Abstract: A monitor having a hollow semipermeable casing with a test strip is agitated in a sample volume of suspect liquid. The monitor is partially filled with tiny colored beads confined to its interior by the size of the openings in the semipermeable structure. Adhered to the beads are antibodies matched to the antigen characterizing the suspect substance. The test strip is segregated into collection and control regions. Antibodies matched to the suspect antigen are adhered only to the collection region. If the sample fluid contains the suspect substance, it will bind to both the bead antibodies and the collector antibodies, resulting in an accumulation of colored beads in the collection region but not the control region. A significant color differential between the two is a positive indication of the suspect substance. This invention has significant potential in screening for the date rape drugs, GHB and rohypnol.