Green-emitting Carbon Research Articles

Integrating sol-gel and carbon dots chemistry for the fabrication of fluorescent hybrid organic-inorganic films

Highly fluorescent blue and green-emitting carbon dots have been designed to be integrated into sol-gel processing of hybrid organic-inorganic materials through surface modification with an organosilane, 3-(aminopropyl)triethoxysilane (APTES). The carbon dots have been synthesised using citric acid and urea as precursors; the intense fluorescence exhibited by the nanoparticles, among the highest reported in the scientific literature, has been stabilised against quenching by APTES. When the modification is carried out in an aqueous solution, it leads to the formation of silica around the C-dots and an increase of luminescence, but also to the formation of large clusters which do not allow the deposition of optically transparent films. On the contrary, when the C-dots are modified in ethanol, the APTES improves the stability in the precursor sol even if any passivating thin silica shell does not form. Hybrid films containing APTES-functionalized C-dots are transparent with no traces of C-dots aggregation and show an intense luminescence in the blue and green range.

Self-Enhanced Carbonized Polymer Dots for Selective Visualization of Lysosomes and Real-Time Apoptosis Monitoring.

SummaryProtons are highly related to cell viability during physiological and pathological processes. Developing new probes to monitor the pH variation could be extremely helpful to understand the viability of cells and the cell death study. Carbonized polymer dots (CPDs) are superior biocompatible and have been widely applied in bioimaging field. Herein, a new type of extreme-pH suitable CPDs was prepared from citric acid and o-phenylenediamine (CA/oPD-CPDs). Due to the co-existence of hydrophilic and hydrophobic groups, CA/oPD-CPDs tend to aggregate in neutral condition with a dramatic decrease of fluorescence, but disperse well in both acidic and alkaline conditions with brighter emission. This specialty enables them to selectively illuminate lysosomes in cells. Moreover, CA/oPD-CPDs in the cytoplasm could serve as a sustained probe to record intracellular pH variation during apoptosis. Furthermore, CA/oPD-CPDs present a continuous fluorescence increase upon 2-h laser irradiation in living cells, underscoring this imaging system for long-term biological recording.

Green and Orange Emissive Carbon Dots with High Quantum Yields Dispersed in Matrices for Phosphor-Based White LEDs

Carbon dots (CDs) have aroused more interest in the LED phosphor. High quantum yields and suppressing solid-state luminescence quenching are the key factors for CDs to prepare high-quality phosphor...

One-step synthesis of green emission carbon dots for selective and sensitive detection of nitrite ions and cellular imaging application

In recent years, carbon dot (CD)-based fluorescent sensors for selective ions or small biomolecules have drawn great attention. In this work, highly fluorescent CDs (QY = 21%) were prepared from 2,3-diamino pyridine as the precursor through a facile solvothermal process. The CDs showed high stability and a green emission in aqueous, and the optimal emission wavelength of CDs is 508 nm under the excitation wavelength of 438 nm. Interestingly, a CDs-based nanoprobe was developed for a selective and sensitive fluorescence quenching response to NO2− in water, and the quenching mechanism was investigated in the work. Besides, the recovery rates of NO2− in the range of 98–103.5% were found to be acceptable, indicating that the proposed CDs could be act as potential candidates for determination of nitrite ions in real samples. Meanwhile, the nanoprobe was also successfully employed in a visualization biosensing platform for determination of NO2− in living cells due to its eminent biocompatibility.

Synthesis of green-emitting carbon quantum dots with double carbon sources and their application as a fluorescent probe for selective detection of Cu2+ ions.

Green-emitting carbon quantum dots (G-CQDs) were prepared using tartaric acid and bran by one-pot solvothermal treatment and had photoluminescence quantum yields (PL QY) as high as 46%. The morphology of the G-CQDs is characterized by TEM, which shows the average diameter of G-CQDs is approximately ∼4.85 nm. The FT-IR spectra display the presence of –OH, C–N, N–H and –COOH on the surface of the G-CQDs. The emission wavelength of the G-CQDs was ∼539 nm in the case of ∼450 nm excitation wavelength, which corresponds to the green fluorescence. Furthermore, the G-CQDs were used as a fluorescent probe for detection Cu2+ ions, and demonstrated a linear distribution between ln(F/F0) and the Cu2+ ions concentration. Specifically, the Cu2+ ion concentration should fall in the G-CQD concentration range of 0–0.5 mM and the detection limit is 0.0507 μM. Thus, due to the excellent chemical stability and good luminescence performance, these G-CQDs could be excellent probes widely used in detection fields.

Biomass-derived Carbon Quantum Dots for Visible-Light-Induced Photocatalysis and Label-Free Detection of Fe(III) and Ascorbic acid

Visible-light-driven photocatalysts prepared using renewable resources are crucial but challenging to develop for the efficient degradation of organic pollutants, which is required to solve ever-increasing water deterioration issues. In this study, we report a visible-light-responsive photocatalyst for the efficient degradation of methylene blue (MB) as a model pollutant dye. Green-emissive carbon quantum dots (CQDs) were synthesized from pear juice via a facile, scalable, one-pot solvothermal process. The as-synthesized CQDs exhibit superior photocatalytic activity under visible-light irradiation owing to their efficient light absorption, electron transfer, and separation of photogenerated charge carriers, facilitating ~99.5% degradation of MB within 130 min. A possible mechanism for the photocatalysis is proposed on the basis of comprehensive active species trapping experiments. Furthermore, the CQDs were used in a specific sensitive assay for Fe(III) and ascorbic acid (AA), even with interference from other metal ions. The fluorescence emission of CQDs was “turned off” specifically upon binding of Fe(III) and “turned on” with AA. The prepared CQDs represent efficient photocatalysts and fluorescent probes that are not restricted by toxicity, cost, or lack of scalability.

Facile Preparation of Boron and Nitrogen Codoped Green Emission Carbon Quantum Dots for Detection of Permanganate and Captopril.

A hydrothermal strategy for preparing boron and nitrogen codoped carbon quantum dots was studied using the precursors of p-amino salicylic acid, boric acid and ethylene glycol dimethacrylate. The boron and nitrogen codoped carbon quantum dots have high fluorescence intensity, good monodispersity, high stability, superior water solubility, and a fluorescence quantum yield of 19.6%. Their average size is 5 nm. Their maximum excitation and emission wavelengths are 380 and 520 nm, respectively. Permanganate (MnO4-) quenched boron and nitrogen codoped carbon quantum dots fluorescence through inner filter effect and static quenching effects. The linear relation between quenching efficiency and MnO4- concentration ranged from 0.05 to 60 μmol/L with a detection limit of 13 nmol/L. In the presence of captopril, MnO4- was reduced to Mn2+ and the fluorescence of boron and nitrogen codoped carbon quantum dots was recovered. The linear range between recovery and captopril concentration was from 0.1 to 60 μmol/L. The limit of detection was 0.03 μmol/L. The developed method can be employed as a sensitive fluorescence sensing platform for MnO4-. It has been successfully used for captopril detection in mouse plasma.

Synthesis of green emissive carbon dots@montmorillonite composites and their application for fabrication of light-emitting diodes and latent fingerprints markers

Multifunctional solid-state luminescent materials are strongly desired in a wide variety of applications. In this work, green emissive carbon dots@montmorillonite (g-CDs@MMT) composites were synthesized based on green emissive carbon dots and MMT clays in a convenient method by embedding g-CDs into the MMT clays. Due to the confinement of g-CDs in the layered structure of the MMT clay matrix, g-CDs are uniformly dispersed in the resulting g-CDs@MMT solid-state composites. This efficiently prevents the aggregation-induced solid-state luminescence quenching of g-CDs, and a photoluminescence quantum yield of 11% could be achieved by the g-CDs@MMT composites under a 405 nm light. Additionally, the g-CDs@MMT composites exhibit low-toxicity, excellent thermal stability, photostability, resistance to organic solvents, and a small particle size. All of these advantages enable applications in fabricating white light-emitting diodes with different color temperatures, where the g-CDs@MMT composites are applied as the color conversion layer. Furthermore, by using the g-CDs@MMT composites as a fluorescence labeling marker, the latent fingerprint detection on a variety of object surfaces could be realized.

Strong acid-assisted preparation of green-emissive carbon dots for fluorometric imaging of pH variation in living cells.

New green-emissive carbon dots (G-CDs) are described here and shown to be viable fluorescent nanoprobes for the detection of changes in cellular pH values. By using m-phenylenediamine as the carbon source, G-CDs with an absolute quantum yield of 36% were solvothermally synthesized in the presence of strong H2SO4. The G-CDs have an average size of 2.3nm and display strong fluorescence with excitation/emission peaks at 450/510nm. The fluorescence intensity depends on the pH value in the range from 6.0 to 10.0, affording the capability for sensitive detection of intracellular pH variation. The nanosensor with excellent photostability exhibited good fluorescence reversibility in different pH solutions, and showed excellent stability against the influence of other biological species. The nanoprobe was successfully used in confocal fluorescence microscopy to determine pH values in SMMC-7721 cells. Graphical abstract Schematic presentation of green-emissive carbon dots (G-CDs)synthesized using m-phenylenediamine and sufuric acid through a solvothermal method for real-timefluorometric monitoring ofintracellular pH values. Mechanism can be ascribed to PET process from the electron lone pair in amino group to the CDs.

2,4-Dinitrobenzenesulfonate-functionalized carbon dots as a turn-on fluorescent probe for imaging of biothiols in living cells.

The authors describe a carbon dot-based fluorescent probe for biothiols. Green emissive carbon dots (g-CDs; with λex/λem maxima of 407/505nm) were synthesized by a one-step solvothermal method starting from 3-diethylaminophenol. They were then covalently functionalized with 2,4-dinitrobenzenesulfonyl chloride to afford 2,4-Dinitrobenzenesulfonate-functionalized CDs (g-CD-DNBS) as a nanoprobe for biothiols. The fluorescence of the g-CD-DNBS is quite weak. Upon addition of biothiols, the DNBS group of the probe is removed by thiol groups. This results in gradual restoration of the green fluorescence. The nanoprobe exhibits high selectivity for biothiols over other amino acids and biological molecules. The detection limits for cysteine, homocysteine and glutathione are 69, 74 and 69nM (S/N = 3), respectively. The probe was applied to image biothiols in SMMC-7721 cells. Graphical abstract Schematic presentation of the mechanism of 2,4-dinitrobenzenesulfonate-functionalized carbon dots (g-CD-DNBS) for the detection of biothiols. g-CDs: green emissive carbon dots.

N-doped carbon dots with tunable emission for multifaceted application: solvatochromism, moisture sensing, pH sensing, and solid state multicolor lighting

Novel N-doped green-emitting carbon dots (N-GCDs) that were responsive to various external stimuli and had high quantum yields (QYs) for multifaceted applications were synthesized from β-resorcylic acid and ethylenediamine using a hydrothermal process followed by a reflux method. The QYs of the N-GCDs were in the range of 17.36%–48.4% and were associated with different photoluminescent color emission in different solvents. Interestingly, the as-synthesized N-GCDs exhibited strict solvent polarity-dependent switchability (solvatochromism) and multicolor excitation-wavelength-independent emission in different solvents. Sensing of an analyte based on the switching of the photoluminescence (PL) emission maxima (λmax) is always preferred over that based on fluorescence quenching to avoid complexity and confusion regarding the initial fluorescence intensity (I0) and thus make the sensing process simple, rapid, ordered, and reliable. The N-GCDs exhibited blue emission in low-polarity organic solvents, but with the increase of the trace water content in the system, the PL emission peak gradually shifted to a higher wavelength (bathochromic shift) at a single-wavelength excitation. Thus, the N-GCDs are sensitive visual probes for the fluorescence detection of the trace water content in organic solvents without sophisticated processes. They also indicate the pH-response behavior. When the pH decreased from 7.6 to 2.4, the fluorescence emission intensity decreased, with a particularly good linear relationship (R2 = 0.990) in the range of 3.8–6.2. Moreover, the polarity-dependent-emission property was observed in the solid state polymer matrices. Multicolor-emissive N-GCD/polymer films were prepared by integrating N-GCDs with the polymer matrices of different polarity, demonstrating the application of carbon dots for solid-state lighting.

Synthesis of carbon dots with a tunable photoluminescence and their applications for the detection of acetone and hydrogen peroxide

Carbon dots (CDs) with multi-color emissive properties and a high photoluminescent quantum yield (PLQY) have attracted great attention recently due to their potential applications in chemical, environmental, biological and photo-electronic fields. Solvent-dependent effect in photoluminescence provides a facial and effective approach to tune the emission of CDs. In this study, green emissive nitrogen-doped carbon dots (N-CDs) are synthesized from p-hydroquinone and ethylenediamine through a simple hydrothermal method. The as-prepared N-CDs possess a robust excitation-independent green luminescence and a high PLQY of up to 15.9%. Further spectroscopic characterization indicates that the high PLQY is achieved by the balance of nitrogen doping states and the surface passivation extent in CDs. The N-CDs also exhibit solvent-dependent multi-color emissive property and distinct PLQY in different solvents (the maximum can reach up to 25.3%). Furthermore, the as-prepared N-CDs are applied as fluorescence probes to detect acetone and H2O2 in water. This method has exhibited a low detection limit of acetone (less than 0.1%) and a quick and linear response to the H2O2 with the concentration from 0 to 120 μmol/L. This work broadens the knowledge of applying CDs as probes in the bio and chemical sensing fields.

Green emission carbon quantum dots from lemon juice for selective detection of Fe3+ ions

In this article carbon quantum dots (Cdots) were prepared by a facile, green, economical hydrothermal method of the mixed deionized water and lemon juice. Optical and structural properties of the Cdots have been extensively studied by UV–visible and fluorescence spectroscopy, x-ray diffraction (XRD) techniques, and high resolution TEM (HR-TEM). Surface functionality of Cdots has been illustrated by Fourier transform infrared spectroscopy (FTIR). The fabricated Cdots emit bright green light with broad spectrum. The Cdots exhibit captivating sensitivity and selectivity toward Fe3+ with a linear range from 0 to 80 ppm and a detection limit of 38.08 ppm.

Dye-sensitized solar cell (DSSC) coated with energy down shift layer of nitrogen-doped carbon quantum dots (N-CQDs) for enhanced current density and stability

Utilizing ultraviolet light by using Energy Down Shift (EDS) of quantum dots is a recent approach to efficiently utilize a broader spectrum of light, for energy harvesting. Other than higher efficiency, EDS is highly promising for increasing the stability of Dye-Sensitized Solar cells (DSSC); as it decreases the UV degradation of the cell. Previously, heavy metals-based (Cadmium etc) quantum dots are used for the purpose, which are not only toxic but also have less stability and have complicated synthesis methods. To overcome these issues, a thin coating of green emissive Nitrogen-doped Carbon Quantum Dots (N-CQDs) on DSSC, as a stable and efficient EDS layer is proposed here. N-CQDs were synthesized by a scalable, green and facile one-pot hydrothermal pyrolysis of citric acid in presence of nitrogen source, with a production yield of 65%, and quantum yield of 70%. The readily dispersible and highly stable colloid of N-CQDs was coated on the device, and with an optimized thickness, the power conversion efficiency was increased by 10%. This increase was further confirmed by external quantum efficiency (EQE) test, i.e. N-CQDs coated device showed EQE enhancement majorly in the UV spectrum and enhanced stability in UV light was recorded. The transmittance of FTO-glass was increased due to EDS and it also has an antireflection effect, which intern produces a small increase in EQE in the visible spectrum.

2D MnO2 nanosheets generated signal transduction with 0D carbon quantum dots: synthesis strategy, dual-mode behavior and glucose detection.

A natural resource such as peony flower has been employed for the first time as a new carbon precursor to prepare green-emitting carbon nanodots (CDs). The emission peak is situated at 523 nm and the excitation wavelength can be extended to the visible light range (452 nm). Due to the formation of CD-MnO2 nanocomposites, the emission intensity of CDs is sharply reduced as a consequence of Förster resonance energy transfer (FRET). Moreover, glucose can be recognized due to the enzymatic conversion of glucose by glucose oxidase to generate H2O2. The MnO2 nanosheets are reduced to form Mn(ii) ions, and the fluorescence of CDs can be recovered. The fluorescence intensity has been improved linearly based on the increasing concentration of glucose (0.5-250 μM) with a detection limit as low as 0.18 μM. This strategy gives a new selection of eco-friendly precursors in carbon nanomaterials and such a consecutive recognition process provides valuable insights for bio-analysis.

Green-emitting carbon dot loaded silica nanoparticles coated with DNA-cross-linked hydrogels for sensitive carcinoembryonic antigen detection and effective targeted cancer therapy.

Herein, we have designed bifunctional composite nanospheres for carcinoembryonic antigen (CEA) sensing and targeted drug delivery, based on carbon dot loaded silica nanoparticles coated with DNA-cross-linked hydrogels. As a result, highly sensitive and selective CEA detection was achieved in vitro, and an effective cytotoxic effect was realized in vivo after loading doxorubicin.

Highly Green Emissive Nitrogen-Doped Carbon Dots with Excellent Thermal Stability for Bioimaging and Solid-State LED.

In this study, nitrogen-doped green emissive carbon dots (N-doped CDs) are synthesized via a convenient one-step solid state reaction method. The N-doped CDs show excitation-dependent fluorescence behavior with a maximum emission of 540 nm. Upon the optimum excitation at 400 nm, the quantum yield (QY) of the green emissive CDs is determined to be 13.4% and 50.3% in deionized water and ethanol, respectively. The higher quantum yield of N-doped CDs in ethanol could be caused by a strong hydrogen-bonding. In addition, the obtained N-doped CDs demonstrate excellent thermal stability, which is supported by the fact that the emission intensity nearly has no change after keeping the sample at 90 °C for 120 min. Moreover, the N-doped CDs exhibit green emission after entering into the HeLa cell membrane, indicating their potential to be used as bioimaging agent. Furthermore, the N-doped CDs are dispersed in PVA matrix for solid state film, where the solid-state quenching is effectively avoided. A green LED is fabricated by packing the CDs-PVA composite on the top of a 395 nm n-UV-Chip, which provides a potentially healthy green light.

The Recognition of Sweat Latent Fingerprints with Green-Emitting Carbon Dots.

The recognition of fingerprints has played an extremely important role in criminal investigations, due to its uniqueness. This paper reports on the recognition of sweat latent fingerprints using green-emitting, environment-friendly carbon dots prepared with DL-malic acid and ethylenediamine, and the exploration of impacting factors in the development process of fingerprints. The experiments showed that better fingerprint images could be obtained when the latent fingerprints are developed in green-emitting carbon dots with pH 9 for 30 min, at room temperature. The reported method was also effective for latent fingerprints on a variety of substrates, as well as for those water-immersed ones, where the developed fingerprint remained stable after long-term preservation. Furthermore, the fluorescent three-dimensional fingerprint image could provide direct and simple evidence on pressing habits. The objective of this paper was to present this method. The method may help to narrow the range of suspects during criminal investigations and in forensic science.

A rapid microwave synthesis of green-emissive carbon dots with solid-state fluorescence and pH-sensitive properties.

The emerging carbon quantum dots (CQDs) have been attracting significant attention for their prominent fluorescence, excellent stability and outstanding biocompatibility. Here, we report a facile one-step synthesis of highly fluorescent CQDs by using phthalic acid and triethylenediamine hexahydrate as precursors through a simple microwave-assisted method. The reaction time needed is only 60 s, which is less time-consuming than most previous reports. The phthalic acid with a benzene ring can improve the photoluminescence properties of CQDs as it can provide foreign sp2 conjugating units, and then finally result in long-wavelength emission. The synthesized CQDs were fully characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Besides, the impacts of different freed ratio on physical and chemical properties of CQDs were investigated in detail. The prepared CQDs exhibited strong green fluorescence with a broad maximum emission wavelength. The quantum yields of the CQDs can reach 16.1% in aqueous solution and they were successfully used in cell imaging with good biocompatibility. Moreover, in solid state, the CQDs with the feed ratio of 1 : 0.5 showed a strong green–yellow fluorescence which may have great potential to fabricate optoelectronic devices. Furthermore, the prepared CQDs also showed high pH sensitivity and can act as a fluorescence nanosensor for pH sensing.

Applicability Evaluation of Bright Green-Emitting Carbon Dots in the Solid State for White Light-Emitting Diodes.

Self-quenching-resistant and bright green-emitting carbon dots (CDs) in the solid state were synthesized via a facile hydrothermal method. Their structure, optical properties together with their thermal and photostabilities, as well as their applicability in white LEDs were investigated. The obtained CDs have nearly spherical shape with a size around 4-5 nm. The resulting powder CDs show excitation-independent emission behavior, and can be excited over a broad range from 300-450 nm. Under optimal excitation at 400 nm, the resultant powder CDs yield bright and broad green emission around 505 nm with full width at half maximum (FWHM) of about 110 nm and under 360 nm excitation with lifetime of 15.8 ns. A potential application of the green-emitting CDs was evaluated by constructing a white light-emitting diode lamp. The fabricated white LED lamp emitted bright, warm white light with excellent color rendering properties (a color rendering index of 86.9 and a correlated color temperature of 3863 K).