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.     

A Novel Fluorescent Silver Ion Biosensor Based on Nucleic Acid Molecular “Light Switch”

As one of nucleic acid molecular “light switch”, Ru(bipy)₂(dppx)²⁺ is a good probe for the determination of double-helical DNA, which displays intense fluorescence when double-helical DNA is present. However, the fluorescence of Ru(bipy)₂(dppx)²⁺ is quenched when Ag⁺ is added to the Ru(bipy)₂(dppx)²⁺-DNA system. Based on the quenching of the fluorescence of Ru(bipy)₂(dppx)²⁺-DNA system by Ag⁺, a simple, rapid and specific method for Ag⁺ determination was proposed. In the optimum conditions, Ag⁺ concentration versus Ru(bipy)₂(dppx)²⁺ fluorescence intensity gave a linear response in the range from 0.2 to 6.0 μM with a detection limit (3σ) of 3.2 × 10⁻⁸ M. The proposed method has been applied to determine the Ag⁺ in water samples and sulfadiazine silver cream successfully. Because of the intense fluorescence of Ru(bipy)₂dppx²⁺ when DNA is present, the interaction between Ag⁺ and DNA was confirmed by fluorescence microscopy and the phenomenon of the fluorescence images agreed well with the results. The possible mechanism of the reaction was also discussed by circular dichroism spectra and isothermal titration calorimetry.     

Novel Turn-on Fluorescence Probes for Al<Superscript>3+</Superscript> Based on Conjugated Pyrazole Schiff Base

One novel turn-on fluorescence probe founded on conjugated pyrazole Schiff base for detecting Al³⁺ was invented. The UV–vis and fluorescence spectrometer were employed to explore optical properties of this probe. The results got from those experiments indicated that this fluorescence probe manifested excellent sensitivity and selectivity for Al³⁺ compared with other cations examined(Ag⁺, Co²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Pb²⁺,and Zn²⁺). In addition, this probe displayed a more rapid response and remained stable between pH 6 and 9 by investigating the fluorescence intensity under different response time and various pH values. Remarkably, the detection limit for Al³⁺ could lower to 1.0×10^?9M. Therefore, the probe could be potentially applied to the environment for the detection of Al³⁺, and the availability in biological range of pH that could be further studied to make this probe apply to biological systems in the future.     

A Pyrene-based Highly Selective Turn-on Fluorescent Sensor for Copper(II) Ion and its Application in Live Cell Imaging

A new pyrene derivative (chemosensor 1) containing a picolinohydrazide moiety exhibits high selectivity for Cu²⁺ ion detection in mixed aqueous media (CH₃OH:H₂O = 7:3). Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence for the system. The apparent association constant (K _a) of Cu²⁺ binding in chemosensor 1 was found to be 2.75*10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5–8. Moreover, by means of fluorescence microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for detecting Cu²⁺ in living cells.     

Ag+掺杂的立方相Y2O3:Eu纳米晶体粉末发光强度研究

采用化学自燃烧法制备了不同Ag⁺掺杂浓度的Y₂O₃:Eu纳米晶体粉末样品(［Y³⁺］∶［Eu³⁺］∶［Ag⁺］=99∶1∶X，X=0—3.5×10^-2)，以及通过退火处理得到了相应的体材料.根据X射线衍射谱确定所得纳米和体材料样品均为纯立方相.实验表明在纳米尺寸样品中随着Ag离子浓度的增加，荧光发射强度随之增加，当X=2×10^-2时达到最大值，其发光强度比X=0时提高了近50%.当Ag离子浓度继续增加，样品发光强度保持不变.在相应的体材料样品中则没有观察到此现象.通过对各样品的发射光谱，激发光谱，X射线衍射图谱，透射电镜(TEM)照片和荧光衰减曲线的研究，分析了引起纳米样品荧光强度变化的原因是由于Ag离子与表面悬键氧结合，从而使这一无辐射通道阻断，使发光中心Eu³⁺的量子效率提高；Ag⁺的引入所带来的另一个效应是使激发更为有效.这两方面原因使发光效率得到了提高.     

A Dual-emitting Two-dimensional Nickel-based Metal-organic Framework Nanosheets: Eu3+/Ag+ Functionalization Synthesis and Ratiometric Sensing in Aqueous Solution

Using two-dimensional (2D) nickel-based metal organic framework (Ni-MOF) nanosheets as a matrix, Eu³⁺ and Ag⁺ were incorporated to synthesize Ag/Eu@Ni-MOF with double luminescence centers of Eu³⁺ ion (615 nm) and organic ligand (524 nm). And a ratiometric luminescence sensor is constructed based on Ag/Eu@Ni-MOF for sensitive detection of biothiols in aqueous solutions. The dual-emissive fluorescence properties can be tuned by changing the amounts of Ag⁺ ions doping. The results of temperature and pH effects on the fluorescence of Ag/Eu@Ni-MOF indicates that the Ag/Eu@Ni-MOF is a temperature-sensitive material and the fluorescence of Ag/Eu@Ni-MOF can keep stable over a wide pH range. Due to the binding of -SH in cysteine (Cys) and glutathione (GSH) with Ag⁺, the ligand luminescence was significantly inhibited by weakening the Ag?+?influence on the energy transfer process in the MOFs. Therefore, ratiometric fluorescent sensing of biomolecular thiols was realized based on the dual-emission Ag/Eu@Ni-MOF. More importantly, the fluorescence color change can be observed with naked eyes to realize visual detection. The ratiometric fluorescent sensor exhibits high performance for Cys and GSH detection with a wide linear range of 5-250 µM and a relatively low detection limit of 0.20 µM and 0.17 µM, respectively. Furthermore, the biothiols content in human serum was determined with satisfactory results. It proves the Ni-MOF nanosheets can be used as a stable matrix for construction luminescent MOFs for the first time, and validate the great potential of Ag/Eu@Ni-MOF as a ratiometric fluorescent probe for point-of-care testing (POCT) in disease diagnosis.

     

A Label-Free Oligonucleotide Based Thioflavin-T Fluorescent Switch for Ag<Superscript>+</Superscript> Detection with low Background Emission

A novel fluorescent Ag⁺ sensor was developed based on the label-free silver (I) specific oligonucleotide (SSO) and Thioflavine T (ThT) monomer-excimer switch. C-rich SSO which contain C-C mismatched base pairs can selectively bind to Ag⁺ ions and the formed duplexes which constructed by C-Ag⁺-C structure are thermally stabilized without largely altering the double helical structure. ThT give very weak fluorescent in bulk solution and/or in the presence of SSO. However ThT shows high fluorescence in the presence of SSO and Ag⁺ at the same time mainly because ThT excimer, which has the high quantum yield, formed and stabilized in the minor or major groove. Based on the discovery, we developed the novel Ag⁺ sensor. Under the optimum condition, the selectivity of this system for Ag⁺ over other metal ions in aqueous solution is remarkably high, and Ag⁺ can be quantified over the dynamic range of 30–450 nM, with a limit of detection of ~16 nM and a linear correlation coefficient of 0.995.     

Dye‐Sensitized Core/Shell Upconversion Nanoparticles for Detecting Nitrites in Plant Cells

A fluorescent nanoprobe is reported for rapid detection of nitrites (NO₂^?) in plant cells. The probe is fabricated by linking neutral reds (NR) to the surface of upconversion fluorescent core/shell nanocrystalline with the bridging of polyethylene glycol (PEG) molecules. The fluorescence of upconversion nanoparticles (UCNPs) is stored by NR through fluorescence resonance energy transfer (FRET) under 980 nm excitation that can be released by further linking to NO₂^?. It is observed that the intensity rate of green to red emission of NR‐modified UCNPs changes linearly with increasing the amount of NO₂^?. So that concentration of NO₂^? can be accordingly addressed. Worth mentioning is that, comparing with bare core upconversion nanoparticles (NPs), core/shell UCNPs can greatly reduce the surface quenching of the fluorescence induced by solvents instead of NR and thus leading to the enhancement of signal‐to‐noise ratios. Moreover, excitation of core/shell UCNPs requires only a much lower power (0.06 W cm^?2) than bare cores which is beneficial to reducing the decomposition of NR to stabilize the FRET processes. Under the optimum conditions, the detection limit of nitrite in plant cells was 0.1 µg mL^?1.     

Spectroscopic study of mono‐ and bis(styryl) dyes of the pyridinium series containing azathiacrown ether residue

Phenylazathiacrown ether monostyryl and bis(styryl) dyes were synthesized and their complex forming ability was evaluated in acetonitrile by absorption and fluorescence spectroscopy. It was found that dyes are sensitive to the presence of H⁺ and Hg²⁺, Ag⁺, Cu²⁺ cations. The most stable complexes were formed with mercury. Stability constants and UV–Vis spectra of complexes defined stoichiometry were determined with the use of HYPERQUAD program. Evidence was given for the occurrence of two stoichiometries: LM and LM₂. The pronounced optical response on complex formation was found both in absorption and emission spectra that could be used for optical detection of cations. Copyright © 2008 John Wiley & Sons, Ltd.     

Zn2+-Schiff’s Base Complex as an “On–Off-On” Molecular Switch and a Fluorescence Probe for Cu2+ and Ag+ Ions

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of Schiff’s base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H₂L) and its metal complexes with Zn²⁺, Cu²⁺ and Ag⁺ ions. This study aims to investigate the behavior of H₂L and the binuclear Zn²⁺ complex (1) as fluorescent probes for the detection of metal ions (Zn²⁺, Cu²⁺ and Ag⁺) using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The six conformers of the H₂L ligand were optimized using the B3LYP/6–311?+??+?G** level of theory, while the L^?2-metal complexes were optimized by applying the B3LYP functional with the LANL2DZ/6–311?+??+?G** mixed basis set. The gas-phase and solvated Enol-cis isomer (E-cis) was found to be the most stable species. The absorption spectra of the E-cis isomer and its metal complexes were simulated using B3LYP, CAM-B3LYP, M06-2X and ωB97X functionals with a 6–311?+??+?G** basis set for C, O, N and H atoms and a LANL2DZ basis set for the metal ions (Zn²⁺, Cu²⁺ and Ag⁺). The computational results of the B3LYP functional were in excellent agreement with the experimental results. Hence, it was adopted for performing the emission calculations. The results indicated that metal complex (1) can act as a fluorescent chemosensor for the detection of Ag⁺ and Cu²⁺ ions through the mechanism of intermolecular charge transfer (ICT) and as a molecular switch “On–Off-On” via the replacement of Cu²⁺ by Ag⁺ ions, as proved experimentally.

     

New dithiacrown–ether butadienyl dyes: synthesis,structure, and complex formation with heavy metal cations

Benzothiazole type butadienyl dyes containing a dithia‐15‐crown‐5 ( 2a ) or dithia‐18‐crown‐6 ether ( 2b ) moieties were synthesized. The structures of dyes 2a , b and their complexes with Ag⁺ and Pb²⁺ were studied by an X‐ray crystallography. It was found that the conformations of dithiacrown–ether moieties of dyes 2a , b are unfavorable for complex formation and change significantly upon binding of Ag⁺ or Pb²⁺. The complexation of 2a , b with Ag⁺, Cd²⁺, Pb²⁺, and Hg²⁺ in water–acetonitrile mixtures with different contents of water (P_W = 0–75%, v/v) was studied by ¹H NMR, UV–Vis spectroscopy, and polarography. In anhydrous acetonitrile, the stability constants of 1:1 complexes change in the sequence Cd²⁺ < Pb²⁺ ≤ Ag⁺ << Hg²⁺ in the case of 2a and in the sequence Cd²⁺ < Ag⁺ < Pb²⁺ << Hg²⁺ in the case of 2b . As P_W increases, the thermodynamic stability of Ag⁺ complexes increases. The opposite effect is observed for the complexes with Cd²⁺, Pb²⁺, and Hg²⁺. When P_W ～ 50%, the stability constants of complexes with Cd²⁺ and Pb²⁺ become too small to be measured. The selectivity of ligands 2a , b toward Hg²⁺ versus Ag⁺ is very high at any P_W values (selectivity coefficients > 10⁴). The complexation of 2a , b with Hg²⁺ at P_W ≤ 50% is accompanied by a substantial hypsochromic effect. This allows dithiacrown‐containing butadienyl dyes to be used as selective optical molecular sensors for heavy metal ions, in particular, in aqueous solutions. Copyright © 2009 John Wiley & Sons, Ltd.     

金属离子诱导下DNA折叠的不同机理

利用等温滴定量热仪、圆二色谱和荧光光谱,研究和分析了人工合成的DNA单链序列d(T₆C₆T₆C₆T₆C₆T₆)与Hg²⁺和Ag⁺相互作用的折叠过程. 在改变离子添加顺序的情况下,尽管热力学数据显示两种情况下都能通过两种不同反应路径得到一种相对稳定的发夹结构,但等温滴定量热仪数据却显示最终产物形成的机理截然不同.当先加入Hg²⁺时,发夹结构首先通过T-Hg-T碱基对形成然后C-Ag-C碱基对得到进一步稳定. 然而当先加入Ag⁺时,通过圆二色谱和荧光分析确认了一种不常见的金属碱基对T-Ag-C取代了经典的C-Ag-C碱基对.     

Influence of silver on the Sm<Superscript>3+</Superscript> luminescence in “Aerosil” silica glasses

The introduction of silver into the samarium-containing silica glasses prepared by the original solgel method leads to the formation of complex optical centers involving samarium ions and simple and/or complex silver ions. These centers are characterized by the effective sensitization of Sm³⁺ luminescence by Ag⁺, (Ag₂)⁺, and (Ag⁺)₂ ions according to the exchange mechanism for, at least, Sm³⁺-Ag⁺ centers. The formation of Sm-Ag centers is accompanied by an increase in the concentration of nonbridging oxygen ions, which prevent the reduction of silver ions by hydrogen. Silver nanoparticles formed in small amounts upon this reduction are effective quenchers of luminescence from the corresponding excited states of Sm³⁺ ions.     

Formation and photofragmentation properties of isolated aromatic amino acid-silver cluster hybrids

The formation of isolated [ (Trp-2H)+Ag₉] ⁺ and [ (Tyr-2H)+Ag₉] ⁺ amino-acid-Ag₉ hybrids is reported. The photofragmentation yields of the aromatic amino acid-silver cluster hybrids, as well as those of the protonated tryptophan and tyrosine molecules ([Trp+H]⁺ and [Tyr+H]⁺) have been recorded. The fragmentation yields of the complexes are higher than the yields for [Trp+H]⁺and [Tyr+H]⁺ and present an extension of the fragmentation on the red side of the spectrum. The photofragmentation spectrum of [ Trp+Ag₉] ⁺ was recently reported [Mitric et al., J. Chem. Phys. 127, 134301 (2007)]. While the optical spectra of substituted [ (Trp-2H)+Ag₉] ⁺ and non-substituted [ Trp+Ag₉] ⁺ complexes are very similar, a strong modification of the fragmentation channels between the two complexes is observed. The fragmentation channels are sensitive to the type of bonding in aromatic amino acid-silver cluster hybrids and can be used as fingerprints of structures.     

A Highly Selective Turn on Fluorescence Sensor for Hg2+ Based on Rhodamine Derivative

A novel fluorescent rhodamine based chemosensor (E)-3′,6′-bis(diethylamino)-2-((2-(pyridin-2-ylmethoxy)benzylidene)amino)spiro[isoindoline-1,9′-xanthen]-3-one, RSP, had been successfully developed and well characterized by NMR, FT-IR and Mass spectroscopy. The chemosensor exhibits high selectivity for Hg²⁺ over other ions (Ag⁺, Pb²⁺, Cu²⁺, Ni²⁺, Fe³⁺, Co²⁺, Zn²⁺ and Cd²⁺) with fluorescence enhancement in ethanol solution. More over the detection limit of the sensor is in the 10^?6 M level. The binding ratio of RSP-Hg²⁺ complex was determined to be 1:1 according to the Job plot. Test strips based on RSP were fabricated, which showed the application of the sensor for detection of mercuric ions in water by naked eyes.     

Photochromism in Cu-and Ag-doped Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> crystals

The equilibrium and photoinduced absorption spectra of copper-and silver-doped Bi₁₂SiO₂₀ crystals are studied. It is demonstrated that the impurity absorption is due to Ag²⁺, Ag⁺, Cu³⁺, Cu²⁺, and Cu⁺ ions occupying almost octahedral Bi³ positions. A mechanism of photochromism is suggested, involving changes in the charge states of copper and silver impurity ions according to schemes Cu²⁺-e → Cu³⁺ and Ag⁺-e → Ag²⁺.     

Design and Synthesis of Nanosensor Based on CdSe Quantum Dots Functionalized with 8-Hydroxyquinoline: a Fluorescent Sensor for Detection of Al<Superscript>3+</Superscript> in Aqueous Solution

A novel nanosensor based on CdSe quantum dots (QDs) capped with 8-hydroxyqunoline (HQ) was developed for Al³⁺ ions determination in aqueous solutions. The method is based on the fluorescence enhancement of the HQ functionalized QDs in the presence of Al³⁺ ions, due to the strong interaction between Al³⁺ and HQ. Prepared nanosensor exhibited an acceptable selectivity and sensitivity for Al³⁺ ions in the presence of other metal ions. Plot of Log(I/I₀) against Log[Al³⁺] shows a good linearity in the range of 0.02–3.0 mM, and the method could be used for detection of Al³⁺ ions concentration in aqueous solutions.     

Gold‐Cluster‐Based Dual‐Emission Nanocomposite Film as Ratiometric Fluorescent Sensing Paper for Specific Metal Ion

A dual‐emission ratiometric fluorescent sensing film for metal ion detection is designed. This dual‐emission film is successfully prepared from chitosan, graphitic carbon nitride (g‐C₃N₄), and gold nanoclusters (Au NCs). Here, it is shown that the g‐C₃N₄ not only serves as the fluorescence emission source, but also enhances the mechanical and thermal stability of the film. Meanwhile, the Au NCs are adsorbed on the surface of chitosan film by the electrostatic interaction. The as‐prepared dual‐emission film can selectively detect Cu²⁺, leading to the quench of red fluorescence of Au NCs, whereas the blue fluorescence from g‐C₃N₄ persists. The ratio of the two fluorescence intensities depends on the Cu²⁺ concentration and the fluorescence color changes from orange red to yellow, cyan, and finally to blue with increasing Cu²⁺ concentration. Thus, the as‐prepared dual‐emission film can be worked as ratiometric sensing paper for Cu²⁺ detection. Furthermore, the film shows high sensitivity and selectivity, with low limit of detection (LOD) (10 ppb). It is observed that this novel gold‐cluster‐based dual‐emission ratiometric fluorescent sensing paper is an easy and convenient way for detecting metal ions. It is believed that this research work have created another avenue for the detection of metal ions in the environment.     

A Selective Fluorescent Sensor for Hg2+

A novel rhodamine based fluorescent chemosensor RQP was prepared and characterized by ¹HNMR, ¹³CNMR and HR-MS. The properties of RQP were studied through UV–Vis spectroscopy and fluorescence spectroscopy. RQP showed highly selectivity toward Hg²⁺ over other metal ions, including Ag⁺, Cd²⁺, Cu²⁺, Na⁺, Mg²⁺, Ni²⁺, Pb²⁺, Fe³⁺, and Zn²⁺ in aqueous solutions. The recognition process is reversible and confirmed by EDTA experiment.     

Dissociation channels of silver bromide cluster Ag<Subscript>2</Subscript>Br,silver cluster Ag<Subscript>3</Subscript> and their ions studied by using alkali metal target

Various dissociation channels of silver bromide cluster ion Ag₂Br⁺ and silver cluster ion Ag₃ ⁺ were observed in high-energy collisionally-activated dissociation (CAD) using a Cs target. The fragment patterns of the high-energy CAD were compared with those of the metastable dissociation and low-energy CAD. The difference in the fragment patterns between the high-energy CAD and the other dissociation methods was explained in terms of the internal energy distributions. The dissociation mechanisms of neutral silver bromide cluster Ag₂Br and silver cluster Ag₃ were also investigated by charge inversion mass spectrometry using the Cs target. While the fragment ions AgBr^- and Ag₂ ^- were dominantly observed in the charge inversion spectrum of Ag₂Br⁺, the undissociated ion Ag₃ ^- was observed as a predominant peak in the case of Ag₃ ⁺. The dissociation behavior of Ag₂Br^* can be explained on the basis of the calculated thermochemical data. Contrary to this, the predominant existence of the undissociated Ag₃ ^- cannot be explained by the reported thermochemical data. The existence of undissociated Ag₃ ^- suggests that the dissociation barrier is higher than the internal energy of Ag₃ ^* (theoretical: 1.03 eV, experimental: 2.31 eV) estimated from the ionization potentials of Ag₃ and Cs.