N-doped Carbon Quantum Dots Research Articles

Green synthesis of fluorescent N-doped carbon quantum dots from castor seeds and their applications in cell imaging and pH sensing

AbstractWater-soluble fluorescent N-doped carbon quantum dots (N-CQDs) were hydrothermally prepared through a green synthesis route using castor seeds as a single precursor and a hydrothermal method. Several experimental techniques have been used to characterize synthesized N-CQDs to confirm their structure and to verify their applicability in cell imaging and pH sensing. The synthesized N-CQDs were found to have are characterized by amorphous nature with a spherical shape with an average particle size of 6.57 nm as revealed from XRD and TEM measurements. The FTIR results reveal the presence of carboxylic and hydroxyl functional groups on the surface of the CQDs, which was also confirmed by XPS analysis. The fluorescence characterization of the synthesized N-CQDs showed blue emission and excitation dependence with good photostability. It was found that the optimal excitation and emission wavelengths were (λEx = 360) and (λEm = 432) nm, respectively. The fluorescence quantum yield (QY) of about 9.6% at the optimum excitation wavelength 360 nm. Moreover, the fluorescence intensity of N-CQDs showed good linear dependence with the pH values in ranges of 3.5 − 7.5 and 8 − 12 as well as high sensitivity for slight changes of pH values. According to these results, two fluorescent pH sensors were created based on acidic and basic media. The obtained N-CQDs have zeta potential of -21.86 mV and thus have excellent stability in water. Moreover, N-CQDs derived from the castor seeds have antimicrobial activity and exhibits low cytotoxicity to WI-13 cells with IC50 = 394.4 ± 13.8 µg/mL. The results of this study demonstrated that the synthesized N-CQDs derived from castor seeds can be used as pH sensing and antimicrobial materials. On the other hand, they are also promising in applications in cell imaging, thermo-sensing and optoelectronics.

Preparation and performance of self-cleaning synergistic visible light catalytic coatings based on N-CQDs/Bi2WO6 for NO degradation

Due to the intensification of nitric oxide (NO) emissions caused by industrial development, visible light responsive photocatalysts have been selected and applied in building coatings as a new strategy. In this study, N-doped carbon quantum dots (N-CQDs)-Bi2WO6 (NBW) was prepared using an ethylene glycol-assisted solvothermal method. Various techniques, including XRD, FT-IR, SEM, were employed to analyze and characterize NBW. The photocatalytic performance and stability of NBW were evaluated, and the results showed that 52% of NO (Initial concentration: 600 ppb) were oxidized under visible light. NBW was dispersed in an ethyl acetate/polytetrafluoroethylene (PTFE)/polyvinylidene fluoride (PVDF) suspension and modified by 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (PFDTES), to form an easy-to-spray coating referred to as CPFB. Due to the photocatalytic ability of NBW, CPFB oxidized 74% of NO under visible light and reduced the coloring of coating surfaces contaminated with methyl red. The superhydrophobicity of CPFB coating provided the foundation for its self-cleaning ability. In addition, CPFB exhibited hydrophobicity and photocatalytic performance even after tests such as photooxidation, water impact, and wear. Finally, the photocatalytic mechanism of CPFB self-cleaning coating was explored. The significance of CPFB lied in its ability to effectively combine self-cleaning, visible light-responsive photocatalysis, and durability in a single coating. This innovative approach may inspire the development of similar coatings for various applications.

In Vivo Monitoring of GABA by N-Doped Carbon Quantum Dots

<i>In Vivo</i> Monitoring of GABA by N-Doped Carbon Quantum Dots

Synthesis and multifunctional application of two novel carbon quantum dots as corrosion inhibitors

N, S- and N-doped carbon quantum dots (CDs) were synthesized by calcination in the presence of L-cysteine and 2-aminobutyric acid by using P-phenylenediamine as the raw material. The CDs were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and fluorescence spectroscopy. Results show that both kinds of CDs have spherical structures and particle sizes. The CDs were dispersed in 3.5 wt% NaCl solution and doped into the epoxy coating to prepare the composite coating. The two kinds of CDs have good corrosion inhibition effects in both applications.

Nitrogen-doped carbon quantum dots as antimicrobial agents against gram-positive Bacillus subtilis and Staphylococcus aureus under visible white light-emitting diode

Carbon nanomaterials, such as carbon quantum dots (CQDs), are excellent candidates for antibacterial agent development as they are cost-effective. Nitrogen-doped CQDs (N-doped CQDs) exhibit antibacterial activity against gram-positive bacteria. However, investigation of N-CQDs and their efficacy against the selected bacterial strains under visible light irradiation has not been carried out. Here, we aimed to evaluate N-CQDs for their efficacy as a photosensitizer for antimicrobial photodynamic therapy (aPDT). N-CQDs were synthesized using the hydrothermal method with 1,3,6-trinitropyrene (TNP) as the nitrogen and carbon source. Antimicrobial tests of N-CQDs were conducted against gram-positive (Bacillus subtilis NCIB 3610, Staphylococcus aureus Newman, and S. aureus USA300) and gram-negative (Escherichia coli K12) bacteria at different concentrations (0–100 mg/L). The N-CQDs exerted a moderate growth-inhibitory effect on gram-positive bacteria in the dark. However, in the presence of white light generated using 20-W light-emitting diode, N-CQDs could completely kill the bacteria at a low concentration of 20 mg/L. The minimal inhibitory concentration of N-CQDs for the two S. aureus strains (Newman and USA300) was 20 mg/L under light conditions, whereas that for B. subtilis was 100 mg/L. The results demonstrate that N-CQDs may be used as a photosensitizer in aPDT and as an antibacterial agent.

Visual tracking of real-time freshness of fish using an agar hydrogel colorimetric indicator containing CuNPs/NCQDs

A simple, selective, and affordable dual fluorescence-colorimetric indicator for hydrogen sulfide was developed based on a complex of copper nanoparticles and N-doped carbon quantum dots (CuNPs/NCQDs). Real-time and visual freshness tracking of fish was done using a colorimetric indicator by incorporating CuNPs/NCQDs into agar hydrogel (AH-CuNPs/NCQDs). The fluorescence response of the CuNPs/NCQDs solution is quenched upon exposure to H2S. The field-emission scanning electron microscopy image of the AH-CuNPs/NCQDs film revealed a unified structure. The prepared indicator exhibited a good and irreversible response to H2S, with a LOD of 91.36 and a LOQ of 276.86 μM, based on the localized surface plasmon resonance (LSPR) mechanism. The X-ray photoelectron spectrometer and Fourier transform infrared spectrometer results confirmed the formation of a CuS bond in the colorimetric indicator exposed to fish spoilage. The prepared indicator demonstrated good stability and remained unaffected by pH or other volatile compounds. Notably, there was a strong correlation between ΔΕ and fish freshness parameters (pH, TV-BN, and TVC). Light green, pale yellow, and dark yellow colors, respectively, indicated freshness, semi-freshness, and spoilage of fish during storage in the refrigerator. Overall, the prepared indicator can be effectively used for detecting spoilage in meat products as a highly sensitive freshness indicator.

Stagnant liquid layer as “Microreaction System” in submerged plasma Micro-Jet for formation of carbon quantum dots

This study aims to intensify reactivity via bespoke transient hydrodynamics in a plasma-activated three-phase catalyst system. Likewise, three-phase plasma systems in literature are not well designed, understood and commercially available. The synthesised N-doped carbon quantum dots, with application as fertilisers and wastewater treatment was evaluated as a model reaction. A plasma microjet was produced using a commercial plasma system, creating an almost flat, large interface covering a thin stagnant liquid layer with a catalyst bed underneath. In this hydrodynamic regime, plasma can penetrate the catalyst bed via the stagnant thin liquid film and polarise the plasma-liquid interface. The new process regime’s effectiveness is proven by the enhanced reaction rate achieved by raising liquid diffusivity toward the catalyst bed through solvent viscosity reduction. Results indicate that the reaction rate depends on the small surface area interacted with the plasma jet amid an excess of excited species, not the total gas–liquid interface area. The plasma process competes energetically with the best dielectric barrier discharge processes and uses less energy than microfluidic processing in chemical microreactors. High momentum transfer from the plasma jet to the liquid partly evaporates non-water additives, impacting process design and requiring reduction.

L-cysteine modified N-doped carbon quantum dots derived from peach palm (Bactris gasipaes) peels for detection of mercury ions

Establishing an effective strategy for Hg2+ determination with good sensitivity and high selectivity is of particular concern. In this work, N-doped carbon quantum dots (NCQDs) were obtained for the first time from peels of peach palm fruit (Bactris gasipaes) through microwave-assisted one-pot synthesis. Surface NCQDs was modified with l-cysteine (NCQDs/CYS) by a chemical reaction (known as amide coupling) between the nitrogen-containing groups (amine group) of l-cysteine ligand and the carboxyl groups of NCQDs. The chemical bonding was examined by Fourier Transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). NCQDs/CYS nanoparticles exhibited a quantum yield of fluorescence (ΦFL) of 25.4%, high solubility in water, and a surface with thiol groups from l-cysteine. Mercury ions induced quenching of fluorescence of NCQDs/CYS at low concentrations (Limit of Detection, LOD = 0.19 μM) with great sensitivity. A significant preference for Hg2+ ions was found because of the high affinity between the thiolate groups of NCQDs/CYS and the analyte. Time-resolved fluorescence measurements were done to study the way that led to fluorescence quenching when Hg2+ ions were present, evidencing a static quenching fluorescence mechanism. The new NCQDs/CYS material could be applied to accurately measure the concentration of Hg2+ ions in water samples in a fast and cost-effective way.

One-step hydrothermal synthesis of Pt and N-doped carbon quantum dots co-activated as novel electrocatalysts for oxygen reduction reaction

Abstract In this paper, a novel nano-electrocatalyst (Pt@N-CDs/RGO) with reduced graphene oxide as the carrier and platinum (Pt) and nitrogen-doped carbon quantum dots (N-CDs) together as the active sites was prepared by a simple hydrothermal method. By comparing the electrochemical properties of commercial platinum carbon (Pt/C) and Pt@N-CDs/RGO at 20% wt Pt, it was found that Pt@N-CDs/RGO exhibited excellent ORR properties, such as an onset potential (Eonest ) of 1.10 V, a half-wave potential (E1/2) of 0.82 V, a limiting current density of 5.06 mA/cm2, and a number of transferred electrons as high as 3.97. By using the chronoamperometric method (CA) to cycle for 10000 s, it was found that the stability of both, Pt@N-CDs /RGO maintains 18% activity after a cycle of 10000 seconds, which is much higher than Pt/C. The study showcased a new efficient and durable catalyst for PEMFCs.

Indocyanine green-loaded N-doped carbon quantum dot nanoparticles for effective photodynamic therapy and cell imaging of melanoma cancer: in vitro, ex vivo and in vivo study

Background Indocyanine Green (ICG) as an agent for photodynamic therapy (PDT) of melanoma cancer has low quantum yield, short circulation half-life, poor photo-stability, and tendency to aggregation. Purpose N-doped carbon quantum dot (CQD) nanoparticle was applied to encapsulate ICG and overcome ICG obstacle in PDT with simultaneous cell imaging property. Methods CQD was prepared using hydrothermal method. Cell culture study and In vivo assessments on C57BL/6 mice containing melanoma cancer cells was performed. Results Results showed that CQD size slightly enhanced from 24.55 nm to 42.67 nm after ICG loading. Detection of reactive oxygen species (ROS) demonstrated that CQD improved ICG photo-stability and ROS generation capacity upon laser irradiation. Cell culture study illustrated that ICG@CQD could decrease survival rate of melanoma cancer cells of B16F10 cell line from 48% for pure ICG to 28% for ICG@CQD. Confocal microscopy images approved more cellular uptake and more qualified cell imaging ability of ICG@CQD. In vivo assessments displayed obvious inhibitory effect of tumor growth for ICG@CQD in comparison to free ICG on the C57BL/6 mice. In vivo fluorescence images confirmed that ICG@CQD accumulates remarkably more than free ICG in tumor region. Finally, ICG@CQD was proposed as an innovative nanocarrier for PDT and diagnosis.

Optimizing humic acid breakdown and methane production via semiconductor-assisted photo-anaerobic digestion

Humic acids (HAs), whether naturally present in anaerobic digestion (AD) substrates or HAs newly formed during fermentation, can become inhibitory to methanogenesis as their concentrations reach certain levels. This study delved extensively into the mechanism underlying the alleviation of HAs inhibition in photo-AD by N-doped carbon quantum dots (NCQDs). These NCQDs were efficiently synthesized from straw using an environmentally friendly pretreatment method. Our proposed method harnessed the combined effect of light exposure and NCQDs, resulting in synergistic enhancement of the cumulative CH4 yield within the HA-inhibited AD system, achieving a remarkable yield of 293.7 ± 17.7 mL/g VS. In-depth analyses were conducted on the remaining dissolved organic matter (DOM) within digesters using 3D-EEM and ESI FT-ICR MS. Simultaneously, the remaining HAs were extracted and subjected to FT-IR analysis. The findings revealed that NCQDs effectively degraded humic acid-like components in DOM into smaller, more manageable micromolecules characterized by lower carbon numbers and reduced double bond equivalent. Additionally, under the influence of light, NCQDs promoted the degradation of aromatic components within HAs. These resulting micromolecules were made readily available for utilization by microorganisms, further contributing to methanogenesis. Furthermore, photoelectrochemical analysis and specific gene qPCR analysis revealed that the photoelectrons from NCQDs and HAs were received and transferred by Ech (electron acceptors) for methanogenesis. Remarkably, this methanogenesis pathway, akin to photosynthesis, played a pivotal and transformative role in the photo-AD system. This work comprehensively revealed the remarkable potential mechanism of semiconductors within the photo-AD system, offering profound insights that can catalyze the development of innovative AD reactors and semiconductor accelerators.

Stimulus-responsive room-temperature phosphorescence with tunable color for time-resolved advanced dynamic anti-counterfeiting

Multi-stimuli responsive multicolored room-temperature phosphorescent (RTP) carbon quantum dots (CQDs) have recently attracted considerable attention, owing to their potential applications in advanced dynamic anti-counterfeiting. The design and development of carbon dots that exhibit both stimulus response characteristics and multicolor RTP emission remains a significant challenge in the field. In this work, we present a novel approach to control the dynamic phosphorescence color and stimulus response properties of CQDs coated on paper by fine-tuning the surface functional groups of the CQDs. Specifically, histidine and 2,4,6-triaminopyrimidine was separately used to prepare N, O co-doped CQDs (NOCQDs) and N-doped CQDs (NCQDs), respectively. These CQDs were further coated on filter paper substrates to achieve water and heating cascade stimulus–response RTP. These stimuli-responsive properties of NOCQDs can be modulated by deprotonating their surface oxygen-containing groups. Eventually, we achieved time-resolved multicolor dynamic anti-counterfeiting by exploiting the stimuli-response properties and lifetimes differences between NOCQDs and NCQDs, realizing the 5D information encryption in all five stimulus-, pattern-, time-, and color-dependent codes. These findings highlight the potential of NOCQDs as advanced anti-counterfeiting materials and lay a foundation for further exploration into the synthesis and properties of CQDs with tunable stimuli-response features and RTP emission.

Green one-step synthesis of N-doped carbon quantum dots for fluorescent detection of lemon yellow in soft drinks

A new fluorescent sensor for the determination of lemon yellow was developed based on nitrogen-doped carbon quantum dots (N-CQDs), which were prepared via a hydrothermal method with dried pomelo peel and L-tyrosine. The N-CQDs exhibited the blue fluorescence with a quantum yield of 28 %. The sensing principle of N-CQDs was quenched by lemon yellow via static quenching. The potential interfering substances showed no influence on the detection of lemon yellow. The limit of detection was 0.023 mg/L and lower than that of national standard. Furthermore, the synthesized N-CQDs have been successfully applied to the measurement of lemon yellow in real samples. Hence, the N-CQDs would be a promising sensor in food analysis.

Preparation of n-doped carbon quantum dots for the detection of PA in real explosion dust samples

Nitrogen doping carbon quantum dots (N-CQDs) are synthesized using o-phenylenediamine as a carbon and nitrogen source via the water hydrothermal method. The size of the obtained N-CQDs is about 5.51 nm, and FTIR results show that their surface contains many –OH and –NH2 groups. N-CQDs can selectively recognize PA and its homologous (DNP and NP) in the presence of other analytes (including TNT, Tetryl, PETN, RDX, HMX, NC, NG, DNT, NT, NB, DNP, NP, BP, PC, AN, Ca2+, Cl-, Mg2+, Na+, H2O2). A linear correlation is also observed between PA concentration (0 ∼ 10.0 μmol/L) and N-CQDs fluorescence intensity (0.05 mg/mL) at 556 nm. The linear curve is y = -3.64 × 107x + 404.91, and the detection limit is ∼ 70 nmol/L. The Stern-Volmer graphs lack sufficient linearity, confirming the static quenching interaction between N-CQDs and PA. Finally, the N-CQDs are successfully applied to determine PA content in simulated and real samples quantitatively.

Development of a pH-responsive ratiometric fluoroprobe based on GSH-CuNCs-Ce3+ and N-CQDs for rapid/sensitive malathion detection in fruit juices

Herein, we engineered a novel pH-responsive ratiometric assay by virtue of the composite system of Ce3+-enhanced glutathione-encapsulated copper nanoclusters (GSH-CuNCs-Ce3+) and N-doped carbon quantum dots (N-CQDs). The GSH-CuNCs-Ce3+ and N-CQDs were fabricated using one-pot chemical reduction and hydrothermal approaches, respectively, and their morphologies as well as physical and chemical properties were testified in detail by a series of characterization techniques. At 350 nm excitation wavelength, the GSH-CuNCs-Ce3+/N-CQDs system (GCC-NC) featured the 440/650 nm dual-emitting property. The ratios of fluorescence intensities (F650/F440) demonstrated a strong pH-dependence from 3.0 to 5.0 with a coefficient of determination of 0.9982. Consequently, the GCC-NC system was feasible for constructing a pH-responsive dual-emitting fluoroprobe. Based on the catalytic effect of acetylcholinesterase on acetylcholine to yield acetic acid and further trigger varying solution pH, the as-constructed GCC-NC fluoroprobe was satisfactorily applied for detecting malathion. Under optimized conditions, the newly developed GCC-NC fluoroprobe supplied a wider linear range (0.25–200 μM), lower detection limit (0.075 μM), satisfactory recoveries (96.3–106.2%) and higher precision for malathion in several kinds of fruit juice samples. The fortified experiments by malathion’s structural analogues and metal ions provided compelling evidence that this fluoroprobe had strong anti-interference capacity and high specificity for malathion. These findings render us to believe that the as-constructed pH-responsive dual-emitting fluoroprobe holds great promise in trace malathion assay in food matrices.

Engineering Nitrogen-Doped Carbon Quantum Dots: Tailoring Optical and Chemical Properties through Selection of Nitrogen Precursors.

The process of N-doping is frequently employed to enhance the properties of carbon quantum dots. However, the precise requirements for nitrogen precursors in producing high-quality N-doped carbon quantum dots (NCQDs) remain undefined. This research systematically examines the influence of various nitrogen dopants on the morphology, optical features, and band structure of NCQDs. The dots are synthesized using an efficient, eco- friendly, and rapid continuous hydrothermal flow technique. This method offers unparalleled control over synthesis and doping, while also eliminating convention-related issues. Citric acid is used as the carbon source, and urea, trizma base, beta-alanine, L-arginine, and EDTA are used as nitrogen sources. Notably, urea and trizma produced NCQDs with excitation-independent fluorescence, high quantum yields (up to 40%), and uniform dots with narrow particle size distributions. Density functional theory (DFT) and time-dependent DFT modelling established that defects and substituents within the graphitic structure have a more significant impact on the NCQDs' electronic structure than nitrogen-containing functional groups. Importantly, for the first time, this work demonstrates that the conventional approach of modelling single-layer structures is insufficient, but two layers suffice for replicating experimental data. This study, therefore, provides essential guidance on the selection of nitrogen precursors for NCQD customization for diverse applications.

DFT, real sample and smartphone studies of fluorescent probe, N-doped carbon quantum dots for sensitive and selective detection of bilirubin

In this investigation, nitrogen-doped carbon quantum dots (NCQDs) were successfully synthesized, showcasing robust fluorescence characteristics and photostability. These NCQDs demonstrated biocompatibility and were utilized as effective sensing agents for bilirubin (BR) detection. Their remarkable Stern-Volmer constant, attributed to exceptional molar absorptivity and photoluminescence quantum yield, rendered them highly proficient in BR sensing. Various analytical techniques such as X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the synthesized NCQDs, providing comprehensive insights into their structural, elemental, chemical composition, particle size, morphology, and optical properties. For sensing purposes, UV–Vis, steady-state, and time-resolved fluorescence spectroscopic techniques were utilized. The average particle size of the NCQDs was determined to be approximately 4.5 ± 0.3 nm. Notably, the Stern-Volmer constant (Ksv) for BR sensing from these quantum dots surpassed previously reported values in the literature. A linear relationship between emission intensity ratio and BR concentration within a range of 1.35–14.20 μM was observed. Accurate quantification of BR was achieved with a high Stern-Volmer constant (Ksv) S11 of approximately 7.48 × 105 M-1 and a limit of detection (LOD) of 4.86 μM. Leveraging the NCQDs as fluorescent probes, a highly sensitive and selective BR detection method based on the Förster resonance energy transfer (FRET) mechanism was established, with emission occurring at 360 nm. Density functional theory (DFT) studies supported FRET as the primary mechanism for fluorescence quenching, indicating electron transfer from NCQDs to BR, as evidenced by the energies of the lowest unoccupied molecular orbitals (LUMOs) of both NCQDs and BR. Real sample analyses of BR levels in human serum yielded a recovery range of 94.8 % to 104.21 %, validating the practical applicability of the method. Furthermore, smartphone-based BR detection using NCQDs achieved an LOD of 11.74 µM.

N-doped carbon quantum dots obtained from citric acid and L-phenylalanine

Hydrophobic N-doped carbon quantum dots (N-CQDs) were prepared using citric acid and L-phenylalanine through hydrothermal synthesis at optimum conditions (temperature T = 200 °C and time t = 9 h) and thoroughly investigated with different techniques. In organic solvents (ethanol, chloroform, dimethyl formamide, and xylene) under 350 nm excitation wavelength, N-CQDs exhibit intensive blue photoluminescence (PL) with the quantum yield equal to 36.5 %. Being embedded into polymer matrices (poly(methyl methacrylate) and epoxy resin), N-CQDs preserved their high PL.

The Impact of N-Doped Carbon Quantum Dots on Dye-Sensitized Solar Cells Operating Under Diffused- and Low-Light Intensity

The Impact of N-Doped Carbon Quantum Dots on Dye-Sensitized Solar Cells Operating Under Diffused- and Low-Light Intensity

Crystal-phase engineering of BiVO4 induced by N-doped carbon quantum dots for photocatalytic application

Crystal-phase engineering of BiVO4 induced by N-doped carbon quantum dots for photocatalytic application