Highly efficient electrochemiluminescence labels comprising iridium(iii) complexes

Abstract

Improving the performance of labeling agents is crucial to the further development of electrochemiluminescence (ECL) related technologies. Although a large number of ECL luminophores beyond ruthenium complexes have been reported so far, there is still a scarcity of studies involving novel ECL labeling agents. Herein, five novel iridium ECL labels and one control label comprising a ruthenium complex have been rationally designed and thoroughly characterized using photophysical techniques, theoretical calculations and electrochemical characterization to assess the ECL properties in this work. Both in coreactant-assisted potential scan experiments and through an annihilation approach, most of these novel iridium labels exhibit equivalent or even-stronger ECL signals than tri-2,2'-bipyridylruthenium(ii) [abbreviated as Ru(bpy)] under the same experimental conditions. Most importantly, using the same labeling protocol, bovine serum albumin (BSA) labeled with an iridium label (label 3 in this work) exhibits a much more intense ECL signal (1.9 times) than the same amount labeled with a traditional ruthenium complex (Ru-based Label in this work) in ProCell buffer solution. In addition to the advantage of exhibiting various emission colors, the novel iridium labels reported in this work may offer insight for the further development of ECL-based analytical technology.

Iridium(III)‐Doped Core‐Shell Silica Nanoparticles: Near‐IR Electrogenerated Chemiluminescence in Water

“…However, examples of transition metal complexes which are able to give ECL in this emission region have been scarce until very recently . In addition, while many neutral Ir(III) complexes are known to be ECL active in nonaqueous environment, often with an external efficiency much higher than Ru(bpy) 3 2+ ; their very low solubility in aqueous media and high sensitivity to oxygen have so far limited their potential use in chemo‐/bio‐analytical applications.…”

“…[33] However, examples of transition metal complexes which are able to give ECL in this emission region have been scarce until very recently. [34] In addition, while many neutral Ir(III) complexes are known to be ECL active in nonaqueous environment, often with an external efficiency much higher than Ru(bpy) 3 …”

A conceptual framework for the development of iridium(iii) complex-based electrogenerated chemiluminescence labels

“…5 as the [Ru(bpy) 3 ] 2+ complex, even though they were not evaluated under bead-based assay conditions that would limit the ECL pathway to that depicted in Scheme 1b. Examples include Ir(pq) 2 (acac) ( λ em = 609 nm, E 0 ′ = 0.57 V and –2.05 V vs. Fc +/0 ),40 Ir(pph) 2 (pic) ( λ em = 649 nm, E 0 ′ = 0.61 V and –1.94 V vs. Fc +/0 ),16 and [Ir(dmpq) 2 (mbpy-COOH)] + ( λ em = 590 nm, E 0 ′ = 0.78 V and –1.66 V vs. Fc +/0 ),19 where dmpq = 2-(3,5-dimethylphenyl)quinoline.…”

“…2d). 15,18,19 However, this appears to limit the range of electrochemical potentials, emission wavelengths and ECL intensities of the complexes.…”

Water-Soluble Iridium(III) Complexes Containing Tetraethylene-Glycol-Derivatized Bipyridine Ligands for Electrogenerated Chemiluminescence Detection

“…Nevertheless, very few of the iridium(III) complexes examined as ECL luminophores to date are soluble in the aqueous conditions in which most ECL assays are performed (Fernandez-Hernandez et al, 2016;Zhou et al, 2017). As previously reported, the solubility can be improved by incorporating polar functional groups such as sulfonates (Kiran et al, 2009;Jia et al, 2012) or saccharides (Li et al, 2011a,b) on one or more ligands of the complex.…”