R.J.W. Lugtenberg

The design of durable Na+-selective CHEMFETs based on polysiloxane membranes

The design of durable sodium-selective CHEMFETs based on the covalent attachment of a sodium-selective ionophore and tetraphenylborate anions to a polysiloxane membrane matrix is described. Simulations of the membrane potential of such CHEMFETs using an extended version of the model developed previously in our group, revealed that a membrane with a reduced mobile ionophore and completely immobilized anionic sites should give a sub-nernstian response owing to a counteracting diffusion potential. CHEMFETs with all possible combinations of free and covalently bound ionophore and borate anions were prepared and the effect of covalent binding on the sensing behaviour was studied. The attachment of both electroactive components to a polysiloxane membrane matrix results in CHEMFETs that respond to Na+ activities in aqueous solution with good selectivity, and an almost nernstian slope (56.7 mV decade?1). The polarity of the membrane plays a crucial role. The durability is improved by the covalent attachment of the electroactive components (more than 90 days).

Cesium-selective chemically modified field effect transistors with calix[4]arene-crown-6 derivatives

Calix[4]arene-crown-6 derivatives (1–3) in the 1,3-alternate conformation, incorporated in poly(vinylchloride) membranes of CHEMFETs, exhibit good Cs+-selectivity and Nernstian behaviour. The Cs+-selectivity over Na+, i.e., log KpotCs,Na = −3.3, is slightly better than observed for bis(18-crown-6) derivatives (log KpotCs,Na = −3.0). The CHEMFETs respond sub-Nernstian in the presence of NH+4 and K+. Model calculations show that this can be explained by the small difference between the stability constants of the Cs+− and K+-complexes and by the high partition coefficient of NH+4 in favour of the membrane phase, respectively.

The effects of covalent binding of the electroactive components in durable CHEMFET membranes—impedance spectroscopy and ion sensitivity studies

The effects of covalent attachment of the electroactive components (i.e. the cation receptor molecules and the tetraphenylborate anions) in durable CHEMFET membranes is described. CHEMFETs for monovalent cations having either one or both electroactive components covalently bound in the membrane matrix exhibit Nernstian responses and good selectivities for Na+, or K+ ions, however, covalent attachment of borate in the membrane results in non-functioning sensors. Durability studies with CHEMFETs modified with polysiloxane membranes which are selective for Na+, K+ and Pb2+ ions show long lifetimes upon continuous exposure to a water stream. Na+ selective CHEMFETs with covalently attached Na+ ionophores and free borate in the membrane are still Na+ selective after 82 weeks of continuous exposure to water. Similar K+ and Pb2+ selective polysiloxane CHEMFETs showed good selectivities for at least 26 and 19 weeks, respectively. Impedance measurements showed that in all cases the lowest membrane resistance and the most stable CHEMFETs were obtained with polysiloxane membranes containing covalently attached ion-selective calix[4]arene-based receptor molecules and free anionic sites.

Pb2+ and Cd2+ selective chemically modified field effect transistors based on thioamide functionalized 1,3-alternate calix[4]arenes

Novel calix[4]arenes fixed in the 1,3-alternate conformation and functionalized with thioamide groups have been synthesized and their selectivities for Pb2+ and Cd2+ ions in chemically modified field effect transistors (CHEMFETs) have been evaluated. The 25,27-bis(dimethylaminothiocarbonylmethoxy)-26,28-dipropoxycalix[4]arene 3 in the 1,3-alternate conformation is more selective for Pb2+ than the analogous cone conformer. The 1,3-alternate calix[4]arene 8 having, in the 25- and 27-positions, two pairs of vicinal thioamide moieties at the same face of the molecule, has the highest selectivities for Cd2+ reported so far.

Polysiloxane based CHEMFETs for selective detection of Ca2+ ions

Different siloxane copolymers have been used as membrane materials for Ca2+ selective chemically modified field effect transistors (CHEMFETs). CHEMFETs with 3-benzoylaminopropyl-functionalized polysiloxane membranes and 1 wt% borate anions are intrinsically selective for Ca2+ ions. This selectivity can be further enhanced by the incorporation of a Ca2+ selective 1,3 alternate calix[4]arene which is functionalized with four amido groups. The highest Ca2+ selectivties were obtained with CHEMFETs containing this calix[4]arene ionophore in 3-cyanopropyl-functionalized polysiloxane membranes.

Polysiloxane based CHEMFETs for the detection of heavy metal ions

The development of polysiloxane based chemically modified field effect transistors (CHEMFETs) for heavy metal ions is described. Different polar siloxane copolymers have been synthesized via an anionic copolymerization of hexamethylcyclotrisiloxane, [3-(methacryloxy)propyl]pentamethylcyclotrisiloxane and pentamethylcyclotrisiloxanes with a pendant polar group, e.g. ester, ether, amide, keto or cyan group. Well-structured monomodal molecular weight polymers were obtained with molecular weight distributions from 1.3 to 1.7. The siloxane copolymers were used as sensing membranes for Ag+, Cd2+ sand Pb2+ selective CHEMFETs. The intrinsic elastomeric properties of the polysiloxane membrane makes the use of a plasticizer superfluous, which should have a favourable effect on the durability of these CHEMFETs. Siloxane copolymers with 3-cyanopropyl side groups are already intrinsically selective for Ag+ ions and this can be further enhanced by the addition of an Ag+ selective ionophore I. Good Cd2+ selectivity was obtained for CHEMFETs with 3-acetoxypropyl functionalized siloxane membranes in which the Cd2+ selective ionophore 2 was incorporated. CHEMFETs with a [3-(p-acetylphenoxy)propyl]polysiloxane membrane containing the Pb2+ selective ionophore 3 showed good selective responses towards Pb2+.

Chemically Modified Field-Effect Transistors for Measurement of Ion Activities in Aqueous Solution

Chemically modified field effect transistors for the selective detection of several cation and anion activities in aqueous solution are described. For obtaining sensors of high durability, novel polysiloxane membranes have been developed which contain different side groups to tune their intrinsic properties. These polysiloxane membranes show good performance in life time experiments. The ion selectivity has been tuned by incorporation of various novel ion receptor molecules, yielding sensors with high selectivities for sodium, potassium, lead, cupper, cadmium, silver, nitrate, nitrite, fluoride, and dihydrogen phosphate.

Transduction of molecular interactions into macroscopic properties

Synthetic receptor molecules derived from calix[4]arenes have been used in different technological applications. The use of various functionalized calix[4]arenes in selective membrane transport through supported liquid membranes, selective cation detection with chemically modified field effect transistors, as preorganized donor-π-acceptor systems in non linear optics and in the development of monolayers with receptor headgroups is discussed.

A double CHEMFET flow cell system for detection of heavy metal ions and integration in microTAS

A new type of flow cell has been developed for detection of heavy metal ions in aqueous solutions, based on the flow injection method. The cell contains two chemically modified field effect transistors (CHEMFETs) of which one is selective for the supporting electrolyte ion (in this case a 0.1 M potassium ion solution) and the other is selective for the heavy metal ion to be detected (Cd2+, Pb2+). The differential signal of the reference electrode CHEMFET and the heavy metal ion CHEMFET in the flow cell system which has been presently developed will be evaluated for miniaturization and further integration in a micro total analysis system.