Carbon Quantum Dots Concentration Research Articles

Sustainable fabrication of fluorescent carbon quantum dots as an optical amplifier in modern agriculture, anti-counterfeiting, food packing and intelligent pH detection

Carbon quantum dots (CQDs) have received a great deal of attention due to their distinctive luminescent features and exciting potential applications in the fields of agronomy, enhanced anti-counterfeiting, drug tracking and intelligent sensing and detection. The focus of the current effort is on easily transforming toxic, non-biodegradable waste expanded polystyrene foam (WEPS) into extremely luminescent CQDs and investigating their various applications. As a nano-priming agent for Cajanus cajan (L.), the green pigeon pea (GPP), WEPS derived CQDs are used. The outcomes showed that seed priming had beneficial effects at all CQDs concentrations (100-900 mg/L), including accelerated seed germination rate, increased shoot and root length, augmented root vigour, higher chlorophyll content and biomass accumulation in comparison to the control groups. The most crucial data coding can be protected under 365 nm UV light using the optimized CQDs concentration (700 mg/L) blue fluorescent ink. In addition, a straightforward sensing platform with high sensitivity and selectivity is needed for the detection of dual metal ions, as well as one with a "turn-on and turn-off" fluorescence (FL) response. Additionally, a composite film containing well-dispersed CQDs (700 mg/L) in polyvinyl alcohol and strong hydrogen-bond interaction is successfully developed to alleviate the FL quenching caused by CQD aggregation. The resulting film had extraordinary FL performance, good mechanical flexibility and high transparency (transmittance of 90 %). Even more remarkably, this luminescent film showed sensitive pH responsiveness, signifying that when pH is stimulated, the FL intensity changed. A smart pH-detector based on this luminescent film is logically created as a proof-of-concept for real-time sensing and detection of pH changes in human sweat. These results show that WEPS derived CQDs have enormous potential as nano-priming agents for seed germination, seedling development, anti-counterfeiting ink, food packaging and intelligent pH-detector in wearable, real-time health monitoring.

Synthesis of carbon quantum dots from Trigonella foenum-graecum L seeds and their biodistribution in mice as an inorganic isotope label

Nowadays, researchers are paying significant attention to the processing of natural carbon sources in order to improve human safety and reduce environmental pollution by means of green synthesis methods. Based on this, the present study has been investigated the green synthesis of carbon quantum dots (CQDs) with unique properties, by a natural carbon source called Trigonella foenum-graecum L (TF), through one- pot hydrothermal strategy. The results of different analysis methods (FTIR, FESEM, EDAX, TEM, UV–Vis, and PL) provided the necessary confirmations for the synthesized CQDs. Synthesized CQDs with spherical morphology and an average size of ∼ 5 nm have been a quantum efficiency of 18.9 % and optimal fluorescence under the excitation wavelength of 410 nm. Subsequently, the biological effects of CQDs (MTT assay) on CT26 cancer cell line was confirmed to be cytotoxic by observing an increase in the concentration of CQDs along with the IC50 value (∼826 μg/ml). Also, the two factors of colloidal stability and cytotoxicity, which depend on the concentration of CQDs, were considered to investigate the biological distribution of labeled 99mTc-CQDs that were intravenously injected into rats. Taken together, this work has been succeeded in providing data on the potential of CQDs for diagnostic and imaging fields in broader research.

Facile synthesis of hollow carbon fiber/carbon quantum dots composite aerogels for oil sorption

Oil spill accidents are presented as a severe environmental problem because they cause ecological damage in the short and long term, especially in the aquatic environment. For this reason, the development of efficient materials to separate oil/water mixtures is fundamental. Studies have been performed using aerogels to fulfill this purpose because they are materials with a high porosity and high surface area, formed by solid particle networks and interconnected pores; these properties make them ideal for application as petroleum adsorbents. In this study, a simpler synthesis process using only renewable and environmentally friendly reagents for obtaining hollow carbon fiber/carbon quantum dots composite aerogels (CF-QD) is presented. Sorbent materials were prepared using an easy dip-coating technique and pyrolysis. Analyzing the effect of the concentration of carbon quantum dots (CQDs) in aerogels on the properties and adsorption capacity. CF-QD manifested remarkable characteristics, including a high surface area (up to 360.7 m2/g), hydrophobic surface, excellent buoyancy, and good adsorption capacity (up to 84.1 g/g). These features make them a viable option for application as sorbents for organic liquids, including oil.

Carbon quantum dot-induced developmental toxicity in Daphnia magna involves disturbance of symbiotic microorganisms

With the increasing synthesis and application of carbon quantum dots (CQDs), their prevalence as pollution in water environments has increased. However, the toxic effects of CQDs on aquatic organisms are unclear, and their environmental safety must be evaluated. Herein, Daphnia magna was used as a model organism to explore the developmental toxicity of CQDs under a full life-cycle exposure. It was found that the feeding rate and offing number of D. magna decreased with increasing CQD concentration, and the body length of D. magna showed a trend of first increasing and then decreasing. These results indicated that long-term exposure to CQDs has evident toxic effects on D. magna development. Symbiosis analysis showed that the composition of the symbiotic microbial community of D. magna was disturbed by CQDs. The abundance of microorganisms involved in the immune response of D. magna such as Rhodobacter, decreased; those involved in the inflammation such as Gemmobacter, increased; and those involved in the nitrogen cycle, such as Hydrogenophaga and Paracoccus, decreased. When D. magna was subjected to environmental pressure, host-microflora interactive immune regulation was induced. The abundance of probiotics in D. magna, such as Rhodococcus, increased in response to environmental pressure. The results of KEGG function prediction showed that the abundance of symbiotic microorganisms involved in energy absorption and metabolism was affected by CQDs. In addition, the correlation analysis showed that there was a correlation between the changes in the symbiotic microbial community and the damage to D. magna after exposure to CQDs. Thus, it is appealed that as a potential environmental pollutant, CQDs have aquatic environmental risks, and their safe application deserves attention.

Positive responses and mechanisms of nitrifying sludge to carbon quantum dots: reactor performance, microbial behavior, and antioxidant defense.

Extensive application of carbon quantum dots (CQDs) enlarges its concentration in sewage treatment system. The response of nitrifying sludge to CQDs after long-term exposure was investigated. Results showed that CQD concentrations of 0-100mg/L presented positive effect to enzymes involved in nitrification, accelerating NH4+-N degradation and NO2--N transformation. The oxidation rate of NO2--N was significantly improved from 3.14 to 7.91mg/(L h) under the stress of 100mg/L CQDs. Besides, CQDs stimulated the production of sludge biomass and kept the stability of sludge settleability. Additionally, CQDs were mainly captured by loosely bound extracellular polymeric substances, reducing aromatic-like protein. Microbes alleviated CQD stress by secreting tryptophan-like protein and polysaccharides. After few CQDs entered cells, intracellular antioxidant defense was activated. Total antioxidant capacity level was heightened at least 31%. The activities of superoxide dismutase and catalase were enhanced at relatively low and high CQD concentration levels. Hence, microbial metabolic pathways, microbial community, and nitrifying bacteria were not significantly affected by CQDs. The findings of this work provide new insight for understanding the environmental implication of CQDs in the biological treatment system.

Carbon Quantum Dots from Roasted Coffee Beans: Their Degree and Mechanism of Cytotoxicity and Their Rapid Removal Using a Pulsed Electric Field.

Carbon quantum dots (CQDs) from heat-treated foods show toxicity, but the mechanisms of toxicity and removal of CQDs have not been elucidated. In this study, CQDs were purified from roasted coffee beans through a process of concentration, dialysis and lyophilization. The physical properties of CQDs, the degree and mechanism of toxicity and the removal method were studied. Our results showed that the size of CQDs roasted for 5 min, 10 min and 20 min were about 5.69 ± 1.10 nm, 2.44 ± 1.08 nm and 1.58 ± 0.48 nm, respectively. The rate of apoptosis increased with increasing roasting time and concentration of CQDs. The longer the roasting time of coffee beans, the greater the toxicity of CQDs. However, the caspase inhibitor Z-VAD-FMK was not able to inhibit CQDs-induced apoptosis. Moreover, CQDs affected the pH value of lysosomes, causing the accumulation of RIPK1 and RIPK3 in lysosomes. Treatment of coffee beans with a pulsed electric field (PEF) significantly reduced the yield of CQDs. This indicates that CQDs induced lysosomal-dependent cell death and increased the rate of cell death through necroptosis. PEF is an effective way to remove CQDs from roasted coffee beans.

Optimization of electrospun CQDs-Fe3O4-RE loaded PVA-cellulose nanofibrils via central composite design for wound dressing applications: Kinetics and in vitro release study

Wound skin infections can cause significant morbidity and even mortality. Cellulose nanofibrils (CNFs) are a type of nano cellulose that have reached notable attention due to their inimitable properties. In this study, in order to prepare a novel wound dressing, CNFs are composited with poly (vinyl alcohol) (PVA) to enhance mechanical properties and increase cell proliferation and migration. Also, carbon quantum dots (CQDs)- Fe3O4 was introduced as a novel antibacterial, and rosemary extract (RE) was composited with this to reduce its cell toxicity. PVA - CNFs/ CQDs- Fe3O4- RE nanofiber was prepared using the electrospinning method. Then, to maximize tensile strength, total elongation, and percentage swelling of PVA - CNFs/ CQDs- Fe3O4- RE electrospun nanofiber, parameters of crosslinking duration and the concentration of CQDs- Fe3O4-RE were optimized employing central composite design, and optimized electrospun nanofiber (OEN) as a novel wound dressing was prepared. Results exhibited, the high antibacterial properties of CQDs-Fe3O4-RE. Also, CNFs and CQDs- Fe3O4-RE increased the tensile strength of OEN. Moreover, CNFs and RE reduce wound area percentages and increase the percentage of cell viability, respectively. Therefore, OEN was introduced as a suitable wound dressing due to its appropriate surface roughness, mechanical properties, WVTR, biodegradation, prolonged release, non-toxicity, and high cell proliferation and migration ability.

Warm to cool tunable ultra-stable white light emissions from carbon dots -Tb3+ - Eu3+ doped silica

Development of ultra-stable, solid-state, cost-effective phosphors for white light emitting devices with high color rendition is in high demand. In this work, we prepared carbon quantum dots (CQDs) by a hydrothermal method with an average size ranging from 2 to 8 nm which exhibits low toxicity. Optical analysis confirmed the influence of both Cu2+ and Fe3+ ions and the excitation-dependent fluorescence of CQDs are effectively quenched by addition of Fe3+ ions. The excitation dependent emission property of CQDs and degradation resistant blue emission of CQDs-silica are utilized to construct CQDs-Europium–Terbium doped silica matrices for stable multi-colour emissions upon different excitation wavelengths. Optimized composition of CQDs with Terbium and Europium ions produced white light emissions under UV exposure of 370–393 nm. Continuous tuning from warm white emission to cool white emission with moderate CRI is achieved by varying the concentration of CQDs. The ultra-stable white emissions which last long for a year, reveals the potential WLED applications of these solid-state luminescent materials.

New Insights into the Cellular Toxicity of Carbon Quantum Dots to Escherichia coli.

In this study, the cytotoxicity and toxic mechanism of carbon quantum dots (CQDs) to E. coli were evaluated in vitro. The synthetic CQDs were extremely small in size (~2.08 nm) and displayed strong fluorescence. The results demonstrated that CQDs showed good biocompatibility with E. coli within a short culture time. However, when the exposure time exceeded 24 h, the toxicity of CQDs became apparent, and the contents of reactive oxygen species, lactate dehydrogenase, and the crystal violet absorption rate increased significantly. To further explore the cytotoxic mechanism, approaches including confocal laser scanning microscopy, scanning electron microscopy, and biological transmission electron microscopy combined with zeta potential tests, osmotic pressure measurement, and comet assays were performed. On the one hand, the CQDs altered the surface charges of cells and induced lipid peroxidation by adhesion on the surface of E. coli, leading to an increase in the permeability of the cell wall. On the other hand, when the concentration of CQDs reached 200 µg/mL, the osmotic pressure of the extracellular environment was significantly reduced. These are the main factors that lead to cell edema and death. Finally, the comet assays confirmed that CQDs could induce DNA damage, which could inhibit the proliferation of E. coli.

A Versatile Synthetic Pathway for Producing Mesostructured Plasmonic Nanostructures.

Highly branched gold (Au) nanostructures with sharp tips are considered excellent substrates for surface-enhanced Raman scattering (SERS)-based sensing technologies. Here, a simple synthetic route for producing Au or Au-Ag bimetallic mesostructures with multiple sharpened tips in the presence of carbon quantum dots (CQDs) is presented. The morphologies of these mesostructured plasmonic nanoparticles (MSPNs) can be controlled by adjusting the concentration of CQDs, reaction temperatures, and seed particles. The optimal molar ratio for [HAuCl4 ]/[CQDs] is found to be ≈25. At this molar ratio, the diameters of MSPNs can be tuned from 80 to 200nm by changing the reaction temperature from 25 to 80 °C. In addition, it is found that hierarchical MSPNs consisting of multiple Au nanocrystals can be formed over the entire seed particle surface. Finally, the SERS activity of these MSPNs is examined through the detection of rhodamine 6G and methylene blue. Of the different mesostructures, the bimetallic MSPNs have the highest sensitivity with the ability to detect 10-7 m of rhodamine 6G and 10-6 m of methylene blue. The properties of these MSPN particles, made using a novel synthetic process, make them excellent candidates for SERS-based chemical sensing applications.

Smart epoxy/polyurethane/carbon quantum dots hybrid coatings: Synthesis and study of UV-shielding, viscoelastic, and anti-corrosive properties

ABSTRACT This project was performed to synthesize and investigate the properties of the smart hybrid coatings based on epoxy/polyurethane (EP/PU) reinforced with carbon quantum dots (CQDs) with multipurpose applications. To do this, flexible and transparent polymer coatings were prepared by mixing epoxy resin and PU pre-polymer. Strengthening of hybrid coatings by CQDs (1–3 wt%) led to preparing fluorescent coatings with high protection against UV rays (85–98%), and improved tensile strength, flexibility (10–35%), and viscoelastic properties such as storage modulus and Tg. Findings of salt spray test approved that increased CQDs concentration in the coatings resulted in improved anti-corrosive behavior.

Photoluminescence properties of silk–carbon quantum dots composites

In this paper, we report silk fibroin (SF) and carbon quantum dots (CQDs) nanocomposites obtained through a facile solution casting approach. The optical properties of the nanocomposites have been characterised by UV–vis absorption and photoluminescence spectroscopy. Crosslinking of SF and chemical interactions with the CQDs have been investigated by FTIR spectroscopy. In addition, water stability and degradability of the prepared composites have been investigated in terms of mass loss, important for applications in a real scenario. We observed that for a concentration of CQDs above 1%wt aggregation of nanoparticles occurs, affecting the photoluminescence of the material. The results show that the best composition in terms of photoluminescence intensity and water stability is 0.5%wt CQDs.Graphical abstract

Fabrication of carbon quantum dots via ball milling and their application to bioimaging

Carbon quantum dots (CQDs) with an average diameter of 3 nm, exhibiting blue photoluminescence, have been obtained from commercial conductive carbon black by a cost-effective and straightforward exfoliation method using dry ball milling in the presence of sodium carbonate. As a secondary abrasive medium, sodium carbonate provides effective exfoliation of carbon black with a high degree of CQD graphitization and plays an essential role in the functionalization of CQDs with oxygen groups. Due to the low toxicity of CQDs against HeLa cancer cells (cell viability above 90% at a CQD concentration of 200 μg cm−3) and the ability to penetrate cells and emit blue light, CQDs are possibly suitable for biological imaging of cells.

Green synthesis of biomass-derived carbon quantum dots as fluorescent probe for Fe3+ detection

Eco-friendly synthesis of Carbon quantum dots (CQDs) in water is reported, exploiting various typical crop biomasses as carbon sources. The resultant CQDs exhibit strong fluorescence, good dispersion in common solvents and uniformly dispersed particle size. The synthesized CQDs are highly dispersible in water, due to the presence of surface hydroxyl and carboxyl groups. The CQDs suspension exhibits strong blue fluorescence under UV irradiation, with an optimal excitation wavelength in the range from 350 to 390 nm, which varies with the change of CQD concentration. The emission corresponds to two band transitions, which are originated from π → π* of CC bonds and n → π* of CO bonds, respectively. Due to its strong fluorescence and energy transfer, the synthesized CQDs materials can be used as a fluorescent probe for the detection of Fe3+ ions with good selectivity and sensitivity, within the Fe3+ concentration range of 0–500 μM. The research is of significance for converting crop waste to high added-value products, and the obtained CQDs with selective Fe3+ ions determination ability are attractive for the environmental monitoring and medical diagnosis.

Colorimetric determination of sarcosine in human urine with enzyme-like reaction mediated Au nanorods etching

A colorimetric method for sensitive detection of sarcosine was established based on enzyme-like reaction mediated etching of Au nanorods (AuNRs). Carbon quantum dots (CQDs) originated from litchi peel showed peroxidase-like activity, enabling to accelerate the etching of AuNRs in the presence of H2O2 and I− ions. Sarcosine oxidase (SOX) catalyzed the oxidation of sarcosine to release H2O2 which oxidized I− to I2 under the catalysis of CQDs. AuNRs were then etched by I2 along the longitudinal direction, resulting in a blue-shift of the localized surface plasmon resonance (LSPR) peak of AuNRs. The peak-shift was used for the determination of sarcosine. The influences of pH, CQDs concentration and etching time on the signal response were investigated. Under the optimized conditions, the LSPR peak shift of AuNRs was linearly dependent on sarcosine concentration ranged from 0.02 to 1.0 μmol/L, and the detection limit (3σ/k) was calculated to be 0.011 µmol/L. In order to verify its feasibility and reliability, the method was used for determining sarcosine in human urine samples from healthy volunteers with recoveries ranged from 95.7% to 102.2%, indicating the potential application of the developed method.

Carbon quantum dots intercalated in polypyrrole (PPy) thin electrodes for accelerated energy storage

Polypyrrole (PPy) and carbon quantum dots (CQDs) based composite electrodes (PPy/CQDs or PQDs) are designed through one step electro-polymerization technique in aqueous solution for energy storage purposes. Composite electrode, thus obtained exhibits good electrochemical properties due to dotted CQDs structure comprising of high surface area with numerous active sites. Electrical conductivity of PPy was improved noticeably after modifying with CQDs. The charge transfer resistance (Rp) diminishes from 2.7 Ω to 0.11 Ω for PQD composite due to fast charge diffusion. The impact of varied concentration of CQDs was also evaluated for optimizing the electrochemical behavior of PQDs composites and PPy: CQDs as 95: 5 w/w ratio designated as PQD 0.5 was found to be the most effective composition. Various electrochemical properties of PQDs are also correlated at different time intervals to get an effective electro-polymerized output and observed that PQD 0.5 composition processed for 30 min (PQD 30) demonstrates high specific capacitance of 1073.5 F/g at a scan rate of 10 mV/s and mass loading with 1.4 g/cm2 of the optimized composite with a good cyclic stability as 62% even after 2000 cycles of charge/discharge for the electrode.

Carbon quantum dots embedded polysulfone membranes for antibacterial performance in the process of forward osmosis

Carbon quantum dots (CQDs) are a new class of carbon nanomaterials characterised by excellent hydrophilicity, simple synthesis, environment friendliness, low cost, and low toxicity. However, the extensive application of CQDs is limited by the toxicity and high cost of their precursors. Thus, the synthesis of CQDs with green materials is desired. In this work, we proposed a green synthesis of oil palm biomass-based CQD-derived activated carbon embedded into polysulfone-selective layers to develop thin-film composite membranes, denoted as CQDs-PSF, for forward osmosis. The effects of incorporating CQDs into the PSF membrane matrix and their performance in forward osmosis were examined. The physicochemical properties of the synthesised membranes with added CQDs nanoparticles (0.5%, 0.75%, and 1.0% CQD concentration) resulted in a porous and hydrophilic membrane. The membrane with 1.0% CQD concentration exhibited the highest water flux of 226 L/m2.h, and its reverse salt flux was 59.38 mol/m2 h. The antibacterial activities of the CQDs-PSF membranes were also assayed with the Gram-positive Staphylococcus aureus and the Gram-negative Escherichia coli. Results of bacterial diffusion tests of CQDs-PSF membranes indicated enhanced antibacterial activity. Overall, our findings proved that adding CQDs to PSF membrane enabled the effective enhancement of the water flux and improved antibacterial performance.

Organic Field-Effect Transistor Memory Device Based on an Integrated Carbon Quantum Dots/Polyvinyl Pyrrolidone Hybrid Nanolayer

In this work, we present a pentacene-based organic field-effect transistor memory (OFETM) device, which employs one-step microwave-assisted hydrothermal carbon quantum dots (CQDs) embedded in a polyvinyl pyrrolidone (PVP) matrix, to form an integrated hybrid nanolayer as the charge trapping layer. The as-prepared CQDs are quasi-spherical amorphous C, with sizes ranging from 5 to 20 nm, with a number of oxygen-containing groups and likely some graphite-like domains that produce CQDs with excellent electron-withdrawing characteristics. The incorporation of CQDs into PVP dielectric materials results in a bidirectional storage property. By optimizing the concentration of CQDs embedded into the PVP matrix, the OFETM shows excellent memory characteristics with a large memory window of 8.41 V under a programming/erasing (P/E) voltage of ± 60 V and a retention time of up to 104 s.

Carbon quantum dots derived from lysine and arginine simultaneously scavenge bacteria and promote tissue repair

Effectively targeting and killing microbial pathogens is a major challenge in the treatment of infectious diseases. Inspired by the high efficacy of natural antimicrobial peptides (AMPs), in this study we prepared two types of carbon quantum dots (CQDs) by pyrolysis of lysine and arginine, the two major functional moieties of natural AMPs. Both lysine-derived CQDs (Lys-CQDs) and arginine-derived CQDs (Arg-CQDs) exhibited distinctive antibacterial activity against both Gram-negative and Gram-positive bacteria without inducing drug resistance. They also effectively inhibited the formation of bacterial biofilms. Such excellent antibacterial properties might be the result of positive charges derived from the amino acid residues on CQD surface and the generation of rich intracellular reactive oxygen species (ROS). Surprisingly, instead of being cytotoxic, CQDs dramatically promoted the growth of typical mammalian cells. Moreover, no hemolysis of red blood cells (RBCs) happened when CQD concentration was less than 4,000 μg/mL. In vivo, administration of CQDs to infected wounds effectively inhibited bacterium growth and accelerated wound healing. Together, findings from this study indicate that Lys-CQDs and Arg-CQDs can simultaneously kill bacteria and facilitate cell growth, and may therefore be promising candidates for treating bacterial infections and promoting tissue repair.

Electric field-assisted synthesis of Pt, carbon quantum dots-coloaded graphene hybrid for hydrogen evolution reaction

A simple method for preparation of Pt, CQDs-coloaded graphene composite for hydrogen evolution reaction (HER) is established by electrolysis-solvothermal process. Graphene is obtained by electrochemical exfoliation of graphite in cathode, while carbon quantum dots (CQDs) and Pt nanoparticles (NPs) are in-situ generated in the electrolyte simultaneously. CQDs are evolved from propylene carbonate solvent and Pt NPs are derived from reduction of Pt intermediate species generated from anodic dissolution of Pt counter electrode during electrolysis process. Then Pt NPs and CQDs are well dispersed on graphene at subsequent solvothermal process. Work voltage and electrolyte type as the key electrolysis conditions are applied to control the concentration of CQDs and Pt NPs, which decides electrochemically active surface area and HER activity of obtained catalysts. Significantly, the obtained superior catalyst with trace amount of Pt (0.145 wt%), shows markedly enhanced catalytic HER activity with mass activity of 37.5 A mg−1 at −50 mV in acidic solution, 68.2 times more active than Pt/C. This study provides a universal and promising methodology for synthesizing Pt, CQDs coloaded hybrid with the assistance of electric field as cost-effective catalysts for fuel cells.