Improved sensing membrane immobilization for enhanced long-term stability of iodide ion-selective microelectrode

A porous silicon (PS)-based iodide ion-selective microelectrode (I-ISME) was fabricated by using a microelectronic planar process and an electrochemical anodization etching technique. The apparent sensing area of the I-ISME is 100×100 μm². The response time t95% is 8 and 12 s when the concentration change is from low to high and vice versa, respectively. The potentials are constant at pH 1.0-2.0. The calibration curve for the I-ISME is linear within a wide range of 5.0×10^-7-1.0×10 ^-1 M. Its average slope during 12 months is 58.0 mV per decade, which is close to the Nernst response. The detection limit was found to be on the order of 1.0×10^-7 M. The sequence of Hofmeister selectivity coefficient (K^pot_i,j) of the I-ISME were I-Br^- SCN- Cl- SO^2-₄ NO-₃ . Good performances of the I-ISME are attributed to large specific surface area of PS and excellent adhesion between sensing carrier and the surface of PS.