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Title page for ETD etd-11182011-114857


Type of Document Master's Thesis
Author Lubbers, Brad Ryan
Author's Email Address brad.lubbers@vanderbilt.edu
URN etd-11182011-114857
Title Isothermal Titration Calorimetry in Nanoliter Droplets with Sub-Second Time Constants
Degree Master of Science
Department Biomedical Engineering
Advisory Committee
Advisor Name Title
Franz Baudenbacher Committee Member
Joel Tellinghuisen Committee Member
Keywords
  • BIOMEMS
  • microfabrication
  • calorimetry
  • cell physiology
Date of Defense 2011-12-01
Availability unrestricted
Abstract
I reduced the reaction volume in microfabricated suspended-membrane titration calorimeters to nanoliter droplets and improved the sensitivities to below a nanowatt with time constants of around 100ms. The device performance was characterized using exothermic acid-base neutralizations and a detailed numerical model. The finite element based numerical model allowed us to determine the sensitivities within 1% and the temporal dynamics of the temperature rise in neutralization reactions as a function of droplet size. The model was used to determine the optimum calorimeter design (membrane size and thickness, junction area, and thermopile thickness) and sensitivities for sample volumes of 1 nl for silicon nitride and polymer membranes. I obtained a maximum sensitivity of 153 pW/√Hz for a 1 µm SiN membrane and 79 pW/√Hz for a 1 µm polymer membrane. The time constant of the calorimeter system was determined experimentally by using a pulsed laser to increase the temperature of nanoliter sample volumes. For a 2.5 nanoliter sample volume, I experimentally determined a noise equivalent power of 500 pW/√Hz and a 1/e time constant of 110ms for a modified commercially available infrared sensor with a thin-film thermopile. Furthermore, I demonstrated detection of 1.4 nJ reaction energies from injection of 25 pl of 1 mM HCl into a 2.5 nl droplet of 1 mM NaOH.
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