Differentiating between fluorescence-quenching metal ions with polyfluorophore sensors built on a DNA backbone

A common problem in detecting metal ions with fluorescentchemosensors is the emission-suppressing effects of fluorescence-quenching metal ions. This quenching tendency makes it difficult to design sensors with turn-on signal, and differentiate between several metal ions that may yield a strong quenching response. To address these challenges, we investigate a new sensor design strategy, incorporating fluorophores and metal ligands as DNA base replacements in DNA-like oligomers, for generating a broader range of responses for quenching metal ions. The modular molecular design enabled rapid synthesis and discovery of sensors from libraries on PEG-polystyrene beads. Using this approach, water-soluble sensors 1-5 were identified as strong responders to a set of eight typically quenching metal ions (Co(2+), Ni(2+), Cu(2+), Hg(2+), Pb(2+), Ag(+), Cr(3+), and Fe(3+)). They were synthesized and characterized for sensing responses in solution. Cross-screening with the full set of metal ions showed that they have a wide variety of responses, including emission enhancements and red- and blue-shifts. The diversity of sensor responses allows as few as two sensors (1 and 2) to be used together to successfully differentiate these eight metals. As a test, a set of unknown metal ion solutions in blind studies were also successfully identified based on the response pattern of the sensors. The modular nature of the sensor design strategy suggests a broadly applicable approach to finding sensors for differentiating many different cations by pattern-based recognition, simply by varying the sequence and composition of ligands and fluorophores on a DNA synthesizer.     

A novel dansyl-appended glycoluril-based fluorescence sensor for silver ions

Tetra-dansylated diphenyl glycoluril has been synthesized and evaluated for ionic recognition. The synthesized molecular receptor shows selective response to silver ions as determined through the enhancement of fluorescence intensity.     

A FRET system built on quartz plate as a ratiometric fluorescence sensor for mercury ions in water

Due to the hazardous nature of mercury ions, the development of a cost effective, sensitive and field-portable sensor is of high significance for both industry and civilian use. In this work, a FRET-based ratiometric sensor for detecting mercury ions in water was fabricated by depositing a multilayered silica structure on a quartz plate. For the preparation of the film-based sensor, a silica support layer was first deposited on the quartz plate by using the sol-gel spin-coating procedure, and three ultrathin functional layers (donor, spacer and receptor) were then deposited on the support layer by dip-coating in a stepwise manner in toluene solution. As the film-based sensor was placed into an aqueous solution of Hg(2+), the non-fluorescent receptor (a spirolactam rhodamine derivative) on the film surface could form a complex with the mercury ion and act as the acceptor of the energy transfer. Upon excitation, the donor (a nitrobenzoxadiazolyl derivative, NBD) could transfer its excited energy from the donor layer to the acceptor on the film surface via the 'through space' energy transfer process, thus realizing the FRET-based ratiometric sensing for mercury ions. The sensor can selectively detect Hg(2+) in water with the detection limit of 1 μM. This solid film sensor is capable of being easily-portable and visualized detection. This strategy may offer new approaches for constructing other FRET-based solid-state devices.     

DNA polyfluorophores for real-time multicolor tracking of dynamic biological systems

Dye-ing to live: Spectral limitations of common organic dyes make it difficult or impossible to visualize and follow multiple biological components in rapidly moving systems. The development of a multispectral set of improved DNA-scaffolded fluorophores is described. Their use in multicolor cellular imaging (see scheme) and in tracking of biological motions on the subsecond timescale is demonstrated.     

Selective fluorescent sensor for mercury ions in aqueous media using a 1,4-dihydropyridine derivative

Novel 1,4-dihydropyridine (DHP) derivatives containing 3 carboxylic acid units are synthesized via cyclotrimerization of N-substituted β-aminoacrylates followed by basic hydrolysis of the triester. These DHP derivatives are readily soluble in aqueous media buffered at pH 8.0 and the solutions give blue fluorescent signals with quantum yields of 7–23%. One of these compounds, bearing a p-methoxyphenyl N-substituted group, shows specific fluorescent quenching with the mercuric ion (Hg²⁺). The fluorescent signal of the DHP derivative decays over a period of minutes to hours depending on the Hg²⁺ concentration, which implies that the sensing mechanism involves chemical reaction between the Hg²⁺ ion and the DHP compound. The ¹H NMR and MS data suggest that Hg²⁺ mediates the oxidation of the DHP ring into a pyridinium ring. The event is useful for fluorescent detection of Hg²⁺ at the micromolar level within 30 min, with a detection limit of 0.2 μM in aqueous medium.     

Mismatched pyrrolo-dC-modified duplex DNA as a novel probe for sensitive detection of silver ions

A new technology that enables the highly selective and sensitive detection of silver ions has been developed. The method takes advantage of the unique fluorescence property of a mismatched pyrrolo-dC (PdC)-modified duplex DNA, which serves as the key detection component, and the specific interaction of this duplex with silver ions.     

A potentiometric sensor of silver ions based on the Schiff base of diphenol

A potentiometric sensor based on the Schiff base 2,2′-(1E,1′E)-(1,1′-binaphthyl-2,2′-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)diphenol was synthesized and tested as an ionophore PVC-based membrane sensor selective towards silver ions (Ag⁺). Potentiometric testing demonstrated the high affinity of this receptor to silver ions. Seven membranes were fabricated with different compositions, with best performance shown by that with an ionophore composition (w/w) of 1.0?mg, PVC 33.0?mg, 2-nitrophenyl octyl ether 66?mg, and potassium tetrakis(p-chlorophenyl)borate 50?mol% in 1.0?mL tetrahydrofuran. The sensor worked well over a wide range of concentrations (1.0?×?10^?2 to 1.0?×?10^?6?M Ag⁺) at pH?6, showing a slope of 60.99?mV/dec with rapid response times of less than 3?s. The sensor also showed good selectivity towards Ag⁺ in the presence of interfering cations, with the highest selectivity coefficient observed for Hg²⁺ (2.7). A low detection limit of 3.4?×?10^?7?M Ag⁺ was established.     

Studies on purification of plutonium from silver ions

Precipitation and solvent extraction methods have been investigated for the purification of plutonium from silver from the solution generated during oxidative dissolution of plutonium oxide using Ag(II) ions. Initial experiments have been carried out using thorium as representative of plutonium. Selecting the optimum conditions, the experiments were repeated with plutonium. The results revealed that Pu can be purified from silver ions either by precipitating silver as silver chloride or silver metal followed by Pu(IV) oxalate precipitation or by selective extraction of Pu(IV) into 20% Aliquat-336 or 30% TBP.     

Selective lanthanum ions optical sensor based on covalent immobilization of 4-hydroxysalophen on a hydrolyzed triacetylcellulose membrane

An optical sensor membrane is described for the determination of lanthanum(III) ions based on the immobilization of 4-hydroxysalophen on a hydrolyzed triacetylcellulose membrane. 4-Hydroxysalophen is covalently bonded to a transparent hydrolyzed triacetylcellulose film. The sensing membrane in contact with lanthanum ions at pH 4.0 changes color from white-yellow to orange (323 to 433 nm). Under the optimum conditions, the proposed membrane displayed a linear range from 1.0 × 10⁻⁶ to 1.0 × 10⁻² M La(III) with a limit of detection of 1 × 10⁻⁷ M. The response time of the membrane was within 5–6 min depending on the concentration of La(III) ions. The selectivity of the probe towards lanthanum ions was found to be excellent. The sensor was successfully applied to the determination of La(III) in water, industrial waste water, and in NIST-615 (glass matrix) and NIST-3127a (lanthanum solution) samples with satisfactory results.     

Two-photon sensor for metal ions derived from azacrown ether

A two-photon sensor for the metal ions derived from azacrown ether as the receptor is reported. The sensor emits strong two-photon fluorescence when excited by 800 nm laser photons. Moreover, the binding constants measured by the one- and two-photon fluorescence are similar. This result may be useful for the design of efficient two-photon fluorescence probes for biological substrates.     

A highly selective fluorescent sensor for distinguishing cadmium from zinc ions based on a quinoline platform

A fluorescent sensor, N-(quinolin-8-yl)-2-(quinolin-8-yloxy)acetamide (HL), based on 8-aminoquinoline and 8-hydroxyquinoline platforms has been synthesized. This sensor displays high selectivity and sensitive fluorescence enhancement to Cd(2+) in ethanol. Moreover, sensor HL can distinguish Cd(2+) from Zn(2+) via two different sensing mechanisms (photoinduced electron transfer for Cd(2+); internal charge transfer for Zn(2+)). The composition of the complex Cd(2+)/HL or Zn(2+)/L(-) has been found to be 1:1, based on the fluorescence/absorption titration and further confirmed by X-ray crystallography.     

Selective transport of silver ions through bulk liquid membrane using Victoria blue as carrier

Transport of Ag⁺ as Ag(CN)₂⁻ ions through a bulk liquid membrane is reported. The bulk liquid membrane used is a solution of Victoria blue (VB) in chloroform. The effects of pH of the source phase, cyanide concentration in the source phase, sodium hydroxide in the receiving phase, and VB concentration in the organic phase on the efficiency of the transport system were studied. The above system has a high selectivity for Ag⁺ and can selectively and efficiently transport Ag(CN)₂⁻ ion from aqueous solutions containing other cations such as alkali and alkaline earths, Zn²⁺, Pd²⁺, Cu²⁺, Cd²⁺,Hg²⁺, Co²⁺, Fe²⁺, Pb²⁺, Ni²⁺, and Al³⁺.     

Solid membrane sensor for potassium ions

Titanium ferricyanide gel is found to possess good ion-exchange capacity, mechanical and chemical stability, and selectivity. An Araldite-based membrane of this compound can be used to estimate K⁺ ions in the concentration range 10^–1–10^–4 M. The sensor has a very short response time and remains stable for 2 to 3 months. There is no serious interference by bivalent and multivalent ions. Among the monovalent cations only Na⁺ and NH ₄ ⁺ may cause significant interference.     

A polymer membrane potentiometric sensor for silver

Four new sulfur-containing compounds based on pyridine, benzene, 1,8-naphthyridine and 1,10-phenanthroline have been synthesized. These molecules have been incorporated into a polymeric matrix as neutral carriers and evaluated as silver sensors. Two of the compounds (pyridine and benzene) show high selectivity for Ag(+). The sensor with the pyridine-based compound, in particular, shows near-Nernstian response and good sensitivity towards Ag(+) with a short response time (<10s), making it ideal for use in flow analysis.     

基于双发射免标记核酸探针的比率型荧光传感器用于银的检测

构建了一种新型免标记的双发射荧光比率核酸探针(GelRed/[G40]/Tb^3+)并用于Ag+的检测。对于GelRed/[G40]/Tb^3+探针,GelRed作为一种核酸染料嵌入到单链DNA-[G40]中,形成的GelRed/[G40]作为稳定的内置参照标准,在激发波长290 nm处,发射荧光强度固定不变的红色荧光(发射波长为635 nm),而[G40]/Tb^3+作为敏感的响应信号,随着Ag^+浓度的增加,产生的绿色荧光逐渐增强(发射波长为545 nm),[G40]/Tb3+与GelRed/[G40]发射的荧光强度比值也发生相应的改变,从而实现对Ag^+的定量检测。在优化的实验条件下,[G40]/Tb^3+与GelRed/[G40]荧光强度比值和Ag^+浓度在0~7.5μmol/L的范围内具有较好的线性关系,Ag^+检出限为0.156μmol/L。本传感器在10 min内就可完成对Ag^+的分析。方法已用于自来水样中Ag^+的检测,与ICP-MS法检测结果一致。     

Luminescent homochiral silver(I) lamellar coordination networks built from helical chains

The reactions of 2,2'-dimethoxy-1,1'-binaphthyl-3,3'-bis(4-vinylpyridine)(L) with AgNO3 or AgClO4 at 70 degrees C gave rise to two novel luminescent homochiral lamellar coordination polymers, AgL2X (X = NO3- for 1 or ClO4- for 2), which are built from linking helical chains by Ag(I) atoms as hinges.     

Selective electrodes for silver based on polymeric membranes containing cali

Silver ion-selective electrodes were prepared with polymeric membranes based on two calix[4]arene derivatives functionalized by two hydroxy and two benzothiazolylthioethoxy groups. The electrodes all gave a good Nernstian response of 58mV decade(-1) for silver in the activity range 5 x 10(-6)-10(-1) M, the limits of detection reached 10(-5.8) M and exhibited high selectivity towards alkali, alkaline earth and some transition metal ions. The electrode was used as indicator electrode in titrations of Ag+ with Cl- ion.     

Design of a dual-output fluorescent DNA logic gate and detection of silver ions and cysteine based on graphene oxide

In the presence of graphene oxide, upon formation of cytosine-Ag-cytosine the fluorescence wavelength of FAM-labeled DNA exhibited a red shift, and its intensity significantly increased. A novel fluorescent DNA sensor for Ag(+) and cysteine detection, and a dual-output fluorescent DNA INHIBIT logic gate are designed.