Amphiphilic Carbon Dots Research Articles

Dual emissive amphiphilic carbon dots as ratiometric fluorescent probes for the determination of critical micelle concentration of surfactants.

The sensitive determination of the critical micelle concentration (CMC) of surfactants is very important for their practical application. Due to their good sensitivity and simple operation, pyrene and its derivatives have been widely used as fluorescent probes to detect the CMC. However, their virulent and poor water-soluble nature has limited their wide employment. In the present work, environmentally friendly amphiphilic carbon dots (Cdots) with dual-color emission and absolute quantum yield (PLQY) values higher than 50% have been fabricated through a solvothermal process, which could successfully serve as self-calibrative, ratiometric fluorescent probes to estimate the CMC of both non-ionic and ionic surfactants. This work not only provides a new strategy to design green ratiometric fluorescent probes for the CMC measurement of surfactants but also expands the application of Cdots in the colloidal field.

One-step synthesis of ultrabright amphiphilic carbon dots for rapid and precise tracking lipid droplets dynamics in biosystems

Fluorescent probes enabling precisely labeling lipid droplets (LDs) in complex systems are highly desirable in life science for studying LDs-related physiological processes and metabolic diseases. However, most of the current LDs fluorophores fail to achieve rapid wash-free LDs labeling, especially in vivo labeling due to their strong hydrophobicity and poor water solubility. We report here one-step synthesis of highly efficient carbon dots (CDs) that feature robust solvatochromic emission, high quantum yield (QY) up to 76.35% in oil, good water solubility and lipophilicity, thus allowing to stain LDs in a bright and selective manner. Detailed characterizations reveal the presence of a well-defined molecule, 2-dimethylamino-5-fluorobenzimidazole in a large amount in CDs. Its D-π-A structure and dimethylamino-induced spatial torsion configuration and extended π-electron conjugation account for solvatochromic emission with high QY. Notably, the CDs can image LDs with many advanced merits (high brightness, ultrafast staining within 10 s, wash-free, excellent LDs specificity, good biocompatibility) and have been successfully applied to monitor cellular LDs dynamics. Moreover, the CDs for the first time allow in situ labeling of LDs and epidermal cell membranes simultaneously in live zebrafish. This work expands the diversity for optical properties and applications of CDs, facilitating the design of new LDs-targeting CDs.

Solid-State Fluorescent Carbon Dots for Fluorimetric Sensing of Hg2+

This article examines how nitrogen speciation, graphitization, and surface functionality of carbon dots (CDs) can influence the structure–optical property relationship in solution and solid-state. Despite the fact that thousands of reports have already been published, research on carbon dots is still emerging due to its questionable key factors in structure and photoluminescence properties. Here, a simple approach in the synthesis has been established to tune the structural–optical property relationship in CDs using well-known precursors citric acid and m-phenylenediamine. Three distinctive N-doped CDs (CD1:1, CD1:0.5, and CD1:0.1) were synthesized via a one-pot microwave-assisted hydrothermal method. Amphiphilic and solid-state yellow luminescent CDs were revealed, which is attributable to the diverse speciations of the nitrogen content (graphitic N, pyridinic N, pyrrolic N, and amino N) and more disorder in the graphitic carbon core. Interestingly, a simple tuning of the stoichiometric ratio of precursors resulted in solid-state yellow luminescent and dual-emissive CDs. An in-depth investigation was performed using steady-state and time-resolved fluorescence studies to unravel the photoluminescence mechanism and the structure of CDs. In addition, due to the unique optical properties of CDs, we developed fluorescent strips and used them as an ON–OFF fluorescent sensor toward highly sensitive and selective detection of toxic Hg2+ metal ions in an aqueous medium. These findings would provide a strategy to tune the fluorescence and structural properties of CDs and toward the development of a simple strip-based probe for sensor applications.

Surface engineered amphiphilic carbon dots: solvatochromic behavior and applicability as a molecular probe.

Carbon dots (C-dots) have attracted great attention in the fields of nanotechnology and bioengineering owing to their unique and tunable optical properties with excellent photoluminescence characteristics. Herein, we have engineered amphiphilic C-dots (AC-dots) using positional isomers of diamino benzene with citric acid under mild microwave irradiation to minimize any background reactions. The optical properties changed from excitation-dependent to excitation-independent depending on the isomer used. This unique optical property of the AC-dots was studied in the presence of various solvents and we extensively inspected the AC-dot-solvent interactions. The intensity of the emission wavelength varied with solvent polarity and showed a linear relationship. Furthermore, we extended this property to investigate the molecular environment in biomolecular systems such as proteins. Interestingly, we found that, in the presence of various proteins, the emission intensity was enhanced, quenched or remained unchanged depending on the nature of the protein surface. The mode of interaction between AC-dots and protein was determined using temperature-dependent fluorescence spectroscopy. This study could provide vital information about the surfaces of proteins and the potential application of C-Dots as a fluorescent probe to detect biological molecules and environments.

Construction of multi-functional optical sensing materials based on deazapurine-typed carbon dots

Developing multi-functional materials is crucial to manufacture integrated devices and advanced instruments. However, the development of multi-functional properties is limited because most of the materials can only perform single-phase processing or detection. In this current study blue-emitting, amphiphilic purine-doped and amphiphilic carbon dots (CDs) have been synthesized for the construction of multi-functional materials. These multi-functional CDs (MF-CDs) can form stable dispersions of monodisperse nanoparticles or nanoaggregates in organic/aqueous phase, which endow them with the capability to be either processed or used as detectors/sensors in a variety of solvents. The MF-CDs not only can detect pH, metal cations and the polarity of organic solvents via the change of fluorescent signals in the solution state, but also can be applied in the fields of temperature response and laser-stimulus response in a composite film. As a consequence of the architecture of the MF-CDs composite systems multi-functional characteristics can be realized successfully, which provides a new perspective to develop integrated materials at the nanoscale level.

Amphiphilic Carbon Dots with Excitation‐Independent Double‐Emissions

AbstractDeveloping total carbon‐based multicolor emissive carbon dots (Cdots), especially amphiphilic Cdots (A‐Cdots) with several luminescent bands and limited emissive sites, is still a challenge. Herein, A‐Cdots with bright excitation‐independent blue/yellow photoluminescence (PL) bands from two types of fluorophores are synthesized by the solvothermal treatment of citric acid and dodecylamine in cyclohexane (c‐hexane) solution. Due to the hydrogen‐bonding interaction of carboxylic groups linked with A‐Cdots and the hydrophobic effects of long‐chain alkyl groups, assemblies of A‐Cdots with reversed micelle‐like structure formed in c‐hexane solution lead to remarkable yellow‐PL (y‐PL) with quantum yield of 33.1%. Time‐resolved fluorescence and the distinct solvation effects of A‐Cdots conclude that the blue‐PL and y‐PL are from the radiative recombination of emissive sites of amide and carboxylic groups. For the solvent‐dependent optical properties and the amplification effect of dual‐color PL, the A‐Cdots exhibit good potential in the very sensitive detection of trace impurities in alkane solution, such as ethanol in c‐hexane with content as low as 0.033% (v/v). With A‐Cdots as phosphors, white‐light‐emitting diodes (WLEDs) are successfully constructed with luminous efficiency of 52.72 lm W−1. This work provides a new thinking for the design of multicolor luminous Cdots materials and their potential applications.

A convenient and universal platform for sensing environmental nitro-aromatic explosives based on amphiphilic carbon dots

2,4,6-trinitrophenol (TNP) is environmentally deleterious substance that has been of pressing societal concern. Therefore, developing a convenient and reliable platforms for its fast and efficient detection is of paramount importance from security point of view. Herein, amphiphilic fluorescent carbon dots (CDs) were prepared by a simple solvothermal method. CDs exhibit high selectivity and sensitivity on TNP in the polar and apolar solvent and even natural water samples. Moreover, the simple and portable indicator paper can be prepared conveniently and used for sensing TNP visually with high sensitivity and fast response. Research findings obtained from this study would assist in the development of portable devices for the on-site and real-time detection of environmental hazards.

Microwave synthesis of amphiphilic carbon dots from xylose and construction of luminescent composites with shape recovery performance

Carbon dots (CDs) have sparked tremendous attention owing to their unique properties and great potential in various fields. Herein, novel amphiphilic CDs (ACDs) were synthesized solvothermally by microwave heating a mixture of xylose and ethylenediamine in N, N-dimethylacetamide. The xylose-derived ACDs were monodisperse nanoparticles with an average diameter of about 1.81 nm, and exhibited excitation-dependent emission behavior in both aqueous and several common organic solvents. Furthermore, the synthesized ACDs can be uniformly dispersed into polyvinyl alcohol (PVA) solution to fabricate transparent luminescent composites, the as-prepared PVA/ACDs composites not only exhibited excellent fluorescence with excitation-dependent emission performance, but also achieved water-induced shape memory behavior. The intrinsic reason and pH sensitivity of shape recovery were investigated, the results confirmed that a faster shape recovery can be obtained in water at pH 4 within 180 s. Further investigation illustrated that the sensitivity of additional hydrogen bonding between PVA and ACDs to the water molecular was highly related to the shape recovery of the luminescent composite. The green synthesis route for xylan-derived ACDs and fabrication of smart luminescent composite will open many possibilities for the valuable application of low-cost biomass.

Close-Packed Langmuir Monolayers of Saccharide-Based Carbon Dots at the Air-Subphase Interface.

Carbon dots (CDs) are zero-dimensional carbon-based spherical nanoparticles with diameters less than 10 nm. Here, we report for the first time CDs forming stable Langmuir monolayers at the air-subphase interface. Langmuir monolayers are of great interest both fundamentally to study the interactions at the interfaces and for many applications such as the development of sensors. However, CDs usually do not form Langmuir monolayers because of their highly hydrophilic nature. In this study, amphiphilic CDs were prepared through hydrothermal carbonization using saccharides as the precursors. The surface chemistry behavior and optical properties of CDs at the air-subphase interface were studied. CDs derived from saccharides consistently formed stable Langmuir monolayers which show all essential phases, namely, gas, liquid-expanded, liquid-condensed, and solid phases. The compression-decompression cycle method showed minimum hysteresis (4.3%), confirming theretaining capacity of the CDs as a monolayer. Limiting CD areas from surface pressure-area isotherm at the air-subphase interface were used to calculate the average diameter of the CDs at the air-subphase interface. UV/vis absorption spectra of CDs dispersed in water and in Langmuir monolayers had the same bands in the UV region. The intensity of the UV/vis absorption increases with increasing surface pressure at the air-subphase interface. Interestingly, photoluminescence (PL) of the Langmuir monolayer of CDs was excitation-independent, whereas the same CDs had excitation-dependent PL when dispersed in water.

Self-assembly of surface functionalized amphiphilic carbon dots: tuning in morphological manifestations.

Despite the continuous surge of interest in supramolecular chemistry, the design and synthesis of building blocks to develop diverse examples of self-assemblies is still challenging. During the past decades, formation of self-assemblies such as micelles, vesicles, and gels with a fibril network using amphiphiles has been investigated at length. Considering the increasing applications of these self-aggregates across the scientific domain, it is crucial to adopt an alternative strategy for the preparation of self-aggregates using a new building block that has been applied in diverse domains. With this aim, surface functionalized carbon dots (CDs) with varying aliphatic/aromatic (cholesteryl, palmitoyl, naphthyl) substitutions linked with spacers such as ethylenediamine, p-phenylenediamine, 2,2'-(ethylenedioxy)bis(ethylamine) were developed. The surface passivated CDs formed self-assemblies in dimethylsulfoxide-water (DMSO-H2O, 2 : 1, v/v). The roles of surface functionalities and spacer units in the formation of self-assemblies using the synthesized CDs were investigated by microscopic and spectroscopic studies. Progressive morphological transition was found from vesicle-to-fiber in DMSO-H2O (2 : 1, v/v) which was dependent on surface passivating substitutions of the CDs from cholesteryl to naphthyl to palmitoyl. Together with the exclusive formation of self-assemblies using amphiphilic CDs, the present study enabled the tuning of self-organization behaviour of the CD by alteration of its surface functionality.

Nontoxic amphiphilic carbon dots as promising drug nanocarriers across the blood-brain barrier and inhibitors of β-amyloid.

The blood-brain barrier (BBB) is a main obstacle for drug delivery targeting the central nervous system (CNS) and treating Alzheimer's disease (AD). In order to enhance the efficiency of drug delivery without harming the BBB integrity, nanoparticle-mediated drug delivery has become a popular therapeutic strategy. Carbon dots (CDs) are one of the most promising and novel nanocarriers. In this study, amphiphilic yellow-emissive CDs (Y-CDs) were synthesized with an ultrasonication-mediated methodology using citric acid and o-phenylenediamine with a size of 3 nm that emit an excitation-independent yellow photoluminescence (PL). The content of primary amine and carboxyl groups on CDs was measured as 6.12 × 10-5 and 8.13 × 10-3 mmol mg-1, respectively, indicating the potential for small-molecule drug loading through bioconjugation. Confocal image analyses revealed that Y-CDs crossed the BBB of 5-day old wild-type zebrafish, most probably by passive diffusion due to the amphiphilicity of Y-CDs. And the amphiphilicity and BBB penetration ability didn't change when Y-CDs were coated with different hydrophilic molecules. Furthermore, Y-CDs were observed to enter cells to inhibit the overexpression of human amyloid precursor protein (APP) and β-amyloid (Aβ) which is a major factor responsible for AD pathology. Therefore, data suggest that Y-CDs have a great potential as nontoxic nanocarriers for drug delivery towards the CNS as well as a promising inhibiting agent of Aβ-related pathology of the AD.

Amphiphilic carbon dots derived by cationic surfactant for selective and sensitive detection of metal ions

Carbon Dots (CDs) the kind of recently exposed fluorescent nanomaterials have become increasingly popular in the precedent decade due to their distinctive physical and optical properties. Relating to above recognition for the first time we present the synthesis of CDs by cationic surfactant, Cetylpyridinium Bromide (CPB). Due to good carbon content amphiphilicity, and existence of heteroaromatic π system, CPB reveals three advantageous properties including a good carbon source, stabilizing agent, and contributing fluorophore in the CDs system. The as prepared CDs synthesized by hydrothermal technique reveals excellent fluorescent properties having strong green emission at 525 nm when excited over 470 nm. The FTIR results showed the presence of CC, CO, NH, CH and OH bonds. The presence of hydrophilic groups such as carboxyl and hydroxyl groups present on the surface confer them water solubility. The HRTEM results revealed the size of prepared CDs to be in the range of 7–10 nm. The XPS spectrum confirms the presence of Carbon, Oxygen and Nitrogen, suggesting that the CDs have good purity and very little impurities. Latterly CDs were used for the selective and sensitive detection towards Fe2+ ions. Also the as prepared CDs were utilized for real sample analysis.

One-step solvothermal synthesis of high-emissive amphiphilic carbon dots via rigidity derivation.

In nanoscience, amphiphilic carbon dots (ACDs) are of great importance due to their excellent transferability for application in biological sensing, imaging and labelling. However, facile synthetic strategies are still limited, especially for obtaining high-emissive ACDs. Since the development of a high-emissive feature is strongly desired for improving the practical resolution in vivo, here we report a chemical strategy that uses rigid molecules to straightforwardly construct amphiphilic carbon dots (ACDs) with high luminescence quantum yields (QYs). By using 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate (HATU), a typical coplanar compound, as the only precursor, well-defined ACDs were prepared via a one-step solvothermal process which exhibited a superior QY of up to 29%, largely superior to those prepared from precursors with less rigid structures. The effect can be mainly attributed to a significant suppression of the competition of non-radiative decay through rigidity derivation. Metal ionic doping during the synthesis resulted in a further improvement of the crystallinity and monodispersity of the materials, with retention of the high-emissive ability. This high-emissive photoluminescence behavior of the ACDs is accompanied with an excitation-wavelength dependence, a high biocompatibility and a low toxicity, which together make the ACDs advantageous for application in multi-channel bioimaging.

两亲性壳聚糖基聚合物碳点的合成及其在载药方面的应用

两亲性壳聚糖基聚合物碳点的合成及其在载药方面的应用

Green synthesis of amphiphilic carbon dots from organic solvents: application in fluorescent polymer composites and bio-imaging.

Carbon dots (CDs) have sparked tremendous attention due to their unique properties and vast potential in diverse fields. Herein, we report a green and cost-effective hydrothermal route for the synthesis of a series of CDs from readily available organics solvents. Since the organics were completely recyclable after the separation of CDs, this method holds immense potential for the large-scale synthesis of CDs. We found the DMF-CDs and DMAc-CDs possessed amphiphilicity and the diameter of amphiphilic DMF-CDs was ca. 3.5 nm with a narrow distribution. Moreover, these amphiphilic CDs emitted blue light under UV irradiation (365 nm) and the quantum yield could reach more than 30%. Due to their good solubility in organic solvent, DMF-CDs were successfully imbedded into polymers (i.e., PS and PMMA), which revealed their potential in painting, coating, and optical devices. In addition, benefiting from high quantum yield and low cytotoxicity, the DMF-CDs in aqueous media were used as fluorescent probes in living cells, which demonstrated their great potential in bio-imaging.

Amphiphilic carbon dots as versatile vectors for nucleic acid and drug delivery.

Carbon dot (CD)-based multifunctional delivery systems have shown great potential in both drug/gene delivery and bio-imaging. In this work, we present a strategy to simply construct amphiphilic CDs (ACDs) by conjugating hydrophobic alkyl epoxide to the surface amino groups of PEI 600-derived CDs. ACDs could well dissolve in water or organic solvents and emit bright fluorescence both in solutions and cells. 1HNMR also suggested that ACDs may form micelle-like structures in water, and their CMC could be determined. Enhanced green fluorescent protein (EGFP) expression and flow cytometry experiments showed that ACDs have higher transfection efficiency than Lipofectamine 2000 in A549 cells. Besides DNA, ACDs could also effectively transfect Sur siRNA toward A549 cells and cause early cell apoptosis. The 3D multicellular spheroids further confirmed their high potential for delivering therapeutic genes into the tumor tissue. On the other hand, ACDs also exhibited good drug loading ability. CLSM experiment results showed that DOX could be effectively internalized by the cell and slowly released from the drug/ACD complex. These results suggest that ACDs may not only serve as versatile delivery vectors with potential for applications in clinical cancer treatment, but also offer an inspiration for the discovery of CD-based gene/drug delivery systems.

Detection of Reactive Oxygen Species by a Carbon-Dot-Ascorbic Acid Hydrogel.

Detection of reactive oxygen species (ROS) is important in varied biological processes, disease diagnostics, and chemotherapeutic drug screening. We constructed a ROS sensor comprising an ascorbic-acid-based hydrogel encapsulating luminescent amphiphilic carbon-dots (C-dots). The sensing mechanism is based upon ROS-induced oxidation of the ascorbic acid units within the hydrogel scaffold; as a consequence, the hydrogel framework collapses resulting in aggregation of the C-dots and quenching of their luminescence. The C-dot-hydrogel platform exhibits high sensitivity and detected ROS generated chemically in solution and in actual cell environments. We demonstrate application of the C-dot-hydrogel for evaluating the efficacy of a chemotherapeutic substance, underscoring the potential of the system for drug screening applications.

Amphiphilic carbon dots for sensitive detection, intracellular imaging of Al3+

In this paper, a simple and effective method was designed to synthesize hydrophobic carbon dots. Subsequently, amphiphilic fluorescent carbon dots (A-CDs) were synthesized by further surface modification. The result A-CDs show excellent optical properties with a quantum yield of 16.9%. It was interestingly found that morin (MR) and its fluorescent metal-ion complex (MR-Al3+) can successfully coordinate on the surface of A-CDs, the emission of A-CDs completely overlapped the absorption peak of MR-Al3+. Thus, the prepared A-CDs can be used as an effective fluorescent probe for Al3+ based on a fluorescence resonance energy transfer process. The sensing platform can realize real-time detection of Al3+ within 0.5 min. The fluorescence signals of the system were linearly correlated with the concentration of Al3+ over a range of 8–20 μM, with a detection limit of 0.113 μM. The method was also successfully applied to image the distribution of Al3+ in Human Umbilical Vein Endothelial Cells.

Synthesis of "amphiphilic" carbon dots and their application for the analysis of iodine species (I2, I(-) and IO3(-)) in highly saline water.

"Amphiphilic" carbon dots (A-CDs) with a strong green fluorescence emission were synthesized by a simple and green method at room temperature. The characterization demonstrated that the synthesized A-CDs have both hydrophilic and hydrophobic properties and could be dispersed well in aqueous and organic solutions. As a fluorescent probe, the fluorescence of A-CDs could be obviously quenched in the presence of iodine (I2) and the quenching rate is proportional to the concentration of I2. Therefore, the A-CDs could be used as fluorophores for the detection of I2 with higher selectivity and sensitivity, and the linear working range for the I2 sensor is 80 nM-10 μM with a detection limit of 3.5 nM (S/N = 3). More interesting is that IO3(-) and I(-) could be transformed to I2 with different sample treatment processes, therefore, the I2 sensor based on A-CDs could also be used for the analysis of iodine species (I2, I(-) and IO3(-)) in samples. The possible mechanism has also been discussed in this work, and the high selectivity response to I2 can be attributed to the amphiphilic properties of A-CDs, which bring I2 closer to A-CDs and quench their fluorescence. The proposed I2 sensor has been successfully used for the analysis of iodine species in highly saline water, and the satisfactory results of detection and analysis of iodine species in samples demonstrate that the developed I2 sensor based on A-CDs has potential application in the fields of environment and clinical medicine.

Solvatochromic fluorescent carbon dots as optic noses for sensing volatile organic compounds

Amphiphilic carbon dots (CDs) with strong solvatochromism were synthesized via solvothermal method.