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

hPorous-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 x 100 mu m(2). 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 similar to 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 X 10(-7) M. The potentiometric selectivity coefficients (KPi,jpot) 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.