Fluorescent Carbon Nanomaterials Research Articles

Carbon dots: Discovery, structure, fluorescent properties, and applications

Abstract Nanotechnology has become one of the most important topics since the beginning of the twenty-first century in numerous fields including drug synthesis and delivery, environmental protection, electronics manufacture, and astronomy due to their nanoscale particles and their properties. The traditional semi-quantum dots are replaced by a new category of fluorescent carbon nanomaterials. Carbon dots (CDs) have been explored in the last few years for their simple synthetic accession, good bio-consonance, and several revelation applications. This review explains the fluorescent properties of CDs in brief, giving also a background on CDs discovery, structure, and composition, as well as on nanocomposites, green synthesis, and their applications. Resources conservation can be achieved by using recycled substances for sustainable development which lead to a new technology. Fluorescent CDs synthesized from food wastes like bananas, orange peel waste, sugarcane bagasse, Trapa bispinosa peels, bread, and jaggery have several applications such as sensing, drug delivery, gene transfer, biological imaging, and food safety. In this study, we concentrate on CDs greener methods to prepare effective and biocompatible CDs.

Precise Blood Glucose Sensing by Nitrogen‐Doped Graphene Quantum Dots for Tight Control of Diabetes

Graphene quantum dots (GQD) are novel fluorescent carbon nanomaterials based on a graphite structure. Thanks to extraordinary properties such as high surface area and enhanced prevalent optical properties, they have received more interest for special applications. Glucose sensing is a critical factor for the diagnosis, and treatment of diabetes plays an important role and could contribute to the monitoring of diabetes and other related parameters, which has been effectively underscoring the health society. Detecting glucose has been cultivated through different systems, for example, electrochemical or optical techniques. Novel transducers made with GQD that fluorescent coordinate methods have considered the improvement of cutting‐edge glucose sensors with prevalent affectability and accommodation. Currently, detection of glucose by nitrogen‐doped GQD frameworks concerning the determined objectives has been considerably considered. Here, we explored the properties of fluorescent nitrogen‐doped GQD as an excellent and effective index that significantly could promote nitrogen‐doped GQDs and make them an appropriate candidate for detecting glucose.

Fluorimetric detection of distinct lyotropic anion interactions on nanoscopic surfaces

The molecular structure, stability and function of proteins, nucleic acids, and many other colloidal entities including nanomaterials depend greatly on their highly specific response towards surrounding solvent molecules and inorganic ions. In order to earn an unambiguous mechanistic insight into the origin of these effects, water-soluble fluorescent carbon nanomaterials having amide groups in a hydrophobic microenvironment were successfully employed as the model colloidal system in this research study. Quantum dots with acidic functionalities were first of all prepared using a simple carbon precursor. Subsequently, chemical modification of carbon quantum dots (CQDs) was carried out with isopropylamine to impart protein-like amide richness to the nanoparticle surface. Moreover, the prepared CQDs were found to be highly fluorescent. Fluorescence intensity, interestingly, showed unique modulation patterns on incubation with different types of anions. Lipophilic chaotropic anions such as I−, SCN−, and Br− showed concentration-dependent fluorescence quenching whereas hydrophilic kosmotropic anions like SO42− had almost no impact on the nanomaterial fluorescence. This striking observation in the case of chaotropic anions can be correlated to their strong partitioning affinity for the amide groups on the nanomaterial surface. High charge density anions like sulphate, on the other hand, are mostly excluded from the colloidal interfaces. The current study emphasizes the fact that the functional groups available on the surface of macromolecules as well as anion's inherent thermodynamic parameters in a solvent play a pivotal role in the observed anion specificity.

Hydrothermal synthesis and characterization of nitrogen-doped fluorescent carbon quantum dots from citric acid and urea

As a new type of fluorescent carbon nanomaterials, carbon quantum dots have been widely concerned in recent years because of their good biocompatibility, low cytotoxicity and easy surface functionalization. In this paper, nitrogen-doped carbon quantum dots (N-CQDs) were prepared by one-step hydrothermal method with citric acid as the carbon source and urea as a nitrogen source. The fluorescence spectrophotometer, Fourier infrared spectrometer, X-ray diffractometer, and transmission electron microscope were utilized to discover the luminescence properties, structural characteristics, morphology and size of the synthesized N-CQDs. The results showed that the best reaction conditions for preparing N-CQDs were as follows: the hydrothermal process parameters were 240 °C for 10 h, and the concentration of nitrogen doping was 0.6 wt%. Under these conditions, the prepared N-CQDs with bright blue fluorescence solution was uniform and stable. And the results showed the structural characteristics were weak crystalline graphite carbon, and the shape characteristics were nearly spherical quantum dot with about 5–10 nm diameters.

Directly reusing waste fish scales for facile, large-scale and green extraction of fluorescent carbon nanoparticles and their application in sensing of ferric ions

Fluorescent nanomaterials have important applications in environmental monitoring and biomedicine and imaging. However, their preparation often is cumbersome, expensive, and extremely small-scale, requires harsh conditions, which limit their wide and practical applications. Herein, by directly reusing waste fish scales with intrinsic fluorescent property as precursors, we developed a facile, large-scale, inexpensive, and green method for extraction of fluorescent carbon nanoparticles for sensing of Fe3+. Our preparation approach only requires soaking fish scales in water without harsh conditions and complicated operations, only based on physical exfoliation, not limited by containers. Fish-scale-derived fluorescent carbon nanoparticles with bright blue fluorescence and a quantum yield of 15.6% are irregular spheres with a diameter of more than 60 nm, contained smaller nanodots with a diameter of about 4.2 nm, which has obvious lattice fringes of 0.23 nm. Elemental and functional group analysis confirmed that fluorescent carbon nanoparticles were mainly composed of C, O, and N, had hydroxyl, amine, and carbonyl groups, and similar in composition to collagens and hydroxyapatites. Fluorescent carbon nanoparticles can be used for fluorescent quenching-based detection of Fe3+ with a linear range of 0–6.25 μM and detection limit of 0.144 μM, and have good recoveries for Fe3+ in actual water samples and human serum with low relative standard deviations. This study not only adds a new dimension to provide a large-scale, simple, green, and promising method for reuse of waste fish scales, but also offers a new idea for the large-scale preparation and application of fluorescent carbon nanomaterials.

(Invited) Rational Design of NIR-II Optofunctional Materials for Biomedical Applications

The second near-infrared (NIR-II) biological window operating in the wavelength range of 1000-1700 nm is of considerable current interest for biomedical applications. This is mainly attributed to the high biological tissue penetration depth of the NIR-II light because of the less absorption and low optical scattering. However, previous studies regarding NIR-II optical materials mainly focused on the fluorescent upconversion nanomaterials, carbon nanomaterials, organic molecules and polymers for fluorescent bioimaging, photothermal/photodynamic therapy, and photoacoustic imaging. As is well-known, these optofunctional materials have limitations of low fluorescence efficiency, poor stability and poor multifunctionality. This talk will introduce NIR-II plasmonic materials recently developed in our lab for biomedical applications. We have developed NIR-II plasmonic Au-Ag nanostructures, copper chalcogenides and their hybrids with excellent optical properties tunable by their size, composition and structure. We have demonstrated the excellent plasmonic properties of these materials and systematically elucidated their structure-plasmonic property relationship. We also exemplified the applicability of these NIR-II optofunctional materials for SERS biosensing, photoacoustic imaging, CT, and light-assisted cancer therapy with excellent performance. We believe that these NIR-II plasmonic materials hold considerable potential for multimodality theranostics of cancer.

Complexation and fluorescence behavior of proflavin with chemically engineered amine capped carbon nanodots and its subsequent release into DNA environments

Amine capped carbon dots are prepared by pyrolysis of citric acid. Probable excited-state interactions between PF and CNDs have been studied. A controlled release of PF into ctDNA by CNDs shows their utility as an efficient drug delivery agent.

AS1411 aptamer modified carbon dots via polyethylenimine-assisted strategy for efficient targeted cancer cell imaging.

ObjectivesCarbon dots (CDs), as a fascinating class of fluorescent carbon nanomaterials, have been proven to be powerful tools in the field of bioimaging and biosensing due to their small size, suitable photostability and favourable biocompatibility. However, the cellular uptake of free CDs lacks selectivity and the same negative charges as cell membranes may cause inefficient cell internalization. In this study, an efficient detecting and targeting nanosystem was developed based on the DNA aptamer AS1411 modified CDs with polyethyleneimine (PEI) as connecting bridge.Materials and methodsHydrothermally prepared CDs were assembled with positive‐charged PEI, followed by conjugation with AS1411 through electrostatic interaction to form CDs‐PEI‐AS1411 nanocomplexes. The CDs, CDs‐PEI and CDs‐PEI‐AS1411 were characterized by transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectra, UV–vis spectra, zeta potential measurements and capillary electrophoresis characterizations. The cytotoxicity investigation of the CDs‐PEI‐AS1411 and CDs‐PEI in both MCF‐7 and L929 cells was carried out by the CCK‐8 assay. The cellular uptake of the CDs‐PEI‐AS1411 was studied with confocal microscopy and flow cytometry.ResultsThe as‐prepared nanosystem possessed good photostability and no obvious cytotoxicity. On the basis of the confocal laser scanning microscope observation and the flow cytometry studies, the cellular uptake of CDs‐PEI‐AS1411 nanosystem in MCF‐7 cells was significantly higher than that of L929 cells, which revealed the highly selective detection ability of nucleolin‐positive cells.ConclusionsThe results of this study indicated that the CDs‐PEI‐AS1411 nanosystem had a potential value in cancer cell targeted imaging.

Carbon dots derived from water hyacinth and their application as a sensor for pretilachlor

Recently,carbon-based nanomaterials have been attracted much interest among the scientific community due to its extraordinary properties and applications. Mostly the fluorescent carbon nanomaterials are prepared from commercially available precursors. In this work, develop a new strategy for producing carbon nanoparticles (carbon dots) using phosphoric acid as an activating agent from water hyacinth present in Assam, India. These carbon nanoparticles show green fluorescence under UV light, and the sizes are found below 10 nm. These carbon dots are applied as a fluorescence sensor for detecting the herbicide (pretilachlor). The developed PL sensor is exclusively selective and sensitive for detection of this herbicide, and the limit of detection is found to be 2.9 μM.This sensor is also tested for real samples like soil contaminated with pretilachlor.

Recent Advancements in Doped/Co-Doped Carbon Quantum Dots for Multi-Potential Applications

Carbon quantum dots (CQDs)/carbon nanodots are a new class of fluorescent carbon nanomaterials having an approximate size in the range of 2–10 nm. The majority of the reported review articles have discussed about the development of the CQDs (via simple and cost-effective synthesis methods) for use in bio-imaging and chemical-/biological-sensing applications. However, there is a severe lack of consolidated studies on the recently developed CQDs (especially doped/co-doped) that are utilized in different areas of application. Hence, in this review, we have extensively discussed about the recent development in doped and co-doped CQDs (using elements/heteroatoms—e.g., boron (B), fluorine (F), nitrogen (N), sulphur (S), and phosphorous (P)), along with their synthesis method, reaction conditions, and/or quantum yield (QY), and their emerging multi-potential applications including electrical/electronics (such as light emitting diode (LED) and solar cells), fluorescent ink for anti-counterfeiting, optical sensors (for detection of metal ions, drugs, and pesticides/fungicides), gene delivery, and temperature probing.

Selective, Sensitive and Label-Free Detection of Fe3+ Ion in Tap Water Using Highly Fluorescent Graphene Quantum Dots.

Graphene quantum dots (GQDs) as a new type of fluorescent carbon nanomaterials, showing excellent photoluminescence properties, biocompatibility, photoelectric properties, have become the current research focus. Iron element as an essential element in the human body and an important part of hemoglobin, is very important for human health, so the detection of ferric ions has great significance. In this paper, GQDs with strong blue light emission were prepared through pyrolysis treatment using citric acid as a carbon source. Through characterization by transmission electron microscopy (TEM) and fluorescence spectrometer, it was observed that the GQDs have a uniform particle size distribution and highly fluorescent intensity with a quantum yield of 27.4%. Due to the strong quenching effect of Fe3+ on GQDs fluorescence, GQDs was used as a green and facile fluorescence sensor to detect Fe3+ selectively and sensitively. The GQDs fluorescence sensor shows a sensitive response to Fe3+ in a wide linear range (3.5 × 10-6-6.7 × 10-4M), a low detection limit of 1.6μM (S/N = 3) and good selectivity. Importantly, the new sensor realizes the detection of Fe3+ ions in tap water because of its low detection limit, wide linear range, and high sensitivity.

Carbon quantum dots: synthesis, properties, and sensing applications as a potential clinical analytical method

Carbon quantum dots (CDs) are a novel class of fluorescent carbon nanoparticles and nanomaterials with fascinating properties, which have attracted worldwide attention and have been applied in different fields during the last decade.

Tailoring of low grade coal to fluorescent nanocarbon structures and their potential as a glucose sensor

Lignite is an abundantly utilized feedstock for the facile synthesis of fluorescent carbon dots and carbon nanomaterials. Its value is appreciated as an energy source for combustion for long time. Herein we report a novel top-down strategy to synthesis lignite based fluorescent nano carbon structures by combined acidic oxidation and chemical reflux. The nanocarbon crystallites in lignite are converted to oxygenated nano carbon dots and graphene sheets. They exhibited stable fluorescence property in the visible region depending on their size, functionalities and defects which were highly stable in all the pH conditions. These nanocarbon structures are an effective probe for fluorescent sensing of label-free and selective detection of glucose ions with detection limit as low as 0.125 mM, promising real-world sensor applications. These findings establish a scalable method for the production of fluorescent carbon based glucose sensor from lignite.

Structure and solvents effects on the optical properties of sugar-derived carbon nanodots

Carbon nanodots are a new and intriguing class of fluorescent carbon nanomaterials and are considered a promising low cost, nontoxic alternative to traditional inorganic quantum dots in applications such as bioimaging, solar cells, photocatalysis, sensors and others. Despite the abundant available literature, a clear formation mechanism for carbon nanodots prepared hydrothermally from biomass precursors along with the origins of the light emission are still under debate. In this paper, we investigate the relationships between the chemical structure and optical properties of carbon nanodots prepared by the hydrothermal treatment of glucose. Our major finding is that the widely reported excitation-dependent emission originates from solvents used to suspend the as-prepared carbon nanodots, while emission from dry samples shows no excitation-dependence. Another important highlight is that the hydrothermal conversion of biomass-derivatives under subcritical conditions leads to a heterogeneous mixture of amorphous-like nanoparticles, carbon onion-type and crystalline carbons composed of at least three different phases. The potential chemical reaction pathways involved in the formation of these hydrothermal carbon products along with a comprehensive structural and optical characterization of these systems is also provided.

Confined Synthesis of Carbon Nitride in a Layered Host Matrix with Unprecedented Solid-State Quantum Yield and Stability.

Fluorescent carbon nanomaterials have drawn tremendous attention for their intriguing optical performances, but their employment in solid-state luminescent devices is rather limited as a result of aggregation-induced photoluminescence quenching. Herein, ultrathin carbon nitride (CN) is synthesized within the 2D confined region of layered double hydroxide (LDH) via triggering the interlayer condensation reaction of citric acid and urea. The resulting CN/LDH phosphor emits strong cyan light under UV-light irradiation with an absolute solid-state quantum yield (SSQY) of 95.9 ± 2.2%, which is, to the best of our knowledge, the highest value of carbon-based fluorescent materials ever reported. Furthermore, it exhibits a strong luminescence stability toward temperature, environmental pH, and photocorrosion. Both experimental studies and theoretical calculations reveal that the host-guest interactions between the rigid LDH matrix and interlayer carbon nitride give the predominant contribution to the unprecedented SSQY and stability. In addition, prospective applications of the CN/LDH material are demonstrated in both white light-emitting diodes and upconversion fluorescence imaging of cancer cells.

Modified facile synthesis for quantitatively fluorescent carbon dots

A simple yet consequential modification was made to the popular carbonization processing of citric acid - polyethylenimine precursor mixtures to produce carbon dots (CDots). The modification was primarily on pushing the carbonization processing a little harder at a higher temperature, such as the hydrothermal processing condition of around 330 °C for 6 h. The CDots thus produced are comparable in spectroscopic and other properties to those obtained in other more controlled syntheses including the deliberate chemical functionalization of pre-processed and selected small carbon nanoparticles, demonstrating the consistency in CDots and reaffirming their general definition as carbon nanoparticles with surface passivation by organic or other species. Equally significant is the finding that the modified processing of citric acid - polyethylenimine precursor mixtures could yield CDots of record-setting fluorescence performance, approaching the upper limit of being quantitatively fluorescent. Thus, the reported work serves as a demonstration on not only the need in selecting the right processing conditions and its associated opportunities in one-pot syntheses of CDots, but also the feasibility in pursuing the preparation of quantitatively fluorescent CDots, which represents an important milestone in the development and understanding of these fluorescent carbon nanomaterials.

Development of N and S heteroatom co-doped stable dual emitting carbon ink in aqueous media for sensing applications

This manuscript describes a simple chemical route to synthesize nitrogen and sulfur co-doped highly fluorescent carbon nanomaterials with dual emission fluorescence properties. The fluorescence intensity of the (N,S)-CNPs has been found to be highly responsive towards Hg2+ ions and the pH of the solution.

Synthesis of Nitrogen-Doped Carbon Quantum Dots and Its Application as Fluorescent Sensor for Hg2+

Compared with traditional quantum dots, carbon quantum dots (CQDs) have aroused tremendous research interest among scientists as new fluorescent carbon nanomaterials due to their unique properties (easy surface functionalization, good biocompatibility, and low toxicity). The nitrogen-doped carbon quantum dots (NCDs) was synthesized with one-step hydrothermal treatment with citric acid as carbon source, and ammonia as nitrogen source. The obtained NCDs exhibited excellent water-solubility and high stability. High-resolution Transmission electron microscopy (HRTEM) image showed that the diameter of particles was about 3nm. Fourier transform infrared (FIIR) and X-ray photoelectron spectroscopy (XPS) spectra analysis demonstrated that the NCDs are functionalized with hydroxyl, amino, carbonyl, and carboxylic acid groups, which indicated NCDs has better water-solubility. It was further demonstrated that such NCDs can serve as effective fluorescent sensing platform for Hg2+ ions detection with sensitivity and selectivity. In a PBS butter solution (0.1 mol·L-1 pH 7.0), the fluorescence quenching ratio (F/F0) indicated linear responses with Hg2+ concentration ranging from 0.001 to 0.1 μmol·L-1, with the detection limit of 2.1 nmol·L-1. The fluorescence technique was superior in terms of sensitivity, selectivity and simplicity. It was successfully applied to determination of Hg2+ in samples.

Control of Photoluminescence of Carbon Nanodots via Surface Functionalization using Para-substituted Anilines.

Carbon nanodots (C-dots) are a kind of fluorescent carbon nanomaterials, composed of polyaromatic carbon domains surrounded by amorphous carbon frames, and have attracted a great deal of attention because of their interesting properties. There are still, however, challenges ahead such as blue-biased photoluminescence, spectral broadness, undefined energy gaps and etc. In this report, we chemically modify the surface of C-dots with a series of para-substituted anilines to control their photoluminescence. Our surface functionalization endows our C-dots with new energy levels, exhibiting long-wavelength (up to 650 nm) photoluminescence of very narrow spectral widths. The roles of para-substituted anilines and their substituents in developing such energy levels are thoroughly studied by using transient absorption spectroscopy. We finally demonstrate light-emitting devices exploiting our C-dots as a phosphor, converting UV light to a variety of colors with internal quantum yields of ca. 20%.

A Turn-Off Fluorescent Nanosensor for Iron in Aqueous Solution Based on Fluorescent Carbon Nanoparticles

The water-soluble fluorescent carbon nanomaterials with low toxicity and high biocompatibility are considered as promising materials for biomedical and sensor applications. Here, we report that a nanosensor system has been developed to simultaneously detect two valence states of iron ( Fe 2+ and/or Fe 3+) in aqueous solution based on fluorescent carbon nanoparticles (FCNs). The nanosensor has high selectivity and sensitivity with a limit of detection (LOD) of 5 μM, which is equivalent to 0.3 mg/L (5.36 μM) of iron in drinking water by United States Environment Protection Agency (US-EPA). Furthermore, a distinguishable color change of solution, from pale yellow to red-brown, can be observed as iron concentration reaching 40 μM, which provides way for fast, visible detection of irons.