagent on nanoparticle surface. These two factors could give an enhancement on the electrochemiluminescent reaction.（3） Sensitization of Luminol ECL by ITO Nanoparticle on ITO ElectrodeNanosized ITO particles were prepared from In2O3 and SnO2 with an amount ratio at 9:1. A series of In2O3 nanoparticles at different sizes were synthesized by microemulsion, sol-gel or azeotropic distillation methods, and characterized by a transmission electron microscope （TEM）. In alkaline solution of pH12.5, the influence of In2O3 nanoparticles on the ECL of luminol was studied. The results showed that the ECL intensity of luminol was enhanced obviously in the presence of In2O3 nanoparticles. The sensitization efficiency was related to the content and the size of In2O3 nanoparticles. The paper also discussed the mechanism of the sensitization by UV-Vis spectra and fluorescence spectra.Nanosized SnO2 were synthesized by sol-gel methods and characterized by a transmission electron microscope （TEM）. The result showed that the average particle sizes of nanosized SnO2 was about 10nm.In the chemiluminescence system of luminol-O2,the CL intensity of luminol was enhanced obviously in the presence of nanosized SnO2.This sensitization efficiency was related to the content of nanosized SnO2 and the dissolved oxygen. Based on this, it was educed that the CL intensity of luminol was linear with the content of the dissolved oxygen in the presence of nanosized SnO2.This linear relationship could be used to determine the dissolved oxygen and the detection limit was 0.3mg/L. The paper also discussed the mechanism of the sensitization by UV-Vis spectrum and fluorescence spectrum.ITO nanoparticles with diameter around 10nm were prepared and the highest enhancement of luminol ECL was obtained with ITO content of 0.3mg/mL. When the nanosized ITO was immobilized to the surface of the Pt electrode by using the method of sol-gel, the ECL intensity of luminol is obviously enhanced. The work studied three different ways of sol-gel becoming film（dried by infrared radiation、dried in oven and drying naturally） to immobilize the nanosized ITO to the electrode and the effect to the enhancement of the ECL intensity .The research showed that when the sol-gel became film naturally, the ECL of luminol on the surface of nano ITO modified electrode is strong, the light emission is enhanced about four times and the electrode can be used for about five days. Through experiments we found that the milder the condition the better the film will be, so when the humidity is 60%, the temperature is under 30℃and drying the sol-gel for one night the film is the best .2 The ECL Behavior and Mechanism of Luminol on ITO Electrode（1）The ECL behavior of reactive oxygen species（ROS） on ITO electrode in the alkaline solution was studied. The results showed that when ITO glass as working electrode,the ECL observed was produced by reactive oxygen species in the alkaline solution.The possible mechanism was given: under the pulse voltage, ITO nanoparticles on the surface of ITO glass were excited to a level of energy and the redox reactions of OH-,O2 and H2O2 occurred producing ROS. Meanwhile ITO nanoparticles at a level of energy adsorbed ROS and translated the energy to them so that the active oxygen molecules could reach the state of excited and the light was relieved when they returned to the ground state.（2）The ECL mechanism of luminol on ITO electrode in the alkaline solution was studied. The results indicated that the phenomenon that the ECL of luminol on the ITO electrode could occur under the lower voltage was mainly related to the interaction between luminol molecules and ITO nanoparticles. Luminol molecules could adsorb onto the surface of ITO nanoparticles and it was possible that energy transferred during this process. Under the lower voltage, ITO nanoparticles were excited to a level of energy and when luminol molecules on the surface of ITO electrode were oxidized to a transitional state and the energy was translated from ITO nanoparticles to the middle state luminol. So the luminol molecules could reach the state of excited and the light was relieved when they returned to the ground state.（3） The indium tin oxide （ITO） glass was applied as the electrode to study the electrochemical polymerization and electrochemiluminescent behavior of luminol on its surface. The experimental results had indicated that the luminol could be polymerized on the surface of ITO glass in acidic solution. The cyclic voltammetry and UV-Vis spectrometry were applied to confirm the polymerization of luminol. The polymerized luminol on ITO electrode kept the ECL property and some important effecting factors had been investigated. The influence of I-, S2- and H2O2 on the ECL of polymerized luminol on ITO electrode in alkaline medium has been studied. The iodide could be sensitively determined in the select conditions. The ECL intensity responded linearly to the concentration of iodide within the range from 1.0×10-6mol/L to 8.0×10-6mol/L（r=0.9896）, of S2- within the range from 8.0×10-7mol/L to 1.0×10-5mol/L（r=0.9903） and of H2O2 within the range from 8.0×10-6mol/L to 6.0×10-5mol/L（r=0.9939）.（4） The nanosized TiO2 particles were further modified onto ITO electrode and their performance towards the enhancement of luminol ECL was investigated. Nafion was adopted as the support and homogenously adsorbed onto ITO surface, which provided a good platform for large amount of modification. After calcination under 650°C, nafion was removed and TiO2 particles were tightly held on ITO electrode surface. At the same time, the crystalline of ITO changed into a mixture of anatase and rutile with ratio of 43.64-56.36, which gave the highest sensitization of luminol ECL. The ECL intensity of luminol was enhanced 7.5 times on this electrode compared with the bare ITO glass electrode. The aggregation has been avoided effectively because TiO2 was modified previously and than send to be calcined, so the mixed crystal was obtained while the size of the particles was controlled. A group of seven mixed crystal TiO2/ITO electrodes were used to the detection of ECL and the RSD was 1.88%. One electrode has been used for the detection of ECL for 7 days and the damping is 5.88%. The result shows that this kind of electrode has good stability and reproducibility.3 Development of Flow-injection Analysis Electrochemiluminescent System（1） A self-designed flow-injection analysis electrochemiluminescent （FIA-ECL） system was fabricated. The ECL analysis is a new method with high sensitivity and has the wider application on many special fields. But there is lack of high quality special instrument for research or practice of this method in our country. A specimen was designed and fabricated, which colligated the advantages of sensitivity of ECL analysis, the practicability of flow-injection and the connection feasibility of optical fiber transmission. It has been designed as a computer embedded one with facility of operation and powerful datum processing function. The work studied the effect of flux to the intensity of the ECL, when the flow was 10mL/h there will be a strongest light emission in the FIA-ECL system.（2） In order to get over disadvantages of existing electrochemiluminescent （ECL） cell, a novel micro-electrochemiluminescent （μ-ECL） cell based on flow injection was designed and fabricated. Made of indium tin oxide （ITO） and PDMS, it had solved the problems well and provided hardware for further study. The cell has many advantages and innovations. In this paper, the ECL behavior of luminol on the ITO glass based on the flow cell was studied. The influences of main effect factors on the cell were studied and optimized. The performance and application of the cell were improved after optimization of main effect factors and structure of the cell. Application of the cell to real samples was studied on anti-oxygen ability evaluation of fruits. The ECL intensity of detection cell decreased linearly with the concentration of red grape. The anti-oxygen ability of red grape seed was stronger than red grape flesh, which showed the practical applicability of developed ECL detection cell. The cell has good reproducibility in real sample determination. Its design and function have satisfied the ECL analysis. It also can couple with other technologies, such as HPLC and CE et al. It has a great potential for further application in the real research and analysis. |
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