R. Mlika

Calix[4]arene sensitive thin films for detecting sodium. Surface studies

Abstract In this work, we present experimental results about electrolyte–insulator–semiconductor (EIS)-type sensors based on evaporated p -tert-butylcalix[4]arene sensitive thin films devoted to sodium detection. Several calixarene films of different thicknesses (10–1000 nm) were studied and a significant decay of their detection ability was pointed out for thick samples. To investigate the presence of sodium encaged in the sensitive receptors, during the contact with the electrolyte, two surface analytical methods were used, namely, Rutherford backscattering spectroscopy (RBS) and low energy electron induced X-ray spectrometry (LEEIXS). Both methods show that sodium is incorporated within the membrane and that its surface concentration decreases as the calixarene film thickness increases, due to the growth of microcrystallites in the thickest films as pointed out by atomic force microscopy (AFM) observations.

Calixarene membranes on semiconductor substrates for E.I.S. chemical sensors

Thin p-tert-butyl calix[4]arene and p-tert-butyl calix[6]arene films were deposited using the technique of thermal evaporation under vacuum to fabricate chemical microsensors based on an E.I.S. (Electrolyte-Insulator-Semiconductor) structure. Electrochemical capacity measurements were made to test and calibrate physico-chemical sensors with regards to their sensitivity and selectivity. The sensing properties of calix[4]arene and calix[6]arene towards alkaline and heavy metal ions were tested. Both devices have shown Nernstian response and a wide working pH range. The former responded well to sodium ions and the latter to nickel ions, thus partial selectivity for these ions is shown. The improved lifetime (compared with membranes prepared by physical adsorption techniques) and sensitivity observed for these films indicates that these structures are worthy of further developments.

Study of ion-selective evaporated calixarene film used as a sensitive layer on ISFET sensors

Abstract Thin calix[4]arene and calix[6]arene films were deposited using the technique of thermal evaporation under vacuum to fabricate chemical ion-selective field effect transistor (ISFET) microsensors. A high-performance liquid-phase chromatography (HPLC) method was used to verify the non-degradation of the calixarene layers, after the evaporation process. The sensing properties of these ionophores towards alkaline and heavy metal ions were tested. Both devices have shown Nernstian response and a wide working pH range. The former responded well to sodium ions and the latter to nickel ions, thus partial selectivity for these ions is shown. The improved lifetime membranes and sensitivity observed for these films indicates that these structures are worthy of further developments.

Thin sensitive organic membranes on selective iron-ion sensors

Abstract The organic supramolecular compound synthesized from pyrochatechol units bound in the α-position of a linear dicarboxylic acid (AE6) previously used as a stable chelate iron(III) in solution is applied in this work as an ionophoric reagent on ion-sensitive field-effect transistor (ISFET) and electrolyte—insulator—semiconductor (EIS) structures for iron detection. The surface gate oxide (SiO 2 ) sensitization of sensors was performed, using three deposition methods: chemical grafting to obtain an AE6 monolayer, deposition by vacuum sublimation of an AE6 thin film and incorporation in a polysiloxane gel membrane. Classical electrochemical measurements were made to test the sensitivity towards iron of the AE6 membranes, in EIS and ISFET structures. A Nernstian sensitivity, a good selectivity and a long lifetime were obtained for the evaporated layer and the gel membranes.

Polysiloxane–gel matrices for ion sensitive membrane

Abstract Polysiloxane membranes containing specific receptor molecules (i.e., 2,9-( o -methoxy)-phenoxydecane dicarboxylic acid, α- and β-cyclodextrin) are used in the preparation of electrolyte insulator semiconductor (EIS) devices. Polysiloxane–gel matrices were characterized by spectroscopic methods. Ion sensitivity and selectivity of EIS devices to different ionic species have been tested for Fe 3+ , Pb 2+ and Cd 2+ ions in aqueous solution. The results show a super-Nernstian response for dispersed AE/polysiloxane (DS-AE/PS) film to Fe 3+ ions. A Nernstian response was observed for linked CD/polysiloxane (LK-CD/PS) film to heavy metal ions (i.e., Pb 2+ and Cd 2+ ). LK-(α)CD/PS shows a good affinity to Cd 2+ ions (28 mV/pCd 2+ ), whereas LK-(β)CD/PS was shown to be sensitive to Pb 2+ .

Porous silicon as substrate for ion sensors

Abstract The large interfacial area of the porous silicon is used as ion sensitive membrane support. The porous layer is oxidized by Rapid Thermal Oxidation (RTO) technique and a calix(4)arene layer was evaporated under vacuum. The structure is then used as the working electrode of an electrochemical cell and sensor properties were investigated by capacitance measurements. We observed an over-Nernstian response of the coated porous silicon to the Na + ion.

Cu2+-ISFET type microsensors based on thermally evaporated p-tert-butylcalix[9 and 11]arene thin films1

Abstract Large size odd-numbered calixarenes were used for the first time as ionophoric agents for the functionalization of ISFET microsensors and EIS structures through thermal evaporation process. Both calixarenes have shown a nernstian sensitivity over three decades towards only copper (II) activities. Very low selectivity coefficients were observed for K + and Ca 2+ whereas Cd 2+ and Pb 2+ (less than 10 −3 ) can be considered as interfering ions. Lifetime of around three months for the microsensors were obtained.

Membranes Containing New Large Size Calixarenes on Semiconductor Substrates for Chemical Microsensors.

Abstract New large size calixarenes have been synthesized and tested as ionophores. The applications of these new even-membered macrocycles in the field of chemical sensors have been studied. Thin p-tert-butyl calix[10 and 12]arenes film were deposited using the technique of thermal evaporation under vacuum on ISFET (Ion Sensitive Field Effect Transistor) and EIS structures (Electrolyte Insulator Semiconductor) surfaces. It was verified that by liquid chromatography the calixarene layers, after the sublimation process did not undergo any degradation. Electrochemical measurements with EIS structures and ISFETs were made to test the sensing properties of these calixarene films towards heavy metals. These large size calixarenes have shown a Nernstian sensitivity and a good selectivity towards iron(III) ions for the p-tert-butyl calix[12]arene and silver(I) ions for the p-tert-butyl calix[10]arene. A long lifetime was obtained for these sensors when tested over a large pH range. These materials present a real and great promise for further developments.

Elaboration of thin films based on p-tert-butyl-calix [8] arene. Application to the chemical sensors type EIS and ISFET

Abstract In this paper we report some results about recognition reagents in an EIS (electrolyte—insulator—semiconductor) and ISFET (ion-sensitive field-effect transistor) type sensors, elaborated with a p-tert-butyl-calix [8] arene molecule. This calixarene was deposited by sublimation onto the surface insulator of the samples. Reflexion—adsorption infrared spectroscopy and X-ray diffraction were performed to characterize the chemical properties and the morphology of the layers. Electrochemical measurements were made to study the sensitivity and the selectivity of this sensitive membrane towards earth alkaline cations and the transition metals. A linear sensitivity was obtained only for the Ca2+. These devices exhibit a high chemical stability in liquid media and consequently can be used as sensors.