A detection system (100) and a sensor chip (1) for detecting target molecules, and thus corresponding analytes in a sample is described. Typically the detection system (100) includes a sensor chip (1). The sensor chip (1) comprises on its detection surface (33) a dissolvable reagent layer (5). When the dissolvable reagent layer (5) is in contact with sample fluid, free reagent is generated, assisting in the interaction between a label and target molecules, thus allowing for label based detection. The sample thereby is exposed to mobile reagents in a burst. The reagent layer may contain an enzyme allowing enzymatic assays.