Fabrication and characterization of potassium ion-selective electrode based on porous silicon

Porous-silicon (PS)-based potassium ion-selective microelectrode (K ⁺ISME) was fabricated by using a microelectronic planar process and an electrochemical anodization etching technique. The apparent sensing area of the K⁺ISME is 100 × 100 μm². The response time t_95% is 20 and 31 s when the concentration change is from low to high and vice versa, respectively. The potentials are constant at pH 2-8. The calibration curve for the K⁺ISME is linear within a wide range of pK = 2.0 ∼ 6.0. Its average slope during six months is 56.5 mV per decade, which is close to the Nernst response. The detection limit was found to be on the order of 5 × 10^-7 M. The potentiometric selectivity coefficients (K_i,j^pot) of the K⁺ ISE were 1.8 for NH₄⁺, 3.6 for Li⁺, 4.1 for Na⁺, 4.5 for Mg²⁺, and 4.8 for Ca²⁺, respectively. Good performances of the K⁺ISME are attributed to large specific surface area and excellent adhesion between sensing membrane and the surface of PS.