Note: Three-omega method to measure thermal properties of subnanoliter liquid samples

There are growing needs to measure the thermal properties of small-volume liquid samples in various fields of bioengineering and microfluidics. Accordingly, there have been efforts toward miniaturization of the sensing device without substantially sacrificing the sensitivity. The minimum sample volume required for quantitative thermal analysis is currently in the 10 nl scale. In this work, we describe microfabricated sensors and a modified three-omega data-analysis scheme to determine the thermal conductivity k and volumetric heat capacity rhoc(p) of samples of a few hundred picoliters. In experiments using several reference liquids, the technique measured k and rhoc(p) of 750 and 375 pl samples. The measurement accuracies were approximately 10% for k and approximately 15% for rhoc(p).