Detection of pH variation using modified microcantilever sensors

A micromechanical technique for measuring solution pH using modified silicon (SiO2) and silicon nitride (Si3N4) microcantilevers is described. As the modified surface of the cantilever accumulates charge proportional to the pH of the surrounding liquid, the cantilever undergoes bending due to the differential 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 cantilevers performed robustly over pH range 2–8 (49 nm deflection/pH unit), while Si3N4/Au cantilevers performed well at pH 2–6 and 8–12 (30 nm deflection/pH unit). The influences of other ions on cantilever bending were found to be negligible below 10−2 M concentration.