Ultrasensitive competitive method-based electrochemiluminescence immunosensor for diethylstilbestrol detection based on Ru(bpy)32+ as luminophor encapsulated in metal–organic frameworks UiO-67

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.

Signal-Enhanced Immunosensor-Based MOF-Derived ZrO2 Nanomaterials as Electrochemiluminescence Emitter for D-Dimer Detection

Metal oxide nanomaterials have garnered significant attention in the field of electrochemiluminescence (ECL) sensing due to their efficient, stable, and nontoxic properties. However, the current research on metal oxide nanomaterials has primarily focused on their cathodic luminescence properties, with limited reports on their anodic ECL properties. In this study, we utilized MOF-derived ZrO2 nanomaterials as luminophores to generate stable anodic ECL signals in the presence of the coreactant tripropylamine (TPrA). Additionally, a signal-enhancing immunosensor was developed to analyze D-dimer by incorporating the coreaction accelerator Cu-doped TiO2 (TiO2-Cu). The ZrO2 synthesized by calcining UiO-67 demonstrated nontoxicity and biocompatibility, exhibiting efficient and stable ECL emission in a TPrA solution. The inclusion of TiO2-Cu as a coreaction accelerator in the immunosensor resulted in the formation of a ternary system of ZrO2/TiO2-Cu/TPrA. The Cu doping effectively narrowed the bandgap of TiO2 and enhanced its conductivity. As a substrate, TiO2-Cu reacted with more TPrA, generating sufficient free radicals to effectively enhance the ECL signal of ZrO2. In this article, a short peptide ligand, NFC (NARKFYKGC), was designed to immobilize antibodies and maintain the activity of antigen-binding sites during the construction of the immunosensor. The developed immunosensor was used for the accurate detection of D-dimers, with a wide linear range of 0.05-600 ng/mL and a low detection limit of 21 pg/mL..

Review: Synthesis of metal organic framework-based composites for application as immunosensors in food safety

Ensuring food safety continues to be one of the major global challenges. For effective food safety monitoring, fast, sensitive, portable, and efficient food safety detection strategies must be devised. Metal organic frameworks (MOFs) are porous crystalline materials that have attracted attention for use in high-performance sensors for food safety detection owing to their advantages such as high porosity, large specific surface area, adjustable structure, and easy surface functional modification. Immunoassay strategies based on antigen-antibody specific binding are one of the important means for accurate and rapid detection of trace contaminants in food. Emerging MOFs and their composites with excellent properties are being synthesized, providing new ideas for immunoassays. This article summarizes the synthesis strategies of MOFs and MOF-based composites and their applications in the immunoassays of food contaminants. The challenges and prospects of the preparation and immunoassay applications of MOF-based composites are also presented. The findings of this study will contribute to the development and application of novel MOF-based composites with excellent properties and provide insights into advanced and efficient strategies for developing immunoassays.

Progress and Prospects of Electrochemiluminescence Biosensors Based on Porous Nanomaterials

Porous nanomaterials have attracted much attention in the field of electrochemiluminescence (ECL) analysis research because of their large specific surface area, high porosity, possession of multiple functional groups, and ease of modification. Porous nanomaterials can not only serve as good carriers for loading ECL luminophores to prepare nanomaterials with excellent luminescence properties, but they also have a good electrical conductivity to facilitate charge transfer and substance exchange between electrode surfaces and solutions. In particular, some porous nanomaterials with special functional groups or centered on metals even possess excellent catalytic properties that can enhance the ECL response of the system. ECL composites prepared based on porous nanomaterials have a wide range of applications in the field of ECL biosensors due to their extraordinary ECL response. In this paper, we reviewed recent research advances in various porous nanomaterials commonly used to fabricate ECL biosensors, such as ordered mesoporous silica (OMS), metal–organic frameworks (MOFs), covalent organic frameworks (COFs) and metal–polydopamine frameworks (MPFs). Their applications in the detection of heavy metal ions, small molecules, proteins and nucleic acids are also summarized. The challenges and prospects of constructing ECL biosensors based on porous nanomaterials are further discussed. We hope that this review will provide the reader with a comprehensive understanding of the development of porous nanomaterial-based ECL systems in analytical biosensors and materials science.

Impedimetric aptasensor based on porphyrin-based covalent-organic framework for determination of diethylstilbestrol

An impedimetric sensing strategy was developed for sensitively determining diethylstilbestrol (DES) based on a platform of porphyrin-containing covalent-organic framework (p-COF). The p-COF was synthesized using 5,10,15,20-tetra (4-aminophenyl) porphyrin (TAPP) and 1,3,6,8-tetrakis(4-formylphenyl) pyrene (TFPy) as building blocks via condensation reaction, for which p-COF was named as TAPP-TFPy-COF. Considering the large specific surface area (302.9 m² g^-1), high porosity, rich nitrogen functionality, superior electrochemical activity, and strong bioaffinity toward DNA strands, the TAPP-TFPy-COF-based platform exhibited enhanced, non-label, and amplified electrochemical signal, large number of immobilized DES-targeted aptamer strands, and fast-response toward the analyte. Electrochemical results reveal that the TAPP-TFPy-COF-based aptasensor promoted the sensing performance for the detection of DES, resulting in an extremely low limit of detection of 0.42 fg mL^-1 within a DES concentration ranging from 1 fg mL^-1 to 0.1 pg mL^-1, which was substantially lower than those of most reported DES sensors. Furthermore, the TAPP-TFPy-COF-based aptasensor possessed outperformed stability, high selectivity, ascendant reproducibility, and acceptable applicability in diverse environments. The recovery values for DES detection in milk, tap water, and frozen shrimp were in the range 91.80-118.50% with low relative standard deviation of 0.11-4.26%. This work provides a new sensing electrochemical approach based on COF network for DES detection and shows a deep insight into the construction of COF-based biosensors, which can be extended to be used for other target compounds.

Ratiometric electrochemical immunoassay for procalcitonin based on dual signal probes: Ag NPs and Nile blue A

In order to determine procalcitonin, a sandwich-type ratiometic electrochemical immunosensor was developed by differential pulse voltammetry (DPV). Due to high chemical stability and good biocompatibility, graphitic carbon nitride (g-C₃N₄) could be used as feasible supporter to carry silver nanoparticles (Ag NPs) with an obvious oxidative peak (measured typically at + 0.3 V vs. SCE). Ag NPs loaded onto g-C₃N₄ were not only beneficial to prevent the agglomeration of Ag NPs, but also favorable to improve the electron transfer velocity of g-C₃N₄. Moreover, the g-C₃N₄-Ag NPs as the matrix could immobilize primary antibody by Ag-N bond. Nile blue A (NBA), an excellent redox probe based on the redox reaction with two-electrons, provides a current signal at - 0.38 V (vs. SCE). Zr-based metal organic framework (UiO-67), an ideal framework material with large specific surface area and high porosity, could absorb the substantial water-soluble NBA by electrostatic adsorption. The UiO-67 modified by NBA (NBA-UiO-67) owned admirable biocompatibility and was a qualifying marker to load the secondary antibody. For the immunosensor, the current ratio of NBA to Ag NPs (I_NBA/I_{Ag NPs}) was increased as the concentrations of PCT increased. Under the optimum conditions, the linear range of the immunosensor was 0.005 to 50 ng/mL; the detection limit was 1.67 pg/mL (S/N = 3), which reflected the excellent analytical performance of the sensor. The proposed immunosensor strategy is a simple and dependable platform, with great application potential in biometric analysis.

[Ru(bpy)3]2+@Ce-UiO-66/Mn:Bi2S3 Heterojunction and Its Exceptional Photoelectrochemical Aptasensing Properties for Ofloxacin Detection

A photoelectrochemical (PEC) aptasensor on basis of [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ composites was constructed for detecting ofloxacin (OFL). First, Ce-UiO-66, prepared by a solvothermal method, had Zr⁴⁺-Zr³⁺ and Ce⁴⁺-Ce³⁺ intervalence cycles to increase the charge separation efficiency. Subsequently, Ce-UiO-66 was further modified by [Ru(bpy)₃]²⁺ and Mn:Bi₂S₃ cosensitization to improve the photoelectric activity. [Ru(bpy)₃]²⁺ not only broadened the range of light absorbed but also reacted with an electron donor to maintain the photoelectric conversion process. Among the [Ru(bpy)₃]²⁺@Ce-UiO-66/Mn:Bi₂S₃ heterojunction, Mn:Bi₂S₃ was a photosensitizer, which maximized the efficiency of the electron-hole separation and significantly improved photocurrent. Then, an aptamer was used as a biorecognition unit for OFL-specific detection. Under the best conditions, the PEC aptasensor realized the sensitive detection of OFL, with a detection range of 0.01-100 nmol/L and a detection limit of 6 pmol/L. In addition, the constructed PEC OFL sensor showed good reproducibility, stability, and specificity.

A potential-resolved electrochemiluminescence resonance energy transfer strategy for the simultaneous detection of neuron-specific enolase and the cytokeratin 19 fragment

An electrochemiluminescence resonance energy transfer (ECL-RET) immunosensor was developed based on the potential-resolved technology for the simultaneous detection of neuron-specific enolase (NSE) and the cytokeratin 19 fragment (CYFRA21-1). The absorption spectrum of gold nanorods (AuNRs) perfectly overlapped with the ECL spectra of SnS2@Pt and Ru(bpy)32+/Zn-MOF, so they exhibited an excellent ECL-RET effect with high efficiency. Zn-MOF possesses a large surface area, which allows for the loading of Ru(bpy)32+. This results in a signal probe of Ru(bpy)32+/Zn-MOF/Ab1 showing a strong ECL emission. Simultaneously, owing to the excellent electronic conductivity of PtNPs, they can increase the electron transfer rate between S2O82- and tin disulfide nanoflowers (SnS2NFs). Hence, the ECL signal of SnS2NFs can be enhanced. Under the optimal conditions, the linear range for NSE is 0.2 pg mL-1-20 ng mL-1 with a detection limit of 79 fg mL-1. The linear range for CYFRA21-1 is 1.25 pg mL-1-12.5 ng mL-1 with a detection limit of 0.43 pg mL-1. The proposed immunosensor can be used for the sensitive simultaneous detection of NSE and CYFRA21-1 in human serum and has promise for clinical diagnostics.

The Application of Prussian Blue Nanoparticles in Tumor Diagnosis and Treatment

Prussian blue nanoparticles (PBNPs) have attracted increasing research interest in immunosensors, bioimaging, drug delivery, and application as therapeutic agents due to their large internal pore volume, tunable size, easy synthesis and surface modification, good thermal stability, and favorable biocompatibility. This review first outlines the effect of tumor markers using PBNPs-based immunosensors which have a sandwich-type architecture and competitive-type structure. Metal ion doped PBNPs which were used as T1-weight magnetic resonance and photoacoustic imaging agents to improve image quality and surface modified PBNPs which were used as drug carriers to decrease side effects via passive or active targeting to tumor sites are also summarized. Moreover, the PBNPs with high photothermal efficiency and excellent catalase-like activity were promising for photothermal therapy and O2 self-supplied photodynamic therapy of tumors. Hence, PBNPs-based multimodal imaging-guided combinational tumor therapies (such as chemo, photothermal, and photodynamic therapies) were finally reviewed. This review aims to inspire broad interest in the rational design and application of PBNPs for detecting and treating tumors in clinical research.

Ingenious Electrochemiluminescence Bioaptasensor Based on Synergistic Effects and Enzyme-Driven Programmable 3D DNA Nanoflowers for Ultrasensitive Detection of Aflatoxin B1

Aflatoxin B1 (AFB1), one of the most toxic mycotoxins, has undergone a wide range of studies over the years. The development of rapid, simple, and sensitive analytical methods remains a major challenge for the accurate detection of AFB1 in foodstuffs. In this study, we designed an enhanced and stable ingenious electrochemiluminescence bioaptasensor (IEC-BA) for ultrasensitive detection of AFB1 based on the synergistic effects and enzyme-driven programmable assembled 3D DNA nanoflowers (EPDNs). This synergistic effect was comprised by the competitive impact on auxiliary probes (AP) and the cutting effect of the Hae III. Compared to the traditional aptamer direct-competition method, the synergistic effects ensured that the aptamer was more efficiently and adequately competed away by the target. Also, the redundant double-stranded probes were removed, which greatly facilitates simple, quick, and sensitive detection of AFB1. Besides, a large chunk of positively charged Ru(II) complexes (Ru(bpy)₃²⁺) was accumulated by the utilization of EPDNs, which resulted in tremendous improvement of the sensitivity of the designed method. Thus, even in the presence of trace amounts of AFB1, a sharply visual electrochemiluminescent signal was generated. The proposed method can realize the quantification of AFB1 with a good linear range from 1 ppt (pg mL^-1) to 5 ppb (ng mL^-1) with a detection limit of 0.27 ppt. In addition, it can also be successfully applied for the analysis of AFB1 in a peanut and wheat, with total recoveries ranging from 93.7 to 106.6%. Furthermore, the IEC-BA also exhibited good selectivity, reproducibility, and stability, revealing prospective applications of food safety monitoring and environmental analysis.

Novel Luminescent Nanostructured Coordination Polymer: Facile Fabrication and Application in Electrochemiluminescence Biosensor for microRNA-141 Detection

A series of novel luminescent nanostructured coordination polymers (Ce-Ru-NCPs) with tunable morphologies have been successfully synthesized on a large scale at room temperature by a facile and rapid solution-phase method using Ce³⁺ and tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)₃²⁺). Among them, the flowerlike Ce-Ru-NCP shows good cathodic electrochemiluminescence (ECL) characteristics. The ECL efficiency of the Ce-Ru-NCP/S₂O₈^2- system is about 2.34 times that of the classic tris(2,2'-bipyridyl) ruthenium(II) dichloride/S₂O₈^2- (Ru(bpy)₃²⁺/S₂O₈^2-) system. Hence, we report a sensitive ECL biosensor for microRNA-141 (miRNA-141) detection based on the flowerlike Ce-Ru-NCP as a cathodic ECL luminophore and a bipedal three-dimensional (3D) DNA walking machine as a signal amplifier. Through the bipedal 3D DNA walking machine, trace targets can be converted to substantial secondary targets (marked with the quencher dopamine), and a significant quenching effect on the ECL signal is achieved. As a result, the proposed biosensor exhibits a relatively good sensitivity for miRNA-141 detection and shows a dynamic range from 1.0 × 10^-16 to 1.0 × 10^-6 mol·L^-1 with a limit of detection (LOD) of 33 amol·L^-1 (S/N = 3). The Ce-Ru-NCP with tunable morphologies and high ECL efficiency, intensity, and stability possesses potential applications in ECL analysis.

An electrochemiluminescence biosensor for p53 antibody based on Zn-MOF/GO nanocomposite and Ag+-DNA amplification

An ultrasensitive electrochemiluminescence biosensor was established based on the Zn-MOF/GO nanocomposite. Ag(I)-embedded DNA complexes were used as a signal amplification reagent. In this work, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP) and Zn²⁺ were integrated into a porphyrin paddlewheel framework (Zn-MOF) by a hydrothermal method. The synthesized Zn-MOF material has electrochemiluminescence property, and the luminescence intensity is improved after being composited with graphene oxide (GO). Based on the composite material, we constructed an ultrasensitive ECL biosensor for the p53 antibody detection. The composite material acted as an admirable substrate and then loaded plenty of p53 antigens to recognize the target (p53 antibody) accurately. Because of the bridging effect of streptavidin and biotin-conjugated goat anti-rabbit IgG (bio-ab2), the rich-C DNA with positive correlation with the target was modified on the electrode and then captured the co-reactant accelerator Ag⁺ to amplify the signal. Therefore, the ECL biosensor response increases with increasing p53 antibody concentration. In the range 0.1 fg/mL-0.01 ng/mL, the response signal of the biosensor has a good linear relationship with the p53 antibody concentration. The detection limit is 0.03 fg/mL (S/N = 3). Impressively, the biosensor not only featured high sensitivity, good stability, and excellent specificity for the detection of p53 antibody, but also provides a new way for early detection of cancer. Graphical abstract Schematic representation of the electrochemiluminescence sensor based on a Zn-MOF/GO nanocomposite, which can be applied to the determination of p53 antibody.

Metal-organic frameworks-based sensitive electrochemiluminescence biosensing

Metal-organic frameworks (MOFs) as porous materials have attracted much attention in various fields such as gas storage, catalysis, separation, and nanomedical engineering. However, their applications in electrochemiluminescence (ECL) biosensing are limited due to the poor conductivity, lack of modification sites, low stability and specificity, and weak biocompatibility. Integrating the functional materials into MOF structures endows MOF composites with improved conductivity and stability and facilitates the design of ECL sensors with multifunctional MOFs, which are potentially advantageous over their individual components. This review summarizes the strategies for designing ECL-active MOF composites including using luminophore as a ligand, in situ encapsulation of luminophore within the framework, and post-synthetic modification. As-prepared MOF composites can serve as innovative emitters, luminophore carriers, electrode modification materials and co-reaction accelerators in ECL biosensors. The sensing applications of ECl-active MOF composites in the past five years are highlighted including immunoassays, genosensors, and small molecule detection. Finally, the prospects and challenges associated with MOF composites and their related materials for ECL biosensing are tentatively proposed.

Sensitive Detection of Caffeic Acid and Rutin via the Enhanced Anodic Electrochemiluminescence Signal of Luminol

The electrooxidation of phenolic groups of caffeic acid and rutin promote anodic electrochemiluminescence (ECL) luminol substantially. A sensitive, and cost-effective ECL method has thus been developed to detect caffeic acid, ranging from 0.1 to 5.0 μM, with a detection limit of 0.1 μM and rutin ranging from 0.2 to 25 μM with a detection limit of 0.12 μM. Contrarily, phenolic compounds quench the weak cathodic ECL of luminol. Both of anodic and cathodic ECL mechanisms of luminol in the presence of phenolic compounds are analyzed. The method based on the boomed anodic ECL of luminol is comparable to those based on Ru(bpy)₃²⁺ and S₂O₈^2-/O₂ systems. A lower onset potential and price than the other ECL reagents would realize its widely applications in the detection of phenolic compounds in food and medicine.

Data-Driven Modeling of Smartphone-Based Electrochemiluminescence Sensor Data Using Artificial Intelligence

Understanding relationships among multimodal data extracted from a smartphone-based electrochemiluminescence (ECL) sensor is crucial for the development of low-cost point-of-care diagnostic devices. In this work, artificial intelligence (AI) algorithms such as random forest (RF) and feedforward neural network (FNN) are used to quantitatively investigate the relationships between the concentration of Ru(bpy)32+ luminophore and its experimentally measured ECL and electrochemical data. A smartphone-based ECL sensor with Ru(bpy)32+/TPrA was developed using disposable screen-printed carbon electrodes. ECL images and amperograms were simultaneously obtained following 1.2-V voltage application. These multimodal data were analyzed by RF and FNN algorithms, which allowed the prediction of Ru(bpy)32+ concentration using multiple key features. High correlation (0.99 and 0.96 for RF and FNN, respectively) between actual and predicted values was achieved in the detection range between 0.02 µM and 2.5 µM. The AI approaches using RF and FNN were capable of directly inferring the concentration of Ru(bpy)32+ using easily observable key features. The results demonstrate that data-driven AI algorithms are effective in analyzing the multimodal ECL sensor data. Therefore, these AI algorithms can be an essential part of the modeling arsenal with successful application in ECL sensor data modeling.

A photoelectrochemical aptasensor for the detection of 17β-estradiol based on In2S3 and CdS co-sensitized cerium doped TiO2

In₂S₃ and CdS co-sensitized Ce doped TiO₂ optimized the transmission path of electrons.

A silver nanoparticle-assisted signal amplification electrochemiluminescence biosensor for highly sensitive detection of mucin 1

A novel electrochemiluminescence (ECL) biosensor was developed in this study, which was based on the Ag-NP modified tetrahedral DNA nanostructure.

Au-Luminol-decorated porous carbon nanospheres for the electrochemiluminescence biosensing of MUC1

Electrochemiluminescence (ECL) nanomaterials are usually deposited compactly on the surface of electrodes, which may cause poor mass transfer of reactants, thereby resulting in low ECL efficiency. In this work, we developed a novel kind of luminescent material denoted as C-Au-luminol nanospheres (C-Au-Lum NSs) by high dispersion of luminophores on porous carbon nanospheres (PCNSs). C-Au-Lum NSs were facilely prepared by the in situ reduction of chloroauric acid with the luminescent reagent luminol (Lum) on the nano-pores of PCNSs. Plenty of luminescent Au-Lum NPs were dispersedly concentrated inside the numerous pores and hollow interiors of PCNSs, effectively increasing the mass transfer of reagents and accelerating the electron transport inside the porous nanospheres. This greatly improved the availability of luminophores and endowed C-Au-Lum NSs with excellent ECL emission. After further integrating with enzymatic circulation and strand displacement, an ultrasensitive ECL biosensor was achieved for the ultrasensitive detection of an important tumor biomarker, mucin1. The logarithmically linear range from 0.1 pg mL-1 to 1 ng mL-1 with the detection limit of 47.6 fg mL-1 (S/N = 3) was achieved, demonstrating the superior performance of C-Au-Lum NSs. This work would provide new ideas for the construction of high-performance ECL sensing platforms for diverse applications.

Low fouling and ultrasensitive electrochemical immunosensors with dual assay methods based on Fe3O4 magnetic nanoparticles

Low fouling electrochemical immunosensors with both "signal-off" and "signal-on" analytical methods were developed for the highly sensitive and efficient detection of cancer antigen 15-3 (CA 15-3) in human serum samples. The antifouling sensing interfaces were constructed by assembling multifunctional polyethylene glycol on gold electrodes, followed by covalent conjugation with CA 15-3 antibody. Pure antigens and Fe₃O₄@Ag will competitively bind to the immobilized antibody on the electrode. Fe₃O₄ magnetic nanoparticles attached to the working electrode and collected by a magnetic electrode were treated via electrochemical conversion to generate electroactive Prussian blue as a signal readout. Therefore, these two signals measured independently were complementary, and this design allowed one to choose the assay method according to real situations so as to ensure accuracy of the immunosensor. Moreover, owing to its good antifouling property, the immunosensor was capable of detecting CA 15-3 even in complex human serum samples, demonstrating potential application in quantitative analysis of real patient serum samples.

Electrochemical determination of Salmonella typhimurium by using aptamer-loaded gold nanoparticles and a composite prepared from a metal-organic framework (type UiO-67) and graphene

An aptamer based assay is described for the determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework-graphene composite of type UiO-67/GR is used as the substrate, and an aptamer-gold nanoparticles-horseradish peroxidase (Apt-AuNP-HRP) conjugate the signal amplification probe. A phosphate-terminal and partially complementary DNA (cDNA) of the aptamer is covalently bound to UiO-67/GR via the chemical complexation between phosphate and Zr-OH groups of UiO-67, and then S. typhimurium and cDNA will compete for the binding sites. The binding of Apt-AuNP-HRP to S.typhimurium leads to the formation of strong conjugates. The unbound signal probes then attach to the surface of a glassy carbon electrode via hybridization with cDNA. This generates a large current response (best measured at a potential as low as -0.02 V vs. saturated calomel electrode) under the catalytic action of HRP on the H₂O₂-hydroquinone system. Under the optimal conditions, the differential pulse voltammetric signal decreases linearly in the 2 × 10¹ - 2 × 10⁸ cfu·mL^-1 S.typhimurium concentration range, with a lower detection limit of 5 cfu·mL^-1 (based on S/N = 3). The method was successfully applied to the detection of S. typhimurium in spiked milk samples. Graphical abstract Schematic presentation of electrochemical determination of Salmonella typhimurium (S.typhimurium). A metal-organic framework (type UiO-67) and graphene (GR) composite were used as substrate, and gold nanoparticles carrying horseradish peroxidase (HRP) for signal amplification. HQ: hydroquinone; cDNA: complementary DNA of aptamer.

Versatile High-Performance Electrochemiluminescence ELISA Platform Based on a Gold Nanocluster Probe

This report outlines a versatile high-performance electrochemiluminescence (ECL) enzyme-linked immunosorbent assay (ELISA) platform, which combines the merits of high-quantum-yield Au nanocluster (AuNC) probe-based ECL technology, the efficient ECL-resonance energy-transfer (ECL-RET) strategy, and highly sensitive and specific ELISA technology. The ECL detection procedure was performed on a recyclable MnO₂/AuNC-modified glassy carbon electrode interface by taking advantage of the ECL-RET between the AuNC probe and MnO₂ nanomaterials (NMs) to quench the ECL intensity. The etching of MnO₂ NMs by the product of ALP-based ELISA recovers the ECL signal. Notably, the ELISA process and the ECL detection procedure in this system are independent. Thus, the ECL-ELISA system can effectively avoid the influence of complex biological samples, and the ECL efficiency of the AuNC probe can be used readily. As demonstrated on TNF-α, because of the abovementioned characteristics, the ECL-ELISA platform presented an extremely wide dynamic range, with a detection limit of 2 orders lower than ELISA. Moreover, the system was also applicable for ultrahigh sensitive detection of various disease-related proteins and able to detect trace biomarkers in real serum samples. Therefore, this multifunctional ECL assay platform is versatile, facile, ultrasensitive, recyclable, and sufficiently straightforward for trace biomarker detection in complex biological samples. This approach not only enriches the foundational study of ECL devices but also greatly expands the potential application of ECL sensors in biological testing and clinical high-throughput diagnosis.

Ultrasensitive Immunosensor for Cardiac Troponin I Detection Based on the Electrochemiluminescence of 2D Ru-MOF Nanosheets

Electrochemiluminescence (ECL)-functionalized metal-organic frameworks (MOFs) have attracted increasing attention in biosensing in virtue of their diverse and tunable optical properties. A famous ECL luminophore, carboxyl-rich tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) (Ru(dcbpy)₃²⁺), possesses the characteristics of good water solubility and excellent ECL performance and also has the potential to be the organic ligand of metal-organic frameworks. Herein, functionalized MOF nanosheets (RuMOFNSs) containing plenty of Ru(dcbpy)₃²⁺ in the frameworks were synthesized in aqueous solution by a simple one-pot method. In this protocol, Ru(dcbpy)₃²⁺ acted as organic ligand to coordinate with Zn²⁺ originated from Zn(NO₃)₂, and polyvinylpyrrolidone (PVP) was used as structure-directing agent to control the formation of sheetlike structure. For practical application, a "signal-on" ECL immunosensor was designed for cardiac troponin I (cTnI) detection by employing RuMOFNSs as ECL probe. The immunosensor exhibited high sensitivity and excellent selectivity for cTnI detection in the range from 1 fg/mL to 10 ng/mL with a detection limit as low as 0.48 fg/mL. Finally, the biosensor was successfully applied for the detection of cTnI in human serum sample with satisfactory results, demonstrating its potential application in bioanalysis and clinical diagnosis.

Crystal structure, electrochemical and spectroscopic investigation of mer-tris-[2-(1H-imidazol-2-yl-κN3)pyrimidine-κN1]ruthenium(II) bis-(hexa-fluorido-phosphate) trihydrate

The crystal structure of the title compound, [Ru(C7H6N4)3](PF6)2·3H2O, a novel RuII complex with the bidentate ligand 2-(1H-imidazol-2-yl)pyrimidine, comprises a complex cation in the meridional form exclusively, with a distorted octa-hedral geometry about the ruthenium(II) cation. The Ru-N bonds involving imidazole N atoms are comparatively shorter than the Ru-N bonds from pyrimidine because of the stronger basicity of the imidazole moiety. The three-dimensional hydrogen-bonded network involves all species in the lattice with water mol-ecules inter-acting with both counter-ions and NH hydrogen atoms from the complex. The supra-molecular structure of the crystal also shows that two units of the complex bind strongly through a mutual N-H⋯N bond. The electronic absorption spectrum of the complex displays an asymmetric band at 421 nm, which might point to the presence of two metal-to-ligand charge-transfer (MLCT) bands. Electrochemical measurements show a quasi-reversible peak referring to the RuIII/RuII reduction at 0.87 V versus Ag/AgCl.