This work describes the Master’s Thesis project carried out at the Technical University of Denmark. The goal of the project is to design, fabricate, simulate and characterize a hollow MEMS sensor able to detect individual circulating immuno cells, to study their mechanical properties and also to investigate their response during a specific treatment. Combined density, viscosity, mass spectroscopy and IR absorption spectroscopy can be performed by tracking changes in the sensor’s resonant behavior. Based on a previous work, the design is optimized in order to face the requirements of the current cells shape and dimension leading to the development of a detailed microfabrication process.