Luminescent Nitrogen-doped Carbon Dots Research Articles

Urea–choline chloride deep eutectic solvent-assisted synthesis of luminescent nitrogen-doped carbon dots from chitin and their photocatalytic application in decolourizing malachite green

Luminescent carbon dots (CDs) are emerging carbon nanomaterials whose tunable and exceptional optoelectronic properties have found applications as alternatives to traditional fluorophores and metal-based catalysts. Further, they can be easily prepared from biomass and using green solvents. Biomass sources of CDs, however, often result in the formation of thousands of products, which are difficult to separate. In this study, CDs were synthesized using a urea–choline chloride deep eutectic solvent and shrimp shell-derived chitin as raw materials through a low-temperature solvothermal treatment. This was followed by a facile liquid–liquid extraction with acetone to improve the optical properties and narrow the size distribution of the CDs. The acetone-extracted CDs (ACDs) showed good performance in photocatalytic degradation of the aquatic pollutant, malachite green. They also show good potential in monitoring various toxic water pollutants through the quenching effect of selected pesticides, antibiotics, heavy metals, and anions on the fluorescence of ACDs.

Single precursor-based luminescent nitrogen-doped carbon dots and their application for iron (III) sensing

Iron III (Fe3+) sensing is of great importance for monitoring its levels in different environmental and biological systems since its levels are tightly associated with many environmental concerns and serious diseases. Compared to the ordinary Fe3+ detection methods involving the sophisticated and expensive instruments, the use of fluorescent materials with short response time and low cost attracts much attention. Amongst a variety of fluorescent materials, a nitrogen-doped carbon dot (N-CD) is emerging as promising luminescent materials for biosensing due to their superior photoluminescent properties, good water solubility, and biocompatibility. Herein, N-CD prepared via a green and cost-effective one-pot hydrothermal method using a new single precursor N-(2-hydroxyethyl) ethylenediamine triacetic acid (HEDTA) as both the carbon and nitrogen sources is reported. The blue fluorescent emission of N-CDs is quenched by the addition of Fe3+, and the quenching intensity is concentration dependent in the wide range (0.76–400 μM) with a detection limit of 0.16 μM. The quantum yield for the as prepared N-CDs is 14.17%. The N-CDs also show a high selectivity for Fe3+ chelation amongst a range of biological metal ions. The fluorescent quenching is attributed to the formation of the coordinate covalent bonds between the Fe3+ and N-CDs, and the mechanism is proved to be a static type on the basis of the photoluminescence lifetime and the temperature-dependent fluorescent intensity change. Our eco-friendly and simple strategy will benefit the application of CDs in various fields.

Orange Luminescent Carbon Dots as Fluorescent Probe for Detection of Nitrite

Abstract Orange luminescent nitrogen doped carbon dots (N-CDs) were prepared via one-step hydrothermal treatment with p-phenylenediamine and citric acid as precursors. The morphology and optical properties of the N-CDs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), ultraviolet-visible absorption spectroscopy (UV-vis) and fluorescence (FL) spectroscopy. The synthesized N-CDs had an extreme small size ((1.62 ± 0.35) nm), good water solubility and excellent fluorescent stability. The addition of nitrite (NO2−) caused fluorescence increase of N-CDs. Based on this phenomenon, a new fluorescence analysis method for detecting NO2− was established. Moreover, the possible fluorescence enhancement mechanism was proposed. The constructed fluorescence sensing system was applied to the detection of NO2− in sausage, pickle and tap water samples with recoveries from 97.1% to 104.5% and relative standard deviations (RSDs) of 1.1% to 3.5%.

Green and Facile Synthesis of Highly Photoluminescent Nitrogen-doped Carbon Dots for Sensors and Cell Imaging

Luminescent nitrogen-doped carbon dots (NCDs) with high fluorescence quantum yield (46.01%) are synthesized from ammonium citrate and betaine hydrochloride by a simple and rapid green route of a one-pot hydrothermal method. The as-prepared NCDs exhibit excellent selectivity and sensitive detection for H+ and Hg2+ (detection limit of 1.69 nM for Hg2+). Finally, the low toxicity and highly photoluminescent NCDs are utilized to detect H+ and Hg2+ in SMMC-7721 cells by a laser scanning confocal microscope.

A chemiluminescence resonance energy transfer for the determination of indolyl acetic acid using luminescent nitrogen-doped carbon dots as acceptors

A CRET method was fabricated for the determination of IAA using Ce(iv)–Na2SO3 as the donor and N-CDs as the acceptor.

Construction of a novel "Off-On" fluorescence sensor for highly selective sensing of selenite based on europium ions induced crosslinking of nitrogen-doped carbon dots

A highly blue luminescent nitrogen-doped carbon dots (N-CDs) was prepared, using citric acid and l-lysine via one pot hydrothermal treatment, and applied to the determination of selenite. The synthesized N-CDs exhibited a high photostability, excellent optical features with a high quantum yield (21.5%) and average size of 3nm. The method is based on the competition between oxygen donor atoms in selenite oxyanion with those from carboxylate and hydroxyl groups at the surface of N-carbon dots for europium ions binding. N-CDs could be readily quenched upon the addition of europium ions owing to high affinity of carboxylate and hydroxyl groups at the surface of carbon dots to Eu3+ leading to aggregation of N-CDs (state OFF). After selenite addition, disruption of the aggregated N-CDs takes place, leading to restoration of the quenched fluorescence (State ON). The repeatability was less than 3.2% for selenite in both standard and real samples (n = 3). The method provides a simple procedure enabled selective detection of selenite with a linear range of 0.078–21.4µgmL−1 and a limit of detection of 53.0ngmL−1 (S/N = 3). The accuracy and precision were evaluated based on the detection of selenite in health care products with satisfactory results.

Rapid microwave-assisted synthesis of highly luminescent nitrogen-doped carbon dots for white light-emitting diodes

Highly luminescent nitrogen-doped carbon dots (N-CDs) were synthesized rapidly by one-step microwave-assisted hydrothermal method using citric acid as carbon source and ethylenediamine as dopant. The influences of reaction temperature, reaction time and raw material ratio on the fluorescence performance of N-CDs were investigated. Then N-CDs with the highest quantum yield were selected as fluorescent materials for fabricating white light-emitting diodes (LEDs). Highly luminescent N-CDs with the quantum yield of 75.96% and blue-to-red spectral composition of 51.48% were obtained at the conditions of 180 °C, 8 min and the molar ratio of citric acid to ethylenediamine 2:1. As-prepared highly luminescent N-CDs have an average size of 6.06 nm, possess extensive oxygen- and nitrogen-containing functional groups on their surface, and exhibit strong absorption in ultraviolet region. White LEDs based on the highly luminescent N-CDs emit warm white light with color coordinates of (0.42, 0.40) and correlated color temperature of 3416 K.

Highly fluorescent carbon dots as selective and sensitive “on-off-on” probes for iron(III) ion and apoferritin detection and imaging in living cells

Highly blue luminescent nitrogen-doped carbon dots (N-CDs) with a fluorescence quantum yield of 42.3% were prepared by an efficient one-step pyrolytic route from ethylenediaminetetraacetic acid and urea. The as-synthesized N-CDs were demonstrated as an effective fluorescent probe for label-free, selective and sensitive recognition of Fe3+ with a linear range of 0.5μM to 2mM and a detection limit of 13.6nM due to Fe3+-quenched fluorescence (turn-off). The quenched fluorescence could be turned on after the addition of apoferritin owing to the removal of ferric species from the surface of N-CDs by apoferritin, making complex N-CDs/Fe3+ a selective apoferritin probe with a linear range of 0.1–25μM and a detection limit as low as 2.6nM. In addition, the application of this novel N-CDs-based probe for imaging Fe3+ ions and apoferritin in living cells suggest that this sensing system has great potential applications in biosensing, bioimaging, and many other fields.

Tuning the properties of luminescent nitrogen-doped carbon dots by reaction precursors

Four types of luminescent nitrogen-doped carbon dots (C-dots) are prepared by using glucose (G) or citric acid (C) as carbon source, and dopamine (D) or 4,7,10-trioxa-1,13-tridecanediamine (T) as nitrogen source, named GD-C-dots, GT-C-dots, CD-C-dots and CT-C-dots. The investigation on the optical, pH-sensitivity and photovoltaic properties of these C-dots illustrates that nitrogen source plays a key role in the properties of obtained C-dots. GD-C-dots and CD-C-dots show interesting electrochemical activities, which can provide fluorescent and electrochemical dual signals for practical applications. We demonstrate that not only the optical properties but also other physicochemical properties can be tuned by appropriate choice of the reaction precursors.

One-step Synthesis of Highly Luminescent Nitrogen-doped Carbon Dots for Selective and Sensitive Detection of Mercury(II) Ions and Cellular Imaging.

In this paper, nitrogen-doped carbon dots (N-CDs) with high quantum yield (QY) of 40.5% were prepared through a facile and straightforward hydrothermal route. The as-prepared N-CDs exhibited excellent photoluminescence properties, good water-solublity and photostability, negligible cytotoxicity and favourable biocompatibility. Such N-CDs were found to serve as an effective fluorescent sensor for selective and sensitive detection of Hg(2+) in a wide linear response concentration range of 0 - 8 μM with a limit of detection (LOD) of 0.087 μM and could be applied to the determination of Hg(2+) in environmental water samples. The corresponding mechanisms were discussed in detail. Moreover, another attractive finding was that the N-CDs showed satisfactory performance in bioimaging before and after the addition of Hg(2+) in human lung cancer PC14 cells. With excellent sensitivity, selectivity and biocompatibility, such cheap carbonmaterials are potentially suitable for monitoring of Hg(2+) in environmental applications and promising for biological applications.

Microplasma-assisted rapid synthesis of luminescent nitrogen-doped carbon dots and their application in pH sensing and uranium detection.

Developing a simple synthesis method and expanding the application of carbon dots have attracted increasing attention. In this report, we have developed a facile method to synthesize fluorescent carbon dots (CDs) with the assistance of atmospheric-pressure microplasma. The CDs could be produced within a few minutes with no need of high temperature, external energy input, and multistep procedures. The as-prepared CDs had a relatively uniform size of approximately 2.3 nm. The FTIR spectrum and the XPS analysis showed that carbonyl groups and amide groups exist on the surface of CDs. The CDs showed bright blue luminescence and high stability in high salt concentration and low pH without further modification. A pH-dependent PL behavior was observed and could be applied for pH sensing in the range of 3-14. Moreover, the CDs could be utilized as a reagent capable of detecting U(vi) with a low detection limit and high selectivity.

Lighting up left-handed Z-DNA: photoluminescent carbon dots induce DNA B to Z transition and perform DNA logic operations

Left-handed Z-DNA has been identified as a transient structure occurred during transcription. DNA B-Z transition has attracted much attention because of not only Z-DNA biological importance but also their relation to disease and DNA nanotechnology. Recently, photoluminescent carbon dots, especially highly luminescent nitrogen-doped carbon dots, have attracted much attention on their applications to bioimaging and gene/drug delivery because of carbon dots with low toxicity, highly stable photoluminescence and controllable surface function. However, it is still unknown whether carbon dots can influence DNA conformation or structural transition, such as B-Z transition. Herein, based on our previous series work on DNA interactions with carbon nanotubes, we report the first example that photoluminescent carbon dots can induce right-handed B-DNA to left-handed Z-DNA under physiological salt conditions with sequence and conformation selectivity. Further studies indicate that carbon dots would bind to DNA major groove with GC preference. Inspired by carbon dots lighting up Z-DNA and DNA nanotechnology, several types of DNA logic gates have been designed and constructed based on fluorescence resonance energy transfer between photoluminescent carbon dots and DNA intercalators.