Nitrogen-doped Carbon Dots Research Articles

Construction of fluorescent sensor array with nitrogen-doped carbon dots for sensing Sudan Orange G and identification of various azo compounds

In this study, nitrogen-doped carbon dots (N-CDs) were facilely fabricated by one-pot hydrothermal method with levulinic acid and triethanolamine. A fluorescent sensor array was established for identifying azo compounds including Sudan Orange G (SOG), p-diaminoazobenzene, p-aminoazobenzene, azobenzene and quantitative detection of SOG. Experimental results revealed that azo compounds could quench the fluorescent intensity of N-CDs. Owing to various azo compounds showing different affinities to N-CDs, the sensor array exhibited different fluorescence quenching changes, which were further analyzed with principal component analysis to discriminate azo compounds. The sensor array was able to differentiate and recognize diverse concentrations of azo compounds from 0.25 to 2 mg/L. Simultaneously, a variety of factors affecting the detection of SOG were optimized. Under the optimized conditions, the sensor showed excellent stability and sensitivity. The sensor possessed marvelous linearity in the range of 0.1–1 mg/L and 1–4 mg/L and the detection limit was 27.82 μg/L. Spiked recoveries of 90.8–98.2 % were attained at spiked levels of 0.2 mg/L and 1 mg/L, demonstrating that the constructed fluorescence sensor was dependable and feasible for sensing SOG in environmental water samples.

Enhancing the UV resistance and flame retardancy of epoxy resin composites with fluorescent carbon dots

AbstractCarbon dots (CDs) are a novel class of carbon material which have gained widespread usages owing to their exceptional optical properties, low toxicity, and high biocompatibility. The nitrogen‐doped carbon dots (N‐CDs) using a normal curing agent of 4,4′‐diaminodiphenylmethane as resource was expected to not only have good compatibility with epoxy resin (EP), but also bring luminescent property to EP composites. It was interesting that the N‐CDs‐EP composites with 12.5 wt% addition exhibited a limiting oxygen index value of 31.4% and reached UL‐94 V‐1 grade, indicating a good flame retardancy. Compared with pure EP, the incorporation of N‐CDs formed more residual char and had extra smoke suppression effect. Besides, the N‐CDs‐EP composites exhibited a low transmittance less than 10% for the light wavelength below 490 nm. The N‐CDs contributed to the light shielding capabilities of the N‐CDs‐EP composites, which could effectively shield purple, blue, and cyan light. Furthermore, the mechanical properties including bending strength and impact strength, the dielectric property, and hydrophobicity of N‐CDs‐EP composites were also improved. The simple but effective modification strategy might be expected to be applied in many polymer systems.

Highly effective recognition of Fe3+ and lysine based on hydrosoluble N-doped carbon dots

In this study, dual-color nitrogen-doped carbon dots (NCDs) were synthesized using a simple solvothermal method. These fluorescent NCDs displayed excitation-independent emission in red (598 nm in ethanol) and orange (553 nm in water) due to their effect of two different solvents. Both types of NCDs exhibited high stability under UV irradiation for 80 min. The water-soluble NCDs showed excellent sensitivity to Fe3+ ions by the quenching of their photoluminescent (PL) intensity. Quantitative analysis revealed a gradual decline in PL intensity, with a low detection limit of approximately 0.97 µM. Interestingly, the quenched fluorescence of NCDs caused by Fe3+ could be restored by the addition of lysine to the (NCDs + Fe3+) solution, with an estimated detection limit of about 0.37 µM. This phenomenon could be explained in the terms of non-radiative electron/hole recombination, leading to aggregation through efficient photo-induced electron transfer (PET). Utilizing their high selectivity and sensitivity, these NCDs served as “On-Off-On” switches and were successfully employed for the detection of Fe3+ in real water samples, contributing to environmental safety and control efforts.

Green perspective of N-CDs towards energy crisis and photodegradation of toxic dyes

Here we have presented a general overview of an environmental friendly, one-step, cost-effective, and efficient microwave irradiation method for the preparation of self heteroatom doped Nitrogen doped carbon dots (N-CDs) which demonstrated an average size of less than 10 nm and an interplaner distance of 0.334 nm. These N-CDs possess 2.35 eV energy gap with 65.5% fluorescence quantum yield. The surfaces of these graphitic-like structures are doped with (S, P, K, Mg, Zn) = 1% along with the extra passivating agent nitrogen (N). They have demonstrated wider absorption (between 300 and 550 nm) and emission (between 400 and 600 nm) bands and also managed enormous active surface sites and defects, that further extend its usage in energy harvesting, storage and photo catalysis owing to their unique property of electron transport and collection system. In addition, we have prepared, tested, and optimised new TiO2/N-CDs composite as photo anode and N-CDs/CB composite as photo cathode for application in dye-sensitized solar cells (DSSC). The achieved power conversion efficiency of the DSSC employed photoanode N-CDs/TiO2 and counter electrode carbon black/N-CDs, demonstrated a substantial improvement, in photo current and photo voltage owing to their multiple factor visible light absorption, effective electron separation, and longer recombination time resulted a Jsc. of 22.90 mA cm2, Voc. of 0.780 V, FF. of 74% and an overall PCE of about 13.22% approximating 2.5-fold increase in power conversion efficiency as compared to that of pure TiO2 and platinum based DSSC, where Jsc. (= 10 mA cm2), Voc. (= 0.750 V) and a total of 5.42% power efficiency. Furthermore, TiO2 was modified with Heteroatom-doped N-CDs using a novel ultrasonic immersion technique, and demonstrated greater photocatalytic activity for the degradation of methylene blue (85%) with a rate constant of 0.1068 in accordance with the pure TiO2 film and N-CDs which have showed only 20% and 30% photodegradation with lower rate constants under short UV irradiation, demonstrating the formation of reactive oxygen species and H+ ions in the sample solution resulting enhanced effective mobility of electrons and holes between TiO2/N-CDs composite nanomaterial, resulted greater photo degradation.

Facile synthesis of carbon dots with blue-emitting for fluorescence determination of alizarin yellow R and temperature

Herein, a nontoxic, quick and one-step hydrothermal strategy was used to develop nitrogen and sulfur doped carbon dots (N,S-CDs). Sulfapyridine was selected as a sulfur source, and m-phenylenediamine was applied as a nitrogen source. In addition, the as-developed N,S-CDs indicated excitation-dependent feature, strong blue-emitting fluorescence, excellent photostability and anti-ion effect. Furthermore, the as-established N,S-CDs displayed an excellent linear characteristic for the determination of alizarin yellow R. The detection limit was 0.25 μM. Moreover, the as-developed N-CDs were successfully applied to determine alizarin yellow R in real samples.

Hybrid nanostructures of nitrogen-doped carbon dots and aromatic amino acids: Synthesis, interactions at interfaces and optical properties

Nitrogen-doped carbon dots (NCD) were synthesized using a simple and fast hydrothermal route, employing citric acid and urea as precursors. The resulting NCDs were non-covalently functionalized (conjugated) with aromatic amino acids, namely phenylalanine (Phe) and tryptophan (Trp). Atomic force microscopy revealed that the NCDs exhibit a disk-like morphology with an average diameter of approximately 60 nm and an average height of about 0.5 nm. Following conjugation, the particle height increased to around 3 nm. UV–vis spectroscopy analysis indicated successful conjugation of the amino acids to the NCD nanostructures. Additionally, DFT numerical calculations based on three differently N-doped clusters were performed to elucidate the nature of the non-covalent interactions between NCDs and the corresponding amino acids. Photoluminescent spectra demonstrated a stable and strong fluorescence signal for both hybrids in the UV region. The most significant changes were observed in the case of Trp-conjugation. In contrast to phenylalanine, the non-covalent bonding of tryptophan to NCDs strongly influenced the visible emission (around 500 nm) originating from surface states of the dots.

Smartphone-assisted fluorimetric and colorimetric dual-recognition sensing platform based on nitrogen-doped carbon dots for visual monitoring of acid red 18 in food

The widespread presence of acid red 18 (AR18) in the environment has raised concerns about the potential risks on human health and ecosystems. Herein, upon addition of AR18, nitrogen- doped carbon dots (N-CDs) synthesized with catechol and 3, 3-diaminobenzidine exhibit interactive behavior with AR18. Therein, the emission peaks at 490 nm and 410 nm are quenched by internal filtering effect (IFE) and fluorescence resonance energy transfer (FRET). Notably, the former experiences a rapid decline due to robust FRET efficiencies. On this basis, a N-CDs-based fluorimetric and colorimetric sensor is developed for sensitive and selective detection of AR18 in concentrations ranging from 0.053 to 100 μM with a low detection limit (LOD) of 53 nM. In addition, a smartphone-based dual-recognition device, integrated with composite film that enhances liquid collection in determination zone, is aimed at the sensitive detection of AR18 in food samples. The LODs are determined to be 131 nM and 122 nM respectively under fluorimetric and colorimetric conditions. Concomitantly, the device exhibits satisfying accuracy and precision for practical applications. Therefore, this newly developed dual-recognition device provides reliable means to detect the presence of AR18, demonstrating promising potential for on-site monitoring and intelligent sensing applications.

Fluorescent carbon dots for highly sensitive diosmetin sensing

In this paper, a single signal fluorescent sensor of nitrogen-doped carbon dots (N-CQDs) was established for the micro-determination of diosmetin. In this determination platform, the as-developed N-CQDs with yellow fluorescence were prepared through a facile hydrothermal method with p-phenylenediamine and ascorbic acid as the precursors containing nitrogen and carbon. The as-developed N-CQDs had a classical surface structure and surprising fluorescence stability. The maximum excitation and emission peaks were located at 372 and 528 nm, respectively. Under the optimal sensing conditions, the as-prepared N-CQDs held preeminent immunity towards possible interfering substances. The determination platform’s fluorescence intensity was quenched because of the static quenching and inner filter effect. The fluorescence weakening changes displayed an attractive linear relationship with diosmetin in range of 0.5–150 μM, and the linear equation was ln(F0/F) = 0.014[Q]–0.055 with the R2 of 0.9975 and the detection limit of 0.049 μM. The determination platform could be applied for the trace detection of diosmetin in river water and bovine serum samples. The corresponding recovery rate was 94.8 %–108.8 %, exhibiting that it was a facile and efficient fluorescence sensing strategy.

Microwave-Assisted Grafting of Coal onto Nitrogen-Doped Carbon Dots with a High Quantum Yield and Enhanced Photoluminescence Properties.

The fluorescent nitrogen-doped carbon dots (N-CDs) were synthesized via a facile one-pot solvothermal process using coal (Jin 15 Anthracite and Shaerhu lignite) as raw materials and dimethyl formamide (DMF) as the solvent, employing a microwave pyrolysis method. This approach demonstrates remarkable efficacy in the development of nitrogen-doped carbon dots (N-CDs) with a high quantum yield (QY). The N-CDs prepared have strong photoluminescence properties. Moreover, the obtained N-CDs emit blue PL and are easily dispersed in polymethyl methacrylate (PMMA), preserving the inherent advantages of N-CDs and the PMMA matrix. The JN-CDs exhibit a high quantum yield (QY) of 49.5% and a production yield of 25.7%, respectively. In contrast, the SN-CDs demonstrate a quantum yield of 40% and a production yield of 35.1%. It is worth noting that the production yield and quantum yield of coal-based carbon dots are inversely related indices. The lower metamorphic degree of subbituminous coal favors an enhanced product yield, while the higher metamorphic degree of anthracite promotes an improved quantum yield in the product, which may be attributed to the presence of amorphous carbon within it. Consequently, we propose and discuss potential mechanisms underlying N-CD formation.

Enhanced performance of carbon dots and Mn3O4 composite by phosphate in peroxymonosulfate activation

A composite of nitrogen-doped carbon dots and Mn3O4 (CMO) was synthesized using a facile hydrothermal and precipitation method for peroxymonosulfate (PMS) activation. Surprisingly, high concentrations of H2PO4− (DP, above 20 mM) significantly enhanced the degradation efficiency of bisphenol A (BPA). The improvement was not attributed to the accelerated cleavage of PMS or pH variation. Instead, DP could directly form a complex with CMO, generating Mn(III)-DP with a high potential (0.64 V vs. SCE, 100 mM of DP). Simultaneously, it decreased the oxidative potential of BPA from 0.69 to 0.38 V vs. SCE. The degradation pathways of BPA differed in the CMO/PMS and CMO/DP systems. These findings inspire further exploration of carbon dots-based catalysts in persulfate activation and unveil the origin of enhanced performances by phosphate.

Sensing, detoxification and bactericidal applications of nitrogen-doped carbon dots

Here, a one-pot hydrothermal synthesis technique was used to create nitrogen-doped carbon dots (N-CDs). Their structural and optical properties were assessed using XPS, XRD, Raman, UV–Vis, and fluorescence spectrophotometer. The N-CDs demonstrated encouraging emission quenching towards p-NP (p-Nitrophenol) and developed a sensing approach between 0.25 and 125 μM concentrations, from which a linear equation with a 20 nM detection limit was generated. In comparison to river and circulating water samples, the practicality demonstrated positive recovery rates together with impressive accuracy and precision. Additionally, the multi-functionality of N-CDs was investigated further in the catalytic reduction of methyl orange (MO) dye. With a good regression coefficient(0.9904) (R2) and rate constant (Kcat) (0.0208 min−1), N-CDs were able to reduce the azo groups in 8 min completely. Additionally, the bactericidal efficiency of N-CDs against gram-positive (Staphylococcus aureus, Listeria monocytogenes) and gram-negative (Escherichia coli, Salmonella enterica) bacteria was encouraging. The well-diffusion method demonstrated a good zone of inhibition, and the microdilution method demonstrated a promising minimum bactericidal concentration (MBC) of 470–940 μg/mL and minimum inhibitory concentration (MIC) of 240–470 μg/mL. The suggested fluorescent material may prove useful in the future for creating a fluorescence sensor, catalysts to combat water pollution, and antibacterial sprays to combat dangerous microorganisms.

Synthesis of nitrogen-doped fluorescent carbon dots for determination of nickel ions and morin from aqueous solution simultaneously

Considering the significant impact of heavy metals on environment and food safety inspection in trace determination, the orange photoluminescent carbon dots (O-CDs) was innovative designed by promoting the co-hydrothermal reaction of polyethyleneimine and resazurin. The produced O-CDs exhibit exceptional optical performance, advantageous water solubility and outstanding photostability. It is worth emphasizing that the proposed O-CDs has significant advantages in constructing sequential sensing platform for sensitive determination of Ni2+ and morin. Simultaneous taking Ni2+ for analytes and fluorescence quenching agents on the O-CDs sensing platforms, a good linear relationship can be received in the range of 5–50 μM with satisfactory sensitivity. Subsequently, morin can effectively promote the fluorescence recovery of O-CDs@Ni2+ on account of stronger binding force between morin and Ni2+. Based on the above results, effective recovery of 97.26 %-100.90 % and 98.24 %-101.99 % is observed towards nickel ion and morin in real food samples. These findings provide an original strategy for the construction of long-wavelength emission carbon dots, which provides a pathway for the determination of typical pollutants based on efficient and robust nanosensors in the field of food safety.

Rapid Quantitative Detection for Nitrofurantoin Based on Nitrogen-Doped Highly Photoluminescent Carbon Dots.

Nitrogen-doped carbon dots (NCD) with high fluorescence retention and good stability were successfully fabricated using citric acid and urea via a facile and eco-friendly one-step microwave method, which exhibited superior specificity for detection of nitrofurantoin (NFT). Upon the addition of NFT, the fluorescence intensity of NCD at 450 nm was significantly decreased. Besides, a satisfactory linear relationship between the fluorescence quenching efficiency and concentrations of NFT was obtained. Especially, NCD was qualitatively and quantitatively applied for detection NFT in milk and meat extract samples with a high recovery rate. Consequently, it was suggested that the detection method had potential application in the specific detection of NFT, offering a novel approach for veterinary drug residue detection.

A nanozyme based wearable device for colorimetric monitoring of UV radiation exposure in sunlight

In this study, nanozyme is used for monitoring the dose of ultraviolet (UV) in sunlight for the first time. We find that nitrogen-doped carbon dots (N-doped C-dots) can effectively catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under different UV region including UVA, UVB, and UVC. In comparison, the N-doped C-dots fail to show the catalytic activity under visible light. The finding is applied for distinguishing UV light and visible light through the color change of TMB. More importantly, the photo-oxidation TMB catalyzed by N-doped C-dots can work well in a near neutral pH, which is beneficial for its application in wearable device due to the reducing of acid corrosion. Finally, a wearable bracelet is fabricated by integrating N-doped C-dots and TMB into hydrogels. The bracelet is used for monitoring the UV exposure in sunlight. The color change of TMB in the bracelet can be clearly observed by naked eyes or quantified by a smartphone. The bracelet is also used for distinguishing different weather condition such as sunny/cloudy or different place such as indoor/outdoor during a sunny day. This study provides the first example of nanozyme in wearable UV sensor and will stimulate the applications of nanozyme in wearable device.

A Flexible and Free‐Standing Photonic Crystal‐Hydrogel Film for Enhanced Fluorescence from Nitrogen Doped Carbon Dots

AbstractEnhancement of fluorescence emission in a flexible and free‐standing fluorescing film is a key requirement for sensing platforms with augmented sensitivity. In this context, a study on the enhanced fluorescence emission from nitrogen‐doped carbon dots (NCDs) embedded on a flexible free‐standing photonic crystal hydrogel film prepared via photopolymerization, is presented. The composite structure utilizes the photonic crystal enhanced fluorescence (PCEF) technique and incorporates a self‐assembled 3D photonic crystal (3D PC) onto a photopolymerizable hydrogel matrix containing the NCDs. The 3D PC template is prepared through vertical deposition self‐assembly using monodisperse polystyrene (PS) spheres. By leveraging the enhanced excitation and extraction effect in a PC‐fluorophore composite, the authors’ structure exhibits a fourfold enhancement in fluorescence emission compared to the control sample. The relative positioning of the photonic stopband with the excitation and emission spectra of the fluorophore (NCDs) is thoroughly studied by selecting four different 3D PCs with varied lattice parameters. In addition, the hydrogel matrix offers improved photostability and enhanced lifetime for the NCDs. This structure can be further modified into an efficient sensor through appropriate functionalization.

Nitrogen-Doped Carbon Dots Facilitate CRISPR/Cas for Reducing Antibiotic Resistance Genes in the Environment.

The continued acquisition and propagation of antibiotic resistance genes (ARGs) in the environment confound efforts to manage the global rise in antibiotic resistance. Here, CRISPR-Cas9/sgRNAs carried by nitrogen-doped carbon dots (NCDs) were developed to precisely target multi-"high-risk" ARGs (tet, cat, and aph(3')-Ia) commonly detected in the environment. NCDs facilitated the delivery of Cas9/sgRNAs to Escherichia coli (E. coli) without cytotoxicity, achieving sustained elimination of target ARGs. The elimination was optimized using different weight ratios of NCDs and Cas9 protein (1:1, 1:20, and 1:40), and Cas9/multi sgRNAs were designed to achieve multi-cleavage of ARGs in either a single strain or mixed populations. Importantly, NCDs successfully facilitated Cas9/multi sgRNAs for resensitization of antibiotic-resistant bacteria in soil (approaching 50%), whereas Cas9/multi sgRNAs alone were inactivated in the complex environment. This work highlights the potential of a fast and precise strategy to minimize the reservoir of antibiotic resistance in agricultural system.

In‐situ controllable synthesis of carbon dots for patterned fluorescent wood films rapid fabrication strategy

AbstractFluorescent‐patterned materials are widely used in information storage and encryption. However, preparing a patterned fluorescent display on a matrix currently requires a time‐consuming (hours or even days) and complex multi‐step process. Herein, a rapid and mild technique developed for the in‐situ controllable synthesis of fluorescent nitrogen‐doped carbon dots (NCDs) on eco‐friendly transparent wood films (TEMPO‐oxidized carboxyl wood film [TOWF]) within a few minutes was developed. A wood skeleton was employed as the carbon precursor for NCD synthesis as well as the matrix for the uniform and controlled distribution of NCDs. Moreover, the in‐situ synthesis mechanism for preparing NCDs in TOWF was proposed. The resulting fluorescent wood films have excellent tensile strength (310.00 ± 15.57 MPa), high transmittance (76.2%), high haze (95.0%), UV‐blocking properties in the full ultraviolet (UV) range, and fluorescent performance that can be modified by changing the heating parameters. Fluorescent patterning was simply achieved by regulating the in‐situ NCD synthesis regions, and the fluorescent patterns were formed within 10 s. These fluorescent‐patterned wood films can effectively store and encrypt information, and they can interact with external information through a transparent matrix. This work provides a green and efficient strategy for fabricating fluorescent information storage and encryption materials.

Nitrogen-doped carbon dots as photocatalysts for organic synthesis: Effect of nitrogen content on catalytic activity

Nitrogen-doped carbon dots as photocatalysts for organic synthesis: Effect of nitrogen content on catalytic activity

Nitrogen-doped carbon dots by means of a simple room-temperature synthesis using BSA protein and nucleosides or amino acids

There is considerable interest in the synthesis and applications of carbon dots due to their intriguing tunable optical properties, among which are strong photobleaching resistance and low toxicity for biomedical applications in sensing and biosensing. C-dots are prepared using different fabrication methods that use carbon-rich materials, including carbohydrates, citric acid, proteins, plants and organic waste materials. In this work, we report the synthesis of nitrogen co-doped carbon dots, which is carried out through a simple and quick method at room temperature, with serum bovine albumin as the carbon source, and an amino acid (L-Arginine) or a nucleoside (Adenosine, Cytidine) to be added during the synthesis as the nitrogen source and then crosslinked to surface carbon dots by glutaraldehyde. After twenty hours of synthesis, the solution turned orange, indicating the complete formation of highly stable fluorescent C-dots, characterized by UV−Vis, fluorescence, FTIR, XPS spectroscopies and SEM. The resulting C-dots were all fluorescents, with a mean size of 5 nm, exhibiting the following functional groups on the C-dots surface: CN, NH, CN and CO, confirming the co-doping with nitrogen. Among the prepared samples, the addition of Cytidine yields the strongest emissive colloid, showing a robust yellow fluorescence (maximum emission at 560 nm), with a high quantum yield of 31.4% and good photobleaching resistance to green laser (117 mW/cm2).

On-Off-On Fluorometric Detection of Hg(II) and L-Cysteine Using Red Emissive Nitrogen-Doped Carbon Dots for Environmental and Clinical Sample Analysis.

This research introduces a novel fluorescence sensor 'on-off-on' employing nitrogen-doped carbon dots (N-CDs) with an 'on-off-on' mechanism for the selective and sensitive detection of Hg(II) and L-cysteine (L-Cys). N-CDs was synthesized using citric acid as the carbon precursor and urea as the nitrogen source in dimethylformamide (DMF) solvent, resulting in red emissive characteristics under UV light. Comprehensive spectroscopic analyses, including UV-Vis, fluorescence, FT-IR, XRD, XPS, Raman, and Zeta potential techniques, validated the structural and optical characteristics of the synthesized N-CDs. The maximum excitation and emission of N-CDs were observed at 548 and 622nm, respectively. The quantum yield of N-CDs was calculated to be 16.1%. The fluorescence of N-CDs effectively quenches upon the addition of Hg(II) due to the strong coordination between Hg(II) and the surface functionalities of N-CDs. Conversely, upon the subsequent addition of L-Cys, the fluorescence of N-CDs was restored. This restoration can be attributed to the stronger affinity of the -SH group in L-Cys towards Hg(II) relative to the surface functionalities of N-CDs. This dual-mode response enabled the detection of Hg(II) and L-Cys with impressive detection limits of 15.1 nM and 8.0 nM, respectively. This sensor methodology effectively detects Hg(II) in lake water samples and L-Cys levels in human urine, with a recovery range between 99 and 101%. Furthermore, the N-CDs demonstrated excellent stability, high sensitivity, and selectivity, making them a promising fluorescence on-off-on probe for both environmental monitoring of Hg(II) and clinical diagnostics of L-Cys.