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14 Oct 2002

Volume 81, Issue 16, pp. 2917-3103

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Micromechanical cantilever as an ultrasensitive pH microsensor

R. Bashir, J. Z. Hilt, O. Elibol, A. Gupta, and N. A. Peppas

Appl. Phys. Lett. 81, 3091 (2002); http://dx.doi.org/10.1063/1.1514825 (3 pages) | Cited 89 times

Online Publication Date: 7 October 2002

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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 1 nm/5×10−5 ΔpH. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
82.35.Jk Copolymers, phase transitions, structure
82.80.-d Chemical analysis and related physical methods of analysis
82.70.Gg Gels and sols

Magnetic gradiometer based on a high-transition temperature superconducting quantum interference device for improved sensitivity of a biosensor

SeungKyun Lee, W. R. Myers, H. L. Grossman, H.-M. Cho, Y. R. Chemla, and John Clarke

Appl. Phys. Lett. 81, 3094 (2002); http://dx.doi.org/10.1063/1.1515122 (3 pages) | Cited 30 times

Online Publication Date: 7 October 2002

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We describe a gradiometer based on a high-transition temperature superconducting quantum interference device (SQUID) that improves the sensitivity of a SQUID-based biosensor. The first-derivative gradiometer, fabricated from a single layer of YBa2Cu3O7−x, has a baseline of 480 μm and a balance against uniform fields of 1 part in 150. Used in our SQUID “microscope,” it reduces the response to parasitic magnetic fields generated by the measurement process to the level of the SQUID noise. The gradiometer-based microscope is two orders of magnitude more sensitive to superparamagnetic nanoparticles bound to biological targets than our earlier magnetometer-based microscope. © 2002 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
74.72.-h Cuprate superconductors
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