Ultrasmall near-infrared Ag2Se quantum dots with tunable fluorescence for in vivo imaging

A strategy is presented that involes coupling Na(2)SeO(3) reduction with the binding of silver ions and alanine in a quasi-biosystem to obtain ultrasmall, near-infrared Ag(2)Se quantum dots (QDs) with tunable fluorescence at 90 °C in aqueous solution. This strategy avoids high temperatures, high pressures, and organic solvents so that water-dispersible sub-3 nm Ag(2)Se QDs can be directly obtained. The photoluminescence of the Ag(2)Se QDs was size-dependent over a wavelength range from 700 to 820 nm, corresponding to sizes from 1.5 ± 0.4 to 2.4 ± 0.5 nm, with good monodispersity. The Ag(2)Se QDs are less cytotoxic than other nanomaterials used for similar applications. Furthermore, the NIR fluorescence of the Ag(2)Se QDs could penetrate through the abdominal cavity of a living nude mouse and could be detected on its back side, demonstrating the potential applications of these less toxic NIR Ag(2)Se QDs in bioimaging.     

Preparation and characterization of thiacalix[4]arene coated water-soluble CdSe/ZnS quantum dots as a fluorescent probe for Cu2+ ions

Highly fluorescent water-soluble CdSe/ZnS (core/shell) quantum dots (QDs) as a fluorescent Cu2+ ion probe were synthesized using thiacalix[4]arene carboxylic acid (TCC) as a surface coating agent. Hydrophobic trioctylphosphine oxide (TOPO) capped CdSe/ZnS QDs were overcoated with TCC in tetrahydrofuran at room temperature, and deprotonation of the carboxyl groups of TCC resulted in the formation of water-soluble QDs. The surface structure of the QDs was characterized by using transmission electron microscopy (TEM) and fluorescence correlation spectroscopy (FCS). TEM images showed that TCC-coated QDs were monodispersed with the particle size (core-shell moiety) of approximately 5 nm. Hydrodynamic diameter of the TCC-coated QDs was determined to be 8.9 nm by FCS, showing that the thickness of the surface organic layer of the QDs was approximately 2 nm. These results indicate that the surface layer of TCC-coated QDs forms a bilayer structure consisting of TOPO and TCC molecules. TCC-coated CdSe/ZnS QDs were highly fluorescent (quantum yield, 0.21) compared to the QDs surface-modified with mercaptoacetic acid and mercaptoundecanoic acid. Fluorescence of the TCC-coated QDs was effectively quenched by Cu2+ ions even in the presence of other transition metal ions such as Cd2+, Zn2+, Co2+, Fe2+, and Fe3+ ions in the same solution. The Stern-Volmer plot for the fluorescence quenching by Cu2+ ions showed a linear relationship up to 30 microM of Cu2+ ions. The ion selectivity of TCC-coated QDs was determined by measurements of fluorescence responses towards biologically important transition metal ions (50 microM) including Fe2+, Fe3+, Co2+>Zn2+, Cd2+. The fluorescence of TCC-coated QDs was almost insensitive to other biologically important ions such as Na+, K+, Mg2+, and Ca2+, suggesting that TCC-coated QDs can be used as a fluorescent Cu2+ ion probe for biological samples. A possible quenching mechanism by Cu2+ ions was also discussed on the basis of a Langmuir-type adsorption isotherm.     

Silver(I) ions and cysteine detection based on photoinduced electron transfer mediated by cytosine-Ag(+)-cytosine base pairs

Upon formation of cytosine-Ag(+)-cytosine base pairs as a mediator for the photoinduced electron transfer, the fluorescence of FAM-labeled DNA was quenched and the fluorescence emission wavelength exhibited a red shift. Based on these phenomena a novel dual-output fluorescent DNA sensor for Ag(+) ions and cysteine detection was developed.     

Silver(I)-selective membrane electrodes based on sulfur-containing podands

Some podands, acyclic polyethers, were utilized as membrane active components to prepare Ag(+)-selective polymeric membrane electrodes. The thiapodand-based electrodes exhibited considerable selectivity toward Ag(+) over other heavy metal ions including Cd(2+), Pb(2+), Cu(2+) and Hg(2+). Also, good selectivity over alkali and alkali earth metal ions were observed. Response slopes, pH effects, response time, and signal baseline return of the sensor systems were studied in static mode and/or in a flow-injection system. The Ag(+)-selectivity was explained by the soft-soft interaction of the Ag(+) ion with the sulfur donor atoms as well as the stacking interaction between aromatic end groups of the host molecule on complexation.     

Nanoparticles as scaffolds for FRET-based ratiometric detection of mercury ions in water with QDs as donors

The quenching of quantum dots' emission by some analytes (Hg(2+), Pb(2+), etc.) has long been hindering the fabrication of QD-based 'turn-on' or ratiometric fluorescent sensors for these analytes. In this study, we demonstrate a facile solution for constructing a robust FRET-based ratiometric sensor for Hg(2+) detection in water with CdTe QDs as the donor. By using the reverse microemulsion approach, CdTe QDs were first embedded into nanosized silica particles, forming the QDs/silica cores, a positively charged ultrathin spacer layer was then deposited on each QDs/silica core, followed by the coating of a mercury ion probe on the particle surfaces. The resultant multilayered QDs/silica composite nanoparticles are dispersible in HEPES buffered water; and in the presence of mercury ions, the QDs inside the nanoparticles will not be quenched by mercury ions due to the existence of the positively charged spacer layer, but can transfer their excited energy to the acceptors (probe/Hg(2+) complex), thus achieving the FRET-based ratiometric sensing for mercury ions in totally aqueous media. With its detection limit of 260 nM, this QD-based sensor exhibits high selectivity toward mercury ion and can be used in a wide pH range. This strategy may be used to construct QDs-based ratiometric assays for other ions which quench the emission of QDs.     

Study of fluorescence quenching and dialysis process of CdTe quantum dots, using ensemble techniques and fluorescence correlation spectroscopy

Luminescence properties of quantum dots (QDs) are closely related to their surface structure and chemical properties. In this work some ensemble techniques and fluorescence correlation spectroscopy (FCS) were used to study the fluorescence quenching and dialysis process of CdTe QDs. It is found that when some heavy metal ions, such as silver ions (Ag+), quench QDs, the free Ag+ ions bind with bare Te atoms and form the AgTe structure on the surface. The FCS experimental results show that the quenching process is not the gradual reduction of fluorescence intensity of single QDs, but the decrease in the number of bright QDs with the addition of Ag+ ions. In other words, the bright QDs turn into dark directly in the quenching process. It is observed that some dark QDs converse into the bright QDs in the dialysis experiments and the dialysis process can improve the brightness per QDs. Furthermore, the results of FCS and fluorescence spectroscopy illustrate that the increase of the fluorescence quantum yield (QY) is mainly attributed to the removal of excess unreacted Cd-MPA complex and the possible chemical change of the QDs surface in the dialysis process. These new results can help us to further understand the complex surface structure of water-soluble QDs, improve their surface chemical features, and expand their applications in some fields.     

Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg(2+), Cu(2+), Co(2+), and Ni(2+), exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg(2+) and Cu(2+) ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag(+) ion ranging from 1.25 x 10(-7) to 5.0 x 10(-6)molL(-1) with a detection limit of 2.0 x 10(-8)molL(-1). The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern-Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 x 10(-8) to 7.50 x 10(-7)molL(-1) for Hg(2+) ion, 3.0 x 10(-7) to 1.0 x 10(-5)molL(-1) for Ni(2+) ion, 4.59 x 10(-8) to 2.295 x 10(-6)molL(-1) for Cu(2+) ion, and 1.20 x 10(-7) to 6.0 x 10(-6)molL(-1) Co(2+) ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.     

Synthesis and Characterization of ZnS：Ag Nanocrystals Surface-capped with Thiourea

Ag^＋ -doped ZnS nanocrystals surface-capped with thiourea （expressed as ZnS： Ag/thiourea） were synthesized through sol-gel method with thiourea as a surface modifier and characterized by X-ray diffraction（XRD）, transmission electron microscope（TEM）, X-ray fluorescence spectrum（XRF）, infrared spectrum （IR）, UV-Vis absorption spectrum（ UV-Vis）, and photoluminescence spectrum（PL）. The results show that Ag^＋ ions are doped in ZnS nanocrystals, and the sulfur atoms in thiourea molecules coordinate with metal ions on the surface of the nanocrystals. The spherical ZnS： Ag/thiourea nanocrystals with an average diameter of 5 nm have good fluorescent characteristics, and therefore have great potential for use in molecular assembly and novel luminescence materials.     

Salicylimine-based fluorescent chemosensor for aluminum ions and application to bioimaging

In this study, an assay to quantify the presence of aluminum ions using a salicylimine-based receptor was developed utilizing turn-on fluorescence enhancement. Upon treatment with aluminum ions, the fluorescence of the sensor was enhanced at 510 nm due to formation of a 1:1 complex between the chemosensor and the aluminum ions at room temperature. As the concentration of Al(3+) was increased, the fluorescence gradually increased. Other metal ions, such as Na(+), Ag(+), K(+), Ca(2+), Mg(2+), Hg(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Pb(2+), Cr(3+), Fe(3+), and In(3+), had no such significant effect on the fluorescence. In addition, we show that the probe could be used to map intracellular Al(3+) distribution in live cells by confocal microscopy.     

硫鸟嘌呤修饰的Mn:ZnS QDs磷光探针检测铂(Ⅲ)

通过水相合成法制备了硫鸟嘌呤(TG)修饰的锰掺杂硫化锌量子点(TG-Mn:ZnS QDs)。加入Pt⁴⁺后,Pt⁴⁺会与硫鸟嘌呤上的氮原子结合形成N-Pt⁴⁺配位结构附着在TG-Mn:ZnS QDs的表面,随着Pt⁴⁺浓度的增加,TG-Mn:ZnS QDs-Pt⁴⁺体系发生电子转移而导致磷光逐渐被猝灭,基于此构建了检测Pt⁴⁺的磷光探针。实验中考察了p H、时间对Pt⁴⁺猝灭TG-Mn:ZnS QDs磷光强度的影响。在最佳实验条件下,Pt⁴⁺浓度在0.06～2.4μg/mL范围内与TG-Mn:ZnS QDs的磷光强度呈良好的线性关系y=0.0884x+0.2319,R²=0.991,方法检出限(3σ/n)为1.3μg/mL。该磷光探针适用于实际样品中Pt⁴⁺含量的测定。     

Terphenyl-phenanthroline conjugate as a Zn(2+) sensor: H(2)PO(4)(-) induced tuning of emission wavelength

A new terphenyl-based macrocycle 5 incorporating phenanthroline as a fluorophore has been designed, synthesized and examined for its recognition ability toward various cations (Pb(2+), Hg(2+), Ba(2+), Cd(2+), Ag(+), Zn(2+), Cu(2+), Ni(2+), Co(2+), K(+), Mg(2+), Na(+) and Li(+)) by UV-vis, fluorescence and NMR spectroscopy. The receptor 5 showed highly selective 'Off-On' fluorescence signaling behavior for Zn(2+) ions in THF. Interestingly, the addition of H(2)PO(4)(-) ions to the [5-Zn] complex regulates the binding site for additional Zn(2+) ions and hence leads to a blue-shifted emission band.     

A Convenient “Turn On-off” Phosphorescent Nanosensor for Detection of Biotin Based on Quantum Dots/CTAB

A switchable room-temperature phosphorescence(RTP) nanosensor based on an MPA-capped Mn-doped ZnS QDs/CTAB composite system(MPA=3-mercaptopropionic acid; CTAB=cetyltrimethyl ammonium bromide; QDs=quantum dots) was established for the detection of biotin. The phosphorescence intensity of QDs/CTAB could be regularly quenched with the increase of biotin. Under optimal conditions, this method yielded two linear ranges of 2-20 μg/L and 20-140 μg/L with respective correlation coefficients of 0.993 and 0.990, as well as a detection limit of 0.93 μg/L. Therefore, the analytical potential of the proposed nanosensor was evaluated by detecting biotin in urine and biotin tablets. This approach yielded satisfactory results because of the effective elimination of background fluorescence and light scattering from the sample matrix. This approach provides a practical method for biotin detection.     

Synthesis of Multifunctional Mn‐Doped CdTe/ZnS Core/Shell Quantum Dots

The synthesis of a novel water‐soluble Mn‐doped CdTe/ZnS core‐shell quantum dots using a proposed ultrasonic assistant method and 3‐mercaptopropionic acid (MPA) as stabilizer is descried. To obtain a high luminescent intensity, post‐preparative treatments, including the pH value, reaction temperature, reflux time and atmosphere, have been investigated. For an excellent fluorescence of Mn‐doped CdTe/ZnS, the optimal conditions were pH 11, reflux temperature 100°C and reflux time 3 h under N₂ atmosphere. While for phosphorescent Mn‐doped CdTe/ZnS QDs, the synthesis at pH 11, reflux temperature 100°C and reflux time 3 h under air atmosphere gave the best strong phosphorescence. The characterizations of Mn‐doped CdTe/ZnS QDs were also identified using AFM, IR, powder XRD and thermogravimetric analysis. The data indicated that the photochemical stability and the photoluminescence of CdTe QDs are greatly enhanced by the outer inorganic ZnS shell, and the doping Mn²⁺ ions in the as‐prepared quantum dots contribute to strong luminescence. The strong luminescence of Mn‐doped CdTe/ZnS QDs reflected that Mn ions act as recombination centers for the excited electron‐hole pairs, attributing to the transition from the triplet state (⁴T₁) to the ground state (⁶A₁) of the Mn²⁺ ions. All the experiments demonstrated that the surface states played important roles in the optical properties of Mn‐doped CdTe/ZnS core‐shell quantum dots.     

Zn_(0.15)Cd_(0.85)S量子点复合材料的合成及其对Cu~(2+)的超灵敏测定

合成了高质量的半胱氨酸修饰Zn0.15Cd0.85S量子点复合材料.利用Cu2+对量子点荧光的猝灭作用,实现了Cu2+的定量检测.所合成的Zn0.15Cd0.85S量子点对其他常见的金属离子几乎没有响应,表明该方法具有较好的选择性.在优化条件下,Zn0.15Cd0.85S量子点荧光的猝灭程度与Cu2+浓度呈良好的线性关系,线性范围为6.0nM～1.0μM,检出限为1.0nM.对0.5μM标准溶液平行测定11次,相对标准偏差为2.0%.利用标准加入法对水样中Cu2+含量进行了测定,结果令人满意.     

Chemiluminescent and chemiluminescence resonance energy transfer (CRET) detection of DNA, metal ions, and aptamer-substrate complexes using hemin/G-quadruplexes and CdSe/ZnS quantum dots

Nucleic acid subunits consisting of fragments of the horseradish peroxidase (HRP)-mimicking DNAzyme and aptamer domains against ATP or sequences recognizing Hg(2+) ions self-assemble, in the presence of ATP or Hg(2+), into the active hemin-G-quadruplex DNAzyme structure. The DNAzyme-generated chemiluminescence provides the optical readout for the sensing events. In addition, the DNAzyme-stimulated chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs) is implemented to develop aptamer or DNA sensing platforms. The self-assembly of the ATP-aptamer subunits/hemin-G-quadruplex DNAzyme, where one of the aptamer subunits is functionalized with CdSe/ZnS QDs, leads to the CRET signal. Also, the functionalization of QDs with a hairpin nucleic acid that includes the G-quadruplex sequence in a 'caged' configuration is used to analyze DNA. The opening of the hairpin structure by the target DNA assembles the hemin-G-quadruplex DNAzyme that stimulates the CRET signal. By the application of three different sized QDs functionalized with different hairpins, the multiplexed analysis of three different DNA targets is demonstrated by the generation of three different CRET luminescence signals.     

A squaraine-based colorimetric and "turn on" fluorescent sensor for selective detection of Hg2+ in an aqueous medium

A novel squaraine-based chemosensor SQ-1 has been synthesized, and its sensing behavior toward various metal ions was investigated by UV-vis and fluorescence spectroscopies. In AcOH-H(2)O (40:60, v/v) solution, Hg(2+) ions coordinate with SQ-1 causing a deaggregation which induces a visual color and absorption spectral changes as well as strong fluorescence. In contrast, the addition of other metals (e.g., Pb(2+), Cd(2+), Cu(2+), Zn(2+), Al(3+), Ni(2+), Co(2+), Fe(3+), Ca(2+), K(+), Mg(2+), Na(+), and Ag(+)) does not induce these changes at all. Thus SQ-1 is a specific Hg(2+) sensing agent due to the inducing deaggregation of the dye molecule by Hg(2+).     

ZnS∶Co半导体量子点的制备及其光电化学性质

采用低温水热技术,分别以柠檬酸(CA)和巯基丙酸(MPA)为稳定剂,在70℃的水相中合成了单分散的,粒子尺寸约为4 nm的ZnS∶Co半导体量子点.研究了稳定剂、Co2+掺杂剂及其掺杂量对掺杂量子点发光性能和结构的影响.XRD结果表明,Co2+离子主要掺杂在量子点表面,对主体ZnS晶格没有影响.当采用MPA为稳定剂,掺杂量为5%(摩尔分数)时,掺杂量子点的荧光发射强度最高;而同样掺杂量下采用CA为稳定剂时,量子点的荧光发射强度有所下降.循环伏安研究显示,与空白ZnS量子点相比,Co2+离子的掺杂在ZnS的禁带中形成杂质能级,相应地,ZnS∶Co量子点的吸收边发生红移.与未掺杂ZnS量子点相比,掺杂量子点具有较少的表面非辐射复合中心,因而荧光发射强度显著提高.     

Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots

Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365 nm) photolysis, the PL intensity augmented to ~170% and attained a saturation value after ~100 min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200 °C) and pressures (~120 bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.     

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.     

The molecular recognition of tetra(p-t-butyl)tetrathiocalix[4]arene and its derivatives to heavy metal ions

The molecular recognition of tetra(p-t-butyl)tetrathiocalix[4]arene (I)and its three derivatives to heavy metal ions has been investigated by UV spectroscopy and solvent extraction. These derivatives include 5,11,17,23,-tetra-t-butyl-25,26,27,28-tetrakis(acetylmethoxy)tetrathiocalix[4]arene (II), 5,11,17,23-tetra-t-butyl-25,26,27,28-tetrakis(2'-hydroxypropyloxy) tetrathiocalix[4]arene (III), 5,11,17,23,-tetra-t-butyl-25,27-bis(3'-hydroxy propyloxy)tetrathiocalix[4]arene (IV). The UV spectra and solvent extraction of I show that it has an effective molecular recognition to heavy metal ions, especially to Cd(2+), while IV has a special molecular recognition to Ag(+) ion. These results confirmed the feasibilities for I to be applied in separation for toxic heavy metal ions Pb(2+), Cd(2+) and IV to be used as the sensor compound of Ag(+) ion-selective electrode.