Microelectronic sensor device for optical examinations in a sample medium

The invention relates to a microelectronic sensor device with a light source (21) for emitting an input light beam (L1) into a transparent carrier (11) such that it is totally internally reflected at a contact surface (12) as an output light beam (L2), which is detected by a light detector (31). Frustration of the total internal reflection at the contact surface (12) can then for example be used to determine the amount of target particles (1) present at this surface. The sensor device further comprises a refractive index measurement unit (100, 200, 300) for measuring the refractive index (nB) of the sample medium, and an evaluation unit (50) for evaluating the measurement of the light detector (31) taking the measured refractive index (nB) into account and/or for changing the conditions of total internal reflection of the input light beam (L1). The refractive index measurement unit may particularly be designed to infer the refractive index (nB) from the deflection of a test-light beam (L3) that is transmitted through the sample medium, or from a reflection of a test-light beam (L1) at an interface (12) to the sample medium. In the latter case, it is possible to determine the critical angle of total internal reflection and/or to measure the reflectivity of the interface.