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+.