Droplet-based differential microcalorimeter for real-time energy balance monitoring

Microcalorimeters have been widely used for characterizing molecular interactions in physical, chemical and biological research. Here, we report on a droplet-based micromachined calorimeter for real-time energy balance monitoring. The microcalorimeter was fabricated by a single lithography process and wafer dicing using glass substrate with a diameter and a thickness of ≈ 100 mm and ≈ 100 μm, respectively. The sample with volume of ≈ 0.5 μL was placed on the microcalorimeter and covered with mineral oil to avoid evaporation. The microcalorimeter was operated in differential mode having the temperature and power resolution of ≈ 148 μK and ≈ 42 nW, respectively. With this system, we monitored the energy balance of H₂O₂ decomposition catalyzed by few self-propelled Pt microrobots. Such a simple microcalorimeter has tremendous potential for chemical and biological research such as monitoring the energy balance of living cells or microorganisms and correlating the energy changes with their activities and status.