Enhancing the Electrochemiluminescence of Luminol by Chemically Modifying the Reaction Microenvironment

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.

Vesicles as a Multifunctional Microenvironment for Electrochemiluminescence Signal Amplification

Vesicles as a typical interface-rich microenvironment can promote the reaction rate and the intermediate stability, which are promising for introduction in electrochemiluminescence (ECL) signal amplification. In this work, a kind of multilamellar vesicle obtained from sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was used to modify the electrode surface. The AOT vesicle-modified microenvironment could significantly enhance the ECL performances for the luminol/O2 system in a neutral medium. The mechanism study demonstrated that the nanoscale multilamellar vesicles could maintain the vesicle structure on the electrode surface, which substantially improved the electron transfer and reaction rate, luminescence efficiency of the excited-state 3-aminophthalate anion, and stability of the superoxide anion radical. Alternatively, such a multifunctional microenvironment was also able to enhance the ECL signals from the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+)/tripropylamine (TPrA) system. Moreover, another dodecyl dimethyl(3-sulfopropyl) ammonium hydroxide inner salt (DSB)-based vesicle was constructed to further verify the versatility of the vesicle-modified microenvironment for ECL signal amplification. Our work not only provides a versatile microenvironment for improving the efficiency of various ECL systems but also offers new insights for the microenvironment construction using the ordered assemblies in ECL fields.

Oxygen Free Radical Scavenger PtPd@PDA as a Dual-Mode Quencher of Electrochemiluminescence Immunosensor for the Detection of AFB1

Here, a dual-mode quenched electrochemiluminescence (ECL) immunosensor based on PtPd@PDA was proposed. Among them, nitrogen-doped hydrazide conjugated carbon dots (NHCDs), as an ECL emitter and a donor of resonance energy transfer, were quenched by PtPd@PDA (receptor). At the same time, PDA in PtPd@PDA, as an oxygen radical scavenger, completed the further quenching of the ECL signal by consuming O₂^•- generated by the decomposition of co-reactant H₂O₂. The dual-mode quenching from the above two channels was achieved. In addition, compared with the traditional carbon quantum dots, NHCDs as ECL emitters had lower excitation potential. Moreover, a large number of amino groups provided by aminated MWCNTs could capture more antibodies while connecting with NHCDs. Under the optimum experimental conditions, taking aflatoxin B1 as the target, the proposed sensor with good specificity, stability, and reproducibility had good linearity when the concentration of AFB1 was 0.01-100 ng/mL, with the detection limit of 2.63 pg/mL (S/N = 3). This strategy provided more possibilities for the application of dopamine metal nanocomposites in electrochemiluminescence analysis and offered a new approach to detect AFB1.

A Direct Z-Scheme AgBr/CuBi2O4 Photocathode for Ultrasensitive Detection of Ciprofloxacin and Ofloxacin by Controlling the Release of Luminol in Self-Powered Microfluidic Photoelectrochemical Aptasensors

An innovative self-powered microfluidic photoelectrochemical (PEC) aptasensor was developed that uses photoactive AgBr/CuBi₂O₄ (ACO) composites as the photocathode matrix for ultrasensitive detection of ciprofloxacin (CIP) and ofloxacin (OFL). The formation of direct Z-scheme heterojunctions in ACO composites greatly aided electron/hole pair separation. Meanwhile, ZnIn₂S₄-decorated CdS nanorod arrays (CZIS) as the photoanode were used instead of a platinum counter electrode to provide electrons. The "signal-off" CIP detection was accomplished through the steric hindrance effect in the photoanode due to the combination of aptamer_(CIP) and CIP. To increase the cathodic photocurrent intensity for OFL determination, controlled release of luminol was first used. Luminol molecules were successfully embedded in the porous structure of silicon dioxide nanospheres (PSiO₂) by the electrostatic adsorption between PSiO₂ and aptamer_(OFL). The luminol released by specific recognition between OFL and aptamer_(OFL) could not only react with •O₂^- but also produce chemiluminescence emission, resulting in the "signal-on" state. Because of the signal "on-off-on", the proposed aptasensor exhibited wide linear ranges for CIP (0.001-100 ng/mL) and OFL (0.0005-100 ng/mL) detection. Furthermore, the low detection limits of CIP (0.06 pg/mL) and OFL (0.022 pg/mL) could achieve the ultrasensitive analysis.

A dual-mechanism-driven electrochemiluminescence aptasensor for sensitive detection of β-amyloid peptides

β-Amyloid (Aβ) peptides can bind both Cu²⁺ and heme cofactors simultaneously to form heme-Cu²⁺-Aβ complexes, which are proposed to generate toxic partially reduced oxygen species (PROS, e.g., H₂O₂) and play a vital role in Alzheimer's disease (AD). In this paper, a competitive dual-mechanism-driven electrochemiluminescence (ECL) aptasensor integrating the synergistic enhancement and steric hindrance effect was described for Aβ detection. Specifically, graphite carbon nitride (g-C₃N₄) as an effective ECL luminescent substrate and Au nanoparticles were sequentially assembled on the Au electrode surface, and then a thiol-modified aptamer for capturing Aβ peptide was attached to the surface of the electrode through the Au-S bond. Aβ peptides were simultaneously incubated with heme and Cu²⁺, and the forming heme-Cu²⁺-Aβ complexes were subsequently anchored on the electrode through the specific recognition between the target Aβ and the aptamer. When the concentration of the target Aβ is low, the synergistic enhancement effect arising from K₂S₂O₈ with in situ generated H₂O₂ is predominant, resulting in an increase in the ECL signal of g-C₃N₄. In contrast, when the concentration of Aβ is high, the steric hindrance effect generated from heme-Cu²⁺-Aβ complexes is dominant, leading to a decrease in the ECL signal. The present sensor exhibits a favorable linear response for the detection of Aβ with a relatively low detection limit of 0.24 pM, and provides a more sensitive and selective platform for bioanalysis.

Electrogenerated chemiluminescence sensor for silver ions based on their coordination interaction with cucurbit[6]uril

Strong luminol ECL was obtained at the Q[6]/GCE. The interaction between Ag+ and Q[6] could decrease ECL signal. An ECL sensor for the detection of Ag+ was proposed based on the competitive interaction between luminol, silver ions and Q[6].

Dual-Mode Sensing Platform for Electrochemiluminescence and Colorimetry Detection Based on a Closed Bipolar Electrode

Development of sensors uniting different sensing principles is in line with the concept of reliable, comprehensive, and diversified equipment construction. However, the current exploration in this field is obstructed by compromise of reaction conditions and inevitable mutual interference arising from different sensing modes. This work reported a closed bipolar electrode (c-BPE) strategy for dual-modality detection or dual-target detection. To this end, a c-BPE sensing platform installed in physically separated anode and cathode compartments was well designed and carefully optimized. If luminol was present in the anode section and Prussian blue (PB) was at the cathode part, single stimulation could realize electrochemiluminescence (ECL) from luminol at the anode and conversion of PB to Prussian white (PW) at the cathode. The latter reaction helped elevate the ECL signal and also prepared for colorimetric detection as color change from PW to PB under the trigger of oxidant (like H₂O₂) was used to track the content of the oxidant. Thus, dual signals were obtained for dual-modality detection of single target or the detection of different targets was realized at different poles. Detection of glucose was carried out to validate the application for dual-modality detection, while VLDL/AChE and NADH/H₂O₂ assays illustrated the potential of dual-target detection. The proposed platform possesses outstanding sensing performance including selectivity, repeatability, long-term stability, accuracy, and so forth. This work implements a breakthrough in designing dual-mode sensors and is expected to present a rational basis for development of a diversified sensing platform.

Signal Amplification Strategy Using Atomically Gold-Supported VO2 Nanobelts as a Co-reaction Accelerator for Ultrasensitive Electrochemiluminescent Sensor Construction Based on the Resonance Energy Transfer Platform

Luminol, as a classical luminophore, plays a crucial role in electrochemiluminescence (ECL). However, the traditional luminol-H₂O₂ ECL system suffers from the self-decomposition of H₂O₂ at ambient temperature, which hinders its further application in quantitative analysis. In this work, for the first time, we developed atomically gold-supported two-dimensional VO₂ nanobelts (Au/VO₂) as an advanced co-reaction promoter to speed up the reduction of dissolved oxygen to superoxide radicals (O₂^•-), which react with the luminol anion radical and greatly promote the ECL emission. The ECL resonance energy transfer (ECL-RET) between the hollow manganese dioxide nanospheres and luminol results in a conspicuously decreased ECL signal response, and in the presence of glutathione (GSH), effective redox reaction between manganese dioxide and GSH restores the ECL signal. As a consequence, the designed sensor based on ECL-RET-assisted Au/VO₂ signal amplification showed outstanding performance for "signal-on" detection of GSH in the concentration range of 10^-3 to 10^-10 M, and the detection limit was as low as 0.03 nM. The ECL sensor displayed excellent specificity and was successfully utilized to target GSH in real human serum samples. Importantly, this work not only highlights a powerful avenue for constructing an ultrasensitive ECL sensor for GSH but also provides some inspiration for the further design of high-performance co-reaction accelerators using the ECL technique.

Ultrasensitive detection of cyclin D1 by a self-enhanced ECL immunosensor based on Bi2S3 quantum dots

Bismuth sulfide quantum dots (Bi₂S₃ QDs), which have excellent optical and thermoelectric properties, represent a green and non-toxic semiconductor material that has been widely used in catalysis and photoelectric conversion devices. At present, research on this material has gradually expanded into the biological field. Herein, the biomineralization method mediated by bovine serum albumin (BSA) was utilized to synthesize Bi₂S₃ QDs with monodispersity, excellent colloidal stability, and good biocompatibility. This is the first study on the electrochemiluminescence (ECL) characteristics of Bi₂S₃ QDs and related ECL mechanisms in detail. In addition, on the basis of Bi₂S₃ QDs, an ECL immunosensor was used for the ultrasensitive measurement of cyclin D1 (CCND1). The composite material, namely Au@Cu-Bi₂S₃ QDs was used as a high-sensitivity ECL probe, in which AuNPs were connected with Bi₂S₃ QDs through a copper(ii) ion bridge. PDA-AgNPs made of dopamine (DA) and silver nanoparticles (AgNPs) were utilized as a carrier for fixing the primary antibody (Ab₁), ultimately presenting a relatively wide detection range of 10 fg mL^-1-1 μg mL^-1. Moreover, quite a low detection limit (6.34 fg mL^-1) was also obtained for an assay of CCND1. Results indicated that the immunosensor can provide a potential platform with fine stability and creditable reproducibility for clinical diagnosis.

Advances in electrochemiluminescence co-reaction accelerator and its analytical applications

Electrochemiluminescence (ECL) can be produced through two main routes: annihilation route and coreactant route. The vast majority of applications of ECL are based on coreactant ECL which can be generated in aqueous media at relatively low potentials compared with organic solvents. However, the development of more efficient ECL systems remains a compelling goal. Co-reaction accelerator (CRA) can significantly enhance the ECL signal through promoting more production of the coreactant intermediate. Compared with other ECL enhancement strategies, the CRA protocol is distinctive owing to its diverse, simple, and highly effective features. Various species such as inorganic compound, organic compound, and nanomaterials (NMs) have been developed as CRA and NM CRA has gained particular attention owing to their unique properties of excellent catalytic behavior and large surface area. By integration with the inherent advantages of ECL, bioanalysis based on CRA-enhanced ECL showed excellent performance such as ultrahigh sensitivity, wide dynamic range, low cost, simple instrumentation, and measurements in complex media. It has been extensively applied in various fields including clinical diagnosis, environmental monitoring, and food safety. Therefore, it is of great interest to present a systematic and critical review on the advances in ECL CRA. Herein, the recent progress on CRA and its applications in ECL bioanalysis are summarized by illustrating some representative work and a discussion of the future development trends of CRA ECL is offered.

A highly-enhanced electrochemiluminescence luminophore generated by a metal-organic framework-linked perylene derivative and its application for ractopamine assay

In this study, a sensitive and effective monitoring method for ractopamine (RAC) was developed based on a sensitive electrochemiluminescence (ECL) aptasensor. Here, we employed a perylene derivative (PTC-PEI) with a Cu-based metal-organic framework (HKUST-1), which could accelerate the electron-transfer (ET) rate and strengthen interactions by the amido bond, resulting in enhanced ECL sensitivity and stability. Astonishingly, compared with the response of PTC-PEI and complex, the ECL signal of the MOF-based ECL material was noticeably raised by 6 times higher than that of PTC-PEI. HKUST-1 exhibited an excellent catalytic effect towards the electrochemical reduction process of S₂O₈^2-, thus allowing more sulfate radical anions (SO₄˙^-) to be generated. The strong ECL intensity of HKUST-1/PTC-PEI not only stemmed from the fixation of PTC-PEI that utilized its excellent film-forming abilities but also originated from the high porosity of HKUST-1 that carried more luminophores able to be excited. Satisfyingly, in the presence of the target molecule RAC, we observed an obvious quenching effect of signal, which could be attributed to aptamer recognition resulting in RAC being specifically captured on the electrode. Under optimal conditions, the developed sensor for the RAC assay displayed a desired linear range of 1.0 × 10^-12-1.0 × 10^-6 M and a low detection limit of 6.17 × 10^-13 M (S/N = 3). This ECL sensor showed high sensitivity, good stability and excellent selectivity. More importantly, the proposed aptasensor exhibited excellent determination towards RAC detection and potential practical utility for real samples.

Oxygen Vacancy-Enhanced Electrochemiluminescence Sensing Strategy Using Luminol Thermally Encapsulated in Apoferritin as a Transducer for Biomarker Immunoassay

Oxygen vacancies (OVs) enhanced electrochemiluminescence (ECL) biosensing strategy using luminol thermally encapsulated in apoferritin (Lum@apoFt) as an efficient transducer was investigated for ultrasensitive biomarker detection. By applying the oxygen-defect engineering (ODE) strategy, the OVs enriched cobalt-iron oxide (r-CoFe₂O₄) was fabricated as the sensing substrate to boost the electron mobility and catalyze the generation of superoxide anion radical (O₂^•-) for signal amplification. It should be noted that r-CoFe₂O₄ with higher OVs density dramatically accelerated the ECL reaction between O₂^•- and luminol anionic radicals, achieving 6.5-fold stronger ECL output than CoFe₂O₄ with no or low OVs density. Moreover, facile encapsulation of approximate 412 luminol molecules in a single apoFt cavity was first realized by an efficient thermal-induction method. The obtained Lum@apoFt complexes exhibited well-maintained ECL efficiency and excellent biocompatibility for biological modifications. On this basis, a biosensor was developed for early diagnostics of squamous cell carcinomas by detecting its representative biomarker named cytokeratin 19 fragment 21-1 (CYFRA 21-1), from which excellent linearity was achieved in 0.5 pg/mL to 50 ng/mL with a detection limit of 0.14 pg/mL. This work not only put forward a novel idea of creating OVs enriched sensing interface with excellent signal-amplification function but also proposes a facile and robust methodology to design apoFt-based transducers for developing more practical nanoscale biosensors in early diagnostics of diseases.

A Dynamic DNA Machine via Free Walker Movement on Lipid Bilayer for Ultrasensitive Electrochemiluminescent Bioassay

Herein, an ultrasensitive electrochemiluminescent (ECL) strategy was proposed based on a highly efficient dynamic DNA machine based on microRNA triggered free movement on the lipid bilayer interface. Typically, the lipid bilayer is constructed on the electrode surface modified with nafion@ECL luminophore and gold nanoparticles to immobilize the DNA walker labeled with cholesterol and hairpin nucleotides labeled with cholesterol and ferrocene (Fc), based on the cholesterol-lipid interaction. On this state, Fc was close to the ECL luminophore, performing a quenched ECL emission. In the presence of target microRNA 21, it could trigger the entropy beacon-based DNA amplification to convert microRNA to massive special DNA sequences, which could further hybridize with the blocking DNA on DNA walker to reactivate the DNA walker and thus trigger the DNA walker-based amplification to make Fc to be far from the ECL luminophore, performing a recovered ECL emission related with the concentration of microRNA 21. Compared with the conventional DNA walker immobilized on the interface via chemical bonds or physical adsorption, a higher reaction efficiency could be achieved due to the free movements of DNA walker and its substrates on the interface. As expected, satisfactory performances for the detection of microRNA 21 were achieved with a detection limit of 0.4 fM and quantitative estimation in cells. Furthermore, this dynamic DNA machine-based ECL strategy could be readily expanded for the detection of other biomarkers for clinical diagnosis.

In situ H2O2 generation with gold nanoflowers as the coreactant accelerator for enzyme-free electrochemiluminescent immunosensing

In traditional electrochemiluminescence (ECL) analysis, gold nanomaterials are commonly used as a tool for signal amplification and linking antibodies due to their good electrical conductivity and biocompatibility. Here, we found that multitipped gold nanoparticles-gold nanoflowers (AuNFs) as coreactant accelerator have good catalytic activity for the reduction of dissolved oxygen (O₂) to hydrogen peroxide (H₂O₂) using tris (hydroxymethyl) aminomethane (Tris) as electron donor. Based on this, a new enzyme-free and label-free ECL immunosensor have been constructed for the detection of α-fetoprotein (AFP). In this system, due to the unique geometric and spatial effects of AuNFs, the dissolved O₂ as endogenous coreactant was catalyzed by AuNFs to produce H₂O₂ using Tris as an electron donor. The in situ generated H₂O₂ can more efficiently produce various electrogenerated reactive oxygen species (ROSs) as the important intermediates on the electrode surface. Then, oxidation of luminol reacts with ROSs significantly amplifies the luminol ECL signal. Under optimal experimental conditions, the proposed ECL immunosensor was able to detect the AFP concentration from 0.01 to 100 ng mL^-1, with a low detection limit of 3.4 pg mL^-1 (S/N = 3). In addition, the prepared ITO-based sensor is similar to a micro-test chip and convenient to use, thus making it suitable for clinical use as a disposable device in point-of-care tests (POCTs).

A label-free and signal-on electrochemiluminescence strategy for sensitive amyloid-beta assay

Development of a simple, cost-effective and sensitive biosensing strategy is highly desirable to advance the applications in Alzheimer's disease diagnosis. In this paper, we present a simple, label-free and signal-on electrochemiluminescence (ECL) aptasensor for the detection of amyloid-beta (Aβ) peptide using luminol as ECL emitter and in-situ generated reactive oxygen species (ROS) as coreactant via catalytic reaction between Cu²⁺-Aβ and the dissolved O₂ in the presence of ascorbic acid (AA). Aβ₁₆, the binding site of Cu²⁺ in the monomeric full-length Aβ, was used as a model in present study. As a result, this signal-on ECL aptasensor has exhibited favorable analytical performance for Aβ₁₆ monomer with a linear range of 1.0 × 10^-13 mol/L-1.0 × 10^-8 mol/L and a limit of detection of 3.5 × 10^-14 mol/L (S/N=3). Furthermore, the proposed biosensor was also able to detect the full length Aβ₄₀ not only in the phosphate buffer saline (PBS) solution but also in human serum. The presented biosensor represents a promising, simple, turn-on and label-free diagnostic tool for blood analysis.

An ultrasensitive electrochemiluminescence biosensor for MicroRNA detection based on luminol-functionalized Au NPs@ZnO nanomaterials as signal probe and dissolved O2 as coreactant

In this work, the ZnO nanostars with excellent catalytic performance were firstly used as the coreaction accelerator of luminol-O₂ system to construct a biosensor for ultrasensitively detecting microRNA-21 (miRNA-21) in cancer cells. Specifically, ZnO nanostars could expedite the reduction of dissolved O₂, generating more reactive oxygen species (ROSs) to extremely promote electrochemiluminescence (ECL) luminous efficiency of luminol. Thus luminol-functionalized Au NPs@ZnO (L-Au NPs@ZnO) nanomaterials were employed as signal probe to fabricate sensing nano-platform for achieving significant ECL emission as "signal on" state. Moreover, upon the addition of a tiny minority of target miRNA-21, massive ferrocene (Fc) could be immobilized on the sensing interface through hybridization chain reaction (HCR) triggered-DNA dendrimers self-assembly, in which Fc consumed dissolved O₂ for prominently quenching the ECL emission of signal probe and then reached a "signal off" state. As a result, the biosensor performed a good linearity in 100 aM - 100 pM and a low limit of detection (LOD) down to 18.6 aM. In general, this work utilized a new coreaction accelerator as an efficient amplification approach for ultrasensitively detecting target analyses, providing a promising approach in luminol-centric ECL bioanalysis fields.