An intermolecular hydrogen-bond-induced quench-type Ru(dcbpy)32+/TPA electrochemiluminescence system by nitrogen-doped carbon quantum dots

Amplified electrochemiluminescence of Ru(dcbpy)32+ via coreactant active sites on nitrogen-doped graphene quantum dots

Searching for new alternative to tripropylamine (TPrA) with low toxicity and high chemical stability for the tris(4,4'-dicarboxylic acid-2,2'-bipyridyl)ruthenium (II) (Ru(dcbpy)32+) based coreactant electrochemiluminescence (ECL) system is essential for widespread analytical applications. Here, nitrogen-doped graphene quantum dots (NGQDs) have been discovered to significantly amplify the ECL emission and increase the ECL efficiency of Ru(dcbpy)32+ for the first time. However, the mechanism by which NGQDs act as coreactants is not well comprehended. Therefore, various optical and electrochemical technologies were employed to investigate the ECL mechanism. It is proposed that the amino and carboxyl groups on the surface of NGQDs play crucial roles as the coreactant active sites, catalyzing the oxidation of Ru(dcbpy)32+. Based on this foundation, an "on-off-on" ECL aptasensor for the quantification of acetamiprid was developed, exhibiting a broad linear range and a detection limit of 0.056 pM. Satisfactory recoveries, ranging from 98.0 % to 101.6 %, were achieved in pakchoi samples. Consequently, NGQDs could serve as coreactants for Ru(dcbpy)32+, offering new opportunities for constructing a variety of sensors with extensive analytical applications in the ECL field.

Emerging electrochemical biosensors for lung cancer-associated protein biomarker and miRNA detection

Lung cancer remains a major driver of global morbidity and mortality, and diagnosing lung tumors early in their development is vital to maximizing treatment efficacy and patient survival. Several biomarkers, including CYFRA 21-1, NSE, ProGRP, CEA, and miRNA, have been identified as reliable indicators for early lung cancer detection and monitoring treatment progress. However, the minute changes in the levels of these biomarkers during the early stages of disease necessitate advanced detection platforms. In this space, electrochemical biosensors have currently emerged as robust tools for early lung cancer screening and diagnosis owing to their low costs, rapid responses, and superior sensitivity and selectivity. This review provides an up-to-date overview of the application of electrochemiluminescence, photoelectrochemical, and other electrochemical analytical strategies for detecting lung cancer-associated protein biomarkers, and miRNA. This review compares these techniques to provide a concise overview of the principles underlying these electrochemical analytical methods, the preparation of their components, and the performance of the resulting biosensors. Lastly, a discussion of the challenges and opportunities associated with electrochemical biosensors detection of lung cancer-associated biomarkers are provided.

A simplified molecularly imprinted ECL sensor based on Mn2SnO4 nanocubes for sensitive detection of ribavirin

Conventional single-signal or emerging sandwich-type double-signal electrochemiluminescence (ECL) immunosensors/aptasensors have offered accurate detection of small molecules, yet suffer from complicated setup, long processing time, and non-reusability. Here, we demonstrate a simplified molecularly imprinted ECL sensor based on Mn2SnO4 nanocubes. As an n-type semiconductor, Mn2SnO4 has numerous active sites that can capture electrons to accelerate chemical reactions, resulting in enhanced ECL activity and stability. For the first time, we verify a robust cathodic ECL emission of Mn2SnO4 luminophores in the presence of K2S2O8 coreactants. The proposed ECL sensor applies to the sensitive detection of ribavirin (RBV), endowing a wide linear range (1-2000 ng mL-1), low detection limit (0.85 ng mL-1, S/N = 3), high stability, specificity, and reproducibility, and the detection capability in real milk and chicken samples. This work highlights single semiconductor luminophore-driven molecularly imprinted ECL sensors, meeting the original aspiration of uncomplicated but high-performance sensing in food safety inspection.

Nano-biosensor based on manganese dioxide nanosheets and carbon dots for dual-mode determination of Staphylococcus aureus

A ratiometric fluorescence and colorimetry dual-mode nano-biosensor has been established for Staphylococcus aureus (S. aureus) determination. The prepared approaches of Manganese dioxide nanosheets (MnO2 NSs) and carbon dots (BCDs) were facile, efficient and labor-saving and MnO2 NSs-mediated fluorescence quenching and oxidation could amplify detection signals. The dual-mode determination had a broad linear range of 37 ∼ 3.7 × 106 CFU/mL and low detection limits of 9 CFU/mL (ratiometric fluorescence) and 22 CFU/mL (colorimetry). Meanwhile, the method was applied in real samples with recovery ranging of 90 ∼ 102% and RSD < 4.44%, which was an insignificant difference with standard plate counting. The new dual-mode approach of S. aureus possesses the advantages of superior sensitivity, precision, accuracy and specificity. Moreover, the dual-mode nano-biosensor can be adopted in other foodborne pathogens determination by changing corresponding aptamers and provide an enlightenment in monitoring food safety.

Dual-quenching effects of methylene blue on the luminophore and co-reactant: Application for electrochemiluminescent-electrochemical ratiometric zearalenone detection

Methylene blue (MB) is a common multifunctional indicator, which can be applied as a quencher for electrochemiluminescence (ECL) analysis as well as a classical redox probe. Although it is relatively prevalent for MB to study the mechanism with Ru-based luminophores in ECL systems, there are few studies on the effects between MB and co-reactants. In this work, we proposed the first investigation of MB on the luminophore and co-reactant of the self-enhanced ECL composites (nitrogen-doped graphene quantum dots on Ru(bpy)₃²⁺-doped silica nanoparticles, NGQDs-Ru@SiO₂), respectively. The relatively narrow ECL spectrum of luminophore (Ru@SiO₂) and the suitable ultraviolet-visible absorption spectrum of MB led to the ECL resonance energy transfer between them, meanwhile the appropriate energy levels among them facilitated the electron transfer, resulting in a decreased ECL signal (quench mode I). Additionally, the co-reactant (NGQDs) was prone to π-π conjugation with MB due to its abundant π-electrons, which reduced the concentration of NGQDs' intermediates and triggered a weakened ECL signal (quench mode II). Therefore, the dual-quenching effects are ingeniously integrated and designed in one ECL-electrochemical (ECL-EC) ratiometric aptasensor for zearalenone detection, for demonstrating its efficacy in enhancing the sensitivity, which is 4.8-fold higher than Ru@SiO₂ alone. This innovative ratiometric aptasensor achieved a relatively wide linear range from 1.0 × 10^-15 to 5.0 × 10^-8 g mL^-1, and obtained a low detection limit of 8.5 × 10^-16 g mL^-1. Our proposed dual-quenching interactions between MB and NGQDs-Ru@SiO₂ will open a new prospective for ECL-EC ratiometric aptasensor, which further broaden the application in sensitive and precise analysis of mycotoxins.

Mixed-Ligand-Regulated Self-Enhanced Luminous Eu-MOF as an ECL Signal Probe for an Oriented Antibody-Decorated Biosensing Platform

The self-luminescence behavior of lanthanide MOFs (Ln-MOFs) due to the unique antenna effect is considered to be a promising electrochemiluminescence (ECL) emission for biosensors. It is more challenging for Ln-MOFs on account of the difficulty to stimulate Ln ions with the desired energy-transfer efficiency to produce stronger ECL emissions at a low potential. Here, guided by a second ligand-assisted energy-transfer strategy, we present an efficient self-enhanced luminescence mixed-ligand Eu-MOF as an ECL signal probe for an oriented antibody-decorated biosensing platform with a low detection limit and a broad detection range. Diamino terephthalic acid (NH₂-H₂BDC) and 1,10-phenanthroline (Phen) were selected as the first and second ligands, respectively, to form highly conjugated structures, as well as suppress the nonradiative energy transfer. Impressively, Phen precisely adjusts the energy gap between the triplet ligand and the excited state of Eu³⁺, realizing the self-enhancement of ECL efficiency of the Eu-MOF. The mixed ligand adjusted the molar ratio to obtain the stable and strong ECL signal at a lowered triggering potential (0.83 V). In addition, FeCo@CNT features densely active FeCo sites along with a rich hierarchy conductive carbon nanotube (CNT) network, which is efficiently a co-reaction accelerator to produce more TPA^•+ radicals to accelerate the reduction process of the Eu-MOF for achieving the ECL emission amplification. FeCo@CNT with heptapeptide HWRGWVC (HWR) constructed a matrix biosensing interface that allowed the fragment antigen-binding (Fab) regions to target specific antigens and enhance the incubation efficiency. The present study has gone some way toward designing a self-enhanced luminous Eu-MOF, thus giving new fresh impetus to develop high-performance ECL emitters for biological analysis.

The role of doping strategy in nanoparticle-based electrochemiluminescence biosensing

Doping plays a crucial role in electrochemiluminescence (ECL) due to the followings: (1) Modulation of electronic structure, alteration of the surface state of nanoparticles (NPs), providing effective protection from the surrounding environment, thereby leading to ECL emitters with exceptional properties including tunable spectra, high luminescence efficiency, low excitation potential, and good stability. (2) Employment of doped NPs as promising coreactant alternatives due to the presence of functional groups such as amines induced by NP doping. (3) Serving as novel co-reaction accelerators (CRAs) for ECL through doping induced high catalytic properties. (4) Behaving as excellent carriers to load ECL emitters, recognition elements, and catalysts due to doping-induced larger surface area, higher conductivity and better biocompatibility of NPs. As a consequence, doped NPs have aroused broad interest and found wide applications in various ECL sensing platforms. In this review, the current promising improvements, concepts, and excellent applications of doped NPs for ECL biosensing are addressed. We aim to bring to light the physicochemical characteristics of various doped NPs that endow them with appealing ECL performance, leading to diverse applications in biosensing.

Highly Efficient Electrochemiluminescence of MnS:CdS@ZnS Core-Shell Quantum Dots for Ultrasensitive Detection of MicroRNA

In this work, a novel electrochemiluminescence (ECL) biosensor was developed for ultrasensitive detection of microRNA let-7a (miRNA let-7a) based on MnS:CdS@ZnS core-shell quantum dots (QDs) as ECL luminophores with high ECL efficiency. Impressively, compared to the CdS:Mn@ZnS QDs prepared by ionic doping with ECL efficiency of 0.87%, MnS:CdS@ZnS QDs synthesized by bimetallic clusters (Cd₂Mn₂O₄) doping exhibited high ECL efficiency of up to 15.84% with S₂O₈^2- as cathodic coreactant due to the elimination of the dopants size mismatch and "self-purification" effect, which could achieve the surface defect passivation of MnS:CdS@ZnS QDs for effectively improving the ECL emission. Furthermore, with the help of strand displacement amplification (SDA), the trace target miRNA let-7a was able to be converted to a number of output DNA labeled with ferrocene (Fc) to construct an ultrasensitive ECL biosensor. The well-designed ECL biosensor for miRNA let-7a exhibited high stability and excellent sensitivity of a concentration variation from 10 aM to 1 nM and a low detection limit of 4.1 aM, which was further applied to the analysis of miRNA let-7a from cancer cell (MCF-7) lysate. Thus, this strategy provides a novel method to prepare high-efficient ECL emitters for the construction of ECL biosensing platforms in biological fields and clinical diagnosis.

An ultra-high-sensitivity electrochemiluminescence aptasensor for Pb2+ detection based on the synergistic signal-amplification strategy of quencher abscission and G-quadruplex generation

Signal amplification provides an effective way to improve detection performance. Herein, an ultrasensitive electrochemiluminescence (ECL) aptasensor for Pb²⁺ detection was developed based on a dual signal-amplification strategy of the abscission of a quencher and the generation of a G-quadruplex by one-step and simultaneous way. Nitrogen-doped carbon quantum dots linked with complementary DNA (cDNA-NCQDs) at the sensing interface was applied as the quencher of a tris(4,4'-dicarboxylic acid-2,2'-bipyridyl)ruthenium(II) (Ru(dcbpy)₃²⁺)/tripropylamine system to minimize the ECL signal due to the intermolecular hydrogen bond-induced energy-transfer process. Upon the addition of Pb²⁺, its specific binding with the aptamer triggered the abscission of cDNA-NCQDs, accompanied by the formation of G-quadruplex on the surface of the electrode, both of which amplified the intensity of the light emission. The ECL amplification efficiency induced by the above two mechanisms (78.6%) was valuably greater than that of their sum value (69.3%). This synergistic effect resulted in high detection sensitivity of the ECL aptasensor, which allowed to thereby obtain Pb²⁺ measurements in the range of 1 fM - 10 nM with an ultra-low detection limit of 0.19 fM. The Pb²⁺-mediated synergistic signal-amplification ECL strategy can provide a new approach for integrating various amplification strategies.

Electrochemiluminescence biosensor for cardiac troponin I with signal amplification based on a MoS2@Cu2O–Ag-modified electrode and Ce:ZnO-NGQDs

A sensitive sandwiched electrochemiluminescence (ECL) immunosensor was built for the detection of cTnI. The ECL immunosensor had a low detection limit (2.90 fg mL−1) and wide detection range (10 pg mL−1 to 100 ng mL−1).