Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution, sensing and bioimaging

Efficient anchoring CuO nanoparticles on Ugi four-component-functionalized graphene quantum dots: Colloidal soluble nanoplatform with great photoluminescent and antibacterial properties

In this work, sustainable functionalization of graphene quantum dots (GQDs) obtained citric acid via a neoteric green, facile, and straightforward approach for effectively anchoring CuO nanoparticles (CuO NPs) and accordingly...

Structural Engineering toward High Monochromaticity of Carbon Dots-Based Light-Emitting Diodes

Monochromaticity for light-emitting diodes (LEDs) is an important parameter. However, carbon dots-based light-emitting diodes (CDs-LEDs) usually suffer from broad emission, which limits the development of this material. In this work, high-quality carbon dots (CDs) with a quantum yield of 16.2% were synthesized. When they were mixed with poly(N-vinyl carbazole) (PVK) to form a homogeneous film, the solid-state fluorescence of CDs was realized. After fabrication and systematic optimization of the device, the full width at half-maximum (fwhm) of EL spectra could be narrowed to 64 nm in comparison with the fwhm of 77 nm for PL, demonstrating that structural engineering is an effective approach for improving the color purity of CDs-LEDs. Meanwhile, the performance of the devices is improving. The obtained CDs-LEDs display high monochromaticity with a maximum luminance of 681 cd/m². This work provides a new way to optimize the monochromaticity and performance of CDs-LEDs.

Biomass-Based Carbon Dots: Current Development and Future Perspectives

Carbon dots have been considered as a solution to the challenges that semiconductor quantum dots have encountered because they are more biocompatible and can be synthesized from abundant and nontoxic materials such as biomass. This review will highlight the advantages of these biomass-based carbon dots in terms of synthesis, properties, and applications in the biomedical field. Furthermore, future applications especially in the biomedical field of biomass-based carbon dots as well as the challenges of semiconductor quantum dots such as biocompatibility, photobleaching, environmental challenges, toxicity, and poor solubility will be discussed in detail. Biomass-derived quantum dots, a subsection of carbon dots that are the most desirable for future research, will be focused upon including from synthesis to applications. Finally, the future development of biomass derived quantum dots in the biomedical field will be discussed and evaluated to unlock the potential for their applications.

Production of nitrogen-doped carbon quantum dots with controllable emission wavelength, excellent sensing of Fe3+ in aqueous solution, and potential application for stealth quick response coding in the visible regime

Nitrogen-doped carbon quantum dots (N-CQDs) exhibit a high quantum yield with controllable emission wavelength and intensity in the blue-green regime. N-CQDs were tested and determined to be thermally and optically stable during 150 °C heat treatment and prolonged UV irradiation. Potential applications of N-CQDs were demonstrated, including excellent Fe3+ sensing in aqueous solution, fluorescent polymer fibres, and stealth quick response coding at visible wavelengths.

Solvent Effects on Fluorescence Properties of Carbon Dots: Implications for Multicolor Imaging

Carbon dots (CDs) are synthesized by the solvothermal method with four kinds of solvents including water, dimethylformamide (DMF), ethanol, and acetic acid (AA). The aqueous solutions of the above CDs emit multiple colors of blue (470 nm), green (500 nm), yellow (539 nm), and orange (595 nm). The structures, sizes, and chemical composition of the CDs are characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The optical properties of multicolored CDs are analyzed by UV-vis absorption and photoluminescence (PL) spectra. It has been revealed that DMF is the key solvent to synthesized CDs for the red shift of fluorescence emission, which could be enhanced by adding an AA solvent. The structures of functional groups such as the contents of graphitic N in carbon cores and oxygen-containing functional groups on the surface of CDs are affected by these four solvents. According to the oxidation and selective reduction of NaBH4, the implication for multicolor imaging has been discussed based on the COOH, C-O-C, and C=O functional groups.

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.

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe³⁺, Pb⁺², and Cr³⁺ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe³⁺, Cr³⁺ and Pb²⁺ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.

Urea-doped carbon dots as fluorescent switches for the selective detection of iodide ions and their mechanistic study

A facile and green strategy for the fabrication of fluorescent urea-doped carbon dots (N-CDs) has been explored. Significantly, the fluorescent N-CDs could recognize iodide ions (I-) with high selectivity, and their photoluminescence could be efficiently quenched by the addition of I-. The sensitivity analysis for I- indicated a linear relationship in the range from 12.5 to 587 μM with the detection limit as low as 0.47 μM. Furthermore, the I- induced fluorescence (FL) quenching mechanism was investigated employing a combination of techniques, including UV-vis/fluorescence spectroscopy, Density Functional Theory (DFT) calculation, TEM and time-resolved fluorescence decay measurements. The DFT calculation results demonstrated that the amino- and amide groups of N-CDs play a significant role in iodide recognition through the formation of multiple N-H⋯I-, C-H⋯I- and C([double bond, length as m-dash]O)N-H⋯I- interactions with I-. The TEM experiment confirmed the aggregation process when I- was added to the N-CDs solution. Moreover, the radiative decay rate of N-CDs, which was first measured and reported the kinetic behaviors of the FL-quenching process, decreased from 3.30 × 107 s-1 to 1.95 × 107 s-1 after the coordination with I- ions. The reduced lifetime demonstrated that the excited energy dissipation led to a dynamic quenching process. Therefore, such carbon materials can function as effective fluorescent switches for the selective detection of I- ions.

Energy transfer processes and structure of carboxymethyl cellulose-Tb/Eu nanocomplexes with color-tunable photoluminescence

A series of fluorescent nanocomplexes of carboxymethyl cellulose (CMC)/Terbium (Tb)- Europium (Eu) were successfully synthesized without introducing a second ligand. By adjusting the concentration of the coordinated ions, these nanocomplexes exhibit favorably visibly tunable luminescence properties with colors being able to change from green to red. The XPS analysis demonstrates the formation Tb(III)-O^2- and Eu(III)-O^2- between OH and COO^- in CMC and Tb³⁺ or Eu³⁺ ions, which is advantage for light absorption by UV-Vis spectroscopy and fluorescence spectroscopy. The ligand CMC plays a role in coordinating with terbium and europium ions, but also serves as an energy donor to these metal ions by antenna effect. Moreover, the energy transfer also occurred from terbium ions to europium ions in CMC matrix, which is responsible for the tunable luminescence properties of these complexes.

Aluminum-Based Surface Polymerization on Carbon Dots with Aggregation-Enhanced Luminescence

Aggregation-induced luminescence quenching of carbon nanodots (CDs) is the main obstacle for their applications in solid-state light emitting devices. Herein, we developed a one-step synthesis of solid-state emissive CDs with surface aluminum-based polymerization by adding AlCl₃ in citric acid and urea via a microwave-heating dehydration process. Due to the strong coordination ability of Al ions with N and O atoms, considerable steric hindrance of Al-based cross-linked polymerization was introduced on the surface of the CDs, which not only avoided aggregation of the green emissive carbon cores but also facilitated efficient energy transfer from the blue emissive polymerized surface to the green emissive carbon cores in aggregates, leading to enhanced green emissions with a photoluminescence quantum yield (PLQY) of 72.7% in the solid state.

Two-Photon Fluorescent Nanomaterials and Their Applications in Biomedicine

In recent years, two-photon excited (TPE) materials have attracted great attentions because of their excellent advantages over conventional one-photon excited (OPE) materials, such as deep tissue penetration, three-dimensional spatial selectivity and low phototoxicity. Also, they have been widely applied in lots of field, such as biosensing, imaging, photo-catalysis, photoelectric conversion, and therapy. In this article, we review recent advances in vibrant topic of two-photon fluorescent nanomaterials, including organic molecules, quantum dots (QDs), carbon dots (CDs) and metal nanoclus-ters (MNCs). The optical properties, synthetic methods and important applications of TPE nanomaterials in biomedical field, such as biosensing, imaging and therapy are introduced. Also, the probable challenges and perspectives in the forthcoming development of two-photon fluorescent nanomaterials are addressed.

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.

Surface chemistry regulates the optical properties and cellular interactions of ultrasmall MoS2 quantum dots for biomedical applications

Molybdenum disulfide quantum dots (MoS2 QDs) have drawn increasing attention owing to their distinct optical properties and potential applications in many fields such as biosensing, photocatalysis and cell imaging. Elucidating the relationship between the surface chemistry of MoS2 QDs and their optical properties as well as biological behaviors is critical for their practical applications, which remain largely unclear. Herein, by adopting a sulfur vacancy modification strategy, a toolbox of MoS2 QDs functionalized with different thiolate ligands was prepared. The effect of surface chemistry on the optical properties of MoS2 QDs was systematically explored by various spectroscopic techniques, revealing the important role of surface ligands in defining their absorption band gap and luminescence quantum yield. Furthermore, cellular experiments showed that the cytotoxicity and intracellular fate (i.e., lysosomal accumulation) of MoS2 QDs are closely related to the properties of surface ligands. Our results underscore the important roles of surface ligands in regulating the properties and biological interactions of these QDs, which will facilitate the future development of MoS2-based materials with precisely controlled functions for biomedical applications.

Engineering an Injectable Electroactive Nanohybrid Hydrogel for Boosting Peripheral Nerve Growth and Myelination in Combination with Electrical Stimulation

Electrical stimulation (ES) can be used to manipulate recovery after peripheral nerve injuries. Although biomaterial-based strategies have already been implemented to gain momentum for ES and engineer permissive microenvironments for neural regeneration, the development of biomaterials for specific stimuli-responsive modulation of neural cell properties remains a challenge. Herein, we homogeneously incorporate pristine carbon nanotubes into a functional self-assembling peptide to prepare a hybrid hydrogel with good injectability and conductivity. Two-dimensional (on the surface) and three-dimensional (within the hybrid hydrogel) culturing experiments demonstrate that ES promotes axon outgrowth and Schwann cell (SC) migration away from dorsal root ganglia spheres, further revealing that ES-enhanced interactions between SCs and axons result in improved myelination. Thus, our study not only advances the development of tailor-made materials but also provides useful insights into comprehensive approaches for promoting nerve growth and presents a practical strategy of repairing peripheral nerve injuries.

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.

Recent Advances on Graphene Quantum Dots as Multifunctional Nanoplatforms for Cancer Treatment

Graphene quantum dots (GQDs), the latest member of the graphene family, have attracted enormous interest in the last few years, due to their exceptional physical, chemical, electrical, optical, and biological properties. Their strong size-dependent photoluminescence and the presence of many reactive groups on the graphene surface allow their multimodal conjugation with therapeutic agents, targeting ligands, polymers, light responsive agents, fluorescent dyes, and functional nanoparticles, making them valuable agents for cancer diagnosis and treatment. In this review, the very recent advances covering the last 3 years on the applications of GQDs as drug delivery systems and theranostic tools for anticancer therapy are discussed, highlighting the relevant factors which regulate their biocompatibility. Among these factors, the size, kind, and degree of surface functionalization have shown to greatly affect their use in biological systems. Toxicity issues, which still represent an open challenge for the clinical development of GQDs based therapeutic agents, are also discussed at cellular and animal levels.

Far-Red Carbon Dots as Efficient Light-Harvesting Agents for Enhanced Photosynthesis

Sunlight utilization by plants via the photosynthesis process is limited to the visible spectral range. How to expand the utilization spectral range via construction of a hybrid photosynthetic system is a hot topic in this field. In this work, far-red carbon dots (FR-CDs) with excellent water solubility, good biocompatibility, high quantum yield (QY), and superior stability were prepared by a one-step microwave synthesis in 3 min. The as-prepared FR-CDs is an efficient converter transferring ultraviolet A (UV-A) light to 625-800 nm far-red emission, which can be directly absorbed and utilized by chloroplasts. Due to the broader spectral utilization of solar energy and Emerson effect, increased photosynthetic activity can be achieved both in vivo and in vitro when applied for Roman lettuce. The in vitro hybrid photosynthetic system via coating chloroplasts with FR-CDs presents higher electron transfer efficiency between PS II (photosystem II) to PS I (photosystem I), which consequently increases the ATP production. The in vivo experiment further confirms that FR-CDs-treated lettuce can induce a 28.00% higher electron transfer rate compared with the control group, which results in 51.14 and 24.60% enhancement of fresh and dry weights, respectively. This work is expected to provide a way for improving the conversion efficiency from solar energy to chemical energy. (PS II) to photosystem I (PS I), which consequently increases the ATP production. The in vivo experiment further confirms that FR-CDs-treated lettuce can induce a 28.00% higher electron transfer rate compared with the control group, which results in 51.14 and 24.60% enhancement of fresh and dry weights, respectively. This work is expected to provide a way for improving the conversion efficiency from solar energy to chemical energy.

Easy Synthesis of BiVO4 for Photocatalytic Overall Water Splitting

Developing a photocatalyst system to generate hydrogen from water is a topic of great interest for fundamental and practical importance. In this study, we develop a new Z-scheme photocatalytic system for overall water splitting that consists of Rh/K₄Nb₆O₈ for H₂ evolution, Pt/BiVO₄ for O₂ evolution, and I^-/IO₃ ^- for an electron mediator under UV light irradiation. The oxygen evolution photocatalyst BiVO₄ was prepared by the microwave-assisted hydrothermal method. The method is fast and simple, as compared to conventional hydrothermal synthesis. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV-visible spectroscopy. The photocatalytic water splitting is investigated in (i) aqueous AgNO₃ as sacrificial electron scavengers and (ii) a Z-scheme photocatalytic water splitting system. The BiVO₄ photocatalysts prepared by the microwave-assisted hydrothermal method not only showed a very high oxygen evolution rate (2622 μmol g^-1 h^-1) of water splitting reaction in an aqueous AgNO₃ solution but also achieved a high H₂ evolution rate (340 μmol g^-1 h^-1) and O₂ evolution rate (172 μmol g^-1 h^-1) in a Z-scheme overall water splitting system.