A micromechanical technique for measuring solution pH using modified silico
n (SiO2) and silicon nitride (Si3N4) microcantilevers is described. As the
modified surface of the cantilever accumulates charge proportional to the p
H of the surrounding liquid, the cantilever undergoes bending due to the di
fferential surface stress. Results are presented for chemically modified (4
-aminobutyltriethoxysilane, 11-mercaptoundecanoic acid) and metal-modified
(Au/Al) surfaces over a pH range 2-12. Aminosilane-modified SiO2/Au cantile
vers performed robustly over pH range 2-8 (49 nm deflection/pH unit), while
Si3N4/Au cantilevers performed well st pH 2-6 and 8-12 (30 nm deflection/p
H unit). The influences of other ions on cantilever bending were found to b
e negligible below 10(-2) M concentration. (C) 2001 Elsevier Science B.V. A
ll rights reserved.