Recent Advances in Electrochemiluminescence Biosensors for Mycotoxin Assay

Rapid and efficient detection of mycotoxins is of great significance in the field of food safety. In this review, several traditional and commercial detection methods are introduced, such as high-performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS), enzyme-linked immunosorbent assay (ELISA), test strips, etc. Electrochemiluminescence (ECL) biosensors have the advantages of high sensitivity and specificity. The use of ECL biosensors for mycotoxins detection has attracted great attention. According to the recognition mechanisms, ECL biosensors are mainly divided into antibody-based, aptamer-based, and molecular imprinting techniques. In this review, we focus on the recent effects towards the designation of diverse ECL biosensors in mycotoxins assay, mainly including their amplification strategies and working mechanism.

Bioinspired Single-Atom Sites Enable Efficient Oxygen Activation for Switching Anodic/Cathodic Electrochemiluminescence

Exploring advanced co-reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol-O2 electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O2 activation to switch anodic/cathodic ECL is very challenging. Herein, we report that enzyme-inspired Fe-based single-atom catalysts with axial N/C coordination structures (FeN5, FeN4(C) SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN5 sites prefer to produce highly active hydroxyl radicals and afford direct cathodic luminescence by promoting the cleavage of O-O bonds through N-induced electron redistribution. In contrast, FeN4(C) sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN5 SAC-based immunosensor was constructed for the sensitive detection of cancer biomarkers.

3D Plasmonic Nanostructure-Based Polarized ECL Sensor for Exosome Detection in Tumor Microenvironment

Exosomes of cancer cells play an important role in the proliferation, adhesion, and migration of tumors. Especially, exosomes in the tumor microenvironment can reflect the proliferation of tumors directly, thus serving as ideal referenced markers of the possibility and grade of malignancy in neoplasms. However, the sensitive and accurate detection of exosomes remains challenging. In this work, a novel three-dimensional (3D) plasmonic nanostructure was constructed for exosomal miRNA detection. It combined the advantages of Au nanostar monolayer and Ag nanowire monolayer to provide multiple hot spots. Moreover, Au nanostar monolayer changed the isotropic electrochemiluminescence (ECL) into polarized emission. The Ag nanowire monolayer worked as waveguides for the light direction. As a result, the polarized resolution and intensity of ECL signal were improved. The polarized ECL emission was significantly increased by 47.1 times. This high-resolution polarized ECL sensor was used for detecting exosomal miRNA-146b-5p in the thyroid tumor microenvironment. This sensor showed the linear range from 1 fM to 1 nM with a detection limit of 0.3 fM. The satisfactory results indicated the developed 3D plasmonic nanostructure-based ECL sensor had great potential in biosensing and clinical diagnosis.

Aggregation-Induced Enhancement Electrochemiluminescence of Ag Nanoribbons as a Signal Probe for Ultrasensitive Detection of the Halogenase Gene Segment from Aspergillus Ochratoxin

Here, an electrochemiluminescence (ECL) biosensor was developed based on aggregation-induced enhancement ECL of Ag nanoribbons (Ag NRs) as a signal probe and the mismatched bases-fueled DNA walker as the amplification strategy for ultrasensitive detection of the halogenase gene segment (target) from aspergillus ochratoxin to evaluate fungi capable of producing ochratoxin in dairy products. Compared with the existing agminated NCs, the Ag NRs displayed dramatically enhanced ECL emission due to effective electron transfer and less energy dissipation of excited-state Ag NRs based on the metallophilic interaction of Ag(I)-Ag(I). Impressively, the target was conversed mismatched bases-DNA walker to trigger a significant ECL response through toehold-mediated strand displacement amplification. Thus, the strategy realized trace analysis of the halogenase gene segment with a detection limit of 45 aM, which ushered a new detection method for toxin determination in the previous stage of toxin biosynthesis to protect people from toxic damage.

Crystallization Regulation Engineering in the Carbon Nitride Nanoflower for Strong and Stable Electrochemiluminescence

Cathode electrochemiluminescence (ECL) of C₃N₄ material has suffered from weak and unstable ECL emission for a long time, which greatly limits its practical application. Herein, a novel approach was developed to improve the ECL performance by regulating the crystallinity of the C₃N₄ nanoflower for the first time. The high-crystalline C₃N₄ nanoflower achieved a pretty strong ECL signal as well as excellent long-term stability compared to low-crystalline C₃N₄ when K₂S₂O₈ was used as a co-reactant. Through the investigation, it is found that the enhanced ECL signal is attributed to the simultaneous inhibition of K₂S₂O₈ catalytic reduction and enhancement of C₃N₄ reduction in the high-crystalline C₃N₄ nanoflower, which can provide more opportunities for SO₄^• - to react with electro-reduced C₃N₄^• -, and a new "activity passivation ECL mechanism" was proposed, while the improvement of the stability is mainly ascribed to the long-range ordered atomic arrangements caused by structure stability in the high-crystalline C₃N₄ nanoflower. As a benefit from the excellent ECL emission and stability of high-crystalline C₃N₄, the C₃N₄ nanoflower/K₂S₂O₈ system was employed as a Cu²⁺ detection sensing platform, which exhibited high sensitivity, excellent stability, and good selectivity with a wide linear range from 6 nM to 10 μM and a low detection limit of 1.8 nM.

Facial Preparation of Cyclometalated Iridium (III) Nanowires as Highly Efficient Electrochemiluminescence Luminophores for Biosensing

In this study, highly efficient ECL luminophores composed of iridium complex-based nanowires (Ir-NCDs) were synthesized via covalently linking bis(2-phenylpyridine)-(4-carboxypropyl-2,2'-bipyridyl) iridium(III) hexafluorophosphate with nitrogen-doped carbon quantum dots (NCDs). The ECL intensity of the nanowires showed a five-fold increase in ECL intensity compared with the iridium complex monomer under the same experimental conditions. A label-free ECL biosensing platform based on Ir-NCDs was established for Salmonella enteritidis (SE) detection. The ECL signal was quenched linearly in the range of 10²-10⁸ CFU/mL for SE with a detection limit of 10² CFU/mL. Moreover, the relative standard deviations (RSD) of the stability within and between batches were 0.98% and 3.9%, respectively. In addition, the proposed sensor showed high sensitivity, selectivity and stability towards SE in sheep feces samples with satisfactory results. In summary, the excellent ECL efficiency of Ir-NCDs demonstrates the prospects for Ir(III) complexes in bioanalytical applications.

Self-assembly Induced Enhanced Electrochemiluminescence of Copper Nanoclusters Using DNA Nanoribbon Templates

Copper nanoclusters (CuNCs) are attractive electrochemiluminescence (ECL) emitters as Cu is comparatively inexpensive, nontoxic, and highly abundant. However, their ECL yield is relatively low. Herein, we report that orderly self-assembly of CuNCs using DNA nanoribbon as the template (DNR/CuNCs) conferred the CuNCs with improved ECL properties compared with individual CuNCs in both annihilation and co-reactant processes. The DNR/CuNCs resulted in a high ECL yield of 46.8% in K2S2O8, which was ~ 68 times higher than that of individual CuNCs. This strategy was successfully extended to other ECL emitters, such as gold nanoclusters and the Ru(bpy)32+/TPrA system. Furthermore, as an application of DNR/CuNCs, a DNR/CuNC-based ECL biosensor with higher sensitivity was constructed for dopamine determination (two orders of magnitude lower than that previously reported), showing that DNR/CuNCs have a potential for application in ECL bioanalysis as a new type of superior luminophore candidate.

Water Activation for Boosting Electrochemiluminescence

In conventional luminol electrochemiluminescence (ECL) systems, hydrogen peroxide and dissolved oxygen are employed as typical co-reactants to produce reactive oxygen species (ROS) for efficient ECL emission. However, the self-decomposition of hydrogen peroxide and limited solubility of oxygen in water inevitably restrict the detection accuracy and luminous efficiency of luminol ECL system. Inspired by ROS-mediated ECL mechanism, for the first time, we used cobalt-iron layered double hydroxide as co-reaction accelerator to efficiently activate water to generate ROS for enhancing luminol emission. Experimental investigations verify the formation of hydroxyl and superoxide radicals in the process of electrochemical water oxidation, which subsequently react with luminol anion radicals to trigger strong ECL signals. Finally, the detection of alkaline phosphatase has been successfully achieved with impressive sensitivity and reproducibility for practical sample analysis.

MoS2-Carbon Nanodots as a New Electrochemiluminescence Platform for Breast Cancer Biomarker Detection

In this work, we present the combination of two different types of nanomaterials, 2D molybdenum disulfide nanosheets (MoS₂-NS) and zero-dimensional carbon nanodots (CDs), for the development of a new electrochemiluminescence (ECL) platform for the early detection and quantification of the biomarker human epidermal growth factor receptor 2 (HER2), whose overexpression is associated with breast cancer. MoS₂-NS are used as an immobilization platform for the thiolated aptamer, which can recognize the HER2 epitope peptide with high affinity, and CDs act as coreactants of the anodic oxidation of the luminophore [Ru(bpy)₃]²⁺. The HER2 biomarker is detected by changes in the ECL signal of the [Ru(bpy)₃]²⁺/CD system, with a low detection limit of 1.84 fg/mL and a wide linear range. The proposed method has been successfully applied to detect the HER2 biomarker in human serum samples.

A Novel Signal-On Electrochemiluminescence Immunosensor for the Detection of NSCLC Antigen Biomarker Based on New Co-Reaction Accelerators

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer with substantial morbidity and mortality. Herein, a new signal-on electrochemiluminescence (ECL) immunosensor based on multiple amplification strategies is constructed for ultrasensitive detection of cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) biomarker related to NSCLC. Polyethyleneimine (PEI) functionalized MXene is decorated with NiMn layer double hydroxide (NiMn LDH) to form MXene-PEI-NiMn LDH composite. Specially, the La-MOF@ZIF-67 bimetallic organic framework (named as LZBM) and MXene-PEI-NiMn LDH both served as coreaction accelerators to improve the ECL emission of the luminol-H₂ O₂ system. To be specific, Au nanoparticles (AuNPs) coated MXene-PEI-NiMn LDH is applied to immobilize primary CYFRA21-1 antibody (Ab₁ ), while AuNPs decorated LZBM was used for the loading of luminol and secondary CYFRA21-1 antibody (Ab₂ ) to form tracer label. Therefore, the ECL signal of the sandwich-type immunosensor is significantly enhanced due to the high loading capability for luminol and the synergistic catalytic ability for the decomposition of H₂ O₂ into reactive oxygen species (ROS). Under the optimal experimental conditions, the ECL immunosensor exhibited good analytical performances for CYFRA21-1 detection with a wide linear range (100 fg mL^-1 -100 ng mL^-1 ) and a low limit of detection (85.20 fg mL^-1 ), providing a promising method for early diagnosis of NSCLC.

Target-cycling synchronized rolling circle amplification strategy for biosensing Helicobacter pylori DNA

Helicobacter pylori is closely linked to many gastric diseases such as gastric ulcers and duodenal ulcers. Therefore, biosensing H. pylori has attracted wide attention from both scientists and clinicians. Here, we proposed an electrochemiluminescence (ECL)-based platform that could sensitively detect H. pylori DNA. In this platform, a novel target-cycling synchronized rolling circle amplification was used for signal amplification. Silver nanoclusters (Ag NCs) were synthesized on the circle DNA products, embedding them with the ability to catalyze the electrochemical reduction of K₂ S₂ O₈ , in turn resulting in rapid consumption of the ECL co-reactant near the working electrode, and leading to a decrease in the ECL emission intensity. In addition to its excellent stability and selectivity, the proposed strategy had a low detection limit of 10 pM, an indication that it can be beneficially applied to test biosamples. Furthermore, a biosensing chip was designed to improve the throughput and shed new light on large-scale clinical biosensing applications.

Nanoconfinement-Enhanced Electrochemiluminescence for in Situ Imaging of Single Biomolecules

Direct imaging of electrochemical reactions at the single-molecule level is of potential interest in materials, diagnostic, and catalysis applications. Electrochemiluminescence (ECL) offers the opportunity to convert redox events into photons. However, it is challenging to capture single photons emitted from a single-molecule ECL reaction at a specific location, thus limiting high-quality imaging applications. We developed the nanoreactors based on Ru(bpy)₃²⁺-doped nanoporous zeolite nanoparticles (Ru@zeolite) for direct visualization of nanoconfinement-enhanced ECL reactions. Each nanoreactor not only acts as a matrix to host Ru(bpy)₃²⁺ molecules but also provides a nanoconfined environment for the collision reactions of Ru(bpy)₃²⁺ and co-reactant radicals to realize efficient in situ ECL reactions. The nanoscale confinement resulted in enhanced ECL. Using such nanoreactors as ECL probes, a dual-signal sensing protocol for visual tracking of a single biomolecule was performed. High-resolution imaging of single membrane proteins on heterogeneous cells was effectively addressed with near-zero backgrounds. This could provide a more sensitive tool for imaging individual biomolecules and significantly advance ECL imaging in biological applications.

Dual-Mode Sensing Platform for Cancer Antigen 15-3 Determination Based on a Silica Nanochannel Array Using Electrochemiluminescence and Electrochemistry

An electrochemiluminescence-electrochemistry (ECL-EC) dual-mode sensing platform based on a vertically-ordered mesoporous silica films (VMSF) modified electrode was designed here for the sensitive and selective determination of cancer antigen 15-3 (CA 15-3), a specific biomarker of breast cancer. VMSF was assembled through a rapid electrochemically assisted self-assembly (EASA) method and plays a crucial role in signal amplification via a strong electrostatic interaction with the positively charged bifunctional probe Ru(bpy₎₃²⁺. To construct the biorecognition interface, epoxy functional silane was linked to the surface of VMSF for further covalent immobilization of the antibody. As a benefit from the specific combination of antigen and antibody, a non-conductive immunocomplex layer was formed in the presence of CA 15-3, leading to the hinderance of the mass and electron transfer of the probes. Based on this strategy, the dual-mode determination of CA 15-3 ranging from 0.1 mU/mL to 100 mU/mL with a LOD of 9 μU/mL for ECL mode, and 10 mU/mL to 200 U/mL with a LOD of 5.4 mU/mL for EC mode, was achieved. The proposed immunosensor was successfully employed for the detection of CA 15-3 in human serum without tedious pretreatment.

Electrochemiluminescence Amplification in Bead-Based Assays Induced by a Freely Diffusing Iridium(III) Complex

Heterogeneous electrochemiluminescence (ECL) assays employing tri-n-propylamine as a co-reactant and a tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)₃]²⁺) derivative as an emissive label are integral to the majority of academic and commercial applications of ECL sensing. This model system is an active research area and constitutes the basis of successfully commercialized bead-based ECL immunoassays. Herein, we propose a novel approach to the enhancement of such conventional ECL assays via the incorporation of a second metal coordination complex, [Ir(sppy)₃]^3- (where sppy = 5'-sulfo-2-phenylpyridinato-C²,N), to the experimental system. By employing ECL microscopy, we are able to map the spatial distribution of ECL emission at the surface of the bead, from [Ru(bpy)₃]²⁺ labels, and solution-phase emission, from [Ir(sppy)₃]^3-. The developed [Ir(sppy)₃]^3--mediated enhancement approach elicited a significant improvement (70.9-fold at 0.9 V and 2.9-fold at 1.2 V vs Ag/AgCl) of the ECL signal from [Ru(bpy)₃]²⁺ labels immobilized on the surface of a polystyrene bead. This dramatic enhancement in ECL signal, particularly at low oxidation potentials, has important implications for the improvement of existing heterogeneous ECL assays and ECL-based microscopy, by amplifying the signal, opening new bioanalytical detection schemes, and reducing both electrode surface passivation and deleterious side reactions.

Assembled Photonic Crystal/Gold Nanoparticle Interface: A Dual Amplifying Electrochemiluminescent Aptasensor for the Ultrasensitive Detection of an Amyloid-β Monomer

Amyloid-β (Aβ) protein is considered to be a key biomarker that is closely associated with Alzheimer's disease (AD). The level of Aβ, particularly its subtle fluctuation, indicates early neuropathological changes, which poses a considerable challenge in predicting AD, considering the detection limit of sensing technologies. Herein, a new label-free sensor based on luminol electrochemiluminescence (ECL) was proposed by developing a close-packed monolayered-SiO2 array with gold (Au) nanoparticles (NPs) entrapped in their gaps as the basal electrode. The well-organized SiO2 NPs with a quasiphotonic crystal structure amplified the ECL signal via light scattering, while Au NPs amplified the signal by directly catalyzing luminol oxidation. Owing to the dual signal amplification, the proposed electrode furnished an ∼64-fold-intensified ECL signal of luminol as the sensing background. Further, the as-prepared ECL electrode served as the substrate to develop an aptasensor for the sensitive detection of Aβ. The inhibition of the ECL signal due to the suppressed diffusion of luminol to the sensor surface acts as an indicator to quantify the amount of Aβ. The transfer dynamics mechanism provides a label-free sensing strategy and facilitates the high sensitivity of the aptasensor for Aβ detection. Under optimal conditions, the developed aptasensor exhibits an ultrasensitive performance for Aβ with a very low limit of detection of 5 fM, providing a new prospect for clinical research on Aβ and a promising approach in the field of ECL sensing.

Portable paper-based electrochemiluminescence test incorporating lateral-flow immunosensors for detection of interferon-γ levels

Tuberculosis (TB) poses a serious threat to human health and social development. Accurate diagnosis of mycobacterium tuberculosis infection plays a critical role in the prevention and treatment of tuberculosis. Interferon-γ (INF-γ) release assay (IGRA) is currently the only quantitative tuberculosis infection diagnosis method. An accurate, fast, and easily handled INF-γ detection method is the key to obtaining accurate results. Herein, we report a novel paper-based electrochemiluminescence (ECL) method based on lateral flow immunosensors that combines the easy handling characteristics of immunochromatography and the high sensitivity of electrochemiluminescence to detect IFN-γ. To our knowledge this is the first INF-γ detection method that combines immunochromatography with electrochemiluminescence. The paper-based ECL-LFI test consists of a sample pad, conjugation pad (with binding antibody IFN-γ-Ab1 conjugated with ruthenium tripyridine), detection pad (with capture antibody IFN-γ-Ab2 immobilized on nanospheres), absorbent pad, and electrode for signal activation. The ECL signal is obtained by cyclic voltammetry scanning at a speed of 0.1 V/s in the detection area of the paper-based ECL-LFI test. In our experiments, the paper-based ECL-LFI test exhibited a minimum detection limit of 2.57 pg/mL within 12 min, and a broad detection range of 2.57-5,000 pg/mL, with repeatability of 8.10% and stability of 4.97%. With the advantage of high accuracy and sensitivity, easy handling, and low user training requirements, this ECL-LFI test might be used as point-of-care testing (POCT) in the IGRA for tuberculosis diagnosis.

Porphyrin Functionalized Carbon Quantum Dots for Enhanced Electrochemiluminescence and Sensitive Detection of Cu2

Porphyrin (TMPyP) functionalized carbon quantum dots (CQDs-TMPyP), a novel and efficient carbon nanocomposite material, were developed as a novel luminescent material, which could be very useful for the sensitive detection of copper ions in the Cu²⁺ quenching luminescence of functionalized carbon quantum dots. Therefore, we constructed a sensitive "signal off" ECL biosensor for the detection of Cu²⁺. This sensor can sensitively respond to copper ions in the range of 10 nM to 10 μM, and the detection limit is 2.78 nM. At the same time, it has good selectivity and stability and a benign response in complex systems. With excellent properties, this proposed ECL biosensor provides an efficient and ultrasensitive method for Cu²⁺ detection.

Tuning Dimensionality of Benzimidazole Aggregates by Using Tetraoctylammonium Bromide: Enhanced Electrochemiluminescence Studies

Exploring the depolymerization strategy of liposoluble luminophores in the aqueous phase is vital for the development of electrochemiluminescence (ECL). In this work, tetraoctylammonium bromide (TOAB) with four long hydrophobic chains and short hydrophilic ends is used as a template to limit the aggregation of benzimidazole (BIM). By adjusting the loading of BIM on the hydrophobic chains of TOAB, a two-dimensional lamellar BIM/TOAB is formed, the ECL intensity of which is 6.4 times higher than that of the aggregated BIM (H₂O₂ as the coreactant). In terms of ECL spectroscopies, cyclic voltammetry , ECL transients, and the adjustment of the scanning potential range, the ECL mechanism is thoroughly studied. This work provides a new way to depolymerize organic luminophores and reveals a possible pathway in the annihilation ECL mechanism.

Cascade-Gates Guarded Asymmetrical Nanochannel Membrane: An Interference-Free Device for Straightforward Detection of Trace Biomarker in Undiluted Serum

Accurate detection of trace biomarkers in biological samples is a key task in diagnostic testing, but it remains challenging due to the high concentration of other physiologically relevant interferences. This work presents a new electrochemiluminescence (ECL) sensing device based on a bio-inspired nanochannel membrane (NM) guarded with two differential gates. The recognition event at the aptamer gate is followed by the permitting of stimulator transport toward the metal-organic framework (MOF) gate. Proof of concept application is evaluated using cytochrome C (Cytc) as the analyte, and glucose, a commonly existing nutriment as the stimulator. The oxidase-mimic plasmonic nanoparticles induce an effective release of ECL luminophore from the MOF gate. This cascade-gates guarded NM can effectively separate biological matrices from the detection cell. Consequently, the proposed system can achieve direct sensing of 1.0 nm Cytc in undiluted serum within the threshold concentrations of leukemia and lymphoma, making it attractive for point-of-care applications.

Recent Progress in Plasmonic based Electrochemiluminescence Biosensors: A Review

Electrochemiluminescence (ECL) analysis has become a powerful tool in recent biomarker detection and clinic diagnosis due to its high sensitivity and broad linear range. To improve the analytical performance of ECL biosensors, various advanced nanomaterials have been introduced to regulate the ECL signal such as graphene, gold nanomaterials, and quantum dots. Among these nanomaterials, some plasmonic nanostructures play important roles in the fabrication of ECL biosensors. The plasmon effect for the ECL signal includes ECL quenching by resonant energy transfer, ECL enhancement by surface plasmon resonance enhancement, and a change in the polarized angle of ECL emission. The influence can be regulated by the distance between ECL emitters and plasmonic materials, and the characteristics of polarization angle-dependent surface plasmon coupling. This paper outlines the recent advances of plasmonic based ECL biosensors involving various plasmonic materials including noble metals and semiconductor nanomaterials. The detection targets in these biosensors range from small molecules, proteins, nucleic acids, and cells thanks to the plasmonic effect. In addition to ECL biosensors, ECL microscopy analysis with plasmonic materials is also highlighted because of the enhanced ECL image quality by the plasmonic effect. Finally, the future opportunities and challenges are discussed if more plasmonic effects are introduced into the ECL realm.

High-Intensity Focused Ultrasound Combined with Ti3C2-TiO2 to Enhance Electrochemiluminescence of Luminol for the Sensitive Detection of Polynucleotide Kinase

Luminol is a classic electrochemiluminescence (ECL) luminophore. The luminol-O₂ ECL system suffers from a problem, that is, the conversion rate of dissolved O₂ into reactive oxygen species (ROS) is low. In this work, we used high-intensity focused ultrasound (HIFU) pretreatment combined with Ti₃C₂-TiO₂ to construct a highly sensitive luminol-O₂ ECL system for the specific detection of polynucleotide kinase (PNK) first. On the one hand, HIFU generated ROS in situ as a coreactant via the cavitation effect to boost the luminol emission. On the other hand, Ti₃C₂-TiO₂ was prepared in situ via Ti₃C₂ as a reducing agent, and it can aggregate and catalyze ROS generated in situ by HIFU. Moreover, the Ti on the Ti₃C₂-TiO₂ surface could bind to phosphate groups through chelation, thereby realizing highly specific detection of PNK. The sensor has a linear relationship range of 1.0 × 10^-5 to 10.0 U mL^-1, and the limit of detection is 1.48 × 10^-7 U mL^-1, which is superior to most existing methods. The sensor performance in HeLa cell lysate was measured with a satisfactory result. The designed ECL biosensor has potential applications in biological analysis and clinical diagnosis.

Point-of-Care Diagnostic Biosensors to Monitor Anti-SARS-CoV-2 Neutralizing IgG/sIgA Antibodies and Antioxidant Activity in Saliva

Monitoring biomarkers is a great way to assess daily physical condition, and using saliva instead of blood samples is more advantageous as the process is simple and allows individuals to test themselves. In the present study, we analyzed the titers of neutralizing antibodies, IgG and secretory IgA (sIgA), in response to the SARS-CoV-2 vaccine, in saliva. A total of 19 saliva and serum samples were collected over a 10-month period 3 weeks after the first vaccine, 8 months after the second vaccine, and 1 month after the third vaccine. The ranges of antibody concentrations post-vaccination were: serum IgG: 81-15,000 U/mL, salivary IgG: 3.4-330 U/mL, and salivary IgA: 58-870 ng/mL. A sharp increase in salivary IgG levels was observed after the second vaccination. sIgA levels also showed an increasing trend. A correlation with trends in serum IgG levels was observed, indicating the possibility of using saliva to routinely assess vaccine efficacy. The electrochemical immunosensor assay developed in this study based on the gold-linked electrochemical immunoassay, and the antioxidant activity measurement based on luminol electrochemiluminescence (ECL), can be performed using portable devices, which would prove useful for individual-based diagnosis using saliva samples.

Sandwich-Type Electrochemiluminescence Immunosensor Based on CDs@dSiO2 Nanoparticles as Nanoprobe and Co-Reactant

In general, co-reactants are essential in highly efficient electrochemiluminescence (ECL) systems. Traditional co-reactants are usually toxic, so it is necessary to develop new environmentally friendly co-reactants. In this work, carbon dots (CDs) were assembled with dendritic silica nanospheres (CDs@dSiO₂ NPs) to form a co-reactant of Ru(bpy)₃²⁺. Subsequently, a sandwich immunosensor for detecting human chorionic gonadotropin (HCG) was constructed based on CDs@dSiO₂ NPs as co-reactants, the nanoprobe loaded with the secondary antibody, and Ru(bpy)₃²⁺ as a luminophore. In addition, compared to directly as a signal probe, the luminophore Ru (bpy)₃²⁺ as a part of the electrolyte solution is simpler in this work. The immunosensor has an extremely low limit of detection of 0.00019 mIU/mL. This work describes the synthesis of low-toxic, efficient, and environmentally friendly CDs, which have become ideal co-reactants of Ru(bpy)₃²⁺, and proposes an ECL immunosensor with excellent stability and selectivity, which has great potential in clinical applications.

Programmable T-Junction Structure-Assisted CRISPR/Cas12a Electrochemiluminescence Biosensor for Detection of Sa-16S rDNA

Herein, a strand displacement amplification (SDA)-assisted CRISPR/Cas12a (LbCpf1) electrochemiluminescence (ECL) biosensor was fabricated for ultrasensitive identification of Staphylococcus aureus (Sa)-16S rDNA. A porphyrinic Zr metal-organic framework (MOF) (PCN-224) nanomaterial was prepared as the coreactant accelerator, which promoted the conversion of S₂O₈^2- and SO₄^*-, thus enhancing the reaction with CdS quantum dots (QDs) and amplifying the ECL emission signal. Meanwhile, with the presence of Sa-16S rDNA, the auxiliary probes and primers stimulated the SDA reaction under the action of Klenow fragment (3'-5' exo-) and Nt. BbvCI specifically recognized Sa-16S rDNA to form a defective T-junction structure and generated second primers to initiate the cycles. Such a structure transformed the input signal (Sa-16S rDNA) into substantial single-stranded DNA products (SP) through SDA. SP acted as activators and activated arbitrary side chain cleavage of CRISPR/Cas12a (trans-cleavage) and further realized effective annihilation of ECL signals. This ECL platform demonstrated desirable assay performance for Sa-16S rDNA with a wide response range of 1 fM to 10 nM, and the limit of detection was 0.437 fM (S/N = 3), showing good sensitivity and specificity. Therefore, the method not only expanded the applications of CRISPR/Cas12a but also opened up a novel strategy for clinical diagnosis.

Addressing the Origin of Single-Atom-Activated Supports Monitored by Electrochemiluminescence

Currently, much attention has been paid to the efforts to stabilize and regulate single atoms through supports to obtain decent electrocatalytic behaviors. However, little concern was given to the effect of single atoms on modulating the electronic structure of supports, despite the catalytic activities and large quantities of supports in the catalytic reactions. Herein, we have localized Ru single atoms onto two-dimensional layered double hydroxide (NiFe-LDH) and studied the role of Ru single atoms in adjusting the electronic structure of the NiFe-LDH support. Spin polarization of 3d electrons for Fe and electron redistribution in NiFe-LDH were effectively modulated through the interaction between Ru single atoms and NiFe-LDH. As a result, the luminol redox reaction and reactive oxygen revolution were simultaneously promoted by Ru single-atom-modulated NiFe-LDH, manifested as boosted electrochemiluminescence (ECL). Therefore, we have provided valid information to reveal the regulation effect of single atoms on the spin state and electronic structure of the supports. It is anticipated that our strategy may arouse wide interest in manipulating single-atom-modulated supports.