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

Crosslinkable polar siloxane copolymers for ion detection devices

Functionalized polysiloxanes can be used as sensing membranes in ion‐sensitive field effect transistors (ISFETs). A new 0 ue‐Si and reproducible route for obtaining well‐de‐fined polysiloxane copolymers–the anionic copolymerization of cyclotetrasiloxanes with different side groups (one of which is shown in the Figure)–is reported and the characterization and use of the copolymers in CHEM‐FETS described

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.\ud \u

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+. \u

Membrane characterization of anion-selective CHEMFETs by impedance spectroscopy

Impedance spectroscopy can be used to determine the influence of several membrane parameters on the membrane resistance of anion selective CHEMFETs. The concentration of the ammonium sites in the membrane, the anion-receptor complex stoichiometry, and the polarity of the membrane matrix are of particular importance. In general the resistance of polysiloxane membranes is higher than that of PVC membranes. However, in polysiloxane membranes the membrane polarity can be influenced by the type or concentration of polar substituents on the polysiloxane chain. Polysiloxane ion-exchange membranes with 25 mol % of polar sulfone substituents exhibit the same conductance as NPOE plasticized PVC membranes. Remarkably, the membrane resistance of cation-selective polysiloxane membranes is much lower and is much less dependent on the substituents