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Nowadays, novel and efficient signal amplification strategy in electrochemiluminescence (ECL) platform is urgently needed to enhance the sensitivity of biosensor. In this work, the dual ECL signal enhancement strategy was constructed by the interactions of Pd nanoparticles attached covalent organic frameworks (Pd NPs@COFs) with tris (bipyridine) ruthenium (RuP) and Exonuclease III (Exo.III) cycle reaction. Within this strategy, the COFs composite was generated from the covalent reaction between 2-nitro-1,4-phenylenediamine (NPD) and trialdehyde phloroglucinol (Tp), and then animated by glutamate (Glu) to attach the Pd NPs. Next, the "signal on" ECL biosensor was constructed by the coordination assembly of thiolation capture DNA (cDNA) onto the Pd NPs@COFs modified electrode. After the aptamer recognition of progesterone (P4) with hairpin DNA 1 (HP1), the Exo. III cycle reaction was initiated with HP2 to generate free DNA, which hybridized with cDNA to form double-stranded DNA (dsDNA). For that, the RuP was embedded into the groove of dsDNA and achieved the ultrasensitive detection of P4 with a lower limit of detection (LOD) down to 0.45 pM, as well as the excellent selectivity and stability. This work expands the COFs-based materials application in ECL signal amplification and valuable DNA cyclic reaction in biochemical testing field., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nowadays, organic emitters suffer from insufficient electrochemiluminescence (ECL) efficiency in aqueous solutions, and their practical applications are severely restricted in the bio-sensing field. In this work, palladium nanospheres-embedded metal–organic frameworks (Pd@MOFs) were exploited to enhance the ECL efficiency of 2,6-dimethyl-8-(3-carboxyphenyl)4,4′-difluoroboradiazene (BET) prepared by a one-pot method in aqueous environment. First, the Pd@MOFs were generated via in situ reduction of Pd nanospheres anchored onto the MOFs, and fabricated by orderly coordination of palladium chloride (PdCl2) with 1,2,4,5-benzenetetramine (BTA) tetrahydrochloride. Then, the influence of protons on the ECL response of BET was studied in detail to obtain stronger ECL emission using potassium persulfate (K2S2O8) as co-reactant in aqueous environment. As a result, a 1.47-fold ECL efficiency enlargement of BET/K2S2O8 was harvested at the Pd@MOFs/GCE, where Ru(bpy)32+ behaved as a standard. Based on the fact that the ECL signals of the BET-covered Pd@MOFs modified glassy carbon electrode (simplified as BET/Pd@MOFs/GCE) can be quenched by Cu2+, the as-built ECL sensor showed a wide linear range (1.0–100.0 pM) and a limit of detection (LOD) as low as 0.12 pM. Hence, such research offers huge potential to promote the development of organic emitters in ECL biosensors and environmental monitoring. [ABSTRACT FROM AUTHOR]

Aptamer-based bioassay of biomarker has broad applications in clinical research and disease diagnosis. In this work, a label-free aptamer biosensor for ultrasensitive thrombin (TB) detection was constructed based on highly enhanced electrochemiluminescence (ECL) of functional palladium nanocones (Pd NCs) with tripropylamine (TPA) system. Herein, well-defined Pd NCs were initially functionalized by mercaptoethanol (MCH) as an ECL emitter and immobilized onto the glassy carbon electrode (GCE) initially grafted with amine-terminated polyamidoamine (PAMAM) via electro-oxidation reaction. Under optimal conditions, the ECL intensity of the Pd NCs/TPA system was about 2.5 times enhancement when compared to that of bare GCE. The ECL and cyclic voltammetry (CV) were synchronously employed to illustrate the enhanced ECL mechanism. By virtue of the linkage of the modified Pd NCs with specified TB aptamer (TBA) containing sulfydryl group, a label-free ECL detection platform was designed. After full coverage of the nonspecific sites with bovine serum albumin (BSA), an ECL biosensor for TB detection was constructed by taking the advantage of the steric hindrance effects, showing the wider linear range, lower detection limit of TB (even down to 6.76 fM), superb selectivity and stability. The current strategy provides a highly sensitive platform for detection of various biomolecules in bioanalysis. Image 1 • Pd NCs were efficiently functionalized with MCH as a superb ECL emitter. • PAMAM dramatically improved the electron-transfer rates and amplify the ECL intensity of the Pd NCs/TPA system. • A label-free aptamer biosensor was developed for ultrasensitive TB detection. [ABSTRACT FROM AUTHOR]

Development of ultra-sensitive and high specific aptasensors is important for early diagnosis of prostate cancer. Herein, ultrasensitive detection of prostate specific antigen (PSA) aptasensor was realized based on the "on-off-on" model via fluorescence (FL) covalent energy transfer between g-C 3 N 4 quantum dot (g-CNQDs) and palladium triangular plates (Pd TPs). Specifically, the Pd TPs were primarily linked with PSA aptamer (PA) as the reporter probe, followed by attaching them onto the g-CNQDs surfaces, causing the highly enlarged FL quenching rate (ca. 75%). After the introduction of PSA, the FL intensities recovered again because of the distinctively stronger affinity of PA to PSA than that of g-CNQDs. The bond of pyridine N with Pd was identified as efficient energy transfer pathway through the X-ray photoelectron spectroscopy (XPS) and FL measurements. The surface plasmon resonance (SPR) experiments certified the remarkably different affinity of PA towards g-CNQDs and PSA. The as-constructed FL aptasensor can accurately quantify PSA with wide linear range of 10 pg mL−1-50 ng mL−1 and ultra-low limit of detection (LOD, 4.2 pg mL−1), indicating the promising applications in clinical assay and biological detection. Image 1 • Pd TPs were synthesized under solvothermal conditions and acted as effective fluorescent quencher. • The Pd TPs-PA behaved as signal reporter for constructing a FL aptasensor. • The aptasensor was applied for PSA detection with low detection limit and high specificity. [ABSTRACT FROM AUTHOR]

• ZnPPIX-Pd NCs work as an ECL emitter with high ECL intensity and lower excitation potential. • The ECL was irradiated from single oxygen via electrocatalytic reduction of ZnPPIX-Pd NCs. • A fast and ultrasensitive ECL sensor was constructed for Zn2+ detection based on "signal on" mode. Zinc ions (Zn2+) act as a transcription factor in eukaryotic cells for mediating protein-protein interactions in human healthy. The simple and sensitive detection of Zn2+ is the crucial mission in analytical field. This work demonstrated a novel and fast Zn2+ detection strategy based on "signal on" mode with electrochemiluminescence (ECL) luminophore, in which singlet oxygen was generated via electrocatalytic reduction of zinc proto-porphyrin IX grafted onto Pd nanocubes (ZnPPIX-Pd NCs). In protocol, Pd NCs were synthetized under hydrothermal conditions and aminated through thermal oxidative polymerization of 3-aminopropyltriethoxysilane (APTES), followed by further linking with PPIX via amide reaction. The resulting PPIX-Pd NCs effectively captured Zn2+ in chelation and monitored by Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) absorption spectroscopy. By virtue of the metal resonance responses of Pd NCs, an intense monochromic, potential shuffling and enhanced ECL irradiation shows up for the hybrid nanocomposite with H 2 O 2 as the coreactant. To this end, an ultrasensitive method based on the nanocomposite with a "signal-on" model was developed for Zn2+ detection with a low detection limit down to 0.38 nM (based on a S / N = 3), excellent precision and high stability. The ECL strategy reveals the potential application in molecular diagnosis and offers a new avenue for bioassay of structural Zn(II) proteins and zinc finger-binding nucleotides. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Well-defined Pd nanocones were facilely obtained by the PLL-mediated one-pot hydrothermal method. • Pd nanocones were firstly employed as an anodic ECL emitter, where TPA served as the coreactant. • An ultrasensitive ECL sensor was constructed for DA detection with a wider linear range and the lower detection limit. Abstract Electrochemiluminescence (ECL) has attracted significant interest because of its superior properties and potential applications in bioanalysis, and therefore many luminescent nanomaterials have been developed. Herein, well-defined Pd nanocones (Pd NCs) were facilely obtained by a one-pot hydrothermal method with poly- l -lysine (PLL) as a green protecting ligand, which were mainly characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Then, the as-obtained Pd NCs were first explored as an anodic ECL emitter, where tripropylamine (TPA) worked as the coreactant to boost the ECL emission. The possible ECL mechanism of Pd NCs/TPA system was extensively explored by ECL and electrochemical techniques. Briefly, the ECL emission underwent the oxidation-reduction route, in which both Pd NCs and TPA were initially oxidized, and then the oxidized TPA lost an proton to form reducing agent (TPA·) strongly reacted with the oxidized Pd NCs generating Pd NCs* for the emission. Furthermore, using dopamine (DA) as an ECL quencher, an ultrasensitive sensor was constructed for DA detection. The fabricated ECL sensor shows high sensitivity and selectivity, good stability, and wide linear range with the low detection limit of 0.46 pM. It offers a new avenue to exploit ECL illuminant and enriches the ECL emission theory. [ABSTRACT FROM AUTHOR]