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Micro-mechanical Cantilever as an Ultra-Sensitive pH Micro-sensor

Authors
Type
Published Article
Journal
Applied Physics Letters
Publisher
American Institute of Physics
Publication Date
Oct 16, 2002
Volume
81
Issue
16
Pages
3091–3093
Identifiers
DOI: 10.1063/1.1514825
Source
LIBNA
License
White

Abstract

We report on a pH sensor with ultrahigh sensitivity based on a microcantilever structure with a lithographically-defined crosslinked copolymeric hydrogel. Silicon-on-insulator wafers were used to fabricate cantilevers on which a polymer consisting of poly(methacrylic acid) (PMAA) with poly(ethylene glycol) dimethacrylate was patterned using free-radical UV polymerization. As the pH around the cantilever was increased above the pKa of PMAA, the polymer network expanded and resulted in a reversible change in surface stress causing the microcantilever to bend. Excellent mechanical amplification of polymer swelling as a function of pH change within the dynamic range was obtained, with a maximum deflection sensitivity of 1nm/5×10−5ΔpH.

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