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A Microsensor Based on a Microcantilever Patterned with an Environmentally Sensitive Hydrogel

Published online by Cambridge University Press:  01 February 2011

J. Zachary Hilt ,
Amit K. Gupta ,
Rashid Bashir  and
Nicholas A. Peppas
J. Zachary Hilt
Affiliation:
NSF Program on Therapeutic and Diagnostic Devices Biomaterials and Drug Delivery Laboratories, School of Chemical Engineering
Amit K. Gupta
Affiliation:
Department of Electrical and Computer Engineering
Rashid Bashir*
Affiliation:
NSF Program on Therapeutic and Diagnostic Devices Department of Electrical and Computer Engineering Department of Biomedical Engineering Purdue University West Lafayette, IN 47907-1283 U.S.A.
Nicholas A. Peppas
Affiliation:
NSF Program on Therapeutic and Diagnostic Devices Biomaterials and Drug Delivery Laboratories, School of Chemical Engineering Department of Biomedical Engineering Purdue University West Lafayette, IN 47907-1283 U.S.A.
*
*To whom correspondence should be addressed
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Abstract

A process was developed for patterning thin films of environmentally sensitive hydrogels onto silicon microcantilevers. Microcantilevers have been shown to be ultra-sensitive transducers for chemical, physical, and biological microsensors. By patterning environmentally sensitive hydrogels onto silicon microcantilevers, novel microsensors were prepared for MEMS and BioMEMS applications. Specifically, a cross-linked poly(methacrylic acid) (PMAA) network containing significant amounts of poly(ethylene glycol) dimethacrylate (PEGDMA) was studied. This hydrogel exhibits a swelling dependence on pH. By increasing the environmental pH above the pKa of PMAA to cause ionization of the carboxylic acid groups, electrostatic repulsion is produced along the main polymer chain causing the polymer network to expand and swell. Therefore, a pH change induces swelling or shrinking of the polymer network and creates stress on the microcantilever surface causing it to bend. In this study, silicon microcantilevers were fabricated on p-type (100) SOI wafers. Covalent adhesion was gained between the polymer and the silicon surface through the modification of the silicon surface with γ-methacryloxypropyl trimethoxysilane. Hydrogels were patterned onto the silicon microcantilevers utilizing a mask aligner to allow for precise positioning. The micropatterned hydrogels were analyzed using optical microscopy and profilometry. The bending response of patterned cantilevers with a change in environmental pH was observed, providing proof-of-concept for a MEMS/BioMEMS sensor based on microcantilevers patterned with environmentally sensitive hydrogels.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 729: Symposium U – MEMS and BioMEMS , 2002 , U4.8
Copyright
Copyright © Materials Research Society 2002

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