New Multifunctional Porous Materials Based on Inorganic–Organic Hybrid Single‐Walled Carbon Nanotubes: Gas Storage and High‐Sensitive Detection of Pesticides

Single‐walled carbon nanotubes (SWNTs) that are covalently functionalized with benzoic acid (SWNT‐PhCOOH) can be integrated with transition‐metal ions to form 3D porous inorganic–organic hybrid frameworks (SWNT‐Zn). In particular, N₂‐adsorption analysis shows that the BET surface area increases notably from 645.3 to 1209.9 m² g^?1 for SWNTs and SWNT‐Zn, respectively. This remarkable enhancement in the surface area of SWNT‐Zn is presumably due to the microporous motifs from benzoates coordinated to intercalated zinc ions between the functionalized SWNTs; this assignment was also corroborated by NLDFT pore‐size distributions. In addition, the excess‐H₂‐uptake maximum of SWNT‐Zn reaches about 3.1 wt. % (12 bar, 77 K), which is almost three times that of the original SWNTs (1.2 wt. % at 12 bar, 77 K). Owing to its inherent conductivity and pore structure, as well as good dispersibility, SWNT‐Zn is an effective candidate as a sensitive electrochemical stripping voltammetric sensor for organophosphate pesticides (OPs): By using solid‐phase extraction (SPE) with SWNT‐Zn‐modified glassy carbon electrode, the detection limit of methyl parathion (MP) is 2.3 ng mL^?1.     

A H+/Ag+ Dual‐Target Responsive Label‐Free Light‐Up Probe Based on a DNA Triplex

We developed a dual‐target responsive sensor for label‐free light‐up fluorescent detection of protons (H⁺) and silver ions (Ag⁺) using an “OR′′ logic gate. Berberine, a cost‐effective and non‐toxic indicator, partially intercalates the formed triplex DNA in the presence of H⁺ or Ag⁺, generating enhanced fluorescence. The designed Ag⁺ probe has high selectivity and desirable sensitivity, which is necessary for practical use. The robust ”OR“ logic gate is capable of a rapid and reversible response to the H⁺ and/or Ag⁺ inputs.     

Cytidine-stabilized gold nanocluster as a fluorescence turn-on and turn-off probe for dual functional detection of Ag and Hg

In this study, we have developed a label-free, dual functional detection strategy for highly selective and sensitive determination of aqueous Ag⁺ and Hg²⁺ by using cytidine stabilized Au NCs and AuAg NCs as fluorescent turn-on and turn off probes, respectively. The Au NCs and AuAg NCs showed a remarkably rapid response and high selectivity for Ag⁺ and Hg²⁺ over other metal ions, and relevant detection limit of Ag⁺ and Hg²⁺ is ca. 10 nM and 30 nM, respectively. Importantly, the fluorescence enhanced Au NCs by doping Ag⁺ can be conveniently reusable for the detection of Hg²⁺ based on the corresponding fluorescence quenching. The sensing mechanism was based on the high-affinity metallophilic Hg²⁺–Ag⁺ interaction, which effectively quenched the fluorescence of AuAg NCs. Furthermore, these fluorescent nanoprobes could be readily applied to Ag⁺ and Hg²⁺ detection in environmental water samples, indicating their possibility to be utilized as a convenient, dual functional, rapid response, and label-free fluorescence sensor for related environmental and health monitoring.     

Preparation of Fluorescent Thiol Group‐Functionalized Silica Microspheres for the Detection and Removal of Silver Ions in Aqueous Solutions

We demonstrate that silica microspheres can act as a sensitive fluorescent sensor and adsorbent of Ag⁺ in aqueous media. These thiol‐functionalized silica microspheres are doped with quantum dots (QDs) using organosilane chemistry in a one‐step preparation. Ligand exchange takes place between the thiolated organosilane and acid‐capped QDs, making the doping easy. Ag⁺ adsorption by the silica microspheres causes the decrease of fluorescence intensity of the QDs. The detection limit for Ag⁺ is found to be 10 μmol/L. The abundance of thiol groups on the surface of the microspheres could effectively remove Ag⁺ through strong interaction. When microspheres with a diameter of 1.1 μm are used as the adsorbents, the adsorption capacity for Ag⁺ reached 102 mg/g. This excellent adsorption ability is due to the abundance of thiol groups that act as the active sites, facilitating the adsorption of the massive metal ions on the surface of the microspheres. Furthermore, the adsorption isotherm data follows the Freundlich model. The structure and content of the silica microspheres were investigated by scanning and high‐resolution transmission electron microscopy, energy dispersive X‐ray spectroscopy, and Raman analysis, and the fluorescence properties were characterized by fluorescence microscopy.     

Fluorescent detection of silver(I) and cysteine using SYBR Green I and a silver(I)-specific oligonucleotide

We report on a novel method for the determination of silver ion (Ag⁺) and cysteine (Cys) by using the probe SYBR Green I (SGI) and an Ag+-specific cytosine-rich oligonucleotide (C-DNA). The fluorescence of SGI is very weak in the absence or presence of randomly coiled C-DNA. If, however, C-DNA interacts with Ag⁺ through the formation of cytosine-Ag⁺-cytosine (C-Ag⁺-C) base pairs, the randomly coiled C-DNA undergoes a structural changes to form a hairpin-like structure, thereby increasing the fluorescence of SGI. This fluorescence turn-on process allows the detection of Ag⁺ in the 10–600?nM concentration range, with a detection limit of 4.3?nM. Upon the reaction of Ag⁺ with Cys, Cys specifically removes Ag⁺ from the C-Ag⁺-C base pairs and destroys the hairpin-like structure. This, in turn, results in a decrease in fluorescence intensity. This fluorescence turn-off process enables the determination of Cys in the 8–550?nM concentration range, with a detection limit of 4.5?nM. The method reported here for the determination of either Ag⁺ or Cys is simple, sensitive, and affordable, and may be applied to other detection systems if appropriately selected DNA sequences are available.

Real‐Time Nitrophenol Detection Using Single‐Walled Carbon Nanotube Based Devices

Single‐walled carbon nanotube (SWNT) based devices have been developed for the real‐time detection of nitrophenols in aqueous solution. SWNTs are assembled to electrodes using AC dielectrophoresis technique. The SWNT devices exhibit not only high sensitivity to nitrophenol compounds, but also good reusability. Charge transfer between nitro group and SWNTs, and the metal‐nanotube interface modification are hypothesized to be the possible origins of conductance change. These results indicated that the SWNT devices can be utilized as a simple, low cost, sensitive, and reusable platform for real‐time detection of nitrophenol compounds.     

Impedimetric DNA‐Based Biosensor for Silver Ions Detection with Hemin/G‐Quadruplex Nanowire as Enhancer

A DNA‐based biosensor was reported for detection of silver ions (Ag⁺) by electrochemical impedance spectroscopy (EIS) with [Fe(CN)₆]^4?/3? as redox probe and hybridization chain reaction (HCR) induced hemin/G‐quadruplex nanowire as enhanced label. In the present of target Ag⁺, Ag⁺ interacted with cytosine‐cytosine (C? C) mismatch to form the stable C? Ag⁺? C complex with the aim of immobilizing the primer DNA on electrode, which thus triggered the HCR to form inert hemin/G‐quadruplex nanowire with an amplified EIS signal. As a result, the DNA biosensor showed a high sensitivity with the concentration range spanning from 0.1 nM to 100 µM and a detection limit of 0.05 nM.     

Bifunctional Ion‐Selective Electrode Based on C60‐Cryptand 22 for Silver and Iodine Ions

Fullerence C60‐cryptand 22 was prepared and successfully applied as the electric carrier in the PVC electrode membrane of a bifunctional ion‐selective electrode for cations, e.g., Ag⁺ ions as well as anions, e.g., I^? ions. The bifunctional ion‐selective electrode based on C60‐cryptand 22 can be applied as a Silver (Ag⁺) ion selective electrode with an internal electrode solution of 10^?3 M AgNO₃ in water (pH = 6.3), or as an Iodide (I^?) ion selective electrode with an acidic internal electrode solution of 10^?4 M KI_(aq) (pH = 2) in which the cryptand 22 is protonated, and the C60‐cryptand 22 is changed to C60‐Cryptand22–H⁺ and becomes an anionic electro‐carrier to absorb the I^? ion. The Ag⁺ ion selective electrode based on C60‐cryptand 22 gave a linear response with a near‐Nernstian slope (59.5 mV decade^?1) within the concentration range 10^?1‐10^?3 M Ag⁺_(aq). The Ag⁺ ion electrode exhibited comparatively good selectivity for silver ions, over other transition‐metal ions, alkali and alkaline earth metal ions. The Ag⁺ ion selective electrode with good stability and reproducibility was successfully used for the titration of Ag⁺_(aq) with Cl^? ions. The Iodide (I^?) Ion selective electrode based on protonated C60–cryptand22‐H⁺ also showed a linear response with a nearly Nernstian slope (58.5 mV decade^?1) within 10^?1 ‐ 10^?3 M I^? _(aq) and exhibited good selectivity for I^? ions and had small selectivity coefficients (10^?2–10^?3) for most of other anions, e.g., F^? , OH^?, CH₃COO^?, SO₄^2?, CO₃^2?, CrO₄^2?, Cr₂O₇^2? and PO₄^3? ions.     

Orthogonal Dual‐Triggered Shape‐Memory DNA‐Based Hydrogels

DNA‐based shape‐memory hydrogels revealing switchable shape recovery in the presence of two orthogonal triggers are described. In one system, a shaped DNA/acrylamide hydrogel is stabilized by duplex nucleic acids and pH‐responsive cytosine‐rich, i‐motif, bridges. Separation of the i‐motif bridges at pH 7.4 transforms the hydrogel into a quasi‐liquid, shapeless state, that includes the duplex bridges as permanent shape‐memory elements. Subjecting the quasi‐liquid state to pH 5.0 or Ag⁺ ions recovers the hydrogel shape, due to the stabilization of the hydrogel by i‐motif or C‐Ag⁺‐C bridged i‐motif. The cysteamine‐induced transformation of the duplex/C‐Ag⁺‐C bridged i‐motif hydrogel into a quasi‐liquid shapeless state results in the recovery of the shaped hydrogel in the presence of H⁺ or Ag⁺ ions as triggers. In a second system, a shaped DNA/acrylamide hydrogel is generated by DNA duplexes and bridging Pb²⁺ or Sr²⁺ ions‐stabilized G‐quadruplex subunits. Subjecting the shaped hydrogel to the DOTA or KP ligands eliminates the Pb²⁺ or Sr²⁺ ions from the respective hydrogels, leading to shapeless, memory‐containing, quasi‐liquid states that restore the original shapes with Pb²⁺ or Sr²⁺ ions.     

Highly Stable Double‐Stranded DNA Containing Sequential Silver(I)‐Mediated 7‐Deazaadenine/Thymine Watson–Crick Base Pairs

The oligonucleotide d(TX)₉, which consists of an octadecamer sequence with alternating non‐canonical 7‐deazaadenine (X) and canonical thymine (T) as the nucleobases, was synthesized and shown to hybridize into double‐stranded DNA through the formation of hydrogen‐bonded Watson–Crick base pairs. dsDNA with metal‐mediated base pairs was then obtained by selectively replacing W‐C hydrogen bonds by coordination bonds to central silver(I) ions. The oligonucleotide I adopts a duplex structure in the absence of Ag⁺ ions, and its stability is significantly enhanced in the presence of Ag⁺ ions while its double‐helix structure is retained. Temperature‐dependent UV spectroscopy, circular dichroism spectroscopy, and ESI mass spectrometry were used to confirm the selective formation of the silver(I)‐mediated base pairs. This strategy could become useful for preparing stable metallo‐DNA‐based nanostructures.     

Polymer‐based colorimetric and “turn off” fluorescence sensor incorporating benzo[2,1,3]thiadiazole moiety for Hg2+ Detection

A conjugated polymer was synthesized by the polymerization of 4,7‐dibromobenzo[2,1,3]thiadiazole ( M‐1 ) with tri{1,4‐diethynyl‐2,5‐bis(2‐(2‐methoxyethoxy)‐ethoxy)}‐benzene ( M‐2 ) via Pd‐catalyzed Sonogashira reaction. The polymer shows strong orange fluorescence. The responsive optical properties of the polymer on various metal ions were investigated through photoluminescence and UV–vis absorption measurements. The polymer displays highly sensitive and selective on‐off Hg²⁺ fluorescence quenching property in tetrahydrofuran solution in comparison with the other cations including Mg²⁺, Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, and Pb²⁺. More importantly, the fluorescent color of the polymer sensor disappears after addition of Hg²⁺, which could be easily detected by naked eyes. The results indicate that this kind of polymer sensor incorporating benzo[2,1,3]thiadiazole moiety as a ligand can be used as a novel colorimetric and fluorometric sensor for Hg²⁺ detection. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

i-Motif-modulated fluorescence detection of silver(I) with an ultrahigh specificity

A novel Ag⁺ sensor has been designed based on the mechanism that i-motif formation induced by Ag⁺ was sensitively recognized by a cyanine dye. The sensor exhibited an over 130–16,000 fold selectivity toward Ag⁺ than that toward other metal ions. This research not only provides a step forward toward the development of Ag⁺ detection but also represents a new application for i-motif DNA.     

An Anion‐Conjugated Polyelectrolyte Designed for the Selective and Sensitive Detection of Silver(I)

A novel conjugated polyelectrolyte P1, having a meta‐substituted monopyridyl in the backbone, is designed and synthesized for Ag⁺ detection in aqueous solution. As a chemosensor, P1 shows high sensitivity, low detection limit, and excellent selectivity for Ag⁺ over other metal ions. The sensing mechanism is based on the specific interaction between Ag⁺ and the pyridyl group of P1. The aggregated state of the polymer in water can amplify its quenching efficiency.     

A Highly Stabilizing Silver(I)‐Mediated Base Pair in Parallel‐Stranded DNA

The first parallel‐stranded DNA duplex with Hoogsteen base pairing that readily incorporates an Ag⁺ ion into an internal mispair to form a metal‐mediated base pair has been created. Towards this end, the highly stabilizing 6 FP ‐Ag⁺‐ 6 FP base pair comprising the artificial nucleobase 6‐furylpurine ( 6 FP ) was devised. A combination of temperature‐dependent UV spectroscopy, CD spectroscopy, and DFT calculations was used to confirm the formation of this base pair. The nucleobase 6 FP is capable of forming metal‐mediated base pairs both by the Watson–Crick edge (i.e. in regular antiparallel‐stranded DNA) and by the Hoogsteen edge (i.e. in parallel‐stranded DNA), depending on the oligonucleotide sequence and the experimental conditions. The 6 FP ‐Ag⁺‐ 6 FP base pair within parallel‐stranded DNA is the most strongly stabilizing Ag⁺‐mediated base pair reported to date for any type of nucleic acid, with an increase in melting temperature of almost 15 °C upon the binding of one Ag⁺ ion.     

Sensitive and Selective Fluorescent and Colorimetric Sensor for Ag+ Based on the Supramolecular Self‐Assembly in Semi‐Water

Specific recognition of ultratrace levels of ions in semi‐water using super‐quicker methods is still a challenge for environmental monitoring. Herein we report a fluorescent and colormetric sensor ( ZH ) based on supramolecular self‐assembly, whose structure was destroyed by the addition of ultratrace of silver ions. The process promoted either naked eye visible color changes or fluorescence intensity quenched in conjunction with a wide pH range. Systematic studies revealed very high selectivity (0.07 µmol/L) for silver ions, and other common cations, e.g ., Hg²⁺, Cu²⁺, Cd²⁺, Pb²⁺ had nearly no influence on the sensing behavior. This sensor also served as a multiple use of component in sensing materials by addition of I⁻ into the mixture of ZH and Ag⁺ (about 5 times). What's more, ZH containing filter paper emerged distinct color and fluorescence changes upon exposure to silver (Ag⁺), which could be used as a portable method to undertake field testing for Ag ⁺ .     

Surface plasmon resonance detection of silver ions and cysteine using DNA intercalator-based amplification

We report the development of a surface plasmon resonance sensor based on the silver ion (Ag⁺)-induced conformational change of a cytosine-rich, single-stranded DNA for the detection of Ag⁺ and cysteine (Cys) in aqueous solutions. In the free state, single-stranded oligonucleotides fold into double-helical structures through the addition of Ag⁺ to cytosine–cytosine (C–C) mismatches. However, in the presence of Cys, which competitively binds to Ag⁺, the formation of the C–Ag⁺–C assembly is inhibited, resulting in free-state, single-stranded oligonucleotides. To enhance sensitivity, the DNA intercalator, daunorubicin, was employed to achieve signal enhancement. The detection limit for Ag⁺ was 10 nM with a measurement range of 50–2,000 nM, and the detection limit for Cys was 50 nM with a measurement range of 50–2,000 nM. This simple assay was also used to individually determine the spiked Ag⁺ concentration in water samples and Cys concentrations in biological fluid samples.     

基于T-T碱基错配的荧光传感器特异性检测汞离子

在本文中,我们研制了一种基于T-T碱基错配特异性键合汞离子的荧光传感器用于汞离子的检测。该传感器由两条分别标记了荧光基团（F）和淬灭基团（Q）的DNA探针组成,并且含有两对用于结合汞离子的T-T错配碱基。当汞离子存在时,两条探针之间形成T-Hg2+-T结构,作用力增强,从而拉近了荧光基团与淬灭基团之间的距离,发生能量转移,使荧光信号在一定程度上被淬灭。在优化的条件下,我们使用该传感器对汞离子进行检测,动力学响应范围为50nM到1000nM,线性相关方程为y= 5281.13 - 1650.56 lg[Hg2+] ( R2 = 0.985),检测下限为79nM。此外,我们还考察了该传感器的选择性,当用其它干扰离子（浓度都为1.0µM）代替待测离子进行实验时,没有发生明显的荧光淬灭,说明该传感器具有较高的选择性。该传感器的构建为汞离子的检测提供了一条快速、简便的新途径。     

Silole‐Infiltrated Photonic Crystal Films as Effective Fluorescence Sensor for Fe3+ and Hg2+

We develop a highly effective silole‐infiltrated photonic crystal (PC) film fluorescence sensor with high sensitivity, good selectivity and excellent reproducibility for Fe³⁺ and Hg²⁺ ions. Hexaphenylsilole (HPS) infiltrated PCs show amplified fluorescence due to the slow photon effect of PC because the emission wavelength of HPS is at the blue band edge of the selected PC’s stopband. The fluorescence can be quenched significantly by Fe³⁺/Hg²⁺ ions owing to electron transfer between HPS and metal ions. The amplified fluorescence enhances the sensitivity of detection, with a detection limit of 5 nM for Fe³⁺/Hg²⁺ ions. The sensor is negligibly responsive to other metal ions and can easily be reproduced by rinsing with pure water due to the special surface wettability of PC. As a result, a highly effective Fe³⁺/Hg²⁺ ions sensor based on HPS‐infiltrated PC film has been achieved, which will be important for effective and practical detection of heavy metal ions.     

A Highly Copper‐Selective Ratiometric Fluorescent Sensor Based on BODIPY

A new ratiometric fluorescent sensor ( 1 ) for Cu²⁺ based on 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) with di(2‐picolyl)amine (DPA) as ion recognition subunit has been synthesized and investigated in this work. The binding abilities of 1 towards different metal ions such as alkali and alkaline earth metal ions (Na⁺, K⁺, Mg²⁺, Ca²⁺) and other metal ions ( Ba²⁺, Zn²⁺, Cd²⁺, Fe²⁺, Fe³⁺, Pb²⁺, Ni²⁺, Co²⁺, Hg²⁺, Ag⁺) have been examined by UV‐vis and fluorescence spectroscopies. 1 displays high selectivity for Cu²⁺ among all test metal ions and a ～10‐fold fluorescence enhancement in I₅₈₂/I₅₅₈ upon excitation at visible excitation wavelength. The binding mode of 1 and Cu²⁺ is a 1:1 stoichiometry determined via studies of Job plot, the nonlinear fitting of the fluorometric titration and ESI mass.     

Lighting‐Up of the Dye Malachite Green with Mercury(II)–DNA and Its Application for Fluorescence Turn‐Off Detection of Cysteine and Glutathione

This work describes a novel strategy for the highly sensitive and selective detection of cysteine (Cys) and glutathione (GSH) based on the Hg²⁺–AGRO100–malachite green (MG) complex system. The dye MG, which has a very low quantum yield in aqueous solution by itself, can bind with the thymine‐rich DNA AGRO100 in the presence of Hg²⁺ ions to generate a striking fluorescence intensity enhancement of 1000‐fold. As sulfur‐containing amino acids, Cys and GSH effectively sequester Hg²⁺ ions from the Hg²⁺–AGRO100–MG complex structure to switch the ‘lit‐up’ chemosensor to the ‘off’ state (about a 50‐fold fluorescence intensity decrease), thus providing a facile, but effective, method to probe for Cys/GSH. The fluorescence titration, UV absorption, CD, and Raman spectra provide some insight into the structural and chemical basis for the enhancement effect. The formation of the Hg²⁺–AGRO100–MG complex significantly affects the electronic structure and conformation of the MG molecule by leading to an extended π system, which is the likely origin of the observed striking fluorescence intensity enhancement. Notably, the proposed sensing platform exhibits exquisite selectivity and sensitivity toward Cys/GSH with limits of detection of 5 nM for Cys and 10 nM for GSH, respectively. Furthermore, the straightforward assay design avoids labeling of the probe, uses only commercially available materials, and still displays comparable sensitivity and excellent selectivity.