Inertial mass measurements at the microscale in liquid

Mass is a fundamental property of matter that gives rise to both inertia and gravity, and its accurate quantification is central to the development of science and technology. Different technologies and methods have been developed that enable us to determine the mass of systems across length scales, from the subatomic world all the way to the cosmic scale, with such measurements generally performed in vacuum or air conditions. However, directly measuring the actual mass of objects or systems while they are submerged in liquid environments such as water remains challenging and highly debated, limiting technological developments and the understanding of fundamental processes such as the regulation of a mammalian cell's mass. Here, we use a photothermally actuated custom-built inertial picobalance to perform cantilever-based mass measurements of well-defined silicon microweight samples in liquid environments. Our experiments demonstrate that it is possible to determine the actual mass of the samples attached to the cantilevers when submerged in water, and even within a liquid with a higher density than that of the samples themselves. We anticipate that this study will contribute to and stimulate the development and application of mass sensing techniques, facilitate the creation of new metrology solutions, and improve understanding of the behavior of microresonators in liquid environments.