New Electrochemiluminescence Strageties For Bioanalysis

Electrochemiluminescence(ECL)is a luminescence process resulting from the relaxation of electronically excited products to the ground state after an electrochemical reaction overall combining an electrochemical initiation step and an optical readout.The technology has the advantages of high sensitivity and strong controllability,and thus,it could be applied to build sensors for bioanalysis and clinic test according to different luminophores and biological components.Considering the optical readout in ECL,an important development of this technique is its implementation for parallel measurement of samples,or observation of electrochemical and/or biological events at the regions of interest(ROI)with high spatial and temporal resolutions.The current challenging for ECL imaging is to obtrain enhanced luminescence intensity for higher spatial and temporal resolution.In this dissertation,new electrochemiluminescence strageties on the electrode artitecture and luminescence probes are developed to enhance ECL for higher detection sensitivity in bioanalysis.The main work is as following:1.Localized Electrochemiluminescence from Nanoneedle Electrodes for Very-High-Density Electrochemical SensingIn the second chapter,localized electrochemiluminescence(ECL)was visualized from nanoneedle electrodes that achieved very-high-density electrochemical sensing.The localized luminescence at the nanometer-sized tip observed was ascribed to enhanced mass transfer of the luminescence probe at the tip than on the planar surface surrounding the tip,which provided higher luminescence at the tip.The size of the luminescence spots was restricted to 15 ?m permitting the electrochemical analysis with a density over 4 ×103 spots/mm2.The positive correlation between the luminescence intensity at the tips and the concentration of hydrogen peroxide supported the quantitative ECL analysis using nanoneedle electrodes.The further modification of glucose oxidase at the electrode surface conceptually demonstrated that the concentration of glucose ranging from 0.5 to 5mM could be quantified using the luminescence at the tips,which could be further applied for the detection of multiple molecules in the complex biosystem.This successful localized ECL offers a specific strategy for the development of very-high-density electrochemical arrays without the complicated chip design.2.Enhanced Electrochemiluminescence from Cyclometalated Iridium(?) ComplexesAggregation-induced emission has been extensively found in organic compounds and metal complexes,however,aggregation-induced electrochemiluminescence(AI-ECL)is rarely observed.In the third chapter,we employ tridentate ligands[2,2':6',2"-terpyridine(tpy)and 1,3-bis(1Hbenzimidazol-2-yl)benzene(bbbiH3)]to construct a cyclometalated iridium-(?)complex,[Ir(tpy)(bbbi)](1),showing strong AI-ECL.Its crystal structure indicates that neighboring[Ir(tpy)(bbbi)]molecules are connected through both ?-?-stacking interactions and hydrogen bonds,which can facilitate the self-assembly of complex 1 into nanoparticles in an aqueous solution.The efficient restriction of molecular vibration in these nanoparticles leads to strong AI-ECL emission of complex 1.In a dimethyl sulfoxide-water mixture,complex 1 showed a?3 9-fold increase in the ECL intensity when the H2O fraction increases from 20%to 98%.This highest intensity from complex 1 was?4 times as high as that of[Ru(bpy)3]2+ under the same experimental conditions.Moreover,the binding of bovine serum albumin to the nanoparticles of complex 1 can improve the ECL emission of this complex,demonstrating the feasibility of AI-ECL for bioanalysis.3.Confined Electrochemiluminescence in Vertically Ordered SilicaMesochannels for the Imaging of Hydrogen Peroxide released from Single CellsECL imaging of single cells is significant to invesitigate the distribution and trafficking of molecules.However,the lateral diffusion of the intermediate in ECL process results in the challenging for the accurate measurement of the target molecule at regions of interest(ROIs).To address this challenging,vertically ordered silica mesochannels(SMCs)modified ITO electrode was prepared to map the efflux of hydrogen peroxide from single living cells.These vertically aligned mesochannels at the indium tin oxide(ITO)slides restrict the lateral diffusion of the intermediates generated in the ECL process.Accordingly,the cross-talking of luminescence intensity from the micro-regions nearby is minimized for higher spatial-resolution single-cell ECL imaging.The visualization limit of hydrogen peroxide at SMCs coated ITO electrode was determined to be 5 ?M,providing high sensitivity for the imaging of hydrogen peroxide efflux from cells.Approx.4 fold more luminescence intensity is observed from individual stimulated cells at SMCs coated ITO than that at bare ITO slide slides that suggests a better electrode surface for single cell ECL imaging.4.Impedance electrochemiluminescence(I-ECL)imaging to realize the label-free visualization of antigen at plasma membrane at single cellsIn this chapter,impedance electrochemiluminescence(I-ECL)imaging is firstly established to realize the label-free visualization of antigen at plasma membrane at single cells.This novel strategy utilize the local impedance change upon the binding of antibody and cellular antigen that results in the alternation of potential drop(AV)across the double layer at this region and the corresponding ECL intensity from aqueous luminol and hydrogen peroxide.The relative high frequency of potential modulation at 1.5 kHz is determined to maximize the value of ? V for better discrimination of ECL at the binding region and surrounding area.The relative high frequency of potential modulation at 100 Hz is determined to A detection limit of CEA antigen as low as 1 pg mL-1 is visualized using this I-ECL.The further application of this strategy achieves the imaging of CEA antigen at MCF-7 cells,as well.As compared with the classic ECL immunoassay,no labeling at the recognized antibody is needed that facilitates the detection.The success in this I-ECL will open a new approach for the label-free immunoassay,and be potential for single molecules detection.