The transduction of host-guest interactions into electronic signals by molecular systems

Synthetic receptor molecules that selectively bind charged guests can store chemical information. The transduction of this information into electronic signals connects the chemical and electronic domains. Field effect transistors (FETs) are attractive transducing elements because these microdevices are able to register and amplify chemical changes at the gate oxide surface of the semiconductor chip. Integration of molecular receptors and field effect transistors into one chemical system gives a device that can communicate-changes of substrate activities in aqueous solution. Simulations of a system in which the receptor molecules are directly attached to the FET gate oxide indicate serious limitations with respect to sensitivity, dynamic range and extreme requirements for complex stability. Therefore we have concentrated on the integration of covalently attached thin membranes. The problem of the thermodynamically ill-defined oxidemembrane ipterface has been solved by applying a covalently linked hydrophilic polyhydroxyethylmethacrylate (polyHEMA) gel between the sensing membrane and the silylated gate oxide. A buffered aqueous electrolyte solution in the hydrogel renders the surface potential at the gate oxide constant via the dissociation equilibrium of the residual silanol groups. The subsequent attachment of a polysiloxane membrane that has the required dielectric constant, glass transition temperature Tg, and receptor molecule, provides a stable chemical system that transduces the complexation of cationic species into electronic signals (CHEMFET). The response to changing K concentrations in a solution of 0.1 M NaCl is fast (<1 sec) and linear in the concentration range of 10-5-1.0 M (55-58 mV /decade). A reference FET (REFET) based on the same technology is obtained when the intrinsic sensitivity to changes in ion concentration is eliminated by the addition of 2.10-5 mol g-1 of didodecyldimethyl ammonium bromide to the ACE membrane. Differential measurements with a REFET/CHEMFET combination showed excellent linear K response over long periods of time. All chemical reactions used are compatible with planar IC technology and allow fabrication on wafer scale

Nonaqueous Interfacial Polymerization-Derived Polyphosphazene Films for Sieving or Blocking Hydrogen Gas

A series of cyclomatrix polyphosphazene films have been prepared by nonaqueous interfacial polymerization (IP) of small aromatic hydroxyl compounds in a potassium hydroxide dimethylsulfoxide solution and hexachlorocyclotriphosphazene in cyclohexane on top of ceramic supports. Via the amount of dissolved potassium hydroxide, the extent of deprotonation of the aromatic hydroxyl compounds can be changed, in turn affecting the molecular structure and permselective properties of the thin polymer networks ranging from hydrogen/oxygen barriers to membranes with persisting hydrogen permselectivities at high temperatures. Barrier films are obtained with a high potassium hydroxide concentration, revealing permeabilities as low as 9.4 × 10-17 cm3 cm cm-2 s-1 Pa-1 for hydrogen and 1.1 × 10-16 cm3 cm cm-2 s-1 Pa-1 for oxygen. For films obtained with a lower concentration of potassium hydroxide, single gas permeation experiments reveal a molecular sieving behavior, with a hydrogen permeance of around 10-8 mol m-2 s-1 Pa-1 and permselectivities of H2/N2 (52.8), H2/CH4 (100), and H2/CO2 (10.1) at 200 °C.</p

Functionalized Anion-Exchange Membranes Facilitate Electrodialysis of Citrate and Phosphate from Model Dairy Wastewater

In this study, the preparation of a new, functional anion-exchange membrane (AEM), containing guanidinium groups as the anion-exchanging sites (Gu-100), is described as well as the membrane characterization by XPS, water uptake, permselectivities, and electrical resistances. The functional membrane was also employed in pH-dependent electrodialysis experiments using model dairy wastewater streams. The properties of the new membrane are compared to those of a commercially available anion-exchange membrane bearing conventional quaternary ammonium groups (Gu-0). Guanidinium was chosen for its specific binding properties toward oxyanions: e.g., phosphate. This functional moiety was covalently coupled to an acrylate monomer via a facile two-step synthesis to yield bulk-modified membranes upon polymerization. Significant differences were observed in the electrodialysis experiments for Gu-0 and Gu-100 at pH 7, showing an enhanced phosphate and citrate transport for Gu-100 in comparison to Gu-0. At pH 10 the difference is much more pronounced: for Gu-0 membranes almost no phosphate and citrate transport could be detected, while the Gu-100 membranes transported both ions significantly. We conclude that having guanidinium groups as anion-exchange sites improves the selectivity of AEMs. As the presented monomer synthesis strategy is modular, we consider the implementation of functional groups into a polymer-based membrane via the synthesis of tailor-made monomers as an important step toward selective ion transport, which is relevant for various fields, including water treatment processes and fuel cells.</p

Effect of charge of quaternary ammonium cations on lipophilicity and electroanalytical parameters : Task for ion transfer voltammetry

The electrochemical behavior of three differently charged drug molecules (zwitter-ionic acetylcarnitine, bi-cationic succinylcholine and tri-cationic gallamine) was studied at the interface between two immiscible electrolyte solutions. Tetramethylammonium was used as a model mono cationic molecule and internal reference. The charge and molecular structure were found to play an important role in the drug lipophilicity. The studied drugs gave a linear correlation between the water – octanol (logPoctanol) partition coefficients and the electrochemically measured water – 1,2-dichloroethane (logPDCE) partition coefficients. Comparison with tetraalkylammonium cations indicating that the correlation between logPoctanol and logPDCE is molecular structure dependent. The highest measured sensitivity and lowest limit of detection were found to be 0.543 mA·dm3·mol− 1 and 6.25 μM, respectively, for the tri-cationic gallamine. The sensitivity for all studied ions was found to be a linear function of molecular charge. The dissociation constant of the carboxylic group of zwiter-ionic acetylcarnitine was calculated based on voltammetric parameters and was found to be 4.3. This study demonstrates that electrochemistry at the liquid – liquid interface is powerful technique when it comes to electroanalytical or pharmacokinetic drug assessment

Design and properties of a flow-injection analysis cell using potassium-selective ionsensitive field-effect transistors as detection elements

The combination of flow-injection analysis (FIA) and chemically modified ion-sensitive field-effect transistors (CHEMFETs) is described. In a wall-jet cell, two identical potassium-selective CHEMFETs were used for a differential measurement using a platinum (pseudo-)reference electrode. Silicone-rubber membrane materials, chemically bound to the SiO2 gate oxide, were used with valinomycin as the ionophore. The optimized FIA system showed a linear response of 56 mV per decade for potassium concentrations above 5 × 10−5 M. Preliminary results of potassium determinations in human serum and urine samples are presented

Lactate biosensors: current status and outlook

Many research efforts over the last few decades have been devoted to sensing lactate as an important analytical target in clinical care, sport medicine, and food processing. Therefore, research in designing lactate sensors is no longer in its infancy and now is more directed toward viable sensors for direct applications. In this review, we provide an overview of the most immediate and relevant developments toward this end, and we discuss and assess common transduction approaches. Further, we critically describe the pros and cons of current commercial lactate sensors and envision how future sensing design may benefit from emerging new technologies

Selective transport of polyfunctional cations through bulk liquid membranes assisted by macrocyclic polyethers

In the past decade, the role of complementary size, shape, and functionality in the molecular recognition of neutral molecules has been pointed out. Artificial receptor molecules have been designed with multiple recognition sites and a well-defined geometry, capable of strong and selective binding of the appropriate substrates by hydrogen bonding, ionic interaction, and/or hydrophobic interactions. 2-8 Rebek et al.2 have used molecular clefts with acidic functions for the complexation of diamines, such as imidazole. Our group has shown that additional hydrogen-bond donors9 or electrophilic metal centers,10 incorporated in the cavities of macrocyclic polyethers, improve strongly the complexation of urea. This type of cocomplexation of a neutral guest by a host molecule either by hydrogen bonding or by coordination with a metal ion, is frequently observed in (metal1o)enzymes