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

Sensitive electrochemiluminescence immunosensor based on a novel luminescent europium metal-organic framework and antenna effect for detecting pro-gastrin-releasing peptide

Sensitive detection of pro-gastrin-releasing peptide (Pro-GRP) is crucial because it is a highly sensitive and specific tumor marker for small cell lung cancer. Herein, we synthesized an efficient luminescent europium metal-organic framework and developed a sandwich ECL immunosensor for the sensitive detection of Pro-GRP, which used Eu3+ as the central ion and 2,4,6-tri (4-carboxyphenyl)-1,3,5-triazine (H3TATB) as the organic ligand. H3TATB acted as a strong absorbing reagent and transferred its energy to Eu3+ via the antenna effect to enhance the ECL response signal of Eu3+. As per calculations, the ECL efficiency of Eu-TATB, which was a promising ECL luminophore, was up to 130 %. The Cu2O cube worked as a substrate to assist the electron transfer and was used as a co-reaction accelerator to catalyze S2O82- to produce more SO4•- and then enhance the ECL intensity of Eu-TATB. Under optimal experimental conditions, the ECL immunosensor had a linear range of 5 fg mL-1-50 ng mL-1 for detecting Pro-GRP with a detection limit of 1.6 fg mL-1; moreover, it demonstrated excellent stability and specificity and has been successfully applied for detecting Pro-GRP in the human serum.

A dual-emitting fluoroprobe fabricated by aloe leaf-based N-doped carbon quantum dots and copper nanoclusters for nitenpyram detection in waters by virtue of inner filter effect and static quenching principles

Fluorescence sensing technique has been used in environmental analysis due to its simplicity, low cost, and visualization. Although the fruit pulp-based biomass carbon quantum dots (CQDs) have excellent luminescent properties, aloe leaves possess the superiority of being easily accessible in all seasons compared to fruit pulp. Thus, we fabricated Aloe carazo leaf-based nitrogen doping-CQDs (N-CQDs) using a facile hydrothermal approach, which emitted bright blue fluorescence with a quantum yield of 21.4 %. By comparison, the glutathione-encapsulated copper nanoclusters (GSH-CuNCs) displayed strong red fluorescence. A blue/red dual emission based on the N-CQDs/CuNCs mixture was established for nitenpyram detection. At the 350-nm excitation, the N-CQD/CuNCs system produced dual-wavelength emitting peaks at 440 and 660 nm, respectively. Moreover, when nitenpyram was introduced into the system, the fluorescence intensities (FIs) of N-CQDs significantly decreased, whereas the FIs of GSH-CuNCs varied slightly; simultaneously, the solution color changed from bright blue to dark red. Both the spectral overlapping between nitenpyram's UV-Vis absorption and N-CQDs' excitation and almost unchanged fluorescence lifetimes indicated the occurrence of inner-filtering effect (IFE) in the dual-emitting fluoroprobe. In addition, the Stern-Volmer constant (Ksv = 6.92 × 103 M-1), temperature effect, as well as UV-Vis absorption of N-CQD/CuNCs before and after the addition of nitenpyram corroborated the static-quenching behavior. Consequently, the fluorescence-quenching of N-CQDs by nitenpyram was attributable to the joint IFE and static-quenching principles. A good linearity existed between the F660/F440 values and nitenpyram concentrations (0.5-200 μM) with a method detection limit of 0.15 μM. The dual-emitting fluoroprobe provided the satisfactory recoveries (95.0%-107.0 %) for nitenpyram detection in real-world waters, which were comparable with the results of traditional liquid chromatography coupled to tandem mass spectrometry method. Owing to its simple operations, low-cost, and adaptability for on-site outdoor monitoring, the newly developed dual-emitting fluoroprobe possesses great potential applications in routine monitoring of nitenpyram under field conditions.

HOF-101-based dual-mode biosensor for photoelectrochemical/electrochemiluminescence detection and imaging of oxytetracycline

A unique hydrogen-bonded organic frameworks (HOF-101)-based photoelectrochemical (PEC) and electrochemiluminescence (ECL) dual-mode biosensor using polydopamine nanoparticles (PDAs) as quencher was constructed for ultrasensitive detection and imaging of oxytetracycline (OXY). In particular, HOF-101 was a superior ECL material and can be observed with the naked eye. Furthermore, it also had outstanding PEC signal, so HOF-101 was a new dual-signal material with excellent performance, thus it was explored to realize dual-mode detection. As the main component of natural melanin, PDAs not only had good biocompatibility, but also contained rich functional groups on the surface. Additionally, PDAs had excellent light absorption ability and poor conductivity, which made it the excellent photoquencher. In this work, PDAs were introduced on the surface of HOF-101 to quench its ECL and PEC signals by using the dual-aptamer sandwich method, achieving ultrasensitive detection of antibiotic OXY. Particularly for ECL detection, HOF-101 was firstly used to visually detect OXY. The detection range can reach 0.1 pM-100 nM, and the limit of detection (LOD) can reach 0.04 pM. This work showed a great contribution to the development of new ECL-PEC materials and ECL visualization analysis, which had outstanding application potential in the fields of food safety and biochemical analysis.

Ligand-induced Assembly of Copper Nanoclusters with Enhanced Electrochemical Excitation and Radiative Transition for Electrochemiluminescence

Copper nanoclusters (CuNCs) are emerging electrochemiluminescence (ECL) emitters with unique molecule-like electronic structures, high abundance, and low cost. However, the synthesis of CuNCs with high ECL efficiency and stability in a scalable manner remains challenging. Here, we report a facile gram-scale approach for preparing self-assembled CuNCs (CuNCsAssy ) induced by ligands with exceptionally boosted anodic ECL and stability. Compared to the disordered aggregates that are inactive in ECL, the CuNCsAssy shows a record anodic ECL efficiency for CuNCs (10 %, wavelength-corrected, relative to Ru(bpy)3 Cl2 /tripropylamine). Mechanism studies revealed the unusual dual functions of ligands in simultaneously facilitating electrochemical excitation and radiative transition. Moreover, the assembly addressed the limitation of poor stability of conventional CuNCs. As a proof of concept, an ECL biosensor for alkaline phosphatase detection was successfully constructed with an ultralow limit of detection of 8.1×10-6  U/L.

Co-amplification of luminol-based electrochemiluminescence immunosensors based on multiple enzyme catalysis of bimetallic oxides CoCeOx and NiMnO3 for the detection of CYFRA21-1

The accelerated energy supply of co-reactants is an extremely effective strategy for achieving highly sensitive electrochemiluminescence analysis, and binary metal oxides would be an excellent tool for this purpose owing to the nano-enzyme acceleration of mixed metal valence states. Herein, an electrochemiluminescent (ECL) immunosensor for monitoring the concentration of cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) was developed based on a co-amplification strategy triggered by two bimetallic oxides, CoCeO_x and NiMnO₃, with luminol as the luminophore. CoCeO_x derived from an MOF exhibits a large specific surface area and excellent loading capacity as a sensing substrate, and the peroxidase properties enable the catalysis of hydrogen peroxide to provide energy supply to the underlying radicals. The dual enzymatic properties of flower-like NiMnO₃ were employed as probe carriers for luminol enrichment. The peroxidase properties built on Ni²⁺/Ni³⁺ and Mn³⁺/Mn⁴⁺ binary redox pairs resulted in the integration of highly oxidative hydroxyl radicals, and the oxidase properties provided additional superoxide radicals via dissolved oxygen. The practically proven multi-enzyme-catalyzed sandwich-type ECL sensor easily accomplished an accurate immunoassay of CYFRA21-1, harvesting a detection limit of 0.3 pg mL^-1 in the linear range of 0.001-150 ng mL^-1. In conclusion, this work explores the cyclic catalytic amplification of mixed-valence binary metal oxides with nano-enzyme activity in the field of ECL and develops an effective pathway for ECL immunoassay.