Near Infrared Electrochemiluminescence of Rod-Shape 25-Atom AuAg Nanoclusters That Is Hundreds-Fold Stronger Than That of Ru(bpy)3 Standard

Pyrene-Based Metal-Organic Frameworks with Coordination-Enhanced Electrochemiluminescence for Fabricating a Biosensing Platform

Enhancing the electrochemiluminescence (ECL) properties of polycyclic aromatic hydrocarbons (PAHs) is a significant topic in the ECL field. Herein, we elaborately chose PAH derivative luminophore 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy) as the organic ligand to synthesize a new Ru-complex-free ECL-active metal-organic framework Dy-TBAPy. Interestingly, Dy-TBAPy exhibited a more brilliant ECL emission and higher ECL efficiency than H4TBAPy aggregates. On the one hand, TBAPy luminophores were assembled into rigid MOF skeleton via coordination bonds, which not only enlarged the distance between pyrene cores to eliminate the aggregation-caused quenching (ACQ) effect but also obstructed the intramolecular motions of TBAPy to diminish the nonradiative relaxation, thus realizing a remarkable coordination-enhanced ECL. On the other hand, the ultrahigh porosity of Dy-TBAPy was beneficial to the diffusion of electrons, ions, and coreactant (S2O82-) in the skeleton, which efficiently boosted the excitation of interior TBAPy luminophores and led to a high utilization ratio of TBAPy, further improving ECL properties. More intriguingly, the ECL intensity of the Dy-TBAPy/S2O82- system was about 4.1, 87.0-fold higher than those of classic Ru(bpy)32+/TPrA and Ru(bpy)32+/S2O82- systems. Considering the aforementioned fabulous ECL performance, Dy-TBAPy was used as an ECL probe to construct a supersensitive ECL biosensor for microRNA-21 detection, which showed an ultralow detection limit of 7.55 aM. Overall, our study manifests that coordinatively assembling PAHs into MOFs is a simple and practicable way to improve ECL properties, which solves the ACQ issue of PAHs and proposes new ideas for developing highly efficient Ru-complex-free ECL materials, therefore providing promising opportunities to fabricate high-sensitivity ECL biosensors.

Recent Advances in Luminophores for Enhanced Electrochemiluminescence Analysis

Electrochemiluminescence (ECL) detection is widely applied in many fields, including chemical measurement, biological analysis, and clinic tests, due to its high sensitivity. Currently, the fast development of many new electrochemical luminophores is continuously improving the ECL-based detection ability. Besides the enhancement of luminescence emission for a high detection sensitivity, minimizing the effect of co-reactants on ECL detection and achieving multiple analysis in one sample are also the main directions in this field. This review focuses on a summary of recently prepared new luminophores to achieve the three aims mentioned above. Especially, the review is composed by three parts, focusing on the luminophores or materials with high ECL efficiency, self-enhancing properties, and multi-color ECL luminophores. The fabrication of biosensors using these molecules is also reviewed to exhibit the advances in biological applications.

Anchoring Frustrated Lewis Pair Active Sites on Copper Nanoclusters for Regioselective Hydrogenation

In recent years, the concept of Frustrated Lewis Pairs (FLPs), which consist of a combination of Lewis acid (LA) and Lewis base (LB) active sites arranged in a suitable geometric configuration, has been widely utilized in homogeneous catalytic reactions. This concept has also been extended to solid supports such as zeolites, metal oxide surfaces, and metal/covalent organic frameworks, resulting in a diverse range of heterogeneous FLP catalysts that have demonstrated notable efficiency and recyclability in activating small molecules. This study presents the successful immobilization of FLP active sites onto the surface of ligand-stabilized copper nanoclusters with atomic precision, leading to the development of copper nanocluster FLP catalysts characterized by high reactivity, stability, and selectivity. Specifically, thiol ligands containing 2-methoxyl groups were strategically designed to stabilize the surface of [Cu34S7(RS)18(PPh3)4]2+ (where RSH = 2-methoxybenzenethiol), facilitating the formation of FLPs between the surface copper atoms (LA) and ligand oxygen atoms (LB). Experimental and theoretical investigations have demonstrated that these FLPs on the cluster surface can efficiently activate H2 through a heterolytic pathway, resulting in superior catalytic performance in the hydrogenation of alkenes under mild conditions. Notably, the intricate yet precise surface coordination structures of the cluster, reminiscent of enzyme catalysts, enable the hydrogenation process to proceed with nearly 100% selectivity. This research offers valuable insights into the design of FLP catalysts with enhanced activity and selectivity by leveraging surface/interface coordination chemistry of ligand-stabilized atomically precise metal nanoclusters.

Smart modulation by bifunctional probes PNAI@Co3O4/Au NPs of the light/electric response of Au-Ag NCs to realize the dual-channel precise detection of AOH

Mycotoxin contamination currently poses a significant concern and presents a major challenge to global food safety management. In this research, gold‑silver nanoclusters (Au-AgNCs) were utilized as platforms for electrogenerated chemiluminescence (ECL) and electrochemical (EC) responses, while polyaniline-coated cobalt tetraoxide and gold (PANI@Co3O4/AuNPs) served as bifunctional probes with intelligently modulated light/electric signals to develop a dual mode adaptor sensor for sensitive detection of alternariol (AOH). The sensor's benefits are evident in three areas:(1) Bandgap modulation allows Au-Ag to exhibit enhanced light/electric response;(2) PANI@Co3O4/AuNPs exhibit both ECL quenching effects and the capability to activate KHSO5, along with improved electrical conductivity, which collectively improves the sensor's detection performance;(3) The dual-channel signal outputs significantly reduce the risk of false detections. Testing results indicated that the ECL and EC sensors performed exceptionally well across AOH concentration ranges of 0.001-100 ng/mL and 0.01-1000 ng/mL, with detection limit of 0.803 pg/mL and 0.378 pg/mL, respectively.

Confinement Effect Enhanced Bipolar Electrochemistry: Structural Color Coding Coupled with Wireless Electrochemiluminescence Imaging Technology

In this work, SiO2/CNTs photonic crystal beads were constructed by doping CNTs into SiO2 photonic crystals, which have an angle-independent responsive structural color and can be used as bipolar electrodes due to their good electrical conductivity. In addition, the bipolar electrode-electrochemiluminescence (BPE-ECL) experiments and finite element simulation prove that the low driving voltage can trigger the bipolar electrode electrochemical reactions by confinement effect. Inspired by this, it is the first to combine the SiO2/CNTs structural color coding scheme with low-drive voltage induced wireless BPE-ECL imaging based on the confinement effect of microchannels to achieve simultaneous immune detection of ovarian cancer biomarkers (CA125, CEA, AFP). The detection limits of successfully constructed high-throughput BPE-ECL biosensor for AFP, CEA, and CA125 are 0.72 ng/mL, 0.95 ng/mL, and 1.03 U/mL, respectively, and have good stability and specificity, which expands the application of electrochemiluminescence and lays a foundation for the development of electrochemiluminescence coding technology.

Recent Advances in Electroluminescent Metallic Nanoclusters: From Materials to Devices

Metallic nanoclusters (MNCs) were developed rapidly in recent decades, owing to their unique electronic structures and excited state characteristics, leading to their wide applications. Luminescence as one of the most important functions for MNCs has also been used to realize biodetection, displays, and lighting, through either electrochemiluminescence (ECL) or electroluminescence (EL). Both emissive properties and electrochemical activities of MNCs were utilized to enhance ECL and EL through facilitating exciton formation and radiation, rendering the rapid emerging of the latter in the last ten years. Through ligand modification, radiative excited-state components were increased to realize state-of-the-art photo- and electroluminescence efficiencies up to ∼100% and ∼30%, as well as ultralow biodetection limits. Nonetheless, material selection space and processing technologies are still limited. Herein, we overview and discuss recent advances of MNCs-based ECL and EL, through both aspects of materials/systems and devices, which would enlighten continuous innovations in optoelectronic MNCs.

1,1,2,2-Tetra(4-carboxylphenyl)ethylene-Based Metal-Organic Gel as Aggregation-Induced Electrochemiluminescence Emitter for the Detection of Aflatoxin B1 Based on Nanosurface Energy Transfer

In this Letter, a sensitive DNA sensing platform was developed using an indium-ion-coordinated 1,1,2,2-tetra(4-carboxylphenyl)ethylene (TPE) metal-organic gel (In-MOG) as an aggregation-induced electrochemiluminescence (AIECL) emitter and nanosurface energy transfer (NSET) as an efficient quenching strategy for detecting aflatoxin B1 (AFB1), the most dangerous food toxin. The coordination occurred in indium ions, and carboxyl groups restricted the internal rotation and vibration of TPE molecules, forcing them to release photons via radiative transitions. The quenchers of microfluidic-produced gold nanoparticles were embedded in a long-tailed triangular DNA structure, where the quenching phenomenon aligned with the theory of ECL-NSET under the overlap of spectra and appropriate donor-acceptor spacing. The proposed analytical method showed a sensitive ECL response to AFB1 in the wide concentration range of 0.50-200.00 ng/mL with a limit of detection of 0.17 ng/mL. Experimental results confirmed that constraining luminescent molecules using coordination and bonding to trigger the AIECL phenomenon was a promising method to prepare signal labels for the trace detection of food toxins.

Enhancing electrochemiluminescence for chloramphenicol detection based on the synergistic effect of doped Ti3C2 with ultrasound

Chloramphenicol (CAP) is known to be harmful to the environment and food, posing a threat to human health. Developing an effective and convenient method for detecting CAP is crucial. An electrochemiluminescence (ECL) biosensor has been designed for sensitive detection of CAP. The improved ECL behavior was attributed to the synergistic effect of N and P co-doped Ti3C2-Apt1 (N, P-Ti3C2-Apt1) nanoprobes and high intensity focused ultrasound (HIFU) pretreatment. The doping of N and P could improve the electrochemical performance of Ti3C2. HIFU pretreatment generated more reactive oxygen species (ROS) in the luminol-O2 system. N, P-Ti3C2 could aggregate and catalyze ROS, causing an increase in ECL intensity. Furthermore, N, P-Ti3C2 as a carrier loaded more aptamer, which could recognize CAP with high specificity. The detection limit was 0.01 ng/mL. This biosensor has been successfully applied in milk and environmental water samples, highlighting its potential in the field of food and environmental analysis.

Tailored Cis-Trans Isomeric Metal-Covalent Organic Frameworks for Coordination Configuration-Dependent Electrochemiluminescence

Precise manipulation of the coordination configuration within substances can modulate the band structure and catalytic properties of the target material. Metal-covalent organic frameworks (MCOFs), a crystal material amalgamating the benefits of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), can integrate a predetermined coordination environment into the frameworks for amplifying the catalytic effect. In this study, we delicately synthesize isomeric MCOFs using bis(glycinato)copper as the aminoligand via kinetically and thermodynamically favorable pathways to yield cis-MCOF and trans-MCOF products, respectively, thereby introducing a cis-trans isomeric coordination field into the framework. Moreover, the twisted skeleton derived from the flexibility of amino acid and β-ketoenamine linkages endows trans-MCOF with surprising water dispersibility. Compared to cis-MCOF, the trans isomerism displays a significant enhancement in cathodic electrochemiluminescence via the catalysis of Cu nodes toward K2S2O8. The density of states analysis shows that the d-band center of trans-MCOF is closer to the Fermi level, leading to more stable adsorption binding to promote the catalysis. This study is the first report on constructing predesign coordination configuration MCOFs via an easy-handling method, which gives the guidelines for the design of amino acid-based MCOF materials.

Eight-Electron Copper Nanoclusters for Photothermal Conversion

Owing to distinct physicochemical properties in comparison to gold and silver counterparts, atomically precise copper nanoclusters are attracting embryonic interest in material science. The introduction of copper cluster nanomaterials in more interesting fields is currently urgent and desired. Reported in this work are novel copper nanoclusters of [XCu54Cl12(tBuS)20(NO3)12] (X=S or none, tBuSH=2-methyl-2-propanethiol), which exhibit high performance in photothermal conversion. The clusters have been prepared in one pot and characterized by combinatorial techniques including ultraviolet-visible spectroscopy (UV-vis), electrospray ionization mass spectrometry (ESI-MS), and X-ray photoelectron spectroscopy (XPS). The molecular structure of the clusters, as revealed by single crystal X-ray diffraction analysis (SCXRD), shows the concentric three-shell Russian doll arrangement of X@Cu14@Cl12@Cu40. Interestingly, the [SCu54Cl12(tBuS)20(NO3)12] cluster contains 8 free valence electrons in its structure, making it the first eight-electron copper nanocluster stabilized by thiolates. More impressively, the clusters possess an effective photothermal conversion (temperature increases by 71 °C within ~50 s, λex=445 nm, 0.5 W cm-2) in a wide wavelength range (either blue or near-infrared). The photothermal conversion can be even driven under irradiation of simulated sunlight (3 sun), endowing the clusters with great potency in solar energy utilization.

Synthesis of silica-encapsulated tetraphenylethylene with aggregation-induced electrochemiluminescence resonance energy transfer for sensitively sensing microcystin-LR

The reported organic electrochemiluminescence (ECL) luminophors for the detection of various markers often suffer from intermolecular π-π stacking-induced luminophore quenching. Herein, we demonstrate one-pot synthesis of a new aggregation-induced electrochemiluminescence (AIECL) emitter (i.e., TPE@SiO2/rGO composite) for sensitive measurement of microcystin-leucine arginine (MC-LR). The TPE@SiO2/rGO composite is constructed by embedding the silica-encapsuled 1,1,2,2-tetra(4-carboxylphenyl)ethylene (TPE) in the reduced graphene oxide. In comparison with the monomer TPE, this composite exhibit high luminescence efficiency and strong ECL emission, because the AIECL phenomenon triggered by the spatial confinement effect in the SiO2 cage induces the restriction of the internal motion and vibration of molecules. Notably, this composite has distinct advantages of easy preparation, simple functionalization, and stable luminescence. Especially, the TPE@SiO2/rGO-based ECL-RET system exhibits a high quenching efficiency (ΦET) of 69.7%. When target MC-LR is present, it triggers DNA strand displacement reaction (SDR), inducing the quenching of the ECL signal of TPE@SiO2/rGO composite due to ECL resonance energy transfer between TPE@SiO2/rGO composite and methylene blue (MB). The proposed biosensor enables highly sensitive, low-cost, and robust measurement of MC-LR with a large dynamic range of 7 orders of magnitude and a detection limit of 3.78 fg/mL, and it displays excellent detection performance in complex biological matrices, holding potential applications in food safety and water monitoring.

Low-Triggering-Potential and Narrow-Potential-Window Electrochemiluminescence of Silver Nanoclusters for Gene Assay

A low-triggering potential and a narrow-potential window are anticipated to decrease the electrochemical interference and cross talk of electrochemiluminescence (ECL). Herein, by exploiting the low oxidative potential (0.82 V vs Ag/AgCl) of dihydrolipoic acid-capped sliver nanoclusters (DHLA-AgNCs), a coreactant ECL system of DHLA-AgNCs/hydrazine (N2H4) is proposed to achieve efficient and oxidative-reduction ECL with a low-triggering potential of 0.82 V (vs Ag/AgCl) and a narrow-potential window of 0.22 V. The low-triggering-potential and narrow-potential-window nature of ECL can be primarily preserved upon labeling DHLA-AgNCs to probe DNA and immobilizing DHLA-AgNCs onto the Au surface via sandwiched hybridization, which eventually enables a selective ECL strategy for the gene assay at +0.82 V. This gene assay strategy can sensitively determine the gene of human papillomavirus from 10 to 1000 pM with a low limit of detection of 5 pM (S/N = 3) and would open a way to improve the applied ECL bioassay.

Timescale correlation of shallow trap states increases electrochemiluminescence efficiency in carbon nitrides

Highly efficient interconversion of different types of energy plays a crucial role in both science and technology. Among them, electrochemiluminescence, an emission of light excited by electrochemical reactions, has drawn attention as a powerful tool for bioassays. Nonetheless, the large differences in timescale among diverse charge-transfer pathways from picoseconds to seconds significantly limit the electrochemiluminescence efficiency and hamper their broad applications. Here, we report a timescale coordination strategy to improve the electrochemiluminescence efficiency of carbon nitrides by engineering shallow electron trap states via Au-N bond functionalization. Quantitative electrochemiluminescence kinetics measurements and theoretic calculations jointly disclose that Au-N bonds endow shallow electron trap states, which coordinate the timescale of the fast electron transfer in the bulk emitter and the slow redox reaction of co-reagent at diffusion layers. The shallow electron trap states ultimately accelerate the rate and kinetics of emissive electron-hole recombination, setting a new cathodic electrochemiluminescence efficiency record of carbon nitrides, and empowering a visual electrochemiluminescence sensor for nitrite ion, a typical environmental contaminant, with superior detection range and limit.

Dynamic surface reconstruction of individual gold nanoclusters by using a co-reactant enables color-tunable electrochemiluminescence

Here we report for the first time the phenomenon of continuously color-tunable electrochemiluminescence (ECL) from individual gold nanoclusters (Au NCs) confined in a porous hydrogel matrix by adjusting the concentration of the co-reactant. Specifically, the hydrogel-confined Au NCs exhibit strong dual-color ECL in an aqueous solution with triethylamine (TEA) as a co-reactant, with a record-breaking quantum yield of 95%. Unlike previously reported Au NCs, the ECL origin of the hydrogel-confined Au NCs is related to both the Au(0) kernel and the Au(i)-S surface. Surprisingly, the surface-related ECL of Au NCs exhibits a wide color-tunable range of 625-829 nm, but the core-related ECL remains constant at 489 nm. Theoretical and experimental studies demonstrate that the color-tunable ECL is caused by the dynamic surface reconstruction of Au NCs and TEA radicals. This work opens up new avenues for dynamically manipulating the ECL spectra of core-shell emitters in biosensing and imaging research.

Visible to NIR-II Photoluminescence of Atomically Precise Gold Nanoclusters

Atomically precise gold nanoclusters (NCs) have emerged as a new class of precision materials and attracted wide interest in recent years. One of the unique properties of such nanoclusters pertains to their photoluminescence (PL), for it can widely span visible to near-infrared-I and -II wavelengths (NIR-I/II), and even beyond 1700 nm by manipulating the size, structure, and composition. The current research efforts focus on the structure-PL correlation and the development of strategies for raising the PL quantum yields, which is nontrivial when moving from the visible to the near-infrared wavelengths, especially in the NIR-II regions. This review summarizes the recent progress in the field, including i) the types of PL observed in gold NCs such as fluorescence, phosphorescence, and thermally activated delayed fluorescence, as well as dual emission; ii) some effective strategies that are devised to improve the PL quantum yield (QY) of gold NCs, such as heterometal doping, surface rigidification, and core phonon engineering, with double-digit QYs for the NIR PL on the horizons; and iii) the applications of luminescent gold NCs in bioimaging, photosensitization, and optoelectronics. Finally, the remaining challenges and opportunities for future research are highlighted.

Engineered Electrochemiluminescence Biosensors for Monitoring Heavy Metal Ions: Current Status and Prospects

Metal ion contamination has serious impacts on environmental and biological health, so it is crucial to effectively monitor the levels of these metal ions. With the continuous progression of optoelectronic nanotechnology and biometrics, the emerging electrochemiluminescence (ECL) biosensing technology has not only proven its simplicity, but also showcased its utility and remarkable sensitivity in engineered monitoring of residual heavy metal contaminants. This comprehensive review begins by introducing the composition, advantages, and detection principles of ECL biosensors, and delving into the engineered aspects. Furthermore, it explores two signal amplification methods: biometric element-based strategies (e.g., HCR, RCA, EDC, and CRISPR/Cas) and nanomaterial (NM)-based amplification, including quantum dots, metal nanoclusters, carbon-based nanomaterials, and porous nanomaterials. Ultimately, this review envisions future research trends and engineered technological enhancements of ECL biosensors to meet the surging demand for metal ion monitoring.

Self-enhanced Electrochemiluminescence Luminophore Based on Pd Nanocluster-Anchored Metal Organic Frameworks via Ion Annihilation for Sensitive Cell Assay of Human Lung Cancer

Electrochemiluminescence (ECL) has attracted significant interest in the analysis of cancer cells, where the ruthenium(II)-based emitter demonstrates urgency and feasibility to improve the ECL efficiency. In this work, the self-enhanced ECL luminophore was prepared by covalent anchoring of Pd nanoclusters on aminated metal organic frameworks (Pd NCs@MOFs), followed by linkage with bis(2,2'-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) (RuP). The resultant luminophore showed 214-fold self-magnification in the ECL efficiency over RuP alone, combined by promoting the interfacial photoelectron transfer. The enhanced mechanism through ion annihilation was critically proved by controlled experiments and density functional theory (DFT) calculations. Based on the above, a "signal off" ECL biosensor was built by assembly of tyrosine kinase 7 (PTK-7) aptamer (Apt) on the established sensing platform for analysis of human lung cancer cells (A549). The built sensor showed a lower detection limit of 8 cells mL-1, achieving the single-cell detection. This work reported a self-enhanced strategy for synthesis of advanced ECL emitters, combined by exploring the ECL biosensing devices in the single-cell analysis of cancers.

Bandgap-Regulated Electrochemiluminescence Enhancement Strategy for Florfenicol Detection Based on ZrCuO3: A Multimodal Luminophore

The low electrochemiluminescence (ECL) efficiency issue of zirconia (ZrO2) has been a pressing problem since its discovery. In this study, a bandgap-regulated ECL enhancement strategy was developed to improve the ECL efficiency of ZrO2. Specifically, through the calcination of metal-organic frameworks (MOFs), the MOF-derived bimetallic oxide ZrCuO3 was synthesized. Compared to ZrO2, the synthesized ZrCuO3 exhibited a narrower bandgap and higher electron transfer efficiency, leading to enhanced ECL efficiency. Further investigation of the ECL emitter revealed that ZrCuO3 exhibited multimodal ECL emission: annihilation ECL and co-reactant participation ECL (including anodic ECL with tripropylamine as a co-reactant and cathodic ECL with K2S2O8 as a co-reactant). The anodic ECL with the highest efficiency was selected as the main mode for detecting the target in the aptasensor. Annihilation ECL and cathodic ECL served as alternative modes to ensure stability and continuity of the sensing system. Based on the bandgap-regulated strategy of ZrCuO3, a sensing chip with ITO as the working electrode was designed for the sensitive detection of florfenicol (FF). The constructed signal "off-on-off" aptasensor exhibited excellent detection performance for FF in the range of 0.0005-200 ng/mL. The proposed method provided a novel strategy for the analysis of other antibiotics or biomolecules.

Antenna effect of perylene-sensitized up-conversion luminescent material amplifies the signal of electrochemiluminescence biosensor platform for the ultra-sensitive detection of enrofloxacin

Recently, up-conversion luminescent (UCL) materials have caught extensive sight on account of their excellent biocompatibility and weak automatic fluorescence background, but the low optical signal makes researchers shy away. Organic dye-sensitized UCL materials can improve the low optical signal drawback of UCL and rejuvenate it with adjustable optical properties and unique antenna effects. In this work, an efficient, simple and selective electrochemiluminescence (ECL) sensing platform was developed for determination of enrofloxacin (ENR). 3,4,9,10-perylene tetracarboxylic acid (PTCA) was successfully used as an "antenna" to improve the ECL performance of the UCL nanoparticles (PEI-NaYF4: Yb, Er) due to its appropriate excitation spectrum position and superior electron transfer rate. The specific recognition function of the aptamer enabled the sensor to eliminate the interference from conspecific impurity. In the presence of ENR, the specific combination of ENR with aptamer made the aptamer fall from surface of the electrode, thus we could see a considerable enhancement of signal. Under the most favourable conditions, the aptasensor based on antenna effect displayed a wide detection range (1.0 × 10-14∼1.0 × 10-6 M), low limit of detection (LOD = 3.0 × 10-15 M) and receivable recoveries (96.0%-102.4%) during water samples analysis. At this point, antenna effect provides a powerful strategy to expand the application of UCL in the field of ECL biosensing.

Bright near-infrared circularly polarized electrochemiluminescence from Au9Ag4 nanoclusters

Metal nanoclusters are excellent electrochemiluminescent luminophores owing to their rich electrochemical and optical properties. However, the optical activity of their electrochemiluminescence (ECL) is unknown. Herein, we achieved, for the first time, the integration of optical activity and ECL, i.e., circularly polarized electrochemiluminescence (CPECL), in a pair of chiral Au9Ag4 metal nanocluster enantiomers. Chiral ligand induction and alloying were employed to endow the racemic nanoclusters with chirality and photoelectrochemical reactivity. S-Au9Ag4 and R-Au9Ag4 exhibited chirality and bright-red emission (quantum yield = 4.2%) in the ground and excited states. The enantiomers showed mirror-imaged CPECL signals at 805 nm owing to their highly intense and stable ECL emission in the presence of tripropylamine as a co-reactant. The ECL dissymmetry factor of the enantiomers at 805 nm was calculated to be ±3 × 10-3, which is comparable with that obtained from their photoluminescence. The obtained nanocluster CPECL platform shows the discrimination of chiral 2-chloropropionic acid. The integration of optical activity and ECL in metal nanoclusters provides the opportunity to achieve enantiomer discrimination and local chirality detection with high sensitivity and contrast.

Impact of the metal core on the electrochemiluminescence of a pair of atomically precise Au20 nanocluster isomers

Although the electrochemiluminescence (ECL) of metal nanoclusters has been reported, revealing the correlation between structure and ECL at an atomic level is highly challenging. Here, we reported the impact of the metal core of Au₂₀(SAdm)₁₂(CHT)₄ (Au₂₀-AC for short; SAdm = 1-adamantanethiolate; CHT= cyclohexanethiol) and its isomer Au₂₀(TBBT)₁₆ (TBBT = 4-tert-butylthiophenol) on their solution-state and solid-state electrochemiluminescence. In self-annihilation ECL experiments, Au₂₀-AC showed a strong cathodic ECL but a weak anodic ECL, while the ECL signal of Au₂₀(TBBT)₁₆ was weak and barely detectable. Density functional theory (DFT) calculations showed that the Au₇ kernel of [Au₂₀-AC]^- is metastable, weakening its anodic ECL. Au₂₀-AC in solution-state displayed an intense co-reactant ECL in the near-infrared region, which is 7 times higher than that of standard Ru(bpy)₃²⁺. The strongest solid-state ECL emissions of Au₂₀-AC and Au₂₀(TBBT)₁₆ were at 860 and 770 nm, respectively - 15 nm red-shifted for Au₂₀-AC and 20 nm blue-shifted for Au₂₀(TBBT)₁₆, compared to their corresponding solid-state photoluminescence (PL) emissions. This work shows that ECL is significantly affected by the subtle differences of the metal core, and offers a potential basis for sensing and immunoassay platforms based on atomically precise emissive metal nanoclusters.

Luminophore-Surface-Engineering-Enabled Low-Triggering-Potential and Coreactant-Free Electrochemiluminescence for Protein Determination

Coreactant-free electrochemiluminescence (ECL) is promising for removing the exogenous effects of coreactant and simplify the operation procedures and setups of commercialized ECL bioassays. Herein, an electrosterically involved strategy for achieving a low-triggering-potential (+0.21 V vs Ag/AgCl) and coreactant-free ECL from dual-stabilizer-capped CdTe nanocrystals (NCs) is proposed with mercaptopropionic acid (MPA) and hexametaphosphate (HMP) as the capping agents of luminophores. Upon employing the CdTe NCs as the ECL tag for the immunoassay, all the tags in the bioconjugates of the CdTe NCs and the secondary antibody (Ab₂|CdTe) as well as in the final achieved sandwich-type immunocomplexes can exhibit efficient coreactant-free ECL with an electrosterically involved triggering potential nature. The bioconjugates of Ab₂|CdTe with Ab₂ no more than 30 kDa, such as the thyroid stimulating hormone (30 kDa) and the recombinant pro-gastrin releasing peptide (ProGRP, 14 kDa), merely exhibit coreactant-free ECL around +0.24 V, while bioconjugates of Ab₂|CdTe with an Ab₂ beyond 30 kDa only give off coreactant-free ECL around +0.82 V. Due to the further enhanced electrosteric effect in sandwich-type immunocomplexes, only the ECL immunosensor with ProGRP as the target can give off coreactant-free ECL around +0.24 V. The electrosterically involved and coreactant-free ECL of CdTe NCs is consequently utilized to sensitively and selectively determine the molecular protein ProGRP, which demonstrates a wide linearity range from 0.1 to 2000 pg/mL and a low limit of detection at 0.05 pg/mL (S/N = 3). This low-triggering-potential and coreactant-free combined ECL platform indicates that engineering the surface of CdTe NCs with a protein can improve the performance of ECL tags in a protein-weight-involved electrosterical way.

Electrochemiluminescence Distance and Reactivity of Coreactants Determine the Sensitivity of Bead-Based Immunoassays

Herein we report the study of electrochemiluminescence (ECL) generation by tris(2,2'-bipyridyl)ruthenium (Ru(bpy)₃ ²⁺ ) and five tertiary amine coreactants. The ECL distance and lifetime of coreactant radical cations were measured by ECL self-interference spectroscopy. And the reactivity of coreactants was quantitatively evaluated in terms of integrated ECL intensity. By statistical analysis of ECL images of single Ru(bpy)₃ ²⁺ -labeled microbeads, we propose that ECL distance and reactivity of coreactant codetermine the emission intensity and thus the sensitivity of immunoassay. 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (BIS-TRIS) can well balance ECL distance-reactivity trade-off and enhance the sensitivity by 236 % compared with tri-n-propylamine (TPrA) in the bead-based immunoassay of carcinoembryonic antigen. The study brings an insightful understanding of ECL generation in bead-based immunoassay and a way of maximizing the analytical sensitivity from the aspect of coreactant.

Electrostatic Interaction-Induced Aggregation-Induced Emission-Type AgAu Bimetallic Nanoclusters as a Highly Efficient Electrochemiluminescence Emitter for Ultrasensitive Detection of Glial Fibrillary Acidic Protein

Herein, the aggregation-induced emission (AIE)-type carboxymethyl chitosan (CMCS)@6-aza-2-thiothymine (ATT) templated AgAu bimetallic nanoclusters (CMCS@ATT-AgAu BMNCs) with superior electrochemiluminescence (ECL) emission were first synthesized to construct a biosensor for the ultrasensitive detection of glial fibrillary acidic protein (GFAP). Impressively, unlike the traditional AIE-type bimetallic nanoclusters (BMNCs) obtained by complicated multi-step synthesis, the AIE-type CMCS@ATT-AgAu BMNCs were prepared by the electrostatic interaction between the negatively charged ATT and positively charged CMCS, in which the molecule ATT was served as a capping and reducing agent of bimetal ions. In addition, a rapidly moving cholesterol labeled DNA walker was constructed to move freely on the lipid bilayer to increase its moving efficiency, and the well-regulated DNA was intelligently designed to further improve its walking efficiency for rapid and ultrasensitive detection of GFAP with a limit of detection (LOD) as low as 73 ag/mL. This strategy proposed an avenue to synthesize highly efficient BMNCs-based ECL emitters, which have great potential in ultrasensitive biosensing for early diagnosis of diseases.

Electrochemiluminescence nanoemitters for immunoassay of protein biomarkers

The family of electrochemiluminescent luminophores has witnessed quick development since the electrochemiluminescence (ECL) phenomenon of silicon nanoparticles was first reported in 2002. Moreover, these developed ECL nanoemitters have extensively been applied in sensitive detection of protein biomarker by combining with immunological recognition. This review firstly summarized the origin and development of various ECL nanoemitters including inorganic and organic nanomaterials, with an emphasis on metal-organic frameworks (MOFs)-based ECL nanoemitters. Several effective strategies to amplify the ECL response of nanoemitters and improve the sensitivity of immunosensing were discussed. The application of ECL nanoemitters in immunoassay of protein biomarkers for diagnosis of cancers and other diseases, especially lung cancer and heart diseases, was comprehensively presented. The recent development of ECL imaging with the nanoemitters as ECL tags for detection of multiplex protein biomarkers on single cell membrane also attracted attention. Finally, the future opportunities and challenges in the ECL biosensing field were highlighted.

Voltammetric Study and Modeling of the Electrochemical Oxidation Process and the Adsorption Effects of Luminol and Luminol Derivatives on Glassy Carbon Electrodes

Luminol is one of the most widely used electrochemiluminescence (ECL) reagents, yet the detailed mechanism and kinetics of the electrochemical oxidation of luminol remain unclear. We propose a model that describes the electrochemical oxidation of luminol as multiple electron transfer reactions followed by an irreversible chemical reaction, and we applied a finite element method simulation to analyze the electron transfer kinetics in alkaline solutions. Although negligible at higher pH values, the adsorption of luminol on the glassy carbon electrode became noticeable in a solution with pH = 12. Additionally, various types of adsorption behaviors were observed for luminol derivatives and analogues, indicating that the molecular structure affected not only the oxidation but also the adsorption process. The adsorption effect was analyzed through a model with a Langmuir isotherm to show that the saturated surface concentration as well as the reaction kinetics increased with decreasing pH, suggesting a competition for the active sites between the molecule and OH^-. Moreover, we show that the ECL intensity could be boosted through the adsorption effect by collecting the ECL intensity generated through the electrochemical oxidation of luminol and a luminol analogue, L012, in a solution with pH = 13. In contrast with luminol, a significant adsorption effect was observed for L012 at pH = 13, and the ECL intensity was enhanced by the adsorbed species, especially at higher scan rates. The magnitude of the enhancement of the ECL intensity matched well with the simulation using our model.

Wireless electrochemical light emission in ultrathin 2D nanoconfinements

Spatial confinement of chemical reactions or physical effects may lead to original phenomena and new properties. Here, the generation of electrochemiluminescence (ECL) in confined free-standing 2D spaces, exemplified by surfactant-based air bubbles is reported. For this, the ultrathin walls of the bubbles (typically in the range of 100-700 nm) are chosen as a host where graphene sheets, acting as bipolar ECL-emitting electrodes, are trapped and dispersed. The proposed system demonstrates that the required potential for the generation of ECL is up to three orders of magnitude smaller compared to conventional systems, due to the nanoconfinement of the potential drop. This proof-of-concept study demonstrates the key advantages of a 2D environment, allowing a wireless activation of ECL at rather low potentials, compatible with (bio)analytical systems.

Electrochemiluminescence Systems for the Detection of Biomarkers: Strategical and Technological Advances

Electrochemiluminescence (ECL)-based sensing systems rely on light emissions from luminophores, which are generated by high-energy electron transfer reactions between electrogenerated species on an electrode. ECL systems have been widely used in the detection and monitoring of diverse, disease-related biomarkers due to their high selectivity and fast response times, as well as their spatial and temporal control of luminance, high controllability, and a wide detection range. This review focuses on the recent strategic and technological advances in ECL-based biomarker detection systems. We introduce several sensing systems for medical applications that are classified according to the reactions that drive ECL signal emissions. We also provide recent examples of sensing strategies and technologies based on factors that enhance sensitivity and multiplexing abilities as well as simplify sensing procedures. This review also discusses the potential strategies and technologies for the development of ECL systems with an enhanced detection ability.

Aggregation-Induced Emission of Gold Nanoclusters by Ionic Liquids for White Light-Emitting Diode and Multiple-Ion Probe Applications

White light-emitting diodes (WLEDs) require stable luminophores with bright emission, a large Stokes shift, and good processability. Herein, we fabricate WLEDs on the basis of synergetic aggregation-induced emission (AIE) of Au nanoclusters (NCs) induced by ionic liquids. Au NCs with orange emission at 615 nm are electrostatically bonded to 1-ethyl-3-methyl-imidazolium acetate (EmimOAc). The electrostatic bonding not only introduces complementary blue emission (from EmimOAc) into Au NCs but also enhances cluster emission via an intercluster AIE mechanism. Overall white emission of Au NC-EmimOAc composites can be further improved by their encapsulation into nanogels templated by cationic chitosan. Color conversion films constructed from these nanogels manifest ultrabright white emission on a commercial GaN ultraviolet LED chip, featuring a CIE 1931 color coordinate of (0.366, 0.368) and greatly enhanced mechanical strength. By properly selecting ionic liquids, we are also able to achieve multiple-ion detection of Cu²⁺, Sn²⁺, and Fe³⁺.

Kinetics-Based Ratiometric Electrochemiluminescence Analysis for Signal Specificity: Case Studies of Piperazine Drug Discrimination with Au Nanoclusters

A multi-parameter calibration and analysis strategy has been developed based on the kinetics of charge transfer reactions. Absolute and ratiometric electrochemiluminescence signals are elucidated from single measurements for the detection of hydroxyzine and cetirizine as prototype drugs which greatly enhance the near-infrared electrochemiluminescence from atomically precise Au₂₂ nanoclusters stabilized with lipoic acid ligands on ITO electrodes. The signal-on sensing mechanism eliminates the need for recognition elements and highly excess co-reactants in conventional electrochemiluminescence practice. The rates of sequential charge transfer reactions render specificity in electrochemiluminescence intensity and kinetics toward the target molecular/electronic structures and are conveniently controlled/optimized by operation parameters. Signal kinetic profiles, in stark contrast to steady-state or single-point recordings, not only improve the signal/noise ratio but also offer greater resolving power to differentiate analogue species and nonspecific interference. The fundamental kinetics-based ratiometric concept/strategy is not limited to a specific luminophore or a co-reactant and is thus generalizable. The case studies successfully detect and discriminate drug compounds at sub-nanomolar physiological ranges, with efficacy validated using synthetic urine toward point-of-care applications in therapeutic/abuse drug monitoring.

Low-Triggering-Potential Single-Color Electrochemiluminescence from Bovine Serum Albumin-Stabilized Unary Au Nanocrystals for Immunoassays

Herein, low-triggering-potential (LTP) electrochemiluminescence (ECL) with an onset around 0.0 V (vs Ag/AgCl) is proposed with bovine serum albumin (BSA)-stabilized Au nanocrystals (BSA-AuNCs) as a luminophore and hydrazine hydrate (N₂H₄) as a coreactant. The BSA-AuNCs/N₂H₄ system can exhibit efficient LTP-ECL around 0.37 V with the luminophore of both monodispersed and surface-confined states. The LTP-ECL of BSA-AuNCs/N₂H₄ is a kind of single-color emission with a maximum emission wavelength around 740 nm, which is obviously red-shifted for 80 nm from that of BSA-AuNCs PL, and indicates that the ECL is generated in a surface-defect-involved route instead of the band-gap-engineered route. Importantly, BSA-AuNCs can be utilized as ECL tags to perform sandwich-type immunoassays with acceptable sensitivity and selectivity, which exhibits a wide linear response for determining CA125 from 0.5 to 1000 mU/mL and a limit of detection of 0.05 mU/mL (S/N = 3).

Progress and Prospects of Electrochemiluminescence Biosensors Based on Porous Nanomaterials

Porous nanomaterials have attracted much attention in the field of electrochemiluminescence (ECL) analysis research because of their large specific surface area, high porosity, possession of multiple functional groups, and ease of modification. Porous nanomaterials can not only serve as good carriers for loading ECL luminophores to prepare nanomaterials with excellent luminescence properties, but they also have a good electrical conductivity to facilitate charge transfer and substance exchange between electrode surfaces and solutions. In particular, some porous nanomaterials with special functional groups or centered on metals even possess excellent catalytic properties that can enhance the ECL response of the system. ECL composites prepared based on porous nanomaterials have a wide range of applications in the field of ECL biosensors due to their extraordinary ECL response. In this paper, we reviewed recent research advances in various porous nanomaterials commonly used to fabricate ECL biosensors, such as ordered mesoporous silica (OMS), metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and metal-polydopamine frameworks (MPFs). Their applications in the detection of heavy metal ions, small molecules, proteins and nucleic acids are also summarized. The challenges and prospects of constructing ECL biosensors based on porous nanomaterials are further discussed. We hope that this review will provide the reader with a comprehensive understanding of the development of porous nanomaterial-based ECL systems in analytical biosensors and materials science.

Recent progress of metal nanoclusters in electrochemiluminescence

Metal nanoclusters (MeNCs), composed of a few to hundreds of metal atoms and appropriate surface ligands, have attracted extensive interest in the electrochemiluminescence (ECL) realm owing to their molecule-like optical, electronic, and physicochemical attributes and are strongly anticipated for discrete energy levels, fascinating electrocatalytic activity, and good biocompatibility. Over the past decade, huge efforts have been devoted to the synthesis, properties, and application research of ECL-related MeNCs, and this field is still a subject of heightened concern. Therefore, this perspective aims to provide a comprehensive overview of the recent advances of MeNCs in the ECL domain, mainly covering the emerged ECL available MeNCs, unique chemical and optical properties, and the general ECL mechanisms. Synthesis strategies for desirable ECL performance are further highlighted, and the resulting ECL sensing applications utilizing MeNCs as luminophores, quenchers, and substrates are discussed systematically. Finally, we anticipate the future prospects and challenges in the development of this area.

Evidence for triplet-state-dominated luminescence in biicosahedral superatomic molecular Au25 clusters

In photoluminescence (PL) quenching and triplet fusion upconversion experiments with fluorescent organic-molecule quenchers, it was revealed that a rod-shaped, phosphine- and thiolate-protected biicosahedral Au₂₅ cluster (a representative di-superatomic molecule) exhibits only phosphorescence, not fluorescence, at room temperature with an intersystem crossing quantum yield of almost 100%. By virtue of these photophysical properties, this cluster can be used as a triplet sensitizer that undergoes direct singlet-triplet transitions in the near-infrared (NIR) region (730-900 nm), inducing photon upconversion from NIR to visible light.

Enhanced Plasmon Based Ag and Au Nanosystems and Their Improved Biomedical Impacts

Numerous specialists and academics have backed the improved physicochemical characteristics of metal substrate (Ag, Au) based composite nanoparticles for a number of applications, including pharmaceuticals, optoelectronics, and environmental impact. Insights of Ag and Au NPs-based nanomaterials will be discussed, as well as important production, physicochemical, and biotechnological characteristics. The plasmon capacities of Ag and Au NPs, along with their customisable form, scale, and surface modification could be described by specified geometries and constituent contents. It was revealed that interaction dynamics of Ag and Au implanted nanomaterials with dopants/defects ratios seem to be more effective in stimulating pathogens by interrupting biochemical reactions. As a result, we focus on defect science in Ag and Au-based nanoscale materials, taking into account surface morphology, ionic packing, and chemical phase assessment. This chapter will cover the important optical, geometrical, and physicochemical features of Ag and Au nanomaterials, and their pharmacological significance.

Near-Infrared Electrogenerated Chemiluminescence from Simple Copper Nanoclusters for Sensitive Alpha-Fetoprotein Sensing

Exploiting low cost, water-soluble, and near-infrared (NIR) emissive electrochemiluminophores (ECLphores) is significantly important for biological applications. In this study, bright and NIR electrogenerated chemiluminescence (ECL) emissive copper nanoclusters (Cu NCs) were synthesized through a facile one-pot wet chemical reduction method. ECL properties of obtained Cu NCs were examined in the presence of potassium persulfate, resulting in maximum intensity at 735 nm, at least 135 nm red-shifted with respect to all other Cu NCs. Electrochemistry, photoluminescence (PL), and spooling ECL spectroscopies were used to track NIR ECL emission of Cu NCs ascribed to the monomeric excited states. Due to the abundant binding sites of bovine serum albumin (BSA) to anchor target biomolecules, a sandwich-type ECL immunosensor was thus fabricated using such BSA-templated Cu NCs as tags and alpha fetoprotein antigen (AFP) as a model protein for the first time. Without assisting any signal amplification strategies, the proposed NIR ECL biosensor exhibited a wide linear range (1-400 ng mL^-1) and low detection limit (0.02 ng mL^-1) as well as superior selectivity and reproducibility and was successfully applied in real human serum sample determination. This work sets the stage for the development of novel non-noble metal nanoclusters for large-scale and emerging nanotechnology applications.

Lighting Up Electrochemiluminescence-Inactive Dyes via Grafting Enabled by Intramolecular Resonance Energy Transfer

Due to near-zero optical background and photobleaching, electrochemiluminescence (ECL), an optical phenomenon excited by electrochemical reactions, has drawn extensive attention, especially for ultrasensitive bioassays. Developing diverse ECL emitters is crucial to unlocking their multiformity and performances but remains a formidable challenge due to the rigorous requirements for ECL. Herein, we report a general strategy to light up ECL-inactive dyes in an aqueous solution via grafting, a well-developed concept for plant propagation since 500 BCE. As a proof of concept, a series of luminol donor-dye acceptor-based ECL emitters were grafted with near-unity resonance energy transfer (RET) efficiency and coarse/fine-tunable emission wavelengths. Rather than the sophisticated design of new skeleton-based molecules to meet all of the prerequisites for ECL in a constrained manner, each unit in the proposed ECL ensemble performed its functions maximally. As a result, beyond traditional two-dimensional (2D) ones, a three-dimensional (3D) coordinate biosensing system, simultaneously showing a calibration curve and selectivity, was established using the new ECL emitter. This lighting up strategy would generally address the scarcity of ECL emitters and enable unprecedented functions.

Ultrasensitive Glutathione-Mediated Facile Split-Type Electrochemiluminescence Nanoswitch Sensing Platform

Seeking for an advanced electrochemiluminescence (ECL) platform is still an active and continuous theme in the ECL-sensing realm. This work outlines a femtomolar-level and highly selective glutathione (GSH) and adenosine triphosphate (ATP) ECL assay strategy using a facile split-type gold nanocluster (AuNC) probe-based ECL platform. The system utilizes GSH as an efficient etching agent to turn on the MnO₂/AuNC-based ECL nanoswitch platform. This method successfully achieves an ultrasensitive detection of GSH, which significantly outperformed other sensors. Based on the above excellent results, GSH-related biological assays have been further established by taking ATP as a model. Combined with the high catalytic oxidation ability of DNAzyme, this ECL sensor can realize ATP assay as low as 1.4 fmol without other complicated exonuclease amplification strategies. Thus, we successfully achieved an ultrahigh sensitivity, extremely wide dynamic range, great simplicity, and strong anti-interference detection of ATP. In addition, the actual sample detection for GSH and ATP exhibits satisfactory results. We believe that our proposed high-performance platform will provide more possibilities for the detection of other GSH-related substances and show great prospect in disease diagnosis and biochemical research.

Insights into Electrochemiluminescence Dynamics by Synchronizing Real-Time Electrical, Luminescent, and Mass Spectrometric Measurements

Electrochemiluminescence (ECL) comprises a sophisticated cascade of reactions. Despite advances in mechanistic studies by electrochemistry and spectroscopy, a lack of access to dynamic molecular information renders many plausible ECL pathways unclear or unproven. Here we describe the construction of a real-time ECL mass spectrometry (MS) platform (RT-Triplex) for synchronization of dynamic electrical, luminescent, and mass spectrometric outputs during ECL events. This platform allows immediate and continuous sampling of newly born species at the Pt wire electrode of a capillary electrochemical (EC) microreactor into MS, enabling characterization of short-lived intermediates and the multi-step EC processes. Two ECL pathways of luminol are validated by observing the key intermediates α-hydroxy hydroperoxide and diazaquinone and unraveling their correlation with applied voltage and ECL emission. Moreover, a “catalytic ECL route” of boron dipyrromethene (BODIPY) involving homogeneous oxidation of tri-n-propylamine with the BODIPY radical cation is proposed and verified.

A real-time electrochemiluminescence mass spectrometry platform (RT-Triplex) was developed for revealing ECL mechanisms by synchronization of dynamic electrical, luminescent, and mass spectrometric signals at the electrode–electrolyte interface.

Ultrasensitive near-infrared aptasensor for enrofloxacin detection based on wavelength tunable AgBr nanocrystals electrochemiluminescence emission triggered by O-terminated Ti3C2 MXene

Toxic-free and easily accessible electrochemiluminescence (ECL) emitter/luminophore with near-infrared (NIR) emission is highly anticipated for ECL biosensor evolution. In this study, well-dispersed AgBr nanocrystals (NCs) decorated Ti₃C₂ MXene nanocomposites (Ti₃C₂-AgBrNCs) were prepared using a simple wet chemical technique and demonstrated highly efficient NIR ECL emission. For the first time, Ti₃C₂-AgBrNCs displayed wavelength-tunable ECL emission with varied Ti₃C₂ contents. Interestingly, further experimental data revealed that the ECL emission wavelength of Ti₃C₂-AgBrNCs red-shifted from 550 to 665 nm as Ti₃C₂ content increased, which can be attributed to the surface-defect effect generated by the oxygen-containing functional groups in Ti₃C₂ MXene. In particular, the ECL emission at 665 nm of Ti₃C₂-AgBrNCs nanocomposites not only revealed a 3.5 times increased ECL intensity but also a more stable ECL signal compared to pure AgBr NCs. As a proof of concept, a direct-type NIR ECL aptasensor with signal-on strategy was constructed with the Ti₃C₂-AgBrNCs nanocomposites as an ECL platform and enrofloxacin (ENR) as a model analyte. The NIR ECL aptasensor exhibited high sensitivity, a wide linear range from 1.0 × 10^-12 mol/L to 1.0 × 10^-6 mol/L and a low detection limit (5.97 × 10^-13 mol/L). This research offered a viable alternative way for producing toxic-free and efficient near-infrared ECL luminophores in bioanalysis and wavelength-tuning light-emitting devices.

Identifying Highly Photoelectrochemical Active Sites of Two Au21 Nanocluster Isomers toward Bright Near-Infrared Electrochemiluminescence

Thus far, no correlation between nanocluster structures and their electrochemiluminescence (ECL) has been identified. Herein, we report how face-centered-cubic and hexagonal close-packed structures of two Au₂₁(SR)₁₅ nanocluster isomers determine their chemical reactivity. The relationships were explored by means of ECL and photoluminescence spectroscopy. Both isomers reveal unprecedented ECL efficiencies in the near-infrared region, which are >10- and 270-fold higher than that of standard Ru(bpy)₃²⁺, respectively. Photoelectrochemical reactivity as well as ECL mechanisms were elucidated based on electrochemistry, spooling photoluminescence, and ECL spectroscopy, unfolding the three emission enhancement origins: (i) effectively exposed reactive facets available to undergo electron transfer reactions; (ii) individual excited-state regeneration loops; (iii) cascade generations of various exited states. Indeed, these discoveries will have immediate impacts on various applications including but not limited to single molecular detection as well as photochemistry and electrocatalysis toward clean photon-electron conversion processes such as light-harvesting and light-emitting technologies.

Intrareticular charge transfer regulated electrochemiluminescence of donor-acceptor covalent organic frameworks

The control of charge transfer between radical anions and cations is a promising way for decoding the emission mechanism in electrochemiluminescence (ECL) systems. Herein, a type of donor-acceptor (D-A) covalent organic framework (COF) with triphenylamine and triazine units is designed as a highly efficient ECL emitter with tunable intrareticular charge transfer (IRCT). The D-A COF demonstrates 123 folds enhancement in ECL intensity compared with its benzene-based COF with small D-A contrast. Further, the COF's crystallinity- and protonation-modulated ECL behaviors confirm ECL dependence on intrareticular charge transfer between donor and acceptor units, which is rationalized by density functional theory. Significantly, dual-peaked ECL patterns of COFs are achieved through an IRCT mediated competitive oxidation mechanism: the coreactant-mediated oxidation at lower potential and the direct oxidation at higher potential. This work provides a new fundamental and approach to improve the ECL efficiency for designing next-generation ECL devices.

Programmable Metal Nanoclusters with Atomic Precision

With the recent establishment of atomically precise nanochemistry, capabilities toward programmable control over the nanoparticle size and structure are being developed. Advances in the synthesis of atomically precise nanoclusters (NCs, 1-3 nm) have been made in recent years, and more importantly, their total structures (core plus ligands) have been mapped out by X-ray crystallography. These ultrasmall Au nanoparticles exhibit strong quantum-confinement effect, manifested in their optical absorption properties. With the advantage of atomic precision, gold-thiolate nanoclusters (Au_n (SR)_m ) are revealed to contain an inner kernel, Au-S interface (motifs), and surface ligand (-R) shell. Programming the atomic packing into various crystallographic structures of the metal kernel can be achieved, which plays a significant role in determining the optical properties and the energy gap (E_g ) of NCs. When the size increases, a general trend is observed for NCs with fcc or decahedral kernels, whereas those NCs with icosahedral kernels deviate from the general trend by showing comparably smaller E_g . Comparisons are also made to further demonstrate the more decisive role of the kernel structure over surface motifs based on isomeric Au NCs and NC series with evolving kernel or motif structures. Finally, future perspectives are discussed.

Efficient Near-Infrared Electrochemiluminescence from Au18 Nanoclusters

Bright, near-infrared electrochemiluminescence (NIR-ECL) of Au₁₈ nanoclusters is reported herein. Spooling ECL and photoluminescence spectroscopy were used to track and link NIR emissions at 832 and 848 nm to three emissive species, Au₁₈ ⁰ *, Au₁₈ ¹⁺ * and Au₁₈ ²⁺ *, with a considerably high ECL efficiency of 5.5 relative to that of the gold standard Ru(bpy)₃ ²⁺ /TPrA (with 5-6 % reported ECL efficiency). The unprecedentedly high efficiency is due to the overlapped oxidation potentials of Au₁₈ ⁰ and tri-n-propylamine as co-reactant, the exposed facets of Au₁₈ ⁰ gold core, and electrocatalytic loops. These discoveries will add a new member to the efficient NIR-ECL gold nanoclusters family and bring more potential applications.