Unusually Strong Electrochemiluminescence from Iridium-Based Redox Polymers Immobilized As Thin Layers or Polymer Nanoparticles

Self-Assembled Tetraphenylethene-Based Nanoaggregates with Tunable Electrochemiluminescence for the Ultrasensitive Detection of E. coli

As an effective ECL emitter, tetraphenylethene (TPE)-based molecules have recently been reported with aggregation-induced electrochemiluminescence (AIECL) property, while it is still a big challenge to control its aggregation states and obtain uniform aggregates with intense ECL emission. In this study, we develop three TPE derivatives carrying a pyridinium group, an alkyl chain, and a quaternary ammonium group via the Menschutkin reaction. The resulting molecules exhibit significantly red-shifted FL and enhanced ECL emissions due to the tunable reduction of the energy gap between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs). More importantly, the amphiphilicity of the as-developed molecules enables their spontaneous self-assembly into well-controlled spherical nanoaggregates, and the ECL intensity of nanoaggregates with 3 -CH2- (named as C3) is 17.0-fold higher compared to that of the original 4-(4-(1,2,2-triphenylvinyl)phenyl)pyridine (TPP) molecule. These cationic nanoaggregates demonstrate a high affinity toward bacteria, and an ECL sensor for the profiling of Escherichia coli (E. coli) was developed with a broad linear range and good selectivity in the presence of an E. coli-specific aptamer. This study provides an effective way to enhance the ECL emission of TPE molecules through their derivatization and a simple way to prepare well-controlled AIECL nanoaggregates for ECL application.

Chiral Ru-Based Covalent Organic Frameworks as An Electrochemiluminescence-Active Platform for the Enantioselective Sensing of Amino Acids

Although several studies related with the electrochemiluminescence (ECL) technique have been reported for chiral discrimination, it still has to face some limitations, namely, complex synthetic pathways and a relatively low recognition efficiency. Herein, this study introduces a facile strategy for the synthesis of ECL-active chiral covalent organic frameworks (COFs) employed as a chiral recognition platform. In this artificial structure, ruthenium(II) coordinated with the dipyridyl unit of the COF and enantiopure cyclohexane-1,2-diamine was harnessed as the ECL-active unit, which gave strong ECL emission in the presence of the coreactant reagent (K2S2O8). When the as-prepared COF was used as a chiral ECL-active platform, clear discrimination was observed in the response of the ECL intensity toward l- and d-enantiomers of amino acids, including tryptophan, leucine, methionine, threonine, and histidine. The biggest ratio of the ECL intensity between different configurations was up to 1.75. More importantly, a good linear relationship between the enantiomeric composition and the ECL intensity was established, which was successfully employed to determine the unknown enantiomeric compositions of the real samples. In brief, we believe that the proposed ECL-based chiral platform provides an important reference for the determination of the configuration and enantiomeric compositions.

Investigating the Impact of Packing and Environmental Factors on the Luminescence of Pt(N^N^N) Chromophores

Four Pt(II)(N^N^N) compounds featuring DMSO coordination at the fourth position were synthesized. Ligands varied in terms of pyridyl central ring (hydrogen/chlorine substituent) and lateral rings (triazoles with CF3 substitution or tetrazoles). Coordination to pyridine yielded tetra-nitrogen coordinated Pt(II) complexes or Pt-functionalized polymers using commercial 4-pyridyl polyvinyl (PV) or dimethylaminopyridine. Luminescence behaviors exhibited remarkable environmental dependence. While some of the molecular compounds (tetrazole derivatives) in solid state displayed quenched luminescence, all the polymers exhibited 3MMLCT emission around 600 nm. Conversely, monomer emission was evident on poly(methyl methacrylate) or polystyrene matrices. DFT calculations were used to analyze the aggregation of the complexes both at the molecular level and coordinated to the PV polymer and their influence on the HOMO-LUMO gaps.

Facile preparation of poly-(styrene-co-maleic anhydride) encapsulated Iridium(III) complexes as highly efficient electrochemiluminescence indicators for sensitive immunoassay of CYFRA 21-1

Exploring facile strategy for developing highly efficient emitters using water-insoluble luminophores has become a vital topic in electrochemiluminescence (ECL) immunoassay. In this work, an ECL-active and water-dispersive iridium(III) complex-based polymer dots (IrPdots) was fabricated by encapsulating water-insoluble tris[1-phenylisoquinolinato-C2, N] iridium(III) complexes [Ir(piq)₃] into poly-(styrene-co-maleic anhydride) (PSMA) matrix by a controllable nanoprecipitation process. The obtained IrPdots generated strong ECL signals in the presence of tri-n-propylamine (TPrA) and were used to label detection antibody (Ab₂) to act as ECL probes to indicate the signal changes when analyzing target antigen. To construct a sandwich immunosensor, Pd nanoparticles (NPs) decorated MoS₂/Ti₃C₂T_x MXene nanocomposites (MoS₂/Ti₃C₂T_x MXene/Pd) were fabricated as substrates to bind capture antibody (Ab₁), which could further amplify ECL signals via a coreaction-accelerating pathway to improve the detection sensitivity. When the cytokeratin 19 fragment 21-1 (CYFRA 21-1) was chosen as model analyte, the developed immunosensor displayed a good linear relationship ranging from 0.1 pg/mL to 50 ng/mL with a low detection limit of 95 fg/mL (S/N = 3) was achieved as well. This research proposed a facile and effective method of fabricating IrPdots as ECL probes for immunoassay using water-insoluble iridium complexes, which expanded the application scope of those water-insoluble luminophores for aqueous bioanalysis.

Au@SiO2 SERS nanotags based lateral flow immunoassay for simultaneous detection of aflatoxin B1 and ochratoxin A

Agricultural products are frequently contaminated by mycotoxins. Multiplex, ultrasensitive, and rapid determination of mycotoxins is still a challenging problem, which is of great significance to food safety and public health. Herein, a surface-enhanced Raman scattering (SERS) based lateral flow immunoassay (LFA) for the simultaneous on-site determination of aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) on the same test line (T line) was developed, in this study. In practice, two kinds of Raman reporters 4-mercaptobenzoic acid (4-MBA), and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) encoded silica-encapsulated gold nanotags (Au^4-MBA@SiO₂ and Au^DNTB@SiO₂) were used as detection markers to identify the two different mycotoxins. Through systematic optimization of the experimental conditions, this biosensor has high sensitivity and multiplexing with the limits of detection (LODs) at 0.24 pg mL^-1 for AFB₁ and 0.37 pg mL^-1 for OTA. These are far below the regulatory limits set by the European Commission, in which the minimum LODs for AFB₁ and OTA are 2.0 and 3.0 μg kg^-1. In the spiked experiment, the food matrix are corn, rice, and wheat, and the mean recoveries of the two mycotoxins ranged from 91.0% ± 6.3%-104.8% ± 5.6% for AFB₁ and 87.0% ± 4.2%-112.0% ± 3.3% for OTA. These results demonstrate that the developed immunoassay has good stability, selectivity, and reliability, which can be used for routine monitoring of mycotoxin contamination.

Determination of nitrite in food based on its sensitizing effect on cathodic electrochemiluminescence of conductive PTH-DPP films

Herein, a novel strategy for electrochemiluminescence (ECL) detection of nitrite based on its sensitization effect on cathode ECL emission of 3,6-di(2-thienyl)-2,5-dihydropyrrolo [3,4-c] pyrrole-1,4-dione (TH-DPP) polymeric films (PTH-DPP) was formulated, by means of a one-step electropolymerization of TH-DPP with a short time on the glassy carbon electrode (GCE). It was shown that the PTH-DPP film-modified GCE exhibited a strong ECL response when S₂O₈^2- was used as a co-reactant. The ECL emission could be greatly enhanced by PTH-DPP with nitrite in a K₂S₂O₈/PBS solution system and occurred at a relatively lower potential in comparison with traditional cathode ECL emitter, leading to high sensitivity and good selectivity. The ECL sensor exhibits excellent linear relationship in the ranges of 0.3 to 100 μM and 100 to 1000 μM for nitrite detection, with an outstanding detection limit of 0.08 μM (S/N = 3). The ECL sensor provides an impressive outcome for the detection of practical samples.

Electrochemiluminescent sensor based on an aggregation-induced emission probe for bioanalytical detection

In recent years, with the rapid development of electrochemiluminescence (ECL) sensors, more luminophores have been designed to achieve high-throughput and reliable analysis. Impressively, after the proposed fantastic concept of "aggregation-induced electrochemiluminescence (AIECL)" by Cola, the application of AIECL emitters provides more abundant choices for the further improvement of ECL sensors. In this review, we briefly report the phenomenon, principle and representative applications of aggregation-induced emission (AIE) and AIECL emitters. Moreover, it is noteworthy that the cases of AIECL sensors for bioanalytical detection are summarized in detail, from 2017 to now. Finally, inspired by the applications of AIECL emitters, relevant prospects and challenges for AIECL sensors are proposed, which is of great significance for exploring more advanced bioanalytical detection technology.

Aggregation-induced delayed fluorescence luminogens: the innovation of purely organic emitters for aqueous electrochemiluminescence

Due to overcoming the limitation of aggregation caused quenching (ACQ) of solid-state emitters, aggregation-induced emission (AIE) organic luminogens have become a promising candidate in aqueous electrochemiluminescence (ECL). However, restricted by the physical nature of fluorescence, current organic AIE luminogen-based ECL (AIECL) faces the bottleneck of low ECL efficiency. Here, we propose to construct de novo aqueous ECL based on aggregation-induced delayed fluorescence (AIDF) luminogens, called AIDF-ECL. Compared with the previous organic AIE luminogens, purely organic AIDF luminogens integrate the superiorities of both AIE and the utilization of dark triplets via thermal-activated spin up-conversion properties, thereby possessing the capability of close-to-unity exciton utilization for ECL. The results show that the ECL characteristics using AIDF luminogens are directly related to their AIDF properties. Compared with an AIECL control sample based on a tetraphenylethylene AIE moiety, the ECL efficiency of our AIDF-ECL model system is improved by 5.4 times, confirming the excellent effectiveness of this innovative strategy.

Aggregation-Induced Emission in Electrochemiluminescence: Advances and Perspectives

The discovery of aggregation-induced electrochemiluminescence (AIECL) in 2017 opened new research paths in the quest for novel, more efficient emitters and platforms for biological and environmental sensing applications. The great abundance of fluorophores presenting aggregation-induced emission in aqueous media renders AIECL a potentially powerful tool for future diagnostics. In the short time following this discovery, many scientists have found the phenomenon interesting, with research findings contributing to advances in the comprehension of the processes involved and in attempts to design new sensing platforms. Herein, we explore these advances and reflect on the future directions to take for the development of sensing devices based on AIECL.

Ultrasensitive Nucleic Acid Assay Based on AIE-Active Polymer Dots with Excellent Electrochemiluminescence Stability

Aggregation-induced emission (AIE) active Pdots are attractive nanomaterials applied in electrochemiluminescence (ECL) fields, while the irreversible redox reaction of these Pdots is a prevailing problem, resulting in instability of ECL emission. Herein, we first designed and synthesized an AIE-active Pdot with reversible redox property, which contains a tetraphenylethene derivate and benzothiadiazole (BT) to achieve stable ECL emission. BT has a good rigid structure with excellent electrochemical behaviors, which is beneficial for avoiding the destruction of the conjugated structure as much as possible during the preparation of Pdots, thus maintaining good redox property. The tetraphenylethene derivate, as a typical AIE-active moiety, provides a channel for highly efficient luminescence in the aggregated states. The Pdots exhibited reversible and quasi-reversible electrochemical behaviors during cathodic and anodic scanning, respectively. The stable annihilation, reductive-oxidative, and oxidative-reductive ECL signals were observed. Subsequently, we constructed an ultrasensitive ECL biosensor based on the oxidative-reductive ECL mode for the detection of miRNA-21 with a detection limit of 32 aM. This work provides some inspiration for the future design of ECL materials featuring AIE-active property and stable ECL emission.

Polymer Electrochemiluminescence Featuring Thermally Activated Delayed Fluorescence

Electrochemiluminescence (ECL) based on conjugated polymers or oligomers is persistently being pursued owing to its huge application scope ranging from ultra-sensitive bioanalysis to ultra-resolution imaging and spectroscopy. Because of the theoretical limit in radiative exciton generation yield (typically ∼25 %) of those polymers or oligomers, the corresponding ECL efficiency is still limited, which hampers its ECL performance and its related applications. Herein, we report ECL based on a thermally activated delayed fluorescence (TADF) polymer scaffold, which is characteristic of all-exciton harvesting in the ECL process, and thus potentially capable of achieving ∼100 % ECL efficiency. These desired properties of the TADF polymer ECL is attributed to a fast and efficient up-conversion process from non-radiative triplet to radiative singlet states under thermal activation, which is absent in conventional fluorescent polymers/oligomers, such as F8BT. In this study, various ECL modes, including annihilation or co-reactant mode using TPrA or S₂ O₈ ^2- as co-reactant, are confirmed for our model TADF polymer ECL system, which was different from fluorescent polymer ECL counterpart. Furthermore, solid-state ECL sensing on L-cysteine (an important marker of disease) is also evaluated by using the model TADF polymer. Ultralow detection limit in combination with high sensitivity and good specificity are achieved for this model system, indicative of a high potential of the TADF polymer scaffold for applications in the broad field of ECL.

Linear-Organic-Polymer-Supported Iridium Complex as a Recyclable Auto-Tandem Catalyst for the Synthesis of Quinazolinones via Selective Hydration/Acceptorless Dehydrogenative Coupling from o-Aminobenzonitriles

A linear-organic-polymer-supported iridium complex Cp*Ir@P4VP, which is designed and synthesized by the coordinative immobilization of [Cp*IrCl₂]₂ on poly(4-vinylpyridine), was proven to be an efficient heterogeneous autotandem catalyst for synthesizing quinazolinones via selective hydration/acceptorless dehydrogenative coupling from o-aminobenzonitriles. Furthermore, the synthesized catalyst was recycled five times without an obvious decrease in the catalytic activity.

Aggregation-Induced Electrochemiluminescence of Conjugated Pdots Containing a Trace Ir(III) Complex: Insights into Structure-Property Relationships

An approach to the design of iridium(III)-contained polytetraphenylethene Pdots that could exhibit highly efficient electrochemiluminescence (ECL) was proposed. The relationships of ECL performance between the iridium complex-embedded and end-capped aggregation-induced emission (AIE) active Pdots in aqueous media were investigated for the first time. The iridium complexes with cyclometalated ligand 6-phenylphenanthridine (pphent) were incorporated into the copolymers by either embedding (P0, P2-P5) or end-capping (P1) into the backbone via an ancillary 2,2'-bipyridine (bpy) ligand. Subsequently, the corresponding Pdots of P0-P5 encapsulated with poly(styrene-co-maleicanhydride) could be obtained by the nanoprecipitation method. Compared to Pdots0, Pdots2-Pdots5 with (pphent)₂Ir(bpy) (M1) complex embedding, as the iridium complex content increases, ECL signals were decreased in the order of Pdots0 > Pdots2 > Pdots3 > Pdots4 > Pdots5; whereas among these Pdots of P0-P5, Pdots1 with M1 complex end-capping exhibited the highest ECL efficiency (relative to a Ru(bpy)₃²⁺ system of 18.9%) and 4.7-fold enhancement of the ECL signal compared to the parent Pdots of P0, which was mainly attributed to the good film conductivity of the completely conjugated architectures, thus prompting the intramolecular electron transfer. This work opened new avenues for designing highly efficient ECL emitters.

Highly Efficient Aggregation-Induced Electrochemiluminescence of Polyfluorene Derivative Nanoparticles Containing Tetraphenylethylene

The aggregation-induced electrochemiluminescence (AIECL) of polyfluorene derivative nanoparticles containing tetraphenylethylene (TPE) in aqueous media is reported in this work. The TPE unit limits the intramolecular free rotation of phenyl rings, as well as the π-π stacking interactions of molecules, which significantly enhances ECL signal of the polyfluorene nanoparticles. With co-reactants of tri-n-propylamine (TPrA) and S2O82-, the copolymer nanoparticles show visualized ECL emissions at both positive and negative potentials. The ECL efficiency of copolymer nanoparticles in solid state is 163% compared with that of standard ECL species, Ru(bpy)32+. And at negative potential, the ECL intensity of copolymer nanoparticles is even stronger with 6.5 times compared with that at positive potential. The ECL generation mechanisms are analyzed detailed by annihilation and co-reactant route transient ECL test (millisecond scale). This work provides a reference for the organic structure design for AIECL and shows promising potential in luminescent device and biological applications.

A cyclometalated trinuclear Ir(iii)/Pt(ii) complex as a luminescent probe for histidine-rich proteins

A trinuclear luminescent organometallic Pt–Ir–Pt complex acts as an efficient protein staining agent due to reversible binding to histidine-rich proteins.

Recent Advances in Aggregation-Induced Electrochemiluminescence

The emergence of the rising alliance between aggregation-induced emission (AIE) and electrochemiluminescence (ECL) is defined as aggregation-induced electrochemiluminescence (AIECL). The booming science of AIE has proved to be not only distinguished in luminescent materials but could also inject new possibility into ECL analysis. Especially in the aqueous phase and solid state for hydrophobic materials, AIE helps ECL circumvent the dilemma between substantial emission intensity and biocompatible media. The wide range of analytes makes ECL an overwhelmingly interesting analytical technique. Therefore, AIECL has gained potential in clinical diagnostics, environmental assays, and biomarker detections. This review will focus on introduction of the novel concept of AIECL, current applied luminophores, and related applications developed in recent years.

An aptasensor for troponin I based on the aggregation-induced electrochemiluminescence of nanoparticles prepared from a cyclometallated iridium(III) complex and poly(4-vinylpyridine-co-styrene) deposited on nitrogen-doped graphene

An ultrasensitive electrochemiluminescence (ECL) disposable aptamer sensor (aptasensor) is presented for detection of myocardial infarction biomarker by quantification of troponin I in blood serum. A screen-printed electrode was modified with (a) aptamer-modified gold nanoparticles, (b) cyclometallated iridium(III)-poly-4-vinylpyridine nanoparticles, and (c) nitrogen-doped graphene in order to increase the loading capacity and conductivity of the aptasensor. If the aptasensor is exposed to troponin I, it will bind to the aptamer and desorb the aptamer from gold nanoparticles and the surface of the electrode. This generates an enhancement in ECL emission depending on troponin I concentration. ECL emission is strongly improved by aggregation-induced phenomenon, which is caused by inhibition of the water and oxygen quenching effect on the iridium complex ECL in aqueous media. Under optimum conditions, the aptasensor has a wide dynamic range that extends from 0.1 pM to 10 nM, with a 20 fM detection limit (S/N = 3) and a relative standard deviation of 3.1%. The ECL aptasensor was successfully applied to 20 individual human serum for the detection of troponin I biomarker. Graphical abstract Schematic presentation of electrochemiluminescence aptamer assay fabrication for detection of Troponin I. Carbon screen printed electrode (CSPE) was modified with nitrogen doped graphene (NG), gold nanoparticles (AuNPs), cyclometallated iridium(III)-polyvinylpyridine polymer nanoparticles, ionic liquid and bovine serum albumin.