Reaction‐Based Colorimetric and Ratiometric Fluorescence Sensor for Detection of Cyanide in Aqueous Media

A stilbene‐based compound ( 1 ) has been prepared and was highly selective for the detection of cyanide anion in aqueous media even in the presence of other anions, such as F^?, Cl^?, Br^?, I^?, ClO₄^?, H₂PO₄^?, HSO₄^?, NO₃^?, and CH₃CO₂^?. A noticeable change in the color of the solution, along with a prominent fluorescence enhancement, was observed upon the addition of cyanide. The color change was observed upon the nucleophilic addition of the cyanide anion to the electron‐deficient cyanoacrylate group of 1 . The spectral changes induced by the reaction were analyzed by comparison with two model compounds, such as compound 2 with dimethyl substituents and compound 3 without a cyanoacrylate group. An intramolecular charge‐transfer (ICT) mechanism played a key role in the sensing properties, and the mechanism was supported by DFT/TDDFT calculations.     

Turn‐On Fluorogenic Probes for the Selective and Quantitative Detection of the Cyanide Anion from Natural Sources

We report new indene derivatives that are good fluorogenic probes for the cyanide anion, one of which is a highly selective and sensitive fluorogenic probe for the fluorescent detection—as well as reliable quantification—of the cyanide anion in water or buffer, with a 10³‐fold increase of fluorescence and low detection limit. It is therefore useful for the quantification of natural cyanide from aqueous extracts of green almond seeds, thus proving that the system is suitable for fast detection and quantification of cyanide from natural sources.     

Reaction‐Based Fluorescent Probe for Detection of Endogenous Cyanide in Real Biological Samples

Herein, two compounds ( 1 a and 1 b ) were rationally constructed as novel reaction‐based fluorescent probes for CN^? by making use of the electron‐withdrawing ability of the cyano group that was formed from the sensing reaction. Notably, this design strategy was first employed for the development of fluorescent CN^? probes. The experimental details showed that probe 1 a exhibited a fluorescence turn‐on response to CN^?, whereas other anions, biological thiols, and hydrogen sulfide gave almost no interference. The detection limit of probe 1 a for CN^? was found to be 0.12 μM . The sensing reaction product of 1 a with CN^? was characterized by NMR spectroscopy and mass spectrometry. TD‐DFT calculations demonstrated that the formed cyano group drives the intramolecular charge transfer (ICT) process from coumarin dye to the cyano group and thus the original strong ICT from the coumarin dye to the 3‐position pyridyl vinyl ketone substituent is weakened, which results in recovery of coumarin fluorescence. The practical utility of 1 a was also examined. By fabricating paper strips, probe 1 a can be used as a simple tool to detect CN^? in field measurements. Moreover, probe 1 a has been successfully applied for quantitative detection of endogenous CN^? from cassava root.     

A Reversible Dual Mode Chemodosimeter for the Detection of Cyanide Ions in Natural Sources

Herein, we report the synthesis of two indolium probes 1 and 2 based on anthracene and pyrene derivatives and their interactions with various anions. Of these probes, the pyrene conjugate 2 acts as a dual colorimetric and fluorescent chemodosimeter for the selective and sensitive detection of cyanide ions. The detection limit of probe 2 for CN^? ions was found to be 10 ppb (30 nM ). The nature of interaction has been thoroughly studied through various techniques such as ¹H NMR and IR spectroscopy, HRMS, and isothermal calorimetric (ITC) studies. These studies confirm that probe 2 forms a 1,2‐adduct in the presence of CN^? ions. Kinetic studies using probe 2 showed the completion of the reaction within 15 s with a rate constant of k′=0.522±0.063 s^?1_. This probe can be coated on a solid surface (dipstick) and a polymer matrix for the on‐site analysis and quantification of endogenous cyanide ions in natural sources such as Indian almonds.     

An Efficient Probe for Rapid Detection of Cyanide in Water at Parts per Billion Levels and Naked‐Eye Detection of Endogenous Cyanide

A new molecular probe based on an oxidized bis‐indolyl skeleton has been developed for rapid and sensitive visual detection of cyanide ions in water and also for the detection of endogenously bound cyanide. The probe allows the “naked‐eye” detection of cyanide ions in water with a visual color change from red to yellow (Δλ_max=80 nm) with the immediate addition of the probe. It shows high selectivity towards the cyanide ion without any interference from other anions. The detection of cyanide by the probe is ratiometric, thus making the detection quantitative. A Michael‐type addition reaction of the probe with the cyanide ion takes place during this chemodosimetric process. In water, the detection limit was found to be at the parts per million level, which improved drastically when a neutral micellar medium was employed, and it showed a parts‐per‐billion‐level detection, which is even 25‐fold lower than the permitted limits of cyanide in water. The probe could also efficiently detect the endogenously bound cyanide in cassava (a staple food) with a clear visual color change without requiring any sample pretreatment and/or any special reaction conditions such as pH or temperature. Thus the probe could serve as a practical naked‐eye probe for “in‐field” experiments without requiring any sophisticated instruments.     

A Chemodosimetric Probe Based on a Conjugated Oxidized Bis‐Indolyl System for Selective Naked‐Eye Sensing of Cyanide Ions in Water

A new bis‐indolyl‐based colorimetric probe has been synthesized. This allows a Michael‐type adduct formation for the detection of cyanide ions. The probe shows a remarkable color change from red to colorless upon addition of the cyanide ions in pure water. The cyanide ion reacts with the probe and removes the conjugation of the bis‐indolyl moiety of the probe with that of the 4‐substituted aromatic ring. This renders the probe colorless. The mechanism of the reaction of the probe with the cyanide ion was established by using ¹H and ¹³C NMR spectroscopy, mass spectrometry, and kinetic studies.     

Sulfonium Boranes for the Selective Capture of Cyanide Ions in Water

Going fishing ! The sulfonium borane [ 1 ]⁺ complexes cyanide in pure water at the maximum allowable concentration of 50 ppb recommended by the European Union. The high cyanide ion affinity displayed by this compound arises from favorable Coulombic effects augmented by a direct bonding interaction between the cyano and sulfonio groups.

     

Reaction‐Based and Single Fluorescent Emitter Decorated Ratiometric Nanoprobe to Detect Hydrogen Peroxide

A novel reaction‐based cross‐linked polymeric nanoprobe with a self‐calibrating ratiometric fluorescence readout to selectively detect H₂O₂ is reported. The polymeric nanoprobe is fabricated by using hydrophobic H₂O₂‐reactive boronic ester groups, crosslinker units, and environmentally sensitive 3‐hydroxyflavone fluorophores through a miniemulsion polymerization. On treatment with H₂O₂, the boronic esters in the polymer are cleaved to form hydrophilic alcohols and subsequently lead to a hydrophobic–hydrophilic transition. Covalently linked 3‐hydroxyflavones manifest the change in polarity as a ratiometric transition from green to blue, accompanied by a 500‐fold increase in volume. Furthermore, this nanoprobe has been used for ratiometric sensing of glucose by monitoring the H₂O₂ generated during the oxidation of glucose by glucose oxidase, and thus successfully distinguished between normal and pathological levels of glucose.     

含水介质中高选择性比色识别氰根离子的配合物型传感器分子

以前设计合成的基于香豆素氨基硫脲衍生物的传感器分子L能在含水介质中单一选择性比色识别铜离子. 鉴于铜离子能与氰根离子(CN^-)结合形成稳定的配合物, 在以前工作基础上, 研究了L与铜离子形成的配合物对CN^-的连续识别性能. 结果表明, L与Cu²⁺能形成稳定的绿色配合物CuL₂, 该配合物能专一选择性高灵敏度比色识别水中的 CN^-. 在CuL₂的DMSO/H₂O (V:V=3:1) HEPES (N-2-羟乙基哌嗪-N'-2-乙磺酸)的缓冲体系(pH=7.0)中分别加入F^-, Cl^-, Br^-, I^-, AcO^-, HSO₄^-, ClO₄^-, N₃^-, SO₄^2-, NO₃^-, SCN^-和CN^-等阴离子的水溶液后, 只有CN^-的加入使得溶液颜色由绿色变为无色, 同时在紫外光谱中, CuL₂在446 nm处的最大吸收峰消失, 这一识别过程不受其它阴离子的干扰. CuL₂对CN^-的裸眼最低检测限为8.0×10^-6 mol/L, 紫外光谱检测限为4.0×10^-7 mol/L (0.4 μmol·L^-1), 低于世界卫生组织规定的正常饮用水中CN^-的含量标准(<1.9 μmol·L^-1). 结果表明CuL₂是一种良好的CN^-比色识别受体, 在含水介质中对CN^-具有选择性好、灵敏度高以及抗干扰强的性能. 制备了基于CuL₂的CN^-检测试纸, 该试纸可以方便快捷的检测水中的CN^-.     

A Multifunctional Bimetallic Molecular Device for Ultrasensitive Detection,Naked‐Eye Recognition,and Elimination of Cyanide Ions

A new bimetallic Fe^II–Cu^II complex was synthesized, characterized, and applied as a selective and sensitive sensor for cyanide detection in water. This complex is the first multifunctional device that can simultaneously detect cyanide ions in real water samples, amplify the colorimetric signal upon detection for naked‐eye recognition at the parts‐per‐million (ppb) level, and convert the toxic cyanide ion into the much safer cyanate ion in situ. The mechanism of the bimetallic complex for high‐selectivity recognition and signaling toward cyanide ions was investigated through a series of binding kinetics of the complex with different analytes, including CN^?, SO₄^2?, HCO₃^?, HPO₄^2?, N₃^?, CH₃COO^?, NCS^?, NO₃^?, and Cl^? ions. In addition, the use of the indicator/catalyst displacement assay (ICDA) is demonstrated in the present system in which one metal center acts as a receptor and inhibitor and is bridged to another metal center that is responsible for signal transduction and catalysis, thus showing a versatile approach to the design of new multifunctional devices.     

Pattern‐Based Detection of Toxic Metals in Surface Water with DNA Polyfluorophores

Heavy metal contamination of water can be toxic to humans and wildlife; thus the development of methods to detect this contamination is of high importance. Here we describe the design and application of DNA‐based fluorescent chemosensors on microbeads to differentiate eight toxic metal ions in water. We developed and synthesized four fluorescent 2′‐deoxyribosides of metal‐binding ligands. A tetramer‐length oligodeoxy‐fluoroside (ODF) library of 6561 members was constructed and screened for sequences responsive to metal ions, of which seven sequences were selected. Statistical analysis of the response patterns showed successful differentiation of the analytes at concentrations as low as 100 nM . Sensors were able to classify water samples from 13 varied sites and quantify metal contamination in unknown specimens. The results demonstrate the practical potential of bead‐based ODF chemosensors to analyze heavy metal contamination in water samples by a simple and inexpensive optical method.     

Dipyrenylcalix[4]arene—A Fluorescence‐Based Chemosensor for Trinitroaromatic Explosives

A new chemosensor‐based approach to the detection of nitroaromatics is described. It involves the analyte‐induced quenching of excimer emission of a dipyrenyl calix[4]arene ( L ). The chemical and photophysical properties of the complexes formed between L and mono‐, di‐, and trinitrobenzene, and di‐ and trinitrotoluene were studied in acetonitrile and chloroform by using ¹H NMR, UV/Vis, and fluorescence spectroscopy. Fluorescence spectroscopy revealed that the trinitroaromatics engendered the largest response among the various substrates tested, with the sensitivity for these analytes being correspondingly high. Quantitative analysis of the fluorescence titration profile generated from the titration of L with TNT provided evidence that this particular functionalized calix[4]arene receptor allows for the detection of TNT down to the low ppb level in CH₃CN. A single‐crystal X‐ray diffraction analysis revealed that in the solid state the complex L? TNT consists of a supramolecular crystalline polymeric structure, the formation of which appears to be driven by intermolecular π–π interactions between two pyrene units and a TNT molecule held at a distance of 3.2–3.6 Å, as well as by intra‐ and intermolecular hydrogen‐bonds among the amide linkages. Nevertheless, the changes in the ¹H NMR, UV/Vis, and fluorescence spectrum, including sharp color changes, are ascribed to a charge‐transfer interaction arising from complementary π–π overlap between the pyrene subunits and the bound trinitroaromatic substrates. A number of ab initio calculations were also carried out and, considered in concert, they provide further support for the proposed charge‐transfer interactions, particularly in the case of L? TNT.     

A Stimuli‐Responsive Nanogel‐Based Sensitive and Selective Fluorescent Sensor for Cr3+ with Thermo‐Induced Tunable Detection Sensitivity

Stimuli‐responsive poly(N‐isopropylacrylamide) nanogel with covalently labeled rhodamine B urea derivatives (P(NIPAM‐co‐RhBUA)) is utilized as a sensitive fluorescent probe for Cr³⁺ in aqueous solution, and its thermo‐induced tunable detection capacity is investigated. At 20 °C, non‐fluorescent nanogel can selectively bind with Cr³⁺ over some other metal ions, leading to prominent fluorescence OFF–ON switching due to the recognition of RhBUA with Cr³⁺. Upon heating above the phase transition temperature, enhanced fluorescence intensity is observed (≈61‐fold increase at 45 °C) for the nanogel in the presence of Cr³⁺, accompanied with an improved detection sensitivity, which suggest that hydrophobic microenvironment generated in the collapsed nanogel plays an active role for their detection performance.

     

A New Fluorescent Chemosensor for Metal Ions Based upon 1,8‐Naphthalimide and 8‐Hydroxyquinoline

A new fluorescent chemosensor based upon 1,8‐naphthalimide and 8‐hydroxyquinoline was synthesized, and its fluorescent properties in the presence of different metal cations (Hg²⁺, Ag⁺, Zn²⁺, Fe²⁺, Cd²⁺, Pb²⁺, Ca²⁺, Cu²⁺, Mg²⁺, and Ba²⁺) were investigated. It displayed fluorescence quenching with some heavy and transition metal (HTM) ions, and the quenching strongly depended on the nature of HTM ions.     

Ratiometric Fluorescent Chemosensor for Selective Detection Cr3+ based on Carbazole and Benzimidazole

A novel Cr³⁺‐selective ratiometric fluorescent chemosensor 1‐substitued‐2‐carbazoleylbenzoimidazole ( L ) based on benzimidazole and carbazole was synthesized and characterized by nuclear magnetic resonance (¹H/¹³C NMR), Fourier transform infrared spectrometry (FTIR), and mass spectroscopy. L could selectively detect Cr³⁺ over other metal ions by UV–vis absorption and fluorescence emission spectroscopic methods in CH₃CN. L showed ratiometric fluorescent recognition of Cr³⁺; the fluorescent responses could be observed by naked eye under a UV lamp. The binding stoichiometry ratio of the L –Cr³⁺ complex was found to be 1:1 according to Job’s plot and MALDI‐TOF MS analysis. The results of DFT calculation supported this conclusion.     

Riboflavin‐Based Fluorogenic Sensor for Chemo‐ and Enantioselective Detection of Amine Vapors

A novel turn‐on fluorogenic chiral sensory system has been developed using a protonated riboflavin and riboflavin‐derived cationic polymer as a fluorophore precursor and a specific amine receptor, respectively, which enables the solid‐state chemo‐ and enantioselective fluorogenic visual detection of primary and secondary amine vapors.