Enhanced Ratiometric pH Sensing Using SNAFL-2 on Silver Island Films: Metal-enhanced Fluorescence Sensing

We have explored the opportunities for enhanced ratiometric pH sensing using the well-known carboxy seminaphthofluorescein (SNAFL-2) and silver island films (SiFs). Our results show that the metallic surfaces can provide up to a 40-fold increase in probe fluorescence intensity as compared to nonmetallic surfaces with the same probe coverage. However, while the S/N is significantly better for pH sensing, the emission wavelength ratiometric values are similar to that obtained in solution, due to the fact that the emission of both the acidic and basic forms of the probe are enhanced to similar extents. To the best of our knowledge this is the first report of enhanced ratiometric fluorescence sensing on metallic surfaces.     

比率荧光纳米水凝胶的制备以及在pH探测中的应用

基于再沉淀方法制备了一种具有比率荧光发射的纳米水凝胶,适用于检测生理范围的pH值。通过在聚氨酯水凝胶中引入pH值指示剂以及具有共振能量传递关系的荧光染料分子,赋予原本非pH响应和非荧光型的水凝胶以pH探测能力。随着pH值由酸性渐变为碱性,纳米水凝胶的绿色荧光强度逐渐增强,而红色荧光逐渐减弱。所制备的纳米水凝胶由于具有灵敏度高、亲水性好、稳定性好、响应快以及pH值检测范围恰好涵盖了生理pH值范围(pH值6～8)等优点,因此在细胞内pH值探测领域具有广阔应用前景。     

Electroporative Adjustment of pH in Living Yeast Cells: Ratiometric Fluorescence pH Imaging

A number of vital cell functions including modulation of signaling pathways and regulation of the cellular transport critically depends on the cytoplasmic pH. Many pathological cellular changes are related to the abnormal cytosolic pH as well. Reliable and well-calibrated methods for quantification of the cytosolic pH are therefore of high importance. The pH calibration is particularly difficult in walled cells since standard methods fail. In this report we evaluated the new electroporative calibration method of the cytosolic pH in yeasts by the fluorescence microscopy. The calibration was done on living cells using pyranine as a ratiometric pH-sensitive probe. The probe was electroporatively delivered to the cytosol. We have shown that unlike the measurements in suspension the fluorescence microscopy reveals cell subpopulations with different sensitivity to the pH calibration. While the majority of the cells were well calibrated, there was found subpopulation of uncalibrated cell as well as singular cells exhibiting anomalous pH calibration due to the staining of acidic organelles. Resolution of cell subpopulations helps to achieve better pH calibration compared to the calibration in cuvette on a cell suspension.     

pH响应型碳点的荧光机制和生物医学应用

碳点(CDs)作为一种新型的零维碳基纳米材料,由于其优异的荧光性质、良好的生物兼容性、低细胞毒性以及丰富的表面官能团等性质,在荧光传感和生物医学领域具有巨大的应用潜力。特别是针对肿瘤弱酸性的微环境特点,设计pH响应型碳点来实现对肿瘤的特异性治疗将尤为重要。本文对近年来基于pH响应型碳点的研究工作进行了系统的调研,综述了pH响应型碳点的荧光机制及其在pH传感、生物成像及癌症治疗等生物医学领域的应用,并对pH响应型碳点目前面临的主要挑战以及未来发展的方向进行了展望。     

溶剂热法合成橙-绿双波段荧光碳点

荧光碳点具有激发波长依赖的独特性质,有望基于此制备检测溶液pH值的荧光探针。以柠檬酸和尿素为原料、N,N-二甲基甲酰胺为溶剂,采用一步溶剂热法在200℃下保温12 h制备了一种新型的具有橙-绿双波段荧光发射性能的水溶性碳点。采用透射电子显微镜、X射线衍射、拉曼光谱、傅里叶变换红外光谱和X射线光电子能谱等方法对荧光碳点的组成和形貌进行了表征,还通过荧光发射光谱和紫外-可见吸收光谱对其光学性能进行了研究。结果表明,制备的碳点粒径为2.7～4.3 nm,表面带有大量含氧官能团,具有良好的水分散性。在440 nm和540 nm波长光激发下分别呈现绿色(500 nm)和橙色(590 nm)双波段荧光发射。合成的荧光碳点发光性能对pH值具有敏感性:在强碱性溶液中,590 nm的荧光强度比水溶液中提高了6.71倍,同时吸收峰的蓝移使得自然光下其溶液颜色发生了明显改变,具有强碱性指示剂的作用;在pH值为2～6的酸性溶液中,500 nm与590 nm发光峰强度比与pH值之间呈现良好的线性关系,展现了作为pH值比率荧光探针的应用潜力。     

碳量子点/曙红Y比率型荧光探针测定L-抗坏血酸

以天然生物质去皮的蓖麻为碳源,采用一步水热法合成了荧光性能优良的绿色荧光蓖麻碳量子点(CO-CQDs),对其形貌和发光性能进行了表征。通过将该CO-CQDs与荧光极强的卤代荧光素染料曙红Y(EY)复合,二者可形成荧光发射峰相距较远的新型CO-CQDs/EY复合物。在pH=4.00的Na₂HPO₄-柠檬酸缓冲溶液中,在320 nm的激发波长下,CO-CQDs/EY复合物于405 nm和540 nm处显示出两个独立的荧光发射峰。在该体系中加入Cr(Ⅵ),405 nm和540 nm两处的荧光信号均显著猝灭。L-抗坏血酸(L-ascorbic acid,AA)的加入可使复合物于540 nm的荧光信号恢复,而405 nm处的荧光强度基本不变。据此建立了一种以CO-CQDs/EY复合物为比率型荧光探针测定AA的新方法。实验测定了荧光信号恢复的最佳条件和影响荧光恢复的因素,初步探讨了反应机理。在优化的实验条件下,该探针于540 nm/405 nm两处的荧光强度比值与AA的浓度在5.0×10^-8～4.0×10^-6 ...     

比率型碳点荧光传感器检测机理与应用研究进展

比率型荧光传感器由于具有抗干扰能力强和灵敏度高等优点,在食品安全、金属离子检测、环境污染分析等许多领域显示出巨大的应用潜力。而碳点作为一种新型荧光材料,不仅具有优良的荧光性能,而且毒性低、易于表面功能化,非常适合构建比率型荧光传感器。本文就近年来比率型碳点荧光传感器在检测领域的研究进展进行综述,重点阐述了碳点的荧光检测机理,并根据碳点使用情况的不同,对不同类型的比率型碳点荧光传感器进行了分类总结。最后提出了该领域亟待解决的困难和问题,并对其在分析物检测方面的发展方向进行了展望。     

Toward Uniform Optical Properties of Carbon Dots

Carbon dots possess versatile optical properties that have prompted their investigation in applications including photocatalysis, photovoltaics, imaging, and drug delivery, among others. However, the preparation of these nanodots is accompanied by the formation of fluorophores and intermediates, which can be difficult to separate. In the absence of thorough purification protocols, the reported optical properties are often heterogeneous, which hinders understanding of their physicochemical and optical properties and concrete application development. Here, two hydrophilic carbon dot systems starting with citric acid and diethylenetriamine are prepared. The impact of purification, including dialysis, ultrafiltration, and organic washes, on the properties of the dots is demonstrated. It is shown that monitoring the purification endpoint using near-infrared, fluorescence, and absorbance spectroscopies is possible. Moreover, it is demonstrated that fluorescence quantum yields can be a reliable tool to determine the purification endpoint. This work shows that even carbon dots derived from the same chemical precursors can have different purification profiles and purification requirements. However, the developed approach can be used to determine the proper purification procedure and endpoint for any carbon dot system regardless of the starting materials. Finally, it is envisioned that this work can be easily extended toward the purification of other hydrophilic nanomaterials.     

Large Scale Synthesis of Highly Stable Fluorescent Carbon Dots Using Silica Spheres as Carriers for Targeted Bioimaging of Cancer Cells

In this paper, fluorescent carbon dots (CDs) loaded on silica (SiO₂) spheres are synthesized by the one‐pot hydrothermal route, and then folic acids (FA) are covalently conjugated on the surface of SiO₂ spheres. The formed SiO₂@CDs‐FA composites can target specific tissues, e.g., cancer. The key of this method is the employment of (3‐aminopropyl)trimethoxysilane as bridge joint, which not only serves as surface passivation agents allowing the large scale synthesis of CDs with high quantum yield, but also enables SiO₂@CDs composites further covalent conjugation of FA. The resultant SiO₂@CDs composites have many advantages such as easy separation and purification, highly stable, well water‐soluble, and biocompatible. Moreover, the SiO₂@CDs‐FA could be used as fluorescent probes for biological imaging in vitro. The uptake of the SiO₂@CDs‐FA into HeLa cells is receptor‐mediated endocytosis, which is confirmed by a comparative study using FR‐negative 293T cells. Findings from this study suggest that the SiO₂@CDs‐FA composites could be used as a platform for cancer diagnosis studies in various biological systems.     

以醇溶剂为碳源制备碳点的荧光性能

以乙二醇和丙三醇为碳源,用一元醇（异丙醇和乙醇）为对比,通过溶剂热法制备得到碳点。通过傅里叶红外光谱、紫外-可见吸收光谱和激发光谱对所制得的碳点进行表征和分析,探讨了不同碳源对碳点的表面官能团、荧光性能等的影响,从而分析其荧光的发光机理。结果表明：乙二醇与丙三醇制备的碳点含有C=C键和C=O键,均在365 nm光激发后在450 nm处有荧光峰;而一元醇是由C-OH基团中的孤对电子产生荧光,碳源分子中羟基含量对碳点的荧光性能有很大影响,羟基含量越高,越容易形成双键结构。     

Metal Nanoclusters–Based Ratiometric Fluorescent Probes from Design to Sensing Applications

Ratiometric fluorescent probes have many advantages including improved sensitivity, high reliability and accuracy, visualization sensing, etc. Herein, the development of metal nanoclusters (NCs)‐based ratiometric fluorescent probes in the recent years is summarized. NCs, an emerging new class of fluorescent nanomaterials, have demonstrated excellent optical properties, good biocompatibility, great aqueous solubility, low cost, and simple synthesis, and NCs‐based ratiometric fluorescent probes have attracted much attention. In this progress report, the preparation and properties of NCs and the design of ratiometric fluorescent probes are summarized. Sensing of a broad range of analytes including cations, gas, small molecules, macromolecules, temperature, and pH is discussed. In addition, the challenges and future directions for NCs‐based ratiometric fluorescent probes are also presented.     

氨基化碳量子点荧光猝灭法测定焦性没食子酸的研究

以葡萄糖为原料,通过一步水热法合成稳定性高的碳量子点,并用乙二胺使其表面氨基化。焦性没食子酸能使氨基化的碳量子点荧光明显猝灭,由此建立一种简便、高效检测焦性没食子酸的新方法。考察了缓冲体系p H、反应时间、反应温度等对焦性没食子酸测定的影响。结果表明,在pH=11.20的三酸缓冲溶液中,室温反应20 min时,体系的F0/F与焦性没食子酸的浓度呈良好的线性关系,其线性范围为4.0×10~(-6)~9.0×10~(-5)mol·L~(-1),相关系数r=0.997 4,检出限为3.5×10~(-6)mol·L~(-1)。该方法快速简便,适用于水样中焦性没食子酸的检测。     

Nonlinear Optics to Glucose Sensing: Multifunctional Nitrogen and Boron Doped Carbon Dots with Solid-State Fluorescence in Nanoporous Silica Films

Multifunctional triple color photoluminescent (PL) nitrogen–boron doped carbon quantum dots (CQDs) with high quantum yield (QY) of 58% are fabricated by one step femtosecond pulsed laser irradiation of a single precursor (2-aminopyrimidine-5-boronic acid) in solution. In situ generated non-linear and linear emissions are used to monitor CQDs formation which results in enhanced second harmonic generation, two photon absorption (2PA), and linear fluorescence; implying triple mode emission. These CQDs present blue, green, and possible red color rendering which are mostly independent to the respective excitation wavelengths (λ) with large stokes shift of 100 nm. Solid-state photoluminescence with QY of 46% is achieved by incorporating CQDs into thin transparent nanoporous silica (pSiO₂) films (thickness 50 µm) to form a CQDs-pSiO₂ composite which exhibits reverse saturable absorption at λ = 800 nm with 2PA coefficient and excited state absorption cross-section of 4.94 × 10⁻¹⁰ m W⁻¹ and 6.23 × 10⁻¹⁷ cm², respectively. CQDs-pSiO₂ is also sensitive to glucose concentration down to 1.0 mg dL⁻¹ in a wide linear range up to 100 mg dL⁻¹. This work therefore demonstrates facile, controllable, and up-scalable bottom-up fabrication of CQDs forming multifunctional solid-state CQDs-pSiO₂ with proven application in optical limiting and glucose sensing.     

碳量子点荧光猝灭法测定饮料中日落黄

以柠檬酸为碳源制备碳量子点(CQDs),所得碳量子点被394 nm的光激发后在484 nm处有较强的荧光发射,最大吸收波长为482 nm的日落黄能强烈猝灭碳量子点的荧光。基于该现象,发展了一种以碳量子点为荧光探针测定日落黄的分析方法,并探讨了荧光猝灭机理。在选定的实验条件下,该分析方法的线性检测范围为0.1~100μmol/L,检出限(3σ/k)为0.051μmol/L。     

基于碳量子点荧光恢复的三聚氰胺测定方法

在碳量子点溶液中加入汞离子,量子点的荧光被猝灭,加入三聚氰胺后荧光恢复。据此,建立了基于碳量子点荧光恢复测定三聚氰胺的新方法并应用于实际样品的分析。研究结果表明,在汞离子和碳量子点浓度之比为15∶10000且碳量子点浓度为4.0 g/L、pH值为7.5的实验条件下,方法的线性范围为3.0~60.0mg/L,检出限(3σ/k)为2.2 mg/L。方法应用于实际样品测定时,其回收率为95%~103%。     

Synthesizing Red Fluorescent Carbon Dots from Rigid Polycyclic Conjugated Molecules: Dual-Mode Sensing and Bioimaging in Biochemical Applications

Red fluorescent carbon dots (R-CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp² domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5-diamino-4,8-dihydroxyanthraquinone (DDAQ), based self-doped R-CDs with PL emission at 635 nm is reported. Further investigations reveal that the expanding, hybrid sp² domain with indanthrone tannin structure from DDAQ is mainly responsible for the obtained red fluorescence of R-CDs. Taking advantage of optical properties, R-CDs are considered to construct a colorimetric/fluorescent dual mode sensing array for quantifying trace levels of Fe³⁺ and glyphosate based on the static quenching, and a biomarker for cell imaging. The CD-based sensors exhibit outstanding recovery, high selectivity, and sensitivity, also facilitated dual-mode detection with the naked-eye. The R-CDs have low cytotoxicity, good cell membrane penetration for rapid cell entry, and high resolution, demonstrating their potential for biolabeling and bioanalytic applications.     

Cyclodextrin Functionalized Carbon Dots Using IFE and FRET Dual Mechanism for Sequential Detection of Morin and Al3+

Carbon dots (CDs) are emerging photoluminescent materials with excellent optical properties. However, the lack of active sites in primitive CDs has limited their development applications. Herein, functionalized carbon dots (Z-CDs) are successfully prepared by surface modification of CDs with mono (6-amino-6-deoxy) cyclodextrin (β-CD). The introduction of β-CD increases the spatial potential resistance between CDs, which effectively reduces the self-quenching effect. Moreover, the conjugated domains of Z-CDs are expanded, which improves the optical properties with a quantum yield of 48.74%. Z-CDs are able to be used in the sequential detection of morin and Al³⁺, and the fluorescence mechanisms are confirmed to be internal filtration effect and fluorescence resonance energy transfer, respectively. The limits of detection are 0.817 and 0.231 × 10⁻⁶ m . This study not only provides an idea to solve the problem of self-quenching of CDs but also enriches the detection means of flavonoids and ions, which is expected to be applied to biosensing and environmental monitoring.     

基于谷胱甘肽配体的ZnSe量子点对pH响应的时间分辨荧光光谱特性

当前,有关量子点pH响应方面的研究主要集中在含Cd（镉）类量子点,且都是研究其稳态荧光光谱对pH值的响应。然而,Cd类量子点对生物体系具有一定的毒性,且稳态荧光光谱法由于受浓度等因素的影响具有一定的不稳定性,因此应用于生物体系中作为pH探针具有明显的缺点。基于以上分析,通过水相合成法,我们制备出了基于谷胱甘肽配体的水溶性ZnSe量子点,该量子点具有毒性小,生物兼容性好等特点,适合被应用于生物体系中。利用所制备的ZnSe量子点,采用时间相关单光子计数技术,结合紫外可见吸收光谱和稳态荧光光谱,对pH值在5~11不同环境下的ZnSe量子点荧光动力学进行了系统性的研究。ZnSe量子点荧光衰减具有两个寿命组分,拟合得到分别为4和24 ns。通过采集不同探测波长下ZnSe量子点荧光衰减曲线,发现其长寿命组分随探测波长的增加而增加,而短寿命组分基本不随探测波长的改变而改变,结合有关报道分析判断,短寿命和长寿命组分分别来源于核内非局域载流子复合和表面态局域载流子复合。实验发现,处于不同pH值的环境下的ZnSe量子点具有不同的荧光寿命,其荧光寿命与pH值的变化呈负相关。通过比较ZnSe量子点两种荧光寿命组分随pH值的变化关系,发现ZnSe量子点的荧光寿命对pH值的响应主要来源于长寿命组分即表面态寿命,且在不同pH值范围内响应的灵敏度不同,在6~8的pH值范围内响应最为显著,表现为长寿命组分随pH值的增加出现一个较大幅度的衰减。实验进一步发现,ZnSe量子点两个寿命组分的比值在不同pH值范围内具有较好的线性相关性,但在不同pH值范围内斜率不同,通过比较,最大值在pH值为6~8的范围内。另外,与金属钠离子相互作用实验及相关报道表明,金属离子对ZnSe量子点荧光寿命的影响较小。以上研究表明,ZnSe量子点在生物体系pH值检测中具有良好的应用前景。     

Role of Acids in Producing Ultrabright,Dual-Emissive Carbon Dots and their Urea/Biuret Composites with Ultralong Afterglow

Since 2015, m-phenylenediamines (mPD) have become a popular carbon source for the synthesis of carbonized polymer dots (CPDs). However, their exact fluorescence mechanism is still obscure. To elucidate this, inorganic acids that are carbon-free are chosen as additives for a comparative study. It is found that the green fluorescence quantum yield (nearly 80%), photostability, and reaction yield (over 90%) can be enhanced by introduction of most of inorganic acids with moderate amount. Besides, green-blue dual emission is observed in acid-assisted groups. UV-vis absorption, Fourier-transform infrared spectroscopy, and surface-enhanced Raman scattering results indicate that the green fluorescence center is composed of quinoid rings, whereas the blue fluorophore contains benzenoid rings. Moreover, room-temperature afterglow with lifetime up to 1.25 s is observed exclusively in acid-assisted CPDs composites with urea/biuret. The blue chromophore is proposed to be the origin of the triplet level that induces the long afterglow. This work provides an in-depth understanding on the macromolecular structures of CPDs derived from phenylenediamines, and contributes a new line of thought to the origin of phosphorescence in N-doped carbon dots.