The continued efforts in the biological community to optimize methodologies such as PCR and to characterize biological reactions and processes are motivating reductions in sample volume. There is a growing need for the detection of thermal phenomena in these small volumes, such as the heat released by recombination and the effective conductivities and capacities in extremely small fluidic regions. While past work has focused largely on heat transport in essentially bulk fluid volumes, there is a need to scale these techniques to the much smaller volumes of interest for biological and biomedical research.”
This work applies the 3ω measurement technique to μL volumes by using heaters with dimensions of 200–700μm in lengths and 2–5μm in widths. We investigate fluid samples of DI water, silicone oil, and a salt buffer solution to experimentally determine their temperature-dependent thermal properties from 25°C to 80°C. Validation is achieved through comparison of these values of thermal conductivity κ and volumetric heat capacity Cν to literature. The work also demonstrates the device capability to conduct temperature-dependent measurements down to pL droplet volumes by conducting a volume analysis given the dimensions of heaters used, independent of droplet boundary conditions. Sensitivity and uncertainty analyses based on these heater dimensions and surrounding material stack show the detection capabilities of these heaters, as they are optimally designed to maximize signal while accommodating the size restrictions of small volume droplets.