Pyrolysis Of Citric Acid Research Articles

Size Characterization of Graphene‐coated Silver Nanoparticles for Drug Delivery System Design

Nanoparticles prove to be a promising tool for drug delivery due to their modifiable properties, such as size, which may offer more targeted delivery. Silver nanoparticles (AgNPs) have been shown to exert anticancer effects such as antiangiogenesis. Size control is crucial for the use of AgNPs as drug delivery systems because smaller AgNPs amplify cytotoxicity in both cancerous and healthy cells. Another way that AgNPs are cytotoxic is through the release of silver (Ag+) ions. It has been shown that AgNPs below 10 nm in size have a comparable toxicity to Ag+ ions. In this study, AgNPs were coated with graphene quantum dots. Graphene quantum dots (GQDs) are nanosheets of carbon. These nanosheets of carbon may control the release of silver ions and provide additional benefits such as increased surface area for drug loading and increased drug solubility. The objective of this study is to synthesize graphene quantum dot‐coated silver nanoparticles (AgGQDs) to serve as drug delivery systems. We hypothesize that our methods will produce AgGQDs larger than 10 nm to avoid excessive cytotoxicity. The GQDs were synthesized by pyrolysis of citric acid and used as reducing agents for the synthesis of AgGQDs. The GQDs were characterized using X‐ray Photoelectron Spectroscopy (XPS). The AgGQDs were characterized via Transmission Electron Microscopy (TEM) and in situ Energy‐dispersive X‐ray Spectroscopy (EDS). EDS confirmed that the images observed were silver nanoparticles. TEM images showed that the AgGQDs were spherical and had a size of approximately 20‐25 nm in diameter. Based on these results, we can conclude that our AgGQDs will not be drastically cytotoxic due to their intermediate size.

Microwave-assisted one-pot synthesis of carbon dots for highly sensitive and selective detection of selenite

Herein, a label-free, sensitive, and selective fluorescence method for the detection of trace selenite (Se(IV)) in water sample by carbon dots (CDs) was reported. The fluorescence CDs probe was simply and rapidly synthesized within 4 min by microwave-assisted pyrolysis of citric acid and 3,3′-diaminobenzidine (DAB), with a relatively uniform size of approximately 2.6 nm. The fluorescence emission of as-prepared CDs was 450 nm upon the excitation of 400 nm with a quantum yield of about 8% against quinine sulfate as reference standard, which can be quenched by the addition of selenite. Benefit from the strong surface chelating reaction between DAB and Se(IV), the proposed sensor owned the advantage of high sensitivity (limit of detection = 0.5 ng/mL), wide linear range (1–100 ng/mL range, relative standard deviation: 3.8%), and excellent selectivity in the presence of various ions, even other forms of selenium, including selenate (Se(VI)), Selenomethionine (SeMet), and L-Selenocystine (SeCys) etc. Preliminary study on fluorescence quenching mechanism studied. The sensor was successfully exemplified for real water samples and exhibits comparative performance.

A ratiometric fluorescence platform based on carbon dots for visual and rapid detection of copper(II) and fluoroquinolones.

A simple smartphone-integrated ratiometric fluorescent sensing system for visual determination of copper ions (Cu2+) and fluoroquinolones (FQs) was developed based on carbon dots (CDs) which were synthesized through the high-temperature pyrolysis of citric acid. In this system, with the fluorescence resonance energy transfer effect between CDs and 2,3-diaminophenazine (oxOPD), the detection of Cu2+ and ciprofloxacin (CIP, an example for FQs) was realized. Cu2+ catalyzes the oxidation of OPD to form oxOPD with yellow fluorescence, resulting in the quenching of CDs. In addition, CIP can inhibit the catalytic activity of Cu2+ and induce the recovery of CDs fluorescence. Under the excitation of 400nm, the changes of CDs fluorescence at 472nm and oxOPD fluorescence at 556nm were monitored. The detection results showed that the sensing system exhibited good selectivity and sensitivity to Cu2+ and CIP with the limit of detection of 2.32 × 10-8mol L-1 and 0.2ngmL-1, respectively. In addition, a smartphone was developed as a portable analyzer to capture the change of fluorescence color and quickly analyze the concentration of Cu2+ and CIP. The proposed smartphone-based sensing platform has satisfactory sensitivity, and it has application prospects for detecting Cu2+ and FQs in food safety monitoring.

Field-amplified sample injection and graphene quantum dot dual preconcentration in the analysis of melamine and dicyandiamide by capillary electrophoresis

通过热解法制备了硫掺杂的石墨烯量子点(S-GQDs),同石墨烯量子点(GQDs)相比,S原子的引入有效改善了GQDs的表面状态和化学特性、增强其对正电荷的捕获能力,使其更易与阳离子相互作用。以S-GQDs为载体,结合电堆积富集技术,发展了一种基于场放大进样(FASI)和S-GQDs放大的双重富集毛细管电泳(CE)分离检测三聚氰胺和双氰胺的方法。三聚氰胺和双氰胺在酸性介质中带正电荷,电动进样时快速迁移到毛细管入口端进行FASI预富集;同时带负电荷的S-GQDs向阳极端迁移,在样品与缓冲溶液的界面处通过静电作用吸附样品离子,S-GQDs作为载体使检测信号进一步放大。实验考察了缓冲溶液中S-GQDs的体积分数、缓冲溶液的组成及pH、进样时间等因素对富集分离效果的影响。当缓冲溶液的pH为4.6时,进样时间可延长至450 s。同常规电动进样(10 kV×10 s)相比,采用FASI与S-GQDs双重放大技术可使检测灵敏度提高1.6×105倍。该方法对三聚氰胺和双氰胺检测的线性范围是1.0×10-14~1.0×10-8mol/L,相关系数(r2)大于0.999,检出限分别为2.6×10-15和5.7×10-15mol/L。实现了对盐酸二甲双胍中三聚氰胺和双氰胺的高灵敏检测,回收率分别为95.9%~102.4%和92.0%~106.0%,相对标准偏差(RSD)小于5%。该方法操作简单,分离效果好,准确度高,重现性好,适用于分离检测不同盐酸二甲双胍制剂中的三聚氰胺和双氰胺。

Graphene quantum dots/carbon nitride heterojunction with enhanced visible-light driven photocatalysis of nitric oxide: An experimental and DFT study

Visible light-driven photocatalysis for the degradation of nitric oxide (NO) has attracted considerable attention. Graphene quantum dots/graphite phase carbon nitride (GQDs/CN) heterojunctions were proposed as efficient visible-light responsive photocatalysts for NO treatment under the guidance of density function theory (DFT) simulation. Then, the GQDs/CN was synthesized via hydrothermal combination of GQDs and g-C3N4 (CN) produced from pyrolysis of citric acid (CA) and melamine, respectively. Afterwards, the GQDs/CN composite samples were characterized using XRD, XPS, FE-SEM, TEM, HR-TEM, BET, UV–Vis DRS, PL, photocurrent tests, and EIS. Later, the photocatalytic activity of the prepared GQDs/CN composites was evaluated by degrading NO at ppm level under visible light irradiation at conditions of 20 ppm of NO, 5% of O2, and 50% of relative humidity. Results show that 9GQDs/CN outperforms its counterparts. Compared to CN, the 9GQDs/CN increases the NO conversion rate from 61% to 90%, the selectivity of nitrate formation from 53% to 74%, and the value of DeNOx index from −0.25 to 0.19. The enhanced performance results from the inclusion of GQDs, which increases the specific surface area, promotes the absorption of light, boosts the separation of photogenerated electrons and holes, and inhibits their recombination. Furthermore, we used active species detection experiment, IC, in-situ DRIFTS, ESR measurement, XPS VB, Mott-Schottky, and DFT calculations to systematically explore the mechanism behind the degradation of NO using GQDs/CN, and confirmed the formation of Type-Ⅱ heterojunction between GQDs and g-C3N4. In addition, 9GQDs/CN maintains a high NO conversion rate after 5 cycles of experiments, indicating its potential in industrial applications.

Graphene quantum dot and iron co-doped TiO2 photocatalysts: Synthesis, performance evaluation and phytotoxicity studies

The present study reports the synthesis, photocatalytic decolorization of reactive black 5 dye and phytotoxicity of graphene quantum dots (GQDs) and iron co-doped TiO2 photocatalysts via modified sol gel method. GQDs were synthesized by direct pyrolysis of citric acid (CA). Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS), Raman spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), Brunauer–Emmett–Teller (BET) and photoluminescence spectroscopy (PL) were used to determine the physicochemical properties of the best performing photocatalysts. The results indicated improved physicochemical properties of GQD-0.1Fe-TiO2-300 with root mean square roughness (Rz) (33.82 nm), higher surface area (170.79 m2 g−1), pore volume (0.08 cm3 g−1), and bandgap (2.94 eV). Moreover, GQD-0.1Fe co-doping of TiO2 greatly improved the photocatalytic decolorization efficiency for RB5 dye. The photocatalytic reaction followed the pseudo first order reaction with gradual decrease in Kapp values for increment in RB5 concentration. The KC value was obtained as 2.45 mg L−1 min−1 while the KLH value was 0.45 L mg−1 indicating the heterogeneous reaction system followed the Langmuir-Hinshelwood isotherm and simultaneously occurring adsorption and photocatalytic processes. Photocatalytic reaction mechanism studies exhibited the holes and OH radicals as the main active species in the GQD-0.1Fe-TiO2-300 responsible for the decolorization of RB5. The proposed reaction pathway showed that both Fe-TiO2 and GQDs play important role in generation of electrons and holes. Additionally, GQD-0.1Fe-TiO2-300 were durable up to four cycles. Phytotoxicity assay displayed that treated water and best performing photocatalysts had no effect on Lycopersicon esculentum seed germination. Therefore, the proposed system can pave a viable solution for safe usage of dye loaded wastewater and effluent for irrigation after treatment.

Engineering Mitochondriotropic Carbon Dots for Targeting Cancer Cells.

Aiming to understand and enhance the capacity of carbon dots (CDs) to transport through cell membranes and target subcellular organelles—in particular, mitochondria—a series of nitrogen-doped CDs were prepared by the one-step microwave-assisted pyrolysis of citric acid and ethylenediamine. Following optimization of the reaction conditions for maximum fluorescence, functionalization at various degrees with alkylated triphenylphosphonium functional groups of two different alkyl chain lengths afforded a series of functionalized CDs that exhibited either lysosome or mitochondria subcellular localization. Further functionalization with rhodamine B enabled enhanced fluorescence imaging capabilities in the visible spectrum and allowed the use of low quantities of CDs in relevant experiments. It was thus possible, by the appropriate selection of the alkyl chain length and degree of functionalization, to attain successful mitochondrial targeting, while preserving non-toxicity and biocompatibility. In vitro cell experiments performed on normal as well as cancer cell lines proved their non-cytotoxic character and imaging potential, even at very low concentrations, by fluorescence microscopy. Precise targeting of mitochondria is feasible with carefully designed CDs that, furthermore, are specifically internalized in cells and cell mitochondria of high transmembrane potential and thus exhibit selective uptake in malignant cells compared to normal cells.

High-Temperature Carbonized Ceria Thermophotovoltaic Emitter beyond Tungsten.

Thermophotovoltaics (TPVs) require emitters with a regulated radiation spectrum tailored to the spectral response of integrated photovoltaic cells. Such spectrally engineered emitters developed thus far are structurally too complicated to be scalable, are thermally unstable, or lack reliability in terms of temperature cycling. Herein, we report wafer-scale, thermal-stress-free, and wavelength-selective emitters that operate for high-temperature TPVs equipped with GaSb photovoltaic cells. One inch crystalline ceria wafers were prepared by sequentially pressing and annealing the pellets of ceria nanoparticles. The direct pyrolysis of citric acid mixed with ceria nanoparticles created agglomerated, pyrolytic carbon and ceria microscale dots, thus forming a carbonized film strongly adhering to a wafer surface. Depending on the thickness of the carbonized film that was readily tuned based on the amount of citric acid used in the reaction, the carbonized ceria emitter behaved as a tungsten-like emitter, a graphite-like emitter, or their hybrid in terms of the absorptivity spectrum. A properly synthesized carbonized ceria emitter produced a power density of 0.63 W/cm2 from the TPV system working at 900 °C, providing 13 and 9% enhancements compared to tungsten and graphite emitters, respectively. Furthermore, only the carbonized ceria emitter preserved its pristine absorptivity spectrum after a 48 h heating test at 1000 °C. The scalable and facile fabrication of thermostable emitters with a structured spectrum will prompt the emergence of thermal emission-harnessed energy devices.

Tuneable properties of carbon quantum dots by different synthetic methods

Carbon quantum dots (CQD) were prepared from three different precursors and by three bottom-up synthesis methods: classical pyrolysis of citric acid (CAP), microwave irradiation of glucose (GM), and hydrothermal treatment of glucosamine hydrochloride (GAH). CQD were further functionalized using various nitrogen-containing compounds: 6-aminohexanoic acid, 1,6-diaminohexane, N-octylamine, dimethylamine, and tryptophan. Special attention was dedicated to investigate how the combination of synthetic method and starting material affected the nature and properties of CQD. The analysis indicated that CAP were good candidates for covalent post-functionalization, GM allowed an easy passivation, and GAH permitted the direct introduction of nitrogen into the core. The size distribution showed a core–shell structure for CQD functionalized with an aminoacid by microwave irradiation, whereas the thermal decomposition evidenced the degradation of functionalizing molecules and the presence of pyridinic and pyrrolic nitrogen after hydrothermal synthesis. Photoluminescence spectra revealed important differences between the synthesis techniques, related to the occurrence of surface states, and the highest fluorescence quantum yield for hydrothermally prepared CQD. These approaches led to CQD with properties that can be exploited in many fields from energy conversion to sensing.

A potential trackable bone filler: Preparation and characterization

AbstractThis study reported the synthesis of fluorescent hydroxyapatite/alginate/carbon quantum dots (HA/Alg/CQDs) nanocomposites via the co‐precipitation technique. The N‐doped CQDs as a new class of fluorescent materials were prepared by the citric acid pyrolysis method, with an average size around 4 nm. Physical, chemical, and optical properties of the synthesized nanocomposites were investigated by X‐ray diffraction (XRD), Fourier‐transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM), field‐emission scanning electron microscopy (FESEM), UV–visible spectroscopy, and photoluminescence (PL) spectroscopy, respectively. The PL spectroscopy data verified the favorable in vitro luminescent emission of the HA/Alg/CQDs nanocomposites in comparison with HA/Alg and HA samples. The XRD patterns of the prepared samples confirmed the formation of crystalline HA in all composites, possessing a Ca/P ratio around 1.5 as obtained by EDX elemental analysis. The FESEM analysis exhibited HA nanoplates that homogeneously distributed throughout the alginate matrix. Therefore, the synthesized nanocomposites could be regarded as potential trackable drug carriers for hard tissue engineering applications.

Hemin Covalently Functionalized Carbon Nanobranch with Enzyme‐Like and Photocatalytic Activities for Synergistic Dye Degradation and Antibacterial Therapy

AbstractThe development of artificial enzymes with excellent enzyme‐like activities and unique features is highly desirable for their practical applications. Herein, a one‐pot facile method to synthesize hemin covalently functionalized carbon nanobranch (CN‐hemin) via direct pyrolysis of citric acid and covalent coupling of hemin to the formed carbon skeleton, is reported. This strategy is reasonably straightforward, cheap, and environmentally friendly, without any extraneous oxidant, reductant, and harmful additives during the preparation process. Furthermore, the obtained dendritic hybrids possess good water‐solubility, intrinsic peroxidase‐like activity, and satisfactory photocatalytic performance in visible light. These extraordinary properties are mainly due to the structure of CN‐hemin which contains iron porphyrin, aromatic carbon, and citric acid residues. Most importantly, under visible light irradiation, the as‐prepared hemin‐incorporated nanohybrid can act as robust agents for synergistic dye degradation and antibacterial therapy toward Staphylococcus aureus and methicillin‐resistant S. aureus. It is expected that this study can shed valuable light on developing advanced multifunctional nanozymes with combined favorable properties for highly efficient elimination of environmental pollutants and antibacterial treatment.

Ultratrace Detection of Nickel(II) Ions in Water Samples Using Dimethylglyoxime-Doped GQDs as the Induced Metal Complex Nanoparticles by a Resonance Light Scattering Sensor.

This study aimed to synthesize dimethylglyoxime (DMG) (N-source)-doped graphene quantum dots (N-GQDs) via simultaneous pyrolysis of citric acid and 1.0% (w/v) DMG. The maximum excitation wavelength (λmax, ex = 380 nm) of the N-GQD solution (49% quantum yield (QY)) was a red shift with respect to that of bare GQDs (λmax, ex = 365 nm) (46% QY); at the same maximum emission wavelength (λmax, em = 460 nm), their resonance light scattering (RLS) intensity peak was observed at λmax, ex/em = 530/533 nm. FTIR, X-ray photoelectron spectroscopy, XRD, energy-dispersive X-ray spectroscopy, and transmission electron microscopy analyses were performed to examine the synthesized materials. The selective and sensitive detection of Ni2+ using the RLS intensity was performed at 533 nm under the optimum conditions consisting of both 25 mg L–1 N-GQDs and 2.5 mg L–1 DMG in the ammonium buffer solution of pH 9.0. The linearity of Ni2+ was 50.0–200.0 μg L–1 with a regression line, y = 5.031x – 190.4 (r2 = 0.9948). The limit of detection (LOD) and the limit of quantitation (LOQ) were determined to be 20.0 and 60.0 μg L–1, respectively. The method precision expressed as % RSDs was 4.90 for intraday (n = 3 × 3) and 7.65 for interday (n = 5 × 3). This developed method afforded good recoveries of Ni2+ in a range of 85–108% when spiked with real water samples. Overall, this innovative method illustrated the identification and detection of Ni2+ as a DMG complex with N-GQDs, and the detection was highly sensitive and selective.

Sensitive recognition of ractopamine using GQDs-DPA as organic fluorescent probe.

A novel spectrofluorimetric sensing platform was designed for Ractopamine measurement in aqueous and plasma samples. d-penicillamine functionalized graphene quantum dots (DPA-GQDs) was utilized as a fluorescence probe, which was synthesized through the pyrolysis of citric acid in the presence of DPA. This one-pot down-top strategy causes to high-yield controllable synthesis method. The reaction time and probe concentration were optimized. Then, the fluorescence intensity of aqueous samples containing different Ractopamine concentrations and 500 ppm DPA-GQDs were measured at 25°C with an excitation wavelength of 274 nm. The sensing platform was also applied to detect Ractopamine in untreated plasma samples. The fluorescence spectroscopy technique responses indicated a linear relationship between the peak fluorescence intensity and ractopamine concentration in the range of 0.25-15 ppm with low limit of quantification of 0.25 ppm was for aqueous and plasma samples, respectively.

Poly-l-lysine-Functionalized Green-Light-Emitting Carbon Dots as a Fluorescence Turn-on Sensor for Ultrasensitive Detection of Endotoxin.

Herein, we report a facile, ultrasensitive, and selective fluorescence turn-on sensing strategy based on green-light-emitting functional nanodots for the detection of bacterial lipopolysaccharide (LPS) endotoxin. In this protocol, first, the pure carbon dots (CDs) with a fairly high quantum yield were prepared by microwave-assisted pyrolysis of citric acid in the presence of urea. Subsequently, the carboxyl-group-rich surfaces of the CDs were allowed to conjugate with the poly-l-lysine (PLL) using an EDC-NHS amidization method to obtain the PLL-modified CDs (PLL-CDs). The LPS could specifically bind to the PLL at the PLL-CD surfaces, and this binding enabled an electron transfer from the phosphate groups of LPS to the carbon core through the PLL bridge, thus resulting in a fluorescence enhancement. Interestingly, this fluorescent turn-on sensor provided a detection limit of 68.3 fM in PBS (pH 7.4), which is the lowest ever reported among all of the synthetic assays for LPS detection. Furthermore, our fluorescent probe was able to show a remarkable selectivity toward LPS over a range of commonly known interfering substances. Thus, this study demonstrated the feasibility of using specific LPS binding to PLL to drive molecular recognition in aqueous medium and offered an effective fluorescence turn-on sensing strategy to detect bacterial endotoxin in diverse clinical and biological applications.

Hybrid ultrafiltration membranes based on PES and MOFs @ carbon quantum dots for improving anti-fouling performance

Metal organic frameworks (MOFs) have raised considerable interest because of their favorable impacts on the performance of water treatment membranes. Herein, the novel nanocomposite based on both nanoporous MOFs and hydrophilic carbon quantum dots (CQDs) was exploited as a novel dopant for the fabrication of PES ultrafiltration (UF) membranes. CQDs were synthesized via pyrolysis of citric acid, and UiO-66-NH2@CQDs were synthesized via the condensation reactions of CQDs and UiO-66-NH2 using EDC and NHS as the condensating agents. The properties of resulting membranes on the porosity, membrane morphology, hydrophilicity, permeability and anti-fouling performance were adequately investigated. The membranes incorporated with UiO-66-NH2@CQDs exhibited significantly improved water flux (up to 358.5 Lm−2h−1), which was ~1.82 times that of pristine PES membrane. Additionally, the BSA rejections rates for the hybrid membranes were all maintained above 95.0%. Furthermore, the hybrid membranes exhibited enhanced anti-fouling performance and the highest flux recovery ratio (FRR) of the hybrid membrane with 0.5% UiO-66-NH2@CQDs reached 77.6%. The membranes incorporated with UiO-66-NH2@CQDs exhibited better permeability and anti-fouling performance than those incorporated with CQDs or UiO-66-NH2. This work reveals that the novel hydrophilic nanofillers combining CQDs and MOFs exhibit great potential for application in water treatment membranes.

Hierarchical Lignin-Based Carbon Matrix and Carbon Dot Composite Electrodes for High-Performance Supercapacitors.

This work adopts an efficient chemical-wet method to build a three-dimensional (3D) carbon composite as an electrode material for high-performance supercapacitors (SCs). Carbon dots (CDs), prepared by thermal pyrolysis of citric acid and urea under microwaves at 280 °C, are homogeneously coated onto lignin-based activated carbons (ACs), thus forming the 3D composites possessing an interior surface decorated with CD binding sites. Benefiting from the hydrophilicity and ultrafine size of CDs, the affinity of the electrode surface toward aqueous electrolytes is significantly improved with the addition of CDs, leading to the enhanced effective surface area (i.e., abundant electroactive sites) and a decreased ionic diffusion path. The capacitance of the SCs is improved from 125.8 to 301.7 F g–1 with CD addition. The SC with CD addition possesses improved cycle stability with a coulombic efficiency around 100% after 3000 cycles. After cycling, the ion diffusion coefficient of the CD@AC-11 electrode is enhanced by 25.5 times as compared to that of the pristine AC one. This unique and robust carbon framework can be utilized for engineering the desired pore structure and micropore/mesopore fraction within the AC electrodes. This strategy of CD@AC electrodes demonstrates a promising route for using renewable porous carbon materials in advanced energy-storage devices.

Study and Comparison on Purification Methods of Multicolor Emission Carbon Dots.

Recent years have witnessed a rapid development of carbon dots (CDs), due to their outstanding luminescence properties and excellent biocompatibility. However, the internal structure and photoluminescent (PL) mechanism of CDs are still the subject of considerable debate, which is due to the fact that reaction products usually contain mixtures of several CD fractions as well as molecular intermediate and side products. Therefore, careful purification of the CDs is significant for analysis of structure and luminescence mechanism. Here, multicolor emission CDs were prepared by a one-pot pyrolysis of citric acid in formamide. Then, the precipitation method, dialysis and gel permeation chromatography (GPC) are successively employed to purify the multicolor emission CDs. This post-treatment allowed us to compare the optical properties of CDs obtained by different separation methods and provide a valuable guidance for the purification of CDs.

Role of surface oxygen-containing functional groups of graphene oxide quantum dots on amyloid fibrillation of two model proteins.

There are many reports demonstrating that various derivatives of carbon nanoparticles are effective inhibitors of protein aggregation. As surface structural features of nanoparticles play a key role on modulating amyloid fibrillation process, in the present in vitro study, bovine insulin and hen egg white lysozyme (HEWL) were selected as two model proteins to investigate the reducing effect of graphene oxide quantum dots (GOQDs) on their assembly under amyloidogenic conditions. GOQDs were prepared through direct pyrolysis of citric acid, and the reduction step was carried out using ascorbic acid. The prepared nanoparticles were characterized by UV-Vis, X-ray photoelectron, and FT-IR spectroscopies, transmission electron and atomic force microscopies, zeta potential measurement, and Nile red fluorescence assay. They showed the tendencies to modulate the assembly of the proteins through different mechanisms. While GOQDs appeared to have the capacity to inhibit fibrillation, the presence of reduced GOQDs (rGOQDs) was found to promote protein assembly via shortening the nucleation phase, as suggested by ThT fluorescence data. Moreover, the structures produced in the presence of GOQDs or rGOQDs were totally nontoxic. We suggest that surface properties of these particles may be part of the differences in their mechanism(s) of action.

Interlayer transition in graphene carbon quantum dots

AbstractGraphene Carbon Quantum Dots (GCQDs) are multi-layered carbon nanostructures that have attracted considerable attention due to its unique properties. Many technological applications, such as batteries, biological imaging, capacitors, solar cells, light emitting diodes, among others, could benefit from the low toxicity and the chemical and physical stability of these nanostructures. Despite much research, many optical properties, such as absorption and photoluminescence, of GCQDs are not completely understood yet. GCQD absorption spectra show a number of different bands whose origin is still on discussion. Many interpretations are made considering a single graphene layer. In this work, GCQD samples synthesized by the pyrolysis of citric acid was characterized by absorption spectroscopy measurements and Density Functional Theory simulations considering multi-layered structures. Density of States and electronic response functions calculations were also performed. From the results of these calculations, the absorption band associated to a π-π* (CC) transition could be also associated to a transition between different graphene layers.

An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination of Hg2.

Hg2+-sensitive carbon dots (CDs) were synthesized by microwave-assisted pyrolysis of citric acid, sodium fluoride, and urea. The CDs as a signal report unit and rhodamine B (RhB) as a reference were then encapsulated in a nanosphere of chitosan assembled by a nonsolvent-induced chitosan colloidal formation and in situ cross-linking to construct a ratiometric probe for Hg2+ (chitosan-CDs-RhB). Interestingly, without any assistance from acids to improve the solubility of chitosan, the nanosphere containing CDs and RhB had an ultrasmall size of 9.7nm with only approximately 1.1-nm-thick layers of chitosan enclosing one dot. In order to keep the residual functional groups on the nanosphere from compromising the fluorescence response of CDs to Hg2+, Co2+ was used as a fluorescently intact metal ion to saturate the functional groups. The saturated chitosan-CDs-RhB was thus potentially developed for determining Hg2+ in the fruit bodies and mycelia of edible and medicinal fungi. Limits of detection (LODs) of 2.24, 5.29, and 2.03μM and recoveries in the ranges 98.3 to 101.8%, 99.5 to 104.6%, and 97.4 to 100.9% were estimated for the determination of Hg2+ in the fruit bodies of Pleurotus ostreatus, Lentinus edodes, and Hypsizygus marmoreus, respectively. Chitosan-CDs-RhB was further developed as a fluorescent ratiometric probe for quantitatively determining intracellular Hg2+ in fungal mycelia with a linear calibration curve of RIgreen/Ired = - 0.145c + 1.69 within the range 0.013 to 0.356μgg-1. Graphical abstract An ultrasmall chitosan nanosphere encapsulating carbon dots and rhodamine B as a ratiometric probe for the determination of Hg2+.