Green Synthesis of Red‐Emitting Carbon Nanodots as a Novel “Turn‐on” Nanothermometer in Living Cells

Temperature measurements in biology and medical diagnostics, along with sensitive temperature probing of living cells, is of great importance; however, it still faces significant challenges. Herein, a novel “turn‐on” carbon‐dot‐based fluorescent nanothermometry device for spatially resolved temperature measurements in living cells is presented. The carbon nanodots (CNDs) are prepared by a green microwave‐assisted method and exhibit red fluorescence (λ_em=615 nm) with high quantum yields (15 %). Then, an on–off fluorescent probe is prepared for detecting glutathione (GSH) based on aggregation‐induced fluorescence quenching. Interestingly, the quenched fluorescence could be recovered by increasing temperature and the CNDs–GSH mixture could behave as an off–on fluorescent probe for temperature. Thus, red‐emitting CNDs can be utilized for “turn‐on” fluorescent nanothermometry through the fluorescence quenching and recovery processes, respectively. We employ MC3T3‐E1 cells as an example model to demonstrate the red‐emitting CNDs can function as “non‐contact” tools for the accurate measurement of temperature and its gradient inside a living cell.     

Multicolor biomass based carbon nanodots for bacterial imaging

Biomass-based carbon nanodots(CNDs) are becoming promising fluorescent materials due to their superior optical properties and excellent biocompatibility. However, most fluorescent CNDs are prepared under high temperatures with artificial chemicals as precursors. In this work, multicolor biomass-based CNDs have been prepared by employing natural biomass as precursors through an ultrasonic-assisted method at room temperature. The multicolor biomass-based CNDs can be prepared within 10 min, and cav...     

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1–3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

The pollutant reactive red 2 was employed to synthesize fluorescent carbon nanodots allowing biological imaging in vitro and in vivo.     

A carbon–carbon hybrid – immobilizing carbon nanodots onto carbon nanotubes

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis.     

Fluorescent turn-off/on bioassay for hemoglobin based on dual-emission carbon nanodots-graphene oxide system with multi-detection strategies

As two members of the carbon materials family, carbon nanodots (CNDs) and graphene oxide (GO) possess many excellent optical properties resulting in a wide range of applications. In this work, the fluorescence of resultant dual-emission carbon nanodots (DECNDs) could be quenched by GO. In the presence of hemoglobin (Hb), the fluorescence would recover resulting from two interactions: one was the direct stacking effect of Hb on GO; the other one was that Hb could cover the surfaces of DECNDs; both of them would prevent the fluorescence quenching of DECNDs by GO. In the light of this mechanism, a novel fluorescent turn-off/on method has been developed for the detection of Hb based on DECNDs-GO system. By virtue of the dual emissions of these CNDs, it is noteworthy that both a single emission and ratiometric of dual emissions can be used to establish linear relationships of Hb: 0.05–300 nM (λem = 386 nm), 5–500 nM (λem = 530 nm), and 50–500 nM (I₅₃₀/I₄₁₀), with the corresponding limit of detection (LOD) as low as 20 pM, 2 nM and 20 nM, respectively. This present system is highly selective toward Hb over other proteins and this reliable method has been successfully applied for the detection of Hb in whole blood samples.     

One‐pot synthesis of carbon dots@ZrO2 nanoparticles with tunable solid‐state fluorescence

In recent years, fluorescent carbon dots (CDs) have been developed and showed potential applications in biomedical imaging and light‐emitting diodes (LEDs) for their excellent fluorescent properties. However, it still remains a challenge to incorporate fluorescent CDs into the host matrix in situ to overcome their serious self‐quenching. Herein, a one‐pot hydrothermal method is used to prepare nano‐zirconia with CDs (CDs@ZrO₂) nanoparticles. During the reaction, CDs and nano‐zirconia are generated simultaneously and connected with silane coupling agent. The CDs@ZrO₂ nanoparticles exhibit tunable emission wavelength from 450 to 535 nm emission by regulating the content of citric acid in the feed. The quantum yield of the CDs@ZrO₂ is up to 23.8%. Furthermore, the CDs@ZrO₂ nanoparticles with regulable fluorescence emission can be used for the fluorescent material to prepare white LEDs. The prepared LED has significant white light emission with color coordinates of (0.30, 0.37) and its color rendering index (CRI) is 67.1. In summary, we have developed the solid‐state CDs@ZrO₂ nanoparticles with tunable emission by a valuable strategy, that is, one‐pot method, for white LEDs.     

Upconverting Carbon Nanodots from Ethylenediaminetetraacetic Acid (EDTA) as Near-Infrared Activated Phototheranostic Agents

This work describes the synthesis of nitrogen-doped carbon nanodots (CNDs) synthesized from ethylenediaminetetraacetic acid (EDTA) as a precursor and their application as luminescent agents with a dual-mode theranostic role as near-infrared (NIR) triggered imaging and photodynamic therapy agents. Interestingly, these fluorescent CNDs are more rapidly and selectively internalized by tumor cells and exhibit very limited cytotoxicity until remotely activated with a NIR illumination source. These CNDs are excellent candidates for phototheranostic purposes, for example, simultaneous imaging and therapy can be carried out on cancer cells by using their luminescent properties and the in situ generation of reactive oxidative species (ROS) upon excitation in the NIR range. In the presence of CNDs, NIR remote activation induces the in vitro killing of U251MG cells. Through the use of flow imaging cytometry, we have been able to successfully map and quantify the different types of cell deaths induced by the presence of intracellular superoxide anions ( ^. O₂⁻) and hydrogen peroxide (H₂O₂) ROS generated in situ upon NIR irradiation.     

Intrinsically fluorescent carbon dots with tunable emission derived from hydrothermal treatment of glucose in the presence of monopotassium phosphate

A facile method is developed to synthesize intrinsically fluorescent carbon dots by hydrothermal treatment of glucose in the presence of monopotassium phosphate. The fluorescence emission of the carbon dots thus produced is tunable by simply adjusting the concentration of monopotassium phosphate.     

β-Cyclodextrin derived full-spectrum fluorescent carbon dots: The formation process investigation and biological applications

Carbon dots (CDs), a new building unit, have been revolutionizing the fields of biomedicine, bioimaging, and optoelectronics with their excellent physical, chemical, and biological properties. However, the difficulty of preparing excitation-dependent full-spectrum fluorescent CDs has seriously hindered their further research in fluorescence emission mechanisms and biomedicine. Here, we report full-spectrum fluorescent CDs that exhibit controlled emission changes from purple (380 nm) to red (613 nm) at room temperature by changing the excitation wavelength, and the excitation dependence was closely related to the regulation of sp² and sp³ hybrid carbon structures by β-cyclodextrin-related groups. In addition, by regulating the content of β-cyclodextrin, the optimal quantum yields of full-spectrum fluorescent CDs were 8.97%, 8.35%, 7.90%, 9.69% and 17.4% at the excitation wavelengths of 340, 350, 390, 410 and 540 nm, respectively. Due to their excellent biocompatibility and color tunability, full-spectrum fluorescent CDs emitted bright and steady purple, blue, green, yellow, and red fluorescence in MCF-7 cells. Moreover, we optimized the imaging conditions of CDs and mitochondrial-specific dyes; and realized the mitochondrial-targeted co-localization imaging of purple, blue and green fluorescence. After that, we also explored the effect of full-spectrum fluorescent CDs in vivo fluorescence imaging through the intratumorally, subcutaneously, and caudal vein, and found that full-spectrum fluorescent CDs had good fluorescence imaging ability in vivo.     

Mass production of highly fluorescent full color carbon dots from the petroleum coke

Heavy oil is treated as an undesirable raw material in traditional refining markets because of its low yield. However, its rich natural aromatic structure and heteroatomic compounds make it possible to be a precursor to large-scale production of carbon materials. Using heavy oil and three SDA products as precursors, we synthesized highly fluorescent multi-color carbon dots (CDs) by hydrothermal method, which can precisely control the photoluminescence wavelength in the range of 350?650 nm. The synthesized carbon dots have the advantages of good long-term stability and stability under extreme pH conditions and low price. Importantly, the carbon dots synthesized with asphalt as the precursor have the highest fluorescence quantum yield. X-ray photoelectron spectroscopy (XPS) is used to elucidate the effects of different precursor on emission color change and photoluminescence quantum yield (PLQY), thus providing a controlled tuning of the system for the functionalization of CDs. And we further used the CDs in macrophage labeling. This pathway gives a reliable and repeatable industry possibility and may boost the applications of CDs into reality.     

Carbogenic Nanodots: Photoluminescence and Room‐Temperature Ferromagnetism

Herein, blue fluorescent carbogenic nanodots (CNDs) with room‐temperature ferromagnetism were synthesized by thermal decomposition of organic precursors at different temperatures. Photoluminescence (PL) studies show excitation‐wavelength‐dependent emission properties and PL excitation (PLE) studies confirm the triplet ground state of carbene at the zigzag edge as the fluorescent center. Room‐temperature magnetic studies reveal the ferromagnetic nature of CNDs and temperature‐dependent studies show the presence of an antiferromagnetic phase along with a ferromagnetic phase below 50 K. EPR studies reveal the presence of conduction electrons and localized spins with different g factors. Localized spins at zigzag edges are the origin of the unconventional magnetic behavior, whereas exchange coupling between conduction and localized spins are responsible for long‐range magnetic ordering.     

基于头孢他啶测定的CQDs内标型比率荧光探针的构建

以天然生物质蒲公英为碳源,加入乙二胺,通过一步水热法合成氨基化蒲公英碳量子点(DE-CQDs).该DE-CQDs可与罗丹明6G(Rh6G)通过静电吸附作用形成具有特征双发射信号的DE-CQDs/Rh6G复合物.单一激发波长343 nm下,BR缓冲溶液pH 3.0时,复合物DE-CQDs/Rh6G于425 nm和550 ...     

8-Hydroxypyrene-1,3,6-trisulphonate and octanesulphonate co-assembled layered double hydroxide and its controllable solid-state luminescence by hydrothermal synthesis

8-Hydroxy-pyrene-1,3,6-trisulphonate (HPTS) and octanesulphonate (OS) have been co-intercalated into the ZnAl layered double hydroxide (LDH) host by a hydrothermal co-precipitation method, with samples denoted as HPTS (x%)-OS/Zn₂Al-LDH (x stands for the molar percentage content of HPTS with respect to total amount of HPTS and OS). The structure and chemical compositions of the as-prepared compounds were characterized by X-ray diffraction (XRD) and elemental analysis. The steady-state and time-decay fluorescent studies show that HPTS (2%)-OS/Zn₂Al-LDH has the optimal luminous emission and the longest fluorescent lifetime. Moreover, these samples exhibit controllable dual fluorescence between the blue and green regions upon changing the interlayer HPTS content, external pH values, and host–guest interaction, illustrating that these organic–inorganic samples have potential application in the field of tunable solid luminescent materials.     

电化学方法调控荧光碳点的研究

作为零维碳基发光纳米材料,碳点是对现有发光纳米材料的重要补充. 精准控制粒径及表面结构对实现碳点的性质调控及其应用至关重要. 本文介绍了本课题组在利用电化学方法研究荧光碳点方面的进展. 重点展示了利用电化学方法实现对碳点粒径的控制,对表面氧化程度的调节以及对其发光机理的研究. 电化学方法可对只有几纳米厚度的材料表面进行有效的控制,可操作性强且经济环保. 通过对碳点的粒径及表面的调控,作者也进一步揭示了碳点的发光与表面结构的相关性. 这些工作为碳点的合成及其性质调控提供了可循的规律,有利于推动碳点在生物医生成像、传感检测、催化及能源转化等领域的应用.     

Intramolecular Hydrogen Bonds Quench Photoluminescence and Enhance Photocatalytic Activity of Carbon Nanodots

Understanding the photoluminescence (PL) and photocatalytic properties of carbon nanodots (CNDs) induced by environmental factors such as pH through surface groups is significantly important to rationally tune the emission and photodriven catalysis of CNDs. Through adjusting the pH of an aqueous solution of CNDs, it was found that the PL of CNDs prepared by ultrasonic treatment of glucose is strongly quenched at pH 1 because of the formation of intramolecular hydrogen bonds among the oxygen‐containing surface groups. The position of the strongest PL peak and its corresponding excitation wavelength strongly depend on the surface groups. The origins of the blue and green emissions of CNDs are closely related to the carboxyl and hydroxyl groups, respectively. The deprotonated COO^? and CO^? groups weaken the PL peak of the CNDs and shift it to the red. CNDs alone exhibit photocatalytic activity towards degradation of Rhodamine B at different pH values under UV irradiation. The photocatalytic activity of the CNDs is the highest at pH 1 because of the strong intramolecular hydrogen bonds formed among the oxygen‐containing groups.     

Sensitive pH probe developed with water-soluble fluorescent carbon dots from chocolate by one-step hydrothermal method

In present work, fluorescent carbon dots (CDs) with an average diameter of 2.5 nm were firstly synthesised by a simple, convenient and low-cost hydrothermal method from chocolate. The obtained CDs possessed fine monodispersity and bright blue fluorescence that was strongest at an excitation wavelength of 360 nm and had a comparable quantum yield of 12% (in case of dots prepared in presence of nitric acid). The emission peak depended on the excitation wavelength in the range from 320 to 440 nm. Ionic strength had a weak effect up to 1.0 M and then no significant change was found in the range of 1.0–4.5 M. The fluorescence intensity of CDs displayed good pH adaptability and a linear dependence on the pH change in the range of pH 1.0–3.0 and pH 9.0–12.5, which have promising potentials for pH sensor.     

基于聚乙烯亚胺碳纳米点的桑色素比率型荧光探针

利用水热合成法制备了一种基于聚乙烯亚胺的荧光碳纳米点,用光谱方法研究了其对桑色素的识别作用.结果表明,该碳纳米点对桑色素具有比率型荧光响应,且响应速度快、选择性和灵敏度高、抗干扰能力强.将桑色素加入到碳纳米点溶液中后,碳纳米点自身的荧光(460 nm)立即被猝灭,同时在555 nm处出现新的荧光发射峰并逐渐增强;其新发射峰(555 nm)与原发射峰(460 nm)的强度比值在此过程中呈线性增加.基于此,在1.0×10^-6～4.0×10^-5mol/L浓度范围内,可实现对桑色素的检测,该比率荧光响应非常灵敏,检出限可达3.0×10^-8mol/L.另外,该碳纳米点与常见金属离子、氨基酸及其它具有类似桑色素结构的黄酮醇均不反应,显示出对桑色素的高选择性.该检测方法的荧光强度随桑色素浓度的增加而逐渐增强,并伴随着由蓝色到黄色的荧光颜色变化,可实现对桑色素的可视化检测;同时该碳纳米点还可用于稀释胎牛血清中桑色素的定量检测.