Electrogenerated Chemiluminescence from Heteroleptic Iridium(III) Complexes with Multicolor Emission

Electrochemiluminescence bioassay with anti-fouling ability for determination of matrix metalloproteinase 9 secreted from living cells under external stimulation

An electrochemiluminescence (ECL) bioassay with high sensitivity and anti-fouling ability was developed for determination of matrix metalloproteinase 9 (MMP-9) secreted from living cells under external stimulation. A peptide with sequence of CLGRMGLPGK and a new cyclometalated iridium(III) complex bearing carboxyl group, (pq)2Ir(dcbpy) (pq = 2-phenylquinoline, dcbpy = 2,2'-bipyridyl-4,4'-dicarboxyli acid, abbreviated as Ir) were employed as molecular recognition substrate and ECL emitter, respectively. The peptide was labelled with the Ir to form Ir-peptide as ECL probe. Ir-peptide was self-assembled onto Nafion and gold nanoparticles (AuNPs) modified glassy carbon electrode (AuNPs/Nafion/GCE) and then both of 6-mercapto-1-hexanol (MCH) and zwitterionic peptide as blocking reagents were co-assembled on Ir-peptide/AuNPs/Nafion/GCE to form an anti-fouling ECL peptide-based biosensor. MMP-9 can be quantified in the range 1.0-50 ng·mL-1 with a detection limit of 0.50 ng·mL-1 based on the decreased ECL intensity. Relative standard derivation was 2.3% for six fabricated anti-fouling ECL peptide-based biosensors after reaction with 50 ng·mL-1 MMP-9. The anti-fouling ECL peptide-based biosensor can be used to monitor MMP-9 secreted from living cells under external stimulation. 96.0%-108.0% of recoveries were obtained in 60-diluted cell culture media. This study demonstrates that the ECL biosensor by the combination of iridium(III) complex-based sensitive ECL method and the anti-fouling interface provides a promising way for the determination of MMP-9 in biological sample, which is viable in clinical diagnosis and point-of-care test of protease.

Recent advances and challenges in developing electrochemiluminescence biosensors for health analysis

This Feature Article simply introduces principles and mechanisms of electrochemiluminescence (ECL) biosensors for the determination of biomarkers and highlights recent advances of ECL biosensors on key aspects including new ECL reagents and materials, new biological recognition elements, and emerging construction biointerfacial strategies with illustrative examples and a critical eye on pitfalls and discusses challenges and perspectives of ECL biosensors for health analysis.

The design and synthesis of green emissive iridium(III) complexes guided by calculations of the vibrationally-resolved emission spectra

A key challenge in developing emissive materials for organic light-emitting diodes is to optimize their colour saturation, which means targeting narrowband emitters. In this combined theoretical and experimental study, we investigate the use of heavy atoms in the form of trimethylsilyl groups as a tool to reduce the intensity of the vibrations in the 2-phenylpyridinato ligands of emissive iridium(III) complexes that contribute to the vibrationally coupled modes that broaden the emission profile. An underutilised computational technique, Frank-Condon vibrationally coupled electronic spectral modelling, was used to identify the key vibrational modes that contribute to the broadening of the emission spectra in known benchmark green-emitting iridium(III) complexes. Based on these results, a family of eight new green-emitting iridium complexes containing trimethylsilyl groups substituted at different positions of the cyclometalating ligands has been prepared to explore the impact that these substituents have on reducing the intensity of the vibrations and the resulting reduction in the contribution of vibrationally coupled emission modes to the shape of the emission spectra. We have demonstrated that locating a trimethylsilyl group at the N4 or N5 position of the 2-phenylpyridine ligand damps the vibrational modes of the iridium complex and provides a modest narrowing of the emission spectrum of 8-9 nm (or 350 cm^-1). The strong correlation between experimental and calculated emission spectra highlights the utility of this computational method to understand how the vibrational modes contribute to the profile of the emission spectra in phosphorescent iridium(III) emitters.

In Vitro and In Vivo Antitumor Assay of Mitochondrially Targeted Fluorescent Half-Sandwich Iridium(III) Pyridine Complexes

Half-sandwich iridium(III) complexes show potential value in the anticancer field. However, complexes with favorable luminescence performance are rare, which limits further investigation of the anticancer mechanism. In this paper, 10 triphenylamine-modified fluorescent half-sandwich iridium(III) pyridine complexes {[(η⁵-Cp^x)Ir(L)Cl₂]} (Ir1-Ir10) were prepared and showed potential antiproliferative activity, effectively inhibiting the migration of A549 cells. Ir6, showing the best activity among these complexes, exhibited excellent fluorescence performance (absolute fluorescence quantum yield of 15.17%) in solution. Laser confocal detection showed that Ir6 followed an energy-dependent cellular uptake mechanism, specifically accumulating in mitochondria (Pearson co-localization coefficient of 0.95). A Western blot assay further confirmed the existence of a mitochondrial apoptotic channel. Additionally, Ir6 could arrest the cell cycle at the G₂/M phase, catalyze NADH oxidation, reduce the mitochondrial membrane potential, induce an increase in the level of intracellular reactive oxygen species, and exhibit a mechanism of oxidation. An in vivo antitumor assay confirmed that Ir6 can effectively inhibit tumor growth and is safer than cisplatin.

G-quadruplex-selective iridium(III) complex as a novel electrochemiluminescence probe for switch-on assay of double-stranded DNA

In this work, we synthesized an iridium(III) complex and studied its selective ability to interact with a specific G-quadruplex DNA sequence (GTGGGTAGGGCGGGTTGG). Results showed that the iridium(III) complex exhibits high selectivity for the G-quadruplex DNA and could be used as an efficient electrochemiluminescence (ECL) probe in a switch-on assay format for the detection of double-stranded DNA (dsDNA). To construct the assay, a hairpin-structured capture probe (CP) which was modified by thiol at its 3' end and contained the G-quadruplex sequence at its 5' end was firstly immobilized on a gold electrode. Upon the specific recognition of the dsDNA sequence with the corresponding CP, the hairpin structure of the CP was opened to free G-quadruplex sequence, forming the G-quadruplex structure with the assistance of K⁺. Then, the iridium(III) complex was able to specifically interact with the G-quadruplex to produce an obvious ECL signal that was proportional to the dsDNA concentration. Notably, this iridium(III) complex/G-quadruplex-based strategy was universal and was not limited to the analysis of DNA using specific sequences, thus opening a new avenue for the application of the G-quadruplex-selective iridium(III) complex in the field of ECL.

Ultrasensitive Nucleic Acid Assay Based on Cyclometalated Iridium(III) Complex with High Electrochemiluminescence Efficiency

This work developed a sensitive electrochemiluminescence (ECL) biosensor based on a cyclometalated iridium(III) complex ((bt)₂Irbza), which was synthesized for the first time. Annihilation, reductive-oxidative, and oxidative-reductive ECL behaviors of (bt)₂Irbza were investigated, respectively. The oxidative-reductive ECL intensity was the strongest compared with the other two, which showed 16.7 times relative ECL efficiency compared with commercial [Ru(bpy)₃]²⁺ under the same experimental conditions. Therefore, an ECL biosensing system with (bt)₂Irbza as the anodic luminophore was established for miRNA detection based on a closed bipolar electrode (BPE). Combined with both steric hindrance and catalytic effects induced by hemin/G-quadruplex in the cathodic reservoir of BPE that changed the Faraday current of the cathode and thus mediated the ECL intensity of (bt)₂Irbza in the anode of BPE, the ECL sensor stated an ultrahigh sensitivity for microRNA (miRNA-122) analysis with a detection limit of 82 aM.

An Efficient Probe of Cyclometallated Phosphorescent Iridium Complex for Selective Detection of Cyanide

A cyclometallated phosphorescent iridium-based probe to detect CN^- was prepared through a cyanide alcoholize reaction based on the C^N type main ligand and N^N type ancillary ligand (2-phenyl pyridine and 1,10-phenanthroline-5-carboxaldehyde, respectively). The efficient probe exhibited good sensitivity in response to CN^- in an CH₃CN and H₂O (95/5) mixture within a 1.23 μM detection limit. The response of PL is directly in line with the concentration of CN^- from 0 to 2.0 equiv. The PL investigation of other reactive anions proved the great selectivity to CN^-. Additionally, upon adding 1.0 equiv. of cyanide, the formation of cyanohydrin was correctly elucidated in ¹H NMR, FT-IR, and mass spectra studies. The conspicuous results indicate that the iridium complex has the potential possibility of application in other biosystems related to CN^-.

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

Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(iii) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for ligand binding assays necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]+ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(iii) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(iii) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.

Rapid "turn-on" photoluminescence detection of bisulfite in wines and living cells with a formyl bearing bis-cyclometalated Ir(iii) complex

A new photoluminescence (PL) probe based on a formyl bearing bis-cyclometalated Ir(iii) complex, [Ir(ppy)2phen-CHO]+PF6- (1), is synthesized and applied to the selective detection of a bisulfite anion (HSO3-). Probe 1 is prepared using 2-phenylpyridine (ppy) as the C^N main ligand and 1,10-phenanthroline-5-carboxaldehyde (phen-CHO) as the N^N ancillary ligand. Probe 1 displayed excellent selective PL enhancement in response to HSO3- in acetic acid-sodium acetate buffer solution (pH = 5.0). The increase of PL signal is directly proportional to the concentration of HSO3- in the range of 2 μM to 45 μM with a detection limit of 0.9 μM using 50 μM probe 1 and in the range of 0.5 μM to 6 μM with a detection limit of 0.3 μM using 10 μM probe 1. More importantly, probe 1 can respond to HSO3- rapidly within 40 s. Furthermore, probe 1 was successfully applied to detect HSO3- in real white wines and the bioimaging of HSO3- in living cells. The superior properties of probe 1 make it of great potential use for studying the effects of HSO3- in other biosystems.

Iridium(iii) complex-based electrochemiluminescent probe for H2S

(Azmb-ppy)₂Ir(acac) showed high “turn-off” ECL response for H₂S.

Recent advances in electrogenerated chemiluminescence biosensing methods for pharmaceuticals

Electrogenerated chemiluminescence (electrochemiluminescence, ECL) generates species at electrode surfaces, which undergoes electron-transfer reactions and forms excited states to emit light. It has become a very powerful analytical technique and has been widely used in such as clinical testing, biowarfare agent detection, and pharmaceutical analysis. This review focuses on the current trends of molecular recognition-based biosensing methods for pharmaceutical analysis since 2010. It introduces a background of ECL and presents the recent ECL developments in ECL immunoassay (ECLIA), immunosensors, enzyme-based biosensors, aptamer-based biosensors, and molecularly imprinted polymers (MIP)-based sensors. At last, the future perspective for these analytical methods is briefly discussed.

Bidirectional Electrochemiluminescence Color Switch: An Application in Detecting Multimarkers of Prostate Cancer

A selective excitation of [Ir(df-ppy)₂(pic)] and [Ru(bpy)₃]²⁺ through tuning the electrode potential is reported in this work. Bidirectional color change from blue-green to red could be observed along with increase and decrease of the potential, which was ascribed to the dual-potential excitation property of [Ir(df-ppy)₂(pic)]. Similar to the three-electrode system, selective excitation of ECL could be achieved at the anode of the bipolar electrode (BPE). Both increase and decrease of the faradic reactions at the cathode of the BPE could induce ECL reporting color at the other pole switched from blue-green to red. We applied a closed BPE device for the bioanalysis of multicolor ECL since the organic solvent containing electrochemiluminophores could be separated from the bioanalytes. On the basis of BPE arrays coupled with the ECL switch, the detection of three biomarkers of prostate cancer, PSA, microRNA-141, and sarcosine were integrated in a same device. The cutoff values of the biomarkers could be recognized directly by the naked eye. Such a device holds great potential in the early diagnosis of prostate cancer.

The amplified electrochemiluminescence response signal promoted by the Ir(iii)-containing polymer complex

A novel Ir(iii)-containing polymer complex can emit an apparently enhanced ECL signal using TPrA as a co-reactant in CH₃CN solution due to the effective intramolecular metal–ligand charge transfer (MLCT) from the Ir(iii)-complex centre to the polymer backbone.

Protein staining agents from low toxic platinum(ii) complexes with bidentate ligands

Low toxic platinum(ii) complexes with bidentate ligands have been developed as novel protein staining agents.

Highly efficient electrochemiluminescence labels comprising iridium(iii) complexes

Highly efficient iridium ECL labels exhibiting various emission colors have been developed. Importantly, BSA labeled with the novel iridium labels displays much more intense ECL than the same amount labeled by a traditional ruthenium label in ProCell buffer solution.

Electrochemiluminescent chemodosimetric probes for sulfide based on cyclometalated Ir(iii) complexes

We developed highly sensitive and selective electrochemiluminescent chemodosimetric probes for sulfide.

Cyclometalated iridium(III) chelates-a new exceptional class of the electrochemiluminescent luminophores

Recent development of the phosphorescent cyclometalated iridium(III) chelates has enabled, due to their advantageous electrochemical and photo-physical properties, important breakthroughs in many photonic applications. This particular class of 5d(6) ion complexes has attracted increasing interest because of their potential application in electroluminescence devices with a nearly 100 % internal quantum efficiency for the conversion of electric energy to photons. Similar to electroluminescence, the cyclometalated iridium(III) chelates have been successfully applied in the electricity-to-light conversion by means of the electrochemiluminescence (ECL) processes. The already reported ECL systems utilizing the title compounds exhibit extremely large ECL efficiencies that allow one to envisage many potential application for them, especially in further development of ECL-based analytical techniques. This review, based on recently published papers, focuses on the ECL properties of this very exciting class of organometallic luminophores. The reported work, describing results from fundamental as well as application-oriented investigations, will be surveyed and briefly discussed. Graphical abstract Depending on the chemical nature of the cyclometalated irdium(III) chelate different colours of the emitted light can be produced during electrochemical excitation.

Synthesis of Ir(III) complexes with Tp(Me2) and acac ligands and their reactivity with electrophiles

The reaction of the bis(ethylene) complex [Tp(Me2)Ir(C2H4)2] () (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate) with an excess of 2,4-pentanedione (acetylacetone, Hacac) at 70 °C produced a mixture of the Ir(iii) complex [Tp(Me2)Ir(acac)(C2H5)] () as a major product (67% yield) and two other side complexes [Tp(Me2)Ir(acac)(H)] () and [Tp(Me2)Ir(C9H14O2)] () in 20 and 13% yields, respectively. According to the proposed reaction mechanism and DFT calculations, complexes and are generated from an 18e(-) intermediate [Tp(Me2)Ir(C2H4)(acac)(C2H3)] () which undergoes either hydrogen insertion or β-hydride elimination followed by the subsequent loss of a molecule of ethylene. The lowest yielding complex which features a 2-iridafuran is presumably generated from an unusual thermal coupling between one vinylic and one acac moiety. The availability of the acidic α-proton of the acac ligand was tested by the treatment of complex with Br2 and Cu(NO3)2 rendering the substitution complexes [Tp(3-Br,Me2)Ir(3-Br-acac)Br] () and [Tp(Me2)Ir(3-NO2-acac)(C2H5)] () in good yields. The series of heteroleptic iridium(iii) compounds display air and moisture stability and have been characterized by NMR, IR, and elemental analyses, and, in the case of , and , by single-crystal X-ray diffraction analyses.

Heteroleptic iridium(iii) complexes bearing a coumarin moiety: an experimental and theoretical investigation

Three mononuclear heteroleptic Ir(iii) complexes have been synthesized. The electronic structure and the spectral properties of the complexes were calculated applying the DFT-TDDFT method. The chemical shift was also computed by the GIAO-DFT method.