Aptamer based electrochemiluminescent determination of bisphenol A by using carboxylated graphitic carbon nitride

Double-enhanced sandwich electrochemiluminescence aptasensor based on g-C3N4-Au-luminol nanocomposites and ZnCuS nanosheets for highly sensitive detection of mucin 1

The traditional luminol electrochemiluminescence (ECL) sensing suffers from low signal response and instability issues. Here, an Au/ZnCuS double-enhanced g-C3N4-supported luminol ECL aptasensor is constructed for the sensitive detection of human mucin 1 (MUC1). In this platform, g-C3N4 of a large specific surface area is beneficial to load more luminol illuminants. Au nanoparticles promote the decomposition of H2O2 coreactants to generate more reactive oxygen (•OH and O2•-) intermediates, while ZnCuS can immobilize the aptamer and simultaneously catalyze H2O2 decomposition, realizing the double-wing signal amplification. Under optimal conditions, this sensor shows a good detection capability within 1.0 × 10-4-1.0 × 103 ng mL-1 and a low detection limit of 5.0 × 10-5 ng mL-1, as well as ideal stability, selectivity, and reproducibility. This double-enhanced aptasensor highlights a new signal-enhancement approach for early biomarker detection.

Electrochemiluminescent assay based on Co-MOF and TiO2 for determination of bisphenol A

An electrochemiluminescence (ECL) sensor for determining bisphenol A (BPA) was prepared based on titanium dioxide (TiO2) and Co-MOF. TiO2 is a co-reaction promoter that amplifies the ECL signal in the Ru(bpy)32+-trinpropylamine (TPrA) system. When the electrode is modified with Co-MOF the ECL signal is significantly enhanced. This is because Co-MOF can not only be used as a co-reaction accelerator but also as a carrier to adsorb more luminescent substances. Possible mechanisms for amplifying the original signal through the synergistic action of the two substances are investigated. The ECL strength decreases with increasing concentrations of BPA, and the amount of BPA can be determined by the change in ECL signal strength (ΔI). Under optimal experimental conditions, the linear range of BPA was 2.0 × 10-10 to 2.0 × 10-5 M, with a determination limit of 6.7 × 10-11 M (3σ/m). The relative standard deviation (RSD) of the signal for ten consecutive measurements was 1.5%. The sensor can be used to detect BPA in bottled samples with recoveries of 96 to 105%.

Aggregation-induced enhancement of pyrene-based metal-organic framework as a new electrochemiluminescence emitter for ultrasensitive detection of sulfadimethoxine

In this study, a signal-on electrochemiluminescence (ECL) aptasensor for ultrasensitive detection of sulfadimethoxine (SDM) was constructed based on a competitive aptamer strategy. Specifically, cerium-metal-organic framework (Ce-MOF) with large specific surface area and excellent electrical conductivity was combined with gold nanoparticles (AuNPs) to form a substrate, followed by the immobilisation of double-stranded DNA (dsDNA) via AuN bonds. In the presence of SDM, the aptamer tended to form an aptamer-SDM complex, which caused dsDNA to dissociate. After release of the aptamer, the capture probe (CP) combined with the tracer label to enhance the ECL signal. As expected, the prepared sensor displayed an ideal linear response range from 10.0 fg mL-1 to 100 ng mL-1 with a limit of detection (LOD) of 1.28 fg mL-1 and successfully detected SDM in milk and quality control samples.

Synthesis and up-to-date applications of 2D microporous g-C3N4 nanomaterials for sustainable development

In recent years, with the development of industrial technology and the increase of people's environmental awareness, the research on sustainable materials and their applications has become a hot topic. Among two-dimensional (2D) materials that have been selected for sustainable research, graphitic phase carbon nitride (g-C3N4) has become a hot research topic because of its many outstanding advantages such as simple preparation, good electrochemical properties, excellent photochemical properties, and better thermal stability. Nevertheless, the inherent limitations of g-C3N4 due to its relatively poor specific surface area, rapid charge recombination, limited light absorption range, and inferior dispersion in aqueous and organic media have limited its practical application. In the review, we summarize and analyze the unique structure of the 2D microporous nanomaterial g-C3N4, its synthesis method, chemical modification method, and the latest application examples in various fields in recent years, highlighting its advantages and shortcomings, with a view to providing ideas for overcoming the difficulties in its application. Furthermore, the pressing challenges faced by g-C3N4 are briefly discussed, as well as an outlook on the application prospects of g-C3N4 materials. It is expected that the review in this paper will provide more theoretical strategies for the future practical application of g-C3N4-based materials, as well as contributing to nanomaterials in sustainable applications.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

An Overview of Aptamer-Based Sensor Platforms for the Detection of Bisphenol-A

Endocrine disruptive compounds are natural or anthropogenic environmental micropollutants that alter the function of the endocrine system ultimately damaging the metabolism. Bisphenol A (BPA) is the most common of these pollutants and it is often used in epoxy coatings and polycarbonates as a plasticizer. Therefore, monitoring BPA levels in different environments is very important and challenging. In recent years, an increasing number of BPA detection methods have been proposed. This article presents a critical review of aptamer-based electrochemical, fluorescence-based, colorimetric, and several other BPA detection platforms published in the last decade. Furthermore, a statistical evaluation has been made using principle component analysis showing analytical performance parameters do not create very different clusters. Comparisons to other BPA detection methods are also presented so that the reader has an overall literature overview.

Plasmon-Enhanced Nitrogen Vacancy-Rich Carbon Nitride Electrochemiluminescence Aptasensor for Highly Sensitive Detection of miRNA

The development of biosensors for biologically important substances with ultralow content such as microRNA is of great significance. Herein, a novel surface plasmon-enhanced electrogenerated chemiluminescence-based aptasensor was developed for ultrasensitive sensing of microRNA by using nitrogen vacancy-rich carbon nitride nanosheets as effective luminophores and gold nanoparticles as plasmonic sources. The introduction of nitrogen vacancies improved the electrochemiluminescence behavior due to improved conductance and electrogenerated chemiluminescence activity. The introduction of plasmonic gold nanoparticles increased the electrochemiluminescence signal intensity by more than eightfold. The developed surface plasmon-enhanced electrogenerated chemiluminescence aptasensor exhibited good selectivity, ultrasensitivity, excellent stability, and reproducibility for the determination of microRNA-133a, with a dynamic linear range of 1 aM to 100 pM and a limit of detection about 0.87 aM. Moreover, the surface plasmon-enhanced electrogenerated chemiluminescence sensor obtained a good recovery when detecting the content of microRNA in actual serum.

Bismuth telluride decorated on graphitic carbon nitrides based binary nanosheets: Its application in electrochemical determination of salbutamol (feed additive) in meat samples

The design and fabrication of effective electrochemical sensor for ultrasensitive detection of feed additive and multidrug are highly significant in food analysis. In this work, we explored to develop the possibility for rapid detection of feed additive drug using bismuth telluride (Bi₂Te₃) decorated graphitic carbon nitrides (GCN) nanostructures as a modified electrode for electrochemical sensing. Herein, the modified electrode was focused on the development of electrocatalytic performances for the determination of salbutamol in food products. The electrochemical sensors are developed by bismuth telluride sheets interconnected with graphitic carbon nitrides sheets (Bi₂Te₃/GCN) on to a screen-printed carbon electrode. The binary nanosheets of Bi₂Te₃/GCN exhibited an enhanced electrocatalytic ability towards salbutamol detection owing to their selective adsorption, by the combination of electrostatic interaction of binary nanosheets and the formation of charge assisted interactions between salbutamol and Bi₂Te₃/GCN surfaces. A nanomolar limit of detection (1.36 nM) was calculated in 0.05 M phosphate buffer (PB) supporting electrolyte (pH 7.0) using differential pulse voltammetry. The linear dynamic ranges with respect to salbutamol concentration were 0.01-892.5 μM, and the sensitivity of the sensor was 36.277 μA μM^-1 cm^-2. The sensor stability and reproducibility performances were observed. However, the obtained results are highly satisfactory which suggest the application of binary nanosheets in real-time food analysis.

Rapid, ultrasensitive and non-enzyme electrochemiluminescence detection of hydrogen peroxide in food based on the ssDNA/g-C3N4 nanosheets hybrid

Hydrogen peroxide (H2O2) is usually used as a fungicide in food, it is carcinogenic, accelerates aging or inducing toxic effects such as cardiovascular disease. Herein, to meet the demand for effective and fast detection of H2O2 in food, a novel non-enzymatic electrochemiluminescence (ECL) sensor based on single-stranded DNA (ssDNA)/g-C3N4 nanosheets (NS) was established. The ssDNA/g-C3N4 NS hybrid was prepared by simple mixing g-C3N4 NS and ssDNA solution together. The prepared ssDNA/g-C3N4 NS exhibited improved peroxidase-like activity and was modified on a glassy carbon electrode to catalyze the ECL reaction of luminol-H2O2 to amplify the luminescence signal. Under the optimized conditions, the proposed sensor exhibits high sensitivity with a limit of detection (LOD) as low as 33 aM H2O2, which is much lower than the vast majority of reported methods. This method enables the reliable responding to H2O2 from the milk samples within 1 min.

A ratiometric nanoprobe based on carboxylated graphitic carbon nitride nanosheets and Eu3+ for the detection of tetracyclines

A convenient and rapid method that combines a fluorescent nanoprobe based on C-g-C₃N₄-Eu³⁺ with a smartphone and test paper has been developed for the in situ detection of tetracyclines.

Emerging Chemical Functionalization of g-C3N4: Covalent/Noncovalent Modifications and Applications

Atomically 2D thin-layered structures, such as graphene nanosheets, graphitic carbon nitride nanosheets (g-C₃N₄), hexagonal boron nitride, and transition metal dichalcogenides are emerging as fascinating materials for a good array of domains owing to their rare physicochemical characteristics. In particular, graphitic carbon nitride has turned into a hot subject in the scientific community due to numerous qualities such as simple preparation, electrochemical properties, high adsorption capacity, good photochemical properties, thermal stability, and acid-alkali chemical resistance, etc. Basically, g-C₃N₄ is considered as a polymeric material consisting of N and C atoms forming a tri-s-triazine network connected by planar amino groups. In comparison with most C-based materials, g-C₃N₄ possesses electron-rich characteristics, basic moieties, and hydrogen-bonding groups owing to the presence of hydrogen and nitrogen atoms; therefore, it is taken into account as an interesting nominee to further complement carbon in applications of functional materials. Nevertheless, g-C₃N₄ has some intrinsic limitations and drawbacks mainly related to a relatively poor specific surface area, rapid charge recombination, a limited light absorption range, and a poor dispersibility in both aqueous and organic mediums. To overcome these shortcomings, numerous chemical modification approaches have been conducted with the aim of expanding the range of application of g-C₃N₄ and enhancing its properties. In the current review, the comprehensive survey is conducted on g-C₃N₄ chemical functionalization strategies including covalent and noncovalent approaches. Covalent approaches consist of establishing covalent linkage between the g-C₃N₄ structure and the chemical modifier such as oxidation/carboxylation, amidation, polymer grafting, etc., whereas the noncovalent approaches mainly consist of physical bonding and intermolecular interaction such as van der Waals interactions, electrostatic interactions, π-π interactions, and so on. Furthermore, the preparation, characterization, and diverse applications of functionalized g-C₃N₄ in various domains are described and recapped. We believe that this work will inspire scientists and readers to conduct research with the aim of exploring other functionalization strategies for this material in numerous applications.

Graphitic Carbon Nitride: A Highly Electroactive Nanomaterial for Environmental and Clinical Sensing

Graphitic carbon nitride (g-C3N4) is a two-dimensional conjugated polymer that has attracted the interest of researchers and industrial communities owing to its outstanding analytical merits such as low-cost synthesis, high stability, unique electronic properties, catalytic ability, high quantum yield, nontoxicity, metal-free, low bandgap energy, and electron-rich properties. Notably, graphitic carbon nitride (g-C3N4) is the most stable allotrope of carbon nitrides. It has been explored in various analytical fields due to its excellent biocompatibility properties, including ease of surface functionalization and hydrogen-bonding. Graphitic carbon nitride (g-C3N4) acts as a nanomediator and serves as an immobilization layer to detect various biomolecules. Numerous reports have been presented in the literature on applying graphitic carbon nitride (g-C3N4) for the construction of electrochemical sensors and biosensors. Different electrochemical techniques such as cyclic voltammetry, electrochemiluminescence, electrochemical impedance spectroscopy, square wave anodic stripping voltammetry, and amperometry techniques have been extensively used for the detection of biologic molecules and heavy metals, with high sensitivity and good selectivity. For this reason, the leading drive of this review is to stress the importance of employing graphitic carbon nitride (g-C3N4) for the fabrication of electrochemical sensors and biosensors.

Voltammetric aptasensor for bisphenol A based on double signal amplification via gold-coated multiwalled carbon nanotubes and an ssDNA-dye complex

An aptasensor is described for the electrochemical determination of bisphenol A (BPA). Gold-coated multiwalled carbon nanotubes (Au/MWCNTs) and a single-stranded DNA-dye complex are used as a double signal-amplification system. The BPA-binding aptamer was assembled on a disposable electrode modified with Au/MWCNTs. Methylene blue (MB) was then intercalated into the immobilized aptamer with an approximately molecular ratio of 4 to form a complex. Upon interaction with BPA, the immobilized aptamer underwent a conformational change. This causes the intercalated MB to be released from the complex into solution. As a result, the electrochemical signal of the intercalated MB, typically measured using square wave voltammetry at a potential of -0.20 V (vs. Ag/AgCl (saturated KCl)) decreases. The fabrication of the aptasensor was characterized by the scanning electron microscopy, atomic force microscopy, and electrochemical techniques. Under optimal experimental conditions, the current drops linearly with the logarithm of BPA concentrations over the range from 10 fM to 1 nM, and the limit of detection is 8 fM. The assay was applied to the determination of BPA in plastic drinking bottles, tap water, and milk. Graphical AbstractSchematic illustration of fabricating the aptasensor for bisphenol A (BPA) based on double signal amplification via gold-coated multiwalled carbon nanotubes (Au/MWCNT) and an aptamer-dye complex. PET: poly(ethylene terephthalate).

An electrochemiluminescence immunosensor for the N-terminal brain natriuretic peptide based on the high quenching ability of polydopamine

A sandwich-type electrochemiluminescence (ECL) immunosensor for the N-terminal brain natriuretic peptide (NT-proBNP) is described. The assay is based on the quenching of the ECL of graphite-like carbon nitride (g-C₃N₄) by polydopamine (PDA). Two-dimensional g-C₃N₄ is grown in-situ on titanium dioxide nanoflowers (TiO₂ NFs). The macroporous structure of the NFs enhances the interfacial stability of g-C₃N₄, and also promotes the ECL reaction of g-C₃N₄ with the co-reactant. The introduction of gold nanoparticles into the matrix further enhances the ECL and facilitates the immobilization of capture antibodies. The nanoquencher used to label the secondary antibody is synthesized by catalytic polymerization of dopamine in the presence of bimetallic NiPd nanoparticles. The nanoquencher preserves the high reactivity of polydopamine and quenches the ECL of the g-C₃N₄/TiO₂ system. Compared to other methods, the detection limit for NT-proBNP is decreased to 50 fg∙mL^-1. Graphical abstract Schematic presentation of the electrochemiluminescence (ECL) process of the immunosensor: titanium dioxide nanoflowers@graphite-like carbon nitride-gold nanoparticles (TiO₂ NFs@g-C₃N₄-Au) as luminophor, and polydopamine (PDA) as nanoquencher.

Nitrogen-doped graphene quantum dots coated with gold nanoparticles for electrochemiluminescent glucose detection using enzymatically generated hydrogen peroxide as a quencher

Nitrogen-doped graphene quantum dots (N-GQDs) were prepared from dicyandiamide and then used as both an electrochemiluminescence (ECL) emitter and a reductant to produce gold nanoparticles (Au-N-GQDs) on their surface without using any reagent. In order to avoid resonance energy transfer, the Au-N-GQDs were stabilized with chitosan. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), UV-vis spectroscopy (UV-vis) and ECL methods were used to characterize the nanocomposite. The materials was placed on a glassy carbon electrode (GCE), and the ECL signals are found to be strongly quenched by hydrogen peroxide that is enzymatically produced by oxidation of glucose. With the applied typical potential of -1.7 V, the ECL of the Au-N-GQDs modified GCE decreases linearly in the 10 nM to 5.0 μM glucose concentration range, and the lower detection limit is 3.3 nM. The influence of H₂O₂ to the signal has been discussed and a possible mechanism has been presented. Graphical abstract Schematic presentation of the reduction of gold nanoparticles with nitrogen-droped graphene quantum dots (N-GQDs) to form Au-N-GQDs. They were used to detect glucose by electrochemiluminescence through a signal off strategy.

Photoelectrochemical aptamer-based sensing of the vascular endothelial growth factor by adjusting the light harvesting efficiency of g-C3N4 via porous carbon spheres

A "signal-off" sensor is described for sensitive photoelectrochemical (PEC) determination of the vascular endothelial growth factor (VEGF₁₆₅). Graphitic carbon nitride (g-C₃N₄) is used as the signalling material, and porous carbon spheres as efficient quenchers of the photocurrent. The quenching efficiency of carbon spheres is the result of two effects, viz. (a) the competitive light absorption and (b) competitive electron donor activity which decreases the number of light-generated electrons and holes and also reduces the charge separation efficiency. This new mechanism differs from the previous quenching mechanisms which usually are based on the suppression of electron transport or steric hindrance. A glassy carbon electrode was modified with an aptamer against VEGF₁₆₅. On binding of analyte (VEGF₁₆₅), the reduction of current is measured (at a typical potential of 0 V) using H₂O₂ as the electrochemical probe. The sensor has a linear response in the 10^-5 nM to 10² nM VEGF₁₆₅ concentration range, and the detection limit is 3 fM. Graphical abstract Schematic presentation of the quenching mechanism of carbon spheres: the competitive light absorption and competitive electron donor reduce the number of light-generated electrons in the conduction band (CB) and holes in the valence band (VB) and also reduce the charge separation efficiency.