Polyaniline Nanoparticle-Based Solid-Contact Silicone Rubber Ion-Selective Electrodes for Ultratrace Measurements

Silicone rubber (SR)-based solid-contact ion-selective electrodes (ISEs) have been prepared for the first time with an electrically conducting polymer as the solid-contact (SC) layer. The Ca(2+)- and Ag(+)-selective electrodes were based on the ionophores ETH 1001 and o-xylylenebis(N,N-diisobutyl dithiocarbamate), respectively, integrated in room temperature vulcanizing silicone rubber (RTV 3140). The SC consisted of a polyaniline nanoparticle dispersion, which was found to considerably lower the impedance of the SCISEs in comparison to the SR-based coated wire electrodes (CWE). For the CaSCISEs, the bulk membrane resistance decreased from 700 MΩ (CaCWE) to 35 MΩ. Both the Ca(2+)- and Ag(+)-selective SCISEs exhibited nanomolar detection limits with fast Nernstian responses down to 10(-8) M. The potential response of the SCISEs was not influenced by light. The selectivities of the CaSCISEs were similar and for the AgSCISE better than their plasticized PVC-based analogues. Thus, SR seems to be a viable alternative to PVC membranes in ISE applications that require low water uptake, good adhesion, and robust and fast potential responses at submicromolar sample concentrations.