A method and a microelectronic sensor device for making optical examinations in an investigation region at the contact surface of a carrier, wherein an input light beam is sent from a light source towards the investigation region, and wherein an output light beam coming from the investigation region is detected by a light detector. An evaluation unit that is coupled to the light detector is adapted to determine the wetting grade of the investigation region based on a characteristic parameter of the output light beam. The evaluation unit may be adapted to determine a change in the light intensity caused by a liquid contacting the contact surface. The wetting grade may be detected in a test region that is located adjacent to the investigation region and that has a higher roughness than the investigation region.