Maria Skowronska-Ptasinska

Modification of ISFESTs by covalent anchoring of poly(hydroxyethyl methacrylate) hydrogel. Introduction of a thermodynamically defined semiconductor-sensing membrane interface

Silicon dioxide ion-sensitive field effect transistors were modified by silylation with methacryloxypropyltrimethoxysilane (MPTS) and with in situ photopolymerized poly(hydroxyethyl methacrylate). Subsequently, the covalently linked methacrylate was swollen with a buffered potassium chloride solution, prior to the introduction of a hydrophobic sensing membrane. The introduced hydrogel layer effects a significant reduction in the peak-to-peak noise levels and eliminates completely interference from carbon dioxide. The method is compatible with integrated circuit photolithographic techniques and improves the development of potentiometric biosensors and chemical sensors.

How electrical and chemical requirements for refets may coincide

After discussing the features of a differential ISFET/REFET measuring concept, the published attempts to construct a proper REFET are summarized. It is concluded that the present REFETs are based upon the addition of a blocking polymeric layer to the gate surface of an ISFET, but that this approach fails with respect to the required insensitivity to ionic strength variations as well as with respect to the electrical stability. As a solution to these problems, this paper describes the development of a REFET concept that is based on the chemical attachment of a non-blocking polymeric layer. Characterization methods of these layers with respect to the electrical as well as the chemical behaviour are given and discussed. Finally, the experimental results of an acrylate/polyHEMA-REFET are shown in a differential ISFET/REFET system.

New membrane materials for potassium-selective ion-sensitive field-effect transistors

Several polymeric materials were studied as membrane materials for potassium-selective ion-sensitive field-effect transistors (ISFETs) to overcome the problems related with the use of conventional plasticized poly(vinyl chloride) membranes casted on ISFET gate surfaces. Several acrylate materials, such as ACE, Epocryl and derivatives, showed no reproducible results. Three room-temperature vulcanizing (RTV)-type silicone rubbers were tested. The addition-type RTV-2 silicone rubber was not suitable as a membrane material, but the condensation-type RTV-1 and especially the RTV-2 silicone rubber showed good results. ISFETs with a Silopren membrane showed a durability of at least 2 months.

Ion-sensing using chemically-modified ISFETs

Synthetic macrocyclic polyether ion receptors are the active components for the selective and sensitive detection of potassium ions in chemical sensors based on modified ISFETs. Covalent chemical anchoring of the sensing membrane to the gate oxide of the ISFET is essential in order to increase the lifetime of the sensor system to more than three months.

Reference field effect transistors based on chemically modified ISFETs

Different hydrophobic polymers were used for chemical modification of ion-sensitive field effect transistors (ISFETs) in order to prepare a reference FET (REFET). Chemical attachment of the polymer to the ISFET gate results in a long lifetime of the device. Properties of polyacrylate (polyACE) REFETs are described in detail. The polyACE-REFET is superior to other polymer modified REFETs, showing an excellent pH insensitivity (1 mV pH−1), a long lifetime and an electrically identical behaviour as an unmodified pH ISFET or a cation-selective PVC-MEMFET (membrane FET). The cation permeselectivity of the polymer can be significantly reduced by addition of immobile cations. The applicability of a polyACE-REFET in differential measurements with a pH ISFET and a K+ MEMFET is demonstrated.

Effect of different dialkylamino groups on the regioselectivity of lithiation of O-protected 3-(dialkylamino)phenols

Etude de la lithiation de dialkylamino-3 phenols (dialkylamino=pyrrolidino, piperidino, morpholino et dimethylamino) O-proteges par un groupe methyl, methoxymethyl ou carbamoyl

Membrane potentials of membranes with fixed ionic sites

A theoretical model has been developed to simulate the formation of a membrane potential as a function of physically accessible parameters. The description is an extension of the well-known Teorell-Meyer-Sievers (TMS) model, now including free and fixed ionic sites and free and fixed neutral ligands. The model shows that selectivity loss appears as the molar ratio of [ligand]/[ionic site] < 1 in the case of fixed ionic sites. The effect of complete immobilization of the neutral ligand has been simulated by gradually decreasing the mobility ratio α of the cation-ligand complex and free cation in the membrane phase. At lower α, the membrane potential is reduced by a counteracting diffusion potential. This effect is not present if the product of the association constant β1, the total ligand concentration L and α is larger than 104. Furthermore, it is shown that cation permselectivity of ion-selective membranes that contain fixed anionic sites cannot be eliminated by the incorporation of an equal amount of fixed cationic sites.

Intraannular functionalization of macrocyclic polyethers via organolithium chemistry; x-ray structure of 2-sulfinyl-1,3-xylyl-15-crown-4

The conversion of 2-lithio-1,3-xylyl crown ethers (2), obtained by reaction of the 2-bromo-1,3-xylyl crown ethers (1) with n_-butyllithium at −70 °C, with an electrophile is a generally applicable method for the synthesis of 1,3-xylyl crown ethers with intraannular acidic groups.