Blue Fluorescent Carbon Dots Research Articles

Synthesis of blue fluorescent carbon dotsfor sensitive and selective detection of glucose in biological samples

This Article describes a technique for the preparation of blue fluorescent carbon dots (CDs) showing fluorescence emission at 450nm. CDs were prepared using ultra-sonication technique using citric acid and glycerol as precursors. Since glucose quenches the fluorescence of CDs, depending upon this fact, a fluorescent sensor for glucose determination has been established. Under optimized conditions, linear response in therange of 0.1-100µM was obtained for glucose concentration. Limit of detection is found to be 0.08µM. This method was promisingly used for the glucose determination in serum albumin samples and urine samples from different human beings.

Multi-Functional Carbon Dots from an Ayurvedic Medicinal Plant for Cancer Cell Bioimaging Applications.

The combination of an Ayurvedic wisdom and nanotechnology may help us to resolve the complex healthcare challenges. A facile and economical one-pot hydrothermal synthesis method has been adopted for preparing a blue fluorescent carbon dots (CDs) with a quantum yield of 15.10% from an Ayurvedic medicinal plant Andrographis paniculata (AP). The Andrographis paniculata derived CDs (AAPCDs) were then characterized using different techniques. Through High Performance Thin Layer Chromatography (HPTLC) profiling of the AP extract and the CDs, it was found that some of the phytoconstituents are retained as such while others may have been converted into their derivatives during the process of formation of CDs. The CDs are designed to possess cellular imaging of human breast carcinoma cells (MCF-7), apart from free radicals sensing and scavenging capabilities. AAPCDs showed minimal cytotoxicity in Multi Drug Resistant clinically isolated strains of gram positive and gram negative bacteria which may be employed for microbiology oriented experiments. These results suggest potential of multi-functional AAPCDs as nano-probes for various pharmaceutical, biomedical and bioengineering applications.

Self-assembly of DNA-templated copper nanoclusters and carbon dots for ratiometric fluorometric and visual determination of arginine and acetaminophen with a logic-gate operation.

This work describes the synthesis of red-emitting copper nanoclusters (CuNCs) by using DNA as the template. DNA-templated CuNCs combined with blue-emitting carbon dots (CDs) form the self-assembled complex DNA-CuNC/CDs through electrostatic interactions. In the presence of arginine (Arg), the blue fluorescence of CDs (with excitation/emission maxima at 350/440nm) is quenched. Addition of acetaminophen (AP) induces the competitive combination of Arg and AP for the CDs. This results in the release of Arg from CDs and the recovery of blue fluorescence. On addition of both Arg and AP, the red fluorescence of CuNCs (with excitation/emission maxima at 350/670nm) undergoes only slight changes. Hence, the DNA-CuNC/CD complex can serve as a dually emitting ratiometric probe to determine both Arg and AP, with detection limits of 0.35μM and 0.26μM, respectively. The probe also enables on-site, visual determination of Arg and AP in aqueous samples, best by placing the system in cuvettes or dropping it onto filter paper strips. An "INHIBIT" logic gate was designed based on this ratiometric and visual fluorometric assay, with Arg and AP as the inputs. Graphical abstractSchematic presentation of self-assembly of DNA-templated copper nanoclusters and carbon dots to construct novel dual-emitting nanoprobes for ratiometric fluorometric and visual determination of arginine and acetaminophen in aqueous solutions and on wetting filter paper strips.

Fe3+ detection, bioimaging, and patterning based on bright blue-fluorescent N-doped carbon dots.

Bright blue fluorescent N-doped carbon dots (N-CDs) with satisfactory yield (54%) were successfully fabricated by one-step hydrothermal treatment of astragalus. The obtained N-CDs possessed superior stability, solubility and high resistance to photo bleaching, and can be used as label-free nanosensors for the determination of Fe3+. The quantitative analysis of Fe3+ showed a linear range of 50 to 250 μM with the detection limit as low as 42 nM. Moreover, the as-prepared N-CDs have been used in cellular imaging owing to their distinct merits of simplicity, convenience, fast response and good selectivity towards Fe3+. Besides, the N-CDs could also be further used as fluorescent inks for drawing luminescent patterns.

"On-off-on" detection of Fe3+ and F-, biological imaging, and its logic gate operation based on excitation-independent blue-fluorescent carbon dots.

A fluorescent nanoprobe based on carbon dots (CDs) has been facilely synthesized by a one-step hydrothermal pyrolysis of salicylic acid and utilized for the sequential detection of Fe3+ and F- invitro. The fluorescence of CDs can be extinguished dramatically by Fe3+ based on static quenching and subsequently recovery upon addition of F- due to the formation of stabler FeF3. The probe exhibits high selectivity and sensitivity toward Fe3+ and F- with a good linearity in the range of 10-300 μM and 0.1-200 μM, respectively, and a low detection limit of 52 nM and 8.5 nM, respectively. More importantly, as-prepared CDs with exceedingly fluorescence stability, negligible toxicity and superior biocompatibility have been expanded for detection Fe3+ and F- in living cell and Escherichia coli. Furthermore, an "AND" logic gate based on as-obtained CDs has been constructed.

Facile hydrothermal synthesis of nitrogen rich blue fluorescent carbon dots for cell bio-imaging of Candida albicans

Abstract Nitrogen doped carbon dots (N-CDs) are well documented as an outstanding fluorogenic material for protein tags, live cell imaging and protein-receptor based fluorescence sensors owing to its good optical features with less cytotoxicity and better water solubility. In this regard, the present work describes the synthesis of nitrogen rich blue fluorescent carbon dots (NR-CDs) through hydrothermal treatment of citric acid monohydrate (CA) and 2-aminopyridine (2-AP). The optical properties of NR-CDs are further analyzed by common analytical methods viz., Fourier transform infrared (FT-IR), UV–visible (UV–vis) and Fluorescence spectroscopies. The surface chemical composition and morphology of NR-CDs are acquired by X-ray photo electron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM), respectively. The NR-CDs produce blue fluorescent at 421 nm at the excitation wavelength of 310 nm, the calculated quantum yield is about 18% with respect to standard quinine sulfate. The synthesized NR-CDs contains 15.03 wt % of N revealed by XPS results. Further, the NR-CDs are used as a fluorescence staining agent for cell imaging of Candida albicans (C. albicans) and the cytotoxicity are also measured. All the outcomes proposed that the NR-CDs act as good staining agent for C. albicans with less cytotoxicity.

Carbon dots and AuNCs co-doped electrospun membranes for ratiometric fluorescent determination of cyanide

Due to the extremely toxic nature of cyanide, the World Health Organization (WHO) has set 1.9 μM as the maximum acceptable level in drinking water. Therefore, methods for facile screening and on-site detection of cyanide is urgently needed. In this work, a ratiometric fluorescent method for cyanide detection was developed based on blue-emitting carbon dots (CDs) and red-emitting AuNCs. To suit an on-site detection, the two fluorophores were incorporated into a nanofibrous membrane through electrospinning, yielding the core-shell structure of CDs/AuNCs-PVA@CA. Upon reaction with cyanide, the red fluorescence of AuNCs was quenched but the blue fluorescence of CDs was retained, resulting in ratiometric fluorescence change. Besides, both CDs and AuNCs can be excited with a handheld UV lamp (365 nm), and the resultant visible fluorescence color change could be visualized with naked eye. The proposed ratiometric method provided a limit of detection (LOD) 0.15 μM for cyanide, which was far lower than 1.9 μM. The membrane was further employed for screening analysis of cyanide in tap water samples. After collection of 500 analytical results, only 5.6% of the results located outside the X¯±2s criteria, while for the X¯±3s criteria, there is no outlier. The statistical results indicated that the proposed method may be potentially useful for screening analysis of cyanide in water samples.

Synergistic effect of fluorescence recovery and enhancement on ultrasensitive visual assay of cyanide anions based on N-Acetyl-L-Cysteine-Capped CdTe quantum dots and carbon dots

Developing a reliable fluorescent nanosensor for cyanide anions (CN−), with the potential to enable visual discrimination by naked eye, is highly sought after yet is limited by low sensitivity and selectivity. Herein based on the synergistic effect of fluorescence recovery and enhancement, a specific dual-emission nano-system was designed for ultrasensitive detection of CN−, by employing carbon dots (peaking at 443 nm) as a reference and N-acetyl-L-cysteine (NALC)-capped CdTe quantum dots (QDs, peaking at 611 nm) as a reporter. The red fluorescence of CdTe QDs is first quenched by Cu2+ primarily with electron transfer. Upon addition of CN−, CN− coordinates with Cu2+ to form [Cu(CN)n](n−1)− complex, causing the Cu2+ to detach from the QDs, and consequently fluorescence recovery. More importantly, the CN− can undergo a nucleophilic addition reaction with the carbonyl group of NALC ligands, inducing 1.3-fold fluorescence enhancement towards the original QDs while the blue fluorescence of carbon dots remains constant. This results the fluorescence intensity ratios (I611/I443) are proportional to the concentrations of CN− in the ranges of 0.02―10 and 15―80 μM, and an ultra-low detection limit down to 10.35 nM is achieved. By using both Cu2+-promoted complexation and addition reaction as recognition units, the present method also showed excellent selectivity for CN− over other coexisting anions. Especially, we have already demonstrated, by spiked tests, the practicability of monitoring the concentration changes of CN− in both environmental water and cassava samples, and further realized visual monitoring of CN− changes in aqueous solution and test paper.

A composite consisting of bromine-doped carbon dots and ferric ions as a fluorescent probe for determination and intracellular imaging of phosphate.

A composite probe has been developed for fluorometric determination and imaging of phosphate in real water samples and in cells. The method is based on the use of weakly blue fluorescent bromine-doped carbon dots (C-dots) containing aromatic carbon-bromine groups and loaded with Fe3+ ions. The carboxy, phenolic hydroxy and aldehyde groups on the surface of the C-dots can coordinate with Fe3+ to form an adsorbed complex that reduces the blue fluorescence through an inner filter effect. If phosphate is added, it will capture Fe3+ on the surface of C-dots and restore fluorescence by ~88% via a displacement approach. The probe, best operated at excitation/emission maxima of 370/418nm, has a linear response in the 0.4 to 22μM phosphate concentration range and a 0.25μM of detection limit. The relative standard deviation (at a phosphate level of 8.0μM) is 3.6% (for n = 5). The method was applied to confocal imaging of phosphate in HeLa cells. Graphical abstractSchematic representation of the synthesis of bromine-doped carbon dots (C-dots) by a "one-step" approach. They are shown to be capable of (a) detecting phosphate in real water samples through the displacement approach, and (b) of imaging intracellular phosphate.

Aptamer-based fluorometric determination for mucin 1 using gold nanoparticles and carbon dots.

A fluorometric method is described for the determination ofmucin 1 (MUC1). It is based on the specific binding of MUC1 by anti-MUC1 aptamers and by exploiting the inner filter effect (IFE) exerted by gold nanoparticles (AuNPs) on the blue fluorescence of carbon dots (CDs). When CDs are mixed with AuNPs, their fluorescence is reduced due to an IFE. The IFE efficiency can be modulated by the adsorption and the aggregation state of AuNPs. The latter can be induced by addition of salt, thereby allowing the fluorescence of the CDs to recover. The aptamer is adsorbed on the AuNPs and protects the AuNPs from salt-induced aggregation which is accompanied by a color change from red to blue. If aptamer is added to a mixture of CDs and AuNPs in presence of salt, the aggregation of the AuNPs is inhibited. Thus, the blue fluorescence of the CDs (best measured at excitation/emission wavelengths of 365/448nm) is reduced. If, however, the aptamers bind MUC1, the aptamers will be released from the surface of the AuNPs. This decreases the salt tolerance of AuNPs and leads to the recovery of the blue fluorescence. The fluorescence intensity increases with the concentration of MUC1. The method has a linear response in the 5.3 to 200ng·mL-1 MUC1 concentration range and a lower detection limit of 5.3ng·mL-1. The method displays excellent selectivity towards MUC1 against other proteins. Graphical abstract Schematic illustration of (I) the influence of IFE of free AuNPs and NaCl aggregated AuNPs and (II) the influence of specific interaction between MUC1 and aptamers on the NaCl-induced aggregation of AuNPs and the IFE efficiency.

Versatile Coffee Carbon Dots as Lead (ii) and Copper (ii) ion Fluorescence Detectors and Copper Corrosion Inhibitor

A simple and green tandem hydrothermal and pyrolysis method was developed for the synthesis of blue fluorescence carbon dots from coffee green bean powder and urea as raw materials. The carbon dots were characterized by ultraviolet visible spectrophotometer, Fourier-transform infrared spectroscopy and ocean optics spectrophotometer. The carbon dots had a bright blue emission centered at 505 nm under UV light with the excitation wavelength at 360 nm. The carbon dots also showed a quenching effect with lead (ii) ions and copper (ii) ions. Furthermore, a method for copper (ii) and lead (ii) ion detection in aqueous solution was developed with acceptable linearity of 97.26% and 99.41% respectively and selectivity to some common ions. The carbon dots also demonstrated the ability to act as copper corrosion inhibitors in 1% sodium chloride solution showing an inhibition efficiency of 77% at 1000 ppm. It is worth noting that the synthesized fluorescent carbon dots are eco-friendly and inexpensive. They could find application in chemical sensing and copper corrosion inhibition in salt environments.

A facile hydrothermal method for preparation of fluorescent carbon dots on application of Fe3+ and fingerprint detection

The carbon dots (CDs) was prepared by a facile hydrothermal treatment of citric acid and glycine at 180 °C. The CDs at around 3.2 nm was collected after filtration and dialysis. The sample displayed green fluorescence (G-CDs) with a quantum yield of 3.7% in high concentration and the strongest emission peak was at 545 nm under the excitation wavelength of 480 nm; the blue fluorescence CDs (B-CDs) with a quantum yield of 29.8% was obtained after diluted either in solution or in powder, the strongest emission peak was located at 475 nm under the excitation wavelength of 380 nm. The G-CDs possessed a high selectivity to Fe3+, which was in a linear range of 0–3.5 μM with the detection limit of 0.21 μM. The CDs powder with blue fluorescence at a relative low content was obtained and adaptable for the fingerprint detection on substrates of litmus paper, resin tabletop, glass, and orange plastic ruler.

A carbon dot-based ratiometric fluorometric and colorimetric method for determination of ascorbic acid and of the activity of ascorbic acid oxidase.

A dual-mode method was developed for the determination of ascorbic acid (AA) and of ascorbic acid oxidase (AA-Ox) activity. It combines the advantages of ratiometric fluorometry and colorimetry. The assay is based on the oxidation of o-phenylenediamine (OPDA) by permanganate (KMnO4). A yellow substance (referred to as oxOPDA) with an absorption peak at 425nm is rapidly produced in the presence of the oxidant. oxOPDA reduces the blue fluorescence of carbon dots (C-dots) peaking at 450nm (upon 380-nm excitation), and a new emission peak is found at 565nm. If AA is pesent, it consumes acertain fraction of KMnO4, so that less OPDA will be oxidized. This is accompanied by a decrease in the intensity of the fluorescence at 565nm and an increase in the intensity at 450nm. In parallel, the color of the solution changes from yellow to colorless. The determination of the activity of ascorbic acid oxidase (AA-Ox) is performed as follows: AA is oxidized by AA-Ox. This causes the fluorescence and colors to change in the opposite directions compared with AA detection. The ratio of fluorescences (I565/I450) becomes larger if the color the solution turns from colorless to yellow. Thus, the fluorescence intensity ratio (I565/I450) and colorimetric "bare-eye" readout can be used for determination of both the concentration of AA and the activity of AA-Ox. The fluorometric assay for AA has a linear range that extends from 0.6 to 40μM, and the colorimetric assay from 0.2 to 70μM. The respective data for AA-Ox activity are 0.04 ~ 5mU·mL-1 and 0.04 ~ 8mU·mL-1, respectively. The limits of detection for AA are 9 and 40nM, and the LODs for AA-Ox activity are 0.017 and 0.012mU·mL-1. Graphical abstract Schematic presentation of the assay. Permanganate (KMnO4) rapidly oxidizes ortho-phenylenediamine oxide to form a product (oxOPDA) having a yellow fluorescence peaking at 565 nm. The yellow color of oxOPDA can be detected visually. It also reduces the intensity of the blue fluorescence of carbon dots (C-dots) peaking at 450 nm. Ascorbic acid (AA) can consume permanganate, and this results less oxidation of OPDA. Ascorbic acid oxidase (AA-Ox) catalyzes the oxidization of AA by oxygen, and this - in turn - causes the changes in absorbance and fluorescence to change in the opposite directions.

Tuning of carbon dots emission color for sensing of Fe3+ ion and bioimaging applications

Herein, we report a facile one-step synthetic strategy for fabrication of three (blue, green and yellow) fluorescent color carbon dots (CDs) from tomato (Solanum lycopersicum). The as-synthesized CDs showed emission peaks at 450, 520 and 560 nm for blue, green and yellow color CDs when excited at 370, 420 and 460 nm, respectively. Using tomato as a carbon source, the fabricated three fluorescent color CDs showed good water dispersity and high quantum yield. The analytical performances of three fluorescent color CDs are evaluated by detecting Fe3+ ion in biofluids and iron tablets. Upon the addition of Fe3+ ion under optimal conditions, the fluorescence intensity of three fluorescent color CDs was quenched linearly over the range of 0.1 to 2.0 μM. This method opens a new analytical strategy to quantify Fe3+ ion in iron tablets and biofluids with high sensitivity. Further, the uptake of three fluorescent color CDs into HeLa cells was confirmed by confocal laser scanning microscopy. Intracellular experiments demonstrated that the three fluorescent color CDs were effectively internalized the cells and show excellent biocompatibility and low toxicity, suggesting that the CDs can be used as good candidates for biomedical applications.

Fluorometric determination of pesticides and organophosphates using nanoceria as a phosphatase mimic and an inner filter effect on carbon nanodots.

Nanoceria with a remarkable phosphatase mimicking activity was synthesized and used to catalyze the hydrolysis of phosphate esters in pH10 solution. The catalytic effect of nanoceria was firstly investigated by selecting p-nitrophenyl phosphate as a model substrate. The pH value, incubation temperature, reaction time, and concentration of nanoceria were optimized. The catalytic effect was then confirmed by using methyl-paraoxon as a substrate. The p-nitrophenol anionreleased by the enzyme mimic is yellow andexerts an inner filter effect on the fluorescence of the carbon dots (with excitation/emission maxima at 400/520nm). Response to methyl-paraoxon is linear in the 1.125-26.25μmolL-1 concentration range. The method was applied to the determination of pesticides in spiked Panax quinquefolius and water samples. Recoveries ranged from 85 to 103% (n = 3). The technique is rapid, reliable, and can be used for on-site detection of pesticides and organophosphates. Graphical abstract Schematic presentation of a fluorometric technique for the detection of organophosphate compound and pesticide using nanoceria as a phosphatase mimic and an inner filter effect on the bluefluorescence of carbon dots (with excitation/emission maxima at 400/520nm).

Preparation of carbon dots from succinic acid and glycerol as ferrous ion and hydrogen peroxide dual-mode sensors and for cell imaging

Fluorescent carbon dots are optically unique materials that have many applications, including photocatalysis, drug delivery, and biosensing. In this work, carbon dots were synthesized in high yields from succinic acid and glycerol using a green, one-step hydrothermal method, and without the addition of acid or base catalysts. Blue- and green-fluorescence could be selected for simply by varying the reaction time, at quantum efficiencies of 11% and 7%, respectively. The blue-fluorescent carbon dots were tested as dual-mode sensors for the detection of ferrous ion (Fe2+) and hydrogen peroxide (H2O2). They were shown to be selective to Fe2+ and H2O2 in solutions, with limits of detection of 21.9 and 0.7 μM, respectively. The carbon dots were used to prepare paper-based sensors that can be used to determine Fe2+ and H2O2 concentrations as low as 30 μM and 400 nM, respectively. Fe2+ and H2O2 in several real water samples were determined with excellent recovery and repeatability. They were also demonstrated to be luminescent in the polymeric materials, giving them a wide range of potential solid-state applications. In the tests of cell imaging, they were shown to have excellent biocompatibility, with cell viability of 90% at carbon dot concentrations of up to 1 g L−1. Our carbon dots are thus suitable for use as chemical and intracellular probes.

Green Synthesis of Blue Fluorescent P-doped Carbon Dots for the Selective Determination of Picric Acid in an Aqueous Medium.

A fluorescence method for the determination of picric acid (PA) using phosphorus-doped carbon dots (P-CDs), synthesized from β-cyclodextrin and sodium pyrophosphate, is described. The P-CDs are very uniform and monodisperse with a diameter of about 2.8 nm. Under an excitation of 350 nm, the P-CDs emit bright blue fluorescence with an emission peak at 440 nm. The as-synthesized P-CDs serve as a sensitive, selective, and label-free fluorescent probe for the detection of PA. Based on an inner filter effect between PA and P-CDs, a linear response is obtained for PA from 0.1 to 10 μM with a detection limit of 82 nM. Finally, this sensing system has been demonstrated to have practicability for PA detection in the environmental water samples.

Highly selective fluorescent visual detection of perfluorooctane sulfonate via blue fluorescent carbon dots and berberine chloride hydrate.

As a kind of emerging persistent organic pollutants, perfluorooctane sulfonate (PFOS) and its salts have caused global ecosystem pollution. To develop rapid, sensitive and low-cost detection method of PFOS is of great importance. In this work, a novel sensing method has been proposed for the highly selective fluorescent visual detection of PFOS in aqueous solution based on carbon dots (CDs) and berberine chloride hydrate (BH). It was found that the fluorescence of CDs decreased apparently in the presence of berberine chloride hydrate in pH 6.09 Britton-Robinson (BR) buffer solution. When PFOS was added to the system, the fluorescence was restored slightly at 448 nm and enhanced apparently at 533 nm, but no phenomenon occurred with other perfluorinated compounds. As a consequence, an obviously distinguishable fluorescence color variation (from blue to light yellow) of solution was observed. Under the optimized experimental conditions, the enhanced fluorescence intensities at 533 nm are in proportion to the concentration of PFOS in the range of 0.22-50.0 μmol/L (R2 = 0.9919), with a detection limit of 21.7 nmol/L (3σ). The proposed approach has been successfully applied to the detection of PFOS in environmental water samples with RSD ≤ 1.1%.

Facile and green synthesis of fluorescent carbon dots with tunable emission for sensors and cells imaging

Most carbon dots (CDs) conventional fabrication approaches produce single colored fluorescent materials, different methods are required to synthesize distinct carbon dots for specific optical applications. Herein, using one-pot hydrothermal treatment of Syringa obtata Lindl, a facile, low-cost and green assay is achieved in the controllable synthesis of blue and green fluorescent carbon dots. The fluorescent emission of CDs can be well-tuned by adding sodium hydroxide in the precursor solution. Blue fluorescent CDs are applied to Fe3+ sensing with a low detection limit of 0.11 μM of linear range from 0.5 to 80 μM, and then further extended to analysis river water samples. Green fluorescent CDs can be applied to pH detection, which show a remarkable linear enhancement in the green fluorescence emission region when the pH is increased from 1.98 to 8.95. Eventually, the detection of Fe3+ and pH are applied for the living cells fluorescent images in MCF-7 cells are achieved successfully, indicating as-synthesized CDs potential toward diverse application as promising candidate.

Carbon dots derived from carboxymethylcellulose for sensing isoniazid and H2O2

Herein, blue-fluorescence carbon dots (CDs) derived from carboxymethylcellulose have been innovatively synthesized with well-distributed sizes.