Amphiphilic Egg-Derived Carbon Dots: Rapid Plasma Fabrication, Pyrolysis Process, and Multicolor Printing Patterns

Synthesis of Multicolor Carbon Dots Catalyzed by Inorganic Salts with Tunable Nonlinear Optical Properties

The nonlinear optical properties of carbon dots have been in the spotlight in recent years. In light of the complexity and diversity of factors affecting the nonlinear optical properties of carbon dots, how to reveal the origin and physical mechanism of the nonlinear optical properties of carbon dots accurately has become a problem. In this work, a template-free method was designed to prepare carbon dots via solid-phase reaction with phloroglucinol as a single carbon source and sodium bisulfate as the catalyst. This method is simple, green, safe, and easy to be prepared on a large scale. Three carbon dots with different luminous colors were obtained by simply adjusting the reaction temperature. The rise of reaction temperature affects the surface functional groups, and then hinders the luminescence of surface states, leading to the change of luminescence properties. The nonlinear optical properties of carbon dots were analyzed by the Z-scan technique. Surprisingly, all carbon dots have nonlinear optical responses, but there are differences in performance. Results prove the increase in sp2 domains may contribute to the significant improvement of the nonlinear optical properties of carbon dots, indicating a direction to improve the nonlinear optical properties of carbon dots.

One-pot synthesis of N-doped carbon dots from microwave-irradiated egg white: application to raspberry ketone assay by photo-induced charge transfer fluorescence sensing

In this article, we designed one-step economic eco-harmonious microwave-assisted procedure to prepare nitrogen-doped carbon dots. We selected egg white as a cheap glycoprotein-based carbon source without the assistance of any chemicals. The synthetic process requires only 3 min during which carbonization and nitrogen doping are realized at the same time. The fabricated carbon dots were characterized for particle size, structure and photoluminescence behaviour. The nanodots were amorphous carbon-rich naturally nitrogen-doped particles with plentiful attached hydrophilic functional groups. They had average particle size 2.98 ± 1.57 nm, emitted strong blue fluorescence and showed excitation-dependant emission behaviour. What is more, the practical use of this system for raspberry ketone determination in commercially available weight loss dietary supplement product is demonstrated successfully. In ethylene glycol medium, the addition of raspberry ketone enhances the emission intensity of the synthesized carbon dots. The effect of reaction time and solvent was investigated. After optimization, the intensity enhancement was linear to the amount of raspberry ketone added to the assay solution in the concentration range of 100–1000 ng/ml, with detection and quantitation limits of 15.10 and 45.45 ng/ml, respectively. The method was validated in accordance to International Conference on Harmonization (ICH) guidelines and further applied to raspberry ketone capsules showing excellent results.

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Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Organic dots (O-dots) for theranostic applications: preparation and surface engineering

Organic dots is a term used to represent materials including graphene quantum dots and carbon quantum dots because they rely on the presence of other atoms (O, H, and N) for their photoluminescence or fluorescence properties. They generally have a small size (as low as 2.5 nm), and show good photostability under prolonged irradiation. The excitation and emission wavelengths of O-dots can be tailored according to their synthetic procedure, where although their quantum yield is quite low compared with organic dyes, this is partly compensated by their large absorption coefficients. A wide range of strategies have been used to modify the surface of O-dots for passivation, improving their solubility and biocompatibility, and allowing the attachment of targeting moieties and therapeutic cargos. Hybrid nanostructures based on O-dots have been used for theranostic applications, particularly for cancer imaging and therapy. This review covers the synthesis, physics, chemistry, and characterization of O-dots. Their applications cover the prevention of protein fibril formation, and both controlled and targeted drug and gene delivery. Multifunctional therapeutic and imaging platforms have been reported, which combine four or more separate modalities, frequently including photothermal or photodynamic therapy and imaging and drug release.

The Rapid and Large-Scale Production of Carbon Quantum Dots and their Integration with Polymers

Carbon quantum dots (CDs) have inspired vast interest because of their excellent photoluminescence (PL) performances and their promising applications in optoelectronic, biomedical, and sensing fields. The development of effective approaches for the large-scale production of CDs may greatly promote the further advancement of their practical applications. In this Minireview, the newly emerging methods for the large-scale production of CDs are summarized, such as microwave, ultrasonic, plasma, magnetic hyperthermia, and microfluidic techniques. The use of the available strategies for constructing CD/polymer composites with intriguing solid-state PL is then described. Particularly, the multiple roles of CDs are emphasized, including as fillers, monomers, and initiators. Moreover, typical applications of CD/polymer composites in light-emitting diodes, fluorescent printing, and biomedicine are outlined. Finally, we discuss current problems and speculate on their future development.

Studies on carbon-quantum-dot-embedded iron oxide nanoparticles and their electrochemical response

A report on the synthesis of carbon-quantum-dot-embedded iron oxide nanoparticles (CQD@Fe₃O₄NPs) and their improved electrochemical studies is presented. Fe₃O₄NPs and CQD@Fe₃O₄NPs were synthesized by the wet-chemical co-precipitation method. X-ray diffraction measurements exhibited pure cubic phase with Fd3m space group in Fe₃O₄NPs and CQD@Fe₃O₄NPs. Fourier-transform infrared spectroscopy measurements confirmed the functionalization of Fe₃O₄NPs with CQDs. Dynamic light scattering measurements revealed a hydrodynamic radius of 520 nm and 319 nm for Fe₃O₄NPs and CQD@Fe₃O₄NPs, respectively. Moreover, zeta potential measurements showed positively charged Fe₃O₄NPs and negatively charged CQD@Fe₃O₄NPs. High-resolution transmission electron microscopy measurements showed nearly spherical structure with an average size of around 7 nm for Fe₃O₄ in both samples, whereas CQDs were nearly 2 nm in size in CQD@Fe₃O₄NPs. A biocompatibility study showed that CQD@Fe₃O₄NPs were more biocompatible than the bare Fe₃O₄NPs. CQD@Fe₃O₄NPs were then dispersed in chitosan (CHIT) solution, and drop-casted onto an indium tin oxide (ITO) glass substrate for further study. Atomic force microscopy results showed improved surface roughness of the CQD@Fe₃O₄-CHIT/ITO electrode, providing a better biosensing platform. The electrochemical response studies of CQD@Fe₃O₄-CHIT/ITO also showed enhanced electrochemical signal compared to Fe₃O₄-CHIT/ITO electrodes. Thus, a CQD@Fe₃O₄-CHIT/ITO electrode was used for the detection of vitamin D₂ (10-100 ng ml^-1) using a differential pulse voltammetry technique. The sensitivity and limit of detection were obtained as 0.069 µA ng^-1 ml cm^-2 and 2.46 ng ml^-1, respectively.

Fluorescent patterning of paper through laser engraving

While thermal treatment of paper can lead to the formation of aromatic structures via hydrothermal treatment (low temperature) or pyrolysis (high temperature), neither of these approaches allow patterning the substrates. Somewhere in between these two extremes, a handful of research groups have used CO2 lasers to pattern paper and induce carbonization. However, none of the previously reported papers have focused on the possibility to form fluorescent derivatives via laser-thermal engraving. Exploring this possibility, this article describes the possibility of using a CO2 laser engraver to selectively treat paper, resulting in the formation of fluorescent compounds, similar to those present on the surface of carbon dots. To determine the most relevant variables controlling this process, 3 MM chromatography paper was treated using a standard 30 W CO2 laser engraver. Under selected experimental conditions, a blue fluorescent pattern was observed when the substrate was irradiated with UV light (365 nm). The effect of various experimental conditions (engraving speed, engraving power, and number of engraving steps) was investigated to maximize the fluorescence intensity. Through a comprehensive characterization effort, it was determined that 5-(hydroxymethyl)furfural and a handful of related compounds were formed (varying in amount) under all selected experimental conditions. To illustrate the potential advantages of this strategy, that could complement those applications traditionally developed from carbon dots (sensors, currency marking, etc.), a redox-based optical sensor for sodium hypochlorite was developed.

Carbon Dots as a Promising Green Photocatalyst for Free Radical and ATRP-Based Radical Photopolymerization with Blue LEDs

Carbon dots (CDs) have been used for the first time as a sensitizer to initiate and activate free radical and controlled radical polymerization, respectively, based on an ATRP protocol with blue LEDs. Consideration of diverse heteroatom-doped CDs indicated that N-doped CDs could serve as an effective photocatalyst and photosensitizer in combination with LEDs emitting either at 405 nm or 470 nm. Free radical polymerization was initiated by combining the CDs with an iodonium or sulfonium salt in tri(propylene glycol) diacrylate. Polymerization of methyl methacrylate (MMA) by photo-induced ATRP was achieved with CDs and ethyl α-bromophenylacetate using CuII as catalyst in the ppm range. The polymers obtained showed temporal control, narrower dispersity ≲1.5, and chain-end fidelity. The first-order kinetics and ON/OFF experiments additionally gave evidence of the constant concentration of polymer radicals. No remarkable cytotoxic activity was observed for the CDs, underlining their biocompatibility.

Rapid and Large-Scale Production of Multi-Fluorescence Carbon Dots by a Magnetic Hyperthermia Method

The intrinsic low yield of carbon dots (CDs) is a barrier that limits practical application. Now, a magnetic hyperthermia (MHT) method is used to synthesize fluorescent CDs on a large scale (up to 85 g) in one hour (yield ca. 60 %). The reaction process is intensified by MHT since the efficient heating system enhances the energy transfer. CDs with blue, green, and yellow luminescence are synthesized by using carbamide and citrate with three different cations (Zn²⁺ , Na⁺ , K⁺ ), respectively. The CDs exhibit bright fluorescence under UV light and show excellent monodispersity and solubility in water. The alternation of photoluminescence (PL) emissions of these CDs is probably due to the difference in particle sizes and surface state. A bar coating technique is used to construct large-area emissive polymer/CDs films. CDs can insert themselves into the polymer chains by hydrogen bonding and electrostatic interactions. Wound healing efficiency can be enhanced by the Zn-CDs/PCL nanofibrous scaffold.

Loading Photochromic Molecules into a Luminescent Metal-Organic Framework for Information Anticounterfeiting

Stimuli-responsive photoluminescent materials have attracted considerable attention owing to their potential applications in security protection because the information recorded directly in materials with static luminescent outputs are usually visible under either ambient or UV light. Herein, we realize reversible information anticounterfeiting by loading a photoswitchable diarylethene derivative into a lanthanide metal-organic framework (MOF). Light triggers the open- and closed-form isomerization of the diarylethene unit, which respectively regulates the inactivation and activation of the photochromic FRET process between the diarylethene acceptor and lanthanide donor, resulting in reversible luminescence on-off switching of the lanthanide emitting center in the MOF host. This photoresponsive host-guest system allows for reversible multiple information pattern visible/invisible transformation by simply alternating the exposure to UV and visible light.

Highly efficient and ultra-narrow bandwidth orange emissive carbon dots for microcavity lasers

Luminescent materials with high efficiency, narrow emission bandwidth and long emission wavelength have attracted extensive attention in recent years. However, for novel luminescent carbon dots, it is still a major challenge to obtain these properties simultaneously. Here, this type of carbon dot was proposed using 1,4-diaminonaphthalene as the initial source. The carbon dots demonstrate strong orange emission with the highest quantum yield of 82% and an extremely narrow emission bandwidth of 30 nm. It is found that the orange emission of carbon dots is attributed to the high defect amounts including nitrogen and oxygen doping. The high carboxyl group content leads to a high efficiency and the uniform size distribution results in a narrow bandwidth. The carbon dots are used as the gain medium of a whispering gallery mode microcavity laser. A low excitation threshold of 12 kW cm-2 and a high quality factor of ∼3600 can be obtained from the microcavity lasers. This work has provided a didactic example to develop high-quality long emission-wavelength carbon dots with strong emission and an ultra-narrow emission bandwidth, which makes it possible to expand the application of original and high-performance lasers or other optical devices.

Synthesis of photoluminescent carbon dots and its effect on chondrocytes for knee joint therapy applications

In the process of natural precursors examining for the carbon dots (CDs) synthesis, a bio-friendly and highly luminescent CDs synthesis is being reported herein. For the first time, we are reporting CDs synthesis using Selenicereus grandiflorus plant materials without any use of additional oxidizing agents like ethanol which was used in the earlier mentioned reports. Ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron (HR-TEM) microscopy and Raman spectroscopy. This method is entirely safe to use in all biological practices because no toxic chemicals were used in this method. Further, we studied the toxicity of CDs against chondrocytes obtained from the knee joint. In order to inquire about the feasible harmful effects of exposing CD on the knee cells, we carried out CD treatment in SW-1353 chondrocytes. Cytotoxicity outcomes displayed a dosage-dependent reduction of cell viability. Therefore, we studied the toxic effects of CDs on the knee, indicating the important prospectives of CDs in future knee therapy.

New carbon dots based on glycerol and urea and its application in the determination of tetracycline in urine samples

The current study proposes a fast one-pot microwave assisted synthesis of new carbon dots (CDs) based on glycerol and urea. The novel carbon nanoparticles (GUCDs) have been appropriately characterized and exhibited good luminescent properties with a quantum yield of about 9.8%. Interestingly, the GUCDs are able to selectively interact with tetracycline class antibiotics, which produce a decrease in the native fluorescence of the CDs. On the base of these features, a new analytical method has been developed for the determination of tetracycline. The proposed method has shown satisfactory analytical parameters, such as good linearity range -between 0.5 and 25 μM (R² = 0.999₇)- and an acceptable detection limit (165 nM). Moreover, the new method has been successfully applied for tetracycline determination in urine samples with good recoveries (94.7-103%) and precision (4.6 RSD%).

Non-Metal-Heteroatom-Doped Carbon Dots: Synthesis and Properties

Carbon dots (CDs) are new materials with applications in bioimaging, optical devices, catalysis, and many other fields. Their advantages, such as ease of large-scale preparation, low-costing precursors, highly tunable photoluminescence, satisfactory biocompatibility, and photostability against photobleaching, make them competitive alternatives to conventional semiconductor-based quantum dots and organic dyes. To overwhelm other luminescent materials in applications, their functionalities still need to be improved in spite of the abovementioned advantages. In recent years, it has been proven that heteroatom doping is an effective approach to improve the optical and electronic performance of CDs by tuning their carbon skeleton matrices and chemical structures. In this review, the development of non-metal-heteroatom-doped CDs, including heteroatom categories, preparation methods, and physicochemical properties, are discussed. Progressive trends in heteroatom-doped CDs are also discussed at the end of this review.

Water-Borne Perovskite Quantum Dot-Loaded, Polystyrene Latex Ink

Highly lipophilic nanocrystals (NCs) of cesium lead halides were successfully embedded in polystyrene (PS) particles by deliberately controlling the swelling of the PS particles in the mixtures of good and bad organic solvents. The resulting composite particles were readily transferred into water via simple stepwise solvent exchange, which yielded water-borne perovskite NC-based inks with outstanding structural and chemical stability in aqueous media. Minimal change in the photoluminescence (PL) of the NCs loaded in the PS particles was visible after 1 month of incubation of the composite particles in water in a broad pH range from 1 to 14, which could otherwise be hardly realized. Loading into the PS particles also made the NCs highly stable against polar organic solvents, such as ethanol, intense light irradiation, and heat. The NC PL intensity slightly changed after the composite particles were heated at 75°C and under irradiation of strong blue light (@365 nm) for 1 h. Furthermore, the PS matrices could effectively inhibit the exchange of halide anions between two differently sized perovskite NCs loaded therein, thereby offering a considerable technical advantage in the application of multiple perovskite NCs for multicolor display in the future.

Synthesis, Structural, Optical and Dielectric Studies on Carbon Dot-Zinc Oxide Nanocomplexes

In the present manuscript, we have reported the synthesis, structural, optical, AC conductivity and dielectric studies of carbon dot-zinc oxide (CDZO) nanocomplexes. CDZO nanocomplexes were synthesized by the wet chemical method. The refinement of X-ray powder diffraction data reveals that the sample possesses hexagonal structure of ZnO. The low intensity diffraction peaks corresponding to carbon come to existence, it is suggested that phase segregation has occurred in the CDZO nanoparticles. The strong absorption band observed in the UV region for the prepared samples can be attributed to the band edge absorption. Dielectric property and AC conductivity have been studied as a function of frequency (100[Formula: see text]Hz and 1[Formula: see text]kHz) of the applied AC signal in the temperature range 30[Formula: see text]C to 150[Formula: see text]C. The result showed that AC conductivity increases with increase of temperature. Dielectric loss and DC conductivity increase with increase of temperature.

An ultrathin photosensitizer for simultaneous fluorescence imaging and photodynamic therapy

An ultrathin photosensitizer was prepared by immobilization of chlorin e6 (Ce6) and carbon dots (CDs) onto layered double hydroxide (LDH) nanosheets, which exhibited excellent fluorescence imaging and photodynamic therapy performance toward cancer theranostics.

The enhancement of photocatalytic performance of SrTiO3 nanoparticles via combining with carbon quantum dots

Carbon quantum dots were prepared by a simple chemical process using activated carbon as carbon source. The as-prepared carbon quantum dots are fine with a narrow size distribution and show excellent hydrophilicity. The carbon quantum dots were combined with SrTiO3 nanoparticles through a simple impregnation process to obtain a carbon quantum dots/SrTiO3 nanocomposite. The photocatalytic reaction rate of carbon quantum dots/SrTiO3 nanocomposite is about 5.5 times as large as that of pure SrTiO3 in the degradation of rhodamine B under sunlight irradiation. The enhanced performance in the degradation of rhodamine B may be attributed to the interfacial transfer of photogenerated electrons from SrTiO3 to carbon quantum dots, leading to effective charge separation in SrTiO3. Carbon quantum dots show potential applications in high-efficiency photocatalyst design.

Folic acid-conjugated green luminescent carbon dots as a nanoprobe for identifying folate receptor-positive cancer cells

Early diagnosis is pivotal in subsequent prognosis and treatment of cancer. Herein, folic acid-conjugated carbon dots (FA-CDs) as a fluorescent nanoprobe were fabricated for identifying cancer cells visually. Green luminescent carbon dots (CDs) from active dry yeast (ADY) were readily prepared in scale-up to reach macroscopic production with a high yield of ~50% via a facile and rapid microwave approach. The as-prepared CDs were further combined with folic acid (FA) by covalent bonding to fabricate the FA-CDs for identification of cancer cells over-expressing folate receptor (FR). Experimental outcomes demonstrated that the resultant FA-CDs noninvasively entered into cancer cells via receptor-mediated endocytosis and could differentiate FR-positive HepG2 cells from a cell mixture by fluorescence imaging, which suggests a promising prospect of the FA-CDs as an efficient probe for cancer diagnosis and succeeding personalized therapy.

Carbon dot/polyvinylpyrrolidone hybrid nanofibers with efficient solid-state photoluminescence constructed using an electrospinning technique

Carbon dots (CDs) are the promising candidates for application in optoelectronic and biological areas due to their excellent photostability, unique photoluminescence, good biocompatibility, low toxicity and chemical inertness. However, the self-quenching of photoluminescence as they are dried into the solid state dramatically limits their further application. Therefore, realizing efficient photoluminescence and large-scale production of CDs in the solid state is an urgent challenge. Herein, solid-state hybrid nanofibers based on CDs and polyvinylpyrrolidone (PVP) are constructed through an electrospinning process. The resulting solid-state hybrid PVP/CD nanofibers present much enhanced photoluminescence performance compared to the corresponding pristine colloidal CDs due to the decrease in non-radiative recombination of electron-holes. Owing to the suppressed self-quenching of CDs, the photoluminescence quantum yield is considerably improved from 42.9% of pristine CDs to 83.5% of nanofibers under the excitation wavelength of 360 nm. This has great application potential in optical or optoelectronic devices.

Natural-Product-Derived Carbon Dots: From Natural Products to Functional Materials

Nature provides an almost limitless supply of sources that inspire scientists to develop new materials with novel applications and less of an environmental impact. Recently, much attention has been focused on preparing natural-product-derived carbon dots (NCDs), because natural products have several advantages. First, natural products are renewable and have good biocompatibility. Second, natural products contain heteroatoms, which facilitate the fabrication of heteroatom-doped NCDs without the addition of an external heteroatom source. Finally, some natural products can be used to prepare NCDs in ways that are very green and simple relative to traditional methods for the preparation of carbon dots from man-made carbon sources. NCDs have shown tremendous potential in many fields, including biosensing, bioimaging, optoelectronics, and photocatalysis. This Review addresses recent progress in the synthesis, properties, and applications of NCDs. The challenges and future direction of research on NCD-based materials in this booming field are also discussed.

Microwave-assisted synthesis of water-soluble Eu3+ hybrid carbon dots with enhanced fluorescence for the sensing of Hg2+ ions and imaging of fungal cells

Eu³⁺ ion hybrid carbon dots as a novel fluorescent probe for the assay of Hg²⁺ ions and cellular imaging of Fomitopsis sp.

Bamboo leaf-based carbon dots for efficient tumor imaging and therapy

In this study, carbon dots synthesized from bamboo leaf cellulose were used simultaneously as a staining agent and for doxorubicin delivery to target cancer cells.

Conversion of invisible metal-organic frameworks to luminescent perovskite nanocrystals for confidential information encryption and decryption

Traditional smart fluorescent materials, which have been attracting increasing interest for security protection, are usually visible under either ambient or UV light, making them adverse to the potential application of confidential information protection. Herein, we report an approach to realize confidential information protection and storage based on the conversion of lead-based metal-organic frameworks (MOFs) to luminescent perovskite nanocrystals (NCs). Owing to the invisible and controlled printable characteristics of lead-based MOFs, confidential information can be recorded and encrypted by MOF patterns, which cannot be read through common decryption methods. Through our conversion strategy, highly luminescent perovskite NCs can be formed quickly and simply by using a halide salt trigger that reacts with the MOF, thus promoting effective information decryption. Finally, through polar solvents impregnation and halide salt conversion, the luminescence of the perovskite NCs can be quenched and recovered, leading to reversible on/off switching of the luminescence signal for multiple information encryption and decryption processes.

Materials with switchable fluorescence possess great potential for information encryption applications, but systems where the off state is invisible are lacking. Here the authors print patterns of colourless metal organic frameworks and reversibly transform these inks into fluorescent perovskite nanocrystals

Piezochromic Carbon Dots with Two-photon Fluorescence

Piezochromic materials, which show color changes resulting from mechanical grinding or external pressure, can be used as mechanosensors, indicators of mechano-history, security papers, optoelectronic devices, and data storage systems. A class of piezochromic materials with unprecedented two-photon absorptive and yellow emissive carbon dots (CDs) was developed for the first time. Applied pressure from 0-22.84 GPa caused a noticeable color change in the luminescence of yellow emissive CDs, shifting from yellow (557 nm) to blue-green (491 nm). Moreover, first-principles calculations support transformation of the sp² domains into sp³ -hybridized domains under high pressure. The structured CDs generated were captured by quenching the high-pressure phase to ambient conditions, thus greatly increasing the choice of materials available for a variety of applications.