Fluorescent Nitrogen-doped Graphene Quantum Dots Research Articles

Design of Polymeric Nanoparticles for Theranostic Delivery of Capsaicin as Anti-Cancer Drug and Fluorescent Nitrogen-Doped Graphene Quantum Dots.

In recent years, multifunctional nanocarriers that provide simultaneous drug delivery and imaging have attracted enormous attention, especially in cancer treatment. In this research, we designed a biocompatible fluorescent multifunctional nanocarrier for the co-delivery of capsaicin (CPS) and nitrogen-doped graphene quantum dots (N-GQDs) using the pH sensitive amphiphilic block copolymer (poly(2-ethyl-2-oxazoline)-b-poly(ε-caprolactone), PEtOx-b-PCL). The effects of the critical formulation parameters (the amount of copolymer, the concentration of poly(vinyl alcohol) (PVA) as a stabilizing agent in the inner aqueous phase, and volume of the inner phase) were evaluated to achieve optimal nanoparticle properties using Central Composite Design (CCD). The optimized nanoparticles demonstrated a desirable size distribution (167.8±1.4nm) with a negative surface charge (-19.9±0.4) and a suitable loading capacity for capsaicin (70.80±0.05%). The CPS & N-GQD NPs were found to have remarkable toxicity on human breast adenocarcinoma cell line (MCF-7). The solid fluorescent signal was acquired from cells containing multifunctional nanoparticles, according to the confocal microscope imaging results, confirming the significant cellular uptake. This research illustrates the enormous potential for cellular imaging and enhanced cancer therapy offered by multifunctional nanocarriers that combine drug substances with the novel fluorescent agents. This article is protected by copyright. All rights reserved.

Operando time and space-resolved liquid-phase diagnostics reveal the plasma selective synthesis of nanographenes.

Coupling atmospheric-pressure low-temperature plasmas to electrochemical reactors enables the generation of highly reactive species at plasma-liquid interfaces. This type of plasma electrochemical reactor (PEC) has been used to synthesize fluorescent nitrogen-doped graphene quantum dots (NGQDs), which are usable for multifunctional applications in a facile, simple, and sustainable way. However, the synthesis mechanism remains poorly understood, as well as the location of synthesis. To research these issues, we present an in situ diagnostics study on liquid phase chemistry during the PEC synthesis of NGQDs from chitosan. Monitoring of the photoluminescence and UV-VIS absorption at different depths in the reaction medium during plasma treatment reveals that the NGQD production initiates at the plasma-liquid interface but its completion and/or accumulation occurs at a few millimetres depth below the interface, where the liquid ceases to flow convectively, as determined by particle image velocimetry. Our study provides insights into the plasma synthesis of fluorescent GQDs/NGQDs from carbon precursors that may prove useful for achieving the scalability of PEC processes up to continuous-flow or array reactors.

Highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) synthesized from Pennisetum purpureum for selective and sensitive detection of Fe3+ ions

The synthesis of nitrogen-doped Graphene Quantum Dots (N-GQDs) employing Pennisetum purpureum (elephant grass) as the carbon precursor and ethylenediamine (EDA) as the nitrogen source was conducted. This study highlights the potential applications of nitrogen-doped multi-fluorescent graphene quantum dots (N-GQDs) in the detection of Fe3+. The synthesized N-GQDs have been studied using UV–vis spectrophotometry, fluorescence spectrometry, Raman spectrometry, FT-IR spectrometry, x-ray spectroscopy, selected-area electron diffraction, transmission and high-transmission electron microscopy. The acquired N-GQDs were observed to have an almost hexagonal shape with a lateral size of 2.42 nm and exhibited a comparable quantum yield of approximately 26%. The N-GQDs that have been prepared with consistent size distribution and a significant amount of nitrogen and oxygen-based functional groups showcase outstanding water dispersity. The N-GQDs exhibited the capability to identify the Fe3+ ions in a broad range concentration of 1–600 μM by creating an N-GQDs-Fe3+ complex through the occurrence of functional groups like nitrogen, carbonyl, and carboxyl on N-GQDs surface, has a lower limit of detection at approximately 60 nM. Our study provides evidence that the N-GQDs produced a strong and persistent fluorescence, which is highly soluble in water, notably the precise and selective detection of Fe3+ in water-based solutions.

Facile preparation of highly fluorescent nitrogen-doped graphene quantum dots for sensitive Fe3+ detection

Nitrogen-doped graphene quantum dots (N-GQDs) were synthesized by the hydrothermal method. The results of the transmission electron microscope and atomic force microscopy indicated that the average diameter and height of the homogeneously distributed N-GQDs were approximately 5 nm and less than 10 nm, respectively. The results of the X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed the successful incorporation of the N element into GQDs. The aqueous solution of N-GQDs dispersed in water remained stable and homogeneous at room temperature for 3 months. N-GQDs had a higher fluorescence intensity than GQDs and presented low toxicity and the survival rate of cells (3T3-Swiss albino) was more than 85% in the cytotoxicity test. To better understand the luminescence mechanism, the band gaps of GQDs and N-GQDs were calculated using the density functional theory (DFT). The effect of the pH value on the fluorescence intensity of N-GQDs before and after the addition of Fe3+ ions was investigated. N-GQDs were applied to selectively detect Fe3+ ions, and the results exhibited a wide linear correlation between the fluorescence intensity and the Fe3+ concentration of 0–100 uM with a detection limit of 0.74 uM. This study provided a simple and efficient synthesis method and proved the ultra-high Fe3+ detection selectivity and sensitivity of N-GQDs, offering the experimental and theoretical basis for N-GQDs’ applications in biosensing, bioimaging, environmental monitoring, etc.

One-pot synthesis of fluorescent nitrogen-doped graphene quantum dots for portable detection of iron ion

Nitrogen-doped graphene quantum dots (N-GQD) were synthesized by direct thermal decomposition of ammonium citrate tribasic. With the increment of torrefaction temperature, the average size of N-GQD was increased from 2.56 to 3.73 nm. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy analysis (XPS) proved the successful doping of nitrogen atoms. Besides, the N-GQDs showed blue fluorescence which was quenched by Fe3+ ions, and the fluorescence intensity of N-GQDs decayed exponentially. Accordingly, the same quenching effect was observed on a test paper prepared by soaking paper in N-GQDs dispersion. The quenching mechanism was due to electron transfer between Fe3+ and functional groups on the surface of N-GQDs which could be confirmed by XPS and diameter growth. Therefore, through this simple method, N-GQDs with high blue fluorescence and high production yield (64%) can be prepared, which provided a new strategy for monitoring and collecting Fe3+ in environmental water.

Color-tunable fluorescent nitrogen-doped graphene quantum dots derived from pineapple leaf fiber biomass to detect Hg2+

In this study, nitrogen-doped graphene quantum dots (N-GQDs) exhibiting high water solubility were produced based on the hydrothermal approach. Ethylenediamine (EDA) was used as the nitrogen dopant and microcrystalline cellulose (MCC), extracted from pineapple leaf fiber (PALF) biomass, used as the carbon source. The as-prepared N-GQDs exhibited an average size of 3.7 nm, 8-10 layers and the excitation wavelength-dependent fluorescence. It was noteworthy that controlling the pH value of the EDA solution in the hydrothermal process could change the fluorescence color of the N-GQDs, exhibiting unique green, cyan and blue light. Besides, because of the effective fluorescence quenching effect of N-GQDs by mercury (II) ions (Hg 2+ ), the as-prepared N-GQDs were successfully employed as the efficient nanosized fluorescence sensors to selectively detect Hg 2+ in aqueous solutions with the detection limit of 0.25 nM and a linear range of 0∼30 μM. The selectivity experiments indicated that as-prepared N-GQDs were specific for Hg 2+ even with interference by high concentrations of other metal ions. Notably, the N-GQDs could be well adopted to determine Hg 2+ in river water samples.

Hyaluronic acid conjugated nitrogen-doped graphene quantum dots for identification of human breast cancer cells

Accurate distinguish of cancer cells through fluorescence plays an important role in cancer diagnosis. Here we synthesized a blue fluorescent nitrogen-doped graphene quantum dots (N-GQDs) from citric acid and diethylamine via one-step hydrothermal synthesis method which was simple and quick to avoid by-products, and highlighted the binding sites to achieve precise combination. Due to the nitrogen element doping, amide II bond was amply obtained and abundant binding sites were provided for hyaluronic acid (HA) conjugation. N-GQDs solution with different pH value was then conjugated to HA via an amide bond for the recognition of human breast cancer cells (MCF-7 cells), and the formation of amide bond was more favorable under alkaline conditions. HA conjugated N-GQDs (HA-N-GQDs) were combined with CD44 which was over expressed on the surface of MCF-7 cells, resulting in MCF-7 cells performing stronger fluorescence. HA-N-GQDs showed high fluorescence, low toxicity, and good cytocompatibility, which held it play a role in fluorescence imaging for accurate identification of cancer cells.

Highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) as an efficient nanoprobe for imaging of microbial cells

Carbon, being a material of the era, has vast usefulness in the synthesis of many novel compounds. One of them is graphene quantum dots (GQDs) have drawn a great deal of attention to the scientific community owing to their low cytotoxicity, higher optical stability, and tremendous photoluminescence (PL) property, which show a new insight in the field of bio-sensing and bio-imaging. Herein, we have demonstrated a facile method to synthesise N-doped GQDs from graphene oxide (GO) using solvothermal treatment with aprotic solvent. GO was synthesised using a modified Hummers’ method. The as-prepared N-GQDs showed stronger green emission with 326 nm wavelength. PL study showed that PL characteristics of as-synthesised N-GQDs are mainly due to the surface π→π* and n→π* transitions of N containing functional groups with skeletal carbons of the graphene oxide sheet. The N-GQDs were also examined for bio-imaging of microbial cells including E. coli and Saccharomyces cescerevisiae yeast. The results (blue and green emissions under a fluorescence microscope) of this study showed biocompatibility and the photostability of N-GQDs for their application in the fields ranging from energy to biomedicine.

Rapid Synthesis of Highly Fluorescent Nitrogen-Doped Graphene Quantum Dots for Effective Detection of Ferric Ions and as Fluorescent Ink.

Graphene quantum dots (GQDs) have attracted much attention of many researchers because of their low cytotoxicity, good optical stability, and excellent photoluminescence property, which make them novel nanostructured materials in many application fields ranging from energy to biomedicine and the environment. In this work, highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) were synthesized through microwave heating using sodium citrate and triethanolamine as raw materials. The as-prepared N-GQDs showed considerable bright blue fluorescence with a quantum yield of 8% and excellent uniform dispersion with an average diameter of approximately 5.6 nm; they also exhibited excellent stability and pH-sensitive properties. Furthermore, we demonstrated the application of N-GQDs as probes for metal ion detection. The results indicated that N-GQDs responded rapidly toward Fe3+ because of the static quenching mechanism. A detection method was proposed, with detection linear in two ranges from 20 to 70 nM (F = −0.9666 CFe3+ (nM) + 608.85 (R = 0.9740)) and from 1 to 100 μM (F = −12.04 CFe3+ (μM) + 1191.94 (R = 0.9541)); the lowest detection limit of 9.7 nM for Fe3+ was obtained. The results obtained in this work lay the foundation for the development of high-performance and robust metal ion detection sensors. Moreover, it can also possibly be used as a new type of fluorescent ink.

Fluorometric atrazine assay based on the use of nitrogen-doped graphene quantum dots and on inhibition of the activity of tyrosinase

A fluorometric assay is described for the determination of theherbicide atrazine. The assay is based on the use of tyrosinase and fluorescent nitrogen-doped graphene quantum dots (N-GQDs). The N-GQDs were synthesized via one-pot hydrothermal reaction starting from citric acid and ammonia. Their fluorescence excitation and emission maxima are at 355 and 435nm, and the quantum yield is 18%. Tyrosinase catalyzes the oxidation of dopamine to form dopaquinone which reduces the fluorescence of the N-GQDs through a dynamic quenching process. On addition of atrazine, the catalytic activity of tyrosinase is inhibited. This leads to less formation of dopaquinone and less reduction of fluorescence. The assay has a linear response in the 2.5-100ng·mL-1 atrazine concentration range, and the detection limit is 1.2ng·mL-1. The assay was applied to the determination of atrazine in spiked environmental water samples. Graphical abstract Schematic presentation of the fluorometric assay of atrazine detection based on tyrosinase-induced fluorescence (FL) quenching effect on the nitrogen-doped graphene quantum dots (N-GQDs) and inhibitory effect of atrazine on tyrosinase.

Interaction of synthesized nitrogen enriched graphene quantum dots with novel anti-Alzheimer’s drugs: spectroscopic insights

Alzheimer’s disease (AD) is considered as one of widespread dementia with no approved diagnosis, cure or prevention. Currently, only symptomatic relief can be provided upon administration of anti-AD drugs generally belonging to a category of anticholinesterases and antagonists of N-methyl-D-aspartate (NMDA) receptors. In present investigation, a sensing platform has been designed for studying recently developed anti-AD drugs viz., PC-25 (N-(2-{4-[(4-bromophenyl)methyl]piperazin-1-yl}ethyl)-7-methoxy-1,2,3,4-tetrahydroacridin-9-amine trihydrochloride), PC-37 (7-methoxy-N-(2-{4-[(3-methylphenyl)methyl]piperazin-1-yl}ethyl)-1,2,3,4-tetrahydroacridin-9-amine trihydrochloride) and PC-48 (N-(2-{4-[(3-bromophenyl) methyl]piperazin-1-yl}ethyl)-7-methoxy-1,2,3,4-tetrahydroacridin-9-amine trihydrochloride) and two known standard tacrine (THA) and donepezil drugs for their estimation of in vitro potency towards AD using spectroscopic method. Anti-AD drugs have been accounted for individually with highly fluorescent nitrogen-doped graphene quantum dots (NGQDs). The designed anti-AD drugs exerted the efficacy related to cholinergic hypothesis of AD. While the enzyme action is sensed by interacted species of NGQDs and acetylcholine, the fluorescence of NGQDs is quenched by the hydrolyzing action of acetylcholinesterase (AChE) enzyme but the lost fluorescence is recovered upon addition of anti-AD drugs. These alterations in fluorescence of NGQDs are expected to have biological relevance akin to sensing. Moreover, these results advocate that out of all the drugs tested PC-37 displayed maximum inhibition efficiency. Our investigations suggest that synthesized drugs have the AD treating potential and can be entrusted in the near future for AD treatment. The validation parameters such as LOD, LOQ and recovery (%) were calculated in the range of 2.87 mM, 9.58 mM and 85–96%, respectively.Communicated by Ramaswamy H. Sarma

Highly Fluorescent Nitrogen-Doped Graphene Quantum Dots’ Synthesis and Their Applications as Fe(III) Ions Sensor

Nitrogen-doped graphene quantum dots (N-GQDs) with strong blue fluorescence and a high quantum yield of 88.9% were synthesized via a facile one-pot hydrothermal treatment with citric acid (CA) and ethylenediamine (EDA) as carbon and nitrogen sources, respectively. The blue fluorescence emission is independent of the excitation wavelengths. These N-GQDs dispersed well in water and ethyl alcohol and showed a highly selective and sensitive detection of hazardous and toxic Fe3+in the range of 1600μmol/L to 6000μmol/L through a fluorescence quenching process with a detection limit of 2.37μmol/L. Based on the excellent sensitivity and selectivity of N-GQDs to heavy metal ions, paper-based sensors can be fabricated by inkjet printing, which are rapid but low cost. So the visual instant on-site identification of heavy metal ion will be realized in the future.

Manganese(ii) enhanced fluorescent nitrogen-doped graphene quantum dots: a facile and efficient synthesis and their applications for bioimaging and detection of Hg2+ ions.

Manganese ion (Mn2+) bonded nitrogen-doped graphene quantum dots (Mn(ii)-NGQDs) with water solubility have been successfully synthesized by a simple, one-pot hydrothermal carbonization, using sodium citrate, glycine and manganese chloride as raw materials. The photoluminescence (PL) characteristics of Mn(ii)-NGQDs were studied in detail. The resulting Mn(ii)-NGQDs show a remarkably enhanced PL intensity and quantum yield (QY = 42.16%) compared with the product without Mn(ii)-doped (named as NG, QY = 27.06%) and the product doped with other metal ions. The Mn(ii)-NGQDs not only display low toxicity and high cellular uptake efficiency for fluorescence live cell imaging in biological evaluations but also exhibit a fast, highly selective and sensitive fluorescence quenching effect toward Hg2+ ions, with a detection limit of 3.4 × 10−8 mol L−1.

Highly fluorescent nitrogen-doped graphene quantum dots as a green, economical and facile sensor for the determination of sunitinib in real samples

The preparation of nitrogen-doped graphene quantum dots (N-GQDs), by a simple and inexpensive synthetic procedure, is reported with blue emission and a high quantum yield of 78%.

A green synthesis of highly fluorescent nitrogen-doped graphene quantum dots for the highly sensitive and selective detection of mercury(ii) ions and biothiols

A green synthesis of nitrogen-doped GQDs for the detection of mercury(ii) ions and biothiols.

One-pot synthesis of highly greenish-yellow fluorescent nitrogen-doped graphene quantum dots for pyrophosphate sensing via competitive coordination with Eu3+ions

Highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) with greenish-yellow emission and quantum yield of 13.2% have been synthesized via a one-pot hydrothermal method. The obtained N-GQDs displayed excellent optical properties, high photostability and resistance to strong ion strength. Based on the higher affinity of pyrophosphate (PPi) than carboxyl and amido groups on the surface of the N-GQDs to Eu(3+), a Eu(3+)-modulated N-GQD off-on fluorescent probe for PPi detection was constructed with a detection limit of 0.074 μM. The detection process was simple in design, easy to operate, and showed a highly selective response to PPi in the presence of co-existing anions. This work widens the applications of N-GQDs with versatile functionality and reactivity in clinical diagnostics and as biosensors.

A facile synthesis of highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-trinitrophenol in aqueous solution.

A facile bottom-up method for the synthesis of highly fluorescent nitrogen-doped graphene quantum dots (N-GQDs) has been developed via a one-step pyrolysis of citric acid and tris(hydroxymethyl)aminomethane. The obtained N-GQDs emitted strong blue fluorescence under 365 nm UV light excitation with a high quantum yield of 59.2%. They displayed excitation-independent behavior, high resistance to photobleaching and high ionic strength. In addition to the good linear relationship between the fluorescence intensity of the N-GQDs and pH in the range 2-7, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of 2,4,6-trinitrophenol (TNP). A sensitive approach has been developed for the detection of TNP with a detection limit of 0.30 μM, and a linearity ranging from 1 to 60 μM TNP could be obtained. The approach was highly selective and suitable for TNP analysis in natural water samples.

A simple one-pot synthesis of highly fluorescent nitrogen-doped graphene quantum dots for the detection of Cr(vi) in aqueous media

A new method for selective determination of Cr(VI) in environmental water samples was developed based on its quenching effect on the fluorescent N-doping graphene quantum dots (N-GQDs). The N-GQDs were synthesized by a simple one-step method using citric acid as the carbon source and ammonia as the nitrogen source with a 65% yield, showing that mass production of the N-GQDs is possible. The obtained N-GQDs with oxygen-rich functional groups exhibited a strong blue emission with a quantum yield of 18.6%, which was 7 times greater than that of graphene quantum dots (GQDs). Due to the selective coordination to Cr(VI), the N-GQDs can be used as a green and facile sensing platform for label-free sensitive and selective detection of Cr(VI) ions in aqueous solution and real water samples. Compared to GQDs, the N-GQDs as a fluorescent probe promises much improved selectivity for sensing of Cr(VI). The N-GQDs fluorescence probe shows a sensitive response to Cr(VI) in a wide concentration range of 0–140 μM with a detection limit of 40 nM. The N-GQDs-based fluorescence method was successfully used to selectively detect Cr(VI), and discriminate it and Cr(III) as well in aqueous samples.

Synthesis of highly fluorescent nitrogen-doped graphene quantum dots for sensitive, label-free detection of Fe (III) in aqueous media

Heteroatom doping can drastically alter the electronic characteristics of graphene quantum dots (GQDs), thus resulting in unusual properties and related applications. Herein, we develop a simple and low-cost synthetic strategy to prepare nitrogen-doped GQDs (N-GQDs) through hydrothermal treatment of GQDs with hydrazine. The obtained N-GQDs with oxygen-rich functional groups exhibit a strong blue emission with 23.3% quantum yield (QY). Compared to GQDs, the N-GQDs exhibit enhanced fluorescence with blue-shifted energy. Due to the selective coordination to Fe3+, the N-GQDs can be used as a green and facile sensing platform for label-free sensitive and selective detection of Fe (III) ions in aqueous solution and real water samples. The N-GQDs fluorescence probe shows a sensitive response to Fe3+ in a wide concentration range of 1–1945μM with a detection limit of 90nM (s/N=3). Interestingly, it is also found that both dynamic and static quenching processes occur for the detection of Fe3+ by N-GQDs, while the quenching effect of Fe3+ on the fluorescence of GQDs is achieved by affecting the surface states of GQDs.