Confinement-enhanced electrochemiluminescence of copper nanoclusters on 3D layered double hydroxide for ultrasensitive detection of GFAP.

In this work, the copper nanoclusters (Cu NCs) were confined on 3D layered double hydroxide (3D-LDH) to form Cu NCs@3D-LDH with outstanding electrochemiluminescence (ECL) for constructing ultrasensitive biosensor to detect of glial fibrillary acidic protein (GFAP) implicated in Alzheimer's Disease (AD). More importantly, compared to the individual Cu NCs, Cu NCs@3D-LDH presented strong and stable ECL response, since 3D-LDH could not only gather more Cu NCs but also limit the intramolecular free motion to reduce nonradiative transition for obtaining high ECL intensity. In addition, the improved cascade amplification method combining proximity ligation assay (PLA) with DNAzyme could transform tiny amount of target protein into a large amount of output DNA to improve sensitivity of biosensor. The ECL biosensor realized ultrasensitive detection of GFAP with the detection limit of 2 ag/mL and it had been successfully applied to the evaluation of GFAP in the serum of patients with neurological diseases. This research offered a general and facile method to improve ECL performance of Cu NCs for sensitive detection of biomarkers for disease diagnosis.

Dual-Ligand Europium-Organic Gels as a Highly Efficient Anodic Annihilation Electrochemiluminescence Emitter for Ultrasensitive Detection of MicroRNA.

In this study, a novel europium dual-ligand metal-organic gel (Eu-D-MOGs) with high-efficient anodic annihilation electrochemiluminescence (ECL) was synthesized as an ECL emitter to construct a biosensor for ultrasensitive detection of microRNA-221 (miR-221). Impressively, compared to the ECL signal of europium single-ligand metal-organic gels (Eu-S-MOGs), the ECL signal of Eu-D-MOGs was significantly improved since the two organic ligands could jointly replace the H2O and coordinate with Eu3+, which could remarkably reduce the nonradiative vibrational energy transfer caused by the coordination between H2O and Eu3+ with a high coordination demand. In addition, Eu-D-MOGs could be electrochemically oxidized to Eu-D-MOGs•+ at 1.45 V and reduced to Eu-D-MOGs•- at 0.65 V to achieve effective annihilation of ECL, which overcame the side reaction brought by the remaining emitters at negative potential. This benefited from the annihilation ECL performance of the central ion Eu3+ caused by its redox in the electrochemical process. Furthermore, the annihilation ECL signal of Eu3+ could be improved by sensitizing Eu3+ via the antenna effect. In addition, combined with the improved rolling circle amplification-assisted strand displacement amplification strategy (RCA-SDA), a sensitive biosensor was constructed for the sensitive detection of miR-221 with a low detection limit of 5.12 aM and could be successfully applied for the detection of miR-221 in the lysate of cancer cells. This strategy offered a unique approach to synthesizing metal-organic gels as ECL emitters without a coreactant for the construction of ECL biosensing platforms in biomarker detection and disease diagnosis.

Selenium and nitrogen co-doped carbon dots with highly efficient electrochemiluminescence for ultrasensitive detection of microRNA.

In this work, selenium and nitrogen co-doped carbon dots (SeN-CDs) possessing highly efficient electrochemiluminescence (ECL) and excellent biocompatibility were synthesized as a new emitter with S2O82- as a coreactant for constructing a biosensor to detect microRNA-221 (miRNA-221) sensitively. Notably, the SeN-CDs exhibited superior ECL performance compared with the N-doped CDs, in which selenium with excellent redox activity served as a coreaction accelerator for facilitating the electroreduction of S2O82- to significantly improve ECL efficiency. Furthermore, target-induced T7 exonuclease (T7 Exo)-assisted double cycle amplification strategy could convert traces of target miRNA-221 into large amounts of output DNA to capture three-dimensional (3D) nanostructures (DTN-Au NPs-DOX-Fc) loaded with large amounts of ECL signal quencher. The constructed biosensor could realize ultrasensitive detection of miRNA-221 and has a low detection limit reaching 2.3 aM, with a successful application to detect miRNA-221 in lysate of Hela and MHCC97-L cancer cell. This work explored a novel method to strengthen the ECL performance of CDs to construct an ECL biosensing platform with sensitive detecting of biomarkers and disease diagnosis.

Aggregation-Induced Electrochemiluminescence of Copper Nanoclusters by Regulating Valence State Ratio of Cu(I)/Cu(0) for Ultrasensitive Detection of MicroRNA.

In this work, Cu nanoclusters (Cu NCs) with strong aggregation-induced electrochemiluminescence (AIECL) as emitters were used to construct an ECL biosensor for ultrasensitive detection of microRNA-141 (miR-141). Impressively, the ECL signals enhanced with the increased content of Cu(I) in the aggregative Cu NCs. When the ratio of Cu(I)/Cu(0) in aggregative Cu NCs was 3.2, Cu NCs aggregates showed the highest ECL intensity, in which Cu(I) could enhance the cuprophilic Cu(I)···Cu(I) interaction to form rod-shaped aggregates for restricting nonradiative transitions to obviously improve the ECL response. As a result, the ECL intensity of the aggregative Cu NCs was 3.5 times higher than that of the monodispersed Cu NCs. With the aid of the cascade strand displacement amplification (SDA) strategy, an outstanding ECL biosensor was developed to achieve the ultrasensitive detection of miR-141, whose linear range varied from 10 aM to 1 nM with a detection limit of 1.2 aM. This approach opened an avenue to prepare non-noble metal nanomaterials as robust ECL emitters and provided a new idea for detection of biomolecules for diagnosis of disease.

Ultra-Sensitive MicroRNA Biosensor Based on Strong Aggregation-Induced Electrochemiluminescence from Bidentate Ligand-Stabilized Copper Nanoclusters in Polymer Hydrogel.

Herein, dihydrolipoic acid (DHLA)-stabilized copper nanoclusters (Cu NCs) with high aggregation-induced electrochemiluminescence (AIECL) in polymer hydrogel were prepared to construct an ECL biosensor for detection of microRNA-21. DHLA, a small molecule ligand with two sulfhydryl groups, was used as a protective agent to synthesize Cu NCs, which improved the ECL stability and intensity of Cu NCs. Furthermore, the Cu NCs were loaded into the (PVP-PVA)hydrogel to form the DHLA-Cu NCs@(PVP-PVA)hydrogel composite, which showed effective AIECL performance. The confinement of Cu NCs into the hydrogel increased the local concentration of Cu NCs, which could not only prevent oxides from entering the copper core, but also limit the vibration to reduce non-radiative transitions of Cu NCs, leading to a distinct AIECL emission. Then, combined with the self-priming clip trigger isothermal amplification (SCTIA) technology, an ECL biosensor was constructed to realize the sensitive detection of miRNA-21. Interestingly, SCTIA technology was a simple and efficient strategy that realized multiple-cycle amplified processes to acquire a mass of output DNA, achieving remarkable signal amplification. Therefore, this strategy provided an efficient approach in the preparation of Cu NCs with high AIECL emission and target amplification technology, which might have promising potential in clinical application.

Enhanced Electrochemiluminescence of Graphitic Carbon Nitride by Adjustment of Carbon Vacancy for Supersensitive Detection of MicroRNA.

Herein, a supersensitive biosensor was constructed by using graphitic carbon nitride with a carbon vacancy (VC-g-C3N4) as an efficient electrochemiluminescence (ECL) emitter for detection of microRNA-21 (miRNA-21). Impressively, VC-g-C3N4 could be prepared by formaldehyde (HCHO)-assisted urea ploycondensation, and the concentration of the carbon vacancy could be controlled by adjusting the dosage of HCHO to improve the ECL performance, in which the carbon vacancy could improve the charge carrier transfer to enhance the conductivity and it also could be used as an electron trap to prevent electrode passivation and facilitate the adsorption of coreactant S2O82- to accelerate its reduction. Compared with original g-C3N4, the introduction of carbon vacancies resulted in a significant enhancement of the ECL efficiency of VC-g-C3N4. With the aid of improved cascade strand displacement amplification (IC-SDA), the ECL biosensor realized sensitive detection of miRNA-21 with a low detection limit of 3.34 aM. This successful strategy promoted the development of g-C3N4 in the ECL field to construct the sensitive biosensor for molecular and disease diagnoses.

High efficiency electrochemiluminescence of 3D porous g-C3N4 with dissolved O2 as co-reactant and its sensing application for ultrasensitive detection of microRNA in tumor cells.

In this work, the electrochemiluminescence (ECL) phenomenon of three-dimensional graphitic carbon nitride (3D g-C3N4) was reported. Firstly, the proposed 3D g-C3N4 possessed 3D porous interconnected open-framework which enabled faster charge transport and efficient penetration of co-reactants due to "pore confinement effect". Then, we found that the dissolved O2 could serve as an excellent co-reactant for cathodic ECL of 3D g-C3N4. And the high specific surface area was beneficial to better adsorbing and gathering of dissolved O2 and reactive oxygen species (ROSs), which made them full contact on the surface or inside of 3D g-C3N4, giving a more sufficient ECL reaction and higher ECL signal. Based on the proposed 3D g-C3N4-O2 ECL system, a sensitive biosensor was constructed for microRNA-21 (miRNA-21) detection with assistance of 3D spherical tracks assisted 3D DNA walking machine, which exhibited superior performance for miRNA-21 with detection limit of 0.22 fM. The proposed 3D g-C3N4-O2 ECL system with high ECL efficiency and the effective target conversion and amplification strategies were beneficial to construct ultra-sensitive ECL sensing platform, which would be better applied to clinical bioanalysis.

K-Doped Graphitic Carbon Nitride with Obvious Less Electrode Passivation for Highly Stable Electrochemiluminescence and Its Sensitive Sensing Analysis of MicroRNA.

In this study, upon potassium (K) element doping, the electrochemiluminescence (ECL) excitation potential of graphitic carbon nitride (g-C3N4) obviously shifted from -1.57 to -0.74 V. Compared with other reported methods, this work was the first one that could reduce the ECL excitation potential of g-C3N4 to below the critical value of -0.9 V. It could more effectively overcome electrode passivation and significantly improve the ECL intensity and stability. Meanwhile, the lower excitation potential could significantly reduce other side reactions caused by high voltage, and the introduction of the K element could obviously increase the water solubility to shorten the preparation time. The apparent decrease of the excitation potential was due to the doping of the K element, which could reduce the band gap, increase the in-plane spacing, and expand π-conjugated systems. Furthermore, using K-doped g-C3N4 with highly stable electrochemiluminescence at lower potential as an emitter, a biosensor for microRNA-141 (miRNA-141) sensitive detection was constructed with the assistance of an innovative nicking enzyme-assisted strand displacement amplification (N-SDA). Compared to the traditional SDA, a nicking enzyme was introduced to obviously improve the utilization rate of the fuel chain and increase the number of cycles, finally resulting in higher signal amplification efficiency. Therefore, the constructed biosensor showed excellent performance in the ultrasensitive detection of miRNA-141 with the limit of detection (LOD) being 44.8 aM. This work gave a more effective means to obviously improve the ECL property of g-C3N4 caused by electrode passivation and provided a more efficient and convenient detection method for biochemical analysis.

Ultrasensitive Electrochemiluminescence Biosensor Using Sulfur Quantum Dots as an Emitter and an Efficient DNA Walking Machine with Triple-Stranded DNA as a Signal Amplifier.

In this study, sulfur quantum dots (SQDs) with superior near-infrared electrochemiluminescence (ECL) performance were synthesized by the H2O2-assisted top-down approach. Through H2O2 etching, the size and dispersity of SQDs were adjusted, reducing the aggregation-caused quenching effect and obviously promoting the ECL performance. Using the obtained SQDs as an emitter, a super-sensitive ECL biosensor of microRNA-21 (miRNA-21) detection was constructed, which was based on an efficient DNA walking machine with triple-stranded DNA (tsDNA) nanostructures as tracks. Compared with the common single-stranded DNA or double-stranded DNA, the tsDNA nanostructures on the electrode interface could avert probe entanglement and decrease local overcrowding effects. The walking efficiency of the DNA walking machine was also improved and the signal-amplification efficacy was greatly enhanced, which was benefited from the fact that tsDNA nanostructures were highly rigid scaffolds and provided orderly tracks for the DNA walking machine to walk. Thus, the designed ECL biosensor demonstrated outstanding performance for miRNA-21 detection in the concentration range of 20 aM to 1 nM with a low detection limit of 6.67 aM. Remarkably, this work enriched the application of pure element quantum dots in the ECL field and offered a new avenue for ultra-sensitive detection in clinical and biochemical analysis.