Electrochemical immunoassay for the carcinoembryonic antigen based on Au NPs modified zeolitic imidazolate framework and ordered mesoporous carbon

Development of an electrochemical sensitive aptasensor based on a zeolite imidazolate framework-8 and gold nanoparticles for the determination of Staphylococcus aureus bacteria

Staphylococcus aureus (S. aureus) is one of the most important pathogens that cause illness and food poisoning. In this research, using a glassy carbon electrode (GCE) modified with zeolite imidazolate framework-8 (ZIF 8) and gold nanoparticles (AuNPs), a sensitive electrochemical aptasensor has been made for the detection of the S. aureus bacteria. The morphology of the prepared AuNPs-ZIF 8 nanocomposite has been carefully characterized by means of transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS). In the manufacturing process, the S. aureus aptamer is immobilized on the AuNPs-ZIF 8 surface. Electrochemical impedance spectroscopy (EIS) method has been used for quantitative determination of S. aureus bacteria. The changes in the charge transfer resistance (Rct) of the aptamer due to the change in the concentration of bacteria are considered as the analytical signals. The proposed aptasensor has linear response in the concentration range of 1.5 × 101 to 1.5 × 107 CFU mL-1 of S. aureus bacteria. The detection limit of the method is 3.4 CFU mL-1. Using the developed aptasensor, it is possible to determine S. aureus bacteria in water and milk samples.

Electrochemical immunosensor based on hollow Pt@Cu2O as a signal label for dual-mode detection of procalcitonin

As a reliable biomarker to evaluate the severity of sepsis, sensitive and accurate detection of procalcitonin (PCT) is essential. In this study, a dual-mode electrochemical immunosensor based on Au/ZIF-8 as substrate and Pt@Cu2O as signal label was constructed for the detection of PCT. By loading Au nanoparticles onto rhombic dodecahedral ZIF-8, the substrate (Au/ZIF-8) has large specific surface area and can immobilize antibody (Ab1) by Au-N bonds. Meanwhile, hollow Pt@Cu2O nanocomposite with excellent peroxidase-like activity and electrocatalytic activity were synthesized as signal label. In the process of electrochemical testing, Pt@Cu2O catalyzed the reduction of hydrogen peroxide (H2O2) and further promotes the oxidation of hydroquinone (HQ) to achieve the synergistic amplification of electrochemical signals. The proposed immunosensor detected PCT by amperometric i-t and differential pulse voltammetry (DPV) tests with a good linear response and low limit of detection (i-t: 0.70 fg/mL and DPV: 0.40 fg/mL) in the range of 10 fg/mL∼100 ng/mL. The immunosensor exhibited excellent sensitivity and accuracy, indicating the potential application of this method for PCT detection.

Probe-labeled electrochemical approach for highly selective detection of 5-carboxycytosine in DNA

5-carboxycytosine (5caC) plays a critical role as an intermediate form in DNA methylation and demethylation processes. Its distribution and quantity significantly influence the dynamic equilibrium of these processes, thereby impacting the normal physiological activities of organisms. However, the analysis of 5caC presents a significant challenge due to its low abundance in the genome, making it almost undetectable in most tissues. In response to this challenge, we propose a selective method for 5caC detection using differential pulse voltammetry (DPV) at glassy carbon electrode (GCE), hinging on probe labeling. The probe molecule Biotin LC-Hydrazide was introduced into the target base and the labeled DNA was immobilized onto the electrode surface with the help of T4 polynucleotide kinase (T4 PNK). Leveraging the precise and efficient recognition of streptavidin and biotin, streptavidin-horseradish peroxidase (SA-HRP) on the surface of the electrode catalyzed a redox reaction involving hydroquinone and hydrogen peroxide, resulting in an amplified current signal. This procedure allowed us to quantitatively detect 5caC based on variations in current signals. This method demonstrated good linearity ranging from 0.01 to 100 nM with a detection limit as low as 7.9 pM. We have successfully applied it to evaluate the 5caC levels in complex biological samples. The probe labeling contributes to a high selectivity for 5caC detection, while the sulfhydryl modification via T4 PNK efficiently circumvents the limitation of specific sequences. Encouragingly, no reports have been made about electrochemical methods for detecting 5caC in DNA, suggesting that our method offers a promising alternative for 5caC detection in clinical samples.

MOF-Based Biosensors for the Detection of Carcinoembryonic Antigen: A Concise Review

Cancer has been considered one of the most serious diseases in recent decades. Early diagnosis of cancer is a crucial step for expedited treatment. Ideally, detection of cancer biomarkers, which are usually elevated because of cancer, is the most straightforward approach to detecting cancer. Among these biomarkers, the carcinoembryonic antigen (CEA) is considered one of the most important tumor markers for colorectal cancer. The CEA has also been recognized as a biomarker for other types of cancers, including breast, gastric, ovarian, pancreatic, and lung cancers. Typically, conventional CEA testing depends on immunoassay approaches, which are known to be complex, highly expensive, and time consuming. Accordingly, various types of biosensors have been designed for the detection of cancer biomarkers. The main prerequisites of these biosensors are high sensitivity, fast response, and low cost. Many nanostructures have been involved in the design of biosensors, such as nanoparticles of certain metals and metal oxides that are further functionalized to contribute to the sensing of the biomarkers. Alternatively, metal organic frameworks (MOFs), which are extended crystalline structures comprising metal clusters surrounded by organic linkers, have been shown to be highly promising for the development of biosensors. The 3D structure of MOFs results in a combination of high surface area and high interconnected porosity, which are believed to facilitate their function in the design of a biosensor. This review briefly classifies and describes MOF-based biosensor trials that have been published recently for the aim of detecting CEA.

Metal-organic frameworks/metal nanoparticles as smart nanosensing interfaces for electrochemical sensors applications: a mini-review

Metal-organic frameworks (MOFs) are porous materials with huge specific surface area and abundant active sites, which are composed of metal ions or clusters and organic ligands in the form of coordination bonds. In recent years, MOFs have been successfully applied in many fields due to their excellent physical, chemical, and biological properties. Electrochemical sensors have advantages such as economy, portability, and sensitivity, making them increasingly valued in the field of sensors. Many studies have shown that the electrode materials will affect the performance of electrochemical sensors. Therefore, the research on electrode materials is still one of the hotspots. MOFs are also commonly used to construct electrochemical sensors. However, electrochemical sensors prepared from single MOFs have shortcomings such as insufficient conductivity, low sensitivity, and poor electrochemical catalytic ability. In order to compensate for these defects, a new type of nanocomposite material with very ideal conductivity was formed by adding metal nanoparticles (MNPs) to MOFs. The combination of the two is expected to be widely applied in the field of sensors. This review summarizes the applications of various MNPs/MOFs composites in the field of electrochemical sensors and provides some references for the development of MNPs/MOFs composites-based electrochemical sensors in the future.

Application of a Novel Au@ZIF-8 Composite in the Detection of Bisphenol A by Surface-Enhanced Raman Spectroscopy

Bisphenol A (BPA) is an endocrine disruptor which is widely present in fish under the influence of environmental pollution. It is essential to establish a rapid detection method for BPA. Zeolitic imidazolate framework (ZIF-8) is a typical metal-organic framework material (MOFs) with a strong adsorption capacity, which can effectively adsorb harmful substances in food. Combining MOFs and surface-enhanced Raman spectroscopy (SERS) can achieve rapid and accurate screening of toxic substances. In this study, a rapid detection method for BPA was established by preparing a new reinforced substrate Au@ZIF-8. The SERS detection method was optimized by combining SERS technology with ZIF-8. The Raman peak at 1172 cm^-1 was used as the characteristic quantitative peak, and the lowest detection concentration of BPA was as low as 0.1 mg/L. In the concentration range of 0.1~10 mg/L, the linear relationship between SERS peak intensity and the concentration of BPA was good, and R² was 0.9954. This novel SERS substrate was proven to have great potential in rapidly detecting BPA in food.

Multilayered Mesoporous Composite Nanostructures for Highly Sensitive Label-Free Quantification of Cardiac Troponin-I

Cardiac troponin-I (cTnI) is a well-known biomarker for the diagnosis and control of acute myocardial infarction in clinical practice. To improve the accuracy and reliability of cTnI electrochemical immunosensors, we propose a multilayer nanostructure consisting of Fe₃O₄-COOH labeled anti-cTnI monoclonal antibody (Fe₃O₄-COOH-Ab₁) and anti-cTnI polyclonal antibody (Ab₂) conjugated on Au-Ag nanoparticles (NPs) decorated on a metal–organic framework (Au-Ag@ZIF-67-Ab₂). In this design, Fe₃O₄-COOH was used for separation of cTnI in specimens and signal amplification, hierarchical porous ZIF-67 extremely enhanced the specific surface area, and Au-Ag NPs synergically promoted the conductivity and sensitivity. They were additionally employed as an immobilization platform to enhance antibody loading. Electron microscopy images indicated that Ag-Au NPs with an average diameter of 1.9 ± 0.5 nm were uniformly decorated on plate-like ZIF-67 particles (with average size of 690 nm) without any agglomeration. Several electrochemical assays were implemented to precisely evaluate the immunosensor performance. The square wave voltammetry technique exhibited the best performance with a sensitivity of 0.98 mA mL cm⁻² ng⁻¹ and a detection limit of 0.047 pg mL⁻¹ in the linear range of 0.04 to 8 ng mL⁻¹.

Photochromic immunoassay for tumor marker detection based on ZnO/AgI nanophotocatalyst

A photochromic immunoassay was built for tumor marker detection based on ZnO/AgI nanophotocatalyst. Frist, ZnO/AgI nanoparticles were synthesized and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and Fourier transform infrared spectrometry (FTIR). The color development is caused by tetramethyl benzidine (TMB) solution oxidated by ZnO/AgI nanomaterials. The electron transitions in ZnO/AgI nanomaterials are driven by visible light irradiation, generating photogenerated hole and oxidizing TMB to blue solution. Appropriate band width between ZnO and AgI promotes separation of photogenerated electrons and holes and enhances oxidation efficiency. A sandwich-type immunoassay was constructed based on ZnO/AgI nanomaterial as labels. The absorbance at 650 nm of reaction solution is positively correlated with antigen concentration. The developed immunoassay showed good performance for carcinoma embryonic antigen (CEA) detection in the range 0.1-7.0 ng/mL with a detection limit of 65 pg/mL. The photochromic immunoassay also exhibited preferable selectivity, repeatability, and stability. A novel colorimetric immunoassay was constructed based on ZnO/AgI photocatalyst. ZnO/AgI nanomaterials occur electron transitions under visible light irradiation and generate photogenerated hole, which can oxidize TMB to blue solution. Carcinoembryonic antigen in sample was detected sensitively due to the high catalytic efficiency of ZnO/AgI nanomaterials.

A label-free and signal-amplifiable assay method for colorimetric detection of carcinoembryonic antigen

In this work, an innovative colorimetric assay method for the determination of carcinoembryonic antigen is developed with aptamer probes utilized as recognition element. DNA hybridization chain reaction is used as signal amplification technique, and peroxidase-mimicking hemin/G-quadruplex-assisted catalytic oxidation of 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) is deployed as signal reporting mechanism. The detection principle was firstly verified by using gel electrophoresis analysis and absorbance measurements. After condition optimization, a detection limit was theoretically determined as 24.8 ng/ml. Furthermore, the method exhibited good selectivity and satisfactory recovery rates (92.2%-108.6%) in serum samples. Moreover, the sensing scheme is easily extended for the detection of other analytes via similar target-aptamer recognition principle. To sum up, this is an enzyme- and label-free, cost-effective yet signal-amplifiable assay scheme for the determination of tumor markers with promising simplicity and selectivity, practical utility, and potential universality.

Research and Application of Highly Selective Molecular Imprinting Technology in Chiral Separation Analysis

Since residual chiral pollutants in the environment and toxic or ineffective chiral components in drugs can threat human health, there is an urgent need for methods to separation and analyze chiral molecules. Molecular imprinting technology (MIT) is a biomimetic technique for specific recognition of analytes with high potential for application in the field of chiral separation and analysis. However, since MIT has some disadvantages when used for chiral recognition, such as poor rigidity of imprinted materials, a single type of recognition site, and poor stereoselectivity, reducing the interference of conformationally and structurally similar substances to increase the efficiency of chiral recognition is difficult. Therefore, improving the rigidity of imprinted materials, increasing the types of imprinted cavity recognition sites, and constructing an imprinted microenvironment for highly selective chiral recognition are necessary for the accurate identification of chiral substances. In this article, the principle of chiral imprinting recognition is introduced, and various strategies that improve the selectivity of chiral imprinting, using derivative functional monomers, supramolecular compounds, chiral assembly materials, and biomolecules, are reviewed in the past 10 years.

An electrochemical immunosensor for the detection of carcinoembryonic antigen based on Au/g-C3N4 NSs-modified electrode and CuCo/CNC as signal tag

Carcinoembryonic antigen levels in the human body reflect the conditions associated with a variety of tumors and can be used for the identification, development, monitoring, and prognosis of lung cancer, colorectal cancer, and breast cancer. In this study, an amperometric immunosensor with CuCo/carbon nanocubes (CuCo/CNC) as the signal label is constructed. The bimetal-doped carbon skeleton structure has a high specific surface area and exhibits good electrocatalytic activity. In addition, Au/g-C₃N₄ nanosheets (Au/g-C₃N₄ NSs) are used to modify the substrate platform, facilitating the loading of more capture antibodies. The reaction mechanism was explored through electrochemical methods, X-ray powder diffraction, X-ray photoelectron spectroscopy, and other methods. Kinetic studies have shown that CuCo/CNC have good peroxidase-like activity. In addition, the electrocatalytic reduction ability of CuCo/CNC on hydrogen peroxide can be monitored using amperometric i-t curve (- 0.2 V, vs. SCE), and the response current value is positively correlated with the CEA antigen concentration. The prepared electrochemical immunosensor has good selectivity, precision, and stability. The dynamic range of the sensor was 0.0001-80 ng/mL, and the detection limit was 0.031 pg/mL. In addition, the recovery and relative standard deviation in real serum samples were 97.7-103 % and 3.25-4.13 %, respectively. The results show that the sensor has good analytical capabilities and can provide a new method for the clinical monitoring of CEA.

Light-Regulated Natural Fluorescence of the PCC 6803@ZIF-8 Composite as an Encoded Microsphere for the Detection of Multiple Biomarkers

The use of color-encoded microspheres for a bead-based assay has attracted increasing attention for high-throughput multiplexed bioassays. A fluorescent PCC 6803@ZIF-8 composite was prepared as a bead-based assay platform by a self-assembled zeolitic imidazolate framework (ZIF-8) on the surface of inactivated PCC 6803 cells. The composite fluorescence owing to the presence of pigment proteins in PCC 6803 could be gradually bleached with the prolongation of the ultraviolet light irradiation time. The composites with different fluorescence intensities were therefore obtained as encoded microspheres for the multiplexed assay. ZIF-8 provides a stable, rigid shell and a large specific surface area for composites, which prevent the composites from breakage during use and storage, simplify the protein immobilization procedure, reduce non-specific adsorption, and enhance the detection sensitivity. The encoded composites were successfully used to detect multiple DNA insertion sequences of Mycobacterium tuberculosis. The presented strategy offers an innovative color-encoding method for high-throughput multiplexed bioassays without the need of using chemically synthesized fluorescent materials.

Assay for TET1 activity and its inhibitors screening with signal amplification by both nanoparticles and Ru(III) redox recycling

Ten-eleven translocation protein 1 (TET1) is one member of TET proteins family which plays a key role in dynamic DNA methylation-demethylation process. Herein, a novel biosensor was constructed for TET1 detection and its inhibitors screening utilizing restriction digestion of endonuclease enzyme MspI. Half-methylated oligonucleotide (5mC DNA) was used as target and Ru(NH₃)₆³⁺ as electrochemical signal probe. After the treatment by TET1 and T4 β-glucosyltransferase (T4 β-GT), target oligonucleotide would not be recognized and digested. If there was no TET1, the target would be digested and the response of biosensor decreased greatly. The current difference of biosensor with and without the incubation with TET1 was therefore dependent on the concentration of TET1. To increase sensitivity of the biosensor, nanostructured film at electrode surface and nanoparticles modified oligonucleotides were employed as signal amplification elements for Ru(NH₃)₆³⁺ recycling. Finally, this biosensor showed high performance with a wide linear range of TET1 concentration from 3.5-21 ng/μL and a low detection limit of 0.33 ng/μL, which is superior to other existing methods. The inhibition effects of Bobcat339 on TET1 was successfully proved by our biosensor with an IC₅₀ of 38 μM. Not only that, but the feasibility of the biosensor for inhibitors screening was evaluated and further confirmed by other compounds including two anticancer drugs and three active ingredients of traditional Chinese medicine.

A sandwich-configuration electrochemiluminescence immunoassay based on Cu2O@OMC-Ru nanocrystals and OMC-MoS2 nanocomposites for determination of alpha-fetoprotein

A sandwich-format electrochemiluminescence (ECL) immunosensor has been developed for alpha-fetoprotein (AFP) detection based on the use of ordered mesoporous carbon-molybdenum disulfide (OMC-MoS₂) as a sensor platform and cuprous oxide @ ordered mesoporous carbon-Ru(bpy)₃²⁺ (Cu₂O@OMC-Ru) composites as signal tags. OMC alongside MoS₂ plays a synergistic role in improving the electrochemical performance of the electrode in the electron transfer process. The uniform cubic-shaped Cu₂O@OMC-Ru nanocrystals display excellent luminous efficiency, with a signal amplification strategy of OMC-MoS₂ synergistic enhancement and Cu₂O@OMC which is capable of immobilizing more Ru(bpy)₃²⁺ serving as a tracing tag to label antibodies. A detectable ECL emission at a Cu₂O@OMC-Ru nanocrystals modified electrode is initiated at an applied voltage of +1.15 V (scanning range: 0-1.2 V), in the presence of the tripropylamine (TPA) as coreactant. With the increase in AFP concentration, the loading of Cu₂O@OMC-Ru at the electrode increases. Afterward, the ECL detection of AFP shows a wide linear range from 0.1 pg/mL to 10 ng/mL with a correlation coefficient of 0.9964 and a detection limit of 0.011 pg/mL (S/N = 3) under the optimal experimental conditions. The recoveries were in the range 91.2-97.1% with RSD varying from 4.8 to 8.5%. Overall, the novel immunosensor has been successfully applied to the analysis of human serum samples, indicating a great potential for application in clinical diagnostics.

An ultrasensitive disposable sandwich-configuration electrochemical immunosensor based on OMC@AuNPs composites and AuPt-MB for alpha-fetoprotein detection

Early finding and diagnosis are critical for prevention and treatment of hepatocellular carcinoma (HCC). Alpha-fetoprotein (AFP) is a typical biomarker of HCC. Since AFP level can reflect the severity of HCC, it is essential to ensure the accurate detection of AFP. In this study, through a combination of the advantages exhibited by ordered mesoporous carbon (OMC)@gold nanoparticles (AuNPs) composites and AuPt-methylene blue (AuPt-MB), a disposable ultrasensitive sandwich-configuration electrochemical immunosensor for determination of AFP was designed. Characterized by excellent conductivity, highly ordered pore distribution and great surface area, OMC can be effective in promoting electron transfer and loading a large number of AuNPs. In the meantime, AuNPs can also immobilize AFP-Ab₁ through Au-N bonds. As a new redox-active species, rod-like AuPt-MB demonstrates high conductivity, uniform morphology and excellent biocompatibility, which makes it capable not only to fix AFP-Ab₂, but also to release electrochemical signals. A wide linearity of 10 fg mL^-1-100 ng mL^-1 and a low detection limit of 3.33 fg mL^-1 (S/N = 3) were obtained. Moreover, the proposed immunosensor exhibited acceptable selectivity, high stability and reproducibility. The excellent performance in detecting serum samples endows the proposed immunosensor with broad prospects of extensive application in the detection of disease biomarkers.

Au nanoparticle-loaded eggshell for electrochemical detection of nitrite

Eggshell is an extremely large source of domestic waste and has a huge scientific research potential because of its unique porous hierarchical structure. By converting eggshell waste into valuable functional materials, it can be recycled in many fields. Herein, we envisioned an economical and environmentally friendly conversion method for synthesizing Au nanoparticle loaded eggshell nanocomposites (defined as Au/CaCO3 nanocomposites) for the detection of trace amounts of nitrite in oolong tea. Compared with bare electrodes, the prepared Au/CaCO3 nanocomposite-based electrodes have obvious electrochemical enhancement behavior. A wide linear response range of 0.01 to 1.00 mM and a relatively low detection limit of 11.55 nM have been obtained in this study. The "turning waste into treasure" transformation strategy not only provides a practical and low-cost method for comprehensive utilization of eggshells as valuable functional materials, but also provides a new approach for sensitive detection of pollutants.

Bimetallic PtCu nanoparticles supported on molybdenum disulfide-functionalized graphitic carbon nitride for the detection of carcinoembryonic antigen

A molybdenum disulfide based graphite phase carbon nitride (MoS₂/g-C₃N₄) which is supported by a platinum-copper nanoparticle (PtCu) Z-type catalyst was created in this study. The catalyst exploits optoelectronic synergistic effect with large surface area, good catalysis, and biocompatibility to amplify the signal. The electrode impedance of the synthesized MoS₂/g-C₃N₄-PtCu was reduced five times in visible light compared with dark conditions, thereby improving the detection of carcinoembryonic antigen (CEA). At a voltage of - 0.4 V, the immunoprobe constructed with this material is used for CEA detection. A linear relationship between 100 fg mL^-1 and 80 ng mL^-1 concentrations was achieved with a minimum detection limit of 33 fg mL^-1 (S/N = 3). The recovery rate was 103-104%, and the relative standard deviation was 2.9-3.8%. This implies that the sandwich immunosensors have good reproducibility, selectivity, and stability and can be used in various applications. Graphical Abstract.