This paper presents the first results of the fabrication and characterization of a biological sensor based on two complementary parts. A microfluidic channel along with a micromachined stop-band filter are used to detect the type of fluid which flows beneath the electronic circuit. The tridimensional (3D) structure of the microstrip technology is integrated using SU8 material which thus supports the use of buried channels. Besides being a method without contact, this bio-sensor avoids evaporation, contamination, or label fixation. Changes to the cutoff frequency and attenuation allow us to differentiate three values of the salt in water concentration with a maximum variation of attenuation of 6.5%.