Web Release Date: March 20,
A Microfabricated Nanocalorimeter: Design, Characterization, and Chemical Calibration
and
Department of Physics and Astronomy, VU Station B 351807, Vanderbilt Institute for Integrative Biosystems Research and Education, VU Station B 351807, Department of Chemistry, VU Station B 351822, Department of Biomedical Engineering, VU Station B 351631, and Department of Molecular Physiology and Biophysics, 702 Light Hall (0615), Vanderbilt University, Nashville, Tennessee 37232
Received for review October 26, 2007. Accepted December 13, 2007.
Abstract:
A microfabricated titration calorimeter having nanowatt
sensitivity is presented. The device is achieved by modifying a commercial, suspended-membrane, thin-film thermopile infrared sensor. Chemical reactions are studied
by placing a 50.0 nL droplet of one reagent directly on
the sensor and injecting nanoliter droplets of a second
reagent through a micropipette by means of a pressure-driven droplet injector with 1% reliability in volume
delivery. External thermal noise is minimized by a two-layer thermal shielding system. Evaporation is prevented
by positioning the micropipette through a tiny hole in a
cover glass, sealed by a drop of oil. The device is
calibrated using two acid-base reactions: H2SO4 +
HEPES buffer, and NaOH + HCl. The measured power
sensitivity is 2.90(4) V/W, giving a detection limit of 22
nW. The 1/e time constant for a single injection is 1.1 s.
The day-to-day power sensitivity is reproducible to ~2%.
A computational model of the sensor reproduces the
power sensitivity within 10% and the time constant within
20%. For a 50 nL sample and 0.8-1.5 nL titrant injection
volumes, the heat uncertainty of 44 nJ corresponds to a
3
detection limit of 132 nJ, or the binding energy
associated with 2.9 pM of IgG-protein A complex.
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