Study on the fluorescence characteristics of carbon dots

Herein, we prepared water-soluble fluorescent carbon dots with diameter about 1.5 nm from cheap commercial lampblack. These fluorescent carbon nanoparticles are stable toward photobleaching and stable in water for more than half a year without fluorescence decrease. In order to improve its fluorescence properties, we passivated these nanoparticles with bisamino-terminated polyethylene glycol (PEG_1500N). Therefore, both fluorescence quantum yield and lifetime increased after this progress. In addition, the passivated carbon dots were more inert to solvent than the bare one and showed different responses to pH change.     

Spectroelectrochemistry of hollow spherical CdSe quantum dot assemblies in water

The hollow spherical CdSe QD assemblies were synthesized via a sonochemical approach that utilizes β-cyclodextrin as a template reagent in aqueous solution. The hollow nanospheres have an average diameter of 70 nm and are found to consist of an assembly of monodispersed 5 nm sized CdSe quantum dots. Following an electrochemical reaction with persulfate ions, strong electrogenerated chemiluminescence (ECL) was observed from the CdSe nanoassemblies suspended in an aqueous solution of pH ⩽ 7.95. The study indicates that the morphology of the 70 nm nanoassembly plays an important role in generating the stable ECL since individually dispersed quantum dots did not exhibit any significant ECL. The unique ECL intensity and stability of the synthesized spherical nanoassemblies could allow for potential sensor applications of CdSe quantum dots in water.     

Toxicity and bio-distribution of carbon dots after single inhalation exposure in vivo

CDs caused the injury in the lung and liver after single inhalation exposure at 5 mg/kg dosages in mice.     

Synthesis of Sn nanocluster@carbon dots for photodynamic therapy application

Recently, photodynamic therapy (PDT) has been extensively applied in clinical and coadjuvant treatment of various kinds of tumors. However, the photosensitizer (PS) of PDT still lack of high production of singlet oxygen (¹O₂), low cytotoxicity and high biocompatibility. Herein, we propose a facile method for establishing a new core-shell structured Sn nanocluster@carbon dots (CDs) PS. Firstly, Sn⁴⁺@S-CDs complex is synthesized using the sulfur-doped CDs (S-CDs) and SnCl₄ as raw materials, and subsequently the new PS (Sn nanocluster@CDs) is obtained after vaporization of Sn⁴⁺@S-CDs solution. Remarkably, the obtained Sn nanocluster@CDs show an enhanced fluorescence as well as a higher ¹O₂ quantum yield (QY) than S-CDs. The high ¹O₂ QY (58.3%) irradiated by the LED light (400–700 nm, 40 mW/cm²), induce the reduction of 4T1 cancer cells viability by 25%. More intriguingly, no visible damage happens to healthy cells, with little impact on liver tissue due to renal excretion, both in vitro and in vivo experiments demonstrate that Sn nanocluster@CDs may become a promising PS, owning a high potential for application in PDT.     

Insight into the Excitation-Dependent Fluorescence of Carbon Dots

High quantum yield, photoluminescence tunability, and sensitivity to the environment are a few distinct trademarks that make carbon nanodots (CDs) interesting for fundamental research, with potential to replace the prevalent inorganic semiconductor quantum dots. Currently, application and fundamental understanding of CDs are constrained because it is difficult to make a quantitative comparison among different types of CDs simply because their photoluminescence properties are directly linked to their size distribution, the surface functionalization, the carbon core structures (graphitic or amorphous) and the number of defects. Herein, we report a facile one-step synthesis of mono-dispersed and highly fluorescent nanometre size CDs from a ‘family’ of glucose-based sugars. These CDs are stable in aqueous solutions with photoluminescence in the visible range. Our results show several common features in the family of CDs synthesized in that the fluorescence, in the visible region, is due to a weak absorption in the 300–400 nm from a heterogeneous population of fluorophores. Fluorescence quenching experiments suggest the existence of not only surface-exposed fluorophores but more importantly solvent inaccessible fluorophores present within the core of CDs. Interestingly, time-resolved fluorescence anisotropy experiments directly suggest that a fast exchange of excitation energy occurs that results in a homo-FRET based depolarization within 150 ps of excitation.     

Electrochemical detection of quantum dots by stabilization of electrogenerated copper species

The determination of quantum dots is of particular interest as they are frequently used as labels in electrochemical biosensors. In this paper, we describe a method for the detection of very low concentrations of quantum dots using the voltammetric response of copper in ammonia solution. Copper species electrogenerated on the electrode surface are stabilized by the nanoparticles, preventing their oxidation by dissolved oxygen, and a relationship between the concentration of the nanoparticles and the copper voltammetric response can thus be obtained. The reported method shows a linear range between 0.05 and 2 nM of quantum dots, with a limit of detection in the order of 9 × 10⁷ nanoparticles. This method could be employed to improve the detection limit of electrochemical biosensors using quantum dots as labels.     

基于氮掺杂碳量子点荧光猝灭效应检测Fe3+

碳量子点光致发光性质取决于尺寸大小和表面官能团的性质.本研究以还原冶炼过程产生的生物质焦油为前驱体,采用小分子乙二胺进行氮掺杂,通过一步水热法合成荧光产率高、分散性能好的氮掺杂碳量子点,基于Fe3+对氮掺杂碳量子点选择性荧光猝灭效应,实现了对Fe3+快速准确检测.合成的氮掺杂碳量子点为规则的球形,尺寸均一,平均粒径为2.64 nm,晶面间距为0.25 nm,具备石墨碳晶格(100)晶格结构,其荧光量子产率为26.1%;Fe3+与N-CQDs表面官能团配位络合致使N-CQDs荧光猝灭,Fe3+浓度在0.23~600μmol/L范围内,与氮掺杂碳量子点荧光猝灭程度呈良好的线性关系,Fe3+的检出限为230 nmol/L.     

Rapid and Large‐Scale Production of Multi‐Fluorescence Carbon Dots by a Magnetic Hyperthermia Method

The intrinsic low yield of carbon dots (CDs) is a barrier that limits practical application. Now, a magnetic hyperthermia (MHT) method is used to synthesize fluorescent CDs on a large scale (up to 85 g) in one hour (yield ca. 60 %). The reaction process is intensified by MHT since the efficient heating system enhances the energy transfer. CDs with blue, green, and yellow luminescence are synthesized by using carbamide and citrate with three different cations (Zn²⁺, Na⁺, K⁺), respectively. The CDs exhibit bright fluorescence under UV light and show excellent monodispersity and solubility in water. The alternation of photoluminescence (PL) emissions of these CDs is probably due to the difference in particle sizes and surface state. A bar coating technique is used to construct large‐area emissive polymer/CDs films. CDs can insert themselves into the polymer chains by hydrogen bonding and electrostatic interactions. Wound healing efficiency can be enhanced by the Zn‐CDs/PCL nanofibrous scaffold.     

Mn,B, N co-doped graphene quantum dots for fluorescence sensing and biological imaging

The fluorescent and quantum yield (QY) of graphene quantum dots has been improved in recent years by doped atoms, which have good application prospects in fluorescence sensors and biological imaging. Here, a one-step hydrothermal synthesis method was used to synthesize manganese ions bonded with boron and nitrogen-doped graphene quantum dots (Mn-BN-GQDs). Compared with the boron and nitrogen co-doping graphene quantum dots (BN-GQDs), the fluorescence properties and quantum yield of Mn-BN-GQDs are significantly improved. Meanwhile, Mn-BN-GQDs exhibit low toxicity and good fluorescence imaging in living cells and has high selectivity to Fe³⁺ ions. Therefore, this experiment design Mn-BN-GQDs as a fluorescence sensor to detect Fe³⁺ ions, providing strong evidence for the advanced high sensitivity, selectivity and wide detection range of the Mn-BN-GQDs as a fluorescence sensor. These results indicate a dual linear relationship with good linear relationships in the 10–100 μM and 100–800 μM ranges, and limit of detection are 0.78 μM and 9.08 μM, respectively. Cellular imaging results demonstrate that Mn-BN-GQDs can be used as fluorescence sensors in biological imaging. Mn-BN-GQDs can be used for fluorescence sensing in biological imaging in combination with low toxicity, QY and quantum dot lifetime.     

荧光碳点的合成及对酿酒酵母的毒性研究

以葡萄糖为碳源采用溶剂热法合成了荧光碳点。紫外吸收光谱、荧光光谱以及透射电镜照片表明,所合成的荧光碳点发光性能优异,分散性好,且无团聚现象。荧光碳点原溶液出现浓度淬灭现象,稀释60倍情况下荧光最强。以酿酒酵母为模型生物,考察了不同生长时期(调整期、对数期早期、对数期中期)的酿酒酵母与不同浓度的荧光碳点共培养后的生长曲线。结果表明,即使荧光碳点浓度在27.75 mmol.L-1条件下也没有影响酵母菌的生长曲线,可认为基本没有细胞毒性。比较了相同荧光强度下的荧光碳点与CdTe量子点对酿酒酵母的细胞毒性,结果表明荧光碳点的毒性显著低于量子点的毒性。     

Rapid and Large-Scale Production of Multi-Fluorescence Carbon Dots by a Magnetic Hyperthermia Method

The intrinsic low yield of carbon dots (CDs) is a barrier that limits practical application. Now, a magnetic hyperthermia (MHT) method is used to synthesize fluorescent CDs on a large scale (up to 85 g) in one hour (yield ca. 60 %). The reaction process is intensified by MHT since the efficient heating system enhances the energy transfer. CDs with blue, green, and yellow luminescence are synthesized by using carbamide and citrate with three different cations (Zn²⁺, Na⁺, K⁺), respectively. The CDs exhibit bright fluorescence under UV light and show excellent monodispersity and solubility in water. The alternation of photoluminescence (PL) emissions of these CDs is probably due to the difference in particle sizes and surface state. A bar coating technique is used to construct large-area emissive polymer/CDs films. CDs can insert themselves into the polymer chains by hydrogen bonding and electrostatic interactions. Wound healing efficiency can be enhanced by the Zn-CDs/PCL nanofibrous scaffold.     

Synthesis of carbon dots with a tunable photoluminescence and their applications for the detection of acetone and hydrogen peroxide

Carbon dots(CDs) with multi-color emissive properties and a high photoluminescent quantum yield(PLQY) have attracted great attention recently due to their potential applications in chemical,environmental,biological and photo-electronic fields.Solvent-dependent effect in photoluminescence provides a facial and effective approach to tune the emission of CDs.In this study,green emissive nitrogen-doped carbon dots(N-CDs) are synthesized from p-hydroquinone and ethylenediamine through a simple hydrothermal method.The as-prepared N-CDs possess a robust excitation-independent green luminescence and a high PLQY of up to 15.9%.Further spectroscopic characterization indicates that the high PLQY is achieved by the balance of nitrogen doping states and the surface passivation extent in CDs.The N-CDs also exhibit solvent-dependent multi-color emissive property and distinct PLQY in different solvents(the maximum can reach up to 25.3%).Furthermore,the as-prepared N-CDs are applied as fluorescence probes to detect acetone and H2O2 in water.This method has exhibited a low detection limit of acetone(less than 0.1 %) and a quick and linear response to the H_2O_2 with the concentration from 0 to 120 μmol/L.This work broadens the knowledge of applying CDs as probes in the bio and chemical sensing fields.     

Graphene and carbon quantum dots electrochemistry

Graphene and carbon quantum (QDs) dots exhibit interesting and well-defined properties owing to their quantum confinement. In this work, graphene QDs (G-QDs) and carbon QDs of size ~ 6 nm and ~ 2 nm, respectively, were prepared and their potential uses in electrochemistry and electrochemical sensing were subsequently investigated. It was discovered that the C-QDs surface displayed a faster electron transfer rate compared to the G-QDs following analyses with the ferro/ferricyanide redox probe. Studies were also carried out with redox biomarkers such as uric acid (UA) and ascorbic acid (AA), and it was found that while the C-QDs displayed electrocatalytic properties toward the oxidation of both UA and AA, the G-QDs seemed to only have an impact on AA, from the decrease in the oxidation peak potential. This work provides direct electrochemical comparison of the two latest frontiers of carbon nanomaterials and opens the way for their electrochemical sensing applications.     

Boron Doped Carbon Dots with Unusually High Photoluminescence Quantum Yield for Ratiometric Intracellular pH Sensing

Herein we report that boron doping in carbon dots results in increased photoluminescence (PL) quantum yield, which could be used for ratiometric intracellular pH sensing in cancer cell lines. Using a mixture of citric acid monohydrate, thiourea, and boric acid, microwave-assisted synthesis of boron doped blue emitting carbon dots (B-Cdots) with an average size of 3.5±1.0 nm was achieved. For B-Cdots, the maximum quantum yield (QY) was observed to be 25.8 % (11.1 % (w/w) H₃BO₃ input concentration), whereas, the same was calculated to be 16.9 % and 11.4 % for Cdots (synthesized from citric acid monohydrate and thiourea only) and P-Cdots (phosphorus doped carbon dots; synthesized using citric acid monohydrate, thiourea and phosphoric acid) (11.1 % (w/w) H₃PO₄ input concentration), respectively. The observed luminescence efficiencies as obtained from steady state and time-resolved photoluminescence measurements suggest an alternative emission mechanism due to boron/phosphorus doping in carbon dots. We furthermore demonstrated facile composite formation using B-Cdots and another carbon dots with orange emission in presence of polyvinyl alcohol (PVA), resulting in white light emission (0.31, 0.32; λ_ex 380 nm). The white light emitting composite enabled ratiometric pH sensing in the aqueous medium and showed favorable uptake properties by cancerous cells for intracellular pH sensing as well.     

高灵敏CdTe量子点探针的构建及与金属离子的作用

采用变性的牛血清白蛋白(dBSA)对水相合成的CdTe量子点进行修饰, 构建了高灵敏金属离子探针, 研究了其对重金属离子的检测性能并对机理进行了探讨. 通过优化反应条件, 合成了具有高量子产率的以巯基乙酸为稳定剂的水溶性CdTe量子点, 并采用变性的牛血清白蛋白分别对不同粒径的CdTe量子点进行修饰, 确定变性的牛血清白蛋白与不同粒径量子点之间的最佳比例. 在纯化变性的牛血清白蛋白修饰的量子点(dBSA-QDs)的基础上, 研究了该量子点与不同金属离子的作用. 结果表明, 量子点经修饰后, 其量子产率、 抗光漂白性及稳定性得到显著提高; 而且dBSA-QDs的荧光可被重金属离子有效猝灭, 与巯基乙酸稳定的量子点(TGA-QDs)相比, 检测灵敏度显著提高.     

Photoactivated Fluorescence Enhancement in F,N-Doped Carbon Dots with Piezochromic Behavior

Photoactivation in CdSe/ZnS quantum dots (QDs) on UV/Vis light exposure improves photoluminescence (PL) and photostability. However, it was not observed in fluorescent carbon quantum dots (CDs). Now, photoactivated fluorescence enhancement in fluorine and nitrogen co-doped carbon dots (F,N-doped CDs) is presented. At 1.0 atm, the fluorescence intensity of F,N-doped CDs increases with UV light irradiation (5 s–30 min), accompanied with a blue-shift of the fluorescence emission from 586 nm to 550 nm. F,N-doped CDs exhibit photoactivated fluorescence enhancement when exposed to UV under high pressure (0.1 GPa). F,N-doped CDs show reversible piezochromic behavior while applying increasing pressure (1.0 atm to 9.98 GPa), showing a pressure-triggered aggregation-induced emission in the range 1.0 atm–0.65 GPa. The photoactivated CDs with piezochromic fluorescence enhancement broadens the versatility of CDs from ambient to high-pressure conditions and enhances their anti-photobleaching.     

Study of immobilized candida rugosa lipase for biodiesel fuel production from palm oil by flow microcalorimetry

Enzymatic transesterification of palm oil with methanol and ethanol was studied. Of the four lipases that were tested in the initial screening, lipase Candida Rugosa (CR) resulted in the highest yield of mono alkyl esters. Lipase CR was further investigated in immobilized form within an activated carbon as support. The activated carbon was prepared by activation physical. Using the immobilized lipase CR, the effects of water and alcohol concentration, enzyme loading and enzyme thermal stability in the transesterification reaction were investigated. The optimal conditions for processing 50 g of palm oil were: 37 °C, 1:14.5 oil/methanol molar ratio, 1.0 g water and 500 mg lipase for the reactions with methanol, 35 °C, 1:15.0 oil/ethanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol, and 35 °C, 1:10.0 oil/n-butanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol. Subject to the optimal conditions, methyl and ethyl esters formation of 70 and 85 mol% in 1 h of reaction were obtained for the immobilized enzyme reactions. The flow microcalorimetry is an important and novel techniques is used in evaluation of biodiesel production.     

Solvent-free Synthesis of Flowable Carbon Clusters with Customizable Size and Tunable Optical Performance

We propose a rapid and solvent-flee route for synthesizing luminous carbon clusters by controlling carbonization of polyethylene glycol （PEG）. This approach does not involve solvents yet uses the precursor itself as suspend- ing medium, thus features mild and green chemistry, and also enables the formation of uniform-sized carbon clus- ters, of which the diameter can be easily tuned from 0.7 to 3.5 nm via control of reaction time. In term of the di- mension, the resultants are denoted as sub-nano carbon clusters （SNCs） and carbon dots （CDs）, respectively. Bene- fiting from surface anchored PEG segments, both of the two show favorable flowability at room temperature and excellent solubility in aqueous and organic solvents. Comparison of their optical performances and structures re- veals that they share the same chromophores. Particularly, the SNCs demonstrate robust photo- and pH-stable pho- toluminescence and can be directly applied to cell-imaging regarding to its prominent biocompatibility. Moreover, its quantum yield （5.5%）, which is approximately 3 times higher than that of CDs （1.5%）, can be dramatically en- hanced to 18.8% by facile chemical reduction. We anticipate that these PEG derivatives marked with easy synthesis, controllable optical performances and excellent physical properties will be highly appealing in future applications.     

The polymeric characteristics and photoluminescence mechanism in polymer carbon dots: A review

A large amount of emerging research on carbon dots (CDs) has been gradually improving the understanding of their structures, properties and emission mechanism. Distinct from the dominating status of quantum confinement effect in quantum dots, CDs always suffer from the complicated optical properties, deriving from the large differences in raw materials and synthesis methods. The diverse concepts and species puzzle researchers and hinder the further study. Thus, there is an urgent need to unify the definition and clarify the confused relation of CDs. Herein, we classify the raw materials of CDs synthesis into small molecules and polymers, and discuss CDs from the aspects of raw materials. We believe that the polymer-like structures reserved in CDs are universal no matter from the condensation of small molecules or the direct inheritance of polymers. Moreover, many similarities are concluded between CDs and polymers through serious comparisons and enough evidences. The formation processes of CDs are mostly polymerization and the obtained CDs always possess polymeric characteristics, such as abundant reactive functional groups, polydispersity of products, highly crosslinked network structure and other similar properties to non-conjugated fluorescent polymers. Therefore, the new concept, polymer carbon dots (PCDs), is put forward to generalize all kinds of CDs based on the summary of related reports. Besides, the complicated influence factors of photoluminescence (PL) are discussed and mainly classified as molecule state, carbon core state, surface state and crosslink enhanced emission (CEE) effect. In general, this review puts forward PCDs as a unified definition of reported CDs, and summarizes the polymeric characteristics of PCDs from formation process and product properties, as well as simultaneously illustrates the PL mechanism.     

Pyrolysis oil from fast pyrolysis of maize stalk

Maize stalk was fast pyrolysed at temperatures between 420 °C and 580 °C in a fluidized-bed, and the main product of pyrolysis oil was obtained. The experimental results showed that the highest pyrolysis oil yield of 66 wt.% was obtained at 500 °C for maize stalk. Chemical composition of the pyrolysis oil acquired was analyzed by GC–MS and its heat value, stability, miscibility and corrosion characteristics were determined. These results showed that the pyrolysis oil could be directly used as a fuel oil for combustion in a boiler or a furnace without any upgrading. Alternatively, the fuel could be refined to be used by vehicles.