microRNAs are a type of nucleic acid with the potential of biomarkers. In fact, their dysregulation in the blood of a patient is the signal of the presence of inflammations, cancers or other diseases. However, it is still an open challenge to develop a device detecting the microRNAs in a rapid, cheap and portable way, by overcoming the limitations of the traditional techniques. In this Master Thesis I present the technological improvements of the microRNA biosensor developed at the at C2N (Centre des Nanosciences et Nanotechnologies, Palaiseau, France) in the Department of Microsystems and Nanobiofluidics. The biosensor is a so-called Lab on a chip device, and its aim is to concentrate, detect and quantify the microRNA from the sample of a patient.