A novel “on-off” electrochemiluminescence sensor for the detection of concanavalin A based on Ag-doped g-C 3 N 4

Enhanced electrochemiluminescence of dual-defect graphite carbon nitride for ultrasensitive detection of CEA

Herein, a dual-defective graphite carbon nitride (DDCN) was prepared by polymerization under N2 atmosphere combined with oxidation treatment. The luminous intensity of dual-defect graphite phase carbon nitride based on defect state luminescence is significantly improved compared to CN-air. On this basis, a biosensor for CEA detection was constructed based on specific immunobinding of antigen-antibody. It is noted that the biosensor exhibits a wide linear range of 1 × 10-5 ∼ 1 × 102 ng•mL-1, a low detection limit of 3.3 × 10-4 pg•mL-1, a recovery of 94 %∼105 % and RSD less than 4.41 %. In addition, there was no significant difference to the clinical results, indicating that this work has good clinical application prospects.

Electrochemiluminescence in Graphitic Carbon Nitride Decorated with Silver Nanoparticles for Dopamine Determination Using Machine Learning

Electrochemiluminescence (ECL) luminophores with wavelength-tunable multicolor emissions are essential for multicolor ECL imaging detection and multiplexed analysis. In this work, silver nanoparticle (Ag NP)-decorated graphitic carbon nitride (g-CN@Ag) nanocomposites were synthesized. The morphology, chemical composition, structure, and ECL property of g-CN@Ag were investigated. The prepared g-CN, g-CN@Ag1, g-CN@Ag5, and g-CN@Ag10 can produce blue, blue-green, chartreuse, and yellow colored ECL emissions, respectively, by using K2S2O8 as the coreagent. The ECL emission wavelength of g-CN@Ag can be regulated from 460 to 565 nm by modulating the content of the immobilized Ag NPs. Then, a multicolor ECL detection array was fabricated by using g-CN, g-CN@Ag1, g-CN@Ag5, and g-CN@Ag10 as four ECL luminophores. Dopamine was detected based on its inhibition effect on the multicolor ECL emissions. The linear range is from 0.1 nM to 1 mM with the lowest detection limit of 44 pM. Then, machine learning-assisted multiparameter concentration prediction of dopamine was further carried out by combining the deep neural network (DNN) algorithm. This work provides a new avenue to regulate the ECL emission wavelength of g-CN by using the metal nanoparticle modification strategy and presents an effective machine learning-assisted multicolor ECL detection strategy for accurate multiparameter quantitative detection.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C₃N₄) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C₃N₄ a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C₃N₄ unique features, synthesis methods, and g-C₃N₄-based nanomaterials. In addition, recent relevant studies on using g-C₃N₄ in biosensors in regard to improving treatment pathways are reviewed.

The role of doping strategy in nanoparticle-based electrochemiluminescence biosensing

Doping plays a crucial role in electrochemiluminescence (ECL) due to the followings: (1) Modulation of electronic structure, alteration of the surface state of nanoparticles (NPs), providing effective protection from the surrounding environment, thereby leading to ECL emitters with exceptional properties including tunable spectra, high luminescence efficiency, low excitation potential, and good stability. (2) Employment of doped NPs as promising coreactant alternatives due to the presence of functional groups such as amines induced by NP doping. (3) Serving as novel co-reaction accelerators (CRAs) for ECL through doping induced high catalytic properties. (4) Behaving as excellent carriers to load ECL emitters, recognition elements, and catalysts due to doping-induced larger surface area, higher conductivity and better biocompatibility of NPs. As a consequence, doped NPs have aroused broad interest and found wide applications in various ECL sensing platforms. In this review, the current promising improvements, concepts, and excellent applications of doped NPs for ECL biosensing are addressed. We aim to bring to light the physicochemical characteristics of various doped NPs that endow them with appealing ECL performance, leading to diverse applications in biosensing.

A double-potential ratiometric electrochemiluminescence platform based on g-C3N4 nanosheets (g-C3N4 NSs) and graphene quantum dots for Cu2+ detection

A new kind of convenient, low-cost double-potential ratiometric ECL sensing platform for the quantification of Cu²⁺ was developed with carbon nitride nanosheets (g-C₃N₄ NSs) and graphene quantum dots (GQDs) as ECL luminophores. g-C₃N₄ NSs mixed with multi-walled carbon nanotubes (MWCNTs) was immobilized on a glass carbon electrode (GCE) and produced strong cathodic ECL at a potential of -1.2 V (vs. Ag/AgCl), while GQDs in the solution gave anodic ECL at +2.5 V. MWCNTs were used here to amplify the ECL signal of g-C₃N₄ NSs. The addition of Cu²⁺ causes the cathodic ECL signal from g-C₃N₄ to decline, while the anodic ECL signal from GQDs remains unchanged. With the anodic ECL signal as an internal reference, a double-potential ratiometric ECL sensing platform for Cu²⁺ was established. The ratio of the cathodic signal intensity to anodic signal intensity showed a linear response to the Cu²⁺ concentration over a range from 5.0 × 10^-10 to 1.0 × 10^-6 mol L^-1 and the detection limit was 0.37 nmol L^-1 (3σ/S). Such a construction strategy alleviates the interference from the environment and therefore improves the detection accuracy of Cu²⁺. Compared with other methods for Cu²⁺ detection, this method is simpler and more sensitive.

Nitrogen Vacancy Engineering in Graphitic Carbon Nitride for Strong, Stable, and Wavelength Tunable Electrochemiluminescence Emissions

As an attractive electrochemiluminescence (ECL) emitter, graphitic carbon nitride (CN) still suffers from weak and unstable ECL signals for its poor conductivity and the occurrence of electrode passivation. In this study, a simple nitrogen vacancy (NV) engineering strategy has been developed for the improvement of ECL performances (intensity and stability) for the first time. In comparison to pristine CN (RSD = 51.98% for 10 continuous scan), ca. 60 times amplification in ECL intensity and 70 times enhancement in ECL efficiency for CN modified with NVs (CN-NVs) were obtained. In addition, more stable ECL emissions (RSD = 0.53%) were achieved for CN-NV-550 by thermal treatment of pristine CN in a N₂ atmosphere for another 2 h at 550 °C. The mechanism study for the vital role of NVs on the ECL of CN-NVs revealed that NVs can not only facilitate electron transfer to amplify the ECL intensity but also serve as the electron trap to inhibit electrode passivation. More interestingly, a series of CN-NVs exhibited a tunable ECL wavelength range from 470 to 516 nm with different NV contents. Moreover, their ECL spectra showed an obvious red-shift of the wavelength with their corresponding fluorescence spectra. These findings confirmed that the ECL emissions of CN-NVs were susceptible to the relevant surface states of NVs. Our work may open up a promising pathway for improving ECL performances of CN and create new possibilities for multitarget simultaneous detection based on ECL and construction of color tunable light-emitting devices.

Design of a ratiometric fluorescence sensor based on metal organic frameworks and Ru(bpy)32+-doped silica composites for 17β-Estradiol detection

17β-Estradiol (E2), an important endocrine disrupting compound, could be quantitatively detected by fluorescence resonance energy transfer (FRET) aptasensor, designed in this paper. Metal organic frameworks have large specific surface area and easily modifiable groups, which are helpful for the construction of aptasensor. Specifically, streptavidin was immobilized on the synthesized MIL-53-NH₂ by covalent bonding, and further linked with the biotin modified E2 aptamer (apt) through specific bonding between avidin and biotin to obtain the FRET donor probe (MIL-53-apt). Meanwhile, complementary DNA (cDNA) modified Ru(bpy)₃²⁺-doped silica nanoparticles (RuSiO₂-cDNA) were prepared through covalent bonding. They acted as the FRET acceptor probe, since its absorption spectrum showed large overlap with the emission spectrum of MIL-53-apt. In the presence of E2, aptamer modified donor probes tended to bind with E2, owing to their higher selectivity and affinity. Therefore, the optimal distance between FRET pairs was broken, resulting in the fluorescence emission recovery of donor and the fluorescence emission of acceptor decreased. Under optimal conditions, this proposed aptasensor displayed sensitive detection of E2 ranging from 0.5 to 1000 nM with a detection limit of 0.2 nM. Furthermore, the sensor provides a promising method for rapid and sensitive detection of other small biological molecules.

Supramolecular Copolymerization Strategy for Realizing the Broadband White Light Luminescence Based on N-Deficient Porous Graphitic Carbon Nitride (g-C3N4)

The N-deficient porous g-C₃N₄ with broadband white light emission was constructed by supramolecular copolymerization design, which combined organic copolymers cyanuric acid and 2,4,6-triaminopyrimidine with melamine upon the mixture gas environment of (95%)N₂/(5%)H₂. Herein, we achieved great breakthrough in narrowing the band gap of g-C₃N₄ from 2.64 to 1.39 eV. Furthermore, in contrast to pristine g-C₃N₄, we demonstrated that the emission wavelengths of N-deficient porous g-C₃N₄ can be tuned from narrow blue to broadband white range, where the optimal white light coordinate position is (0.297, 0.345). The prepared N-deficient porous g-C₃N₄ overcomes the limitation of the narrow adjusting range of optical properties while using conventional g-C₃N₄ and makes it more promising for applications in solid-state displays.

Electrogenerated chemiluminescence resonance energy transfer between ZnGa2O4/g-C3N4 and gold nanoparticles/graphene and its application in the detection of thrombin

A label-free ECL sensor for thrombin was fabricated based on ECL resonance energy transfer occurred between ZnGa₂O₄/g-C₃N₄ and AuNP/GR nanocomposites, which revealed a new role of spinel-type semiconductor oxides in the fabrication of ECL sensors.

Ultrasensitive aptasensing of insulin based on hollow porous C3N4/S2O82-/AuPtAg ECL ternary system and DNA walker amplification

In this work, a high-efficiency electrochemiluminescence (ECL) ternary system was constructed for ultrasensitive assay of insulin based on hollow porous graphitic carbon nitride (HP-C₃N₄) as novel luminophore, S₂O₈^2- as coreactant and tri-metallic AuPtAg as coreaction accelerator. Specifically, in comparison with C₃N₄-based bulk nanomaterials, the as-prepared HP-C₃N₄ exhibits high luminous efficiency though decreased inner filter effect and minimized inactive ECL emitter. Noteworthy, tri-metallic AuPtAg, possessing the superiority of Au, Pt and Ag, was first used as coreaction accelerator to significantly enhance ECL intensity of HP-C₃N₄ and S₂O₈^2-. As a consequence, with the resultant ECL ternary (HP-C₃N₄/S₂O₈^2-/AuPtAg) system as aptasensing platform, a high-intense initial ECL signal was achieved. Subsequently, ferrocene-labeled quenching probe (Fc-HP2) as ECL quencher was used to quench the initial signal and achieve the low-background noise. Eventually, in the presence of insulin, the target-induced triple-helix molecular switch and Nb.BbvCI-assisted DNA walker amplification were executed to recover a strong ECL signal by releasing Fc-HP2 from the electrode surface. As expected, the constructed aptasensor presents an excellent sensitivity and selectivity for detecting insulin range from 0.05 pg mL^-1 to 100 ng mL^-1 with a detection limit of 17 fg mL^-1. This work provides a new avenue for developing highly efficient HP-C₃N₄ based ECL ternary system as well as ultrasensitive ECL aptasensors for bioanalysis.

Graphitic carbon nitride-based nanocomposites and their biological applications: a review

Quantum dots (QDs) have extensive application prospects in the fields of optics, magnetism, catalysis, and biomedicine. New carbon-doped QDs are currently being used in these research fields. Graphitic carbon nitride QDs (g-CNs) composed of only carbon and nitrogen have attracted attention because of their unique optical and catalytic properties. g-CNs have numerous electronic properties and can be used as photocatalytic modifiers in a wide range of applications in electrochemistry. Additionally, g-CNs also have biological potential and due to their chemical composition have extremely low toxicity; their blue light emission can be applied to biological imaging, and their appropriate energy level (2.7 eV) allows electrons to be deposited on their surface, which allows g-CNs to be used as photosensitizers in optical therapy. Finally, g-CNs can be combined with other nanomaterials to form composite materials, which can result in new advantages not seen in either of the materials alone. In this manuscript, we thoroughly report the most recent findings regarding the synthesis of g-CNs and their respective properties. We report the advantages of g-CNs conferred by their unique properties and their advantages for application in current biology and medicines.

A specific electrochemiluminescence sensor for selective and ultra-sensitive mercury(ii) detection based on dithiothreitol functionalized copper nanocluster/carbon nitride nanocomposites

A novel electrochemiluminescence sensor based on the combination of copper nanoclusters and carbon nitride nanosheets was fabricated for detecting Hg²⁺.

Emerging trends in sensors based on carbon nitride materials

A new class of functional materials, carbon nitrides, has recently attracted the attention of researchers.

Graphitic Carbon Nitride Doped with the s-Block Metals: Adsorbent for the Removal of Methyl Blue and Copper(II) Ions

The synthesis of graphitic carbon nitride (g-C₃N₄) doped with s-block metals is described. The materials were synthesized via thermal polycondensation of cyanamide and the appropriate metal chloride. The inclusion of the metal precursor strongly influenced the surface chemistry features as well as the textural, morphological, and structural properties of the g-C₃N₄. The doping of g-C₃N₄with s-block metals markedly enhanced its adsorption performance, which was studied during the removal of two model solutes (methyl blue and copper ions) from aqueous solutions. The maximum adsorption capacity for the organic dye was increased by 680 times after the doping process. The uptake of copper(II) increased ca. 30 times for the doped g-C₃N₄. The improvement of the adsorption performance is discussed in terms of the surface chemistry and textural features.

Phosphorus doped graphitic carbon nitride nanosheets as fluorescence probe for the detection of baicalein

Phosphorus doped graphitic carbon nitride (P-g-C₃N₄) nanosheets were synthesized by calcination. P-g-C₃N₄ nanosheets were characterized by XRD, XPS, TEM, fluorescence, ultraviolet-visible absorption and Fourier transform infrared spectroscopy. The fluorescence of the P-g-C₃N₄ nanosheets was gradually quenched with the increase in the concentration of baicalein at room temperature. The proposed probe was used for the determination of baicalein in the concentration 2.0-30μM with a detection limit of 53nM. The quenching mechanism was discussed. The P-g-C₃N₄ nanosheets have been successfully applied for effective and selective detection of baicalein in human urine samples and blood samples.

Oxygen Vacancy Engineering in Europia Clusters/Graphite-Like Carbon Nitride Nanostructures Induced Signal Amplification for Highly Efficient Electrochemiluminesce Aptasensing

Oxygen vacancy is an intrinsic defect in metal oxide semiconductors and has a crucial influence on their physicochemical and electronic properties. To boost the electrochemiluminescence (ECL) efficiency of the graphite-like carbon nitride (g-C₃N₄), the wet-chemical-calcination method was developed to introduce an oxygen vacancy in Eu-doped g-C₃N₄ nanostructures for the first time. The morphology and structure characterization suggest that the Eu element was present in the matrix of the europia (Eu₂O₃) clusters. Because of the effect of oxygen vacancy promoting catalytic activity, the doping of Eu caused a great positive shift of onset potential and large signal amplification in cathodic ECL signals compared with pure g-C₃N₄. Furthermore, a novel and ultrasensitive ECL aptasensor was realized with 17β-estradiol (E2) as a prototype target by adsorption of E2 aptamer onto the Eu₂O₃-doped g-C₃N₄ (Eu₂O₃- g-C₃N₄) surface via van der Waals force. Given the specific recognition between aptamer and E2, the ECL signal decreased with the increasing concentration of E2, because the formation of E2-aptamer complex impeded the diffusion of luminophor molecules and the electrons approaching the surface of the electrode. Under the optimal cases, the as-prepared ECL aptasensor showed superior performances and also manifested outstanding selectivity toward E2. The present conceptual strategy offers a novel methodology to boost the sensitivity of the ECL sensor and promote the activity of ECL reagents.

Graphitic-phase carbon nitride-based electrochemiluminescence sensing analyses: recent advances and perspectives

This review describes the current trends in synthesis methods, signaling strategies, and sensing applications of g-C₃N₄-based ECL emitters.

Electrochemiluminescence biosensing based on different modes of switching signals

Electrochemiluminescence (ECL) has attracted much attention in various fields of analysis owing to low background signals, high sensitivity, and excellent controllability.

Enhanced electrogenerated chemiluminescence behavior of C3N4 QDs@ C3N4 nanosheet and its signal-on aptasensing for platelet derived growth factor

A novel g-C₃N₄ nanosheets embedded with C₃N₄ QDs nanocomposites (QD@CNNS) was prepared by simple oxidation using hydrogen peroxide and UV light irradiation. This nanocomposite exhibits more stable and stronger electrochemiluminescent (ECL) behavior compared with CNNS. Coupling this nanocomposite with Fc-labeled aptamer, a signal-on aptasensor for platelet derived growth factor BB (PDGF-BB) is fabricated. Initially, the Fc-labeled aptamer binds onto QD@CNNS via π-π conjugation and electrostatic interaction, quenching ECL emission from QD@CNNS. The introduction of target efficiently recovers the ECL signal by the formation of PDGF-BB/aptamer complex. The ECL intensity is proportion to the concentration of PDGF-BB in the range of 0.02-80nM with a detection limit of 0.013nM. This work demonstrates a simple synthesis method to obtain QD@CNNS with excellent ECL behavior, and opens up the application of g-C₃N₄ nanocomposite in signal-on aptasensing.

A rapid and sensitive electrochemiluminescent sensor for nitrites based on C3N4 quantum dots on C3N4 nanosheets

Nitrite, an inorganic anion, is widely applied in various fields.