Reaction-Based Electrochemiluminescent Sensors for Selective Detection of Biochemical and Environmental Targets

Abstract

Electrogenerated chemiluminescence (ECL) is a luminescent process which generates light through sequential electron transfer reactons on the electrode surface. ECL-based molecular sensors have several advantages over the conventional analytical techniques such as high sensitivity and low background signal. Additionally, the ECL provides the possibility of potential point-of-care-testing and field-monitoring with the simplicity of equipment and the method. However, ECL detection of small molecules is still a great challenge because most of ECL detection methods have been developed via specific biomacromolecular recognition such as antibody-antigen and aptamer-protein interactions. Herein, we report ECL molecular sensors for qualitative and quantitative detection of biologically important and environmentally toxic molecules.In the first part, a chemodosimetric approach will be introduced for one-step analysis of Hcy levels based on the ECL. A rationally designed cyclometalated iridium(III) complex possessing a phenylisoquinoline main ligand underwent a selective ring-formation reaction with Hcy to generate a binding adduct, which produced highly luminescent excited states, and yielded strong ECL signals on the surface of an electrode. The level of Hcy was successfully monitored by the ECL increment with a linear correlation between 0–40 µM in 99.9% aqueous media. The approach required neither sample preparation nor bulky instrument, suggesting the point-of-care testing of Hcy levels, and is potentially useful for routine, cost-effective, and precautionary diagnosis of various cardiovascular diseases. ECL sensors for other biologically important analytes (pyrophosphate, hydrogen sulfide, cysteine, H2O2) and environmentally toxic molecules (thiophenol, glyphosate, Hg(II)) will also be presented.In the second part, we report a totally different approach to discriminate a target among various interferences. This is called potential-dependent electrochemiluminescence. The iridium complex having a dicyanovinyl group on the main ligand cannot perfectly distinguish cyanide from sulfide and cysteine because not only cyanide but also sulfide and cysteine can attack the beta position of the dicyanovinyl group to increase the PL intensity. However, cyanide adduct is electrochemically oxidized at much less positive potential (~ 1.0 V) than those of sulfide and cysteine adducts, and this enables the discrimination of cyanide via ECL approach. This method enables complete removal of the interfering signals from sulfide and other thiols by controlling the potential range (0 – 1.4 V).