N-doped Carbon Nanodots Research Articles

Termite wings derived N-doped carbon nanodots: applications for Cu2+ sensing, fluorescent ink and flexible polymeric film

Termite wings derived N-doped carbon nanodots: applications for Cu2+ sensing, fluorescent ink and flexible polymeric film

Ratiometric fluorometric and colorimetric dual-signal sensing platform for rapid analyzing Cr(VI), Ag(I) and HCHO in food and environmental samples based on N-doped carbon nanodots and o-phenylenediamine

Nitrogen-doped carbon nanodots (N-CNDs) were synthesized simply and efficiently using glutathione. The fluorescence emission of N-CNDs at 430 nm was effectively quenched by the fluorophore 2,3-diaminophenazine (DAP), produced through the oxidation of o-phenylenediamine (OPD) under the catalysis of Cr(VI)/Ag(I). This quenching was attributed to the fluorescence resonance energy transfer effect, while a new fluorescence emission at 560 nm was observed. Furthermore, the redox and chromogenic reaction of Cr(VI) and OPD at pH 5.4 could be effectively inhibited by formaldehyde (HCHO), resulting in the activation of N-CNDs fluorescence and the quenching of DAP fluorescence. Consequently, dual-signal sensing platforms for the rapid analysis of Cr(VI) and Ag(I) using N-CNDs/OPD and HCHO using N-CNDs/OPD/Cr(VI) were successfully constructed. By incorporating a masking reagent such as H2O2 for Cr(VI) and Cl− for Ag(I), the established sensing platform exhibited excellent selectivity and practical applicability for detecting Cr(VI), Ag(I), and HCHO in food and environmental samples.

Highly luminescent graphene core N-doped carbon nanodots prepared under spatial nanoconfinement

Nitrogen-dopped carbon nanodots (CNDs) with an extremely high quantum yield of photoluminescence (up to 95%) have been obtained by thermal treatment of citric acid embedded in the porous structure of silica with immobilized N-[3-(Trimethoxysilyl)propyl]ethylenediamine. Spatial isolation of molecular precursors in nanoreactors permits the preparation of high-quality nanoparticles with spheroidal geometry and size 2–5 nm. The particles obtained at 110–180 °C for 60–600 min demonstrate excitation-independent photoluminescence at 453 nm. HRTEM reveals that the CNDs demonstrate ordered crystalline structures of graphic materials, indicating the catalytic effect of the nanoreactor. The high-resolution XPS experiment proves the N-doping of CNDs with 4.0 at.% of nitrogen atoms incorporated into the graphene core as pyrrolic and ternary fragments.

Laser-induced tuning of carbon nanosensitizers to maximize nitrogen doping and reactive oxygen species production in the visible range

Carbon nanodots (CNDs) have emerged as novel fluorescent nanosensitizers able to expand the photocatalytic response of conventional semiconductors beyond the ultraviolet spectral window. Key aspects of CNDs related with their high photostability, resistance to photobleaching and optical properties (including downconversion and upconversion luminescence) are often associated with the capacity to dope the carbogenic network with light heteroatoms, especially nitrogen. In this work, we present the use of laser pyrolysis as a versatile and convenient synthesis technique to generate different N-doped CNDs. The level of N doping can be tuned through the selection of a single liquid solvent containing N as carbon precursor. This liquid precursor can be alternatively enriched with additional N sources co-fed in the form of gas (i.e. NH3) or disolved solid precursors (i.e. phtalocyanine-Ph). We demonstrate that the N-CNDs retrieved after the additional N cofeeding treatments improve their photoactivity when assembled to P25 nanoparticles towards the conversion of methyl orange (MO) under white LED illumination. All the N-CNDs act as photosensitizers expanding the response of P25 beyond the UV region and exhibit an active role generating different types of Reactive Oxygen Species (ROS) via singlet oxygen, superoxide and hydroxyl radicals that can pave the way for multiple potential applications in environmental and green processes.

Ultra-sensitive and stable N-doped carbon dots for selective detection of uranium through electron transfer induced UO2+(V) sensing mechanism

Unintended leakage of toxic and radioactive uranyl ion (UO22+) ions poses high harmful to human health and environment, hence its monitoring and detection is of utmost significance. Here, we developed a mild synthetic route to prepare stable N-doped carbon nanodots (CDs) with special hydrophilicity functional groups and graphitic N by polymerization and carbonization of novel norfloxacin precursor with nitrogen heterocyclic structure. The morphology, chemical structure, fluorescent properties, sensing competition and selectivity behaviors of CDs-UO22+ were systematically analyzed. Controllable experiments including low and high concentration CDs-UO22+ and another type of carbon dots (TEA-CDs) with low graphitic N amount using triethanolamine (TEA) precursor without nitrogen heterocyclic structure were designed, which further confirmed the effective coordination and interaction mechanism between CDs and UO22+ that graphitic N in CDs induced the formation UO2+(V) by electron transfer. It is very suitable for on-site and real-time monitoring of UO22+ with an ultra-fast response time (∼20 s) and low detection limit of 20.38 nM (4.7 μg L−1), which is lower than the permissible limits (30 μg L−1) defined by the United States Environmental Protection Agency (EPA). More importantly, different form the liquid sensor, solid sensors (printed test strip and hydrogel) were also successfully employed to monitor UO22+ targets quickly, broadening the potential application for the advanced image encryptions.

Excellent anti-corrosion performance of epoxy composite coatings filled with novel N-doped carbon nanodots

Nanofillers play an important role in the field of anticorrosion. This paper focuses on the study of the anticorrosion performance of a novel N-doped carbon nanodots(CNDs) in epoxy coating. N-doped carbon nanodots(CNDs) with a size of about 100 nm is synthesized by hydrothermal method using citric acid as carbon source. The chemical structure and morphology of CNDs are studied by Fourier transform infrared spectroscopy(FT-IR), ultraviolet spectrophotometer(UV–vis), X-ray photoelectron spectroscopy(XPS), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The water absorption of the coating is studied by gravimetric method. The corrosion resistance of the coating is analyzed by electrochemical impedance spectroscopy(EIS). The results reveal that the corrosion resistance of epoxy coating is significantly improved by adding the appropriate amount of CNDs, as it can effectively reduce the porosity of the coating and extend the path of corrosive medium penetrating the coating, thus enhancing the corrosion resistance of the coating. After soaking in 3.5 wt% NaCl solution for 480 h, the low frequency impedance of the 0.15 wt% CNDs/epoxy nanocomposite coating is 1.85x1010 ohm·cm2, which is greatly improved compared with that of the pure epoxy coating (5.43 × 104 O·cm2). The water absorption result shows that the water absorption of the coating with CNDs content of 0.15 wt% is much lower than that of the pure epoxy coating. The corrosion resistance is greatly improved.

Facile Fabrication of Highly Fluorescent N-Doped Carbon Quantum Dots Using an Ultrasonic-Assisted Hydrothermal Method: Optical Properties and Cell Imaging.

Fluorescent N-doped carbon nanodots (CNDs) are a type of environmentally friendly nanomaterial that is promising for application in cell imaging and optoelectronics. In this paper, a natural amino acid (l-glutamic acid) was used as a precursor, and two different morphological and structured N-doped carbon quantum dots (CQDs) were synthesized via a one-step ultrasonic-assisted hydrothermal method at 230 and 250 °C. Various microscopy and spectroscopy techniques were employed to characterize the morphology, structure, optical properties, and stability of the CQDs. The results showed that N-CQDs-1 are new CNDs composed of amorphous carbon with a large amount of pyroglutamic acid, and N-CQDs-2 are composed of pure amorphous carbon. The CQDs exhibit excellent optical properties, such as 40.5% quantum yield, strong photobleaching resistance, and superior photostability. Combining the fluorescence lifetimes and radiative and non-radiative decay constants, the photoluminescence mechanism of the CQDs was qualitatively explained. The two CQDs were used for BV2 cell imaging and showed good results, implying the ultrasonic-assisted hydrothermal approach as a facile method to obtain structure- and morphology-controllable N-doped CQDs with prospect for application in cell imaging.

N-Doped Yellow-Emissive Carbon Nanodots from Gallic Acid: Reaction Engineering, Stimuli-Responsive Red Emission, and Intracellular Localization

An easy one-pot method is utilized for the synthesis of carbon nanodots, which has been investigated primarily from material perspectives. However, this preferred one-pot synthesis method suffers from the untraceability of steps leading to the infusion of the photoluminescence property in the nanodot. To resolve the steps involved, a single-precursor approach has been adopted here for the synthesis of the yellow-fluorescent probe by using a bioresource, gallic acid. The synthesized probe exhibits excitation-energy-independent emission, a typical molecular behavior, but shows an emission-wavelength-dependent lifetime that is often attributed to the red-edge effect most commonly observed for nanodots. We propose here that the observation of the red-edge effect for a synthesized probe in neat solvents is due to proton-transfer controlled solvation, a unique photoprocess. Characterization and computational results of the synthesized product clearly suggest the formation of a molecular fluorophore. Unprecedentedly, the synthesized probe shows proton-triggered red emission. The addition of a proton resulted in molecular aggregation due to a strong H-bonded interaction among product molecules. The presence of multiple phenolic−OH groups in the probe allows the easy formation of molecular chains of crystals on transmission electron microscopy grids, causing the observation of lattice spacing that remains unchanged in an aggregated state as well. We have also explored its possible applications in bioimaging and trivalent metal ion sensing. It has better cell-membrane permeability but remains predominantly in the cytoplasm. Both green and red fluorescence are observed inside the cell. The product molecule possesses a submicromolar detection limit for aluminum ions as well, further confirming the unaltered position of phenolic–OH groups present in the product and substrate.

N-Doped fluorescent carbon nanodots derived out of Gum ghatti for the fluorescence tracking of mercury ions Hg2+ in the aqueous phase

An ecofriendly microwave pyrolysis tactic was employed to synthesize N-doped fluorescent carbon nanodots (N-CNDs) using Gum ghatti and ethylenediamine as a carbon and nitrogen source. The fabricated N-CNDs exhibits high stability in water medium and emits bright blue fluorescence with the quantum yield of 23%. We further established N-CNDs as an excellent visual and selective fluorescent-based nanoprobe for mercury ions (Hg2+ ions) detection. The limit of detection was found to be 4.6 nM. When metal ion chelator ethylenediaminetetraacetic acid (EDTA) was added into the N-CNDs + Hg2+ ions system, the fluorescence was reverted effectively. Moreover, the fluorescent quenching principle of N-CNDs + Hg2+ ions system follows the static quenching mechanism. Finally, the Gum ghatti derived N-CNDs was efficiently applied in environmental water samples like tap and mineral water to determine mercury ions.

Citric acid-based carbon dots: From revealing new insights into their biological properties to demonstrating their enhanced wound healing potential by in vitro and in vivo experiments

Citric acid, as a carbon precursor, has extensively been considered by researchers to synthesize fluorescent carbon nanodots (CNDs), which emit strongly in the blue spectral range. In an endeavor to repurpose CNDs for applications other than those until now reported, non-doped, nitrogen-doped, and nitrogen/sulfur co-doped CNDs, were synthesized using citric acid as one of the most exploited carbon sources. This study explored the effect of heteroatom doping on the biological properties of CNDs placing more emphasis on wound healing. The three CND species were examined with respect to cell proliferation/toxicity, cell migration, bactericidal, anti-inflammatory, and antioxidant properties. From the results, it became apparent that the N,S-doped CNDs exhibit remarkable bactericidal properties, while the N-doped CNDs exhibit the best anti-inflammatory and antioxidant properties. Based on it, in-vitro antioxidant experiments were carried out for the N-doped CNDs, which validated our findings. Next, the N-doped CNDs were evaluated for their wound healing potency by carrying out relevant in-vivo experiments. The results showed that wounds treated with the CNDs were healed four days faster than control wounds. This study provides valuable insights into inspiring new advancements of CNDs and draws a roadmap towards their broader range of biomedical applications underlining the potency in wound healing.

A label-free multifunctional nanosensor based on N-doped carbon nanodots for vitamin B12 and Co2+ detection, and bioimaging in living cells and zebrafish.

Multifunctional N-doped carbon nanodots (N-CNDs) with a fluorescence (FL) quantum yield (QY) of 13.6% have been synthesized via a facile one-step hydrothermal process using Artemisia annua and 1,2-ethylenediamine as precursors. As-prepared N-CNDs showed excellent FL properties and were developed as a multifunctional sensing platform for vitamin B12 (VB12) and Co2+ determination, and bioimaging in living cells and zebrafish. The FL of N-CNDs is quenched efficiently in the presence of VB12 on the basis of the inner filter effect (IFE) or Co2+ by static quenching, respectively. EDTA as a masking agent enables Co2+ to be effectively eliminated and N-CNDs were used to selectively detect VB12 in the presence of both VB12 and Co2+. The present FL nanosensor can detect VB12 and Co2+ in the linear ranges of 0.5-35 μM and 2.5-25 μM with the corresponding detection limits of 47.4 nM and 230.5 nM, respectively. The study proved that the determination of Co2+ was based on the static quenching to form a complex between the amino group of N-CNDs and Co2+. Inspired by these outstanding properties, practical applications of this nanosensor for the detection of VB12 in actual samples (human serum, egg yolk, VB12 tablets and VB12 injection) and Co2+ in water samples were further verified with satisfactory results. The as-constructed N-CNDs have negligible toxicity and good biocompatibility, which facilitates utilization of N-CNDs in bioimaging of A549 cells and zebrafish, and sensing VB12 in living cells.

Use of Nitrogen-Doped Carbon Nanodots for the Photocatalytic Fluoroalkylation of Organic Compounds.

The use of amine-rich N-doped carbon nanodots (NCNDs) for the photochemical radical perfluoroalkylation of organic compounds is reported. This operationally simple approach occurs under mild conditions producing valuable new C-C bonds. The chemistry is driven by the ability of NCNDs to directly reach an electronically excited state upon light absorption, thereby successively triggering the formation of reactive radical species from simple perfluoroalkyl iodides. Preliminary mechanistic studies are also reported.

Laser-driven direct synthesis of carbon nanodots and application as sensitizers for visible-light photocatalysis

We present the first successful synthesis of monodisperse carbon nanodots (CNDs) with tunable photoluminescence (PL) carried out by laser pyrolysis of two common volatile organic precursors such as toluene and pyridine. Remarkably, the initial chemical composition of the precursor determines the formation of undoped or N-doped CNDs and their corresponding absorption response in the visible range (expanded for the latter). We demonstrate the control and versatility of this synthesis method to tune the final outcome and its potential to explore a great number of potential solvent candidates. Furthermore, we have successfully exploited these CNDs (both undoped and N-doped) as effective sensitizers of TiO2 nanoparticles in the visible-light driven photo-degradation of a cationic dye selected as model organic pollutant.

Nitrogen doped MoS2 and nitrogen doped carbon dots composite catalyst for electroreduction CO2 to CO with high Faradaic efficiency

CO2 utilization by direct electroreduction offers an attractive route for preparing valuable chemicals or alternative liquid fuels, and mitigating the hazardous effects of global warming. Unfortunately, the electroreduction CO2 currently suffers from poor efficiency, low produce selectivity, and large overpotential is required to initiate CO2 reduction due to the thermodynamic stability of CO2. Therefore, the development of low-cost transition-metal chalcogenides electrocatalysts for high selectivity electroreduction CO2 under considerably low overpotentials are still challenge, due to its high catalytic activity of hydrogen evolution reaction and poor electronic conductivity. Herein, for the first time, N-doped MoS2 nanosheets and N-doped carbon nanodots (N-MoS2@NCDs) composite was successfully prepared by solvothermal method in the presence of E-MoS2 and DMF solvent. During solvothermal process, N atoms were introduced into MoS2 framework and N-doped CDs were formed on the surface of MoS2 nanosheets at the same time. The optimized N-MoS2@NCDs-180 for electroreduction CO2 displayed a high CO Faradaic efficiency up to 90.2% and a low onset overpotential requirement of 130 mV for CO formation, which were significantly superior to those of the E-MoS2 and other previously reported transition-metal sulfides electrocatalysts. The experiment verified that the N-doped CDs on the surface MoS2 provided a good electrical conductivity, which accelerated electron transport. Moreover, DFT theoretical calculation demonstrated that the N doping into MoS2 could decrease the energy barrier of the COOH* intermediate formation and create more electrons on the edge Mo of N-MoS2, thereby enhancing catalytic activity of CO2 electroreduction to CO.

Tunable ternary nanocomposite prepared by electrodeposition for biosensing of centrally acting reversible acetyl cholinesterase inhibitor donepezil hydrochloride in real samples

This paper describes the decoration of pencil graphite electrode (PGE) with a thin film of solochrome black T (SBT) and N-doped carbon nanodots (N-CNDs)/ cobalt nanoparticles (CoNPs) to amplify signal of the measurement. This nanocomposite was chosen to enhance surface activity and electron transfer toward donepezil HCl (DZ HCl) oxidation. The physical properties of nanocomposite were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), electron impedance spectroscopy (ESI) and energy dispersive X-ray (EDX) spectroscopy. Cyclic voltammetry was utilized to quantify DZ HCl at the modified PGE in Britton-Robinson buffer (pH = 6.5). Under optimized experimental conditions, peak current increased with the increase in the concentration of DZ HCl and was linear between the range of 1.5 nM–400 μM with a relatively low detection limit of 0.0005 μM. Due to high sensitivity, simplicity and cost-effectiveness of the designated sensor; it was used as a simple method for detecting DZ HCl in rabbit plasma and during its pharmacokinetic study.

Biocatalytic C=C Bond Reduction through Carbon Nanodot‐Sensitized Regeneration of NADH Analogues

AbstractLight‐driven activation of redox enzymes is an emerging route for sustainable chemical synthesis. Among redox enzymes, the family of Old Yellow Enzyme (OYE) dependent on the nicotinamide adenine dinucleotide cofactor (NADH) catalyzes the stereoselective reduction of α,β‐unsaturated hydrocarbons. Here, we report OYE‐catalyzed asymmetric hydrogenation through light‐driven regeneration of NADH and its analogues (mNADHs) by N‐doped carbon nanodots (N‐CDs), a zero‐dimensional photocatalyst. Our spectroscopic and photoelectrochemical analyses verified the transfer of photo‐induced electrons from N‐CDs to an organometallic electron mediator (M) for highly regioselective regeneration of cofactors. Light triggered the reduction of NAD+ and mNAD+s with the cooperation of N‐CDs and M, and the reduction behaviors of cofactors were dependent on their own reduction peak potentials. The regenerated cofactors subsequently delivered hydrides to OYE for stereoselective conversions of a broad range of substrates with excellent biocatalytic efficiencies.

Biocatalytic C=C Bond Reduction through Carbon Nanodot-Sensitized Regeneration of NADH Analogues.

Light-driven activation of redox enzymes is an emerging route for sustainable chemical synthesis. Among redox enzymes, the family of Old Yellow Enzyme (OYE) dependent on the nicotinamide adenine dinucleotide cofactor (NADH) catalyzes the stereoselective reduction of α,β-unsaturated hydrocarbons. Here, we report OYE-catalyzed asymmetric hydrogenation through light-driven regeneration of NADH and its analogues (mNADHs) by N-doped carbon nanodots (N-CDs), a zero-dimensional photocatalyst. Our spectroscopic and photoelectrochemical analyses verified the transfer of photo-induced electrons from N-CDs to an organometallic electron mediator (M) for highly regioselective regeneration of cofactors. Light triggered the reduction of NAD+ and mNAD+ s with the cooperation of N-CDs and M, and the reduction behaviors of cofactors were dependent on their own reduction peak potentials. The regenerated cofactors subsequently delivered hydrides to OYE for stereoselective conversions of a broad range of substrates with excellent biocatalytic efficiencies.

Highly fluorescent N-doped carbon nanodots as an effective multi-probe quenching system for the determination of nitrite, nitrate and ferric ions in food matrices

Tris-(hydroxymethyl)-aminomethane and urea were used as low-cost precursor compounds to synthesize highly fluorescent N-doped carbon nanodots (CNDs), in an environmentally-friendly, inexpensive process. The as-prepared CNDs exhibit blue fluorescence, excellent photostability under various conditions, water dispersibility and stability over several parameters, such as a wide range of pH. The N-doped CNDs were applied as a multi-probe fluorescence quenching system to the sensitive detection of nitrite (NO2−), nitrate (NO3−) and ferric (Fe3+) ions in food matrices. The recoveries from spiked food samples were fairly acceptable without significant interferences despite the complexity of the tested matrices. The decrease in fluorescence intensity is in linear relationship with the concentrations of NO2−, NO3− and Fe3+, in the ranges of 0.015–1.11 mM, 0.072–0.60 mM and 2.9–176 μΜ, respectively. The as-synthesized carbon dots were used for the detection of NO2−, NO3− and Fe3+ in food matrices after proper pretreatment, concluding that the multi-probe fluorescence system may potentially be implemented in food control. The FRET mechanism is able to describe the quenching of the CNDs-NO2− system, while the proportional temperature-dependent relationship with the slopes of calibration plots hint at a dynamic quenching mechanism. In the case of the CNDs-Fe3+ system, the slopes exhibit an inverse temperature dependence, indicating a static mechanism while there is no indication of a FRET mechanism.

Light-Powered Nanoconverters Cytotoxic to Breast Cancer Cells

We designed and fabricated a light-powered nanoconverter for cytotoxicity toward human breast cancer cells. The nanoconverter was made from highly-fluorescent N-doped carbon nanodots (C-dots), which were covalently conjugated to semiconductive hematite quantum dots (Q-dots). The function of the nanoconverter was to transform the absorbed near-infrared (NIR) irradiation into reactive oxygen species (ROS) which would induce cell death. The principle of operation was based on the photosensitizing properties of C-dots, which have a two-photon absorption cross section. They absorbed NIR irradiation with wavelength in the range of 700–800 nm. The adsorbed energy was upconverted to photoluminescence that is emitted as higher-energy visible light with a maximum wavelength of ∼470 nm and transferred to the Q-dot moiety. The process was accompanied by ejection of electrons from the conduction band of Q-dots and by this mechanism, the nanoconverter produced aqueous superoxide anions, which oxidized organics and generated additional ROS. Our nanoconverter exposed in vitro to cultured human breast cancer HCC1954 cells induced light-dependent cell death as measured using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. The cell death was minimal when the cells were exposed with C-dots alone or if the nanoconverter was exposed with the cells in dark.

Tracking Hyaluronan: Molecularly Imprinted Polymer Coated Carbon Dots for Cancer Cell Targeting and Imaging.

War against cancer constantly requires new affinity tools to selectively detect, localize, and quantify biomarkers for diagnosis or prognosis. Herein, carbon nanodots (CDs), an emerging class of fluorescent nanomaterials, coupled with molecularly imprinted polymers (MIPs), are employed as a biocompatible optical imaging tool for probing cancer biomarkers. First, N-doped CDs were prepared by hydrothermal synthesis using starch as carbon source and l-tryptophan as nitrogen atom provider to achieve a high quantum yield of 25.1 ± 2%. The CDs have a typical size of ∼3.2 nm and produce an intense fluorescence at 450 nm upon excitation with UV light. A MIP shell for specific recognition of glucuronic acid (GlcA) was then synthesized around the CDs, using the emission of the CDs as an internal light source for photopolymerization. GlcA is a substructure (epitope) of hyaluronan, a biomarker for certain cancers. The biotargeting and bioimaging of hyaluronan on fixated human cervical cancer cells using CD core-MIP shell nanocomposites is demonstrated. Human keratinocytes were used as noncancerous reference cells and indeed, less staining was observed by the CD-MIP.