Nitrate And Bicarbonate Selective Chemfets

The development of durable anion selective CHEMFET micro sensors is described. Selectivity in these sensors is either obtained from differences in hydration energy of the anions (the Hlofmeister series, giving nitrate selectivity) or by introduction of a new class of uranyl salophene ionophores (bicarbonate selectivity). The durability of the nitrate sensor was enhanced by using polysiloxane membranes in which 1 cationic tetraalkylammonium sites were covalently bound to the membrane matrix

Microsomal superoxide anion production and NADPH-oxidation in a series of 22 aziridinylbenzoquinones

Several 2,5-bis(1-aziridinyl)-1,4-benzoquinones (BABQs) can be activated to alkylating species by reduction of the quinone moiety. On the other hand, cytotoxicity of these compounds can be induced by redox cycling. A series of BABQs and their methylated analogues (BMABQs) with different substituents at the 3- and 6-position was synthesized in order to investigate the influence of the substituents on the reduction of the quinone moiety and on the generation of superoxide anion radicals with rat liver microsomes. Superoxide anion production (SAP) ranged from 3.7±0.1 to 742±74 nmoles/min/mg protein with quinone concentrations of 10 nmoles/ml. NADPH-oxidation was measured under the same conditions and it correlated well (r = 0.88, P < 0.001) with SAP. It ranged from 1.4±0.2 to 494±60 nmoles/min/mg protein. SAP for 22 B(M)ABQs showed a good correlation with the summated electronic substituent constant θpara,total (r = 0.86, P < 0.001). It can be concluded that superoxide anion production by 22 B(M)ABQs in rat liver microsomes can be predicted from structural features of the compounds

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

Combinatiorial method for surface-confined sensor desing and fabrication

The procedure for the combinatorial fabrication of new sensing materials for cations and anions based on self-assembled monolayers (SAM) is discussed. A library of different sensitive substrates is generated by sequential deposition of fluorophores and small ligand molecules onto an amino-terminated SAM coated glass. The preorganization provided by the surface avoids the need for complex receptor design, allowing for a combinatorial approach to sensing systems based on individually deposited small molecules. Additionally the sensing system has been miniaturized to the microscale using microcontact printing and integrating the sensory SAMs on the walls of microchannels

High-Resolution Contact Printing with Chemically Patterned Flat Stamps Fabricated by Nanoimprint Lithography

Chemically patterned flat stamps provide an effective solution to avoid mechanical stamp-stability problems currently encountered in microcontact printing. A new method is developed to fabricate chemical patterns on a flat PDMS stamp using nanoimprint lithography. Sub-100 nm gold patterns are successfully replicated by these chemically patterned flat PDMS stamps. \ud \u

Silver selective electrodes based on thioether functionalized calix[4]arenes as ionophores

Silver selective electrodes based on thioether functionalized calix[4]arenes 1 and 2 as ionophores were investigated. For both ionophores the selectivity coefficients (log kAg,M) were lower than −2.2 for Hg(II) and lower than −4.6 for other cations tested. The best results were obtained with membranes containing dithioether functionalized calix[4]arene (ionophore 2), potassium tetrakis(4-chlorophenyl) borate (KTpCIPB) and bis(1-butylpentyl)adipate (BBPA) as a plasticizer. The Ag(I)-response functions exhibited almost theoretical Nernstian slopes in the activity range 10−6–10−1M of silver ions.\ud \u

Catalysis by alkali and alkaline-earth metal ions in nucleophilic attack of methoxide ion on crown ethers bearing an intra-annular acetoxy group

Rates of reaction of methoxide ion with crown ethers bearing an intra-annular acetoxy group are markedly enhanced by alkali and alkaline-earth metal bromides as a result of much stronger interactions of the metal ions with transition states than with reactants.\ud \ud Rates of reactions of methoxide ion with crown ethers bearing an intra-annular acetoxy group markedly enhanced by alkali and alkaline-earth metal bromides as a result of much stronger interactions of the metal ion with transition state than with reactants