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

Quenching study of Cu2S-MPA/NGODs composites in electrochemiluminescence detection by modulating resonance energy transfer and adsorption process

This study explores the principles of resonance energy transfer and adsorption modulation using composites of Cu2S-MPA/NGODs. These composites can efficiently control the quenching process of electrochemiluminescence (ECL). Mercaptopropionic acid (MPA) was added during the synthesis of Cu2S-MPA to enhance its attachment to nitrogen-doped graphene quantum dots (NGODs). The UV absorption peaks of NGODs coincided with the emission peaks of luminol ECL, enabling resonance energy transfer and enhancing the quenching capability of Cu2S-MPA. Meanwhile, there is another quenching strategy. When the readily reducible Cu+ ions underwent partial reduction to Cu when they were bound to NGODs. This weakened the electrocatalytic effect on reactive oxygen species (ROS) and had a detrimental impact on electron transfer. Under optimal conditions, the immunosensor ECL intensity decreased linearly with the logarithm of carcinoembryonic antigen (CEA) concentration in the range of 0.00001-40 ng/mL, with a detection limit of 0.269 fg/mL. The sensor was effectively utilized for the identification of CEA in actual serum samples.

Multiple signal-enhanced electrochemiluminescence aptamer sensors based on carboxylated ruthenium (II) complexes for acetamiprid detection

BACKGROUND

Rapid and sensitive detection for acetamiprid, a kind of widely used neonicotinoid insecticide, is very meaningful for the development of modern agriculture and the protection of human health. Highly stable electrochemiluminescence (ECL) materials are one of the key factors in ECL sensing technology. ECL materials prepared by porous materials (e.g., MOFs) coated with chromophores have been used for ECL sensing detection, but these materials have poor stability because the chromophores escape when they are in aqueous solution. Therefore, the development of highly stable ECL materials is of great significance to improve the sensitivity of ECL sensing technology.

RESULTS

In this work, by combining etched metal-organic frameworks (E-UIO-66-NH2) as carrier with Tris(4,4'-dicarboxylic acid-2,2'-bipyridine)Ru(II) chloride (Ru(dcbpy)32+) as signal probe via amide bonds, highly stable nanocomposites (E-UIO-66-NH2-Ru) with excellent ECL performance were firstly prepared. Then, using MoS2 loaded with AuNPs as substrate material and co-reactant promoter, a signal off-on-off ECL aptamer sensor was prepared for sensitive detection of acetamiprid. Due to the excellent catalytic activity of E-UIO-66-NH2-Ru and MoS2@Au towards K2S2O8, the ECL signals can be enhanced by multiple signal enhancement pathways, the prepared ECL aptamer sensor could achieve sensitive detection of acetamiprid in the linear range of 10-13 to10-7 mol L-1, with the limit of detection (LOD) of 2.78ⅹ10-15 mol L-1 (S/N = 3). After the evaluation of actual sample testing, this sensing platform was proven to be an effective method for the detection of acetamiprid in food and agricultural products.

SIGNIFICANCE AND NOVELTY

The E-UIO-66-NH2-Ru prepared by linking Ru(dcbpy)32+ to E-UIO-66-NH2 via amide bonding has very high stability. The synergistic catalytic effect of MoS2 and AuNPs enhanced the ECL signal. By exploring the sensing mechanism and evaluating the actual sample tests, the proposed signal "on-off" ECL sensing strategy was proved to be an effective and excellent ECL sensing method for sensitive and stable detection of acetamiprid.

A magnetic graphene oxide and UiO-66 based homogeneous dual recognition electrochemical aptasensor for accurate and sensitive detection of aflatoxin B1

Aflatoxin (AFs) contamination is one of the serious food safety issues. Aflatoxin B1 (AFB1) is the most common and toxic aflatoxin, which has been classified as a class 1 carcinogen by the International Agency for Research on Cancer (IARC). It is extremely destructive to liver tissue. Developing a convenient and sensitive detection technique is essential. In this paper, we developed a homogeneous dual recognition strategy based electrochemical aptasensor for accurate and sensitive detection of aflatoxin B1 (AFB1) based on the magnetic graphene oxide (MGO) and UiO-66. The MGO was synthesized for the recognition and magnetic separation of AFB1 from complex samples. UiO-66/ferrocenecarboxylic acid (Fc)/aptamer composites were constructed as both recognition and signal probes. The probes would specifically capture AFB1 enriched by MGO, which enables dual recognition in homogeneous solution, thus further improving the accuracy of AFB1 detection. The electrochemical aptasensor for AFB1 had a linear range from 0.005 to 500 ng mL-1. Additionally, the limit of detection was 1 pg mL-1. It shows a favorable potential for both sensitive and accurate detection of AFB1 in real samples.

Single-Atom Iron Doped Carbon Dots with Highly Efficient Electrochemiluminescence for Ultrasensitive Detection of MicroRNAs

Herein, single-atom iron doped carbon dots (SA Fe-CDs) were successfully prepared as novel electrochemiluminescence (ECL) emitters with high ECL efficiency, and a biosensor was constructed to ultrasensitively detect microRNA-222 (miRNA-222). Importantly, compared with the conventional without single-atom doped CDs with low ECL efficiency, SA Fe-CDs exhibited strong ECL efficiency, in which single-atom iron as an advanced coreactant accelerator could significantly enhance the generation of reactive oxygen species (ROS) from the coreactant S2O82- for improving the ECL efficiency. Moreover, a neoteric amplification strategy combining the improved strand displacement amplification with Nt.BbvCI enzyme-induced target amplification (ISDA-EITA) could produce 4 output DNAs in every cycle, which greatly improved the amplification efficiency. Thus, a useful ECL biosensor was built with a detection limit of 16.60 aM in the range of 100 aM to 1 nM for detecting traces of miRNA-222. In addition, miRNA-222 in cancer cell lysate (MHCC-97L) was successfully detected by using the ECL biosensor. Therefore, this strategy provides highly efficient single-atom doped ECL emitters for the construction of sensitive ECL biosensing platforms in the biological field and clinical diagnosis.

Fluorescent imaging and toxicology study of alga-derived carbon dots in zebrafish

With the widespread application of carbon dots (CDs) in fluorescence imaging, their toxicity has become a focal point of concern. The potential toxicity of CDs synthesized from different raw materials remains an unresolved issue. Laver and wakame, which are commonly popular sea vegetable foods rich in nutrients, were utilized to investigate whether synthetic CDs derived from these alga sources retain medicinal value. Herein, two types of fluorescent alga-derived CDs were prepared through hydrothermal synthesis using laver and wakame respectively. Zebrafish were immersed in both types of CDs to observe their fluorescence imaging effects within the zebrafish bodies. It was observed that laver-derived CDs and wakame-derived CDs exhibited similar luminescence properties but differed in terms of fish egg imaging localization. Additionally, intestinal flora sequencing revealed varying degrees of influence on the zebrafish gut microbiota by the two types of CDs, suggesting that both alga-derived CDs could enhance the abundance of intestinal flora in zebrafish.

Ternary electrochemiluminescence quenching effects of CuFe2O4@PDA-MB towards self-enhanced Ru(dcbpy)32+ functionalized 2D metal-organic layer and application in carcinoembryonic antigen immunosensing

BACKGROUND

Carcinoembryonic antigen (CEA) is a significant glycosylated protein, and the unusual expression of CEA in human serum is used as a tumor marker in the clinical diagnosis of many cancers. Although scientists have reported many ways to detect CEA in recent years, such as electrochemistry, photoelectrochemistry, and fluorescence, their operation is complex and sensitivity is average. Therefore, finding a convenient method to accurately detect CEA is significance for the prevention of malignant tumors. With high sensitivity, quick reaction, and low background, electrochemiluminescence (ECL) has emerged as an essential method for the detection of tumor markers in blood.

RESULTS

In this work, a "signal on-off" ECL immunosensor for sensitive analysis of CEA ground on the ternary extinction effects of CuFe2O4@PDA-MB towards a self-enhanced Ru(dcbpy)32+ functionalized metal-organic layer [(Hf)MOL-Ru-PEI-Pd] was prepared. The high ECL efficiency of (Hf)MOL-Ru-PEI-Pd originated from the dual intramolecular self-catalysis, including intramolecular co-reaction between polyethylenimine (PEI) and Ru(dcbpy)32+. At the same time, loading Pd NPs onto (Hf)MOL-Ru-PEI could not only improve the electron transfer ability of (Hf)MOL-Ru-PEI, but also provide more active sites for the reaction of Ru(dcbpy)32+ and PEI. In the presence of CEA, CuFe2O4@PDA-MB-Ab2 efficiently quenches the excited states of (Hf)MOL-Ru-PEI-Pd by PDA, Cu2+, and methylene blue (MB) via energy and electron transfer, leading to an ECL signal decrease. Under optimal conditions, the proposed CEA sensing strategy showed satisfactory properties ranging from 0.1 pg mL-1 to 100 ng mL-1 with a detection limit of 20 fg mL-1.

SIGNIFICANCE

The (Hf)MOL-Ru-PEI-Pd and CuFe2O4@PDA-MB were prepared in this work might open up innovative directions to synthesize luminescence-functionalized MOLs and effective quencher. Besides, the ECL quenching mechanism of Ru(dcbpy)32+ by MB was successfully explained by the inner filter effect (ECL-IFE). At last, the proposed immunosensor exhibits excellent repeatability, stability, and selectivity, and may provide an attractive way for CEA and other disease markers determination.

Space-Confined Electrochemical Aptasensing with Conductive Hydrogels for Enhanced Applicability to Aflatoxin B1 Detection

Aflatoxin B1 (AFB1) contamination has received considerable attention for the serious harm it causes and its wide distribution. Hence, its efficient monitoring is of great importance. Herein, a space-confined electrochemical aptasensor for AFB1 detection is developed using a conductive hydrogel. Plasmonic gold nanoparticles (AuNPs) and methylene blue-embedded double-stranded DNA (MB-dsDNA) were integrated into the conductive Au-hydrogel by ultraviolet (UV) polymerization. Specific recognition of AFB1 by the aptamer released MB from MB-dsDNA in the matrix. The free DNA migrated to the outer layer due to electrostatic repulsion during the Au-hydrogel formation. The electrochemical aptasensor based on this Au-hydrogel offered a twofold enlarged oxidation current of MB (IMB) compared with that recorded in the homogeneous solution for AFB1 detection. Upon light illumination, this IMB was further enlarged by the local surface plasmon resonance (LSPR) of the AuNPs. Ultimately, the Au-hydrogel-based electrochemical aptasensor provided a detection limit of 0.0008 ng mL-1 and a linear range of 0.001-1000 ng mL-1 under illumination for AFB1 detection. The Au-hydrogel allowed for space-confined aptasensing, favorable conductivity, and LSPR enhancement for better sensitivity. It significantly enhanced the applicability of the electrochemical aptasensor by avoiding complicated electrode fabrication and signal loss in a bulk homogeneous solution.

Electrochemiluminescence resonance energy transfer between a Ru-ZnMOF self-enhanced luminophore and a double quencher ZnONF@PDA to detect NSE

The construction of advanced systems capable of accurately detecting neuron-specific enolase (NSE) is essential for rapidly diagnosing small-cell lung cancer. In this study, an electrochemiluminescence (ECL) resonance energy transfer immunosensor was proposed for the ultra-sensitive detection of NSE. The co-reactants C2O42- and Ru(bpy)32+ were integrated to form a self-enhanced ECL luminophore (Ru-ZnMOF) as the ECL donor. The abundant carboxyl functional groups of Ru-ZnMOF supported antibody 1 via an amidation reaction. Polydopamine-modified zinc dioxide nanoflowers, as ECL acceptors, inhibited Ru-ZnMOF ECL signaling. The linear range of NSE was 10 fg mL-1 to 100 ng mL-1 with a detection limit of 3.3 fg mL-1 (S/N = 3), which is suitably low for determining NSE in real samples.

Accelerated Hybridization Chain Reaction Kinetics Using Poly DNA Tetrahedrons and Its Application in Detection of Aflatoxin B1

Traditional hybridization chain reaction (HCR) as a popular isothermal amplification technique shows some inevitable disadvantages in bioanalysis due to its relatively slow kinetics, which could be markedly promoted when the HCR initiator occurs under tension. Herein, a poly DNA tetrahedrons (pTDNs)-mediated HCR was successfully constructed to make its initiator in a stretched state by long-range electrostatic forces owing to the superimposed electrostatic interactions derived from the synthesized pTDNs, and it was hypothesized that it could remarkably enhance HCR performance, which was testified by theoretical simulations and experimental studies. Consequently, pTDNs-mediated HCR was applied to develop a novel immunoassay for rapid and sensitive detection of aflatoxin B1 as a proof-of-concept, and its signal amplification was attributed to the increased G4 DNAzyme that loaded on the second antibody. Our work paves a promising way using simple DNA frameworks alone to heighten HCR kinetics for reaction speed improvement and signal amplification in bioanalysis.

Dual Signal-Enhanced Electrochemiluminescence Strategy Based on Functionalized Biochar for Detecting Aflatoxin B1

Metal-organic frameworks (MOFs) are often used as carriers in the preparation of electrochemiluminescent (ECL) materials, and ECL materials stabilized in the aqueous phase can be prepared by encapsulating chromophores inside MOFs by an in situ growth method. In this study, nanocomposites MIL-88B(Fe)-NH2@Ru(py)32+ with excellent ECL response were prepared by encapsulating Tris(2,2'-bipyridine)ruthenium dichloride (Ru(py)32+) inside MIL-88B(Fe)-NH2 using the one-step hydrothermal method. MIL-88B(Fe)-NH2 possesses abundant amino groups, which can accelerate the catalytic activation process of K2S2O8, and its abundant pores are also conducive to the enhancement of the transmission rate of co-reactant agents, ions, and electrons, which effectively improves the ECL efficiency. In order to obtain more excellent ECL signals, we prepared aminated biochar (NH2-biochar) using Pu-erh tea dregs as precursor and loaded gold nanoparticles (Au NPs) on its surface as substrate material for modified electrodes. Both NH2-biochar and Au NPs can also be used as a co-reactant promoter to catalyze the activation process of co-reactant K2S2O8. Therefore, a sandwich-type ECL immunosensor was prepared based on a dual signal-enhanced strategy for the highly sensitive and selective detection of aflatoxin B1 (AFB1). Under the optimal experimental conditions, the sensitive detection of AFB1 was achieved in the range of 1 pg·mL-1~100 ng·mL-1 with a detection limit of 209 fg·mL-1. The proposed dual signal-enhanced ECL immunosensor can provide a simple, convenient, and efficient method for the sensitive detection of AFB1 in food and agricultural products.

Simple Immunosensor Based on Carboxyl-Functionalized Multi-Walled Carbon Nanotubes @ Antimony-Doped Tin Oxide Composite Membrane for Aflatoxin B1 Detection

This paper presents a novel nano-material composite membrane for detecting aflatoxin B₁ (AFB₁). The membrane is based on carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) @ antimony-doped tin oxide (ATO)-chitosan (CS). To prepare the immunosensor, MWCNTs-COOH were dissolved in the CS solution, but some MWCNTs-COOH formed aggregates due to the intertwining of carbon nanotubes, blocking some pores. ATO was added to the solution containing MWCNTs-COOH, and the gaps were filled by adsorbing hydroxide radicals to form a more uniform film. This greatly increased the specific surface area of the formed film, resulting in a nano-composite film that was modified on screen-printed electrodes (SPCEs). The immunosensor was then constructed by immobilizing anti-AFB₁ antibodies (Ab) and bovine serum albumin (BSA) on an SPCE successively. The assembly process and effect of the immunosensor were characterized using scanning electron microscopy (SEM), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). Under optimized conditions, the prepared immunosensor exhibited a low detection limit of 0.033 ng/mL with a linear range of 1 × 10^-3-1 × 10³ ng/mL. The immunosensor demonstrated good selectivity, reproducibility, and stability. In summary, the results suggest that the MWCNTs-COOH@ATO-CS composite membrane can be used as an effective immunosensor for detecting AFB₁.

Electrochemiluminescence Immunosensors Based on ECL-RET Triggering between Mn SANE/PEI-Luminol and PtCu/h-MPF for Ultrasensitive Detection of CEA

In this paper, a novel donor-acceptor pair was creatively proposed based on the principle of electrochemiluminescence resonance energy transfer (ECL-RET): luminol immobilized on polyethyleneimine (PEI)-functionalized manganese-based single-atom nanozymes (Mn SANE/PEI-luminol, donor) and a PtCu-grafted hollow metal polydopamine framework (PtCu/h-MPF, acceptor). A quenched ECL immunosensor was constructed for the ultrasensitive analysis of carcinoembryonic antigen (CEA). Mn SANE, as an efficient novel coreaction accelerator with the outstanding performance of significantly activating H₂O₂ to produce large amounts of ROS, was further modified by the coreactant PEI, which efficiently immobilized luminol to form a self-enhanced emitter. As a result, the electron transport distance was effectively shortened, the energy loss was reduced, and luminol achieved a high ECL efficiency. More importantly, PtCu-grafted h-MPF (PtCu/h-MPF) was proposed as a novel quencher. The UV-vis spectra of PtCu/h-MPF partially overlap with the ECL spectra of Mn SANE/PEI-luminol, which can effectively trigger the ECL-RET behavior between the donor and the acceptor. The multiple quenching effect on Mn SANE/PEI-luminol was achieved, which significantly improved the sensitivity of the immunosensor. The prepared immunosensor exhibited good linearity in the concentration range of 10^-5 to 80 ng/mL. The results indicate that this work provides a new method for the early detection of CEA in clinical diagnosis.

Nitrogen-, Sulfur-, and Fluorine-Codoped Carbon Dots with Low Excitation Potential and High Electrochemiluminescence Efficiency for Sensitive Detection of Matrix Metalloproteinase-2

In this study, nitrogen-, sulfur-, and fluorine-codoped carbon dots (NSF-CDs) with high electrochemiluminescence (ECL) efficiency were developed as novel emitters to fabricate an ECL biosensor for sensitive detection of matrix metalloproteinase 2 (MMP-2). Impressively, compared to previously reported CDs, NSF-CDs with narrow band gap not only decreased the excitation voltage to reduce the side reaction and the damage on biomolecules but also had hydrogen bonds to vastly enhance the ECL efficiency. Furthermore, an improved exonuclease III (Exo III)-assisted nucleic acid amplification method was established to convert trace MMP-2 into a mass of output DNA, which greatly improved the target conversion efficiency and ECL signal. Hence, the ECL biosensor has realized the sensitive detection of MMP-2 proteins from 10 fg/mL to 10 ng/mL with a limit of detection of 6.83 fg/mL and has been successfully applied in the detection of MMP-2 from Hela and MCF-7 cancer cells. This strategy offered neoteric CDs as ECL emitters for sensitive testing of biomarkers in medical research.

A universal CRISPR/Cas12a-powered intelligent point-of-care testing platform for multiple small molecules in the healthcare, environment, and food

Growing studies focusing on nuclear acid detection via the emerging CRISPR technique demonstrate its promising application. However, limited works solve the identification of non-nucleic acid targets, especially multiple small molecules. To address challenges for point-of-care testing (POCT) in complex matrices for healthcare, environment, and food safety, we developed CRISPR Cas12a-powered highly sensitive, high throughput, intelligent POCT (iPOCT) for multiple small molecules based on a smartphone-controlled reader. As a proof of concept, aflatoxin B1 (AFB1), benzo[a]pyrene (BaP), and capsaicin (CAP) were chosen as multiple targets. First, three antigens were preloaded in independent microwells. Then, the antibody/antigen-induced fluorescent signals were consecutively transferred from the biotin-streptavidin to CRISPR/Cas12a system. Third, the fluorescent signals were recorded by a smartphone-controlled handheld dark-box readout. Under optimization, detection limits in AFB1, BaP, and CAP were 0.00257, 4.971, and 794.6 fg/mL with wide linear ranges up to four orders of magnitude. Using urine, water, soybean oil, wheat, and peanuts as the complex matrix, we recorded high selectivity, considerable recovery, repeatability, and high consistency comparison to HPLC-MS/MS methods. This work promises a practical intelligent POCT platform for multiple targets in lipid-soluble and water-soluble matrices and could be extensively applied for healthcare, environment, and food safety.

Coreactant-free electrochemiluminescence of polyfluorene nanoparticle coupling double quencher for β-amyloid1-42 detection

β-amyloid_1-42 (Aβ_1-42) is a humoral biomarker for early diagnosis of Alzheimer's disease (AD), and exists at a low level in human body. Its sensitive detection is very valuable. The electrochemiluminescence (ECL) assay of Aβ_1-42 has attracted special attention owing to high sensitivity and simple operation. However, currently reported ECL assays for Aβ_1-42 usually required the introduction of exogenous coreactants to improve the detection sensitivity. Introducing exogenous coreactants will lead to non-negligible repeatability and stability problems. This work exploited poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadazole)] nanoparticles (PFBT NPs) as coreactant-free ECL emitters for detecting Aβ_1-42. The PFBT NPs, first antibody (Ab₁) and antigen Aβ_1-42 were successively assembled on glassy carbon electrode (GCE). Silica nanoparticles served as a carrier to grow polydopamine (PDA) in situ, and further assembled Au nanoparticles (Au NPs) and second antibody (Ab₂), producing the secondary antibody complex (SiO₂@PDA-Au NPs-Ab₂). With its assembly on the biosensor, the ECL signal decreased since both PDA and Au NPs could quench ECL emission from PFBT NPs. The limit of detection (LOD) of 0.55 fg/mL and limit of quantification (LOQ) of 37.45 fg/mL for Aβ_1-42 were obtained. PFBT NPs coupling dual-quencher PDA-Au NPs created an excellent ECL system for bioassays, and constructed a sensitive analytical method for Aβ_1-42.

Microelectromechanical Microsystems-Supported Photothermal Immunoassay for Point-of-Care Testing of Aflatoxin B1 in Foodstuff

Accurate identification of acutely toxic and low-fatality mycotoxins on a large scale in a quick and cheap manner is critical for reducing population mortality. Herein, a portable photothermal immunosensing platform supported by a microelectromechanical microsystem (MEMS) without enzyme involvement was reported for point-of-care testing of mycotoxins (in the case of aflatoxin B₁, AFB₁) in food based on the precise satellite structure of Au nanoparticles. The synthesized Au nanoparticles with a well-defined, graded satellite structure exhibited a significantly enhanced photothermal response and were coupled by AFB₁ antibodies to form signal conversion probes by physisorption for further target-promoted competitive responses in microplates. In addition, a coin-sized miniature NIR camera device was constructed for temperature acquisition during target testing based on advanced MEMS fabrication technology to address the limitation of expensive signal acquisition components of current photothermal sensors. The proposed MEMS readout-based microphotothermal test method provides excellent AFB₁ response in the range of 0.5-500 ng g^-1 with detection limits as low as 0.27 ng g^-1. In addition, the main reasons for the efficient photothermal transduction efficiency of Au with different graded structures were analyzed by finite element simulations, providing theoretical guidance for the development of new Au-based photothermal agents. In conclusion, the proposed portable micro-photothermal test system offers great potential for point-of-care diagnostics for residents, which will continue to facilitate immediate food safety identification in resource-limited regions.