Thermal Characterization and Analysis of Microliter Liquid Volumes using the Three-Omega Method

Roy-Panzer, S., Kodama, T., Lingamneni, S., Panzer, M. A., Asheghi, M., Goodson, K.E., 2015, "Thermal Characterization and Analysis of Microliter Liquid Volumes using the Three-Omega Method," Review of Scientific Instruments (Featured Article, Cover Image), 86, 024901.

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Thermal phenomena in many biological systems offer an alternative
detection opportunity for quantifying relevant sample properties. While
there is substantial prior work on thermal characterization methods for
fluids, the push in the biology and biomedical research communities
towards analysis of reduced sample volumes drives a need to extend and
scale these techniques to these volumes of interest, which can be below
100pL. This work applies the 3ω technique to measure the
temperature-dependent thermal conductivity and heat capacity of
de-ionized water, silicone oil, and salt buffer solution droplets from
24-80°C. Heater geometries range in length from 200-700µm and in width
from 2-5µm to accommodate the size restrictions imposed by small volume
droplets. We use these devices to measure droplet volumes of 2µL and
demonstrate the potential to extend this technique down to pL droplet
volumes based on an analysis of the thermally probed volume. Sensitivity
and uncertainty analyses provide guidance for relevant design variables
for characterizing properties of interest by investigating the
tradeoffs between measurement frequency regime, device geometry, and
substrate material. Experimental results show that we can extract
thermal conductivity and heat capacity with these sample volumes to
within less than 1% of thermal properties reported in the literature.

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