The invention provides a system 10 for detection of at least one analyte present in a fluid, the system comprising a detector 24 comprising an immunoassay 13 or lateral flow assay 15 configured to detect presence of the analyte in the fluid, the detector comprising a specimen sampling region 29 for the fluid and a protective seal 50 partially covering the detector 24, wherein only the specimen sampling region 29 is uncovered by the fluid-protective seal 50, and wherein the fluid-protective seal 50 provides resistance to acid. The fluid may be amniotic fluid and the analyte may be a protein such as alpha-fetoprotein (AFP) or Carcino-embryonic antigen (CEA) or a carbohydrate. The device may be used to detect meconium-stained amniotic fluid. The device may also be used in testing water for toxins, asbestos or 2, 4, 6-trinitrotoluene.
