Carbon Dots Solution Research Articles

Orange red-emitting carbon dots for enhanced colorimetric detection of Fe3.

Carbon dots (CDs) have demonstrated considerable potential for use in sensing and bioimaging applications based on their unique intrinsic properties. However, CDs have typically been used as fluorescence sensors, as opposed to indicators, based on their ultraviolet absorption and discoloration performance. In this study, orange red-emitting CDs with a high quantum yield (QY) of 53% were constructed from 2,3-diaminopyridine via solvothermal synthesis. Different from the fluorescence quenching behavior reported previously, the constructed CDs demonstrated a unique character in their ultraviolet absorption and fluorescence emission in the presence of Fe3+. The color of the CD solution varied from mauve to orange following the addition of Fe3+ at concentrations exceeding 1 μM, which enabled these CDs to be used in the determination of the presence of Fe3+ in lake water. In addition, due to their negligible cytotoxicity, good solubility, and adequate dispersity, an outstanding cellular probe with near-infrared fluorescence was established. Overall, this study presents a unique CD-based sensor, details its fluorescence mechanism, visual colorimetry, and ultraviolet absorption variations, and confirms its applicability in near-infrared cellular imaging and environmental analyses.

Red, green, and blue light-emitting carbon dots prepared from o-phenylenediamine.

Carbon dots (CDs), as the most important type of carbon-based material, have been widely used in many fields because of their excellent properties. In particular, multicolor fluorescent CDs with high photoluminescence quantum yield are the focus of active research. Herein, red, green and blue CDs (RGB CDs) were successfully synthesized by a solvothermal method from o-phenylenediamine under different reaction conditions. The RGB-CDs have stable optical properties and significant photoluminescence characteristics. Structural and elemental analyses propose a conjugated structure and the surface state of the CDs as the main causes for the different color emission of RGB-CDs. In addition, a white fluorescent CD solution was prepared by mixing these multicolor fluorescent CDs in appropriate proportions.

Optical and Photoacoustic Properties of Laser-Ablated Silver Nanoparticles in a Carbon Dots Solution.

This study used the carbon dots solution for the laser ablation technique to fabricate silver nanoparticles. The ablation time range was from 5 min to 20 min. Analytical methods, including Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, transmission electron microscopy, and Raman spectroscopy were used to categorize the prepared samples. The UV-visible and z-scan techniques provided optical parameters such as linear and nonlinear refractive indices in the range of 1.56759 to 1.81288 and 7.3769 × 10−10 cm2 W−1 to 9.5269 × 10−10 cm2 W−1 and the nonlinear susceptibility was measured in the range of 5.46 × 10−8 to 6.97 × 10−8 esu. The thermal effusivity of prepared samples, which were measured using the photoacoustic technique, were in the range of 0.0941 W s1/2 cm−2 K−1 to 0.8491 W s1/2 cm−2 K−1. The interaction of the prepared sample with fluoride was investigated using a Raman spectrometer. Consequently, the intensity of the Raman signal decreased with the increasing concentration of fluoride, and the detection limit is about 0.1 ppm.

Facile synthesis of carbon dots from wheat straw for colorimetric and fluorescent detection of fluoride and cellular imaging.

Colorimetric and fluorescent detection of F- have attracted enormous interest owing to their simplicity, low-cost and high selectivity. However, traditional colorimetric and fluorescent sensors mainly based on the insoluble and toxic organic molecules, which is not favorable for sensing F- in water media and living cells. In this work, we designed fluorescent carbon dots (CDs) with excellent water solubility and good biocompatibility as a colorimetric and fluorescent dual-model probe for the detection of F-. The CDs were prepared by a green, one-step hydrothermal strategy from wheat straw without any additives and surface passivation. The obtained CDs exhibited a bright blue fluorescence, special response to F- and low cytotoxicity. More interestingly, a significant color change from light yellow to red can be observed by the naked eye upon addition of F- ions to the CDs solution probably due to the formation of hydrogen bonding between CDs and F-. Besides, the fluorescence of CDs also can be selectively quenched by F- with the detection limit of about 49μM. Additionally, the CDs are also applied to intracellular imaging and sensing of F- in living cells. This strategy may provide a new method for the detection of F- in water media and biological systems.

Hydrothermal Synthesis of Multi-Color Fluorescent Carbon Dots from Sappan Wood (Caesalpinia sappan) as an Acid-Base Indicator

Caesalpinia sappan L., known as sappan wood, has been extensively explored by many researchers because it contains various structural types of phenolic compounds. This study objectives are to investigate the effect of pH on the flourescent color of carbon dots (CDs) from sappan wood and its application as an acid-base indicator under UV light for the first time. CDs were synthesized through the hydrothermal route in ethanol solvents. The synthesized CDs were further characterized by UV-Vis spectrophotometry, fluorescence and Fourier Transform Infrared (FT-IR) spectroscopy. Based on the results, CD solutions performed multiple flourescent colors (yellow, orange and green) under UV light at 365 nm when the pH was adjusted to be 1, 3, 5, 7, 9 and 11. These multiple colors were produced because of the instability of phenolic compounds in the sample, especially brazilin which was easily oxidized to brazilein in alkaline condition. According to the FT-IR spectra, the most prominent differences of the sample before and after the treatment process was observed in the peak region ranging from 1500-1700 cm-1. The characteristic band of carbonyl groups was identified at 1697 cm-1 in the treated sample (pH 9), but it was unobserved in the spectrum of sappan wood and the treated sample (pH 5). The presence of carbonyl group can be assumed that brazilin has been oxidized to brazilein after the alkaline treatment process and making the flourescent color was gradually shifted from yellow to green. Under normal light, the sappan wood�s extract and CD solution produced yellow and red colors in acidic and alkaline conditions, respectively. However, only CD solutions which have yellow, orange and green emissions in different pH conditions under UV light. Therefore, the synthesized CDs can be used as an acid-base indicator in both different light conditions.

A sensitive “off-on” carbon dots-Ag nanoparticles fluorescent probe for cysteamine detection via the inner filter effect

In this study, we describe the construction of an “off-on” fluorescent probe based on carbon dots (CDs) and silver nanoparticles (AgNPs) mixture for sensitive and selective detection of cysteamine. By mixing AgNPs with CDs solution, the fluorescence of CDs was significantly decreased due to the inner filter effect (IFE). Upon addition of cysteamine to the mixed aqueous of CDs and AgNPs, the silver-sulfur bond between cysteamine and AgNPs caused AgNPs to aggregate, and the quenched fluorescence of CDs could in turn be recovered. The probe was employed to quantitatively detect cysteamine, and the results showed that it could detect cysteamine in a concentration range of 2–16 μM with the detection limit of 0.35 μM (signal-to-noise ratio of 3). The detection of cysteamine spiked into bovine serum samples showed high recovery rates ranging from 95.5 to 111.7%. More importantly, the developed probe had low cytotoxicity and was successfully used for in vivo imaging of HepG2 cells.

One-pot hydrothermal synthesis of dual-emission fluorescent carbon dots for hypochlorous acid detection

In this work, we developed a dual-emission fluorescent carbon dots (CDs) using sodium citrate (SC), triethylenetetramine (TETA) and rose bengal (RB) as raw materials. Under the hydrothermal treatment, the carboxyl group in SC can crosslink with the amino group in TETA to form polymer-like intermediate by amide bond network. The RB molecule, a fluorescein derivative, lost halogen atoms under hydrothermal conditions and integrated with the skeleton structure of the network intermediate. Further dehydration and carbonization resulted in the dual-emission fluorescent CDs. Excited by ultraviolet (UV) light, the CDs exhibited blue and green luminescence centered at 440 nm and 525 nm, respectively. Due to the emission centers of these two colors showed different sensitivity to hypochlorous acid (HClO), we have designed a fluorescence assay to achieve quantitative detection of HClO. Upon addition of different concentrations of HClO to CDs solution in phosphate buffer (pH = 6), the blue emission decreased gradually while the green emission showed only a minimal decrease. By calculating the emission intensity ratio, a good linear relationship was achieved in the range of 0–17 μM, and the limit of detection was as low as 0.75 μM. The results reported here demonstrated a promising way to design organic dye modified CDs for sensing applications.

Green synthesis of fluorescent carbon dots using chloroplast dispersions as precursors and application for Fe3+ ion sensing.

Water-soluble carbon dots (CDs) were synthesized using a one-step hydrothermal treatment of chloroplast dispersions extracted from fresh leaves as a green carbon source. The CD solution showed an emission peak centred at 445 nm when excited at 300 nm. The synthesized CDs were uniform and monodispersed with an average size of 5.6 nm. When adding ferric(III) ions (Fe3+ ) to the solution of the original CDs, the fluorescence intensity decreased significantly. Based on the linear relationship between fluorescence intensity and concentration of Fe3+ ions, an effective method for rapid, sensitive and selective Fe3+ sensing in aqueous solution could be established. Under optimum conditions, the extent of the fluorescence quenching of prepared CDs strongly depended on the Fe3+ ions over a wide concentration range 1.0-100.0 μM with a detection limit (3σ/k) of 0.3 μM. Furthermore, the quantitative determination of Fe3+ ions in environmental water samples was realized.

A solvent-governed surface state strategy for rational synthesis of N and S co-doped carbon dots with multicolour fluorescence

ABSTRACT Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag+ and Fe3+, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field.

Multicolor emissive sulfur, nitrogen co-doped carbon dots and their application in ion detection and solid lighting.

Multicolor emissive carbon dots (CDs) have potential applications in many fields such as photoelectric display, light-emitting devices, and bioimaging. Such CDs by heteroatom doping of nitrogen elements assisted with various solvents has achieved recently, yet generally low efficiency in red-light region. Herein, we developed a facile route to synthesize multicolor-emissive CDs governed by a solvothermal method of tetrahydrofuran solvent. The maximum emission locates at 432, 510, and 584nm with the absolute FL QYs up to 21.1%, 11.0%, and 55.4% for selected B-CDs, G-CDs, and YG-CDs, respectively. By means of the analysis on their PL spectra, fluorescence lifetimes, and microstructures, the different graphitic degrees and surface states formed under the participation of S and N elements in as-prepared CDs determine the fluorescent color, and large sp2-conjugated domains within the YR-CDs is closely related to high QY. They, likewise, endow the YR-CDs with high sensitivity for ion detections of Ag+ and Fe3+, which was further illustrated to have different quenching mechanisms each other due to the affinity interaction with different surface groups of the CDs. High PL QYs of these CDs emission are beneficial to application in solid lighting, phosphors dried by these CDs solutions were mixed with PVP water solution to fabricate CDs/PVP films. The films exhibited stable fluorescence, and three phosphors were also mixed together in proportion to obtain white-light film with a CIE coordinates of (0.34, 0.34), which demonstrates that these CDs are potentially fluorescent nanomaterial in the solid-state lighting field.

Surface structure and fluorescence characteristics of concentrated carbon point

The concentration-dependent fluorescence behaviour of carbon dots (CDs) was observed in concentrated CDs solution, and it was found that the excitation-independent fluorescence behaviour gradually transitioned to excitation-dependent fluorescence behaviour with the increase of CDs concentration. The fluorescence characteristics of CDs solution with various concentrations were explained from the perspective of the surface states by using the fluorescence decay spectra of CDs for the first time. A close relationship between the surface microstructures and the optical properties was demonstrated. Mechanism of concentration-dependent generation fluorescence in concentrated CDs solution was presented and a possible aggregation model of CDs was given. This work offers a novel perspective for tuning the emission wavelength of CDs and endowing them with potential various applications.

Pt catalysts supported on lignin-based carbon dots for methanol electro-oxidation

Pt catalysts supported on lignin-based carbon dots are successfully prepared, and their catalytic performances for methanol electro-oxidation are investigated. Firstly, lignin-based carbon dots (Lg-CDs) are prepared by the acid etching of lignin carbonization products. Then, Pt catalysts supported on lignin-based carbon dots (Pt/Lg-CDs) are synthesized by the reduction of chloroplatinic acid in carbon dots solution. Although Pt/Lg-CDs catalysts aggregate obviously due to the deposition of Pt catalysts on the surface of Lg-CDs, the activity and stability of an optimal Pt/Lg-CDs-800 catalyst are still more outstanding than commercial Pt/C (40%Pt) and PtRu/C (30%Pt+15%Ru) catalysts for methanol electro-oxidation reaction (MOR) in acidic solutions. A large number of oxygen-containing groups on the surface of Lg-CDs-800 facilitate the uniform and stable deposition of Pt catalysts, and make the surface of more Pt catalysts expose to reaction system, thereby improving catalytic performance.

One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag+

ABSTRACTFluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag+ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH2 groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag+ ions, which promises a new approach for efficient detection of Ag+ for the application in industrial pollutants.This figure shows citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method to prepare CDs with blue colour fluorescence and the highest QY of 78.6%. Owing to the excellent fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag+ with high sensitivity and selectivity, and the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH2 groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag+ ions, which promises a new approach for efficient detection of Ag+ for the application in industrial pollutants.

The carbon dots as colorimetric and fluorescent dual-readout probe for 2-nitrophenol and 4-nitrophenol detection

Herein, the fluorescent carbon dots (CDs) has been synthesized by hydrothermal method by using ethylene diamine tetraacetic acid (EDTA) as a raw materials. The prepared CDs exhibited bright blue fluorscence excited by 340 nm with the quantum yield as high as 52%. The CDs possess special fluorescence responses to 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP), and the slump of fluorescence was demonstrated by CDs solution in the case of 2-nitrophenol and 4-nitrophenol existence. The detection limit of 2-NP and 4-NP was calculated at 77 nM and 60 nM, respectively. Meanwhile, the color response to 2-NP and 4-NP can be observed from achromatic solution to yellow by naked eye. All in all, the obtained CDs can be applied as fluorescence and colorimetric probe in environmental protection.

Polymer microsphere for water-soluble drug delivery via carbon dot-stabilizing W/O emulsion

Emulsions, usually oil-in-water emulsions, have been widely applied to the preparation of hydrophobic drug carriers. However, the synthesis of safe, biocompatible and high-performance carriers for water-soluble drugs remains a challenge. So polyacrylamide (PAM) microspheres stabilized by carbon dots (CDs) were fabricated via a water-in-oil Pickering emulsion without the use of any surfactant. The PAM/CD microspheres were spherical with an even distribution of the CDs on their surfaces. The size of the microspheres can be controlled by changing the amount of CDs, which also influenced the drug loading properties. The hydrophilic chemotherapy drug, 5-fluorouracil (5-FU), was successfully loaded into the PAM/CD microspheres through incubation. The encapsulation efficiencies ranged from 68 to 82% with a maximum drug loading of 48%. The 5-FU release profiles depended on the concentration of the drug incubation solution, the concentration of the CD solution and the pH of the drug release environment. The release of 5-FU was relatively steady for the first 12 h and followed non-Fickian diffusion kinetics. This synthetic approach could be extrapolated to loading of other water-soluble drugs into hydrophilic polymers.

One-step hydrothermal synthesis of carbon dots-polymer composites with solid-state photoluminescence

Carbon dots (CDs) and CDs-polymer composites were one-step synthesized in a hydrothermal process using hexamethylenetetramine and polycarbonate as precursors. Their optical properties and the application as solid-state phosphors towards white light-emitting diodes (LEDs) were thoroughly investigated. CDs solutions exhibit strong yellow emission under blue illumination and possess excitation-independent luminescent behavior. Owing to precursor polymerization, CDs-polymer composites were synthesized in one step. The dried CDs-polymer composite powders exhibit excellent optical stability and no luminescence quenching was observed. Under light blue illumination, the powders show broad yellow luminescence with the peak wavelength centered at 550 nm and PL quantum yield of 14.86%. For their practical applications, stable white light emission was demonstrated by coating a 455 nm blue LED with the powders. Our research offers a valuable reference for growing CDs-polymer composites in a facile, low-cost and low-temperature hydrothermal process and developing white LEDs with light blue LEDs and metal-free phosphors.

Controllable Synthesis of Carbon Dots with Excitation‐Wavelength‐Dependent or Independent Photoluminescence for the Selective and Sensitive Detection of Co2+ Ions

AbstractFluorescent carbon dots (CDs) with excitation‐wavelength‐dependent and excitation‐wavelength‐independent emission have been prepared with varying amounts citric acid (CA), ethylenediamin end‐capped polyethylenimine (PEI‐EC) and sodium borohydride (NaBH4), their structure, optical and chemical sensing properties have been also systematically investigated. The varying of NaBH4 and PEI‐EC renders the structure and surface state change as well as photoluminescence (PL) properties. The results indicated that NaBH4 made the CDs sensitive to Co2+ ions, whilst the PEI‐EC served to increase their sensitivity. The synergistic roles that both NaBH4 and PEI‐EC played on the selective and sensitive detection of Co2+ were achieved via a simple adjustment of the mass ratios during synthesis. Furthermore, the PL intensity was gradually recovered until completely restored with the addition of chelating agent ethylenediaminetetraacetic acid (EDTA) to the Co2+ quenched CDs solutions. This work provided quantitatively preparation and controllable synthesis of excitation‐wavelength‐dependent or independent CDs for the development of PL based sensors.

Development of nitrogen and sulfur-doped carbon dots for cellular imaging

Heteroatom-doped carbon dots (CDs) have attracted extensive interest because of their improved electronic and fluorescence properties with heteroatom doping. In this study, a new synthetic method for nitrogen (N) and sulfur (S) -doped CDs was developed via a hydrothermal method using methionine and citric acid as raw materials. The as-prepared CDs exhibit excellent optical properties and good biocompatibility. The spherical N,S-doped CDs have an average diameter of 5 nm. They consist of C, O, N and S, and take on excellent water solubility due to the hydroxyl and carboxyl, amino groups on the surface. The CDs have a photoluminescence quantum yield of 13.8% using quinine sulfate as a reference; the average fluorescence lifetime of the CDs was 3.67 ns. The CDs solution present good photoluminescence properties, and the maximum excitation wavelength and emission wavelength locate at 330 nm and 405 nm, respectively. In addition, their fluorescence intensity almost does not change under the conditions of acid, alkali, and high salt, which indicated their anti-photobleaching property and good light stability. Based on the good biocompatibility and strong fluorescence emission of the CDs, they can be used as fluorescent imaging reagents.

One-pot synthesis of dual carbon dots using only an N and S co-existed dopant for fluorescence detection of Ag+

Luminescent carbon-based nanoparticles, named often as carbon dots (CDs), were synthesized from citric acid (CA) and guanidine thiocyanate (GITC) via an N and S co-doped hydrothermal procedure. In the present structure characterization, N and S elements could be sufficiently doped by means of the heteroatom or the functional groups bonded on the surface of CDs. The as-prepared CDs solution showed blue color fluorescence under ultraviolet excitation, yet the PL spectra exhibited a repetitive emission process from excitation-independent to excitation-dependent. In view of the triexponential feature of fluorescence lifetimes of CDs, one possibility was proposed to be co-existence of two types of CDs with different surface states. Additionally, the as-prepared CDs were used as a sensing probe for the detection of Ag+ taking into consideration of the possible interactions between Ag+ and various fluorophores attached to the CD surface. As expected, the changes of fluorescence intensities were linearly proportional to the different concentration ranges of Ag+, which suggests the complex nature of the quenching mechanism. And for the first time, the SCN group was found to accelerate the quenching of CDs towards Ag+, promising a new approach for efficient detection of Ag+ for the application in industrial pollutants.

Rationally Designed Efficient Dual-Mode Colorimetric/Fluorescence Sensor Based on Carbon Dots for Detection of pH and Cu2+ Ions

A dual-mode colorimetric/fluorescence pH sensor was fabricated from carbon dots (CDs). It exhibited a pH response via both fluorescence and visible colorimetric observation. The CDs solution changed from red to yellow when the pH changed from acid to alkaline. Meanwhile, the color of pH test paper that incorporated the CDs changed from purple-red to orange and then to yellow. The CD fluorescence maximum was at 630 nm in acid solution and 590 nm under neutral and alkaline conditions. The fluorescence of the pH test paper changed from red to orange and then to yellow, which was better than that of the pure CDs solution. The CDs exhibited highly selective and reversible fluorescence quenching with respect to Cu2+ ions because of strong binding and fast chelating kinetics. There was a linear relationship between fluorescence quenching and Cu2+ concentration, suggesting the other promising practical usage of this sensing system. The versatile CDs-based pH sensor thus provides a basis for developing sustainable...