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

Crystallization Regulation Engineering in the Carbon Nitride Nanoflower for Strong and Stable Electrochemiluminescence

Cathode electrochemiluminescence (ECL) of C₃N₄ material has suffered from weak and unstable ECL emission for a long time, which greatly limits its practical application. Herein, a novel approach was developed to improve the ECL performance by regulating the crystallinity of the C₃N₄ nanoflower for the first time. The high-crystalline C₃N₄ nanoflower achieved a pretty strong ECL signal as well as excellent long-term stability compared to low-crystalline C₃N₄ when K₂S₂O₈ was used as a co-reactant. Through the investigation, it is found that the enhanced ECL signal is attributed to the simultaneous inhibition of K₂S₂O₈ catalytic reduction and enhancement of C₃N₄ reduction in the high-crystalline C₃N₄ nanoflower, which can provide more opportunities for SO₄^• - to react with electro-reduced C₃N₄^• -, and a new "activity passivation ECL mechanism" was proposed, while the improvement of the stability is mainly ascribed to the long-range ordered atomic arrangements caused by structure stability in the high-crystalline C₃N₄ nanoflower. As a benefit from the excellent ECL emission and stability of high-crystalline C₃N₄, the C₃N₄ nanoflower/K₂S₂O₈ system was employed as a Cu²⁺ detection sensing platform, which exhibited high sensitivity, excellent stability, and good selectivity with a wide linear range from 6 nM to 10 μM and a low detection limit of 1.8 nM.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Graphitic carbon nitride nanosheets as promising candidates for the detection of hazardous contaminants of environmental and biological concern in aqueous matrices

Monitoring of pollutant and toxic substances is essential for cleaner environment and healthy life. Sensing of various environmental contaminants and biomolecules such as heavy metals, pharmaceutics, toxic gases, volatile organic compounds, food toxins, and pathogens is of high importance to guaranty the good health and sustainable environment to community. In recent years, graphitic carbon nitride (g-CN) has drawn a significant amount of interest as a sensor due to its large surface area and unique electrochemical properties, low bandgap energy, high thermal and chemical stability, facile synthesis, nontoxicity, and electron rich property. Furthermore, the binary and ternary nanocomposites of graphitic carbon nitride further enhance their performance as a sensor making it a cost effective, fast, and reliable gadget for the purpose, and opens a wide area of research. Numerous reviews addressing a variety of applications including photocatalytic energy conversion, photoelectrochemical detection, and hydrogen evolution of graphitic carbon nitride have been documented to date. But a lesser attention has been devoted to the mechanistic approaches towards sensing of variety of pollutants concerned with environmental and biological aspects. Herein, we present the sensing features of graphitic carbon nitride towards the detection of various analytes including toxic heavy metals, pharmaceuticals, phenolic compounds, nitroaromatic compounds, volatile organic molecules, toxic gases, and foodborne pathogens. This review will undoubtedly provide future insights for researchers working in the field of sensors, allowing them to investigate the intriguing graphitic carbon nitride material as a sensing platform that is comparable to several other nanomaterials documented in the literature. Therefore, we hope that this study could reveal some intriguing sensing properties of graphitic carbon nitride, which may help researchers better understand how it interacts with contaminants of environmental and biological concern. Graphitic carbon nitride Nanosheets as Promising Analytical Tool for Environmental and Biological Monitoring of Hazardous Substances.

Chemiluminescence of doped carbon dots with H2O2-KMnO4 system for the detection of Cu2+ and tannin

The carbon dots doped with chlorine and phosphorus (CDs-Cl,P) were used as chemiluminescence (CL) reagent for the sensitive detection of copper ions (Cu²⁺) and tannin (TA). The CDs-Cl,P was found to strongly enhance the reaction of H₂O₂ and KMnO₄ in alkaline medium. The enhanced CL behavior of CDs-Cl,P was investigated and it was found that some radicals such as ^•OH, ^•O₂^- and ¹O₂ appeared in the CL reaction process. The participation of Cu²⁺ could result in an enhanced CL intensity of the CDs-Cl,P-H₂O₂-KMnO₄ system due to the Cu²⁺-catalyzed decomposition of H₂O₂ resulting in more ^•OH generation. Therefore, the CDs-Cl,P-H₂O₂-KMnO₄ system was used to selectively quantify Cu²⁺ in solution by CL emission. A linear increase was observed between CL intensity and Cu²⁺ concentration. The CDs-Cl,P-H₂O₂-KMnO₄ system allowed the detection of Cu²⁺ down to lower concentration of 0.1 μM with a linear range of 0.2-60.0 μM. Moreover, TA as a common polyphenolic compound, could selectively decrease the CL signal of the CDs-Cl,P-H₂O₂-KMnO₄-Cu²⁺ system due to its complexation with Cu²⁺. On this basis, the CL assay for TA was also developed. The detection limit was 0.14 μM and the linear range was from 5.0 μM to 100.0 μM. The proposed method was successfully applied to the determination of Cu²⁺ and TA in water, rice dumplings leaves, sodium copper chlorophyllin and wine samples with satisfactory results.

Detection of Heavy Metal Ions by Ratiometric Photoelectric Sensor

In recent years, heavy metal pollution has become increasingly serious. Heavy metals exist in an environment mainly in the form of ions (heavy metal ions, HMs). They can contaminate food, water, soil, and the atmosphere, leading to serious harm to plants and animals. With high bioavailability and nonbiodegradability, HMs can accumulate through biomagnification. Consequently, heavy metal pollution has become the cause of many fatal diseases threatening human health and ecological environment. Therefore, the accurate detection of HMs is vital and necessary. In this paper, the harm and limit standards of heavy metals were systematically summarized and the common analysis methods were overviewed and compared. Specifically, the latest research progress of ratiometric photoelectric sensor, including optical and electrical sensor, were mainly described. The research status and advantages and disadvantages of a photoelectric sensor were summarized. Furthermore, the future directions were proposed, which provided the reference for the further research and application of the ratiometric photoelectric sensor.

Strategies for Enhancing the Sensitivity of Electrochemiluminescence Biosensors

Electrochemiluminescence (ECL) has received considerable attention as a powerful analytical technique for the sensitive and accurate detection of biological analytes owing to its high sensitivity and selectivity and wide dynamic range. To satisfy the growing demand for ultrasensitive analysis techniques with high efficiency and accuracy in complex real sample matrices, considerable efforts have been dedicated to developing ECL strategies to improve the sensitivity of bioanalysis. As one of the most effective approaches, diverse signal amplification strategies have been integrated with ECL biosensors to achieve desirable analytical performance. This review summarizes the recent advances in ECL biosensing based on various signal amplification strategies, including DNA-assisted amplification strategies, efficient ECL luminophores, surface-enhanced electrochemiluminescence, and ratiometric strategies. Sensitivity-enhancing strategies and bio-related applications are discussed in detail. Moreover, the future trends and challenges of ECL biosensors are discussed.

Sulfur-doped graphitic carbon nitride nanosheets as a sensitive fluorescent probe for detecting environmental and intracellular Ag

Silver is widely used in medical materials, photography, electronics and other industries as a precious metal. The large-scale industrial production of silver-containing products and liquid waste emissions aggravate the environmental pollution. Silver ion is one of the most toxic metal ions, causing pollution to the environment and damage to public health. Therefore, the efficient and sensitive detection of Ag+ in the water environment is extremely important. Sulfur-doped carbon nitride nanosheets (SCN Ns) were prepared by melamine and thiourea via high-temperature calcination. The morphology, chemical composition and surface functional groups of the SCN Ns were characterized by SEM, TEM, XRD, XPS, and FT-IR. The fluorescence of SCN Ns was gradually quenched as the Ag+ concentration increased. The detection limit for Ag+ was as low as 0.28 nM. The quenching mechanism mainly is attributed to static quenching. In this paper, SCN Ns were used as the fluorescent probe for detecting Ag+. SCN Ns have successfully detected Ag+ in different environmental aqueous samples and cells. Finally, SCN Ns were further applied to the visual quantitative detection of intracellular Ag+.

Introducing ytterbium acetate to luminescent CsPbCl3 nanocrystals for enhanced sensitivity of Cu2+ detection

The Yb(OAc)3 promoted the formation of CsPbCl3 nanowires (NWs). The NWs exhibited boost in conductivity and the adsorbed AcO− on the surface of NWs enhanced the adsorption capacity of Cu2+, which enabled NWs with high detection sensitivity of Cu2+.

Dual-wavelength electrochemiluminescence ratiometry for hydrogen sulfide detection based on Cd2+-doped g-C3N4 nanosheets

Herein, a novel and facile dual-wavelength ratiometric electrochemiluminescence-resonance energy transfer (ECL-RET) sensor for hydrogen sulfide (H₂S) detection was constructed based on the interaction between S^2- and Cd²⁺-doped g-C₃N₄ nanosheets (NSs). Cd²⁺-doped g-C₃N₄ NSs exhibited a strong ECL emission at 435 nm. In the presence of H₂S, CdS was formed in situ on g-C₃N₄ NSs by the adsorption of S^2- and Cd²⁺, generating another ECL emission at 515 nm. Furthermore, the overlapping of the absorption spectrum of the formed CdS and the ECL emission spectrum of g-C₃N₄ NSs led to a feasible RET, thus quenching the ECL intensity from g-C₃N₄ at 435 nm. Through an ECL decrease at 435 nm and an increase at 515 nm, a dual-wavelength ratiometric ECL-RET system for H₂S was designed. The sensor exhibited a lower detection limit of 0.02 μM with a wide linear range of 0.05-100.0 μM. In addition, the applicability of the method was validated by plasma sample analysis with a linear range of 80.0-106.0%. We believe that such a proposal would provide new insight into advanced dual-wavelength ECL ratiometric assays.

Carbon Materials in Electroanalysis of Preservatives: A Review

Electrochemical sensors in electroanalysis are a particularly useful and relatively simple way to identify electroactive substances. Among the materials used to design sensors, there is a growing interest in different types of carbon. This is mainly due to its non-toxic properties, low cost, good electrical conductivity, wide potential range, and the possibility of using it in both aqueous and nonaqueous media. The electrodes made of carbon, and especially of carbon modified with different materials, are currently most often used in the voltammetric analysis of various compounds, including preservatives. The objective of this paper is to present the characteristics and suitability of different carbon materials for the construction of working electrodes used in the voltammetric analysis. Various carbon materials were considered and briefly discussed. Their analytical application was presented on the example of the preservatives commonly used in food, cosmetic, and pharmaceutical preparations. It was shown that for the electroanalysis of preservatives, mainly carbon electrodes modified with various modifiers are used. These modifications ensure appropriate selectivity, high sensitivity, low limits of detection and quantification, as well as a wide linearity range of voltammetric methods of their identification and determination.

Graphite-like Carbon Nitride Nanotube for Electrochemiluminescence Featuring High Efficiency, High Stability, and Ultrasensitive Ion Detection Capability

Herein, for the first time, we introduced a novel electrochemiluminescence (ECL) luminophore based on a one-dimensional g-C₃N₄ nanotube using K₂S₂O₈ as the coreactant. The g-C₃N₄ nanotube/K₂S₂O₈ couple displayed very satisfactory ECL performance, i.e., an ECL efficiency (Φ_ECL) of 437% (vs 100% for the Ru(bpy)₃²⁺/K₂S₂O₈ reference) and excellent ECL stability (the relative standard deviation (RSD) = 0.78%). By contrast, Φ_ECL and RSD of the control g-C₃N₄ nanosheet/K₂S₂O₈ couple were merely 196% and 45.34%, respectively. The mechanism study revealed that the g-C₃N₄ nanotube features a large surface area and much lower interfacial impedance in the porous microstructure, which are beneficial for accelerating the charge transfer rate and stabilizing charge/excitons for ECL. Moreover, using the g-C₃N₄ nanotube/K₂S₂O₈ system as a sensing platform, excellent Cu²⁺ detection capability was also achieved. Our work thus triggers a promising g-C₃N₄ nanomaterial system toward ECL application.

Electrochemiluminescent immunoassay enhancement driven by carbon nanotubes

Electrochemiluminescence (ECL) is a leading analytical technique for clinical monitoring and early disease diagnosis. Carbon nanotubes are used as efficient nanomaterials for ECL signal enhancement providing new insights into the mechanism for the ECL generation but also affording application in bead-based immunoassay and ECL microscopy-based bioimaging.