A sensor unit functionally stable in an implant, for performing qualitative and/or quantitative in vivo determination of an analyte, including a connection area (3) having at least one binding site for the analyte (7), the connection area undergoing a spatial change when the analyte binds to the binding site. The sensor unit further includes first (1) and second (5/9) fluorescently active regions bound to the connection area (3) in a manner such that, when a spatial change occurs to the connection area (3) due to the analyte binding to the connection area (3), the distance between the first fluorescently active region (1) and the second fluorescently active region (5/9) changes without the bonds of the fluorescently active regions (1, 5/9) to the connection area (3) being broken, and wherein one or both of the fluorescently active regions (1, 5/9) includes more than 60% by weight of an anorganic material.
