Nanowatt simple microcalorimetry for dynamically monitoring the defense mechanism of Paramecium caudatum

Microcalorimetry has been widely used in measuring cellular metabolic heat to study bioprocesses, such as metabolism. However, it is still limited by insufficient sensitivity and system complexity, especially for the direct measurements of individual cells. Here, we present a droplet-based simple differential microcalorimetric system for determining the real-time energy balance of the ciliate protist, Paramecium caudatum. We utilized the platform to dynamically monitor its defensive behavior and measured the temperature change. Then we used heat balance equation and calculated corresponding dissipated power and energy with an ultimate resolution of ≈14 nW. The results showed that the defensive behavior by the ejection of the trichocysts’ content consumed energy of ≈0.75 mJ per cell, and the dissipated power was ≈303.8 μW. This differential microcalorimetric platform can be used to study the metabolic heat of protist metabolism as well as other individual cells, helping us to understand this widespread, yet little-known, biological phenomenon from a new perspective.