Electrochemistry, Electrogenerated Chemiluminescence, and Excimer Formation Dynamics of Intramolecular π-Stacked 9-Naphthylanthracene Derivatives and Organic Nanoparticles

Potential-Resolved Ratio Electrochemiluminescence Biosensor Based on Perylene Diimide-MOF and DNA Nanoflowers-CdS Quantum Dots for Detection of Dual Targets

BRCA1 gene and carcinoembryonic antigen (CEA) are important markers of breast cancer, so accurate detection of them is significant for early detection and diagnosis of breast cancer. In this study, a potential-resolved ratio electrochemiluminescence (ECL) biosensor using perylene diimide (PDI)-metal-organic framework and DNA nanoflowers (NFs)-CdS quantum dots (QDs) was constructed for detection of BRCA1 and CEA. Specifically, PDI-MOF and CdS QDs can generate potential-resolved intense ECL signals only using one coreactant, so the detection procedure can be effectively simplified. PDI-MOF was first attached to the electrode by graphene oxide, and the dopamine (DA) probe was linked to quench the ECL signal by DNA hybridization. In the presence of target BRCA1, it can form a bipedal DNA walker, so the quenching molecules (DA) were detached from the electrode via the walker amplification process aided by Mg2+, so that the PDI signal at -0.25 V was restored for the BRCA1 assay. Moreover, CdS QDs@DNA NFs as amplified signal probes were formed by self-assembly, and the target CEA-amplified product introduced the CdS QDs@DNA NFs to the electrode, so the QD ECL signal at -1.42 V was enhanced, while the ECL signal of PDI is unchanged; thus, CEA detection was achieved by the ratio value between them. Therefore, the detection accuracy is guaranteed by detection of two cancer markers and a ratio value. This biosensor has a great contribution to the development of new ECL materials and a novel ECL technique for fast and efficient multitarget assays, showing great significance for the early monitoring and diagnosis of breast cancer.

Wireless Multimodal Light-Emitting Arrays Operating on the Principles of LEDs and ECL

Electrochemistry-based light-emitting devices have gained considerable attention in different applications such as sensing and optical imaging. In particular, such systems are an interesting alternative for the development of multimodal light-emitting platforms. Herein we designed a multicolor light-emitting array, based on the electrochemical switch-on of light-emitting diodes (LEDs) with a different intrinsic threshold voltage. Thermodynamically and kinetically favored coupled redox reactions, i. e. the oxidation of Mg and the reduction of protons on Pt, act as driving force to power the diodes. Moreover, this system enables to trigger an additional light emission based on the interfacial reductive-oxidation electrochemiluminescence (ECL) mechanism of the Ru(bpy)3 2+/S2O8 2- system. The synergy between these light-emission pathways offers a multimodal platform for the straightforward optical readout of physico-chemical information based on composition changes of the solution.

Endogenous and exogenous wireless multimodal light-emitting chemical devices

Multimodal imaging is a powerful and versatile approach that integrates and correlates multiple optical modalities within a single device. This concept has gained considerable attention due to its potential applications ranging from sensing to medicine. Herein, we develop several wireless multimodal light-emitting chemical systems by coupling two light sources based on different physical principles: electrochemiluminescence (ECL) occurring at the electrode interface and a light-emitting diode (LED) switched on by an electrochemically triggered electron flow. Endogenous (thermodynamically spontaneous redox process) and exogenous (requiring an external power source) bipolar electrochemistry acts as a driving force to trigger both light emissions at different wavelengths. The results presented here interconnect optical imaging and electrochemical reactions, providing a novel and so far unexplored alternative to design autonomous hybrid systems with multimodal and multicolor optical readouts for complex bio-chemical systems.

Advances in electrochemiluminescence luminophores based on small organic molecules for biosensing

Electrochemiluminescence (ECL) has several advantages, such as a near-zero background signal, high sensitivity, wide dynamic range, simplicity, and is widely used for sensing, imaging, and single cell analysis. ECL luminophores are the key factors in the performance of various applications. Among various luminophores, small organic luminophores exhibit many intriguing features including good biocompatibility, facile modification, well-defined molecular structure, and sustainable raw materials, making small organic luminophores attractive for the use in the ECL field. Although many great achievements have been made in the synthesis of new small organic luminophores, solving various challenges, and expanding new applications, there are almost no comprehensive reviews on small organic ECL luminophores. In this review, we briefly introduce the advantages and emission mechanisms of small organic ECL luminophores, summarize the main types, molecular characteristics, and ECL properties of most existing small organic ECL luminophores, and present the important applications and design principles in sensors, imaging, single cell analysis, sterilization, and other fields. Finally, the challenges and outlook of organic ECL luminophores to be popularized in biosensing applications are also discussed.

Elucidation of an Aggregate Excited State in the Electrochemiluminescence and Chemiluminescence of a Thermally Activated Delayed Fluorescence (TADF) Emitter

The electrochemistry, electrochemiluminescence (ECL), and chemiluminescence (CL) properties of a thermally activated delayed fluorescence (TADF) emitter 4,4'-(1,2-dihydroacenaphthylene-5,6-diyl)bis(N,N-diphenylaniline) (TPA-ace-TRZ) and three of its analogues were investigated. TPA-ace-TRZ exhibits both (a) delayed onset of ECL and (b) long-persistent luminescence, which we have attributed to the formation of an aggregate excited state in excimer or exciplex form. The evidence of this aggregate excited state was consistent across ECL annihilation and coreactant pathways as well as in CL. The absolute ECL efficiency of TPA-ace-TRZ using benzoyl peroxide (BPO) as a coreactant was found to be 0.028%, which was 9-fold stronger than the [Ru(bpy)₃]²⁺/BPO reference coereactant system. Furthermore, the absolute CL quantum efficiency of TPA-ace-TRZ was determined to be 0.92%. The performance and flexibility of the TADF emitter TPA-ace-TRZ under these various emissive pathways are highly desirable toward applications in sensing, imaging, and light-emitting devices.

Wireframe Orbit-Accelerated Bipedal DNA Walker for Electrochemiluminescence Detection of Methyltransferase Activity

In spite of the DNA walkers executing the signal accumulation task in the process of moving along the predetermined paths, the enhancement of walking dynamics and walking path controllability are still challenging due to the unprogrammed arrangements of DNA orbits. Taking these dilemmas into account, a bipedal DNA walker was designed skillfully by the virtue of wireframe orbits assembled by DNA cubes in order, which improved the efficiency and the continuity of walking. It could be attributed to the fact that both the contact chance and the dynamic interaction between walking strands and designated orbits were beneficial to minimize the possibility of derailment and improve the accumulation of signal. In addition, the hollow titanium dioxide nanospheres coated with rubrene (Rub@TiO₂ NSs) were prepared by the etching of inner silicon dioxide nanoparticles (SiO₂ NPs) to regulate the distribution pattern of rubrene (Rub) molecules and expose more electrochemically active sites for high-efficient electrochemiluminescence (ECL). Benefiting by the pore confinement-enhanced ECL, the electron and mass transfer was significantly accelerated because of the hollow structure of Rub@TiO₂ NSs. Subsequently, endogenous dissolved oxygen as the coreactant and palladium nanoparticles (Pd NPs) as the coreaction accelerator were employed to constitute a ternary ECL system with explosive signal response. Combining with this ECL platform, the bipedal walker activated by the target can autonomously and directionally move on the DNA wireframe orbits to release the quenching probes continuously. In this way, the biosensor displayed a low detection limit (2.30 × 10^-8 U·mL^-1) and a wide linear range (1.0 × 10^-7 to 1.0 × 10^-1 U·mL^-1) for the sensitive detection of Dam methyltransferase (Dam MTase) activity. Therefore, a novel strategy for the accurate quantification of epigenetic targets was developed by virtue of improving the walking dynamics of DNA walker and amplifying the ECL of Rub molecules.

Self-luminescent europium based metal organic frameworks nanorods as a novel electrochemiluminescence chromophore for sensitive ulinastatin detection in biological samples

In this work, we developed a novel electrochemiluminescence (ECL) biosensor for ulinastatin (UTI) detection based on self-luminescent metal-organic framework (L-MOF) nanomaterials. The L-MOFs could be simply prepared by one-pot methods using Eu³⁺ and 4,4',4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid (H₃TATAB) as the metallic center and organic ligand, respectively. The Eu-TATAB exhibited high efficiency and stable ECL performance when using K₂S₂O₈ as coreactant. For the established biosensor, Eu-TATAB was both used as the ECL chromophore and protein carrier due to its outstanding biocompatibility and large superficial area, which could load sufficient antibodies to link with antigen in the biosensor for subsequent detection. The established sandwich ECL biosensor showed a wide linear range of 0.1 ng mL^-1 - 10⁵ ng mL^-1 and a low limit of detection of 9.7 pg mL^-1 for UTI detection. In addition, the developed ECL biosensor could also be successfully applied to the real UTI sample determination in serum. The reported biosensor strategy could provide a guide for developing more other novel and promising high-performance ECL nanomaterials, and also be used as a potential method for ultrasensitive UTI detection in disease research.

Efficient blue organic electrochemiluminescence luminophore based on a pyrenyl-phenanthroimidazole conjugate

A pyrenyl-phenanthroimidazole (Py-PI) conjugate emitted strong blue electrochemiluminescence (ECL) emission via the reductive-oxidation co-reactant pathway, with an ECL efficiency 3.3 times higher than that of the 9,10-diphenylanthracene (DPA) reference compound.

Dual-potential electrochemiluminescent film constructed from single AIE luminogens for the sensitive detection of malachite green

Exploiting efficient electrochemiluminescent (ECL) luminogens is crucial for the development of high-performance ECL sensors. Herein, a kind of efficient luminogen (BTPEBT) consisting of benzothiadiazole (BTD) as an electron acceptor and tetraphenylethylene (TPE) as an electron donor was facilely synthesized through a one-step Suzuki reaction. BTPEBT showed typical aggregation-induced emission (AIE) effects with a high solid-state quantum yield of 69.8%. The fabricated solid-state ECL film that is based on single AIE luminogens presented unique dual-potential ECL properties for the first time. The bright ECL of this film could be observed by the naked eye with a satisfactory ECL efficiency of 22.8%. The dense ECL film showed a low electron-transfer resistance, which favors electron transfer among AIE luminogens, electrolytes and the electrode, giving rise to bright ECL emission. The bright ECL film was developed as an ECL sensor for the sensitive and selective detection of malachite green (MG) in a broad linear range from 10^-10 to 10^-5 M. The limit of detection (LOD) was as low as 7.6 × 10^-11 M. Moreover, the ECL sensing platform was further employed to detect MG in a real fish tissue sample with high sensitivity and good specificity. More importantly, the recycled BTPEBT film had good reproducibility for MG detection. The novel dual-potential ECL film constructed from single AIE luminogens provides a promising platform for the sensitive detection of MG in the food industry.

Highly Efficient Aggregation-Induced Enhanced Electrochemiluminescence of Cyanophenyl-Functionalized Tetraphenylethene and Its Application in Biothiols Analysis

Exploring new electrochemiluminescence (ECL) luminophores with high ECL efficiency and good stability in aqueous solution is in great demand for biological sensing. In this work, highly efficient aggregation-induced enhanced ECL of cyanophenyl-functionalized tetraphenylethene (tetra[4-(4-cyanophenyl)phenyl]ethene, TCPPE) and its application in biothiols analysis were reported. TCPPE contains four 4-cyanophenyl groups covalently attached to the tetraphenylethene (TPE) core, generating a nonplanar three-dimensional twisted conformation structure. TCPPE nanoparticles (NPs) with an average size of 15.84 nm were prepared by a precipitation method. High ECL efficiency (593%, CdS as standard) and stable ECL emission (over one month) were obtained for TCPPE NPs in aqueous solution. The unique properties of TCPPE NPs could be ascribed to the efficient suppression of nonradiative transition, the decrease of the energy gap, and the increase of anionic radical stability, which were proved by theoretical calculation and electrochemical and fluorescence methods. Contrasting aggregation-induced ECL chromic emission was first observed for TCPPE NPs. As a proof-of-methodology, an ECL method was developed for three biothiol assays with detection limits of 6, 7, and 300 nM for cysteine, homocysteine, and glutathione, respectively. This work demonstrates that TCPPE NPs are promising ECL luminophores, and the incorporation of appropriate substituents into luminophores can improve ECL efficiency and radical stability.

MicroRNA-Triggered Deconstruction of Field-Free Spherical Nucleic Acid as an Electrochemiluminescence Biosensing Switch

Herein, a new field-free and highly ordered spherical nucleic acid (SNA) nanostructure was self-assembled directly by ferrocene (Fc)-labeled DNA tweezers and DNA linkers based on the Watson-Crick base pairing rule, which was employed as an electrochemiluminescence (ECL) quenching switch with improved recognition efficiency due to the high local concentration of the ordered nanostructure. Moreover, with a collaborative strategy combined with the advantages of both self-accelerated approach and pore confinement-enhanced ECL effect, the mesoporous silica nanospheres (mSiO₂ NSs) were prepared to be filled with rubrene (Rub) as ECL emitters and Pt nanoparticles (PtNPs) as coreaction accelerators (Rub-Pt@mSiO₂ NSs), which demonstrated high ECL response in the aqueous media (dissolved O₂ as coreactant). When the SNA nanostructure was immobilized on the Rub-Pt@mSiO₂ NSs-modified electrode, it presented a "signal off" state owing to the quenching effect of the Fc molecules. As a proof of concept, the SNA-based ECL switch platform was applied in the detection of microRNA let-7b (let-7b). Impressively, in the presence of the target let-7b, a deconstruction of the SNA nanostructure was actuated, causing the Fc to leave the electrode surface and achieved an extremely high ECL recovery ("signal on" state). Hence, a sensitive determination for let-7b was realized with a low detection limit of 1.8 aM ranging from 10 aM to 1 nM by employing the Rub-Pt@mSiO₂ NSs-based ECL platform combined with the target-triggered SNA deconstruction, which also offered an ingenious method for the further applications of biomarker analyses.

Arousing Electrochemiluminescence Out of Non-Electroluminescent Monomers within Covalent Organic Frameworks

Covalent organic frameworks (COFs) with stable long-range ordered arrangements are promising materials for organic optoelectronics. However, their electrochemiluminescence (ECL) from non-ECL active monomers has not been realized. Here, we report a design strategy for ECL-emitting COF family. The donors and acceptors co-crystallized and stacked into the highly aligned array of olefin-linked COFs, so that electrons can be transported freely. By this means, a tunable ECL is activated from non-ECL molecules with the maximum efficiency of 32.1% in water with the dissolved oxygen as an inner coreactant, and no additional noxious co-reactant is needed any more. Quantum chemistry calculations further demonstrate that this design reduces the COFs' band gaps and the overlap of electrons and holes in the excited state for better photoelectric properties and stronger ECL signals. This work exploits a basis to envisage the broad application potential of ECL-COFs for various biosensors and light-emitting display.

Label-free immunosensor for cardiac troponin I detection based on aggregation-induced electrochemiluminescence of a distyrylarylene derivative

Herein, the aggregation-induced electrochemiluminescence (AIECL) of a distyrylarylene derivative, 4,4'-bis(2,2-diphenylvinyl)-1,1'-biphenyl (DPVBi), was investigated for the first time. This luminophore exhibits significantly enhanced photoluminescence (PL) and electrochemiluminescence (ECL) emission with the increases of water content in organic/water mixtures. This high luminescence efficiency of DPVBi in aggregate state is due to the fact that the aggregates can reduce the energy loss by restricting the intramolecular motions. The ECL behavior of DPVBi in acetonitrile was investigated by ECL transients and so-called "half-scan" technology, where singlet-singlet annihilation ECL was generated under continuous potential switching. The DPVBi nanobulks (DPVBi NBs) were prepared to improve its application in aqueous media, which could be conveniently cast on electrode surface for developing sensing platform due to its good film-forming nature. The constructed heterogeneous AIECL platform can produce reductive-oxidative and oxidative-reductive ECL by using trimethylamine (TEA) and potassium peroxodisulfate (K₂S₂O₈) as coreactant. On the basis of the higher ECL efficiency of DPVBi NBs/TEA system, a label free immunosensor for cardiac troponin I (cTnI) was developed with the assistance of electrodeposited gold nanoparticles, and it showed a wide linear range of 20 ng/mL~100 fg/mL and low detection limit of 43 fg/mL. Moreover, the constructed immunosensor also exhibited good specificity, stability and satisfied performance in practical sample analysis.

Swing Arm Location-Controllable DNA Walker for Electrochemiluminescence Biosensing

Here, we described a novel swing arm location-controllable DNA walker based on the DNA tetrahedral nanostructures (DTNs) for nucleic acid detection using the polycyclic aromatic hydrocarbon (PAH) microcrystals (TAPE-Pe MCs) consisting of the nonplanar molecular tetrakis(4-aminophenyl)ethene (TAPE) and planar molecular perylene (Pe) as electrochemiluminescence (ECL) luminophores. Specifically, the swing arm strands and track strands were fixed simultaneously on the DTNs to obtain the location-controllable DNA walker, which possessed an improved reaction efficiency compared to that of a fixed swing arm-based DNA walker due to the quantitative and orderly swing arm on the DTNs. On the other hand, the Pe microcrystals doped by TAPE molecules could decrease the π-π stacking of Pe molecules for the ECL efficiency enhancement, achieving a blue-shifted and intense ECL emission. Therefore, we defined this enhanced and blue-shifted ECL phenomenon as "inhibition of conjugation-driven ECL (IC-ECL)". To prove these principles, a location-controllable DNA walker-based ECL biosensor was developed with microRNA let-7a as target molecules. The ECL biosensor achieved a low detection limit of 4.92 fM within a wide linear range from 10 fM to 100 nM. This approach offers a new insight for ECL efficiency increase and location-controllable strategies with improved reaction efficiency, demonstrating potential in diagnostic analysis.

Electrochemistry and Electrochemiluminescence of Coumarin Derivative Microrods: Mechanism Insights

Organic molecules and related nanomaterials have attracted extensive attention in the realm of electrochemiluminescence (ECL). Herein, a well-known electroluminescence (EL) dopant 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino-[9,9a,1gh] coumarin (C545T) is selected as a new ECL illuminant, which shows a high photoluminescence quantum yield of nearly 100% and excellent ECL performance in the organic phase. For utilizing C545T to achieve ECL detection in aqueous solution, organic microrods of C545T (C545T MRs) were synthesized by a precipitation method. Cyclic voltammetry and differential pulse voltammetry of C545T and C545T MRs in acetonitrile or phosphate buffer showed one reduction and multiple oxidation peaks, suggesting that the multiple charge states of C545T could be produced by continuous electron- or hole-injection processes. The annihilated ECL emission of C545T and C545T MRs was observed using ECL transient technology. In the presence of triethanolamine (TEOA) or potassium persulfate (K₂S₂O₈), C545T MRs can also give bright anodic and cathodic ECL emission at the GCE/water interface. The proposed ECL system not only has multichannel ECL emission but also shows intense yellow emission (569 nm) with a relative ECL efficiency of 0.81 when TEOA was used as a coreactant. Benefiting from the strong ECL emission of the C545T MRs/TEOA system and the quenching effect of dopamine (DA) on ECL, a convenient sensor for DA was developed with high selectivity and sensitivity.

Triptycene-Based Luminescent Materials in Homoconjugated Charge-Transfer Systems: Synthesis, Electronic Structures, AIE Activity, and Highly Tunable Emissions

We have developed a new family of luminescent materials featuring through-space charge transfer from electron donors to acceptors that are electronically separated by triptycene. Most of these molecules are highly fluorescent, and modulation of their emissions was achieved by tuning the electron-accepting strength in a range from the weak triptycene acceptor over triarylborane (BMes) to strongly accepting naphthalimide (Npa) moieties. Pz-Pz shows an aggregation-induced emission in aggregates and in the solid state coupled with a highly red-shifted broad emission (ca. 160 nm) of the excimer, indicating that phenothiazine (Pz) also plays a vital role in the emission responses as an electron donor. This work may help develop new approaches to photophysical mechanism based on the rigid, homoconjugated, and structurally unusual 3D triptycene scaffold.

Asymmetry controlled dynamic behavior of autonomous chemiluminescent Janus microswimmers

Asymmetrically modified Janus microparticles are presented as autonomous light emitting swimmers. The localized dissolution of hybrid magnesium/polymer objects allows combining chemiluminescence with the spontaneous production of H₂ bubbles, and thus generating directed motion. These light-emitting microswimmers are synthesized by using a straightforward methodology based on bipolar electromilling, followed by indirect bipolar electrodeposition of an electrophoretic paint. An optimization of the experimental parameters enables in the first step the formation of well-defined isotropic or anisotropic Mg microparticles. Subsequently, they are asymmetrically modified by wireless deposition of an anodic paint. The degree of asymmetry of the resulting Janus particles can be fine-tuned, leading to a controlled directional motion due to anisotropic gas formation. This autonomous motion is coupled with the emission of bright orange light when Ru(bpy)₃²⁺ and S₂O₈²⁻ are present in the solution as chemiluminescent reagents. The light emission is based on an original process of interfacial redox-induced chemiluminescence, thus allowing an easy visualization of the swimmer trajectories.

Asymmetrically modified Janus microparticles are presented as autonomous light emitting swimmers with shape-controlled trajectories.

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.

Organic Dots Embedded in Mesostructured Silica Xerogel as High-Performance ECL Emitters: Preparation and Application for MicroRNA-126 Detection

Unlike the organic micro/nanocrystals prepared using an emerging reprecipitation method, a novel method of embedding 1-pyrenecarboxaldehyde dots (PycDs) into a mesostructured silica xerogel (PycDs@MSX) for use as electrochemiluminescence (ECL) emitters was first proposed to achieve an extremely strong ECL response, with peroxydisulfate (S₂O₈^2-) used as a coreactant. In this method, (i) PycDs@MSX could ensure the reversal of the PycDs environment from hydrophobic to hydrophilic and (ii) PycDs@MSX could provide massive porous channels, allowing for access of hydrophilic reactive intermediates (i.e., sulfate anion radicals, SO₄^•-), which could accelerate the rate of mass transfer and electron transfer between S₂O₈^2- and PycDs. Using Ag nanoparticles as a coreaction accelerator and a 3D DNA nanomachine as a signal amplification strategy, the proposed ECL biosensing platform was constructed and achieved ultrasensitive detection of microRNA-126 with an excellent linear range (from 100 aM to 100 pM) and a low detection limit (13.0 aM). More importantly, this work not only developed an innovative avenue to improve the ECL efficiency of organic emitters in aqueous phases but also provided a powerful strategy for biochemical analysis and disease diagnosis applications.

Near-infrared aggregation-induced enhanced electrochemiluminescence from tetraphenylethylene nanocrystals: a new generation of ECL emitters

Tetraphenylethylene nanocrystals as new ECL emitters with near-infrared aggregation-induced enhanced electrochemiluminescence exhibited high ECL efficiency and excellent biocompatibility.

Herein, we observed near-infrared electrochemiluminescence (NIR ECL) emission from tetraphenylethylene nanocrystals (TPE NCs), which exhibit high ECL efficiency and excellent biocompatibility compared with the current NIR ECL emitters (such as semiconductor quantum dots and metal nanoclusters). The strong ECL signal of TPE NCs originates from the aggregation-induced enhanced ECL emission via improvement of the efficiency of electron hole recombination and suppression of the nonradiative transition. Impressively, the TPE NCs exhibit an enormous red-shifted ECL emission (678 nm) relative to the blue-light photoluminescence (PL) emission (440 nm). Compared to fluorescence imaging which is limited by photobleaching and autofluorescence, the NIR ECL emission of TPE NCs is highly favorable to diminish background interference over visible light and realize deeper tissue penetration, which expands the ECL emission of organic nanomaterials to the NIR region for broader biological applications.

Excimer-induced high-efficiency fluorescence due to pairwise anthracene stacking in a crystal with long lifetime

Herein, we report an anthracene-based material, 2-(anthracen-9-yl)thianthrene (), whose crystal exhibits excimer fluorescence with an unexpected high luminous efficiency (up to 80%) and long lifetime (163.75 ns), due to pairwise anthracene stacking. These results will update the traditional view that excimers are poorly efficient in photoluminescence.

Aggregation-Induced Enhanced Electrochemiluminescence from Organic Nanoparticles of Donor-Acceptor Based Coumarin Derivatives

Organic nanoparticles (NPs) from donor-acceptor based coumarin derivatives, 6-[4-(N,N-diphenylamino)phenyl]-3-ethoxycarbonyl coumarin (DPA-CM), with an average size of 5.82 nm, were synthesized by a facile reprecipitation method using water as a poor solvent and tetrahydrofuran as a good solvent. Red-shifted absorption, blue-shifted photoluminescence emission, and aggregation-induced enhanced electrochemiluminescence (ECL) emission were observed for the DPA-CM NPs in aqueous solution compared with the original DPA-CM in organic solution. The aggregation-induced enhanced ECL emission is ascribed to the combined effects of the small size of the DPA-CM NPs, the restricted conformational relaxation in the NPs, and the good stability of the cationic radical of DPA-CM. A strong and stable ECL emission is obtained at the DPA-CM NPs modified glassy carbon electrode in the presence of tri-n-propylamine, and the ECL intensity of the DPA-CM NPs modified electrode is quenched linearly in the range of 0.05-50 μM with detection limit of 0.04, 0.2, and 0.4 μM for ascorbic acid, uric acid, and dopamine, respectively. This work shows an example of donor-acceptor based organic NPs as ECL emitters and their analytical applications to monitor biomolecules.

Hemin as electrochemically regenerable co-reaction accelerator for construction of an ultrasensitive PTCA-based electrochemiluminescent aptasensor

In this work, hemin was firstly used as electrochemically regenerable co-reaction accelerator for signal amplification to develop an ultrasensitive aptasensor for Aflatoxin M1 (AFM1) detection. Initially, the perylenetetracarboxylic acid (PTCA) was directly employed as luminophore to construct the ECL sensing nano-platform by combining Au nanoparticles (Au NPs) for immobilizing thiol-terminated hairpin probe (H1). Then with the help of hairpin H2, H3, the AFM1-catalyzed hairpin assembly (CHA) was executed to produce the H1-H3 duplex, which could further initiate the hybridization chain reaction (HCR) to generate dendritic DNA polymers consisting of G-rich sequence for capturing large quantities of hemin on the electrode surface. Herein, hemin as electrochemically regenerable co-reaction accelerator could interact with the co-reactant (S₂O₈^2-) to obviously improve the luminous efficiency of the PTCA. Therefore, a strong and stable ECL signal was achieved by the employment of hemin as electrochemically regenerable co-reaction accelerator. The proposed aptasensor determined AFM1 down to 0.09pgmL^-1 within a linear range of 0.4pgmL^-1 to 400ngmL^-1. With excellent sensitivity and stability, the strategy provided an efficient and simple method for the trace detection of biomolecules in clinical analysis.

Polymorph-Dependent Electrogenerated Chemiluminescence of Low-Dimensional Organic Semiconductor Structures for Sensing

A sensitive electrogenerated chemiluminescence (ECL) sensor with an organic semiconductor as active material for detecting trace amounts of molecules has been highly desired. However, the crystal structure responses of the ECL properties of the organic semiconductor materials, that is, structure-property relationship, is not clear, which limits the development of the sensitive ECL sensors. Herein, for the first time, we reported a novel concept for molecular-stacking-arrangement-dependent electrogenerated chemiluminescence properties of organic semiconductor rubrene microstructures. The rubrene 1D microwires and 2D hexagonal plates with different polymorphs (triclinic and monoclinic) were controllably constructed with the reprecipitation method. The supersaturation of the rubrene molecules plays an important role in the thermodynamically and kinetically dominated process of growth, which affects not only the polymorphs but also the morphology of the obtained microstructures. These microstructures show good optoelectronic properties, which are used as active ECL materials for the construction of ECL sensors. The ECL sensors exhibited distinct electrogenerated chemiluminescence properties, probably related to different inherent crystal-structure-dependent triplet-triplet annihilation rate and charge-transfer rate. The sensors manifested electrogenerated chemiluminescence responses in broad linear range for the monitoring of creatinine molecules.

Electrochemically tuneable multi-colour electrochemiluminescence using a single emitter

A single starting component electrochemiluminescence system from which red, green, blue or white emission can be obtained, depending on the applied potential or the mode of the ECL experiment, is described. The convoluted ECL spectral responses observed at different potentials are readily explained using a 3D-ECL technique, where the ECL spectral profile is continuously monitored as a function of potential during voltammetric scanning. The 3D plots obtained using this technique implicate cross-annihilation ECL reactions involving the complex itself and stable products resulting from its electrolysis. Combining this information with knowledge of the energetic requirements of the various reactions involved, suggests a mechanism involving traces of two emissive products, related to the loss of a methyl group from the triazole moiety. These products, while barely detectable electrochemically, are sufficiently emissive to influence and even dominate the ECL emission under some conditions.

Electrochemiluminescence of Supramolecular Nanorods and Their Application in the "On-Off-On" Detection of Copper Ions

In this work, an "on-off-on" switch system has been successfully applied through the construction of an electrochemiluminscent biosensor for copper ion (Cu(2+) ) detection based on a new electrochemiluminescence (ECL) emitter of supramolecular nanorods, which was achieved through supramolecular interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and aniline. The initial "signal-on" state with strong and stable ECL emission was obtained by use of the supramolecular nanorods with a new signal amplification strategy involving a co-reaction accelerator. In addition, ECL quencher probes (Fc-NH2 /Cu-Sub/nano-Au) were fabricated by immobilizing aminoferrocene (Fc-NH2 ) on Cu-substrate strand modified Au nanoparticles. The quencher probes were hybridized with the immobilized Cu-enzyme strand to form Cu(2+) -specific DNAzyme. Similarly, the "signal-off" state was obtained by the high quenching effect of Fc-NH2 on the ECL of the excited-state PTCA ((1) PTCA*). As expected, the second "switch-on" state could achieved by incubating with the target Cu(2+) , owing to the Cu(2+) -specific DNAzyme, which was irreversibly cleaved, resulting in the release of the quencher probes from the sensor interface. Herein, on the basis of the ECL intensity changes (ΔIECL ) before and after incubating with the target Cu(2+) , the prepared Cu(2+) -specific DNAzyme-based biosensor was used for the determination of Cu(2+) concentrations with high sensitivity, excellent selectivity, and good regeneration.

Electrochemistry and Electrogenerated Chemiluminescence of 1,3,5-Tri(anthracen-10-yl)-benzene-Centered Starburst Oligofluorenes

The electrochemistry and electrogenerated chemiluminescence (ECL) of three 1,3,5-tri(anthracen-10-yl)-benzene-centered starburst oligofluorenes (T1-T3) are reported in this paper. The compounds T1-T3 contain 1,3,5-tri(anthracen-10-yl)-benzene as a core with fluorene as an arm from monofluorene to trifluorene groups (n = 1-3), generating a rigid three-dimensional structure. The electrochemical behaviors of these compounds are likely to be tuned by the fluorene arms. In cyclic voltammograms, both the oxidation and reduction of T1 and T2 are characterized by three reversible one-electron transfers from the core while the oxidation and reduction of T3 are characterized by six reversible one-electron transfers from the core and the arms in acetonitrile:benzene (v:v = 1:1) solvent. The second oxidation and reduction waves of T1 show three reversible one-electron transfers from three fluorene arms, while the second and third oxidation and reduction waves of T2 and T3 exhibit three reversible one-electron transfers from the six fluorene arms. The multiple electron transfers in one molecule are confirmed by chronoamperometry at an ultramicroelectrode, simulations and DFT calculations. The T1-T3 compounds display strong absorption in UV-vis and blue fluorescence emission. Strong blue ECL emissions can be generated from T1, T2 and T3 under ion annihilation condition, which is assigned as S-route.

A new fluorescent sensor for determination of thorium by thin film of 2-(acetyloxy)-N-(5-nitro-2-thiazolyl)-benzamide embedded in sol–gel matrix

A new “turn-off” fluorescent sensor for determination of thorium (Th(iv)) by thin film of 2-(acetyloxy)-N-(5-nitro-2-thiazolyl)-benzamide (L) embedded in sol–gel matrix was introduced.

Electrochemiluminescence Resonance Energy Transfer System: Mechanism and Application in Ratiometric Aptasensor for Lead Ion

In this paper, a novel electrochemiluminescence resonance energy transfer (ECL-RET) system from O2/S2O8(2-) to a kind of amino-terminated perylene derivative (PTC-NH2) was demonstrated for the first time, which was then applied to construct a ratiometric aptasensor for lead ion (Pb(2+)) detection. First, gold-nanoparticles-functionalized fullerene nanocomposites (AuNPs@nano-C60) were coated on a glassy carbon electrode (GCE), and then thiol-modified assistant probes (APs) were attached on AuNPs@nano-C60/GCE. Then the resultant electrode was hybridized with capture probes (the aptamer of the Pb(2+), abbreviated as CPs) to generate DNA duplexes, which could induce PTC-NH2 to be intercalated into the dsDNA grooves by the electrostatic adsorption. Herein, ECL dual peaks at -0.7 V (vs Ag/AgCl) and -2.0 V (vs Ag/AgCl) were obtained when the prepared aptasensor was detected in air-saturated S2O8(2-) solution, which could be attributed to the emission of excited dimmers (π-excimers) ((1)(NH2-PTC)2*) and (1)(O2)2*, respectively. In the presence of Pb(2+), the dsDNA was unwound, and Pb(2+) G-quadruplex structure was generated because of the highly specific affinity between Pb(2+) and CPs, which made the PTC-NH2 release from the electrode surface. As a result, the ECL signal at -0.7 V was decreased, and the ECL signal around -2.0 V was increased. By measuring the ratio of ECL intensities at two excitation potentials, the developed aptasensor exhibited the linear response range from 1.0 × 10(-12) M to 1.0 × 10(-7) M with a detection limit of 3.5 × 10(-13) M (S/N = 3) for Pb(2+), which could offer an alternative analytical method with excellent properties of high selectivity, accuracy, and sensitivity.

Recent advances in electrochemiluminescence

The great success of electrochemiluminescence (ECL) for in vitro diagnosis (IVD) and its promising potential in light-emitting devices greatly promote recent ECL studies. More than 45% of ECL articles were published after 2010, and the first international meeting on ECL was held in Italy in 2014. This critical review discusses recent vibrant developments in ECL, and highlights novel ECL phenomena, such as wireless ECL devices, bipolar electrode-based ECL, light-emitting electrochemical swimmers, upconversion ECL, ECL resonance energy transfer, thermoresponsive ECL, ECL using shape-controlled nanocrystals, and ECL as an ion-selective electrode photonic reporter, a paper-based microchip, and a self-powered microfluidic ECL platform. We also comment on the latest progress in bioassays, light-emitting devices and, the computational approach for the ECL mechanism study. Finally, perspectives and key challenges in the near future are addressed (198 references).

Fabrication of metal–organic single crystalline nanowires and reduced graphene oxide enhancement for an ultrasensitive electrochemical biosensor

Schematic of the copper phthalocyanine nanowire modified glassy carbon electrode with reduced graphene oxide–Nafion composite film used for detecting dopamine.

A catalytic chemodosimetric approach for detection of nanomolar cyanide ions in water, blood serum and live cell imaging

The nano-molar detection of cyanide in live cell imaging and blood serum has been achieved through cyanide catalysed fluorescence enhancement with a TON between 70 and 360.

Graphene platform used for electrochemically discriminating DNA triplex

Triplex DNA has received great attention as new molecular biology tools and therapeutic agents due to their possible novel functions in biology systems. Therefore, it is important to distinguish triplex from among different forms of DNA, such as single-stranded and double-stranded DNA. In this report, several electrochemical techniques, cyclic voltammetry, electrochemical impedance spectroscopy, different pulse voltammetry, and electrochemiluminescence were used for distinguishing this unique structure among different DNA formations by using functionalized graphene/Nafion-Ru(bpy)3(2+) (bpy = 2, 2'-bipyridine) modified glass carbon electrode. The different interactions between nucleotides and graphene surface and Ru(bpy)3(2+) mediated guanine oxidation produced quite different electrochemical responses. Guanine bases are hidden inside the folded triplex DNAs, which are much less susceptible to be oxidized by Ru(bpy)3(3+) produced on electrodes. Furthermore, the effect of guanine bases stacking in triplex also influences the electrochemical behaviors. By changing the different position and distance of guanine bases in DNA sequences, we found that the conjoint way of several guanines strongly influenced the catalytic electrochemical responses on graphene surface. Our results provide new insight into determination of less stable protonated triplex formation by using graphene-based rapid, low-cost and sensitive electrochemical techniques.

Solution-processable electrochemiluminescent ion gels for flexible, low-voltage, emissive displays on plastic

Ion gels comprising ABA triblock copolymers and ionic liquids have received much attention as functional materials in numerous applications, especially as gate dielectrics in organic transistors. Here we have expanded the functionality of ion gels by demonstrating low-voltage, flexible electrochemiluminescent (ECL) devices using patterned ion gels containing redox-active luminophores. The ECL devices consisted only of a 30 μm thick emissive gel and two electrodes and were fabricated on indium tin oxide-coated substrates (e.g., polyester) simply by solution-casting the ECL gel and brush-painting a top Ag electrode. The triblock copolymer employed in the gel was polystyrene-block-poly(methyl methacrylate)-block-polystyrene, where the solvophobic polystyrene end blocks associate into micellar cross-links in the versatile ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). An ECL gel containing ~6.25 wt % Ru(bpy)3Cl2 (relative to [EMI][TFSI]) as the luminophore turned on at an AC peak-to-peak voltage as low as 2.6 V (i.e., -1.3 to +1.3 V) and showed a relatively rapid response (sub-ms). The wavelength of maximum emission was 610 nm (red-orange). With the use of an iridium(III) complex, Ir(diFppy)2(bpy)PF6 [diFppy = 2-(2',4'-difluorophenyl)pyridine; bpy = 2,2'-bipyridyl], the emitting color was tuned to a maximum wavelength of 540 nm (green). Moreover, when a blended luminophore system containing a 60:40 mixture of Ru(bpy)3(2+) and Ir(diFppy)2(bpy)(+) was used in the emissive layer, the luminance of red-orange-colored light was enhanced by a factor of 2, which is explained by the generation of the additional excited state Ru(bpy)3(2+)* by a coreactant pathway with Ir(diFppy)2(bpy)(+)* in addition to the usual annihilation pathway. This is the first time that enhanced ECL has been achieved in ion gels (or ionic liquids) using a coreactant. Overall, the results indicate that ECL ion gels are attractive multifunctional materials for printed electronics.