Green Fluorescent Carbon Dots with Critically Controlled Surface States: Make Silk Shine via Feeding Silkworms.

Feeding silkworms with functional materials as additives to produce naturally modified silk is a facile, diverse, controllable, and environmentally friendly method with a low cost of time and investment. Among various additives, carbon dots (CDs) show unique advantages due to their excellent biocompatibility and fluorescence stability. Here, a new type of green fluorescent carbon dots (G-CDs) is synthesized with a high oil-water partition ratio of 147, a low isoelectric point of 5.16, an absolute quantum yield of 71%, and critically controlled surface states. After feeding with G-CDs, the silkworms weave light yellow cocoons whose green fluorescence is visible to the naked eye under UV light. The luminous silk is sewn onto the cloth to create striking patterns with beautiful fluorescence. Such G-CDs have no adverse effect on the survival rate and the life cycle of silkworms and enable their whole bodies to glow under UV light. Based on the strong fluorescence, chemical stability, and biological safety, G-CDs are found in the digestive tracts, silk glands, feces, cocoons, and even moth bodies. G-CDs accumulate in the posterior silk glands where fibroin protein is secreted, indicating its stronger combination with fibroin than sericin, which meets the requirements for practical applications.

Nitrogen-Doped and Sulfonated Carbon Dots as a Multifunctional Additive to Realize Highly Reversible Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) using the Zn metal anode have been considered as one of the next-generation commercial batteries with high security, robust capacity, and low price. However, parasitic reactions, notorious dendrites and limited lifespan still hamper their practical applications. Herein, an eco-friendly nitrogen-doped and sulfonated carbon dots (NSCDs) is designed as a multifunctional additive for the cheap aqueous ZnSO4 electrolyte, which can overcome the above difficulties effectively. The abundant polar groups (-COOH, -OH, -NH2 , and -SO3 H) on the CDs surfaces can regulate the solvation structure of Zn2+ through decreasing the coordinated active H2 O molecules, and thus redistribute Zn2+ deposition to avoid side reactions. Some of the negatively charged NSCDs are adsorbed on Zn anode surface to isolate the H2 O/SO4 2- corrosion through the electrostatic shielding effect. The synergistic effect of the doped nitrogen species and the surface sulfonic groups can induce a uniform electrolyte flux and a homogeneous Zn plating with a (002) texture. As a result, the excellent cycle life (4000 h) and Coulombic efficiency (99.5%) of the optimized ZIBs are realized in typical ZnSO4 electrolytes with only 0.1 mg mL-1 of NSCDs additive.

Mulberry-Leaves-Derived Red-Emissive Carbon Dots for Feeding Silkworms to Produce Brightly Fluorescent Silk.

Fluorescent silk has promising applications in dazzling textiles, biological engineering, and medical products, but the natural Bombyx mori silk has almost no fluorescence. Here carbon dots (CDs) made from mulberry leaves are reported, which have a strong near-infrared fluorescence with absolute quantum yield of 73% and a full width at half maximum of 20 nm. After feeding with such CDs, silkworms exhibit bright red fluorescence, grow healthily, cocoon normally, and turn to moths finally. The cocoons are pink in daylight and show bright red fluorescence under ultraviolet light. After breaking out of such cocoons, the red-emissive moths can mate and lay fluorescent eggs which would hatch normally. The growth cycle of the second generation of the test silkworm is the same as that of the control group, which means such CDs have excellent biocompatiblility. Dissection and analyses on both the test silkworms and cocoons disclose the metabolic route of the CDs, that is, the fluorescent CDs are absorbed by silkworms from alimentary canals, then transferred to silk glands, and finally to cocoons, while those unabsorbed CDs are excreted with the feces. All experimental results confirm the excellent biocompatibility and fluorescence stability of such CDs.

In-Situ Growth of Mn3 O4 Nanoparticles on Nitrogen-Doped Carbon Dots-Derived Carbon Skeleton as Cathode Materials for Aqueous Zinc Ion Batteries.

Mn3 O4 is a promising cathode material for aqueous zinc ion batteries (ZIBs) which is a new type of low cost, eco-friendly, high security energy storage system, while those previously reported electrochemical capacities of Mn3 O4 are far from its theoretical value. In this work, Mn3 O4 nanoparticles and nitrogen-doped carbon dots (NCDs) are synthesized together through an in-situ hydrothermal route, and then calcined to be a nanocomposite in which Mn3 O4 nanoparticles are anchored on a nitrogen-doped carbon skeleton (designated as Mn3 O4 /NCDs). Although the carbon content is only 3.9 wt.% in the Mn3 O4 /NCDs, the NCDs-derived carbon skeleton provides an electrically conductive network and a stable structure. Such a special nanocomposite has a large specific surface area, plenty of active sites, excellent hydrophilicity and good electronic conductivity. Owing to these structural merits, the Mn3 O4 /NCDs electrode exhibits a preeminent specific capacity of 443.6 mAh g-1 and 123.3 mAh g-1 at current densities of 0.1 and 1.5 A g-1 in ZIBs, respectively, which are far beyond the bare Mn3 O4 nanoparticles synthesized under the similar condition. The electrochemical measurement results prove that carbon dots, as a new type of carbon nanomaterials, have strong ability to modify and improve the performance of existing electrode materials, which may push these electrode materials forward to practical applications.

Red Fluorescent Carbon Dot Powder for Accurate Latent Fingerprint Identification using an Artificial Intelligence Program.

Development and comparison of the latent fingerprints (LFPs) are two major studies in detection and identification of LFPs, respectively. However, integrated research studies on both fluorescent materials for LFP development and digital-processing programs for LFP comparison are scarcely seen in the literature. In this work, highly efficient red-emissive carbon dots (R-CDs) are synthesized in one pot and mixed with starch to form R-CDs/starch phosphors. Such phosphors are comparable with various substrates and suitable for the typical powder dusting method to develop LFPs. The fluorescence images of the developed LFPs are handled with an artificial intelligence program. For the optimal sample, this program presents an excellent matching score of 93%, indicating that the developed sample has very high similarity with the standard control. Our results are significantly better than the benchmark obtained by the traditional method, and thus, both the R-CDs/starch phosphors and the digital processing program fit well for the practical applications.

Efficient Oxygen Electrocatalyst for Zn-Air Batteries: Carbon Dots and Co9S8 Nanoparticles in a N,S-Codoped Carbon Matrix.

Non-noble metal-based bifunctional electrocatalysts for both oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) are an essential component of high-performance rechargeable Zn-air batteries (ZABs). Herein, we report a novel and simple method for preparing Co9S8 nanoparticles embedded in N and S codoped carbon materials with aid of carbon dots (CDs). CDs play a key role in distributing Co9S8 nanoparticles in the matrix uniformly and enhancing the specific surface area and the electric conductivity simultaneously. The obtained Co9S8/CD@NSC exhibits an excellent ORR and OER bifunctional catalytic activity and a great long-term durability, with a half-wave potential of 0.84 V versus reversible hydrogen electrode (RHE) for the ORR and a low potential of 1.62 V versus RHE at 10 mA cm-2, which outperform the popular Pt/C and RuO2 commercial catalysts. Moreover, the Co9S8/CD@NSC catalyst also displays a superior activity and cycling stability as a cathode material in ZABs, which is far better than Pt/C + RuO2 mixture catalysts. Such a ZAB shows a low charge/discharge voltage gap of 0.62 V and great cycling stability over 125 h at 10 mA cm-2.

Robust Negative Electrode Materials Derived from Carbon Dots and Porous Hydrogels for High-Performance Hybrid Supercapacitors.

Hybrid supercapacitors generally show high power and long life spans but inferior energy densities, which are mainly caused by carbon negative electrodes with low specific capacitances. To improve the energy densities, the traditional methods include optimizing pore structures and modifying pseudocapacitive groups on the carbon materials. Here, another promising way is suggested, which has no adverse effects to the carbon materials, that is, constructing electron-rich regions on the electrode surfaces for absorbing cations as much as possible. For this aim, a series of hierarchical porous carbon materials are produced by calcinating carbon dots-hydrogel composites, which have controllable surface states including electron-rich regions. The optimal sample is employed as the negative electrode to fabricate hybrid supercapacitors, which show remarkable specific energy densities (up to 62.8-90.1 Wh kg-1 ) in different systems.

Heteroatom-doped carbon dots based catalysts for oxygen reduction reactions.

Carbon materials doped with heteroatoms are a class of cost-effective and stable electrocatalysts for oxygen reduction reactions (ORR), whose activities are mainly based on the heteroatom-related active sites. Besides the widely reported one-dimensional carbon nanotubes and two-dimensional graphene materials, carbon dots (CDs), as a new kind of zero-dimensional carbon materials, exhibit a range of unique structures and promising catalytic activities for ORR. In order to optimize the complex conditions of carbon-based catalysts, composites consisting of doped CDs and reduced graphene oxide (rGO) (designated as CD/rGO) are prepared hydrothermally, in comparison with directly doped rGO. All produced composites outperform their corresponding directly doped rGO counterparts in ORR measurements. It is noted that nitrogen and sulfur co-doped samples perform better than those doped by individual N or S. Mechanistic relationships between the ORR catalytic activities and the catalyst features are proposed, including type, location, bonding, fraction and synergistic effects of dopants, as well as the composition and structure of the carbon substrates. It is apparent that doping heteroatoms and constructing carbon substrates play a synergistic role in yielding high-performance carbon based catalysts.

Solvent-Controlled Synthesis of Highly Luminescent Carbon Dots with a Wide Color Gamut and Narrowed Emission Peak Widths.

Carbon dots (CDs) have tremendous potential applications in bioimaging, biomedicine, and optoelectronics. By far, it is still difficult to produce photoluminescence (PL) tunable CDs with high quantum yield (QY) across the entire visible spectrum and narrow the emission peak widths of CDs close to those of typical quantum dots. In this work, a series of CDs with tunable emission from 443 to 745 nm, quantum yield within 13-54%, and narrowed full width at half maximum (FWHM) from 108 to 55 nm, are obtained by only adjusting the reaction solvents in a one-pot solvothermal route. The distinct optical features of these CDs are based on their differences in the particle size, and the content of graphitic nitrogen and oxygen-containing functional groups, which can be modulated by controlling the dehydration and carbonization processes during solvothermal reactions. Blue, green, yellow, red, and even pure white light emitting films (Commission Internationale de L'Eclairage (CIE)= 0.33, 0.33, QY = 39%) are prepared by dispersing one or three kinds of CDs into polyvinyl alcohol with appropriate ratios. The near-infrared emissive CDs are excellent fluorescent probes for both in vitro and in vivo bioimaging because of their high QY in water, long-term stability, and low cytotoxicity.

Highly Efficient Red-Emitting Carbon Dots with Gram-Scale Yield for Bioimaging.

Carbon dots (CDs) are a new class of photoluminescent (PL), biocompatible, environment-friendly, and low-cost carbon nanomaterials. Synthesis of highly efficient red-emitting carbon dots (R-CDs) on a gram scale is a great challenge at present, which heavily restricts the wide applications of CDs in the bioimaging field. Herein, R-CDs with a high quantum yield (QY) of 53% are produced on a gram scale by heating a formamide solution of citric acid and ethylenediamine. The as-prepared R-CDs have an average size of 4.1 nm and a nitrogen content of about 30%, with an excitation-independent emission at 627 nm. After detailed characterizations, such strong red fluorescence is ascribed to the contribution from the nitrogen- and oxygen-related surface states and the nitrogen-derived structures in the R-CD cores. Our R-CDs show good photostability and low cytotoxicity, and thus they are excellent red fluorescence probes for bioimaging both in vitro and in vivo.

Self-Assembled ZnO Nanoparticle Capsules for Carrying and Delivering Isotretinoin to Cancer Cells.

ZnO@polymer core-shell nanoparticles are assembled into novel capsule shells with diameters of about 100 nm to load isotretinoin (ISO) with a capacity as high as 34.6 wt %. Although ISO, a widely used drug for acne treatment, by itself is not suitable for treating cancer because of its hydrophobicity, our ZnO-ISO composite showed much stronger anticancer activity. The improved cytotoxicity is ascribed to the synergistic effects of the ZnO@polymer and ISO, where the ZnO@polymer helps in the accumulation of ISO in cancer cells on the one hand, and on the other hand, ISO is released completely through ZnO decomposition under acidic conditions of cancer cells. Such a pH-triggered drug-delivery system exhibits a much improved killing of cancer cells in vitro in comparison with the benchmarks, Nintedanib and Crizotinib, two commercial drugs clinically applied against lung cancer.

Red-Emissive Carbon Dots for Fingerprints Detection by Spray Method: Coffee Ring Effect and Unquenched Fluorescence in Drying Process.

Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.

Facile synthesis of red-emitting carbon dots from pulp-free lemon juice for bioimaging.

In this work, red-emitting carbon dots (R-CDs) with a high quantum yield (QY) of 28% in water were synthesized for the first time by heating an ethanol solution of pulp-free lemon juice. The obtained R-CDs were mono-dispersed with an average diameter of 4.6 nm, and exhibited excitation-independent emission at 631 nm. Meanwhile, these R-CDs featured low cytotoxicity and good photostability, which allow R-CDs to be employed as luminescent probes for in vitro/in vivo bioimaging. In addition, a detailed study on the physical properties and structural compositions of the sodium borohydride (NaBH4) reduced R-CDs with orange emission suggested that surface states on the R-CD surfaces and nitrogen-derived structures in the R-CD cores synergistically caused their intense red luminescence. The low-cost and eco-friendly synthesis method and favorable optical properties of R-CDs make these carbon dots promising for further applications, such as bioimaging and light-emitting diodes.

Carbon Dots/NiCo2 O4 Nanocomposites with Various Morphologies for High Performance Supercapacitors.

A series of carbon dots/NiCo2 O4 composites with various morphologies are prepared and tested for supercapacitors. These samples have good electrical conductivities and efficient ions transport paths, so they exhibit high specific capacitances, superior rate performances, and high cycling stabilities. The optimal composite for hybrid supercapacitor exhibits a high energy density up to 62.0 Wh kg-1 .

ZnO-Based Nanoplatforms for Labeling and Treatment of Mouse Tumors without Detectable Toxic Side Effects.

ZnO quantum dots (QDs) were synthesized with polymer shells, coordinated with Gd(3+) ions and adsorbed doxorubicin (DOX) together to form a new kind of multifunctional ZnO-Gd-DOX nanoplatform. Such pH sensitive nanoplatforms were shown to release DOX to cancer cells in vitro and to mouse tumors in vivo, and reveal better specificity and lower toxicity than free DOX, and even better therapeutic efficacy than an FDA approved commercial DOX-loading drug DOX-Liposome Injection (DOXIL, NDA#050718). The ZnO-Gd-DOX nanoplatforms exhibited strong red fluorescence, which benefited the fluorescent imaging on live mice. Due to the special structure of ZnO-Gd-DOX nanoparticles, such nanoplatforms possessed a high longitudinal relaxivity r1 of 52.5 mM(-1) s(-1) at 0.55 T, which was superior to many other Gd(3+) based nanoparticles. Thus, both fluorescence labeling and magnetic resonance imaging could be applied simultaneously on the tumor bearing mice along with drug delivery. After 36 days of treatment on these mice, ZnO-Gd-DOX nanoparticles greatly inhibited the tumor growth without causing any appreciable abnormality in major organs. The most important merit of ZnO-Gd-DOX was that such a nanoplatform was biodegraded completely and showed no toxic side effects after H&E (hematoxylin and eosin) staining of tumor slices and ICP-AES (inductively coupled plasma atomic emission spectrometry) bioanalyses.

Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism.

Carbon dots (CDs) with tunable photoluminescence (PL) and a quantum yield of up to 35% in water were hydrothermally synthesized in one pot and separated via silica column chromatography. These separated CDs emitted bright and stable luminescence in gradient colors from blue to red under a single-wavelength UV light. They exhibited high optical uniformity; that is, every sample showed only one peak in the PL excitation spectrum, only one peak in the excitation-independent PL emission spectrum, and similar monoexponential fluorescence lifetimes. Although these samples had similar distributions of particle size and graphite structure in their carbon cores, the surface state gradually varied among the samples, especially the degree of oxidation. Therefore, the observed red shift in their emission peaks from 440 to 625 nm was ascribed to a gradual reduction in their band gaps with the increasing incorporation of oxygen species into their surface structures. These energy bands were found to depend on the surface groups and structures but not on the particle size, not as in traditional semiconductor quantum dots. In addition, because of their excellent PL properties and low cytotoxicity, these CDs could be used to image cells in different colors under a single-wavelength light source, and the red-emitting CDs could be used to image live mice because of the strong penetration capability of their fluorescence.

Folic acid functionalized ZnO quantum dots for targeted cancer cell imaging.

Aqueous stable luminescent ZnO quantum dots (QDs) were successfully synthesized with primary amine groups on the surface, which were designed to conjugate with folic acid (FA) to produce the final ZnO-FA QDs. Such ZnO-FA QDs were able to target some specific cancer cells with overexpressed FA receptors on the membranes and thus differentiate the MCF-7 cancer cells from the normal 293T cells. The nanoparticle uptaking experiments by different cells were carried out in parallel and tracked by confocal laser microscopy dynamically. The results confirmed the specificity of our ZnO-FA QDs towards the FA-receptor overexpressed cancer cells, which had potential for diagnosing cancers in vitro.

Hierarchical porous carbon materials with high capacitance derived from Schiff-base networks.

A type of hierarchical porous carbon material was prepared using a Schiff-base network as the precursor and ZnCl2 as the activation agent, and their electrochemical performances were investigated in acid and alkaline aqueous solutions, respectively. The as-prepared materials have high surface areas, appropriate distributions of hierarchical pore sizes, and various forms of nitrogen/oxygen derivatives. These structural advantages guarantee the outstanding performances of such carbon materials as electrodes for supercapacitors, which include high specific capacitances, fast current responses, and high cycling stabilities.

Nitrogen and sulfur co-doped carbon dots with strong blue luminescence.

Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C=N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a wide detection range and excellent accuracy as fluorescent sensors for Fe(3+) ions.

In situ tracking the intracellular delivery of antisense oligonucleotides by fluorescein doped silica nanoparticles.

Antisense oligonucleotides (ASOs) are often utilized to interfere with gene expression at mRNA level for cancer treatment. Here, we synthesized fluorescein doped silica nanoparticles (FSNPs) and coated them by polyethyleneimine (PEI) for carrying ASOs. Agarose gel electrophoresis proved that PEI/FSNPs could load ASOs by a weight ratio as high as 30:1. We tracked the delivery process of ASOs from the ASOs/PEI/FSNPs composites to HeLa cells in situ by the confocal laser scanning microscopy (CLSM) techniques, including nuclear staining and Z-axis scanning. We found the ASOs/PEI/FSNPs composites exhibited their biological effects at specific intracellular localization, and the fluorescence of the FSNPs showed the dynamic delivery process in the cells.