Stable Carbon Dots Research Articles

Amine-Rich Carbon Dots Synthesized from Kappa-Carrageenan and l-Lysine as a Dual Probe for Detection of Folic Acid and Tumor-Targeted Delivery of Therapeutics.

Strategically designed, heteroatom-rich surface functionalized blue fluorescent carbon dots (CDs) were synthesized for high-throughput detection of folic acid (vitamin B9). The highly stable CDs could particularly detect vitamin B9 in the presence of 35 analytes, even up to 40 nM of the vitamin. The versatile CDs were found to have a high affinity for folic acid in wastewater, folic acid tablets, and food samples enriched with folic acid. The hemocompatibility of the CDs was also studied by using a hemolysis assay, confirming the CDs to be nontoxic to human blood samples up to 400 μg/mL. The CDs were then covalently conjugated to biotin, which possesses receptors that are overexpressed in tumor cells. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide dye) assay and confocal bioimaging studies proved the biotin-modified CDs (CDBT) were remarkably nontoxic in healthy cell lines (HEK-293) and highly target-specific toward tumor cells (HeLa), including triple-negative breast cancer cells (MDA-MB-231). The cytotoxicity assay of 5-fluorouracil encapsulated CDs (CDBTFu) showed the IC50 value to be 81 μM in HeLa cells and 185 μM in MDA-MB-231 cells, respectively, and significantly higher in HEK-293 cells (over 300 μM), owing to high specificity toward tumor cells.

Ultrasensitive Dual Fluorophore-Conjugated Carbon Dots for Intracellular pH Sensing in 3D Tumor Models.

The dysregulation of pH has been linked to the onset of chronic conditions, such as cancer and neurological diseases. Consequently, the development of a highly sensitive tool for intracellular pH sensing is imperative to investigate the interplay between pH and the biochemical changes accompanying disease pathogenesis. Here, we present the development of a ratiometric fluorescent nanoprobe, NpRhoDot, designed for precisely measuring pH levels. We demonstrate its efficacy in sensitively reporting intracellular pH in monolayer A549 lung cancer cells, primary fibroblast cells, and 3D tumor spheroids derived from the DLD-1 colorectal adenocarcinoma cell line. NpRhoDot leverages a novel design, where stable carbon dots are functionalized with a pH-responsive ratiometric fluorescent probe comprising a naphthalimide-rhodamine moiety, NpRho1. This design confers NpRhoDot with the high pH sensitivity characteristics of organic fluorescent probes, along with excellent photostability up to 1 h and biocompatibility of carbon dots. Through one-photon and two-photon fluorescence microscopy, we validate the reliability of NpRhoDot for biosensing intracellular pH in monolayer and three-dimensional tumor models from pH 4 to 7.

In-situ embedding of carbon dots in boron nitride for enhancing phosphor stability and fluorescent film heat dissipation

The aggregation-induced quenching effect and poor thermal stability issues of carbon dots (CDs) limit their further development in the solid-state lighting and display field. In this work, a red carbon dot/boron nitride nanosheet (rCDs/BNNS) composite was synthesized using boron nitride as a carrier by in-situ embedding of rCDs. Thanks to the uniform dispersion of rCDs and the restraint of BNNS, the prepared rCDs/BNNS composite has excellent fluorescence stability and thermal stability. rCDs/BNNS composites as fluorescent markers can be used to detect potential fingerprints on various surfaces. Furthermore, rCDs/BNNS were dispersed into polyvinyl alcohol (PVA) polymers to prepare rCDs/BNNS/PVA flexible luminescent films. In addition to the excellent stability inherited from rCDs/BNNS, the thin film also exhibits high heat dissipation by reason of the establishment of a heat transfer channel in the PVA by rCDs/BNNS. Moreover, thin films can still maintain original fluorescence after undergoing hundreds or thousands of bends, while possessing sufficient tensile strength. This study provides a facile pathway for the preparation of highly stable CDs luminescent materials, and has a promising application in the forensic identification and flexible luminescent devices' thermal management fields.

Sustainable and highly-stable carbon dots from cellulose as a fluorescent reference for visual ratiometric pH detection

Fluorescent materials, including organic molecules and quantum dots, usually respond to the environmental changes, such as acidity and basicity. It is challenging to construct highly-stable fluorescent materials. In this work, we fabricated novel carbon dots (CDs) with a high stability and a high quantum yield by using a solvothermal process, in which cellulose was the green precursor and 1-allyl-3-methylimidazolium chloride (AmimCl)/N,N-dimethylformamide (DMF) was the solvent. The resultant CDs had the cationic imidazolium groups on their surface. As a result, they exhibited the excellent fluorescence stability in strong-acidic, strong-basic and high salt solutions. In addition, the CDs also presented a good resistance to the photobleaching under strong UV irradiation conditions. The highly stable CDs can be utilized as a fluorescent reference to significantly improve the responsiveness of the fluorescent materials. For example, the CDs were combined with cellulose acetate fluorescein isothiocyanate (CA-FITC) to obtain a series of ratiometric probes, which can visually detect pH values with a higher sensitivity. Furthermore, based on the outstanding processability and formability of cellulose derivatives, the CDs/CA-FITC was easily fabricated into responsive fluorescent coatings, films, and inks, indicating a huge potential in visual detection, solid-state luminescence, and anti-counterfeiting.

Bright Blue Light‐Emitting Diodes Based on Well‐Modified Carbon Dots by Designing Co‐Host Systems to Balance Carriers’ Injection

AbstractLeveraging bright and stable carbon dots (CDs) for blue light‐emitting diodes (LEDs) is a prospective but challenging topic. Aggregation‐caused quenching (ACQ) of CDs and device engineering of CDs‐LEDs are two issues. Here, blue CDs with quantum yield of 59.75% are synthesized. Hydrogen bonds increase rigidity and facilitate luminescence, while polymer chains increase spatial resistance and resist ACQ. Then, solution‐processed blue CDs‐LEDs are assembled by blending CDs into poly(N‐vinylcarbazole) (PVK) as light‐emitting layer (EML). Furthermore, several other materials are also employed as the second host to reduce injection barrier, facilitate carriers’ transport, and balance carriers’ distribution. In particular, the blue CDs‐LED based on the co‐host system of PVK and 4‐[1‐[4‐[bis(4‐methylphenyl)amino]phenyl]cyclohexyl]‐N‐(3‐methylphenyl)‐N‐(4‐methylphenyl)benzenamine (TAPC) achieves a maximum brightness up to 827.60 cd m−2. This work is a step forward for applying CDs in LEDs.

Stable Carbon Dots from Microwave-Heated Carbon Nanoparticles Generating Organic Radicals for In Situ Additions

Carbon dots (CDots) are small carbon nanoparticles with effective surface passivation by organic functionalization. In the reported work, the surface functionalization of preexisting small carbon nanoparticles with N-ethylcarbazole (NEC) was achieved by the NEC radical addition. Due to the major difference in microwave absorption between the carbon nanoparticles and organic species such as NEC, the nanoparticles could be selectively heated via microwave irradiation to enable the hydrogen abstraction in NEC to generate NEC radicals, followed by in situ additions of the radicals to the nanoparticles. The resulting NEC-CDots were characterized by microscopy and spectroscopy techniques including quantitative proton and 13C NMR methods. The optical spectroscopic properties of the dot sample were found to be largely the same as those of CDots from other organic functionalization schemes. The high structural stability of NEC-CDots benefiting from the radical addition functionalization is highlighted and discussed.

Preparing Colour-Tunable Tannic Acid-Based Carbon Dots by Changing the pH Value of the Reaction System.

Biomass carbon dots (CDs) have the characteristics of being green, nontoxic, inexpensive, and simple to prepare, and they can be used in luminescence-related fields. In this study, red, green, and blue luminescent CDs were synthesised by a simple hydrothermal method under alkaline, neutral, and acidic conditions using TA as carbon source and o-phthalaldehyde as blend. The unique optical properties of these CDs are due to the differences in their degrees of conjugation, which can be controlled by the pH value of the reaction system. These three kinds of biomass CDs have good applications in light-emitting diodes (LEDs). By mixing biomass CDs with epoxy resin, warm, and cold white LEDs with Commission Internationale de l’Elcairage (CIE) coordinates (0.35, 0.36) were successfully constructed on extremely stable multicolour CDs. This study shows that these biomass CDs are a promising material for white LED lighting.

High‐Yield Carbon Dots Interlayer for Ultra‐Stable Zinc Batteries

AbstractThe practical implementation of Zn metal anodes with high volumetric capacity is seriously plagued by the dendritic growth and accompanying interfacial parasitic reactions. Herein, high yield carbon dots (CDs) with abundant polar functional groups (CHO and CN), as a functional artificial interface layer, are rationally designed to optimize electrolyte/Zn interfaces with large‐scale viability. Of particular note, the quantum‐sized CDs with strong Zn affinity can effectively ameliorate the electric field distribution and ensure that more Zn2+ is adsorbed onto the whole electrode, which are beneficial for lowering the barrier of Zn2+ nucleation and inducing homogeneous Zn deposition, thus rendering a dendrite‐free Zn anode, as extensively confirmed by in situ optical microscope observation and finite element simulation. Meanwhile, the dense and insoluble coating layer with abundant polar functional groups is conducive to arousing the repulsion effect, which is good for shielding the active water and SO42−, thus eliminating the water‐mediated parasitic reactions and improving Zn2+ reaction kinetics. More importantly, the electrochemically stable CDs layer endows the Zn anode with a prolonged lifespan of 3000 h at 1 mA cm−2. This feasible and efficient fabrication of functional CDs layer opens a new avenue for stable dendrite‐free metal anodes.

Effect of synthesis methods on the acetone sensing behaviour of fluorescent carbon dots

Carbon dots (CDs) are an emerging family of nanostructures due to their unique optical properties, high chemical stability, biocompatibility, and low toxicity, they have been able to attract a lot of attention and cause significant changes in various scientific fields. In this study, the green synthesis of stable CDs by hydrothermal and pyrolysis methods (H-CDs and P-CDs) is performed from Nigella sativa seeds as a natural precursor. Using these methods, the formation and the surface passivation of the CDs are done simultaneously, resulting in the intrinsic fluorescence emission. The as-prepared CDs are characterised by UV–vis spectroscopy, fluorescence spectroscopy, elemental analysis, dynamic light scattering, Fourier transform infrared spectroscopy, and transmission electron microscopy, from which their structural information and property are interpreted. The fluorescence intensity graph of H-CDs and P-CDs, with excitation wavelengths in 360 nm, shows the highest emissions at 430 and 410 nm, respectively. Particle size distribution was obtained at about 4 nm. The fluorescent quantum yield (QY) of H-CDs and P-CDs was measured to be 7% and 2%, respectively. The synthesised CDs showed good photoluminescence (PL) responses to acetone solution. Acetone had a different effect on the PL properties of CDs obtained from pyrolysis and hydrothermal methods so that in P-CDs, it increased the intensity of PL, and in H-CDs; it decreased the intensity of PL.

Smartphone-based fluorometer for pH detection using green synthesized carbon dots

As a group of heavy-metal-free fluorescent nanomaterials, carbon dots (CDs) have recently received a growing interest as they have high optical absorption activity and are chemically stable, biocompatible, and less toxic. In this paper, the green synthesis of stable CDs by hydrothermal and pyrolysis methods from Parmigiano-Reggiano is performed. An intrinsically emitted fluorescence results from simultaneous generation and the surface passivation of CDs by the mentioned techniques. The responses of hydrothermal CDs to pH occur by emission wavelength at 430 nm under 365 nm excitation. When the pH is increased from 2–12, its emission fluorescence intensity will be reduced. The pH was also analyzed real time by developing a smartphone-based portable recognition platform consisting of an instrument and a self-designed APP called “Image Analyser”. The fluorescence color change of CDs caused by the pH was recorded by the camera of the smartphone and color of pictures was analyzed by APP. The results of both methods are similar, so the CDs based recognition platform are highly practically and efficient tool as they could analyze pH with outstanding functionality, as examined in this study in different samples.

Highly stable and bright blue light-emitting diodes based on carbon dots with a chemically inert surface.

The manufacture of blue light-emitting diodes (LEDs) has always been a tough problem to solve in the display and illumination fields. Inorganic/organic semiconductors and carbon dots (CDs) with a wide band gap still face obstacles such as a low external quantum efficiency (EQE) and poor stability. Herein, we synthesized highly stable and blue emission CDs with a chemically inert surface, and the photoluminescence (PL) peak (in ultra-pure water) of which is located at 446 nm with an absolute PL quantum yield (PLQY) of 26.4%. The LEDs based blue emission CDs exhibit an electroluminescence (EL) peak located at 456 nm and a high brightness of 223 cd m−2 with an EQE of 0.856%. The Commission Internationale del'Eclairage (CIE) coordinates are located at (0.21, 0.23) and the device lifetime with 65% brightness (T65) reaches over 217 h because of the chemically inert surface of the CDs. The results mean the devices are the most stable CDs-LEDs reported to date. This work represents a novel route for the preparation of low cost, highly stable and very bright CDs-LEDs with a short wavelength emission.

Nitrogen-sulfur co-doped pH-insensitive fluorescent carbon dots for high sensitive and selective hypochlorite detection.

Carbon dots (CDs) are novel fluorescent carbon nanomaterial with exceptional properties and have drawn great attention in recent years. However, the preparation and applications of high-quality carbon dots remain challenging. Here, we describe a simple hydrothermal synthesis route using citric acid as a carbon source for stable fluorescent CDs. The CDs are modified with glutathione and exhibit high fluorescent quantum yields (30.2%) and excellent photo-stability. In addition, the fluorescence intensity of CDs remains stable over a wide range of pH values (3-12). Hypochlorite (ClO-) can effectively quench the fluorescence of the CDs by destroying the pyrrolic ring and conjugate structure of the CDs. Thus, the CDs can be used to detect ClO-. Under optimized conditions, the fluorescence intensity changes of CDs correspond selectively to ClO- in the range of 100-800nmol/L with a LOD of 16nmol/L. Practical applications of the proposed method for free chlorine detection in tap water show similar results and recovery compared to the standard DPD-based method. These results suggest that the pH-insensitive CDs prepared via this facile procedure are a promising chemosensor for free chlorine and have great potential in analytical applications.

Soybean-derived blue photoluminescent carbon dots.

Biomass-derived carbon dots (CDs) are biocompatible and have potential for a variety of applications, including bioimaging and biosensing. In this work, we use ground soybean residuals to synthesize carbon nanoparticles by hydrothermal carbonization (HTC), annealing at high temperature, and laser ablation (LA) in a NH4OH solution. The carbon nanoparticles synthesized with the HTC process (HTC-CDs) exhibit photoluminescent characteristics with strong blue emission. The annealing of the HTC-processed carbon particles in the range of 250 to 850 °C causes a loss of the photoluminescent characteristics of the CDs without any significant change in the microstructure (amorphous structure) of the carbon particles. The LA processing of the annealed HTC-processed carbon particles introduces nitrogen-containing surface-functional groups and leads to the recovery of the photoluminescent features that are different from those of the HTC-CDs and dependent on the fraction of nitrogen in the surface-functional groups. The photoluminescence of both the HTC-CDs and LA-CDs is largely due to the presence of N-containing surface-functional groups. The quantum yield of the LA-CDs is more constant than that of the HTC-CDs under continuous UV excitation and does not exhibit a significant reduction after 150 min of excitation. The methods used in this work provide a simple and green strategy to introduce N-surface-functional groups to carbon nanoparticles made from biomass and biowaste and to produce stable photoluminescent CDs with excellent water-wettability.

Cross-Linked Polyamide Chains Enhanced the Fluorescence of Polymer Carbon Dots.

Carbon dots (CDs) have attracted tremendous attention for their outstanding advantages in luminescence. Here, α-amino-substituted lysine derivatives with the determined chemical structure were employed as precursors to obtain bright and highly stable fluorescent CDs through a facile hydrothermal route. The relationships among the chemical structure of precursors, CD fluorescence, and particle size were investigated. The results indicated that increased numbers of functional groups in precursors could promote the degree of cross-linking and lead to a smaller size, better fluorescent properties, and stronger stability of CDs. The C-CDs that were prepared from lysine derivatives with most functional groups showed excitation-dependent dual excitation and dual emission (DE2), high-stability luminescence, strong resistance to photobleaching, and high selectivity to Fe3+ and could be used as a sensitive probe for Fe3+ detection.

Ratiometric fluorescence sensor based on carbon dots as internal reference signal and T7 exonuclease-assisted signal amplification strategy for microRNA-21 detection

The expression level of miRNA-21 is closely related to the occurrence and development of cancer, especially in gastrointestinal cancer. Monitoring miRNA-21 has clinical application in the diagnosis and evaluation of gastrointestinal cancer. A turn-on ratiometric fluorescence bioassay based on the T7 exonuclease-mediated cyclic enzymatic amplification method was developed for miRNA-21 determination by using carbon dots (CDs) and FAM-labeled ssDNA as the signal source. CDs demonstrated the triple functions of built-in internal fluorescence, probe carrier, and quencher in this strategy. In the absence of miRNA-21, FAM-labeled ssDNA would be adsorbed and quenched by CDs. The addition of miRNA-21 induced cycle hydrolysis from the 5′ end by the T7 exonuclease and then released the short-cleaved FAM-labeled oligonucleotides. Then, the increased FAM signal (FFAM) and the stable CD signal (FCDs) would be tested through a ratiometric routine for the quantification of miRNA-21. The FFAM/FCDs value showed a good linear relationship with the concentration of miRNA-21 in the range of 0.05–10 nM, and the detection limit for miRNA-21 was 1 pM with excellent selectivity and reproducibility. Furthermore, this sensor successfully evaluated the expression level of miRNA-21 in clinical blood samples from healthy individuals and gastrointestinal cancer patients, and the results were highly consistent with those of qRT-PCR, suggesting the great clinical application value in the diagnosis of cancer associated with miRNA-21 expression levels.

Highly Stable White-Light-Emitting Carbon Dot Synthesis Using a Non-coordinating Solvent.

In this article, synthesis of white-light-emitting, highly stable carbon dots (CDs) using a colloidal synthesis technique is reported. It has been observed that the use of a non-coordinating solvent plays a vital role in the successful fabrication of highly stable CDs. Dilution-independent emissive behavior in CDs is achieved. Excitation-energy-dependent emissive behavior is observed in CDs. However, by surface passivating the CD core by using hexadecylamine (HDA), excitation wavelength dependence of emission is successfully minimized. Surface-functionalized CDs (SFCDs) show blue to green light tunable emission with the change in synthesis conditions. HDA also plays an important role in achieving dilution-independent emission in SFCDs. Furthermore, the carbon dots synthesized are highly inert, and their emission spectra are unaffected on exposure to an open atmosphere for as long as 9 days. A new class of highly crystalline carbon dots called “carbon onion rings” is reported.

Assembly and copper ions detection of highly sensible and stable carbon dots/hydroxyapatite fluorescence probe

ABSTRACTAlthough fluorescence probes have certain applications in copper ion detection, sensitivity and accuracy are easily affected because of their instability. To improve this situation, a more stable carbon dots (CDs)/hydroxyapatite (HAP) nanocomposite fluorescence probe is designed. The improvement in structure and properties of the CDs/HAP fluorescence probe compared to the CDs shows that the stability of the fluorescence intensity is enhanced. Compared with pure CDs probe, the novel CDs/HAP fluorescence probe exhibits higher stability and sensitivity due to the in-situ composite of HAP. The fluorescence intensity of the probe has shown the best linear response to the concentration of Cu2+ in the range of 10–5 to 10–4mol•L−1 in aqueous solution. These results indicate that the method based on the fluorescence quenching mechanism has enormous potential for the development of highly efficient fluorescence probe towards the detection of heavy metal ions.

2,4,6-Trinitrophenol detection by a new portable sensing gadget using carbon dots as a fluorescent probe.

An optical sensing gadget using fluorescence of carbon dots (CDs) was developed to realize the in-field detection of 2,4,6-trinitrophenol (TNP) in tap water and lake water samples. Fluorescent CDs were prepared through a one-step hydrothermal synthetic route. The fluorescence spectra demonstrated that the CDs could specifically discriminate TNP from other nitroaromatic explosives in an aqueous medium. The fluorescence of the CDs was quenched linearly with the concentration of TNP in the range from 1 to 100 μM, with a detection limit of 0.48 μM (3σ/k). The detection mechanism was ascribed to the synergistic effect of the inner filter effect and electron transfer. In addition, a portable sensing gadget based on a high-precision RGB color sensor and a micro control unit was developed. With use of the sensing gadget and the CDs, TNP detection in tap water and lake water samples was realized. Importantly, the portable sensing gadget combined with highly stable, low-toxicity, and sensitive CDs might have great potential for application in extensive in-field sensing situations. Graphical abstract Carbon dots synthesized with 4-(diethylamino)salicylaldehyde as the initial material were used for 2,4,6-trinitrophenol (TNP) detection. TNP quenches the fluorescence of carbon dots, and the mechanism is ascribed to the synergistic effect of the inner filter effect and electron transfer. A portable sensing gadget based on a 32-bit micro control unit was successfully applied for in-field TNP detection.

Successful entrapment of carbon dots within flexible free-standing transparent mesoporous organic-inorganic silica hybrid films for photonic applications

The effective entrapment of Carbon dots (CDs) into a polymer-silica hybrid matrix, formed as free standing transparent flexible films, is presented. The composite's synthesis, characterization, device application and properties -mechanical, thermal and optical- are being provided and discussed. CDs of 3nm mean size with strong photoluminescence are embedded into a silica matrix during the sol-gel procedure, using tetraethyl orthosilicate as the precursor and F127 triblock copolymer as the structure directing agent under acidic conditions. The final hybrid nanostructure forms free standing transparent films that show high flexibility and long term stable CDs luminescence indicating the protective character of the hybrid matrix. It is crucial that the photoluminescence of the hybrid's CDs is not seriously affected after thermal treatment at 550°C for 30min. Moreover, the herein reported hybrid is demonstrated to be suitable for the fabrication of advanced photonic structures using soft lithography processes due to its low shrinkage and distortion upon drying, both attributable to its porosity. Finally, it is reported that addition of F127 ethanolic solution in aqueous solution of CDs induces a blue-shift of their photoluminescence.

A hydrothermal route to water-stable luminescent carbon dots as nanosensors for pH and temperature

Carbon dots (CDs) as a class of heavy-metal-free fluorescent nanomaterials has drawn increasing attention in recent years due to their high optical absorptivity, chemical stability, biocompatibility, and low toxicity. Herein, we report a facile method to prepare stable CDs by hydrothermal treatment of glucose (glc) in the presence of glutathione (GSH). With this approach, the formation and the surface passivation of CDs are carried out simultaneously, resulting in intrinsic fluorescence emission. The influence of reaction temperature, reaction time and feed ratio of GSH/glc on the photoluminescence property of CDs is studied. The as-prepared CDs are characterized by UV–Vis, photoluminescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscope, from which their structural information and property are interpreted. These CDs may be useful as pH sensors or as versatile nanothermometry devices based on the pronounced temperature dependence of their steady-state fluorescence emission spectra, which changes considerably over the physiological temperature range (15–60°C).