Efficient Near-Infrared Electrochemiluminescence from Au18 Nanoclusters

Spectroscopy and absolute quantum efficiency of near-infrared electrochemiluminescence for a macrocyclic palladium complex

Electrochemiluminescence (ECL) is widely applied as a reliable tool in clinical diagnosis, including immunoassays, cancer biomarker detection, etc. Metal complexes with emission in the near-infrared (NIR) range possess distinct features such as high transmission and minimal tissue auto-absorption, making them versatile for applications in biosensing and other fields. Through ECL spectral studies of an O-linked nonaromatic benzitripyrrin (C^N^N^N) macrocyclic palladium complex (Pd1) with multiple pyrrole structures, we observed emission peaks from the Qx(0,0) and its vibronic Qx(0,1) bands during both photoluminescence (PL) and ECL. Notably, the emission from the Qx(0,1) band was significantly enhanced in the ECL spectrum, demonstrating higher selectivity for near-infrared light at 743 nm. In the ECL annihilation pathway, the appearance of ECL signals showed a strong correlation with the redox processes of the tri-pyrrin structure, revealing a cyclic tri-pyrrin ligand-centered nature with contributions from the metal center. Upon the introduction of tripropylamine (TPrA) and benzoyl peroxide (BPO) coreactants, the ECL signals exhibited enhancements ranging from several hundred to tens of times. Various reaction routes within different coreactant systems are extensively discussed. Additionally, the absolute quantum efficiencies of the Pd1/TPrA coreactant system were determined, showing efficiencies of 0.0032% ± 0.0005% and 0.000074% ± 0.000016% during pulsing and CV scan processes, respectively. This work addresses gaps in the study of palladacycle complexes in ECL and provides insights into the design of NIR luminescent structures that contribute to the fast screening and deep tissue penetration bioimaging techniques.

Solvent-Mediated Hetero/Homo-Phase Crystallization of Copper Nanoclusters and Superatomic Kernel-Related NIR Phosphorescence

Atomically precise superatomic copper nanoclusters (Cu NCs) have been the subject of immense interest for their intriguing structures and diverse properties; nonetheless, the variable oxidation state of copper ions and complex solvation effects in wet synthesis systems pose significant challenges for comprehending their synthesis and crystallization mechanism. Herein, we present a solvent-mediated approach for the synthesis of two Cu NCs, namely, superatomic Cu26 and pure-Cu(I) Cu16. They initially formed as a hetero-phase and then separated as a homo-phase via modulating binary solvent composition. In situ UV/vis absorption and electrospray ionization mass spectra revealed that the solvent-mediated assembly was determined to be the underlying mechanism of hetero/homo-phase crystallization. Cu26 is a 2-electron superatom with a kernel-shell structure that includes a [Cu20Se12]4- shell and [Cu6]4+ kernel, containing two 1S jellium electrons. Conversely, Cu16 is a pure-Cu(I) Cu/Se nanocluster that features a [Cu16Se6]4+ core protected by extra dimercaptomaleonitrile ligands. Remarkably, Cu26 exhibits unique near-infrared phosphorescence (NIR PH) at 933 nm due to the presence of a superatomic kernel-related charge transfer state (3MM(Cu)CT). Overall, this work not only showcases the hetero/homo-phase crystallization of Cu NCs driven by a solvent-mediated assembly mechanism but also enables the rare occurrence of NIR PH within the 2-electron copper superatom family.

Developing tiny-sized particles, different modification behaviors of gold atoms, and nucleating distorted particles

The study of tiny-sized particles is beneficial in many ways. This has been the subject of many studies. The development of a tiny-sized particle depends on the attained dynamics of the atoms. In the development process of a tiny-sized particle, gold atoms must deal with different modification behaviors. Photons traveling along the air-solution interface also alter the characteristics of a developing tiny-sized particle. The electronic structures, modification behaviors, and attained dynamics of the atoms mainly contribute toward the development of tiny-sized particles. Energy under the supplied source and the local resulting forces collectively bind gold atoms. Both internally and externally driven dynamics influence the development process of different tiny-sized particles. Atoms in such developed tiny-sized particles do not experience the collective oscillations upon photons traveling along the air-solution interface. In the study of binding atoms, it is essential to consider the roles of both energy and force. Here, the development of tiny particles having different sizes presents a convincing discussion. Nucleating a distorted particle from the non-uniform amalgamation of tiny-sized particles is also discussed.

Surface-Defect-Involved and Eye-Visible Electrochemiluminescence of Unary Copper Nanoclusters for Immunoassay

A single-stabilizer-capped strategy is proposed for achieving highly efficient and surface-defect-involved electrochemiluminescence (ECL) from unary copper nanoclusters (NCs) via employing l-cysteine (Cys) as a capping agent of luminophore. The Cys-capped CuNCs (Cys-CuNCs) can be electrochemically injected with valence band (VB) holes and exhibit eye-touchable ECL processes around +0.95 and +1.15 V upon employing TPrA as a coreactant. Both accumulated ECL spectra and spooling ECL spectra demonstrated that the two ECL processes are of the same single waveband and spectrally identical to each other with the same maximum emission wavelength of 640 nm. Promisingly, ECL of the Cys-CuNCs/TPrA system is obviously red-shifted for ∼150 nm to PL of Cys-CuNCs, indicating that the bandgap-engineered routes for ECLs of Cys-CuNCs are completely blocked. The oxidative-reduction ECL process of the Cys-CuNCs/TPrA system is a kind of highly efficient, eye-visible, and single-color emission in surface-defect-involved route. The capping agent of Cys can enable the CuNCs/TPrA system with a stronger ECL than other thiol capping agents, so that Cys-CuNCs are utilized as ECL tags for sensitive and selective immunoassays, which exhibit a wide linear response range from 0.05 pg/mL to 0.5 ng/mL and a limit of detection of 0.01 pg/mL (S/N = 3) with carcinoembryonic antigen as the analyte. Moreover, both the luminophore Cys-CuNCs and conjugates Ab₂-CuNCs can be safely stored in aqueous media without any protector, which is promising for the evolution and clinic application of metal NC ECL in the surface-defect-involved route.

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.

Valence-State-Engineered Electrochemiluminescence from Au Nanoclusters

To determine the intrinsic effects of body elements on the electrochemiluminescence (ECL) of metal nanoclusters (NCs), herein, a valence-state engineering strategy is developed to adjust the NCs' ECL with bovine serum albumin (BSA)-stabilized AuNCs as a model, in which engineering the valence state of the Au body element, i.e., Au(0) and Au(I), is performed via successively reducing the precursor AuCl₄^- to Au(I) and Au(0) with BSA. The obtained BSA-AuNCs/N₂H₄ system leads to three anodic ECL processes at 0.37 (ECL-1), 0.85 (ECL-2), and 1.45 V (ECL-3). ECL-1 is generated from the BSA-Au(0) section of BSA-AuNCs in a surface-defect-involved route and is much stronger and red-shifted compared to ECL-2 and ECL-3, which are generated from the BSA-Au(I) section of BSA-AuNCs in the band-gap-engineered route. Each of the anodic ECL processes can be selectively generated and/or suppressed via adjusting the Au(I)/Au(0) ratio of BSA-AuNCs, tunable ECL generation route, and triggering potential, and the emission intensity and waveband of metal NCs are conveniently achieved in body-element-involved valence-state engineering.

Enhanced Electrochemiluminescence of A Macrocyclic Tetradentate Chelate Pt(II) Molecule via Its Collisional Interactions with the Electrode

A macrocyclic tetradentate chelate Pt(II) molecule (Pt1) served as an excellent luminophore in electrochemiluminescence (ECL) processes. The blue ECL of Pt1/S2O82- coreactant system in N,N'-dimethylformamide was found to be 46 times higher than that of the Ru(bpy)2+/S2O82- system or 30 times higher than that of the 9,10-diphenylanthracene/S2O82- system. The unprecedented high ECL quantum efficiencies were caused by the cyclic generation of monomer excited states through collisional interactions of Pt1 molecules with the electrode at an elevated frequency. The ECL is tunable from bright blue to pure white by simply changing the solvent from N,N'-dimethylformamide to dichloromethane. The white ECL of Pt(II) molecule was reported for the first time and the mechanism was proposed to be the simultaneous emissions from the monomer excited state (blue) and excimer (red).

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.