A FRET Fluorescent Sensor for Ratiometric and Visual Detection of Sulfide Based on Carbon Dots and Silver Nanoclusters

In this work, the fluorescent sensor based on fluorescence resonance energy transfer (FRET) and electrostatic interaction (EI) was prepared for the ratiometric and visual detecting S^2–. The FRET fluorescent sensor consists of two fluorophores, with carbon dots (CDs) as energy donors and silver nanoclusters (Ag NCs) as acceptors. At 390 nm excitation, CDs and Ag NCs showed two well-separated peaks at 445 nm and 660 nm, separately. The existence of S^2– caused the red fluorescence at 660 nm to be quenched, whereas the blue fluorescence at 445 nm was restored, and the fluorescence color of the ratiometric sensor changed from pink to blue. It could be employed in ratiometric and visual detecting S^2–. The linear range of quantitative detection S^2– was 0.5–100 μM, and its detection limit was 0.35 μM. CDs-Ag NCs could be used for detecting S^2– in mineral water and tap water. The results showed that the FRET ratiometric fluorescent sensor exhibits good anti-interference and high selectivity for detecting S^2– in environmental water samples.

     

Ratiometric pH Sensing in Living Cells Using Carbon Dots

The ability to precisely sense physiological pH changes in the cellular environment is exceedingly difficult. Novel technologies are thus required to address this challenge. Fluorescent nanomaterials can be exploited to this effect because their optical properties can exhibit strong pH dependence. Herein, an intracellular pH-sensing probe is developed via a facile microwave-reaction synthesis method for the preparation of carbon dots (CDs) using glutathione and formamide. The CDs possess unique optical properties allowing for concomitant fluorescence in the blue and red regions of the spectrum. These dots are investigated as pH-sensors using the red fluorescence signatures at 650 and 680 nm. The two fluorescence bands respond differently following pH changes in their environment and could thus be used for ratiometric measurements. Cytotoxicity studies of the CDs in glioblastoma cells show no decrease in cell viability up to 100 μg mL⁻¹ (24 h). Fluorescence imaging reveals that the dots localize in lysosomal compartments. Moreover, they can sense changes in lysosomal pH in response to serum and amino acid starvation, as well as administration of diclofenac and metformin, drugs currently in clinical trials for combination treatments of cancer. These CDs offer a new self-referencing approach for live intracellular pH sensing in 2D- and 3D-cell models.     

Coal Pitch Derived Yellow-Emissive Carbon Dots and Their Application in Luminescent Solar Concentrators

Using coal pitch as the carbon source to synthesize carbon dots (CDs), one of the most promising photoluminescence (PL) materials, can play an important role in the global demand for carbon neutralization. However, the reported CDs derived from coal pitch are mainly limited blue emission. Here, a new route to synthesize yellow-emissive CDs from coal pitch is developed by extracting the lightweight aromatic compounds from coal pitch and solvothermally treating the extracts in dichloromethane in the presence of a small amount of nitric acid and sulfuric acid. Notably, the obtained CDs exhibit excitation independent yellow emission, large Stokes shift and good photostability. The application of the CDs for luminescent solar concentrators (LSCs) is evaluated. It is found that the CDs can be well dispersed in polymethyl methacrylate (PMMA) matrix and fabricated transparent LSCs. The synthesized LSC (4 × 4 × 0.2 cm³) with the optimal CDs concentration exhibits an optical conversion efficiency (η_opt) of 3.31% and power conversion efficiency (η_PCE) of 1.95% under simulated sun light illumination (100 mW cm⁻²). This research offers a new strategy to synthesize new kind of CDs with desired performance by exploiting the native chemistries of coal pitch.     

Nitrogen-doped carbon dots embedded in a SiO<Subscript>2</Subscript> monolith for solid-state fluorescent detection of Cu<Superscript>2+</Superscript> ions

We describe the simple fabrication of SiO₂ sol-gel monoliths embedding highly luminescent carbon nanodots (CDs) sensitive to metal ions. The pristine CDs we synthesize display an intense dual emission consisting in two fluorescence bands in the green and violet region, and we demonstrate that this photoluminescence is substantially unchanged when the dots are incorporated in the SiO₂ matrix. The emission of these CDs is quenched by interactions with Cu²⁺ ions, which can be used to detect these ions with a detection limit of 1 μM. The chromophores remain accessible to diffusing Cu²⁺ ions even after embedding CDs in the sol-gel monolith, where their detection capabilities are preserved. Such a result provides the proof-of-principle of a new sensing scheme, where CDs are exploited as active sensing centers of metal transition ions within a solid-state device. The different interaction mechanisms of CDs with copper, in liquid and solid phase, are analyzed in detail and discussed in terms of different accessibility of their chromophores when the dots are incorporated in the SiO₂ matrix.     

One-pot synthesis of carbon dots co-doped with N and S: high quantum yield governed by molecular state and fluorescence detection of Ag+

Fluorescent carbon-based nanoparticles, called chronically as carbon dots (CDs), were synthesised from citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method. After a series of micro-structural characterisation, N and S elements could be sufficiently doped by means of the heteroatom in the CDs solution. The as-prepared CDs solution showed blue colour fluorescence with the highest QY of 78.6%, and study on the UV–visible and PL spectra further revealed that the outstanding fluorescence of as-prepared CDs mainly originates from the generated molecular fluorophores instead of the surface state. Owing to the strong fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity. However, the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.

This figure shows citric acid (CA) and 2-Aminothiophenol (2AT) via an N and S co-doped hydrothermal method to prepare CDs with blue colour fluorescence and the highest QY of 78.6%. Owing to the excellent fluorescence, the as-prepared CDs can be used as a sensing probe for the detection of Ag⁺ with high sensitivity and selectivity, and the changes of fluorescence intensity exhibited the complex nature of the quenching mechanism due to the –SH and –NH₂ groups on the fringes of carbonaceous cores or molecular fluorophores to aggregate into another fluorescent cores with the assistance of Ag⁺ ions, which promises a new approach for efficient detection of Ag⁺ for the application in industrial pollutants.     

Synthesis,biocompatibility and luminescence properties of quantum dots conjugated with amino acid-functionalized β-cyclodextrin

A series of CdSe and CdSe/CdS quantum dots (QDs) labeled with amino acid-modified β-cyclodextrin (β-CD) was prepared by a simple ultrasonic method. These amino acid-modified β-CD-coated QDs are very soluble and stable in biological buffer. They also have high colloidal stability and strong optical emission properties that are similar to those of untreated tri-n-octylphosphine oxide (TOPO)-coated QDs. The quantum yields (QYs) of these amino acid-modified β-CD-coated CdSe and CdSe/CdS QDs in biological buffer were found to be very high. In particular, the QYs of the positively charged l-His-β-CD-coated CdSe/CdS QDs were as high as 33.5±1.8%. In addition, the fluorescence lifetime of these QDs was also very long in PBS solutions as determined by frequency domain spectroscopy. For example, the lifetime of l-His-β-CD-coated CdSe/CdS QDs was 8.6 ns. The in vitro cytotoxicity of these QDs in ECV-304, SH-SY5Y and HeLa cells was found to be lower. l-His-β-CD-coated CdSe/CdS QDs were the least cytotoxic (IC₅₀ 95.6±3.2 mg mL^?1 in ECV-304 cells after 48 h). The flow cytometry results show that the positively charged amino acid led to a considerable increase in biocompatibility of QDs. This may be attributed to the presence of an amino acid-modified β-CD outer layer, which enhanced the biocompatibility.     

壳聚糖碳点的水热法制备及其对金属离子的选择性研究

以壳聚糖为碳源通过水热法合成碳点,对影响碳点荧光强度的水热温度、水热时间和壳聚糖质量分数进行考察。通过紫外分光光度计、荧光分光光度计、原子力显微、Fourier红外光谱仪、X-ray光电子能谱、X射线衍射仪对壳聚糖碳点的光学性质、化学结构、晶体结构、形貌结构等进行表征分析。结果表明,在水热温度200℃、水热时间9 h、壳聚糖质量分数2%的条件下制备得到的壳聚糖碳点量子产率为32.86%。碳点呈现出主要尺寸为3～10 nm的球形颗粒状,且在波长335 nm激发下,发射峰位于410 nm(蓝)。对金属离子的选择性研究分析表明,Fe~(3+)对碳点溶液的荧光猝灭效应最显著,说明碳点对Fe~(3+)具有较好敏感性和高选择性,且荧光猝灭效率对Fe~(3+)浓度在0～100μmol/L范围内呈现线性响应,因此有望将碳点作为荧光探针应用于Fe~(3+)的检测表征。     

A Significant Fluorescent Aptamer Sensor Based on Carbon Dots and Graphene Oxide for Highly Selective Detection of Progesterone

In this paper, a fluorescent aptamer sensor was constructed based on the carbon dots (CDs) and graphene oxide (GO). This sensor combines the excellent fluorescence performance of CDs with the high specificity of aptamer, which can detect progesterone (P₄) with high sensitivity and selectivity. In the absence of P₄, the CDs-aptamer system and GO form a fluorescence resonance energy transfer process (FRET), which quenches the fluorescence of the CDs. When P₄ is added, the aptamer specifically binds to it, resulting the fluorescence of the CDs is recovered. At optimal conditions, the fluorescence intensity recovered by the CDs has a linear relationship with the concentration of P₄ in the range of 0.1–120 nM and the detection limit is 3.3?×?10^–11 M. Besides, the sensor has satisfactory detection results of P₄ in milk, indicating that constructed method has enormous potential for application in food safety.

     

One step synthesis of ultra-high quantum yield fluorescent carbon dots for “on-off-on” detection of Hg2+ and biothiols

In this paper, the carbon dots (CDs) with strong blue fluorescence were synthesized through hydrothermal method, which using folic acid, ammonium citrate and ethylenediamine as precursors. The prepared CDs with a high absolute quantum yield of 81.94% and showed excellent stability in high concentration salt solution and different pH conditions. With the addition of Hg²⁺, the signal of CDs was selectively quenched. At the same time, the CDs-Hg²⁺ system could be recovered after the introduction of biothiols. Moreover, the fluorescence of CDs showed a good linear relationship with Hg²⁺ (1–15 µM), and the detection limit as low as 0.08 µM. In addition, the prepared CDs with low toxicity could be used to detect Hg²⁺ in living cells and actual water samples.

     

Versatile Fluorescent Carbon Dots from Citric Acid and Cysteine with Antimicrobial,Anti-biofilm,Antioxidant, and AChE Enzyme Inhibition Capabilities

Nanostructured fluorescent particles derived from natural molecules were prepared by a green synthesis technique employing a microwave method. The precursors citric acid (CA) and cysteine (Cys) were used in the preparation of S- and N-doped Cys carbon dots (Cys CDs). Synthesis was completed in 3 min. The graphitic structure revealed by XRD analysis of Cys CDs dots had good water dispersity, with diameters in the range of 2–20 nm determined by TEM analysis. The isoelectric point of the S, N-doped CDs was pH value for 5.2. The prepared Cys CDs displayed excellent fluorescence intensity with a high quantum yield of 75.6?±?2.1%. Strong antimicrobial capability of Cys CDs was observed with 12.5 mg/mL minimum bactericidal concentration (MBC) against gram-positive and gram-negative bacteria with the highest antimicrobial activity obtained against Staphylococcus aureus. Furthermore, Cys CDs provided total biofilm eradication and inhibition abilities against Pseudomonas aeruginosa at 25 mg/mL concentration. Cys CDs are promising antioxidant materials with 1.3?±?0.1 μmol Trolox equivalent/g antioxidant capacity. Finally, Cys CDs were also shown to inhibit the acetylcholinesterase (AChE) enzyme, which is used in the treatment of Alzheimer’s disease, even at the low concentration of 100 μg/mL.

     

A solvent-governed surface state strategy for rational synthesis of N and S co-doped carbon dots with multicolour fluorescence

ABSTRACT

Multicolour emissive carbon dots (CDs) are widely investigated by virtue of their merits on fluorescent properties. Method on heteroatom doping assisted with various solvents has been proved efficient in achieving multiple-colour-emissive CDs, especially long-wavelength emission. Herein, a synthesis of multicolour-emissive CDs by controlled surface function is reported. By tuning the thermal-pyrolysis temperature and molar ratio of reactants, optimal emission of the resulted CDs gradually shifts from blue to yellow light with the assistance of different solvents. According to the emissive relationship dependent on excitation, fluorescence lifetimes, and FT-IR of these CDs, the different surface states participated with S and N elements on the surface of carbogenic core govern fluorescent colours of the CDs. In terms of the applications, blue CDs (B-CDs) exhibits high sensitivity for ion detections of Ag⁺ and Fe³⁺, which is further illustrated to have different quenching mechanisms each other because that these ions have the affinity interaction with different surface groups of the CDs. Moreover, blue and yellow CDs solutions are mixed with PVP water solution to fabricate white-light CDs/PVP film, which exhibits stable fluorescence with a CIE coordinate of (0.32, 0.33) and endows these CDs as potentially fluorescent nanomaterial in the solid state lighting field.     

生物质碳量子点的绿色制备及对Cu2+的检测

向日葵作为我国主要的油料作物之一,其秸秆是天然的纤维素材料,具有绿色无毒,成本低廉的优势,是制备生物质碳量子点的理想材料之一。近年来,由于含铜农药和化学肥料的不规范使用,大量含铜污染物被排放导致农田土壤和水环境中的铜含量远高于环境背景值。因此,迫切需要开发出一种选择性好、灵敏性强且对环境友好的Cu²⁺检测方法。碳量子点(CDs)是一种粒径小于10 nm的准球形荧光碳纳米材料,因其表面含有丰富的极性官能团,具有良好的水溶性而被广泛研究。与传统的半导体量子点(CdSe, CdTe)相比,CDs具有合成原料广泛、生物相容性好等优点。主要应用于生物成像、光催化、光电转化以及传感检测等领域。然而目前用于碳化合成CDs的前驱体大多为昂贵的化学品,且合成过程复杂污染环境,限制了CDs的大规模生产与应用。开发出一种生态友好,简单、廉价的CDs合成方法是很有意义的。本研究以废弃的向日葵秸秆为碳源,采用简便的水热法合成生物质碳量子点(S-CDs)作为荧光探针,用于检测识别Cu²⁺。通过对S-CDs的一系列光学性质分析与表征,鉴定出其表面官能团主要包括O—H, N...     

A New Dual-peak Fluorescent Probe for Water Content Detection Made From Taxus

In this paper, the leaves of Taxus were used as the sole carbon source, and two kinds of carbon dots blue and red, with different properties, were synthesized by the hydrothermal method under different conditions. The red carbon dots were quenched in the water, and the blue carbon dots had stable fluorescence properties in water environment. The bimodal fluorescence probe formed by mixing could accurately and stably measure the water content in ethanol, which was in the range of 82.5%-100%, is highly correlated with the fluorescence intensity ratio (I₄₈₁/I₆₇₈) of mixed carbon dots under 390 nm excitation light, with R²?=?0.995 and the detection limit as low as 0.31%. The experimental materials are environmentally friendly, low in cost, and simple to operate, as well as the water content measured by proportional fluorescence has high accuracy, which provides a new method for measuring moisture in ethanol.

     

Comparison of Carbon Dots Prepared in Deep Eutectic Solvent and Water/Deep Eutectic Solvent: Study of Fluorescent Detection of Fe3+ and Cetirizine and their Photocatalytic Antibacterial Activity

In this study, two solvents (deep eutectic and water/deep eutectic solvents) were used for N-doped carbon dots (N-CDs) preparation by microwave irradiation. The solvent can influence surface chemical composition, quantum yield, morphology, and fluorescence of CDs. N-CDs synthesized in water/deep eutectic solvent (DES) had better quantum yield (24.5%) with respect to N-CDs synthesized in deep eutectic solvent (17.4%). These carbon dots were used as a rapid and high sensitive “off–on” fluorescent probe for the determination of Fe³⁺ ion and cetirizine. Morphology and structure of the N-CDs were characterized by FT-IR, UV–Vis, XRD and TEM. Linear range and detection limit for N-CDs synthesis in deep eutectic solvent for cetirizine were 0.08–48 µM and 15 nM, respectively and for N-CDs synthesis in water/deep eutectic solvent were 0.03–50 µM and 10 nM, respectively. Applicability of this nanoprobe was tested in cetirizine determination in serum sample. Antibacterial activities of the two synthesized N-CDs were also investigated using agar disk diffusion method.

     

Defects related emission and nanosecond optical power limiting in CuS quantum dots

We report optical and nonlinear optical properties of CuS quantum dots and nanoparticles prepared through a nontoxic, green, one-pot synthesis method. The presence of surface states and defects in the quantum dots are evident from the luminescent behavior and enhanced nonlinear optical properties measured using the open aperture Z-scan, employing 5 ns laser pulses at 532 nm. The quantum dots exhibit large effective third order nonlinear optical coefficients with a relatively lower optical limiting threshold of 2.3 J cm⁻², and the optical nonlinearity arises largely from absorption saturation and excited state absorption. Results suggest that these materials are potential candidates for designing efficient optical limiters with applications in laser safety devices.     

Facile Synthesis of Mg2+‐Doped Carbon Dots as Novel Biomaterial Inducing Cell Osteoblastic Differentiation

Carbon dots (CDs), as an emerging fluorescent nanomaterial with low toxicity, has been widely applied in various bio‐related fields. However, investigations on their capabilities in guiding osteogenic differentiation are rarely seen, which has great significance in osteoporosis therapy and bone regeneration. Herein, for the first time, a new kind of Mg²⁺‐doped CDs is facilely synthesized through a one‐step hydrothermal method from metal gluconate salts. The CDs can serve as nanocarrier of Mg²⁺ ions entering into cells, and the bioessential metal ions subsequently stimulate osteoblastic differentiation by improving alkaline phosphatase (ALP) activity and upregulation related mRNA expression. Noteworthy, the raw material has almost negligible performance on osteoblastic differentiation compared to Mg‐CDs, which is due to the ultrasmall sizes of CDs and the efficient uptake by cells. Moreover, benefitting from the fluorescence properties, Mg‐CDs can also be applied as cell labeling agents. This work proposes a new strategy to synthesize multifunctional metal ion‐doped CDs, which might had great potential in serving as promising nanodrugs for bone loss therapy.     

碳点嫁接海藻酸钙复合结构的制备及其对Cu2+的检测

基于铜离子与碳点的荧光猝灭作用,建立了用碳点作为荧光探针来检测铜离子的新方法。该方法将碳点还原后再嫁接于海藻酸钙,从而得到一种新型的含还原碳点的海藻酸钙薄膜荧光探针。用荧光分光光度计和紫外-可见分光光度计对探针的荧光特性以及探针与金属离子的相互作用进行了研究。研究结果表明：改性后的荧光探针具有很高的荧光强度,因此可以根据探针荧光强度的变化实现对铜离子的检测,并通过乙二胺四乙酸二钠（EDTA）的作用实现对铜离子的重复检测。铜离子浓度在5×10^-6~100×10^-6 mol·L^-1范围内与该荧光探针的荧光猝灭强度呈良好的线性关系。该方法不仅可以对铜离子检测,更实现了对碳点的固载,该技术有望实现荧光探针的回收再利用。     

柿子叶制备碳量子点的光谱性质及对Fe3+的荧光探针

碳量子点作为碳纳米材料中的新成员,具有较高的光学稳定性、低毒性、良好水溶性、原料来源广泛、制备方法多样等多种优点,在分析检测、生物标记、光催化降解以及环境监测等领域具有广泛的应用前景, 对碳量子点的研究引起了国内外学者极大兴趣。水中Fe3+含量的超标会对生活饮用和工业生产造成一定的危害,所以准确快速地检测水中Fe3+的含量,对人体健康具有重要的意义。目前,对Fe3+进行检测的方法有伏安法、荧光光谱法、电化学法以及火焰原子吸收光谱法等,其中荧光光谱法具有快速响应和方法简便的特点,比其他方法更有优势。以柿子叶为碳源,采用水热法制备了发蓝绿色荧光的碳量子点,通过X射线衍射、高分辨透射电子显微镜、傅里叶变换红外光谱、紫外-可见吸收光谱及荧光光谱等技术对碳量子点的结构、微观形态和光谱学性质进行了详细表征。柿子叶制备的碳量子点呈现为分散均匀的球形颗粒,颗粒平均直径大约5.9 nm,碳量子点颗粒表面具有丰富的含氧官能团,在277 nm有明显的紫外吸收,可归因于C═O的n→π*跃迁。碳量子点的发射波长和荧光强度具有明显的激发依赖性,在410 nm光激发下,发射波长峰值为498 nm且荧光峰最强,荧光寿命为4.59 ns。采用多种金属离子对柿子叶制备的碳量子点在荧光传感方面进行了探究,分析发现该碳量子点对金属Fe3+具有极高的选择性,可作为荧光探针检测水中微量的Fe3+含量,其荧光猝灭率F₀/F与金属Fe3+浓度在1~120 μmol·L-1范围内呈现良好的线性关系（R2 = 0.992）,猝灭常数和最低检出限分别为8.84×103 L·mol-1和0.21 μmol·L-1,最低检出限数值明显小于最近一些文献的报导结果。该工作提供了一种原料天然、操作简单、成本低廉的制备工艺,开发了荧光检测水中微量金属铁离子的新方法。     

Fluorescent Carbon Dot as Nanosensor for Sensitive and Selective Detection of Cefixime Based on Inner Filter Effect

Here a simple and sensitive fluorescent assay for detecting Cefixime based on inner filter effect (IFE) has been proven, which is conceptually different from the previously reported CEF fluorescent assays. In this sensing platform, fluorescent carbon dots (CDs) were prepared by one-pot synthesis and was directly used as fluorophore in IFE. The method is based on the complexation reaction between cefixime and palladium ion in the presence of acidic buffer solution (pH 4). The Pd(II)-CEFcomplex was capable of functioning as a powerful absorber in IFE to influence the excitation of fluorophore (CDs). Production Pd(II)-CEFcomplex induced the absorption band transition from 310 to 400 nm, which resulted in the complementary overlap with the excitation spectra of CDs. Due to the competitive absorption, the excitation of CDs was significantly weakened, resulting in the quenching of CDs. The present IFE-based sensing strategy showed a good linear relationship from 0.2 × 10^?6 M to 8 × 10^?6 M (R² = 0.987) and provided an exciting detection limit of 0.5 × 10^?7 (3δ/slope). The proposed method has been successfully applied for the determination of cefixime in raw milk and human urine samples.     

基于碳点“开关”型荧光探针在组氨酸检测中的研究

研究并构建了一种基于荧光碳点(carbon dots, CDs)的新型“开关”探针,利用CDs荧光强度的变化进行痕量组氨酸(histidine, His)的检测。在pH 7.6的溶液中,钌(Ru)能与CDs通过静电吸引作用形成弱的基态化合物,导致CDs的荧光猝灭,此时体系处于“关闭”状态。而His与Ru有更强的亲和力,故向体系中加入 His后,Ru从CDs表面竞争中下来,CDs的荧光得到恢复,此时体系被“打开”。考察了pH、缓冲溶液、反应时间、温度等因素对体系的影响,并初步讨论了Ru对CDs荧光的猝灭类型,得出了Ru对CDs荧光的猝灭属于静态猝灭的结论。实验结果表明,在pH 7.6的溶液中,在20～25 ℃条件下,体系在10 min 内反应完成。His的浓度与碳点荧光的恢复程度呈良好的线性关系,其线性范围为：6.5～219.3×10-6 mol·L-1,检出限为：2.15×10-6 mol·L-1。将方法应用于实际样品氨基酸注射液中组氨酸含量的测定,其RSD≤2.07%,回收率在95.7%～102.4%之间。将具有优良光学特性的CDs应用于构建“开关”型荧光探针,不但拓宽了CDs的应用范围,为一些重要物质的检测提供了参考。