Chemical Sensors Based On Electrochemiluminescence Imaging

Along with people’s attention on the food safety, environmental protection and clinical diagnosis, developing new analytical apparatuses and methods with high sensitivity, wide versatility and user-friendliness was urgently required. Electrochemiluminescence (ECL), where chemiluminescence (CL) is triggered and controlled by electrochemical reaction, has shown great potential in solving this problem. As a powerful method of detection, ECL possesses the intrinsic advantages of both electrochemistry and CL, including simplicity, high sensitivity, wide dynamic range and good controllability. In addition, ECL can be easily coupled with separation technique such as high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), creating a broader space for fundamental investigations and commercial applications.Recently, ECL imaging has been emerged as a novel technique in the field of ECL. Unlike traditional intensity signals (recorded by a photodiode or photomultiplier (PMT)), ECL imaging can offer visualized images, which is beneficial for rapid characterization of surface structures of electrodes, high-throughput analysis and simultaneous multicomponent assays. Based on the ECL imaging technique, novel methods for biomolecules detection have been reported in this thesis by combined with micro-fabrication techniques and preparation of mesoporous silica materials on electrode surface. This thesis was divided into four parts.In Chapter1, the characteristic and development of ECL imaging were briefly introduced. Then the mechanisms of two main ECL systems, namely Ru(bpy)32+/TPrA and luminol/H2O2, were described. Finally, applications of ECL imaging on the characterization of surface electrochemical activity, development of new ECL systems and analytical chemistry were reviewed.In Chapter2, a flexible ECL imaging biosensor array modified with an enzyme/carbon nanotubes/chitosan composite film was proposed for the determination of glucose, choline and lactate. This biosensor array was fabricated by integrating a patterned indium tin oxide (ITO) glass plate with six perforated poly(dimethylsiloxane)(PDMS) covers. After microliter-sized liquid droplets containing luminol and substrates were loaded into micro-cells, the ECL reaction between enzymatically generated hydrogen peroxide (H2O2) and luminol could be triggered under an appropriate externally applied potential. Multiple optical signals from micro-cells were captured by a charge coupled device (CCD) camera. Good linear relationships between the ECL signal and the concentration of substrates were obtained. From the established calibration curves, the detection limits were0.014mM for glucose,0.040mM for lactate and0.097mM for choline, respectively. Moreover, when different types of oxidases were used to separately modify the electrode surface, simultaneous multicomponent assays could also be achieved. This biosensing platform has the advantages of low cost, low-voltage DC power supply and high throughput, which might have potential applications in clinical diagnostics, medicine and food inspection.In Chapter3, significantly enhanced ECL of Ru(bpy)3+/tri-n-propylamine (TPrA) system at ITO electrodes modified with a thin film consisting of silica mesochannels (SMCs) was demonstrated. The SMCs vertically attached to the ITO electrode surface was prepared via the Stober-solution growth approach. Due to the ultrasmall diameter (namely2-3nm) and the negatively charged surface, SMCs exerted a strong electrostatic attraction to the positively charged Ru(bpy)32+to accelerate its mass transport, resulting in a remarkably increased ECL signal. As a model system, when using TPrA as the co-reactant, the intensity of ECL generated at the SMCs-modified ITO electrode was stronger than that at a bare ITO electrode by more than two orders of magnitude (i.e.,-107-fold increase). Therefore, the amount of Ru(bpy)32+required for ECL-based analysis could be significantly reduced. A concentration of Ru(bpy)3+at9μM was demonstrated to be enough for the sensitive determination of TPrA, nicotine and atropine. Both PMT and CCD were used to measure the luminescence from the ECL reaction with a detection limit at the nanomolar range. This method is simple, economic, and can remarkably enhance the ECL intesity as well as spare the usage of Ru(bpy)32+, thus facilitating the sensitivity and reducing the analytical cost of ECL-based detection.In Chapter4, the work presented in this thesis was summarized. An attempt was also made to propose the future research trend of ECL imaging.