<p>The present invention relates to a sensing device (100) for detecting a target substance (2) in an investigation region (113). The sensing device (100) comprises a sensing surface (112) with an investigation region (113) and a reference region (120) thereon. The sensing device (100) further comprises a reference element (121) located at the reference region (120). The reference element (121) is adapted to shield the reference region (120) from the target substance (2) such that light reflected at the reference region (120) under total internal reflection conditions remains unaffected by the presence or absence of the target substance (2). This allows measuring a property, typically the intensity, of light reflected at the reference region (120) independent of the presence or absence of the target substance (2). This measured property of the reflected light can be used for performing an improved correction of light reflected at the investigation region (113).</p>
