Concentration Of Carbon Dots Research Articles

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as in vitro antimicrobial drug nanocarrier

ABSTRACT Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min−1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min−1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL−1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications.

Physicochemical characterization, biodistribution, and bio‐effects of fluorescent carbon dots from roasted Spanish mackerel

AbstractNanoparticles with small sizes formed in the process of food thermal treatment have gained substantial attention due to their safety uncertainty and latent risks to human health. Herein, the physicochemical features of fluorescent carbon dots (CDs) from roasted Spanish mackerel were studied, it was found that the size distribution, fluorescence properties, surface groups, and formation process of CDs were highly dependent on the roasting time of Spanish mackerel. The interaction of CDs with digestive proteases resulted in the structural change and activity inhibition of proteases. When the concentration of CDs was 120 μg mL−1, the enzyme activity of pepsin and trypsin was reduced from 100% to 75.95% and 78.5%, respectively. The CDs caused static fluorescence quenching of pepsin and trypsin as confirmed by the fluorescence analysis. After oral administration, CDs can be transported to the main organs through the blood. The cytotoxicity assessment revealed that the cell viability decreased with the prolonging of roasting time. The CDs roasted at 230°C for 40 min showed a significant hemolytic effect even at a low concentration of 0.5 mg mL−1. Moreover, the cellular uptake level and pathway of CDs were significantly affected by blood protein adsorption. This study helps to evaluate the in vivo biodistribution, the interaction with proteases during gastrointestinal digestion, and the cellular uptake of CDs after transport through the blood, providing a theoretical basis for revealing the potential effects of foodborne nanoparticles.

Carbon Dot Based Multicolor Electroluminescent LEDs with Nearly 100% Exciton Utilization Efficiency.

Carbon dots (CDs) are promising nanomaterials for next-generation lighting and displays due to their tunable bandgap, high photoluminescence quantum yield (PLQY), and high stability. However, the exciton utilization efficiency (EUE) of CD-based films can only reach 25%, fundamentally limiting their application in electroluminescent light-emitting diodes (LEDs). Improving the EUE is therefore of great significance. Herein, we developed composite films containing CDs and poly(9-vinylcarbazole) (PVK). The films were then used to construct a series of high-performance electroluminescent LEDs with tunable emission colors covering the blue to green regions as the concentration of CDs in the films increased, delivering a maximum external quantum efficiency and current efficiency of 2.62% and 5.11 cd/A, respectively. Theoretical calculations and experiments established that the excellent performance at low film PLQY was due to a hot exciton effect in the CDs, achieving nearly 100% EUE. This work provides new design strategies toward high-performance CD-based electroluminescent LEDs.

Mineralization and morphology control of CaCO3 induced by glutamic acid derivatized carbon dots

Calcium carbonate (CaCO3) exhibits multiple morphologies and properties to meet different requirements through biomineralization in nature. In this study, carbon dots (CDs) were prepared by a microwave method using glutamic acid and ethylenediamine as raw materials. The mineralization of CaCO3 was subsequently proceeded in the presence of CDs by means of gas diffusion. The effects of the ratio of glutamic acid to ethylenediamine, the concentrations of CDs and Ca2+ on the mineralization process were studied. Fourier transform infrared (FTIR) spectrometer, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) were employed for characterizations of CDs and CaCO3. The results indicated that the CDs had a uniform size of 4–6 nm and good dispersion in the aqueous phase due to the numerous –COOH groups on the surface. The crystallization of CaCO3 was strongly affected by CDs, presenting various morphologies of rhombic, spherical, hexagonal, hydrangea-shaped, and cobblestone-shaped. The presence of CDs was conducive to the formation and stable existence of vaterite and the content of vaterite was up to 97.61%. The possible mechanism proposed was related to the –COOH groups on CDs. The multiple controllable forms of CaCO3 may provide various applications such as drug sustained release and so on.

Mechanical Force-Induced Color-Variable Luminescence of Carbon Dots in Boric Acid Matrix.

Mechano-luminescent materials that exhibit distinct luminescence responses to force stimuli are urgently anticipated in view of application needs in the fields of sensing, anti-counterfeiting, optoelectronic devices, etc. However, most of the reported materials normally exhibit force-induced changes in luminescent intensity, whereas materials that possess force-induced color-variable luminescence remain rarely reported. Herein, for the first time, a novel mechanical force-induced color-variable luminescence material from carbon dots (CDs) in boric acid (CD@BA) is reported. At low CDs concentration, the luminescence of CD@BA exhibits a grinding-induced color variable from white to blue. This grinding-induced color variable can be switched to yellow-to-white changing by increasing the CDs concentration in BA. The grinding-induced color-variable luminescence originates from dynamic variation in emission ratio of fluorescence and room temperature phosphorescence, due to the influence of oxygen and water vapor in the air. At high CDs concentration, short-wavelength fluorescence undergoes more severe reabsorption compared to room temperature phosphorescence, leading to grinding-induced color-variable switching from white-to-blue to yellow-to-white. Based on the unique properties of CD@BA powder, the applications of recognizing and visualizing fingerprints on the surfaces of various of materials are demonstrated.

Impact of the Concentration Ethylenediamine on Optical Properties of Carbon Dots from Jengkol Peel (Archinendron pauciflorum)

Carbon dots (CDs) are a new member of fluorescent nano carbons that have attracted attention because of their potential applications derived from their optical, chemical, and electrical properties. CDs from jengkol peel via the solvothermal method at 200 oC for 7 h with the addition of ethylenediamine (EDA) as a heteroatom dopant have been successfully carried out. This study aims to determine the effect of concentration EDA on the optical properties of CDs for the possible reason. The results revealed that the CDs solution has fluorescence properties; that bluish-green glow can be observed under ultraviolet radiation (365 nm). The UV - Vis absorption peaks did not depend on the CDs concentration, but the absorbance intensity decreased with increasing EDA concentration. The best fluorescence properties were possessed by 10 % EDA in CDs which produced λex/λem of 370 nm / 518 nm, respectively, with a quantum yield of 42 %. The FTIR spectra of all samples showed that the CDs surface had functional groups such as carboxylic acids, hydroxyl, and amines. The obtained CDs have the potential to be used as heavy metal ion detectors, bioimaging, and antibacterial agents.

Effects of plastic-derived carbon dots on germination and growth of pea (Pisum sativum) via seed nano-priming

Seed nano-priming is a promising technology employed in the agronomic field to promote seed germination and plant growth. However, the effects of carbon dots (CDs) on plant development via seed nano-priming remain unclear. In the present study, CDs synthesized from non-biodegradable plastic wastes were adopted as a nano-priming agent for pea (Pisum sativum) seed treatment. The results demonstrated positive effects of seed priming at all CD concentrations (0.25–2 mg/mL), including accelerated seed germination rate, increased shoot and root elongation, biomass accumulation, and root moisture level compared to the control groups. Surface erosion of seed coat was observed after CD priming, which effectively promoted seed imbibition capability. CD penetration, internalization, and translocation were confirmed using transmission electron microscopy. Furthermore, the CD-plant interaction significantly enhanced seed antioxidant enzyme activity, as well as augmented root vigor, chlorophyll content, and carbohydrate content. These findings exhibit great potential of waste-derived CDs as nano-priming agents for seed germination and seedling development in a cost-effective and sustainable manner.

Effect of Carbon Dots Concentration on Electrical and Optical Properties of Their Composites with a Conducting Polymer.

PSS composites were prepared via the hydrothermal method from glucose carbon quantum dots (CQDs) and an aqueous solution of PEDOT:PSS conducting polymer and their electrical and optical properties were investigated. The morphology and structure of these samples were investigated by AFM, SEM, EDX, and EBSD. It was found that the CQDs and CQD/PEDOT:PSS composites had a globular structure with globule sizes of ~50-300 nm depending on the concentration of PEDOT:PSS in these composites. The temperature dependence of the resistivity was obtained for the CQD/PEDOT:PSS (3%, 5%, 50%) composites, which had a weak activation character. The charge transport mechanism was discussed. The dependence of the resistivity on the storage time of the CQD/PEDOT:PSS (3%, 5%, 50%) composites and pure PEDOT:PSS was obtained. It was noted that mixing CQDs with PEDOT:PSS allowed us to obtain better electrical and optical properties than pure CQDs. PSS (3%, 5%, 50%) composites are more conductive composites than pure CQDs, and the absorbance spectra of CQD/PEDOT:PSS composites are a synergistic effect of interaction between CQDs and PEDOT:PSS. We also note the better stability of the CQD/PEDOT:PSS (50%) composite than the pure PEDOT:PSS film. PSS (50%) composite is promising for use as stable hole transport layers in devices of flexible organic electronics.

Carbon dots fabricated by solid-phase carbonization using p-toluidine and l-cysteine for sensitive detection of copper

In this study, a label-free “turn off” fluorescent sensor has been resoundingly fabricated using carbon dots (CDs) for ultrasensitive detection of copper ions (Cu2+). CDs are prepared by solid phase carbonization method using p-toluidine and l-cysteine as the precursors. The synthesized CDs exhibited the highest fluorescence intensity with excitation and emission wavelengths set at 300 nm and 400 nm, respectively. The CDs were selective and sensitive to Cu2+ due to the static quenching mechanism. The concentration of CDs, and solution pH and incubation time were important parameters for the developed sensor. The experimental results showed that 20 mgL−1 was enough for the analysis. As the solution pH was concerned, it was apparent that the sensor was endowed with an excellent response signal to Cu2+ and provided high sensitivity at pH 12. The interaction occurred very quickly, and the incubation time could be set at 1 min. The sensor provided a two-stage calibration curve to Cu2+ in the range of 0.05–0.7 and 0.7–4 μM with a limit of detection of 47 nM. The obtained results clearly demonstrated that this facile method was fast, reliable and selective for detecting Cu2+, which would explore a prospective strategy for developing effective and low-cost sensors for monitoring metal ions in aqueous environments.

Preparation of a Novel Carbon Dot/Polyvinyl Alcohol Composite Film and Its Application in Food Preservation.

Carbon dots (CDs) were synthesized with the facile hydrothermal method to produce CDs/polyvinyl alcohol (PVA) active food packaging films. The CDs had a diameter ranging from 2.01 to 5.61 nm and were well-dispersed. The effects of different concentrations of CDs on mechanical strength, water resistance, morphology, optical, and thermal performance of the CDs/PVA films were discussed. The incorporation of CDs in the PVA film improved its mechanical properties, water resistance properties, UV blocking properties, and thermal stability and endowed the composite film with antioxidant and antimicrobial properties. The maximum scavenging rates of 2,2-diphenyl-1-picrylhydrazyl and ABTS free radicals by the 0.50% CDs/PVA film were 72.81 and 97.08%, respectively. The inhibition zone diameters of the 0.50% CDs/PVA solution against Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), and Escherichia coli (E. coli) were 9.52, 8.21, and 9.05 mm, respectively. Using the 0.50% CDs/PVA film as active packaging, the shelf life of banana, jujube, and fried meatballs was observed to be extended significantly. These results demonstrate the viability of the CDs/PVA composite film as a promising active food packaging material.

Accelerating the extracellular electron transfer of Shewanella oneidensis MR-1 by carbon dots: The role of carbon dots concentration

The high performance of microbial extracellular electron transfer (EET) is essential for bioremediation and bioenergy generation. Carbon dots (CDs) modified electroactive microorganisms showed an increased electron transfer efficiency. However, the influence of CDs’ concentration the EET has not been illustrated before. Herein, we reported that the addition of CDs increased the current generation by accelerating the EET process. The maximum current output of microbial electrochemical cells with the addition of CDs was increased by more than 5 times compared to pure Shewanella oneidensis MR-1. With CDs addition, the increase of biofilm immobilization and flavins secretion improved the direct and mediated EET process. Electrochemical analyses clarified that the combination of cytochrome c with CDs resulted in a faster electron transfer rate. The overload of CDs would restrict their promotion effect on EET, which may be due to their biotoxicity to bacteria. This work offered the insight of CDs’ concentration on the efficiency of EET, not only promoting the related applications of EET but also inspiring the regulation of microorganism function via nanomaterial.

Aptamer-Adjusted Carbon Dot Catalysis-Silver Nanosol SERS Spectrometry for Bisphenol A Detection.

Carbon dots (CDs) can be prepared from various organic (abundant) compounds that are rich in surfaces with –OH, –COOH, and –NH2 groups. Therefore, CDs exhibit good biocompatibility and electron transfer ability, allowing flexible surface modification and accelerated electron transfer during catalysis. Herein, CDs were prepared using a hydrothermal method with fructose, saccharose, and citric acid as C sources and urea as an N dopant. The as-prepared CDs were used to catalyze AgNO3–trisodium citrate (TSC) to produce Ag nanoparticles (AgNPs). The surface-enhanced Raman scattering (SERS) intensity increased with the increasing CDs concentration with Victoria blue B (VBB) as a signal molecule. The CDs exhibited a strong catalytic activity, with the highest activity shown by fructose-based CDs. After N doping, catalytic performance improved; with the passivation of a wrapped aptamer, the electron transfer was effectively disrupted (retarded). This resulted in the inhibition of the reaction and a decrease in the SERS intensity. When bisphenol A (BPA) was added, it specifically bound to the aptamer and CDs were released, recovering catalytical activity. The SERS intensity increased with BPA over the concentration range of 0.33–66.67 nmol/L. Thus, the aptamer-adjusted nanocatalytic SERS method can be applied for BPA detection.

Carbon dots enhanced gelatin/chitosan bio-nanocomposite packaging film for perishable foods

Carbon dots (CDs) with intriguing fluorescent property, good biocompatibility, high stability, easy interaction with substrates, are burgeoning carbon nanoparticles with large potential in various applications. Incorporating CDs into the polymer matrix is becoming a popular strategy to endow the complex with new functions. Herein, the green-synthesized CDs was integrated into the mixture of gelatin (derived from waste fish scale) and chitosan, and a multifunctional bio-nanocomposite (defined as Gelatin/Chitosan/CDs) film was developed, which showed the excellent antibacterial, antioxidant, pH-sensitivity, UV shielding, and blue-emission properties. The effects of different concentrations of CDs on the physical, mechanical, structural, and functional activity of bio-nanocomposite film were tested. Compared with the Gelatin/Chitosan film, the Gelatin/Chitosan/CDs film with an optimum addition of 20% CDs showed the enhanced antibacterial, antioxidant as well as UV shielding activities. More importantly, it was used as an effective packaging material for fish meat preservation, reducing the loss of nutritional quality consumption, extending the shelf life of food. Besides, the bio-nanocomposite films also possessed the anti-counterfeiting and pH-responsive properties due to the strong fluorescent emission of CDs, and had the great potential in developing the intelligent packaging materials. Our work shed new light on the new application of CDs and the synthesis of bio-nanocomposite film in food industry.

Capillary electrophoresis coupled to chemometrics for analysis of carbon dots in nanoparticles mixtures.

Since their discovery in 2004, carbon dots (CDs) have attracted attention due to their intrinsic physicochemical properties and the easy synthesis from simple precursors. However, quantification of CDs in mixtures of nanoparticles with similar sizes and surface functionality is still a challenging issue for research applications or regulatory purposes. In this work, CDs and silver nanoparticles were first synthesized under alkaline conditions by using glucose as precursor and capping agent, respectively. Mixtures of these nanoparticles were made at micromolar range, without purification, and then analyzed by CE-DAD, using an electrolyte solution composed of 20mM sodium borate and 20mM SDS at pH 8.5, in a total time of <15min. The three-way electrophoretic data were then decomposed by advanced chemometric models, parallel factor analysis and multivariate curve resolution-alternating least-squares. The explained variances for both models were 95.8% (parallel factor analysis) and 85.3% (multivariate curve resolution-alternating least-squares). In both cases, the quality of the results was verified by the root mean square standard deviation coefficient variation, which resulted lower than 5%, and no significant bias was observed at 95% of statistical confidence. Satisfactory prediction for CDs concentration was obtained with recovery values between 80.0% and 115%.

Nanodrug Transmembrane Transport Research Based on Fluorescence Correlation Spectroscopy.

Although conventional fluorescence intensity imaging can be used to qualitatively study the drug toxicity of nanodrug carrier systems at the single-cell level, it has limitations for studying nanodrug transport across membranes. Fluorescence correlation spectroscopy (FCS) can provide quantitative information on nanodrug concentration and diffusion in a small area of the cell membrane; thus, it is an ideal tool for studying drug transport across the membrane. In this paper, the FCS method was used to measure the diffusion coefficients and concentrations of carbon dots (CDs), doxorubicin (DOX) and CDs-DOX composites in living cells (COS7 and U2OS) for the first time. The drug concentration and diffusion coefficient in living cells determined by FCS measurements indicated that the CDs-DOX composite distinctively improved the transmembrane efficiency and rate of drug molecules, in accordance with the conclusions drawn from the fluorescence imaging results. Furthermore, the effects of pH values and ATP concentrations on drug transport across the membrane were also studied. Compared with free DOX under acidic conditions, the CDs-DOX complex has higher cellular uptake and better transmembrane efficacy in U2OS cells. Additionally, high concentrations of ATP will cause negative changes in cell membrane permeability, which will hinder the transmembrane transport of CDs and DOX and delay the rapid diffusion of CDs-DOX. The results of this study show that the FCS method can be utilized as a powerful tool for studying the expansion and transport of nanodrugs in living cells, and might provide a new drug exploitation strategy for cancer treatment in vivo.

Promoting effect of cellulose-based carbon dots at different concentrations on multifunctional photocatalytic degradation of dyes by ZnO

In this work, a novel cellulose based fluorescent carbon dots (CDs) doped ZnO composite, ZnO/CDs-x (x = 10, 20, 30, 40), was developed as a photocatalyst for the photocatalytic degradation of four dyes. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV visible diffuse reflectance spectroscopy (UV–Vis DRS), and transient photocurrent measurements were carried out to study the effects of different concentrations of CDs on the morphology and photocatalytic properties of ZnO/CDs−x (x = 10, 20, 30, 40) composites. When the concentration of CDs increased, the structure of ZnO/CDs−x (x = 10, 20, 30, 40) changed from a peony like structure (x = 10, 20) to a hexagonal prism like structure (x = 30, 40) and assembled into a flower like structure. Flower like ZnO/CDs-20 showed the best photocatalytic performance and good durability under UV light, and three types of excitation effects were observed: mixed light > sunlight > visible light. It was found that the addition of CDs with a concentration of 20 mL in ZnO can significantly enhance the photoabsorption and the separation of photogenerated carriers, which is beneficial to improve the photocatalytic performance.

Antibacterial Properties of Citric Acid/β-Alanine Carbon Dots against Gram-Negative Bacteria.

While multi-drug resistance in bacteria is an emerging concern in public health, using carbon dots (CDs) as a new source of antimicrobial activity is gaining popularity due to their antimicrobial and non-toxic properties. Here we prepared carbon dots from citric acid and β-alanine and demonstrated their ability to inhibit the growth of diverse groups of Gram-negative bacteria, including E. coli, Salmonella, Pseudomonas, Agrobacterium, and Pectobacterium species. Carbon dots were prepared using a one-pot, three-minute synthesis process in a commercial microwave oven (700 W). The antibacterial activity of these CDs was studied using the well-diffusion method, and their minimal inhibitory concentration was determined by exposing bacterial cells for 20 h to different concentrations of CDs ranging from 0.5 to 10 mg/mL. Our finding indicates that these CDs can be an effective alternative to commercially available antibiotics. We also demonstrated the minimum incubation time required for complete inhibition of bacterial growth, which varied depending on bacterial species. With 15-min incubation time, A. tumefaciens and P. aeruginosa were the most sensitive strains, whereas E. coli and S. enterica were the most resistant bacterial strains requiring over 20 h incubation with CDs.

Competition of the roles of π-conjugated domain between emission center and quenching origin in the photoluminescence of carbon dots depending on the interparticle separation

The π-conjugated domain, which is one of frequently-suggested fluorescence origin of carbon dots (CDs), can also act as fluorescence quenching origin in aggregated state. This dual role of the π-conjugated domain in CDs offers a challenge to prediction of photoluminescence (PL) characteristics in solid-state. Here, we focus on the effect of π-conjugated domain on the PL phenomenon for different interparticle separation using three types of CDs with different degree of carbonization. The degree of carbonization was controlled by selecting three alcoholic solvent species for solvothermal reaction, which can influence carbonization of CDs. In dilute dispersion, CDs from three different solvents possessed two emissive centers originated from surface- and core-state with different relative intensities depending on the degree of carbonization. With the increase in concentration of CDs, the higher contents of π-conjugated domain changed the dominant PL center from surface- to core-state due to the greater reduction of surface-derived emission. In aggregated state, the emission from surface-state was totally suppressed, and the π-conjugated domain contents influenced the emission efficiency of core-state. Based on PL decay results, we proposed the PL mechanism of the CDs for different interparticle separation, which would extend the boundary in the interpretation of PL properties of CDs.

Solid-phase synthesis of red dual-emissive nitrogen-doped carbon dots for the detection of Cu2+ and glutathione

Red dual-emissive carbon dots (CDs) were prepared by a novel and facile solvent-free carbonization method using O-phenylenediamine (OPD) as precursor and Al(NO3)3·9H2O as assistant. The prepared CDs manifesting intriguing dual-emission behavior at 600 nm and 650 nm demonstrate good fluorescence quenching rate (99%) on Cu2+, in which the linear range was 6–33 μM and detection limit was 0.145 μM. In addition, the CDs-Cu2+ system shows excellent glutathione (GSH) turn-on detection in the range of 19–52 μM, where a red-shift to 650 nm and 700 nm was observed and the maximum value of F/F0 is 5.8. Reasonable quenching mechanism was speculated to be the combination of static and dynamic quenching. Cytotoxicity measurements displayed good biocompatibility of CDs and cell viability was higher than 83% even under the highest concentration of CDs.

Solid-state photoluminescent silicone-carbon dots/dendrimer composites for highly efficient luminescent solar concentrators

Luminescent solar concentrators (LSCs) with high performances depend on not only the luminescent materials, but their dispersed polymer matrixes. However, carbon dots (CDs)-based LSCs suffer from aggregation-caused fluorescence quenching with the increased concentration of CDs in polymer matrix. To solve this issue, a novel solid-state photoluminescent (PL) silicone-carbon dots (Si-CDs) composites was synthesized by one-step solvothermal treatment of citric acid, dicyandiamide and 3-aminopropyltriethoxysilane (APTES). The solid-state PL Si-CDs showed yellow-green emission at 525 nm under excitation of UV light. For better dispersion of Si-CDs, two types of silicone dendrimers (denoted as D1 and D2) were designed and synthesized via a transesterification and hydrosilylation reaction method. The structure differences between D1 and D2 are the contents of phenyl and methoxy groups. Remarkably, silicone dendrimers with high loading of Si-CDs (up to 35 wt%) could be obtained owing to their good compatibility. Single-layered LSCs could be prepared easily by directly casting the above mixtures on glass substrates followed by room temperature curing. The external optical efficiency (ηopt) of 7.58%, 5.38% had been achieved from D1 and D2 based LSCs (25 × 25 × 1 mm), respectively. This work provides a convenient method for preparing highly efficient LSCs, posing great potential in various specific applications.