Detection of pH variation using modified microcantilever sensors

Abstract

A micromechanical technique for measuring solution pH using modi®ed silicon (SiO 2 ) and silicon nitride (Si 3 N 4 ) 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, 11-mercaptoundecanoic acid) and metal-modi®ed (Au/Al) surfaces over a pH range 2±12. Aminosilane-modi®ed SiO 2 /Au cantilevers performed robustly over pH range 2±8 (49 nm de¯ection/pH unit), while Si 3 N 4 /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 10 À2 M concentration. #

Peer Reviewed: Microcantilever Transducers: A new Approach in Sensor Technology

“…In particular, sub-parts-perbillion detection limits for vapors of aromatic compounds and 10 -9 -M concentrations of ionic species in solution were determined (10,11,18). Self-assembly of amino-and carboxy-terminated straight-chain thiols also provides a convenient means to create cantilever sensors that have controllable pH sensitivities (12,27 ).…”

“…An increasing number of recent reports confirms the potential of MC sensors for environmental and biomedical applications, and the multifaceted functionality of MCs indicates their uniqueness as compared with more traditional sensor designs (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17).…”

Chemical Sensing With Resistive Microcantilevers

“…Selectivity in these experiments is achieved by coating one of the two surfaces of the cantilever with a chemical that interacts preferentially with the analyte of interest. Chemicals, self-assembled monolayers, and polymers have been used in previous studies to achieve selectivity [7,9].…”

Low-noise polymeric nanomechanical biosensors

“…5 On the other hand, silicon surfaces are very reactive to ions present in aqueous solutions. 6 Thus, small fluctuations or drift in the environment properties often obscure the surface stress signals that arise from the molecular recognition events, because these can be as small as 1 -10 mN/ m, equivalent to a deflection of 1 -10 nm in standard microcantilevers. 2,7,8 Cross sensitivities can be reduced or eliminated by using cantilever arrays for measuring the differential cantilever bending with respect to a reference cantilever, whose surface must be passive to the target molecules.…”