High production-yield solid-state carbon dots with tunable photoluminescence for white/multi-color light-emitting diodes

Sawmill waste derived carbon dots as a fluorescent probe for synthetic dyes in soft drinks

Herein, for the first time the carbon dots (CDs) were synthesized by reflux method from sawmill waste material. We also represent a novel strategy based on fluorescent CDs for determination of ponceau 4R and allura red dyes in soft drinks. Interestingly, both the dyes were sensitive and showed effective fluorescence quenching of the CDs owing to the interaction between them. The analytical applicability of CDs were evaluated for detection of both the dyes with a good linear relationship between the concentration range of 0.0 to 3.0 µg mL-1 and having detection limit 0.45 and 0.47 µg mL-1 for allura red and ponceau 4R dyes respectively. Meanwhile, the potential application of this novel fluorescent probe for dyes determination in real samples was validated in different soft drink samples with good accuracy and precision. Thus, these findings provides new insights for the potential risk assessment of both the dyes. Moreover, CDs acted as an excellent fluorescent material in cellular imaging owing to their cellular uptake and localization.

Facile Synthesis of Water-Stable Multicolor Carbonized Polymer Dots from a Single Unconjugated Glucose for Engineering White Light-Emitting Diodes with a High Color Rendering Index

Tunable emission carbonized polymer dots (CPDs) are highly desirable for the preparation of optoelectronic devices, especially white light-emitting diodes (WLEDs). In most available studies, polychromatic CPDs are synthesized using aromatic molecules as precursors. However, few studies report the successful synthesis of polychromatic CPDs using two or more unconjugated precursors. In this work, we prepare multicolor fluorescent CPDs from a single unconjugated precursor, glucose, via a hydrothermal reaction. By controlling the particle size and degree of graphitization of the synthesized CPDs, their emission wavelength can be tuned in the range 440-625 nm (i.e., almost the entire visible region). Furthermore, the CPDs can be used to construct LEDs of varying colors, including WLEDs (CIE coordinates: 0.34, 0.36) with the correlated color temperature and color rendering index of 4997 K and 92.69, respectively. In brief, the strategy proposed in this study successfully converts unconjugated glucose into high-performance LEDs with great application potential.

A Green, Economic "Switch-On" Sensor for Cefixime Analysis Based on Black Soya Bean Carbon Quantum Dots

BACKGROUND

Cefixime is a third-generation oral cephalosporin antibiotic widely used to treat bacterial infections. Typical methods for cefixime analysis use expensive instruments or sophisticated experimental procedures, and thus a sensitive and practical method is urgently needed for cefixime detection and analysis.

OBJECTIVE

To develop a sensitive and robust cefixime "switch-on" sensor based on carbon quantum dots (CQDs).

METHODS

In this study, black soya beans were used as an inexpensive carbon source for a "green" synthesis of fluorescent black soya bean (BS)-carbon quantum dots (CQDs). The fluorescence of these particles could be efficiently quenched by Ce(IV)due to the ground state recombination and electron transfer (ET) between Ce(IV)and BS-CQDs. In the presence of cefixime, the ET was interrupted and the fluorescent signal was recovered.

RESULTS/CONCLUSIONS

This method showed high sensitivity and an impressively low detection limit of 169 nM.

HIGHLIGHTS

This low-cost, simple strategy for cefixime detection exhibits excellent stability, selectivity, and sensitivity. Moreover, it was successfully applied for the detection of cefixime in tablets and in a complex biological environment, confirming its great potential utility for drug analysis, biological process research, and clinical research.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples

Iodine ion is one of the most indispensable anions in living organisms, particularly being an important substance for the synthesis of thyroid hormones. Curcumin is a yellow-orange polyphenol compound derived from the rhizome of Curcuma longa L., which has been commonly used as a spice and natural coloring agent, food additives, cosmetics as well as Chinese medicine. However, excess curcumin may cause DNA inactivation, lead to a decrease in intracellular ATP levels, and trigger the tissue necrosis. Therefore, quantitative detection of iodine and curcumin is of great significance in the fields of food and life sciences. Herein, we develop nitrogen-doped fluorescent carbon dots (NCDs) as a multi-mechanism detection for iodide and curcumin in actual complex biological and food samples, which was prepared by a one-step solid-phase synthesis using tartaric acid and urea as precursors without adding any other reagents. An assembled NCDs-Hg2+ fluorescence-enhanced sensor for the quantitative detection of I- was established based on a fluorescence "turn-off-on" mechanism in a linear range of 0.3-15 μM with a detection limit of 69.4 nM and successfully quantified trace amounts of I- in water samples and urine sample. Meanwhile, the as-synthesized NCDs also can be used as a fluorescent quenched sensor for curcumin detection based on the synergistic internal filtration effect (IFE) and static quenching, achieving a good linear range of 0.1-20 μM with a satisfactory detection limit of 29.8 nM. These results indicate that carbon dots are potential sensing materials for iodine and curcumin detection for the good of our health.

Fluorescent Carbon Dots: Fantastic Electroluminescent Materials for Light-Emitting Diodes

Fluorescent carbon dots (CDs) have emerged as fantastic luminescent nanomaterials with significant potentials on account of their unique photoluminescence properties, high stability, and low toxicity. The application of CDs in electroluminescent light-emitting diodes (LEDs) have aroused much interest in recent years. Herein, the state-of-the-art advances of CD-based electroluminescent LEDs are summarized, in which CDs act as active emission layer and interface transport layer materials is discussed and highlighted. Besides, the device structure of CD-based LEDs and preparation methods of CDs are also introduced. Furthermore, the opportunities and challenges for achieving high performance CD-based electroluminescent LED devices are presented. This review article is expected to stimulate more unprecedented achievements derived from CDs and CD-based electroluminescent LEDs, thus further promoting their practical applications in future solid-state lighting and flat-panel displays.

Quantitatively Switchable pH-Sensitive Photoluminescence of Carbon Nanodots

pH sensing plays a key role in the life sciences as well as the environmental, industrial, and agricultural fields. Carbon nanodots (C-dots) with small size, low toxicity, and excellent stability hold great potential in pH sensing as nanoprobes due to their intrinsic pH-sensitive photoluminescence (PL). Nonetheless, the undesirable sensitivity and response range of C-dot PL toward pH cannot meet the requirements of practical applications, and the unclear pH-sensitive PL mechanism makes it difficult to control their pH sensitivity. Herein, the quantitative correlation of pH-sensitive PL with specific surface structures of C-dots is uncovered for the first time, to our best knowledge. The association of carboxylate and H⁺ increases the ratio of nonradiation to radiation decay of C-dots through excited-state proton transfer, resulting in the decrease of PL intensity. Meanwhile, the dissociation of α-H in β-dicarbonyl forming enolate increases the extent of delocalization of the C-dots conjugated system, which induces the PL broadening to the red region and a decreasing intensity. Based on the understanding of the pH-sensitive PL mechanism, the pH-sensitive PL of C-dots can be switched by quantitative modulation of carboxyl and β-dicarbonyl groups to achieve a desirable pH response range with high sensitivity. This work contributes to a better understanding of the pH-sensitive PL of C-dots and therefore presents an effective strategy for controllably tuning their pH sensitivity, facilitating the rational design of C-dot-based pH sensors.

Water-soluble green-emitting carbon nanodots with enhanced thermal stability for biological applications

High stability and water solubility of fluorescent nanomaterials are considered key factors to evaluate their feasibility for fundamental applications. Herein, water-soluble and thermally stable, green-emitting carbon nanodots (CNDs) have been synthesized via a facile hydrothermal method with an average size of 1.9 nm. CNDs showed green emission centered at 544 nm with the photo-luminescence quantum yield (PLQY) of up to 10.1% under the excitation of 400 nm. The obtained CNDs demonstrated high resistance towards photo-bleaching and an ionic (KCl) environment. Moreover, the aqueous solution of CNDs exhibited excellent stability under harsh thermal conditions from 10 °C to 80 °C. The as-prepared CNDs showed stable performance at high temperatures, even after keeping them at 80 °C for 30 min. Furthermore, the green emissive CNDs were incubated in T-ca cancer cells for bio-imaging applications. The results indicated that CNDs can served as an effective thermally-stable bio-imaging agent in T-ca cells at the physiological temperature range of 25 °C-45 °C. Green emission and excellent thermal stability make these CNDs promising fluorescent materials for potential applications in the medical field, which requires long-wavelength fluorescence and high-temperature imaging.

Polydopamine-carbon dots functionalized hollow carbon nanoplatform for fluorescence-imaging and photothermal-enhanced thermochemotherapy

The low power photothermal therapy can reduce the tissue damage caused by laser irradiation, thus the near-infrared (NIR) absorbing vehicles with high photothermal conversion efficiency are demanded in the low power treatment. Herein, the NIR-absorbing agent polydopamine (PDA) and carbon dots (CDs) were gated on the openings of hollow mesoporous carbon (HMC) to construct a photothermal enhanced multi-functional system (HMC-SS-PDA@CDs). Interestingly, the fluorescence emission wavelength of HMC-SS-PDA@CDs was red-shifted by FRET effect between PDA and CDs, which solved the dilemma of fluorescence quenching of carbon-based materials and was more conducive to cell imaging. The modification of PDA@CDs not only acts as the gatekeepers to realize multi-responsive release of pH, GSH and NIR, but also endows the HMC vehicle with excellent photothermal generation capacity, the possibility for bio-imaging as well as the enhanced stability. Naturally, both the cytological level and the multicellular tumor sphere level demonstrate that the delivery system has good low-power synergistic therapeutic with combination index (CI) of 0.348 and imaging effects. Meanwhile, the combined treatment group showed the highest tumor inhibition rate of 92.6% at 0.75 W/cm². Therefore, DOX/HMC-SS-PDA@CDs nano-platform had broad application prospects in low power therapy and convenient imaging of carbon-based materials.

Accurate SERS monitoring of the plasmon mediated UV/visible/NIR photocatalytic and photothermal catalytic process involving Ag@carbon dots

The excited carriers (electrons and holes) and heat energy that originate from plasmonic metal nanomaterials are crucial to the enhancement of the photocatalytic performance. In this study, an Ag@carbon dots (Ag@CDs) hybrid has been prepared with excellent Fenton-like photocatalytic and photothermal conversion properties for catalyzing H₂O₂ to generate hydroxyl radicals (˙OH) for the degradation of crystal violet (CV) dye under full solar spectrum irradiation based on a unique plasmon effect. We have obtained some intrinsic kinetics information, including the reaction rate and apparent activation energy on the surface of the Ag@CDs, through a surface-enhanced Raman scattering strategy to investigate the contributions made by photocatalytic and photothermal effects in the plasmon mediated reaction under irradiation from ultraviolet (UV)/visible/near-infrared (NIR) light. In the visible light region, the Ag@CDs + H₂O₂ system exhibits the fastest apparent reaction rate owing to the involvement of a large number of hot carriers, which are generated by the strongest plasmon effect, and the presence of the photothermal effect mediated by the plasmonic effect. As the wavelength of the illumination blue-shifts to the UV region, the plasmon effect is weakened, resulting in a decrease in the number of hot carriers. Furthermore, the hot carriers will not be further thermalized because of interband transitions. In addition, the catalytic performance of Ag@CDs in the NIR region is almost dominated by the photothermal effect. This work provides deep insights into understanding the plasmon-mediated photocatalytic mechanism of the Ag@CDs hybrid.

Nitrogen and chlorine co-doped carbon dots with synchronous excitation of multiple luminescence centers for blue-white emission

N,Cl-CDs emit the blue-white lighting, which synchronously contains the two ranges of wavelength that the chloroplast needs for photosynthesis.

Hemicellulose-triggered high-yield synthesis of carbon dots from biomass

Biomass is a major resource for the preparation of carbon dots (CDs) and improving the production yield of CDs is a challenge. Herein, we select corn cobs to prepare CDs with a production yield as high as 55%. Such a high yield derives from the high content of hemicellulose and extremely low lignin content in corn cobs.

Orange red-emitting carbon dots for enhanced colorimetric detection of Fe3+

Orange red-emitting CDs were constructed from 2,3-diaminopyridine and successfully used for visual colorimetry and near-infrared cellular imaging.

Photo-modulated wide-spectrum chromism in Eu3+ and Eu3+/Tb3+ photochromic coordination polymer gels: application in decoding secret information

Photo-switching emission of photochromic materials has paramount importance in the field of optoelectronics. Here, we report synthesis and characterization of a dithienylethene (DTE) based photochromic low molecular weight gelator (LMWG) and self-assembly with lanthanide (Eu3+ and Tb3+) ions to form a photochromic coordination polymer gel (pcCPG). Based on DTE ring opening and closing, the TPY-DTE gel shuttles from pale-yellow coloured TPY-DTE-O to dark blue coloured TPY-DTE-C and vice versa upon irradiating with UV and visible light, respectively, and both the photoisomers show distinct optical properties. Furthermore, integration of Eu3+ and Tb3+ lanthanides with TPY-DTE resulted in red and green emissive Eu-pcCPG (Q.Y. = 18.7% for the open state) and Tb-pcCPG (Q.Y. = 23.4% for the open state), respectively. The photoisomers of Eu-pcCPG exhibit photo-switchable spherical to fibrous reversible morphology transformation. Importantly, an excellent spectral overlap of the Eu3+ centred emission and absorption of DTE in the closed form offered photo-switchable emission properties in Eu-pcCPG based on pcFRET (energy transfer efficiency >94%). Further, owing to the high processability and photo-switchable emission, the Eu-pcCPG has been utilized as invisible security ink for protecting confidential information. Interestingly, mixed Eu3+/Tb3+ pcCPG exhibited photo-modulated multi-spectrum chromism reversibly where the colour changes from yellow, blue, and red to green and vice versa under suitable light irradiation.

Carbonized Polymer Dots with Tunable Room-Temperature Phosphorescence Lifetime and Wavelength

Recently, the room-temperature phosphorescence (RTP) properties of carbon dots (CDs) have attracted significant interest. However, the regulation of RTP emission faces great challenges because of untunable emissive lifetime and wavelength. Here, ultrahigh-yield acrylamide-based N-doped carbonized polymer dots (AN-CPDs) with ultralong RTP lifetime are synthesized by a one-step hydrothermal addition polymerization and carbonization strategy. The RTP lifetime and wavelength of the proposed AN-CPDs can be regulated by changing the carbonization degree. Thus, the AN-CPDs' RTP lifetimes are in the range of 61.4-466.5 ms, while the RTP emission wavelengths vary from 485 to 558 nm. Further experiment and theoretical calculation proved that RTP can be attributed to the polymer/carbon hybrid structure and nitrous functional groups as the molecular state related emission centers. Supramolecular cross-linking in the aggregated state is vital for the RTP emission of the AN-CPDs by restricting the nonradiative transition of the triplet excitons. AN-CPDs of different RTP lifetimes can be applied to time-resolved multistage information encryption and multistage anticounterfeiting. This work facilitates the optical regulation and application potential of CDs and provides profound insights into the effect of the polymer/carbon hybrid structure on the properties of CDs.

Chitosan derived nitrogen-doped carbon dots suppress osteoclastic osteolysis via downregulating ROS

Osteoclasts are the main cells involved in normal bone remodeling and pathological bone destruction in vivo. Overactivation of osteoclasts can lead to osteolytic diseases, including breast cancer, bone tumors, arthritis, the aseptic loosening of orthopedic implants, and Paget's disease. Excessive reactive oxygen species are the main cause of osteoclast overactivation. We have synthesized chitosan derived nitrogen-doped carbon dots (N-CDs) with a high synthetic yield and the ability to scavenge reactive oxygen species (ROS). N-CDs effectively abrogated RANKL-induced elevation in ROS generation and therefore impaired the activation of NF-κB and MAPK pathways. Osteoclastogenesis and bone resorption was effectively attenuated in vitro. Furthermore, the in vivo administration of N-CDs in mice protected them against lipopolysaccharide (LPS)-induced calvarial bone destruction and breast cancer cell-induced tibial bone loss. Based on the good biocompatibility of N-CDs and the ability to efficiently remove ROS, a nanomaterial treatment scheme was provided for the first time for the clinical treatment of osteolytic diseases.

Photochemically Synthesized Ruthenium Nanoparticle-Decorated Carbon-Dot Nanochains: An Efficient Catalyst for Synergistic Redox Reactions

Ruthenium nanoparticle (NP)-decorated carbon dots (Ru/C-dots) were fabricated as a potential catalyst in the application of both oxidation and reduction. The photochemical method was used to synthesize Ru/C-dot nanohybrids. The as-prepared Ru/C-dots exhibited a core-shell-based nanochain structure, in which the spherical nature of C-dots further evolved to a layer structure to homogeneously encapsulate Ru NPs. Such Ru/C-dots have excellent catalytic properties, which were demonstrated in the oxidation of flavonoids and concomitantly reduction of inorganic complex and organic dyes, each yielding a high catalytic rate constant. We also proposed an appropriate catalytic mechanism for each reaction. Higher catalytic activity was achieved by the synergistic effect of the encapsulated Ru NPs and the C-dots layer. Further, this nanohybrid was successfully applied to inspect a real aqueous sample. We anticipated that Ru/C-dots nanohybrid may open up a broad platform for the design of efficient multifunctional catalysts.

Regulation of Autophagy Orchestrates Pyroptotic Cell Death in Molybdenum Disulfide Quantum Dot-Induced Microglial Toxicity

Molybdenum disulfide quantum dots (MoS₂ QDs) represent an emerging class of two-dimensional (2D) atomically layered transition metal dichalcogenide nanostructures with few nanometers in lateral size, which show attractive potential as versatile platforms for theranostic applications in various neurological disorders. However, the potential impacts of MoS₂ QDs on microglia remain unclear. In this report, we showed that exposure of microglia to MoS₂ QDs triggered NLRP3 inflammasome activation as revealed by the cleavage of the inactive precursor of caspase-1 to its active form and the increased release of downstream pro-inflammatory cytokines, resulting in microglia cell death that occurred through caspase-1-dependent pyroptosis. We also found that MoS₂ QDs activated autophagy, and suppression of autophagy by specific inhibitors potentiated MoS₂ QD-induced pyroptosis. Additionally, MoS₂ QDs stimulated mitochondria-derived reactive oxygen species (mtROS) generation in BV-2 cells. However, ROS scavengers could diminish the MoS₂ QD-mediated NLRP3 inflammasome activation and pyroptotic cell death in microglia. Overall, our findings identified pyroptosis as a cellular response to MoS₂ QD exposure in microglial cells, affording novel insights into the neurotoxicity of MoS₂ QDs and facilitating the rational design and application of functional MoS₂ QDs in neuroscience.

Rational Design of Multi-Color-Emissive Carbon Dots in a Single Reaction System by Hydrothermal

As an emerging building unit, carbon dots (CDs) have been igniting the revolutionaries in the fields of optoelectronics, biomedicine, and bioimaging. However, the difficulty of synthesizing CDs in aqueous solution with full-spectrum emission severely hinders further investigation of their emission mechanism and their extensive applications in white light emitting diodes (LEDs). Here, the full-color-emission CDs with a unique structure consisting of sp 3-hybridized carbon cores with small domains of partially sp 2-hybridized carbon atoms are reported. First-principle calculations are initially used to predict that the transformation from sp 3 to sp 2 hybridization redshifts the emission of CDs. Guided by the theoretical predictions, a simple, convenient, and controllable route to hydrothermally prepare CDs in a single reaction system is developed. The prepared CDs have full-spectrum emission with an unprecedented two-photon emission across the whole visible color range. These full-color-emission CDs can be further nurtured by slight modifications of the reaction conditions (e.g., temperature, pH) to generate the emission color from blue to red. Finally a flexible LEDs with full-color emission by using epoxy CDs films is developed, indicating that the strategy affords an industry translational potential over traditional fluorophores.

A rare-earth-free self-activated phosphor: Li2TiSiO5 with TiO5 square pyramids

Li₂TiSiO₅ shows a broad emission band covering the visible region due to the coexistence of TiO₅ and TiO₆ polyhedra.