Studies On The Electrochemiluminescence Of Luminol Excited By A Novel Bi-potentiostatic Mode

Electrochemiluminescence(ECL) has been regarded as a powerful and promising analytical technique in recent years due to its remarkable merits including high sensitivity,simplicity, rapidity, controllability, low background noise and wide dynamic range. It has been widely applied in immunoassay, trace detection and clinical diagnosis etc. The ECL performance is mainly depended on the applied potential including the form, amplitude and period etc. Presently, it is conventionally initiated using cyclic voltammetry(CV) or pulsed potential. However, some shortcomings of these excited modes impede the further improvement of sensitivity and stability. Our previous studies have revealed that the reactive oxygen species(ROSs) played an important role in the intensification of luminol’s ECL. Those electrogenerated ROSs will transform to their supreme exciton, singlet oxygen(1O2), via the Harber-Weiss reaction. Thereafter, 1O2 transfers the energy to the intermediate of luminol to enhance its ECL. Based on this finding, a novel bi-potentiostatic mode to excite the ECL of luminol has been established in this paper. Compared to current excited modes, a stronger and constant ECL intensity can be obtained. Then, as to expand its practical application, we have constructed a new designed luminol-based ECL cell by bi-potentiostatic excitation for flow injection analysis(FIA) and further improved its analytical performance by means of synchronous dual nano-functionalization of two working electrodes with titania nanotubes(Ti NTs) and platinum black(PB).Major innovative research results are as follows:1. A novel luminol-based bi-potentiostatic ECL system has been established. In this system, different electrolytic potentials were exerted on two indium tin oxide(ITO) glass working electrodes respectively with a dual-potentiostat, one is in charge of yielding enough ROSs under low potential and another boosts the oxidative intermediate of luminol under high potential. Compared with current electrolytic potential excited modes such as CV or pulsed mode, more ROSs and the oxidative intermediate of luminol were generated in the vicinity of the working electrodes during the ECL process and then stronger andconstant ECL emission can be obtained through energy transfer between those active species. The mechanism of intensified ECL of luminol in bi-potentiostatic mode in this system was also discussed clearly. After optimizing the experimental conditions, it was demonstrated that the developed ECL system showed excellent sensitivity and stability and provided great potency for quantified assay.2. A new designed FIA system with an ECL detector has been fabricated, and a novel luminol-based ECL flow cell by bi-potentiostatic excitation is a key component of the device. This flow cell has a small size of about 2 ?L, with a thickness of 100 ?m, and an almost zeroed dead volume. Additionally, our design is easy assembly and convenient to replace working electrode. Four electrodes were fixed firmly in this flow cell, a piece of ITO coated glass works as the first working electrode, and a little platinum net works as the second working electrode. Two potentials were exerted on two working electrodes with a dual-potentiostat. Thus, a continuous and constant ECL emission could be obtained rather than other exciting modes. After optimizing the experimental conditions such as applied potentials on two working electrodes, distance between two working electrodes, flow rate etc, the proposed system showed excellent characteristics such as high sensitivity and stability. It works well in assays as shown for the successful quantitation of H2O2 or resveratrol. The detection limits are 7.4×10-11 mol L-1 for H2O2 and 8.8?10-8 mol L-1 for resveratrol respectively. The practicability of the proposed system was successfully evaluated by to use it in the determination of the gross activity of antioxidants in peanut using resveratrol as the index. The results suggested good recoveries within the range from88.8 to 109.1%. Compared with the referential method, there was only the relative error less than ±4.8%.3. A substantial improvement of the ECL of luminol which is widely used in FIA has been described. It is based on synchronous dual sensitization of ECL by using Ti NTs and PB. A piece of ITO glass functionalized with Ti NTs acts as the first working electrode, and a PB-modified platinum plate serves as the second one. By applying two constant potentials to the two working electrodes, strong and consecutive ECL emission of luminol is obtained. The multiplicative effect of ECL enhancement means the synergic action between two working electrodes. After optimizing the experimental conditions, the system works well in assays as shown for the successful quantitation of H2O2, of the antioxidant resveratrol, and of the neutrotransmitter dopamine(DA) in spiked human serum samples.The detection limits for these three species(at a signal-to-noise ratio of 3) are as low as6.6×10-11 mol L-1(H2O2), 2.2 ? 10-8 mol L-1(resveratrol), and 3.0 ? 10-8 mol L-1(DA).Recoveries in assays of DA in spiked serum range from 97.3 to 105.4%. The results suggest that the present method is one of the most sensitive methods among those reported ones. In our perception, the technique of dual sensitization represents a substantial improvement of the detection limits of ECL assays.