Selective and high-sensitive label-free detection of ascorbic acid by carbon nitride quantum dots with intense fluorescence from lone pair states

Graphitic Carbon Nitride Quantum Dots (g-C3N4 QDs): From Chemistry to Applications

Since their emergence in 2014, graphitic carbon nitride quantum dots (g-C3N4 QDs) have attracted much interest from the scientific community due to their distinctive physicochemical features, including structural, morphological, electrochemical, and optoelectronic properties. Owing to their desirable characteristics, such as non-zero band gap, ability to be chemically functionalized or doped, possessing tunable properties, outstanding dispersibility in different media, and biocompatibility, g-C3N4 QDs have shown promise for photocatalysis, energy devices, sensing, bioimaging, solar cells, optoelectronics, among other applications. As these fields are rapidly evolving, it is very strenuous to pinpoint the emerging challenges of the g-C3N4 QDs development and application during the last decade, mainly due to the lack of critical reviews of the innovations in the g-C3N4 QDs synthesis pathways and domains of application. Herein, an extensive survey is conducted on the g-C3N4 QDs synthesis, characterization, and applications. Scenarios for the future development of g-C3N4 QDs and their potential applications are highlighted and discussed in detail. The provided critical section suggests a myriad of opportunities for g-C3N4 QDs, especially for their synthesis and functionalization, where a combination of eco-friendly/single step synthesis and chemical modification may be used to prepare g-C3N4 QDs with, for example, enhanced photoluminescence and production yields.

Orange peel-derived carbon dots/Cu-MOF nanohybrid for fluorescence determination of l-ascorbic acid and Fe3. Anal Chim Acta 2024;1287:342066. [PMID: 38182373 DOI: 10.1016/j.aca.2023.342066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Recycling and reuse of biomass waste in synthesis of nanomaterials have recently received much attention as an effective solution for environmental protection and sustainable development. Herein, nitrogen-doped carbon dots (N-CDs) with blue emission were synthesized from the orange peels as a precursor through a simple hydrothermal method and then, modified with ethylenediamine tetraacetic acid (N-CD@EDTA). The N-CD@EDTA was embedded as a fluorophore in Cu-based metal-organic framework (MOF-199) structure (N-CD@EDTA/MOF-199) to construct fluorescence sensor toward l-ascorbic acid (L-AA) determination. The N-CD@EDTA/MOF-199 nanohybrid significantly and selectively turned on toward L-AA determination during the fluorimetric experiments. Under optimal conditions, the probe showed a suitable linear response in the concentration range of 10 nM-100 μM with a low limit of detection (LOD) of 8.6 nM and high sensitivity of 0.201 μM-1. The possible mechanism of recognition and adsorption, including the reduction of Cu 2+ nodes in the MOF-199 structure in the presence of L-AA and the release of trapped N-CD@EDTA into the solution, was explored. Moreover, the N-CD@EDTA/MOF-199/L-AA (100 μM) system was further applied as a fluorescent "on-off" sensor for Fe3+ determination with a LOD of 1.15 μM. The proposed probe was successfully used in orange juice and water samples to determine L-AA and Fe3+ with satisfactory recovery, which displays the promising capability of sensor in real samples. The recoveries obtained by suggested method are consistent with that obtained from high performance liquid chromatography (HPLC) and atomic absorption spectroscopy which confirm the favorable characteristic of the sensor for accurate determination of L-AA and Fe3+ in practical applications.

Novel "on-off" fluorescence sensing for rapid and accurate determination of Cr3+ based on g-CNQDs

Cr3+ is one of the most essential trace elements in living organisms and plays a vital role in human metabolism. However, both deficiency and excess intake of Cr3+ can be harmful to the human body. Therefore, the quantitative determination of Cr3+ is of great significance in the field of life science. Based on this, in this study, a g-CNQDs@p-acetaminophenol fluorescence sensing system was developed for the quantitative detection of Cr3+ in actual complex samples. G-CNQDs were synthesized with sodium citrate and urea as precursors. The fluorescence signal was enhanced by the synergistic effect between p-acetaminophenol (APAP) and g-CNQDs. The fluorescence quenching phenomenon can be produced when Cr3+ is introduced into the fluorescence-enhanced g-CNQDs@p-acetaminophenol system. An "on-off" fluorescence sensing system was constructed based on g-CNQDs@p-acetaminophenol for the quantitative detection of Cr3+. The experimental data showed a wide linear region in the concentration range of 0.64-63.0 μM, and the detection limit was as low as 0.23 μM. The construction of the sensor system broadens the research field for the practical application of Cr3+.

High quantum yield photoluminescent N-doped carbon dots for switch sensing and imaging

Stable blue fluorescent nitrogen doped carbon dots (N-CDs) with a very high quantum yield up to 81% has been reported for the first time. Novel N-CDs were synthesized through an efficient and rapid one-step hydrothermal synthesis process from diethylenetriamine as nitrogen source and a novel carbon source trans-aconitic acid. The nanosized particles of N-CDs were in the range of 2-8 nm and uniformly distributed in molecular level. The N-CDs showed high selectivity toward Fe³⁺ with low detection limit of 10.42 nmol L^-1 (with corresponding linear range of 2-50 μmol L^-1) enabling them for ion detection application and also exhibited high fluorescence stability in extreme pH conditions. Novel N-CDs also presented a green emission shift under acidic condition (pH~2) which makes them a potential sensing probe for security papers, food packaging and bio-medical detection sensors. A security paper sensor device has been fabricated and its operation function has been validated by making real time detection of color. The novel and facile to manufacture carbon dots has potential applications ranging from biological nano-sensors for security document to color-switch sensing and bio-imaging.

MPA-CdTe quantum dots as "on-off-on" sensitive fluorescence probe to detect ascorbic acid via redox reaction

Mercaptopropionic acid (MPA) capped CdTe quantum dots (MPA-CdTe QDs) were synthesized in aqueous medium by hydrothermal method, which modified by Fe³⁺ could be used as a fluorescent probe to detect ascorbic acid (AA). MPA-CdTe QDs fluorescence probe could be used as successive sensor for metal ions and AA with "on-off-on" process. The fluorescence of QDs was quenched after adding Fe³⁺ to MPA-CdTe QDs. Then, the fluorescence of the Fe³⁺@MPA-CdTe QDs can be sensitively turned on by AA to give an "on-off-on" fluorescence response according to the oxidation-reduction between Fe³⁺ and AA. There was a linear relationship between fluorescence intensity quenching value and the concentration of Fe³⁺ in the range of 2-10 μM since Fe³⁺ sensitively reacted with CdTe QDs. The linear detection range for AA was 0.1-1 μM with a limit of detection of 6.6 nM. The principle is proved by fluorescence emission spectroscopy, nuclear magnetic resonance spectroscopy. The proposed method is successfully used to detect the AA in human plasma sample.

Solvothermal assisted phosphate functionalized graphitic carbon nitride quantum dots for optical sensing of Fe ions and its thermodynamic aspects

A facile method has been proposed for the determination of Ferrous (Fe(II)) and Ferric (Fe(III)) ions using phosphate functionalized graphitic carbon nitride quantum dots (Ph-g-CNQDs) in an aqueous medium. The easy solvothermal procedure using oleic acid as the solvent yielded the Ph-g-CNQDs in less than 30 min. The communication among the Fe(II) and Fe(III) with Ph-g-CNQDs caused quenching of the blue Ph-g-CNQDs fluorescence signals. The Ph-g-CNQDs have been successfully characterized using X-ray diffractometry (XRD), X-ray Photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, UV-vis absorption and photoluminescence spectrophotometry. The temperature dependent behavior of the Ph-g-CNQDs was also observed and various thermodynamic parameters have also been evaluated. The Ph-g-CNQDs displayed an excellent quantum yield of 60.54% using quinine sulfate as the standard reference. The developed method has been applied to water samples collected from different sources and good recoveries were observed which entitles this method as apt for real time monitoring.

Highly rapid and non-enzymatic detection of cholesterol based on carbon nitride quantum dots as fluorescent nanoprobes

In this work, we reported a highly rapid and non-enzymatic method for cholesterol measuring based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes, which were synthesized through chemical oxidation. The obtained CNQDs displayed high quantum yield up to 35% as well as excellent photostability, water solubility and low toxicity. We found that the fluorescence of CNQDs could be quenched more than 90% within 30 seconds by cholesterol through the formation of hydrogen bonds between –NH₂, –NH on the surface of CNQDs and cholesterol containing –OH. According to this phenomenon, a cholesterol detection method was constructed with a wide linear region over the range of 0–500 μmol L⁻¹ and a detection limit as low as 10.93 μmol L⁻¹, and it possessed the obvious advantages of being a very rapid process and avoiding the use of enzymes. In addition, this method showed high selectivity in the presence of various interfering reagents and applicability to the measurement of cholesterol in fetal bovine serum, which indicated its potential application value in clinical settings.

Highly rapid and non-enzymatic method for the detection of cholesterol was constructed based on carbon nitride quantum dots (CNQDs) as fluorescent nanoprobes. The fluorescence of CNQDs could be effectively and rapidly quenched by cholesterol.

Synthesis and biomedical applications of graphitic carbon nitride quantum dots

This review summarizes the synthetic methods and addresses current applications and future perspectives of graphitic carbon nitride quantum dots in the biomedical field.