In this format the sample migrates from the sample pad through the conjugate pad where any target analyte present will bind to the conjugate. The sample then continues to migrate across the membrane until it reaches the capture zone where the target/conjugate complex will bind to the immobilised antibodies producing a visible line on the membrane. The sample then migrates further along the strip until it reaches the control zone, where excess conjugate will bind and produce a second visible line on the membrane. This control line indicates that the sample has migrated across the membrane as intended. Two clear lines on the membrane is a positive result. A single line in the control zone is a negative result. Double antibody sandwich assays are most suitable for larger analytes, such as bacterial pathogens and viruses, with multiple antigenic sites.