Potentiometric sensor for sensitive and selective detection of heparin

A polymeric membrane ion-selective electrode for determination of heparin is described in this paper.Protamine is incorporated into the organic membrane phase and functions as sensing element for selective recognition of heparin.The proposed membrane electrode exhibits high selectivity for heparin over lipophilic anions such as thiocyanide and salicylate.The potentiometric response to the concentration of heparin is Unear in the range of 0.01-0.4 U/mL and a lower detection limit of 0.005 U/mL can be achieved.     

Fluorescent peptide sensor for the selective detection of Cu

A new fluorescent peptidyl chemosensor for Cu²⁺ ions with fluorescence resonance energy transfer (FRET) capabilities has been synthesized via Fmoc solid-phase peptide synthesis. The metal chelating unit, which is flanked by the fluorophores tryptophan (donor) and dansyl chloride (acceptor), consists of the amino acids glycine and aspartic acid (Gly-Gly-Asp-Gly-Gly-Asp-Gly-Gly-Asp-Gly-Gly-Asp-Gly-Gly). Coordination of the Cu²⁺ ions to the metal chelating unit results in fluorescent quenching of both the donor and acceptor fluorophores. Although it was determined that Cu²⁺ binding causes no change in FRET efficiency, emission and Cu²⁺-induced quenching of the acceptor dye can be used to monitor the concentration of the copper ions, with a detection limit of 32 μg L⁻¹. The sensor also demonstrated sensitivity, reversibility and selectivity towards Cu²⁺ in a transition metal matrix at pH 7.0.     

Direct detection of formate ligation in cytochrome c oxidase by ATR-FTIR spectroscopy

The IR signature of binding of formate to the heme a(3-)Cu(B) binuclear site of bovine cytochrome c oxidase has been obtained by perfusion ATR-FTIR spectroscopy. The data show unequivocally that formate binds in its anionic form despite its binding being electroneutral overall. The bound formate can be distinguished from free ligand by the binding-induced sharpening and downshifting of vibrational bands. Formate ligation also causes shifts of vibrational modes of heme a(3) and its substituents and perturbation of histidine residues. The association of the accompanying protonation change with a carboxylate or tyrosine can be ruled out and may involve a histidine metal ligand or, more likely, a simple displacement into the bulk phase of a hydroxide ligand to heme a(3) or CU(B), a reaction which would account for stoichiometric proton uptake and maintenance of net charge within the binuclear center domain.     

Site-selective imination of an anthracenone sensor: selective fluorescence detection of barium(II)

Site-selective imination of anthraquinone-based macrocyclic crown ethers using titanium tetrachloride as the catalyst yields imines where only the external carbonyl group of the anthraquinone forms Schiff-bases. The following aromatic amines yield monomeric compounds (aniline, 4-nitroaniline, 4-pyrrolaniline, and 1,3-phenylenediamine). Reaction of 2 equiv of the macrocyclic anthraquinone host with 1,2- and 1,4-phenylenediamine yields dimeric imine compounds. The 1,2-diimino host acts as a luminescence sensor, exhibiting enhanced selectivity for Ba(II) ion. Spectroscopic data indicate that two barium ions coordinate to the sensor. Due to E/Z isomerization of the imine, the monomeric complexes are nonluminescent. Restricted rotation about the 1,2 oriented C═N groups or other noncovalent/coordinate-covalent interactions acting between neighboring crown ether rings may inhibit E/Z isomerization in this example, which is different from current examples that employ coordination of a metal cation with a chelating imine nitrogen atom to suppress E/Z isomerization and activate luminescence. The 1,4-diimino adduct, where the crown rings remain widely separated, remains nonluminescent.     

Combined spectroscopic studies on post-functionalized Au25 cluster as an ATR-FTIR sensor for cations

Recently, significant research activity has been devoted to thiolate-protected gold clusters due to their attractive optical and electronic properties. These properties as well as solubility and stability can be controlled by post-synthetic modification strategies. Herein, the ligand exchange reaction between Au₂₅(2-PET)₁₈ cluster (where 2-PET is 2-phenylethanethiol) and di-thiolated crown ether (t-CE) ligands bearing two chromophores was studied. The post-functionalization aimed to endow the cluster with ion binding properties. The exchange reaction was followed in situ by UV-vis, ¹H NMR and HPLC. MALDI mass analysis revealed the incorporation of up to 5 t-CE ligands into the ligand shell. Once functionalized MALDI furthermore showed complexation of sodium ions to the cluster. ATR-FTIR spectroscopic studies using aqueous solutions of K⁺, Ba²⁺, Gd³⁺ and Eu³⁺ showed noticeable spectral shifts of the C–O stretching band around 1100 cm⁻¹ upon complexation. Further spectral changes point towards a conformational change of the two chromophores that are attached to the crown ether. Density functional theory calculations indicate that the di-thiol ligand bridges two staple units on the cluster. The calculations furthermore reproduce the spectral shift of the C–O stretching vibrations upon complex formation and reveal a conformational change that involves the two chromophores attached to the crown ether. The functionalized clusters have therefore attractive ion sensing properties due to the combination of binding properties, mainly due to the crown ether, and the possibility for signal transduction via an induced conformational change involving chromophore units.

Using ligand exchange reactions an atomically precise gold cluster was functionalized with a di-thiolated crown ether. Using in situ infrared spectroscopy films of the resulting composite were shown to incorporate metal cations.     

Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion

In the past decades, numerous electrochemical sensors based on exogenous electroactive substance have been reported. Due to non-specific interaction between the redox mediator and the target, the instability caused by false signal may not be avoided. To address this issue, in this paper, a new electrochemical sensor based on spiropyran skeleton, namely SPOSi, was designed for specific electrochemical response to fluoride ions (F⁻). The breakage of Si–O induced by F⁻ based on the specific nucleophilic substitution reaction between F⁻ and silica would directly produce a hydroquinone structure for electrochemical signal generation. To improve the sensitivity, SPOSi probe was assembled on the single-walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE) through the π–π conjugating interaction. This electrode was successfully applied to monitor F⁻ with a detection limit of 8.3 × 10⁻⁸ M. Compared with the conventional F⁻ ion selected electrode (ISE) which utilized noncovalent interaction, this method displays higher stability and a comparable sensitivity in the urine samples.     

A highly selective molecularly imprinted electrochemiluminescence sensor for ultra-trace beryllium detection

A new molecularly imprinted electrochemiluminescence (ECL) sensor was proposed for highly sensitive and selective determination of ultratrace Be²⁺ determination. The complex of Be²⁺ with 4-(2-pyridylazo)-resorcinol (PAR) was chosen as the template molecule for the molecularly imprinted polymer (MIP). In this assay, the complex molecule could be eluted from the MIP, and the cavities formed could then selectively recognize the complex molecules. The cavities formed could also work as the tunnel for the transfer of probe molecules to produce sound responsive signal. The determination was based on the intensity of the signal, which was proportional to the concentrations of the complex molecule in the sample solution, and the Be²⁺ concentration could then be determined indirectly. The results showed that in the range of 7 × 10⁻¹¹ mol L⁻¹ to 8.0 × 10⁻⁹ mol L⁻¹, the ECL intensity had a linear relationship with the Be²⁺ concentrations, with the limit of detection of 2.35 × 10⁻¹¹ mol L⁻¹. This method was successfully used to detect Be²⁺ in real water samples.     

Highly sensitive and selective reversible sensor for the detection of Cr

A new fluorescent sensor capable of sensing Cr³⁺ has been synthesized. Complexing with Cr³⁺ triggers the formation of a highly fluorescent ring-open form which is pink in color. The sensor shows extremely high fluorescence enhancement upon complexation with Cr³⁺ and it can be used as a ‘naked eye’ sensor. Binding of Cr³⁺ was found to be reversible as the pink color disappears with excess EDTA.     

A chemical concentration modulation sensor for selective detection of airborne chemicals

A method for selective detection of airborne chemicals based on concentration-modulated signals is described. A variable energy source (e.g., a heated filament) causes a modulated chemical reaction in a flowing gas stream, and a chemical sensor monitors the resultant modulated concentration signal. A parameter that is specific for a particular chemical species (i.e., a pseudo-activation energy) can be determined. Because this parameter is unique for a particular chemical and set of operating conditions, devices based on this method offer selectivity in sensing chemical vapors. A single detector capable of selectively identifying a large number of chemicals is possible using this approach.     

Benzimidazolium-based new simple ratiometric fluorescent sensor for selective detection of dihydrogenphosphate

A series of pyridine-coupled benzimidazolium-based receptors 1, 2 and 3 have been designed and synthesised. In the series, only receptor 1 is structurally appealing in the selective recognition of H₂PO₄^?  in CHCl₃ as well as in CH₃CN over a series of other anions. The ratiometric change in emission with a triplet band at 420 nm is the distinctive feature of selective recognition of H₂PO₄^?  in CHCl₃. In CH₃CN, a ‘turn on’ response is selectively observed. Binding studies have been carried out using fluorescence, UV–vis, ¹H NMR and ³¹P NMR spectroscopic techniques. Experimental results have been correlated with the theoretical findings.     

Zirconia-based amperometric sensor using ZnO sensing-electrode for selective detection of propene

The sensing characteristics to propene (C₃H₆) were examined at 600 °C under wet condition for the amperometric sensor using a yttria-stabilized zirconia (YSZ) tube and ZnO (+8.5 wt%Pt) sensing-electrode (SE). In order to improve the sensitivity to C₃H₆, the “pulsed-potential method” was adopted here. It was found that the current response varied almost linearly with C₃H₆ concentration in the range of 0–200 ppm when SE was polarized at +1.0 V (vs. Pt/air reference electrode) for a period of 0.3 s. By using the present “pulsed-potential method”, the sensitivity to 100 ppm C₃H₆ was increased about 1000 times, compared with the normal “constant-potential method”. The excellent selectivity to C₃H₆ was also obtained for the present sensor without influence of other hydrocarbons, NO_x, CO, H₂, etc.     

ATR-FTIR在研究环境固液微界面吸附过程中的应用

微界面吸附过程是许多环境微界面反应的初始步骤或关键步骤。通过原位分析方法实时研究环境微界面吸附过程,可以获得更直接的界面反应信息和更可靠的反应机制证据,对于认识污染物在环境中分配转化和迁移传输规律有着重要意义。衰减全反射红外光谱技术由于其独特的采样原理、简便的制样方法和广泛的适应性,正逐渐成为研究微界面反应的一个有力工具。本文在简要介绍原位衰减全反射红外光谱的技术原理的基础上,综述其在环境微界面吸附过程,尤其是矿物-水界面吸附过程中的应用,并探讨其在环境微界面过程研究中的发展前景。     

A new approach to selective detection of gas by an SnO2 solid-state sensor

Tin dioxide (SnO₂) is sensitized for different gaseous compounds by heating at 500 °C in an SO₂—air mixtures. Such treatment induces strong modifications of the electrical properties of SnO₂ and constitutes an attempt to solve the problem of selectivity for chemical sensors. According to the nature of the surrounding gas, the electrical conductance curves as a function of the temperature present a maximum at different temperatures: 400 °C with C₆H₆ and 100 °C with H₂S. These maxima, whose values are related to the gas concentration, can be used for selective gas detection.A benzene detector device using two sensors heated to 400 and 500 °C respectively selectivity for a large number of gaseous compounds.     

Benzene oxidation at boron-doped diamond anode: An electrochemical-impedance spectroscopy study

Benzene oxidation at boron-doped diamond anode in 1 M KCl aqueous solution is studied by electrochemical-impedance spectroscopy method. The measurements of differential capacitance and anodic current showed that in the ideal polarizability region benzene does not adsorb at the diamond electrode (or its adsorption does not affect the electrode capacitance). At more positive potentials adsorption of an inter-mediate of the benzene oxidation occurs, which partially blocks the electrode surface and results in decrease of anodic current. Analysis of the shape of the complex-plane plots of impedance spectra points out to diffusion of part of the adsorbed intermediate into solution.     

Nanocrystalline spinel zinc-substituted cobalt ferrite thick film an efficient ethanol sensor

This study considered Zn-substituted cobalt ferrite (Zn_xCo_1-xFe₂O₄ (x = 0.0–1.0) (ZCF)) thick films structural, morphological, and electrical properties; and gas sensing performance. The ZCF thick film sensor was screen printed on a glass substrate and tested for different analyte gases, including H₂, H₂S, CO₂, Cl₂, NH₃, LPG, and C₂H₅OH. We used X-ray photoelectron spectrometry to investigate composition, chemical state, iron/cobalt or zinc ratio, and cation distribution within Zn-substituted cobalt spinel ferrite tetrahedral and octahedral sites without impurities. FESEM and HR-TEM confirmed grain dimensions between 0.13 and 0.23 μm and porous, nearly spherical to flake-like morphology for the ZCF samples. Sample DC resistivity reduced with increasing temperature, confirming semiconductor nature. Thick film ZCF composition achieved highest the gas response and selectivity to 100 ppm ethanol at room temperature (30 °C). Overall results confirmed that flake-like ZCF sensors could be effective ethanol gas sensors.     

Deposition from dopamine solutions at Ge substrates: an in situ ATR-FTIR study

Deposition from dopamine (DA) solutions at germanium (Ge) model substrates was monitored under stationary conditions using surface sensitive in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra of the interfacial organic layer formed upon contact of TRIS buffered aqueous DA solutions to a Ge internal reflection element (IRE) showed conveniently strong diagnostic IR absorption bands, which were increasing with deposition time up to at least 6 h. Comparison of IR spectra of unreacted pristine DA, surface reacted, and bulk reacted material confirmed chemical reactions of DA to a polymerizate according to the literature. The found IR bands could be assigned to aromatic as well as C-O single bond moieties. The kinetic courses of the diagnostic band integrals showed an initial increase and saturation of the deposition after around 300 min, which could be empirically represented by an exponential damping function revealing a rather small kinetic constant. Highest deposition levels were found at pH = 8.5 (TRIS buffer or NaOH) in contrast to pH = 6.2, where no deposition occurred. Minor deposition was found in the presence of salt or at ZnSe instead of Ge due to the absence of reactive hydroxyl groups. The concentration dependence of DA deposition showed an initial increase and a saturation beginning at around 0.4 mg/mL (0.0022 M), where around 50 nm thick films featuring granular surface morphologies are formed. The adsorbed species are suggested to be smaller bulk reacted DA polymerizate particles with reactive end groups. Rinsing the formed films by pure TRIS buffer resulted in a time dependent release of deposited organic material by ≈23%, which could be represented by an exponential decay function. A saturation of the release after around 100 min and a larger kinetic constant compared to deposition could be determined. The released material is suggested to be larger aggregated bulk reacted DA polymerizate particles loosely bound to the surface by weak interaction forces.     

A nonionic surfactant-decorated liquid crystal sensor for sensitive and selective detection of proteins

Proteins are responsible for most biochemical events in human body. It is essential to develop sensitive and selective methods for the detection of proteins. In this study, liquid crystal (LC)-based sensor for highly selective and sensitive detection of lysozyme, concanavalin A (Con A), and bovine serum albumin (BSA) was constructed by utilizing the LC interface decorated with a nonionic surfactant, dodecyl β-d-glucopyranoside. A change of the LC optical images from bright to dark appearance was observed after transferring dodecyl β-d-glucopyranoside onto the aqueous/LC interface due to the formation of stable self-assembled surfactant monolayer, regardless of pH and ion concentrations studied in a wide range. The optical images turned back from dark to bright appearance after addition of lysozyme, Con A and BSA, respectively. Noteworthy is that these proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl β-d-glucopyranoside, viz. enzymatic hydrolysis, specific saccharide binding, and physical absorption. The LC-based sensor decorated with dodecyl β-d-glucopyranoside shows high sensitivity for protein detection. The limit of detection (LOD) for lysozyme, Con A and BSA reaches around 0.1 μg/mL, 0.01 μg/mL and 0.001 μg/mL, respectively. These results might provide new insights into increasing selectivity and sensitivity of LC-based sensors for the detection of proteins.     

A diamide-diamine based Cu chromogenic sensor for highly selective visual and spectrophotometric detection

A diamide-diamine based sensor 3 possessing anthracene-9,10-dione as a chromogenic moiety has been synthesized and demonstrates a highly selective colour change from red to blue with Cu²⁺ for visual detection of Cu²⁺ (5-50 μM). Other metal ions, viz. Fe²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Ag⁺, Pb²⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ cations do not lead to any change in colour and their presence does not interfere with the visual and quantitative analysis of Cu²⁺. The selective deprotonation of an aryl amine NH by Cu²⁺ is responsible for a bathochromic shift and significant colour changes. Significantly, the stability of the 3·Cu²⁺ complex between pH 7 and 12 allows Cu²⁺ estimation under neutral and basic conditions.