A Host‐Guest‐Recognition‐Based Electrochemical Sensor for Sequence‐Specific DNA Detection

We herein constructed a sensor that converts target DNA hybridization‐induced conformational transformation of the probe DNA to electrochemical response based on host‐guest recognition and nanoparticle label. In the sensor, the hairpin DNA terminal‐labeled with 4‐((4‐(dimethylamino)phenyl)azo)benzoic acid (dabcyl) and thiol group was immobilized on Au electrode surface as the probe DNA by Au‐S bond, and the CdS nanoparticles surface‐modified with β‐cyclodextrins (CdS‐CDs) were employed as electrochemical signal provider and host‐guest recognition element. Initially, the probe DNA immobilized on electrode kept the stem‐loop configuration, which shielded dabcyl from docking with the CdS‐CDs in solution due to the steric effect. After target hybridization, the probe DNA underwent a significant conformational change, which forced dabcyl away from the electrode. As a result, formerly‐shielded dabcyl became accessible to host‐guest recognition between β‐cyclodextrin (β‐CD) and dabcyl, thus the target hybridization event could be sensitively transduced to electrochemical signal provided by CdS‐CDs. This host‐guest recognition‐based electrochemical sensor has been able to detect as low as picomolar DNA target with excellent differentiation ability for even single mismatch.     

Fibre-Optic pH Probe Based on the Use of An Immobilized Amino Fluoresecein Indicator

Optical sensors can offer advantages over electrochemical sensors with respect to reduced interferences and ease of use for remote sensing^[1]. The first fiber optic pH sensor was developed for in vivo measurements by Peterson et al^[2]. This sensor relates pH to the absorbance of the base from of an immobilized dye. Subsequently, a pH sensor based on the fluorescence of immobilized fluoreseinamine was reported. The sensor involves immobilizing the amino fluoresecein (AF) complex within a porous sol-gel-processed film. Sol-gel process has many advantages as a method of immobilization^[3]. At ambient temperature, it allows the fabrication of a tough, inert, porous glass material with a high surface area. Sol-gel technology provides a viable approach to prepare stable, optically transparent host matrices for the design of materials for sensor, optical, chromatographic^[4], and catalytic applications. Alternatively, organosilicon precursors of the general formula can be hydrolyzed and co-condensed with tetraethoxysilane to form an organic-inorganic hybrid. An aliquot of the resultant sol can be spin cast or dip coated on a planar substrate to form a thin film.     

A general and versatile molecular design for host molecules working in water: a duplex-based potassium sensor consisting of three functional regions

A general and versatile molecular design for host molecules was proposed based on the structural motif of antibodies. A water-soluble potassium sensor was developed by this molecular design, which consists of three functional regions, benzo-15-crown-5 ether, DNA, and pyrene as guest-binding, dimerising, and signaling sites, respectively. The molecular sensor emitted the monomer fluorescence of the pyrene fluorophore predominantly when existing as a random structure, while it formed a duplex upon recognition of K+ to bring about monomer-excimer emission switching.     

Discrimination of Avian Influenza Virus Subtypes using Host‐Cell Infection Fingerprinting by a Sulfinate‐based Fluorescence Superoxide Probe

The current gold‐standard diagnosis method for avian influenza (AI) is an embryonic egg‐based hemagglutination assay followed by immunoblotting or PCR sequencing to confirm subtypes. It requires, however, specialized facilities to handle egg inoculation and incubation, and the subtyping methods relied on costly reagents. Now, the first differential sensing approach to distinguish AI subtypes is demonstrated using series of cell lines and a fluorescent sensor. Susceptibility of AI virus differs depending on genetic backgrounds of host cells. Cells were examined from different organ origins, and the infection patterns against a panel of cells were utilized for AI virus subtyping. To quantify AI infection, a highly cell‐permeable fluorescent superoxide sensor was designed to visualize infection. This differential sensing strategy successfully proved discriminations of AI subtypes and demonstrated as a useful primary screening platform to monitor a large number of samples.     

Synthesis and Characterization of Thiacalix[ 4 ] arene Derivatives with Polymerisable Groups

Introduction Calixarenes are versatile host molecules for molecular recognition and supram olecular assembly be-cause its functional groups can be readily introduced in-to the phenolic OH or the para position to realize a wide variety of functions[1-5].     

Supramolecular tandem enzyme assays

We conceptualize a novel approach towards enzyme assays based on the reversible and competitive binding of a fluorescent dye and the substrate as well as product of an enzymatic reaction to a macrocyclic host. This method was termed "supramolecular tandem assay", and has been applied to inhibitor and activator screening, sensor array development, and enantiomeric excess determination of amino acids. The simple and rapid read-out by fluorescence allows their straightforward implementation into high-throughput screening.     

Acidity Constant (pKa) Calculation of Large Solvated Dye Molecules: Evaluation of Two Advanced Molecular Dynamics Methods

pH‐Sensitive dyes are increasingly applied on polymer substrates for the creation of novel sensor materials. Recently, these dye molecules were modified to form a covalent bond with the polymer host. This had a large influence on the pH‐sensitive properties, in particular on the acidity constant (pK_a). Obtaining molecular control over the factors that influence the pK_a value is mandatory for the future intelligent design of sensor materials. Herein, we show that advanced molecular dynamics (MD) methods have reached the level at which the pK_a values of large solvated dye molecules can be predicted with high accuracy. Two MD methods were used in this work: steered or restrained MD and the insertion/deletion scheme. Both were first calibrated on a set of phenol derivatives and afterwards applied to the dye molecule bromothymol blue. Excellent agreement with experimental values was obtained, which opens perspectives for using these methods for designing dye molecules.     

Analyte‐Triggered DNA‐Probe Release from a Triplex Molecular Beacon for Nanopore Sensing

A new nanopore sensing strategy based on triplex molecular beacon was developed for the detection of specific DNA or multivalent proteins. The sensor is composed of a triplex‐forming molecular beacon and a stem‐forming DNA component that is modified with a host–guest complex. Upon target DNA hybridizing with the molecular beacon loop or multivalent proteins binding to the recognition elements on the stem, the DNA probe is released and produces highly characteristic current signals when translocated through α‐hemolysin. The frequency of current signatures can be used to quantify the concentrations of the target molecules. This sensing approach provides a simple, quick, and modular tool for the detection of specific macromolecules with high sensitivity and excellent selectivity. It may find useful applications in point‐of‐care diagnostics with a portable nanopore kit in the future.     

Copper(II) Ion‐Selective Electrodes Based on Dithiosalicylic and Thiosalicylic Acids

Potentiometric carbon paste electrodes for copper(II) based on dithiosalicylic and thiosalicylic acids are described. The sensor based on dithiosalicylic acid (DTS) exhibits a linear response with a nearly Nernstian slope of 27.7 mV per decade, whereas the electrode based on thiosalicylic acid (TS) shows a super‐Nernstian slope. The limits of detection for the DTS sensor and the TS sensor are 10^?7.9and 10^?6.3 M for copper(II) activity, respectively. Selectivity coefficients are tabulated, and the influence of the pH on the response of these ISEs is studied. The DTS electrode is successfully used for potentiometric titration of humic acids with copper in order to get more information about complexing properties of these acids.     

Smart Materials Based on Synthetic Host Molecules: The Role of Host–Guest Chemistry in the Fabrication and Application

Stimuli-responsive or smart materials have recently shown a significant impact on the frontier of material science and engineering. The exponential development of synthetic host molecules (SHMs) over the last decades and their corresponding host–guest chemistry, have empowered researchers with new opportunities to design and construct tailored or guest-specific smart materials. In this Minireview, we present the recent advancements in synthetic host based smart materials, ranging from the fabrication strategies to the state-of-art applications including adsorption, separation, luminescence, self-healing and actuation. The role that the host–guest chemistry plays in these systems is highlighted throughout to give a better prospective of the available possibilities for emerging materials of future economies.     

Turn‐On Fluorogenic and Chromogenic Detection of Small Aromatic Hydrocarbon Vapors by a Porous Supramolecular Host

Benzene, toluene, ethylbenzene, the isomers of xylene, and trimethylbenzene are harmful volatile organic compounds and pose risks to human health and the environment. However, there are currently no effective chemosensors for vapors of these compounds. A porous supramolecular host for turn‐on fluorogenic and chromogenic detection of the vapors of small aromatic hydrocarbons is presented. The host was constructed from a naphthalenediimide derivative that was supramolecularly connected to tris(pentafluorophenyl)borane. The amorphous powder form of the host allowed for effective accommodation of vapors of small aromatic hydrocarbons, resulting in a guest‐dependent fluorescence emission. Increases in the fluorescence yield of 76‐, 46‐, and 37‐fold were observed with toluene, benzene, and m‐xylene, respectively. Negligible responses were obtained with common organic solvents. This simple supramolecular host could be applied as a useful sensor of small aromatic hydrocarbon vapors.     

A Colorimetric Sensor Array for the Detection of the Date‐Rape Drug γ‐Hydroxybutyric Acid (GHB): A Supramolecular Approach

γ‐Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy‐to‐use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host–guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB.     

Colorimetric sensing of anions in aqueous solution using a charge neutral, cleft-like, amidothiourea receptor: tilting the balance between hydrogen bonding and deprotonation in anion recognition

The design, synthesis and physical evaluation of 1, a visible colorimetric 'naked eye' pyridyl based bis-amidothiourea sensor for anions, is described. This charge neutral sensor gives rise to significant changes in the absorption spectra upon interactions with several important biological anions such as AMP and ADP in 4:1 DMSO-H(2)O solution, while ATP was not detected. These colorimetric changes are due to the formation, or the combination of hydrogen bonding complexes and/or deprotonation between these anions and 1.     

The pillar[5]arene-based spun thin films: preparation,characterization, development of optical and mass sensitive sensors for swelling dynamics and gas sensing abilities

Pillar[5]arene (P5)-based materials can be preferable one of the most sensing elements in chemical sensor applications due to their high cavity and their special chiral structure. While the P5-based macrocycle molecules have been utilized as thin-film materials, the reports of chemical sensor application by performing P5 as sensor molecules have been very limited in the available literature. In this report, quinoline P5 (P5-Q) molecules were used to produce thin films via spin coating technique. P5-Q spun films were characterized with Atomic Force Microscopy (AFM) and Ultraviolet–Visible (UV–Vis) spectrophotometer. The gas sensing abilities of these P5-Q spun films were investigated by Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) techniques. In order to illuminate the gas sensing properties of P5-Q spun films, they were prepared as mass-sensitive and optical sensors. These sensors were utilized for its sensing abilities against organic vapours (acetone, methyl alcohol, and ethyl alcohol) by the mechanism of host–guest interaction. The current study also describes the diffusion coefficients of these organic vapors to illuminate the swelling dynamics of P5-Q spun films by performing Fick’s diffusion equation. The responses of P5-based optical (SPR) or mass sensitive (QCM) sensor in terms of the change in reflective intensity or the change in frequency and the values of diffusion coefficients showed that P5-Q molecules can be developed as potential chemical sensor element for acetone vapor compared to alcohol vapors.

     

Novel membrane-based sensor for online membrane integrity monitoring

A novel membrane-based sensor device for upstream membrane integrity monitoring has been developed and evaluated in this study. The sensor is based on relative trans-membrane pressures created by two membranes in series inside the sensor device that detects deposition from the sample stream onto the first of the sensor membranes. The sensor pressure signals can distinguish between intact or damaged membranes in the upstream membrane filtration process. Studies were conducted to evaluate both stabilities and sensitivities of the relative trans-membrane pressure monitoring technique. Sensitivity, based on the response times of the membrane sensor for particle detection, was determined for a range of operating conditions, membrane sandwich configurations, and particle concentrations in both simulated membrane failures and for actual pin-hole defects on a submerged MF membrane. The results showed that both sensitivities and stability strongly depended on membrane sandwich configurations (membrane characteristics) in the sensor, and mode of operation (pressurized or vacuum). The membrane sensor detected bentonite particles with a concentration of 0.3 mg/L (turbidity ∼0.3 NTU) in approximately 35 min in the vacuum mode. The sensor is reliable, sensitive and low cost. It has potential applications in decentralized systems or in multichannel monitoring of local conditions in a large plant. Possible applications of the membrane sensor for fouling monitoring are also discussed.     

An Optical pH Sensor with a Linear Response over a Broad Range Based on Organically Modified Silicate Film

Sol-gel technology provides a viable approach to prepare stable, optically transparent host matrices for the design of materials for sensor, optical, chromatographic, and catalytic applications^[1] Alternatively, organosilicon precursors of the general formula can be hydrolyzed and cocondensed with tetraethoxysilane to form an organic-inorganic hybrid. An aliquot of the resultant sol can be spin cast or dip coated on a planar substrate to form a thin film.     

Integrated electrochemical transistor as a fast recoverable gas sensor

A new design of conductometric chemical sensors based on conducting polymers as chemosensitive elements was suggested. The sensor includes six electrodes. Four inner electrodes coated by chemosensitive polymer are used for simultaneous two- and four-point resistance measurements thus providing information on the bulk polymer resistance and on the resistance of the polymer/electrode contacts. Two outer electrodes wired to inner electrodes by polymeric electrolyte are used for electrical control of redox state of the chemosensitive polymer. The outer electrodes are connected to potentiostat as reference and counter electrodes. It allows us to control redox state of the inner (working) electrodes. This new measurement configuration, resembling chemosensitive electrochemical transistors, provides an internal test of the sensor integrity and an electrically driven sensor regeneration. It was tested as a sensor for the detection of nitrogen dioxide. Polythiophene or polyaniline was used as receptors. Cyclic voltammograms of these polymers on the sensor surface measured in air atmosphere were very similar to that measured in aqueous electrolyte. A control of conductivity of these chemosensitive polymers by electrical potential applied vs. incorporated reference electrode was demonstrated. This effect was used for the regeneration of the chemosensitive material after exposure to nitrogen dioxide: in comparison to usual chemiresistors displaying an irreversible behavior in such test even in the time scale of hours, a completely reversible sensor regeneration within few minutes was observed.     

Photophysical Studies on Terpyridine-Eu3+ Complexes in Sol-Gel Nanocomposite Materials

The luminescence of the terpyridine-Eu³⁺-complex associated with poly(ethyleneoxide) or poly(propyleneoxide) chains has been studied in various fluid or solid environments including silica/poly(alkyleneoxide) nanocomposite materials. Strongly luminescent materials are obtained. Their emission can be tuned by varying the organic/inorganic content and, generally, the structure of the host material. In this respect, the complex luminescence itself is a sensor of the structural aspects of the host material.     

Micro flow sensor based on two closely spaced amperometric sensors

In this communication, a novel micro flow sensor based on two closely spaced amperometric oxygen sensors is proposed and implemented. The simulation results show that the ratio of the responses of these two oxygen sensors is determined by flow rates in the micro-channel. The sensor has been implemented using a micro fabrication technique. The measurement results demonstrate that the technique is able to detect flow rates in the flow range of several microliters per minute when the distance between the working electrodes of two oxygen sensors is 10 microm and the cross-section of the micro-channel is 100 microm x 100 microm. The advantage of the proposed flow sensor is that no additional tracers have to be added or produced during the flow measurement. Information on dissolved oxygen concentration in the liquid is not required either.     

Recent trends in potentiometric sensor arrays--a review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.