Fluorescent Nitrogen-doped Carbon Dots Research Articles

Preparation of strongly photoluminescent nanocomposite from DGEBA epoxy resin and highly fluorescent nitrogen-doped carbon dots

Preparation of strongly photoluminescent nanocomposite from DGEBA epoxy resin and highly fluorescent nitrogen-doped carbon dots

Green Synthesis of Nitrogen-Doped Carbon Dots from Fresh Tea Leaves for Selective Fe3+ Ions Detection and Cellular Imaging.

In this research, we successfully developed a green, economical and effective one–step hydrothermal method for the synthesis of fluorescent nitrogen–doped carbon dots (N–CDs) by utilizing fresh tea leaves and urea as the carbon and nitrogen sources, respectively. The obtained N–CDs were characterized by TEM, XPS and FT–IR. We found that the N–CDs were near–spherical with an average size of about 2.32 nm, and contained abundant oxygen and nitrogen functional groups. The N–CDs exhibited bright blue fluorescence under ultraviolet illumination, with the maximum emission at 455 nm. Meanwhile, the as–prepared N–CDs could be selectively quenched by Fe3+ ions. The quenching of N–CDs is linearly correlated with the concentration of Fe3+ in the range of 0.1–400 μM with a low detection limit of 0.079 μM. Significantly, the N–CDs present excellent biocompatibility and high photostability. The results also depict that multicolor fluorescence is displayed under a fluorescence microscope and successfully applied for the detection of intracellular Fe3+. To sum up, the fluorescent N–CDs are expected to be a sensitive detection probe for Fe3+ in biological systems.

Microwave-assisted synthesis of nitrogen-doped carbon dots using prickly pear as the carbon source and its application as a highly selective sensor for Cr(VI) and as a patterning agent.

Preparation of water-dispersible carbon dots from inexpensive natural carbon precursors and its application for purposes such as sensing, bio-imaging and patterning agents is showing growing interest in recent years. In this study, we have reported the preparation of nitrogen-doped carbon dots (N-CDs) using prickly pear as the carbon source and m-xylylenediamine as the nitrogen source using a one-step microwave-assisted synthetic process. The N-CDs prepared were characterized on the basis of elemental analysis, XPS, powder-XRD, FT-IR, Raman, TEM, UV-vis and fluorescence spectroscopy. Doping of nitrogen in the N-CDs made them highly fluorescent and the study on their ion-recognition property revealed that they detect highly toxic Cr(VI) with high selectivity and sensitivity (LOD, 0.04 μM) and without interference from the other ions used in this study. By immobilizing these N-CDs onto filter paper, sensor strips were prepared for on-site monitoring/field applications and they were successfully used for the detection of Cr(VI) in water. Detailed spectral analysis revealed that the mechanism of Cr(VI) sensing involved a phenomenon called the "inner filter effect" and analysis of the fluorescence lifetime data suggested the "static quenching" of fluorescence intensity. These N-CDs were used to prepare fluorescent carbon ink and were successfully used as patterning agents.

Detection of Baicalin capsule and Scutellariae Radix based on nitrogen-doped carbon dots as a fluorescence probe

Nitrogen-doped fluorescent carbon dots (N-CDs) were prepared via hydrothermal synthesis method using citric acid and ethylenediamine as raw materials. The synthesized N-CDs were characterized by transmission electron microscopy (TEM) and multi-spectroscopic techniques. A fluorescent sensor based on the inner filter effect (IFE) was successfully established using synthesized carbon dots to detect the content of Baicalin in Baicalin capsule and the quality of Scutellariae Radix. The Baicalin linear range of the method is 1.6–72 μg·mL−1 (r = 0.9992), the detection limit is 1.0 μg·mL−1 (3-foldσ), and the precision was 0.2%. Furthermore, the N-CDs probe was used to evaluate quality of Scutellariae Radix.

The highly sensitive "turn-on" detection of morin using fluorescent nitrogen-doped carbon dots.

Herein, a novel "turn-on" fluorescent sensor was designed based on nitrogen-doped carbon dots (N-CDs) for the highly sensitive determination of morin. The N-CDs with orange fluorescent emission were prepared using neutral red and poly(ethyleneimine) as main sources via a hydrothermal approach. Interestingly, an enhanced fluorescence of N-CDs could be observed with the introduction of morin, which was attributed to the aggregation-induced emission-enhancement (AIEE) mechanism. The N-CDs presented a high sensitivity of fluorescence response to morin in the concentration range of 0.033-12.83 μM with a satisfactory detection limit of 29 nM. This method was also utilized for the quantitative determination of morin in human urine and serum samples with recoveries of 97.60%-103.90%. Moreover, the fluorescent hydrogel was further prepared by incorporating N-CDs into agarose and integrated with a smartphone-assisted platform, enabling semi-quantitative visual morin detection. Notably, this fluorescent sensor could also be applied for intracellular morin imaging due to its excellent hypotoxicity and biocompatibility, demonstrating that the proposed methodology holds great promise for biosensing applications.

Quercetin conjugated fluorescent nitrogen-doped carbon dots for targeted cancer therapy application.

In this work, we report the development of nitrogen-doped carbon dots (NDCDs) as a drug carrier using quercetin (QC) as a model drug for anti-cancer drug delivery application. NDCDs were prepared by a simple hydrothermal method using Luffa acutangula as a carbon source. The characterization of QC-NDCDs was done by UV-vis spectroscopy, fluorescence spectroscopy, zeta potential measurements, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and Raman spectroscopy. The as-synthesized NDCDs have a small particle size with hydroxyl and nitrogen-containing groups (pyridinic and amide groups), enhancing the fluorescence properties, and were obtained in a good quantum yield (14%). Furthermore, the in vitro alamarBlue® assay revealed that the NDCDs-QC conjugate was nontoxic to colon cancer cells. This NDCDs-QC conjugate is able to kill cancer cells in the NDCDs-QC form compared to free QC as confirmed by in vitro MTT assay results. Thus, the developed NDCDs conjugate can be used as a promising drug delivery and bio-imaging vehicle in cancer therapy.

BIOLOGICAL ACTIVITY OF RICE STRAW-DERIVED MATERIALS: AN OVERVIEW

RS (RS) waste has been the most widely recognised pollutant in the world for several years. Therefore, it is critical to develop a simple process for converting rice straw (RS) into a useful products. RS is a rich source of phenolic acids (PAs), lignin, condensed tannins, flavonoids, and momilactone that can be extracted using conventional and environmentally friendly methods. These bioactive components of RS have various biological activities such as antibacterial, antifungal, pesticide, antioxidant, etc. Recently, RS-derived fluorescent nitrogen-doped carbon dots (NCDs) were developed for the detection and monitoring of diabetic ketoacidosis in diabetic patients. Herein, various straightforward and non-polluting method for reprocessing RS into value-added materials are discussed.

A nitrogen-doped carbon dots based fluorescent nanosensor for sensitive assay of Fe3+ ions in Dioscorea opposita Thunb

Trace detection of Fe3+ ions in complex matrices requires the development of highly sensitive sensors. Nitrogen-doped carbon dots (N-CDs) with admirable fluorescence efficiency, high photostability, and good biocompatibility have drawn special interest in fluorescent sensing of metal ions. In this work, a facile and economical microwave-assisted strategy was introduced for rapid synthesis of green fluorescence N-CDs, which were comprehensively characterized to display excitation-dependent fluorescent behavior with a high quantum yield of 18.1%, as well as good water solubility and high selectivity to Fe3+ ions. Then, a N-CDs based fluorescent “on-off” nanosensor was successfully fabricated for sensitive assay of Fe3+ ions. In the presence of Fe3+ ions, fluorescence of N-CDs was remarkably quenched due to the formation of N-CDs/Fe3+ complex through static quenching mechanism. Under the optimized synthetic and sensing conditions, the newly-developed nanosensor was free from other interfering metal ions for selective detection Fe3+ ions ranging from 1.0 to 80.0 μM with a low limit of detection of 1.0 μM, which are comparable with other methods. Practical application in Dioscorea opposita Thunb. samples exhibited fascinating recoveries of 98.5%−109.2% with relative standard deviations lower than 4.7%. The N-CDs based fluorescent nanosensor with simple construction, high selectivity and extremely sensitivity contributed a promising tool for rapid and environmental-friendly assay of Fe3+ions in a large number of actual samples.

Exploration of nitrogen-doped grape peels carbon dots for baicalin detection

Baicalin, a flavonoid compound extracted from the rhizome of Scutellar iae Baicalensis, plays a vital role in improving liver function after injury, reducing liver disease and treating primary liver cancer, which is also the first SARS-CoV-2 3CLpro virus inhibitor according to the latest research data published in BioRxiv. Therefore, constructing a simple and highly sensitive analytical method for the determination of baicalin is of great significance for the clinical and pharmacy settings. Herein, for the first time, carbon dots are explored for baicalin detection. Using biomass waste grape peels as the organic carbon source, nitrogen-doped fluorescent carbon dots (PT-NCDs) were fabricated, which were synthesized perfectly by a simple, environmentally friendly and one-step solid-phase thermal method without adding any other organic or acid/base reagents. Based on the synergistic effect of photo-induced electron transfer and dynamic quenching, a quenched fluorescence sensor for the determination of baicalin with a good linear range of 0.1–20 μM and a satisfactory detection limit of 43.8 nM was constructed, which successfully quantified trace amount of baicalin in baicalin capsules, human serum and urine samples. The results indicate that PT-CDs are expected to become potential sensing materials for the real-time monitoring of baicalin in organisms, which is very important for our health.

Preparation of fluorescent nitrogen-doped carbon dots for highly selective on-off detection of Fe3+ ions in real samples

In this work, nitrogen-doped carbon dots (N-CDs) based fluorescent probes were synthesized using m-phenylenediamine and citric acid as both nitrogen and carbon source through the hydrothermal method. The structural and optical properties of synthesized N-CDs were investigated by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), UV–vis spectroscopy, Zeta potential, and photoluminescence (PL). The water-soluble N-CDs showed a narrow size distribution within 6–8 nm. The emission peak with maximum intensity for N-CDs was 535 nm at the excitation wavelength of 470 nm, and the quantum yield of N-CDs was 30.2%. The as-prepared N-CDs could be selectively quenched by Fe 3+ ions with a limit of detection (LOD) of 13.8 nM in a linear range from 0.002 μM to 8 μM. Furthermore, examining the validity of the present fluorescence N-CDs probe showed that the proposed method has enough reliability and sensitivity for detecting Fe 3+ ions in an acceptable recovery range from 97 to 106.4% in the real samples. The probe indicated high stability and selectivity to be a suitable candidate for environmental applications. • N-doped CDs were used in the selective and sensitive detection of Fe 3+ ions with an excellent limit of detection. • The N-CDs have several distinct advantages: Water solubility, biocompatibility, high QY of 30.2%, and emission at 535 nm (λ ex = 470 nm). • Develop a photoluminescence probe that is reliable for detecting Fe 3+ in real samples. • The NCDs fluorescence quenching by Fe 3+ is most likely caused by a static quenching mechanism.

Fluorescent nitrogen-doped carbon dots for high selective detecting p-nitrophenol through FRET mechanism

A facile, friendly and one-step hydrothermal protocol was used to synthesize nitrogen-doped carbon dots (N-CDs) by utilizing hexamethylenetetramine and ethanediamine as the carbon and nitrogen sources. It demonstrated good water solubility and fluorescence properties were stable, whether in acidic or alkaline. Quantum yield (QY) of N-CDs was 8.3% at an excitation wavelength of 325 nm with maximum emission at 425 nm. The fluorescence of N-CDs achieved very high fluorescence quenching of 60% in the detection of p-nitrophenol (p-NP) in aqueous medium via fluorescence resonance energy transfer (FRET) mechanisms. Under optimum conditions, fluorescence probs of N-CDs had strong selectivity to p-NP, and the fluorescence intensity was linearly proportional to p-NP concentration from 0.5 to 70.0 μM with a detection limit of 0.201 μM. The corresponding cell experiments were also performed, indicating that the prepared N-CDs possessed low cytotoxicity and good biocompatibility. Meanwhile, the N-CDs can be used for the determination of p-NP in river water and industrial wastewater.

Detection of Melamine Based on the Fluorescence Changes of Nitrogen-Doped Carbon Dots

In order to determine the concentration of melamine, nitrogen-doped carbon dots (NCDs) were synthesized in one step as a fluorescent probe. Uric acid and diethylenetriamine were used as carbon source and nitrogen source, respectively. The experimental results showed that the fluorescence of NCDs can be quenched by mercury ions (Hg2+). Due to the strong coordination affinity between the carbon-nitrogen heterocyclic of melamine and Hg2+, part of Hg2+ coordinated with melamine when melamine was mixed with Hg2+. Then, the fluorescence of the added NCDs was quenched by the remaining Hg2+. Therefore, the concentration of melamine could be determined. The results show that the method has high sensitivity in wide measuring range that the linear ranges are 50–400 μg/L and 800–2500 μg/L, and the R2 is 0.997 and 0.988, respectively, with the limit of detection (LOD) of 21.76 μg/L. The NCDs are easy to fabricate, and the detection method is easy to implement. In this study, a new method for melamine detection was established, and the proposed method for melamine detection can provide some insights for food safety detection.

Development of an ultrasensitive spectrophotometric method for carmine determination based on fluorescent carbon dots

ABSTRACT A high-efficiency spectrophotometric method based on nitrogen-doped fluorescent carbon dots (N-FCDs) was developed for the ultrasensitive determination of carmine (CRM) in foodstuffs. The N-FCDs were fabricated via a one-pot hydrothermal method with m-phenylenediamine as the starting material. The detection principle was based on the fluorescence quenching effect of N-FCDs by CRM, where their interaction was due to the inner filter effect (IFE) and static quenching. A good linear relationship was established for CRM detection in a concentration range of 0.1–10.0 μM with a detection limit as low as 11.2 nM. The proposed method achieved satisfactory results for CRM determination in commercial food products with recoveries better than 98.6% and relative standard deviations (RSDs) less than 4.07%. The method established in this study was simple, ultrasensitive and reliable for rapid detecting CRM in a food matrix, which could be potentially used as a useful sensing agent for the analysis of additive food colourants.

One-pot synthesis of nitrogen-doped carbon dots for highly sensitive determination of cobalt ions and biological imaging

In this work, a facile, economical and green method for the preparation of nitrogen-doped carbon dots (N-CDs) was established via hydrothermal synthesis using p-phenylenediamine and asparagine. The as-prepared N-CDs were characterized by Transmission electron microscopy (TEM), X-ray diffraction patterns (XRD), Raman, Fourier transform infrared spectroscopy (FT-IR) and other methods. Furthermore, the N-CDs showed high sensitivity toward cobalt (II) ion (Co2+). Interestingly, the fluorescence of N-CDs was quenched linearly in the 0.3–65 μM Co2+ concentrations range, under the optimum conditions, displaying a fast response toward Co2+ with the detection limit as low as 22 nM. Simultaneously, this method was applied in the analysis of water samples with considerable results. Finally, the N-CDs were successfully utilized as the imaging probe of live root tip tissue of Arabidopsis thaliana, demonstrating that the N-CDs possessed significant theoretical research meaning in the fields of biological correlation analysis, environmental monitoring and disease diagnosis.

N-doped carbon dots for highly sensitive and selective sensing of copper ion and sulfide anion in lake water

Water contamination by copper ions (Cu2+) and sulfide anions (S2-) has been a longstanding human health hazard. The limitations of current detection strategies have created a high demand for effectively monitoring the concentrations of these ions in water systems. A facile fluorescent bioassay for Cu2+ and S2- was developed in this study based on “on-off-on” fluorescent nitrogen-doped carbon dots (N-CDs). N-CDs were synthesized for the first time via thermal treatment using hexamethylene-tetramine and ammonium citrate precursors. The obtained CDs were highly stable in aqueous solution, with a strong green emission and a 51.2% quantum yield. The maximum fluorescence emission peak was observed at 478 nm for a 360-nm excitation. Notably, the fluorescence intensity of N-CDs can be quenched by a factor of 6 by Cu2+, which can be applied to Cu2+ assays ranging from 0.05 to 5 μM with a limit of detection (LOD) of 25 nM. Interestingly, further addition of S2- recovered the fluorescence of the N-CD@Cu2+ nanocomplex, which can be used to quantify S2- in a broad range from 0.05 to 10 μM with an LOD of 32 nM. The N-CD and N-CD@Cu2+ nanocomplexes were also demonstrated to be highly specific towards Cu2+ and S2-, respectively. Finally, the sensor was successfully applied to lake water for detecting both Cu2+ and S2-, demonstrating excellent application prospects for analytical chemistry and environmental remediation.

Fluorescent N-doped Carbon Dot-Copper and Silver Nanocomposite - An effective uric acid sensor

Green fluorescent Nitrogen doped Carbon Dots ( N-CDs) was synthesized by solvent free pyrolysis technique . Using the synthesized N-CDs, for first time we report the synthesis of Blue fluorescent Nitrogen doped silver and copper carbon dot nano composite using a Simple, Solvent free Green method. The N-CDs function as reducing agent to reduce Ag+ and Cu2+ ions to Ag0 and Cu0 which leads to the formation of composite. The synthesized N-CDs and nano composites were applied as Uric Acid(UA) sensor. N-CDs and the composites function as a flurophore in the recognition of Uric acid.Both the N-CDs and the composites were characterized using UV-Vis, FTIR, SEM-EDX, TEM and PL spectroscopic techniques. The UV-Vis and FTIR response of N-CDs in comparison with N-doped silver and N-doped copper carbon dot composites confirms that the surface functional groups on N-CDs have been used in the formation of silver and copper carbon dot composite Thesurface morphology and elemental composition of synthesized carbon dots and its nanocomposites were identified using SEM-EDAX analysis. High resolution transmission electron microscopy (HR-TEM) analysis shows that N-Cdot are spherical in shape with an average size of 15.23 nm, Cu/N-Cdot composite is found to be spherical and the size to be in the range of 18.02 nm and Ag/N-Cdot composite is found to be spherical and the size of the composite is found to be 16.40 nm. The PL spectra was also observed for Cu/N-Cdots, Ag/N-Cdots. With addition of Uric acid there was a quench in fluorescence which is immediately visible by our naked eye The quench in fluorescence is due to the synergistic effect between the fluorescence Inner Filter Effect (IFE) and the static quenching effect, with a Lower detection limit (LDL) of 4µM thus functioning as a highly rapid UA biosensor.Simple naked eye observation and the absence of catalytic effect by the metal ion in the detection of UA are the merits of the present study.

In Aqueous Media, Nitrogen-Doped Fluorescent Carbon Dots Efficiently Detect Mg <sup>2+</sup> Ions: Applications for Intracellular Detection and Imaging of Mg <sup>2+</sup> Ions

In Aqueous Media, Nitrogen-Doped Fluorescent Carbon Dots Efficiently Detect Mg <sup>2+</sup> Ions: Applications for Intracellular Detection and Imaging of Mg <sup>2+</sup> Ions

Novel fluorescent nitrogen-doped carbon dots derived from Panax notoginseng for bioimaging and high selectivity detection of Cr6.

Carbon dots (CDs) and photoluminescent carbon dots (Pn-CDs) are promising nanomaterials due to their bioimaging applications and have attracted considerable attention because of their excellent stability, good biocompatibility, and low biotoxicity. Here, the Pn-CDs and highly fluorescent nitrogen-doped CDs (Pn N-CDs) derived from Panax notoginseng were successfully synthesized by a simple hydrothermal method. Pn N-CDs exhibit optical properties and stability superior to those of Pn-CDs and can be better used as fluorescent dyes and probes in biological imaging. The obtained Pn N-CDs can be effectively applied to the imaging of bacteria, fungi, plant cells, and protozoa. In addition, Pn N-CDs can perform specific staining on the membranes of all tested cells. The in vivo imaging of mice revealed that Pn N-CDs exhibit nontoxicity and good biocompatibility and biodistribution. Furthermore, Pn N-CDs can be utilized as fluorescent probes for the rapid and highly selective detection of Cr6+. Hence, a simple, cost-effective, scalable, and green synthetic approach based on traditional Chinese medicine-derived CDs can be used to develop biolabeling, membrane targeting, and optical sensing probes.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples

Iodine ion is one of the most indispensable anions in living organisms, particularly being an important substance for the synthesis of thyroid hormones. Curcumin is a yellow-orange polyphenol compound derived from the rhizome of Curcuma longa L., which has been commonly used as a spice and natural coloring agent, food additives, cosmetics as well as Chinese medicine. However, excess curcumin may cause DNA inactivation, lead to a decrease in intracellular ATP levels, and trigger the tissue necrosis. Therefore, quantitative detection of iodine and curcumin is of great significance in the fields of food and life sciences. Herein, we develop nitrogen-doped fluorescent carbon dots (NCDs) as a multi-mechanism detection for iodide and curcumin in actual complex biological and food samples, which was prepared by a one-step solid-phase synthesis using tartaric acid and urea as precursors without adding any other reagents. An assembled NCDs-Hg2+ fluorescence-enhanced sensor for the quantitative detection of I− was established based on a fluorescence “turn-off-on” mechanism in a linear range of 0.3–15 μM with a detection limit of 69.4 nM and successfully quantified trace amounts of I− in water samples and urine sample. Meanwhile, the as-synthesized NCDs also can be used as a fluorescent quenched sensor for curcumin detection based on the synergistic internal filtration effect (IFE) and static quenching, achieving a good linear range of 0.1–20 μM with a satisfactory detection limit of 29.8 nM. These results indicate that carbon dots are potential sensing materials for iodine and curcumin detection for the good of our health.

Highly fluorescent nitrogen-doped carbon dots for selective and sensitive detection of Hg2+ and ClO− ions and fluorescent ink

A facile one-step hydrothermal strategy using citric acid, ethylenediamine, and fluorescein as the precursors for the synthesis of fluorescent nitrogen-doped carbon dots (NCDs). The obtained NCDs exhibited blue fluorescence with maximum excitation/emission wavelengths at 350/447 nm and fluorescence quantum yield was up to 61%. The blue emission of the NCDs was independent of the excitation wavelength from 330 to 390 nm, while they possessed spherical morphology. The NCDs were also very stable in a wide pH range and in solutions with high ionic strength. More specifically, the fluorescence of the NCDs was effectively quenched by mercuric (Hg2+) and hypochlorite (ClO−) ions, suggesting that the NCDs can be utilized for detecting Hg2+ and ClO− with high selectivity and sensitivity. The linear ranges and limits of detection were 0.05–30 μM and 19 nM for Hg2+, and 0.1–70 μM and 90 nM for ClO−, respectively. Moreover, the NCDs were applied for detecting Hg2+ and ClO− in water samples with satisfactory results, indicating its sensing potential in environmental monitoring. Additionally, it was proven that the synthesized NCDs could be utilized as a fluorescent ink.