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 100times100 mum
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=2.0~6.0. 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 5times10
^-7
M. The potentiometric selectivity coefficients (K
_i,j

^pot
) of the K
⁺
ISE were 1.8 for NH
₄

⁺
, 3.6 for Li
⁺
, 4.1 for Na
⁺
, 4.5 for Mg
²⁺
, and 4.8 for Ca
²⁺
, 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