Detection of pH variation using modi®ed microcantilever sensors

A micromechanical technique for measuring solution pH using modi®ed silicon (SiO2) and silicon nitride (Si3N4) microcantilevers is described. As the modi®ed 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 modi®ed (4-aminobutyltriethoxysilane, 11mercaptoundecanoic acid) and metal-modi®ed (Au/Al) surfaces over a pH range 2±12. Aminosilane-modi®ed SiO2/Au cantilevers performed robustly over pH range 2±8 (49 nm de ̄ection/pH unit), while Si3N4/Au cantilevers performed well at pH 2±6 and 8±12 (30 nm de ̄ection/pH unit). The in ̄uences of other ions on cantilever bending were found to be negligible below 10ÿ2 M concentration. # 2001 Elsevier Science B.V. All rights reserved.