Green-emitting Carbon Dots Research Articles

A novel and highly stable dual-emission carbon dots-based phosphor

A novel green/red dual-emission carbon dots-based phosphor (named as GRCDs phosphor) was successfully prepared by introducing calcium hydroxide [Ca(OH)2] as matrix material mixed with green-emitting carbon dots (CDs) for the first time. The addition of Ca(OH)2 not only prevents fluorescent self-quenching caused by polymerization of CDs in the solid state but also promotes the red emission of CDs due to abundant functional groups on the surface. Furthermore, the detailed characterizations of the structure and optical properties show that the hydroxyl groups play a crucial role for the red emission of GRCDs phosphor. As-prepared GRCDs phosphor possesses outstanding thermal stability as well as excellent water stability. This finding provides a new way for the development of CDs-based phosphors.

Green-Emitting Carbon Dots as Fluorescent Probe for Nitrite Detection

Nitrite (NO2−) is a well-known inorganic pollutant in food and environment that can trigger severe environmental and healthy problems. Consequently, establishing accurate NO2− detection method is very important for food security, environment monitoring and human health. In this work, green fluorescent carbon dots (CDs) with a high fluorescence quantum yield (QY) of 36.13% are prepared for NO2− detection. The CDs are prepared by one-pot hydrothermal carbonization and polymerization of acriflavine. After carbonization, the anti-photobleaching property of CDs significantly enhanced compared to acriflavine. Under acidic conditions, the added of NO2− selectively induces the aggregation and fluorescence quenching of CDs. A good fluorescence linearity response in the range of 50 nM to 10 μM can be developed for NO2− quantitative analysis, with a detection limit of 11.6 nM. Owing to the diazotization reaction of NO2− and the phenylamine groups on the surface of CDs, this method shows excellent selectivity compared to common ions and amino acids. Furthermore, the proposed method shows favorable results in the detection of real water and Cantonese style sausage sample. This study provides a simple and efficient method for NO2− detection in food and environment.

One-step synthesis of blue–green luminescent carbon dots by a low-temperature rapid method and their high-performance antibacterial effect and bacterial imaging

Due to the global infection problem caused by the abuse of antibiotics, the preparation of novel antibacterial nanomaterials is a key and basic requirement for applications in antibacterial and bacterial imaging fields. This paper reports the one-step preparation of blue–green-emitting carbon dots (CDs) under low temperature (80 °C) with glucose as the carbon source, citric acid as the dehydrating agent, and polyethyleneimine as the nitrogen source. Through inhibition zone tests and minimum inhibitory concentration (MIC) experiments, the inhibitory abilities of prepared CDs against various microorganisms, including gram-positive bacteria, gram-negative bacteria and fungi, were compared. It is worth mentioning that the MIC of CDs against Staphylococcus aureus reaches 4.7 μg ml−1, and the CDs exhibit excellent biocompatibility. Moreover, studies on visual-treatment therapy, in which infection treatment can be performed at the same time as bacterial imaging, with the prepared functional antibacterial CDs based on fluorescence confocal imaging would be beneficial to their promising future in medical and biological fields.

Pb(II) detection and versatile bio-imaging of green-emitting carbon dots with excellent stability and bright fluorescence.

Green-emitting carbon dots (G-CDs) were synthesized via a simple and green hydrothermal method using betaine hydrochloride and sulfadiazine as carbon and nitrogen sources, respectively. Excellent luminescence stability with varying pH, salt concentrations, temperature is found with excitation-independent emission. G-CDs can be successfully used for the detection of Pb(ii) in the range of 0-200 μM. There was good linear relationship between the Pb(ii) concentration and G-CD fluorescence intensity with a correlation coefficient of 0.993, and the limit of detection (LOD) was 3.0174 μmol L-1. Due to its good biocompatibility, G-CDs can be successfully applied to zebrafish imaging as well as cell imaging, and the results show that G-CDs is more suitable for the zebrafish embryo imaging. Our results suggested that the obtained G-CDs can be used as multifunctional probes, highlighting their potential in different biological studies.

Correlated color temperature alteration with changing the position of carbon dot film for warm WLEDs

Commercial white light emitting diodes (WLEDs) composed on the blue InGaN chip and YAG:Ce3+ phosphor have been used as a promising illumination sources. WLEDs with an adjustable correlated color temperature (CCT) are very important to the wide variety of applications. Herein, we represent a facile synthetic strategy to prepare green emission carbon dots by solvothermal method using citric acid and urea as a precursor. The carbon dots have a size about 4 nm and emission peak centered at 532 nm. The fabricated WLEDs present white light with variable color temperature from warm (5602 K) to cool white (9242 K) by combining YAG:Ce3+ and carbon dot films. Thus, the results show that the fabricated carbon dot and carbon dot film can be used in white sources in the next generation of lighting application as a CCT converter.

Application of carbon dots in nucleolus imaging to distinguish cancerous cells from normal cells

Fluorescent molecular probes are very critical for detecting the precise location of lesions in fundamental research and clinical applications. Herein, we report a green-emitting carbon dots (m-CDs) with excellent properties including good photostability, high cellular uptake efficiency, low cytotoxicity, and good counterstain compatibility. Digest tests of ribonuclease indicate the significantly higher affinity of m-CDs for nucleolus RNA in both fixed and living cells. Notably, visualizing nucleoli in cells by using m-CDs can accurately achieve its number and morphology information to distinguish cancerous cells from normal cells. In addition, m-CDs can also be used to monitor the nucleolar dynamics during apoptosis of malignant cells induced by doxorubicin (DOX). The m-CDs show great potential as a nucleolus probe, and promising applications in cancerous cells screening and therapeutic efficacy evaluation.

Oil-Dispersible Green-Emitting Carbon Dots: New Insights on a Facile and Efficient Synthesis

Carbon dots (CDs) have been progressively attracting interest as novel environmentally friendly and cost-effective luminescent nanoparticles, for implementation in light-emitting devices, solar cells, photocatalytic devices and biosensors. Here, starting from a cost-effective bottom-up synthetic approach, based on a suitable amphiphilic molecule as carbon precursor, namely cetylpyridinium chloride (CPC), green-emitting CDs have been prepared at room temperature, upon treatment of CPC with concentrated NaOH solutions. The investigated method allows the obtaining, in one-pot, of both water-dispersible (W-CDs) and oil-dispersible green-emitting CDs (O-CDs). The study provides original insights into the chemical reactions involved in the process of the carbonization of CPC, proposing a reliable mechanism for the formation of the O-CDs in an aqueous system. The ability to discriminate the contribution of different species, including molecular fluorophores, allows one to properly single out the O-CDs emission. In addition, a mild heating of the reaction mixture, at 70 °C, has demonstrated the ability to dramatically decrease the very long reaction time (i.e. from tens of hours to days) at room temperature, allowing us to synthesize O-CDs in a few tens of minutes while preserving their morphological and optical properties.

Wide emission shifts and high quantum yields of solvatochromic carbon dots with rich pyrrolic nitrogen

Carbon dots (CDs) with solvatochromic emission colors in different solvents have attracted much attention as a new class of luminescent nanomaterial owing to their facile synthesis and low production cost. In this work, we prepared two kinds of CDs with solvatochromic emissions: green emission CDs (G-CDs) and multicolor emission CDs (M-CDs). G-CDs synthesized from o-phenylenediamine exhibited weak photoluminescence emission (quantum yield 2.8%–6.1%) and 39 nm solvatochromic shifts (492–531 nm). In contrast, M-CDs prepared from o-phenylenediamine and 4-aminophenol showed 87 nm solvatochromic shift range (505–592 nm) and much higher photoluminescence quantum yield (18.4%–32.5%). The two CDs exhibited different emission, absorption, and photoluminescence lifetime. The origin of solvatochromic shifts and the formation mechanism of CDs were demonstrated by analyzing the structures and compositions of two CDs. High percentages of pyrrolic nitrogen and amino nitrogen make wider solvatochromic shifts and higher quantum yields. The results were well supported by density functional theory calculations. This effective strategy to expand solvatochromic shift range and improve quantum yields could open a new window to prepare satisfied solvatochromic carbon dots.

Homogeneous fluorescent immunoassay for the simultaneous detection of chloramphenicol and amantadine via the duplex FRET between carbon dots and WS2 nanosheets

Herein, we proposed a duplex and homogeneous fluorescent immunoassay for the simultaneous detection of amantadine (AMD) and chloramphenicol (CAP) residue in chicken breast with both high sensitivity and short assay time. The immunoassay was based on the fluorescence resonance energy transfer (FRET) between hapten-labeled carbon dots (CDs) and antibody-modified WS2 nanosheets. To achieve the duplex FRET, polyethyleneimine-functionalized blue and green emissive CDs with separated emission were synthesized via a one-pot hydrothermal method and directly coupled with the haptens of AMD and CAP, serving as the energy donors. The antibodies were modified on the surface of WS2 nanosheets with high quenching efficiency to construct the energy acceptor. The specific immunoreaction could trigger the efficient FRET between the donors and the acceptors, causing the fluorescence quenching of CDs. The developed immunoassay was applied to simultaneously detect AMD and CAP, having the detection limit of 0.10 ng g−1 and 0.06 ng g−1, respectively.

High green-emission carbon dots and its optical properties: Microwave power effect

The nature of carbon quantum dot (CD) luminescence is still broadly investigated based on different CD synthesis processes. This study aims at investigating the effect of microwave power on optical characteristics of CDs using microwave radiation techniques. CDs are synthesized with citric acid as a source of carbon and urea as a passivation agent. CDs have been successfully synthesized, and an increase in the CD burn-off percentage was observed with an increase in the microwave power. The TEM test results show that the dimensions of the CDs resulted are in the range of 3.4–9.5 nm with an average size of 6 nm at 450 W. The results of the FTIR functional group structural analysis show that a CD has N—H and O—H stretching bonds. According to the results of UV–Vis analysis, the CDs have absorption peaks at 335 nm and 407 nm, which indicates a π → π* electronic transition from the C=C bond and an n → π* transition from the C=O bond. Using the Tauc-plot method, the CD energy bandgap values were found to be 2.47 eV, 2.51 eV, 2.51 eV, 2.52 eV, and 2.53 eV at CD 300, CD 450, CD 600, CD 850, and CD 1000, respectively. The optical multichannel analyzer test results show that the peak emission waves produced by CDs are 536 nm and 532 nm with the strongest bright green light at CD 1000. Time-resolved photoluminescence testing shows that the CD decay time generally ranges from 5 ns. Overall, an increase in the microwave power causes an increase in the percentage of burn-off, energy bandgap, absorption intensity, and CD emission intensity.

Facile Synthesis of Nitrogen-Doped Green-Emission Carbon Dots as Fluorescent Off-On Probes for the Highly Selective Sensing Mercury and Iodine Ions.

In this work, green-emission carbon dots (CDs) were prepared for detecting mercury ions (Hg(II)) and iodine ions via a facile hydrothermal method using ethylenediamine and methyl red as nitrogen and carbon sources, respectively, without any other complex reagents. The bacteriostasis experiment showed that the CDs were not toxic to the growth of four kinds of bacteria: Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), which indicated that the CDs had good security and could be used for analysis and detection. The CDs exhibited excitation-independent emission, the fluorescence of which could be quenched by Hg(II), and could be recovered by iodine ions. An approach was established to detect Hg(II) based on the fluorescence quenching of CDs by the synergistic action of a photo induced electron transfer (PET) mechanism, and iodine ions were detected based on the fluorescence recovery of CDs by a HgI₂ precipitate formation mechanism. The detection limits for Hg(II) and iodine reached 0.89 μM and 0.50 μM, respectively. Compared to most methods, the method mentioned in this paper has good selectivity, a wider linear range, a lower detection limit and higher security. The synthesized CDs could be probes for sensing Hg(II) and iodine ions.

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.

Bovine Serum Albumin Amplified Reactive Oxygen Species Generation from Anthrarufin-Derived Carbon Dot and Concomitant Nanoassembly for Combination Antibiotic–Photodynamic Therapy Application

Amplification of reactive oxygen species (ROS) generation through covalent conjugation of bovine serum albumin (BSA) with newly synthesized, ROS-producing carbon dots (CDs) upon visible light irradiation is reported for the first time. Derivatization of surface carboxyl functional groups of Anthrarufin-derived, green-emitting CD with the amine functionality of BSA ushers distinct changes in the photophysics of CD including an unprecedented ∼50 nm shift in its excitation maxima, decrease in fluorescence lifetime, and concomitant increase in ROS generation. Substantial conformational changes of BSA were witnessed upon conjugation with CD, rendering the BSA-CD conjugate resistant to pepsinolysis. A protease-proof nanoassembly was derived from the BSA-CD conjugate through desolvation that simultaneously hosts a prototype antibiotic and generates ROS with excellent efficiency, making it an attractive platform for antibacterial photodynamic therapy (A-PDT) applications. Systemic annihilation of both Gram-positive and -negative bacteria was achieved with the BSA-CD nanoassembly and envisioned as alternatives to traditional photosensitizers.

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.