Magnetic N-doped carbon derived from mixed ligands MOF as effective electrochemiluminescence coreactor for performance enhancement of SARS-CoV-2 immunosensor

COVID-19 as an infectious disease with rapid transmission speed is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), so, early and accurate diagnostics of COVID-19 is quite challenging. In this work, the selective and sensitive self-enhanced ECL method to detect of SARS-CoV-2 protein was designed with magnetic N-doped carbon derived from dual-ligand metal-organic frameworks (MOF) (CoO@N-C) with the primary and tertiary amino groups as a novel coreactant that covalently combined with Ru(bpy)2(phen-NH2)2+ as electrochemiluminescence (ECL) emitter. Mixed-ligand strategy and selected nitrogen-containing ligands, 4,4',4''-((1,3,5-triazine-2,4,6-triyl) tris-(azanediyl)) tribenzoic acid (H3TATAB) with 2-aminoterephthalic acid (BDC-NH2) were used for synthesis of the proposed MOF. Also, magnetic CoO@N-C with high synergistically charge transfer kinetics and good stability can be used as an effective platform/coreactor on the ITO electrode which load more Ru-complex as signal producing compound and SARS-CoV-2 N protein antibody to increase the sensitivity of the immunosensor. Furthermore, (CoO@N-C) as coreactor improved the ECL signal of the Ru (II)-complex more than 2.1 folds compared to tripropylamine. In view of these competences, the novel "on-off" ECL biosensor performed with great stability and repeatability for detection of SARS-CoV-2 protein, which exhibited a broad linearity from 8 fg. mL-1 to 4 ng. mL-1 (6 order of magnitude) and an ultra-low limit of detection 1.6 fg. mL-1. Finally, this proposed method was successfully applied to detect of SARS-CoV-2 N protein in serum sample with satisfactory results, indicating the proposed immunosensor has the potential for quick analysis of SARS-CoV-2.

Electrochemiluminescence sensing of HeLa cells labeled with biotinylated ruthenium complex using bipolar electrode based on microwell modified optical fiber

Biotinylated ruthenium complexes exhibit improved photoluminescent (PL) properties when they bind with streptavidin, making them useful labels or probes in bio-related analysis. However, their ECL properties are still unknown to date. Herein, we reported the use of [Ru(bpy)2(biot-bpy)]2+ complexes as a new ECL luminophore, which was functionalized with biotin moiety and exhibited higher ECL efficiency after binding to streptavidin. Moreover, [Ru(bpy)2(biot-bpy)]2+ complexes could be attached to HeLa cells through the biotin-streptavidin binding. A microwell bipolar electrode (MBE) prepared at one end of an optical fiber bundle was applied to produce ECL of the labeled HeLa cells, which was remotely detected at the other end. The [Ru(bpy)2(biot-bpy)]2+-streptavidin binding effect together with the high surface/volume ratio of MBE promoted the ECL generation on HeLa cells, which was applied to sensitively detect HeLa cells with a linear range from 1.56 × 102 to 6.74 × 106 cells/mL and a detection limit of 83 cells/mL. Moreover, ECL images were successfully acquired to resolve the emission on each HeLa cell. Such cytosensor based on [Ru(bpy)2(biot-bpy)]2+ and MBE may extend the applications of ECL for cell detections.

A photoluminescent and electrochemiluminescent probe based on an iridium(III) complex with a boronic acid-functionalised ancillary ligand for the selective detection of mercury(II) ions

Exposure to mercury(II) ions (Hg2+) can cause various diseases such as Minamata disease, acrodynia, Alzheimer's disease, and Hunter-Russell syndrome, and even organ damage. Therefore, real-time and accurate monitoring of Hg2+ in environmental samples is crucial. In this study, we report a photoluminescent (PL) and electrochemiluminescent (ECL) probe based on a cyclometalated Ir(III) complex for the selective detection of Hg2+. The introduction of a reaction site, o-aminomethylphenylboronic acid, on the ancillary ligands allowed a prompt transmetalation reaction to take place between Hg2+ and boronic acid. This reaction resulted in significant decreases of the PL and ECL signals due to the photo-induced electron transfer from the Ir(III) complex to the Hg2+ ions. The probe was applied to the selective detection of Hg2+, and the signal changes revealed a linear correlation with Hg2+ concentrations in the range of 0-10 μM (LOD = 0.72 μM for PL, 8.03 nM for ECL). The designed probe allowed the successful quantification of Hg2+ in tap water samples, which proves its potential for the selective detection of Hg2+ in environmental samples.

Iron Single-Atom Catalyst-Enabled Peroxydisulfate Activation Enhances Cathodic Electrochemiluminescence of Tris(bipyridine)ruthenium(II)

The tris(bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)-tripropylamine anodic electrochemiluminescence (ECL) system has been widely applied in commercial bioanalysis. However, the presence of amine compounds in the biological environment results in unavoidable anodic interference signals, which hinder further extensive use of the system. In contrast, the cathodic Ru(bpy)₃²⁺ ECL system can overcome these limitations. The Ru(bpy)₃²⁺/peroxydisulfate (S₂O₈^2-, PDS) ECL system has been extensively employed due to its ability to produce a sulfate radical anion (SO₄^•-) with strong oxidation ability, which enhances the ECL signal. However, the symmetrical molecular structure of PDS makes it challenging to be activated and causes low luminescence efficiency. To address this issue, we propose an efficient Ru(bpy)₃²⁺-based ternary ECL system that uses the iron-nitrogen-carbon single-atom catalyst (Fe-N-C SAC) as an advanced accelerator. Fe-N-C SAC can efficiently activate PDS into reactive oxygen species at a lower voltage, which significantly boosts the cathodic ECL emission of Ru(bpy)₃²⁺. Benefiting from the outstanding catalytic activity of Fe-N-C SAC, we successfully established an ECL biosensor that detects alkaline phosphatase activity with high sensitivity, demonstrating the feasibility of practical application.

Highly Selective Electrochemiluminescence Chemosensor for Sulfide Enabled by Hierarchical Reactivity

Hydrogen sulfide (H₂S) is a well-known toxic gas with the odor of rotten eggs. Several reaction-based electrochemiluminescence (ECL) chemosensors for H₂S have been developed; however, no homogeneous ECL probe with high selectivity toward H₂S in aqueous media has been reported. Herein, we report an iridium(III) complex-based ECL chemodosimetric probe employing two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) groups known as a photo-induced electron transfer quencher and a reaction site for the selective detection of H₂S; the detection mechanism involves H₂S being clearly distinguished from biothiols based on the different cleavage rates of the two NBD groups and extremely weak ECL interferences caused by reaction by-products. The probe was rationally designed to improve selectivity toward H₂S within the ECL analysis platform by enabling the removal of nonspecific background signals observed via fluorescence analysis. This analytical system exhibited remarkable selectivity toward H₂S, a rapid reaction rate, and high sensitivity (LOD = 57 nM) compared to conventional fluorescence methods. Furthermore, the probe could successfully quantify H₂S in tap water samples and commercial ammonium sulfide solutions, which demonstrates the effectiveness of this probe in field monitoring.

Graphdiyne nanosheet as a novel sensing platform for self-enhanced electrochemiluminescence of MOF enriched ruthenium (II) in the presence of dual co-reactants for detection of tumor marker

Graphdiyne (GDY) is a new two-dimensional carbon material with high charge carrier mobility, excellent conductivity, more suitable band gap, and natural pores was introduced as a new electrochemiluminescent sensing platform. Herein, the metal organic framework (MOFs) used for enrichment of luminophore with grafting Ru(bpy)₂(phen-NH₂)²⁺(Ru-complex) and Ru-complex amine-rich nitrogen-doped carbon nanodots(Ru-NCNDs) via both encapsulating and external decoration and decoration of SmS₂ QDs as coreactant. Then, the MOF enriched Ru-complex (Ru@MOF@NCNDs-Ru@SmS₂ QD) located on a GDY modified ITO electrode developed as a novel and efficient ECL platform. According to the Density Functional Theory (DFT) calculation, the band gap of graphdiyne/Ru(bpy)₂(phen-NH₂)²⁺ system decreased compared to graphdiyne, Ru-complex and also graphene oxide/Ru(bpy)₂(phen-NH₂)²⁺system, which enhanced (2 folds) the signal response of the presented ECL platform. The ECL response signal of the suggested emitter with high ECL efficiency (13.34%) increased 8 and 4 folds compared to GDY/Ru-NCNDs and GDY/Ru@MOF@NCNDs-Ru as platforms, respectively. The proposed ECL platform applied for CA19-9 antigens detection at concentration range 0.0005 UmL^-1 to 200 UmL^-1 and detection limit of 0.00013 UmL^-1.The development of GDY based platform for decorating nano luminophores, not only provides the design of ECL luminophores with high performance but also promises the application of the presented strategy for fabrication of ultrasensitive bio affinity sensors as candidates in clinical monitoring and diseases diagnostics.

Reduced graphene oxide-supported CuO nanoparticles with synergistically enhanced electrocatalytic activity for nitric oxide sensing

This work reports a NO electrochemical sensor based on rGO/CuO composites with excellent electrochemical performance.

Dual Intrareticular Oxidation of Mixed-Ligand Metal-Organic Frameworks for Stepwise Electrochemiluminescence

This work presents a mixed-ligand metal-organic framework (m-MOF) integrated with two ligands, one as a luminophore and the other as a coreactant, on one metal node for self-enhanced electrochemiluminescence (ECL). Both 9,10-di(p-carboxyphenyl)anthracene (DPA) and 1,4-diazabicyclo[2.2.2]octane (D-H₂) ligands can be oxidized, generating the cation radicals DPA^+• and D-H₂^+•, respectively. The latter can be deprotonated to form the neutral radical (D-H^•) and then react with DPA^+• to produce excited DPA* for ECL emission without exogenous coreactants. As a result of the incorporation into the MOF framework and the intrareticular charge transfer between the two ligands, the ECL intensity of the m-MOF was increased 26.5-fold compared with that of the mixture of DPA and D-H₂ in aqueous solution. Moreover, with the process of second oxidation of D-H₂, stepwise ECL emission was observed as a result of local excitation in the DPA unit, which was identified through density functional theory calculations. Overall, the implementation of the mixed-ligand approach, which combines the luminophore and coreactant as linkers in reticular materials, enriches the fundamentals and applications of ECL systems.

An ultrasensitive aptasensor based on self-enhanced Au nanoclusters as highly efficient electrochemiluminescence indicator and multi-site landing DNA walker as signal amplification

Gold nanoclusters (Au NCs) have been shown to be prospective nanoscale electrochemiluminescence (ECL) materials that are being extensively explored in bioanalysis. However, the low ECL efficiency of Au NCs has been a bottleneck barrier for their better bioapplications. To overcome this disadvantage, a low oxidation potential co-reactant N,N-diisopropylethylenediamine (DPEA) was first used to prepare self-enhanced Au NCs (Au-DPEA NCs) for drastically enhancing the ECL efficiency of Au NCs in this study. In addition, an efficient multi-site landing DNA walker with multidirectional motion track and rapid payloads release compared to directional DNA walker was constructed for converting target mucin 1 (MUC1) to intermediate DNA and achieving significant signal amplification. On the basis of the Au-DPEA NCs as efficient ECL signal labels and multi-site landing DNA walker as signal amplification strategy, an ECL aptasensor was established for the ultrasensitive detection of MUC1 in the range from 1 fg mL^-1 to 1 ng mL^-1 with a limit of detection down to 0.54 fg mL^-1. The results demonstrated that the present study opened a new research direction for the development of high-efficiency Au NCs indicator as well as ultrasensitive ECL sensing platform for applications in clinical and bioanalysis.

A highly sensitive luminescent probe based on Ru(II)-bipyridine complex for Cu2+, l-Histidine detection and cellular imaging

A ruthenium(II) bipyridyl complex conjugated with functionalized Schiff base (RuA) has been synthesized and functioned as a luminescent probe. The luminescence of RuA was greatly quenched by Cu²⁺ due to its molecular coordination with paramagnetic Cu²⁺. Subsequently, the addition of l-Histidine can turn on the luminescence of the RuA-Cu(II) ensemble, which can be attributed to the replacement of RuA in RuA-Cu(II) ensemble by l-Histidine. On the basis of the quenching and recovery of the luminescence of RuA, we proposed a rapid and highly sensitive on-off-on luminescent assay for sensing Cu²⁺ and l-Histidine in aqueous solution. Under the optimal conditions, Cu²⁺ and l-Histidine can be detected in the concentration range of 5 nM-9.0 μM and 50 nM-30 μM, respectively, and the corresponding detection limits were calculated to be 0.35 and 0.44 nM (S/N=3), separately. The proposed luminescent probe has been successfully utilized for the analysis of Cu²⁺ and l-Histidine in real samples (drinking water and biological fluids). Furthermore, the probe revealed good photostability, low cytotoxicity and excellent permeability, making it a suitable candidate for cell imaging and labeling in vitro.

Phenoxyaluminum(salophen) Scaffolds: Synthesis, Electrochemical Properties, and Self-Assembly at Surfaces of Multifunctional Systems

Salophens and Salens are Schiff bases generated through the condensation of two equivalents of salicylaldehyde with either 1,2-phenylenediamines or aliphatic diamines, respectively. Both ligands have been extensively exploited as key building blocks in coordination chemistry and catalysis. In particular, their metal complexes have been widely used for various catalytical transformations with high yield and selectivity. Through the modification of the phenol unit it is possible to tune the steric hindrance and electronic properties of Salophen and Salen. The introduction of long aliphatic chains in salicylaldehydes can be used to promote their self-assembly into ordered supramolecular structures on solid surfaces. Herein, we report a novel method towards the facile synthesis of robust and air-stable [Al(Salophen)] derivatives capable of undergoing spontaneous self-assembly at the graphite/solution interface forming highly-ordered nanopatterns. The new synthetic approach relies on the use of [MeAl^III (Salophen)] as a building unit to introduce, via a simple acid/base reaction with functionalized acidic phenol derivatives, selected frameworks integrating multiple functions for efficient surface decoration. STM imaging at the solid/liquid interface made it possible to monitor the formation of ordered supramolecular structures. In addition, the redox properties of the Salophen derivatives functionalized with ferrocene units in solution and on surface were unraveled by cyclic voltammetry. The use of a five-coordinate aluminum alkyl Salophen precursor enables the tailoring of new Salophen molecules capable of undergoing controlled self-assembly on HOPG, and thereby it can be exploited to introduce multiple functionalities with subnanometer precision at surfaces, ultimately forming ordered functional patterns.

Ruthenium bistridentate complexes with non-symmetrical hexahydro-pyrimidopyrimidine ligands: a structural and theoretical investigation of their optical and electrochemical properties

The optical and electronic properties of six Ru complexes with non-symmetrical tridentate ligands have been investigated and, as corroborated by electrochemical data, the presence of the hpp ligand strongly affects the oxidation potential of the metal ion.

Sensitive and selective determination of GSH based on the ECL quenching of Ru(II) 1,10-phenanthroline-5,6-dione complex

Electrochemiluminescence (ECL) material Ru-dpq (Ru(bpy)2dpq(2+), dpq=1,10-phenanthroline-5,6-dione; bpy=2,2'-bipyridine) is found to be produced strong and stable anodic ECL signal, which could be quenched by reduced glutathione (GSH) and exhibits high sensitivity and selectivity simultaneously. According to the mass spectra of Ru-SG (product of Ru-dpq reacted with GSH), and single crystal structure of the final oxidized product Ru-dcbpy ((Ru(bpy)2dcbpy(2+), dcbpy=3,3-dicarboxy-2,2-bipyridine), we propose a new interacted mechanism between Ru-dpq and GSH. A good linear relation is estimated to be from 0.1 pM to 50 μM in the presence of calcium ion and the detection limit is as low as 0.087 pM (with the signal-to-noise ratio of 3). The relative standard deviation is 2.3% (for three repeated measurements). Furthermore, the ECL signal of Ru-dpq under a constant potential (1.2V) is extremely stable and the intensity could be maintained over 600 s, which promotes us to determine the concentration of GSH via chronoamperometry.