Ionophore-containing siloprene membranes: direct comparison between conventional ion-selective electrodes and silicon nanowire-based field-effect transistors

Siloprene-based, ion-selective membranes (ISMs) were drop-casted onto a field-effect transistor device that consisted of a single-chip array of top-down prepared silicon nanowires (SiNWs). Within one array, two sets of SiNWs were covered with ISMs, each containing two different ionophores, allowing the simultaneous sensing of K and Na ions using a flow cell. It is shown that both ions can be effectively detected in the same solution over a wide concentration range from 10^-4 to 10^-1 M without interference. The ISMs were also analyzed in a conventional ISE configuration, allowing a direct comparison. While the responses for K⁺ were similar for both sensor configurations, remarkably, the Na⁺ response of the ISM-covered SiNW device was found to be higher than the one of the ISE configuration. The addition of a Na⁺ buffering hydrogel layer between the SiO₂ of the SiNW and the ISM reduced the response, showing the importance of keeping the boundary potential at the SiO₂/ISM interface constant. The responses of the siloprene-covered SiNW devices were found to be stable over a period of at least 6 weeks, showing their potential as a multichannel sensor device.