Multicolor Emissive Carbon Dots Research Articles

Solvent-Engineered Synthesis of Multicolor Emissive Carbon Dots from Citric Acid and Cyanamide

Solvent-Engineered Synthesis of Multicolor Emissive Carbon Dots from Citric Acid and Cyanamide

Facile Synthesis of B/P Co-Doping Multicolor Emissive Carbon Dots Derived from Phenylenediamine Isomers and Their Application in Anticounterfeiting

Carbon dots (CDs) possess a considerable number of beneficial features for latent applications in biotargeted drugs, electronic transistors, and encrypted information. The synthesis of fluorescent carbon dots has become a trend in contemporary research, especially in the field of controllable multicolor fluorescent carbon dots. In this study, an elementary one-step hydrothermal method was employed to synthesize the multicolor fluorescent carbon dots by co-doping unique phenylenediamine isomers (o-PD, m-PD, and p-PD) with B and P elements, which under 365 nm UV light exhibited signs of lavender-color, grass-color, and tangerine-color fluorescence, respectively. Further investigations reveal the distinctness in the polymerization, surface-specific functional groups, and graphite N content of the multicolor CDs, which may be the chief factor regarding the different optical behaviors of the multicolor CDs. This new work offers a route for the exploration of multicolor CDs using B/P co-doping and suggests great potential in the field of optical materials, important information encryption, and commercial anticounterfeiting labels.

Rapid statistical discrimination of fluorescence images of multiple foodborne pathogens using multicolor-emissive carbon dots

The rapid discrimination of multiple foodborne pathogens is vital and challengeable in ensuring food safety. Herein, a facile fluorescence method was developed to distinguish different bacteria using multicolor-emissive carbon dots (CDs) based on confocal laser scanning microscopy (CLSM) and linear discriminant analysis (LDA). The array employs single CDs as receptors and indicators, two pH solutions and three excitation channels as sensing elements for multicolor imaging and recognition of multiple bacteria. Through one-step staining, the CDs were capable of rapid adsorbing onto all bacteria in 1 min with varying affinities. The discrimination ability of the array was markedly enhanced by means of the synergistic recognition of bacteria and CDs across diverse pH levels and three excitation channels. By using LDA, six kinds of bacteria could be well discriminated with the classification accuracy of 100%. Meanwhile, the feasibility has been successfully expanded to mixture and food samples discrimination.

An Efficient Green Approach to Constructing Adenine Sulfate-Derived Multicolor Sulfur- and Nitrogen-Codoped Carbon Dots and Their Bioimaging Applications.

A cost-effective and environmentally friendly approach is proposed for producing N- and S-codoped multicolor-emission carbon dots (N- and S-codoped MCDs) at a mild reaction temperature (150 °C) and relatively short time (3 h). In this process, adenine sulfate acts as a novel precursor and doping agent, effectively reacting with other reagents such as citric acid, para-aminosalicylic acid, and ortho-phenylenediamine, even during solvent-free pyrolysis. The distinctive structures of reagents lead to the increased amount of graphitic nitrogen and sulfur doping in the N- and S-codoped MCDs. Notably, the obtained N- and S-codoped MCDs exhibit considerable fluorescence intensities, and their emission color can be adjusted from blue to yellow. The observed tunable photoluminescence can be attributed to variations in the surface state and the amount of N and S contents. Furthermore, due to the favorable optical properties, good water solubility and biocompatibility, and low cytotoxicity, these N- and S-codoped MCDs, especially green carbon dots, are successfully applied as fluorescent probes for bioimaging. The affordable and environmentally friendly synthesis method employed to create N- and S-codoped MCDs, combined with their remarkable optical properties, offers a promising avenue for their use in various fields, particularly in biomedical applications.

Formation and Band Gap Tuning Mechanism of Multicolor Emissive Carbon Dots from m-Hydroxybenzaldehyde.

Reported in 2004, carbon dots (CDs) have been widely used in various fields due to their excellent optical properties. However, the mechanism of their fluorescence modulation is still a controversial issue, which also seriously affects the further development of carbon dots. In this paper, m-hydroxybenzaldehyde is used as a raw material to obtain multicolor luminescent CDs by pyrolysis under different reaction conditions, thereby revealing the forbidden band tuning and formation mechanism of CDs. Different acid-base conditions lead to different reaction paths of the precursors, forming molecular fluorophores with different conjugated structures, which aggregate to eventually form CDs and further enhance the photoluminescence of the system by inhibiting the movement of the fluorescent centers.

Synthetic strategies, properties and sensing application of multicolor carbon dots: recent advances and future challenges.

Recently, carbon dots (CDs) as newly developed carbon-based nanomaterials due to advantages such as excellent photostability and easy surface functionalization have generated wide application prospects in fields such as biological imaging and chemical sensing. The multicolor emission carbon dots (M-CDs) were acquired through the selection of different carbon source precursors, change of synthesis conditions and synthesis environment. Therefore, the aim of this review is to summarize the latest research progress in polychromatic CDs from the perspectives of synthesis strategies, luminescent mechanisms, luminescent properties and applications. This review focuses on how to prepare MCDs by changing raw materials and synthesis conditions such as reaction temperature, synthesis time, synthesis pH, and synthesis solvent. This review also presents the optical properties of MCDs, concentration effects, solvent effects, pH effects, elemental doping, and surface passivation on them, as well as their creative applications in the field of sensing applications. It is anticipated that this review will serve as a guide for the development of multifunctional M-CDs and inspire future research on controllable design and preparation of M-CDs.

Assignment of Core and Surface States in Multicolor-Emissive Carbon Dots.

It is important to reveal the luminescence mechanisms of carbon dots (CDs). Herein, CDs with two types of optical centers are synthesized from citric acid in formamide by a solvothermal method, and show high photoluminescence quantum yield reaching 42%. Their green/yellow emission exhibits pronounced vibrational structure and high resistance toward photobleaching, while broad red photoluminescence is sensitive to solvents, temperature, and UV-IR. Under UV-IR, the red emission is gradually bleached due to the photoinduced dehydration of the deprotonated surface of CDs in dimethyl sulfoxide, while this process is hindered in water. From the analysis of steady-state and time-resolved photoluminescence and transient absorption data together with density functional theory calculations, the green/ yellow emission is assigned to conjugated sp2 -domains (core state) similar to organic dye derivatives stacked within disk-shaped CDs; and the broad red emission-to oxygen-containing groups bound to sp2 -domains (surface state), whereas energy transfer from the core to the surface state can happen.

The “ON-OFF” microwave reaction time technique: A novel strategy to impact the fluorescence of multi-color emissive carbon dots

Multi-colored fluorescent carbon dots (CDs) were synthesized via the microwave-assisted technique using citric acid (CA). To the best of our knowledge, the “ON-OFF” microwave-assisted technique was investigated for synthesis CDs for the first time. The impact of the “ON-OFF” strategy was monitored on the morphological, structural, and optical properties of the CDs. By increasing the reaction time from 10 to20 min, a reduction in the particle size was detected from 4.1 ± 0.6 to 1.6 ± 0.2 nm, respectively using a high-resolution transmission electron microscope (HRTEM). A blue shift was detected in the photoluminescence (PL) as a function of the reaction time with optimal fluorescence intensity at 15 min. The quantum yields (QY) were 15.2 %, 22.2 %, and 11.9 % for the reaction time 10, 15, and 20 min, respectively. Three electronic transitions were observed from the UV-Vis spectra, and their corresponding energy band gap (Eg) were calculated using Tauc plot. The first transition was a reaction time-dependent in the range of 5.1–5.8 eV. While the other transitions were reaction time-independent and kept constant at 4.9 and 4.6 eV. A model was hypothesized to correlate the particle size reduction with the reaction time during the formation of the CDs.

A new insights into multicolor emissive carbon dots using Trachelospermum jasminoides leaves for the application of WLEDs

Carbon dots (CDs) have recently emerged as a very encouraging family of materials with augmented performance in WLEDs. Facile synthesis of CDs with high optical tuning using sustainable green precursors is a great challenge in the applications of WLEDs. In this work, we prepare red, green, and blue-color emissive CDs (RGB CDs) using an extract of Star Jasmine leaves (Trachelospermum jasminoides). The red emission originates due to the presence of an extensive conjugated carbonic system with a few esters (-COOR) and amide (-CONR) moieties on their surface. And the shorter wavelength emission appears due to the presence of carboxylic (-COO) moieties. Specifically, in green emissive CDs, the formation of the OZnO bond causes the fluorescence shifting (>100 nm) and a higher lifetime as it restricts the making of the conjugated -COOR/-CONR groups. The detailed study revealed that an average lifetime of CDs has a linear relationship with the core state lifetime. These highly stable and effective naturally produced RGB CDs have been used as fabrication of WLEDs, which exhibited CCT and CIE coordinates of 4283 K and (0.36,0.32), respectively. Additionally, the red CDs detected water and chloroform visually and fluorometrically in a broad range. This work will open up a new route for developing high-performance WLEDs using natural precursors.

Preparation of multicolor-emissive carbon dots with high quantum yields and their epoxy composites for fluorescence anti-counterfeiting and light-emitting devices

Stable multicolor-emissive carbon dots with high quantum yields and their epoxy composites with good tensile strength, transparency, and light-emitting property.

One-step synthesis of nitrogen-doped multi-emission carbon dots and their fluorescent sensing in HClO and cellular imaging.

Tunable multicolor carbon dots (CDs) with a quantum yield reach up to 35% were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. Transmission electron microscopy images reveal that the as-prepared CDs possess a small size distribution below 10nm with bright blue, green, and yellow color emission, designated as b-CDs, g-CDs, and y-CDs, respectively. The in-depth investigations reveal that the multicolor emission CDs with different fraction displays fluorescence emission wavelength ranges from 398nm (b-CDs), 525nm (g-CDs), to 553nm (y-CDs) which could be well modulated by controlling the amount of heteroatom nitrogen especially amino nitrogen onto their surface structures. Further experiments verify the important role of nitrogen content by using rhodamine solely or substituting urea with sulfur containing compounds as precursors to produce corresponding CDs since the performance is lower than that of urea incorporation. Theoretical calculation results also reveal that the increasing amount of amino nitrogen into their surface structures of b-CDs, g-CDs to y-CDs is responsible for reduced band gaps energy, which result in the redshifted wavelength. Benefiting from the excellent photoluminescence properties, wide pH variation range, high photo stability, and low toxicity, these CDs were employed for HClO sensing at 553nm within the range 5 to 140μM with a limit of detection (LOD) of 0.27 ± 0.025μM (n = 3) and multicolor cellular imaging in HeLa cells. Tunable multicolor carbon dots (CDs) were generated directly from rhodamine and urea via one-step hydrothermal approach and purified through silica gel column chromatography. The as-prepared CDs exhibit bright blue, green, and yellow color emission which could be well modulated by controlling the increasing incorporation of heteroatom nitrogen especially amino nitrogen into their surface structures. These CDs were employed for HClO sensing and demonstrated to multicolor cellular imaging in HeLa cells.

Solvent-controlled synthesis strategy of multicolor emission carbon dots and its applications in sensing and light-emitting devices

Carbon dots (CDs), as a new kind of carbon-based luminescent nanomaterials, have drawn widespread attention in the fields of fluorescence sensing, optoelectronic devices, and biological imaging. This work uses citric acid (CA) and Nile Blue A (NBA) as precursors. By simply changing the solvent in the reaction, their bandgaps were systematically controlled, thereby successfully obtaining bright blue, yellow and red fluorescence emission CDs (B-, Y- and RCDs). The higher quantum yield (QY) of B-, Y- and RCDs are 64%, 57% and 51%, respectively. The selected precursors and different solvents are the key to the formation of three emission CDs. Detailed characterization and density functional theory (DFT) calculations further indicate that the difference in emission color of CDs is due to the size of the sp2 conjugate domain. In addition, we used multicolor CDs as fluorescent probes to investigate their performance in detection. Among them, BCDs and YCDs can detect Sudan Red I with high selectivity and sensitivity. In the concentration range of 0 to 80 µM, the detection limits are 56 and 41 nM, respectively. Multicolor emitting phosphors and fluorescent films are also obtained by mixing CDs with other matrices. Using Ultraviolet (UV) chip as the excitation source and combining with multicolor fluorescent film and a certain proportion of B-, Y-, and RCDs/epoxy resin composites, bright monochromatic light-emitting diodes (LEDs) and white LED (WLED) with high color rendering index (CRI) were prepared. The above results indicate that the multicolor CDs prepared by us have great application potential in the fields of food safety control and optical devices.

Study and Comparison on Purification Methods of Multicolor Emission Carbon Dots.

Recent years have witnessed a rapid development of carbon dots (CDs), due to their outstanding luminescence properties and excellent biocompatibility. However, the internal structure and photoluminescent (PL) mechanism of CDs are still the subject of considerable debate, which is due to the fact that reaction products usually contain mixtures of several CD fractions as well as molecular intermediate and side products. Therefore, careful purification of the CDs is significant for analysis of structure and luminescence mechanism. Here, multicolor emission CDs were prepared by a one-pot pyrolysis of citric acid in formamide. Then, the precipitation method, dialysis and gel permeation chromatography (GPC) are successively employed to purify the multicolor emission CDs. This post-treatment allowed us to compare the optical properties of CDs obtained by different separation methods and provide a valuable guidance for the purification of CDs.

Simple synthesis of photoluminescent carbon dots from a marine polysaccharide found in shark cartilage

Abstract Background For more than a decade, water-soluble, eco-friendly, biocompatible, and low-toxicity fluorescent nanomaterials have received considerable attention for their numerous in vivo and in vitro applications in biomedical imaging, disease diagnostics, and environmental monitoring. Owing to their tunable photoluminescence properties, carbon-based luminescent nanomaterials have shown great potential in bioimaging, photocatalysis, and biosensing among other applications. Results Marine environments provide excellent resources for the fabrication of these nanomaterials, because many marine organisms contain interesting trigger organic compounds that can be used as precursors. Herein, we synthesize multi-color emissive carbon dots (CDs) with an intrinsic photoluminescence quantum yield of 20.46%. These nanostructures were achieved through the one-step hydrothermal treatment of marine polysaccharide chondroitin sulfate, obtained from shark cartilage, in aqueous solution. Conclusions We successfully demonstrate the low toxicity of our marine resource-derived CDs in zebrafish, and provide an initial assessment of their possible use as a bioimaging agent. Notably, the newly synthesized CDs localize in the intestines of zebrafish larvae, thereby indicating their biocompatibility and potential use as in vivo dyes. How to cite: Kim KW, Choi TY, Kwon YM, et al. Simple synthesis of photoluminescent carbon dots from a marine polysaccharide found in shark cartilage. Electron J Biotechnol 2020;47. https://doi.org/10.1016/j.ejbt.2020.07.003 .

Wide emission shifts and high quantum yields of solvatochromic carbon dots with rich pyrrolic nitrogen

Carbon dots (CDs) with solvatochromic emission colors in different solvents have attracted much attention as a new class of luminescent nanomaterial owing to their facile synthesis and low production cost. In this work, we prepared two kinds of CDs with solvatochromic emissions: green emission CDs (G-CDs) and multicolor emission CDs (M-CDs). G-CDs synthesized from o-phenylenediamine exhibited weak photoluminescence emission (quantum yield 2.8%–6.1%) and 39 nm solvatochromic shifts (492–531 nm). In contrast, M-CDs prepared from o-phenylenediamine and 4-aminophenol showed 87 nm solvatochromic shift range (505–592 nm) and much higher photoluminescence quantum yield (18.4%–32.5%). The two CDs exhibited different emission, absorption, and photoluminescence lifetime. The origin of solvatochromic shifts and the formation mechanism of CDs were demonstrated by analyzing the structures and compositions of two CDs. High percentages of pyrrolic nitrogen and amino nitrogen make wider solvatochromic shifts and higher quantum yields. The results were well supported by density functional theory calculations. This effective strategy to expand solvatochromic shift range and improve quantum yields could open a new window to prepare satisfied solvatochromic carbon dots.

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.

Interparticle distance as a key factor for controlling the dual-emission properties of carbon dots.

Due to their distinct and useful features, multi-color-emissive carbon dots (CDs) have gained much attention, however, their lack of red emission has so far limited their practical use for various applications, thus understanding of their emission origins is required. Concentration-dependent photoluminescence (PL) is a unique feature of CDs and is regarded as one way to realize tunable PL, providing information on their PL mechanism. In this work, we synthesized concentration-dependent blue/red dual-color-emissive CDs under single excitation at 365 nm. With the increase in concentration, the blue emission band showed a large red-shift from 431 to 500 nm, while the red emission band at around 650 nm showed only a relative intensity change, without a significant spectral shift. We performed spectroscopic analysis by changing the solution environment including the solvent type and pH to investigate the origins of the two emission bands. These results, combined with the zeta potential and fluorescence microscopy results, confirmed that the interparticle distance of CDs is a key factor for their dual-emissive PL behavior. With the advantage of unique PL features, we showed the potential of the CDs for white light-emitting diode (WLED) and ratiometric pH sensing applications.

Multicolor carbon dots with concentration-tunable fluorescence and solvent-affected aggregation states for white light-emitting diodes

Multicolor emissive carbon dots (M-CDs) have tremendous potential applications in manifold fields of bioimaging, biomedicine and light-emitting devices. Until now, it is still difficult to produce fluorescence tunable CDs with high quantum yield across the entire visible spectra. In this work, a type of M-CDs with concentration-tunable fluorescence and solvent-affected aggregation states was synthesized by solvothermal treatment of citric acid (CA) and 1-(2-pyridylazo)-2-naphthol (PAN) and the formation mechanism was monitored by different reaction time and raw material ratio. The fluorescence spectra of M-CDs in organic solvents can range from 350 to 750 nm by adjusting the concentration. M-CDs possess different aggregation states in water and organic solvents, accompanied by different fluorescence emission, which is attributed to the different surface states of various component CDs in M-CDs. Moreover, the obtained products can be uniformly dispersed into polymethylmethacrylate (PMMA) solutions as well as epoxy resins to fabricate transparent CDs/PMMA films and CDs/epoxy composites, which can effectively prevent the aggregation and produce multicolor and white light-emitting diodes (WLED). In addition, the prepared WLED with Commission Internationale de L’Eclairage (CIE) of (0.29, 0.31) by using M-CDs/epoxy resin as packages, demonstrating the M-CDs exhibit potential applications for light-emitting devices.

Multicolor emissive sulfur, nitrogen co-doped carbon dots and their application in ion detection and solid lighting.

Multicolor emissive carbon dots (CDs) have potential applications in many fields such as photoelectric display, light-emitting devices, and bioimaging. Such CDs by heteroatom doping of nitrogen elements assisted with various solvents has achieved recently, yet generally low efficiency in red-light region. Herein, we developed a facile route to synthesize multicolor-emissive CDs governed by a solvothermal method of tetrahydrofuran solvent. The maximum emission locates at 432, 510, and 584nm with the absolute FL QYs up to 21.1%, 11.0%, and 55.4% for selected B-CDs, G-CDs, and YG-CDs, respectively. By means of the analysis on their PL spectra, fluorescence lifetimes, and microstructures, the different graphitic degrees and surface states formed under the participation of S and N elements in as-prepared CDs determine the fluorescent color, and large sp2-conjugated domains within the YR-CDs is closely related to high QY. They, likewise, endow the YR-CDs with high sensitivity for ion detections of Ag+ and Fe3+, which was further illustrated to have different quenching mechanisms each other due to the affinity interaction with different surface groups of the CDs. High PL QYs of these CDs emission are beneficial to application in solid lighting, phosphors dried by these CDs solutions were mixed with PVP water solution to fabricate CDs/PVP films. The films exhibited stable fluorescence, and three phosphors were also mixed together in proportion to obtain white-light film with a CIE coordinates of (0.34, 0.34), which demonstrates that these CDs are potentially fluorescent nanomaterial in the solid-state lighting field.

Conjugated ternary doped carbon dots from vitamin B derivative: Multispectral nanoprobes for targeted melanoma bioimaging and photosensitization

Multi-color emissive carbon dots (CDs) with intrinsic ternary doping were synthesized by a hydrothermal process from a single precursor, vitamin B1 derivative, thiamine pyrophosphate or ThPP. The origin of the multi-color photoluminescence was ascribed to the hybrid doping (N, S, P) in a carbon framework. The subsequent conjugation of CDs with folic acid (FA) enabled targeted bioimaging and photosensitization of the human melanoma cancer cells, SK-MEL28. The unique excitation-dependent multi-color emission of CD-FA probes allowed wide spectral resolution and targeting for amplified whole cell bioimaging including the nucleus. The photosensitization of cancer cells in the multi-color window was accomplished in a deep tissue cell culture setting. The synthesized CD-FAs showed excellent biocompatibility, photostability, and notably, their cellular targeting with enhanced uptake by folate receptor positive (FR+) cancer cells, SK-MEL28 over folate receptor negative (FR-), HEK293T ones in a co-culture model having both diseased and normal cells. The results demonstrate excellent potential for melanoma diagnostic, mapping and phototherapeutic applications with multi-spectral sensitivity.