A sensor is described for optically determining the concentration of an analyte in a body fluid. This sensor comprises a needle arrangement which has at least one hollow needle having a hollow space extending from the distal end to the proximal end, the distal end of which is suitable for lancing. The proximal end of the needle opens into a chamber in which liquid that enters through the distal end of the needle can be collected. A window which is at least partially permeable to infrared radiation is in direct contact with the chamber.
