One-pot synthesis of concentration and excitation dual-dependency truly full-color photoluminescence carbon dots

The paper describes a kind of truly full-color photoluminescence (PL) CDs. The CDs were prepared by using one-pot hydrothermally heating citric acid and formamide at 200 °C for 2 h. The CDs have three fluorescent centers at blue, green, and red light region. Their color was regulated through two means, including changing excitation wavelengths or CDs concentrations. The emission maxima changed from blue to red with the increase of excitation wavelengths or CDs concentrations. The full-color PL behavior of the CDs was inherited and conserved in the solid polymer matrix, giving multicolor CDs/polymer films and light emitting diodes (LEDs). White-light LED (WLED) with the CIE coordinate approaching to (0.31, 0.32) were also achieved.     

Synthesis of orange-red emissive carbon dots for fluorometric enzymatic determination of glucose

The authors describe a method for the preparation of orange-red emissive carbon dots (CDs) with excitation/emission peaks at 520/582 nm. The CDs were hydrothermally prepared by a one-pot strategy from trimesic acid and 4-aminoacetanilide. The fluorescence of the CDs is strongly quenched by hydrogen peroxide. The oxidation of glucose by glucose oxidase (GOx) produces H₂O₂ that quenches the fluorescence via static quenching. Based on this phenomenon, a fluorometric method was established for the determination of glucose. Under the optimum conditions, response is linear in the 0.5 to 100 μM glucose concentration range, with a 0.33 μM limit of detection. The method is selective for glucose over its analogues and was successfully applied to the determination of glucose in diluted human serum and in urine from diabetics and healthy individuals. Recoveries from spiked samples range from 98.7 to 102.5%.

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Graphical abstract (a) One-step synthetic strategy of the CDs; (b) Schematic illustration of the CDs for glucose detection

     

Dually emissive P,N-co-doped carbon dots for fluorescent and photoacoustic tissue imaging in living mice

Hydrothermal treatment of a mixture of ethylene diamine, phosphoric acid and citric acid under ambient pressure generates fluorescent carbon dots that are co-doped with phosphorus and nitrogen. These have features such as (a) both green fluorescence (peaking at 430 nm; 30% quantum yield) and red fluorescence (peaking at 500 nm, quantum yield 78%), (b) wavelength-dependent emission peaks, and (c) insensitivity to changes of pH values, dot concentration and ionic strength. The C-dots are useful for both fluorescent (FL) and photoacoustic (PA) imaging of living tissue. PA imaging warrants better spatial resolution and allows deeper tissues to be imaged compared to most optical imaging techniques. It is essential to assign a photoacoustic contrast agent as most of the diseases do not show a natural photoacoustic contrast in their early stage. The dually emitting C-dots are shown to be a useful contrast agent for PA and FL imaging of mice tumors. Intravenous administration of the C-dots resulted in strong signals in both PA and FL imaging.

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Graphical abstract Photographs of the excitation wavelength-dependent fluorescence of P,N-doped C-dots obtained from ethylenediamine, phosphoric acid and citric acid. Intravenous administration of the C-dots resulted in strong signals in both photoacoustic (PA) and fluorescent (FL) imaging.

     

Large scale synthesis of red emissive carbon dots powder by solid state reaction for fingerprint identification

Red emissive carbon dots(CDs) powder was synthesized on a large scale from phloroglucinol and boric acid by a novel solid state reaction with yield up to 75%. This method is safe and convenient, for it needs neither high pressure reactors nor complicated post-treatment procedures. The as-prepared carbon dots powder exhibited strong red fluorescence with excitation-independent behavior. XPS measurement and PL spectra suggest that such red fluorescence arise from boron-doped structures in CDs, which increases along with the boron concentration on CDs surface but decreases when the concentration quenching effect takes place. To overcome the aggregation induced fluorescence quenching of the solid CDs powder,the conventional methods are dispersing CDs into a large amount of inert substrates. But our present work provides a new strategy to realize strong red fluorescence of CDs in solid state. As a result, such carbon dots powder works well for latent fingerprint identification on various material surfaces.     

Long-wavelength (red to near-infrared) emissive carbon dots: Key factors for synthesis,fluorescence mechanism,and applications in biosensing and cancer theranostics

Carbon dots (CDs), as a new member of carbon nanostructures, have been widely applied in extensive fields due to their exceptional physicochemical properties. While, the emissions of most reported CDs are located in the blue to green range under the excitation of ultraviolet or blue light, which severely limits their practical applications, especially in photovoltaic and biological fields. Studies that focused on synthesizing CDs with long-wavelength (red to near-infrared) emission/excitation features (simply named L-w CDs) and exploring their potential applications have been frequently reported in recent years. In this review, we analyzed the key influence factors for the synthesis of CDs with long wavelength and multicolor (containing long wavelength) emissive properties, discussed possible fluorescence mechanism, and summarized their applications in sensing and cancer theranostics. Finally, the existing challenges and potential opportunities of L-w CDs are presented.     

Yellow emissive carbon dots in ludox silica matrix with anticancer activity for enhanced imaging of developed sweat latent fingermarks

The recognition of fingermarks plays a vital role during a criminal investigation. In the current scenario, fluorescent nano-powders emerged as a potential candidate for latent fingermark detection. We pioneer the use of microwave technology for the synthesis of carbon dots (CDs) with the cationic surfactant (cetylpyridinium chloride). The surfactant-derived CDs exhibit yellow fluorescence and emission at 545 nm with high quantum yield of (QY～34%). The prepared CDs also demonstrated amphiphilic properties. These luminous CDs were combined with ludox HS-30 to develop fluorescent hybrid nano-powders for the detection of sweat latent fingermarks on a non-porous surface. The ludox@CDs accumulate particle size 11.36 ± 1.235 nm and surface area 111 cm³/g^?1. The fluorescent hybrid nano-powders emerged to be successful in creating high contrast and accurate latent fingermark images. Furthermore, cytotoxicity studies on breast cell lines (fR-2 and MCF-7) were conducted by using ludox@CDs. The results revealed that ludox@CDs were less toxic and biocompatible in comparison to the commercialized dusting reagents. Fortunately, ludox@CDs demonstrated anticancer efficacy against MCF-7 breast cancer cell lines. Thus, our findings herald a new age for fluorescent hybrid nano-powders in criminal investigation and biomedical applications.     

A novel phosphorus oxide quantum dots as an emissive nanomaterial for inorganic ions screening and bioimaging

In this work, a novel blue-green fluorescence phosphorous oxide quantum dots (PO QDs) was synthesized by solvothermal method in N-methyl-2-pyrrolidone (NMP) solution without any protection treatment during synthesis. Upon excitation at 400 nm, PO QDs emitted blue-green fluorescence with quantum yield of 0.28. PO QDs exhibited the high inertness to air or moisture, the excellent water solubility, and stable emission intensity in a wide pH range and in high ionic strength solution. Interestingly, PO QDs could give the positive optical response to iron ions (Fe³⁺) and iodine ion (I⁻). The photoluminescence (PL) of PO QDs could be directly quenched by Fe³⁺. While I⁻ quenched the PO QDs PL by means of Ag⁺-mediated PO QDs system via the internal filtration effects (IFE) induced by the formation of AgI. Moreover, the biocompatibility and low toxicity of PO QDs verified in bean sprout and Hela cells indicated the promising application of PO QDs in medicine related fields. Furthermore, PO QDs could also be utilized in luminescent composite film for various application scenarios     

Fluorescence correlation spectroscopy using quantum dots: advances, challenges and opportunities

Semiconductor nanocrystals (quantum dots) have been increasingly employed in measuring the dynamic behavior of biomacromolecules using fluorescence correlation spectroscopy. This poses a challenge, because quantum dots display their own dynamic behavior in the form of intermittent photoluminescence, also known as blinking. In this review, the manifestation of blinking in correlation spectroscopy will be explored, preceded by an examination of quantum dot blinking in general.     

Quantum-sized carbon dots for bright and colorful photoluminescence

We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.     

Bio-safety assessment of carbon quantum dots,N-doped and folic acid modified carbon quantum dots: A systemic comparison

The carbon quantum dots(CQDs) and their functionalized materials are promising in biomedical field because of their unique properties;meanwhile,a growing concern has been raised about the potential toxicity of these modified materials in biosystem.In this study,we synthesized original CQDs and two common functionalized CQDs including N-doped CQDs(NCQDs) and folic acid-modified CQDs(FACQDs),and compared the toxicity and biocompatibility with each other in vitro and in vivo.L929,C6 and normal cell MDCK were selected to detect the adverse reaction of these materials in vitro.No acute toxicity or obvious changes were noted from in vitro cytotoxicity studies with the dose of these CQD materials increasing to a high concentration at 1 mg/mL.Among these materials,the FA-CQDs show a much lower toxicity.Moreover,in vivo toxicity studies were performed on the nude mice for 15 days.The experimental animals in 10 or 15 mg/kg groups were similar with animals treated by phosphate buffer solution(PBS) after 15 days.The results of the multifa rious biochemical parameters also suggest that the functionalized products of CQDs do not influence the biological indicators at feasible concentration.Our findings in vitro and in vivo through toxicity tests demonstrate that CQDs and their modified materials are safe for future biological applications.     

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis.     

Patterned alignment of nematic liquid crystals generated by inkjet printing of gold nanoparticles and emissive carbon dots on both flexible polymer and rigid glass substrates

Patterned homeotropic alignment using nanoparticles (NPs) was achieved using inkjet printing. Two types of gold NPs, one smaller and one larger in core diameter (2 and 5 nm) capped with a monolayer of dodecanethiol, and emissive carbon dots with a core diameter of 2.5 nm featuring a mixed ligand shell of carboxylic acid groups and aliphatic hydrocarbon chains were tested on both rigid glass and flexible polycarbonate substrates. To define the director across the entire cell and not just in the NP-printed areas, alignment ‘underlayers’ were tested, and 30° obliquely evaporated SiO_x as alignment ‘underlayer’ generally provided the best results with the highest quality of the homeotropic alignment as well as the best contrast at the boundary between printed and non-printed (i.e. homeotropic and planar) domains of the fabricated cells. We also report that the chemical nature of the nematic liquid crystal (LC) used, the number of layers printed and the composition of the nano-ink need to be adjusted to obtain pattern alignment devices that positively benefit from both the properties of the LC and the nanomaterial printed.     

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

A facile, low-cost, green, kilogram-scale synthesis of high quality CQDs were synthesized. The throughput of CQDs is 1.4975 kg in one pot and the as-prepared CQDs have a highly crystalline hexagonal structure with remarkable solubility, stability, and biocompatibility. It showed outstanding electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility.     

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

The development of large-scale synthetic methods for high quality carbon quantum dots (CQDs) is fundamental to their applications. However, the macroscopic preparation and scale up synthetic of CQDs is still in its infancy. Here, we report a facile, green, kilogram-scale synthesis of high quality fluorescent CQDs derived from poplar leaves via a one-step hydrothermal method. Notably, the throughput of CQDs can reach a level up to as high as 1.4975 kg in one pot. The structure and properties of the as-prepared CQDs were assessed through TEM, XRD, XPS and various spectroscopic methods. The obtained high quality CQDs with a photoluminescent quantum yield of 10.64% showed remarkable stability in aqueous media, rich functional groups, high photostability, consistent photoluminescence within biological pH range and low cytotoxicity. On account of these good properties, we demonstrated the multifunctional application to electrocatalytic water splitting, Fe³⁺ sensing and bioimaging. It showed remarkable electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility. This study provides a green, facile, inexpensive and large-scale method for producing high quality CQDs, which provides application value for large-scale production of CQDs.     

Graphene and carbon quantum dots electrochemistry

Graphene and carbon quantum (QDs) dots exhibit interesting and well-defined properties owing to their quantum confinement. In this work, graphene QDs (G-QDs) and carbon QDs of size ~ 6 nm and ~ 2 nm, respectively, were prepared and their potential uses in electrochemistry and electrochemical sensing were subsequently investigated. It was discovered that the C-QDs surface displayed a faster electron transfer rate compared to the G-QDs following analyses with the ferro/ferricyanide redox probe. Studies were also carried out with redox biomarkers such as uric acid (UA) and ascorbic acid (AA), and it was found that while the C-QDs displayed electrocatalytic properties toward the oxidation of both UA and AA, the G-QDs seemed to only have an impact on AA, from the decrease in the oxidation peak potential. This work provides direct electrochemical comparison of the two latest frontiers of carbon nanomaterials and opens the way for their electrochemical sensing applications.     

Structural engineering design of carbon dots for lubrication

Carbon dots (CDs) have opened up a new field of carbon nanomaterials and successively attracted increasing attention since their discovery in 2004. Owing to their ultrasmall size, tunable surface functional groups, excellent dispersibility, attractive stability, low toxicity, environmental friendliness, facile synthesis and low-cost precursors, CDs have been developed as green and promising friction-reducing and anti-wear materials in lubrication science, applied to energy conservation and extension of mechanical service life in recent years. However, there are few reviews focusing on the application of CDs in the important field of lubrication. In this review, we comprehensively summarize the development of CDs in lubrication for the first time. Firstly, three strategies for structural engineering design of CDs to improve their tribological characteristics are fully analyzed, in terms of size and shape control, surface modification and heteroatom doping. Secondly, the advance in lubrication application of CDs, including CDs as additives for lubricants, greases, gel and magnetorheological fluids as well as CDs as lubricating coatings, is systematically highlighted. Thirdly, the lubricating mechanisms of CDs as additives are introduced in detail. Furthermore, the remaining major challenges and opportunities for CDs in lubrication field are discussed and outlined.     

Analytical and bioanalytical applications of carbon dots

Carbon dots (CDs) comprise a recently discovered class of strongly fluorescent, emission-color-tuning and non-blinking nanoparticles with great analytical and bioanalytical potential. Raw CDs can be obtained by laser ablation or electrochemical exfoliation of graphite, from soot, or thermal carbonization, acid dehydration or ultrasonic treatment of molecular precursors. Passivation of raw CDs makes them fluorescent and their functionalization confers reactivity towards selected targets. CDs can be excited by single-photon (ultraviolet or near-ultraviolet) and multi-photon (red or near-infrared) excitation, and their luminescence properties are due to surface defects. CDs are being proposed as bioimaging probes because they comprise non-toxic elements and are biocompatible. Passivated and functionalized CDs can be made to sense pH, metal ions and molecular substances.     

Multifunctional N,S co-doped carbon dots for sensitive probing of temperature,ferric ion,and methotrexate

Analytical and Bioanalytical Chemistry - In this paper, we have presented a facile method to fabricate nitrogen and sulfur co-doped carbon dots (N,S-CDs) for blood methotrexate (MTX) sensing...