What are rapid lateral-flow assays, and how are gold sols used in these tests?
The behavior of a molecule as it reacts with ultra-specific receptors while it is being carried along a nitrocellulose membrane can be used to rapidly identify and measure the material. The critical agent for visualizing this reaction is gold particles that are so small (nanometers) that they appear red and remain suspended in water while they are transported along the nitro-cellulose. Ultra-sensitive tests based on this principle are often referred to as “rapid lateral-flow (immuno)assays.” A common example of a rapid lateral-flow assay is the pregnancy test that measures the peptide hormone associated with pregnancy. A good lateral-flow assay is very easy to perform and will provide an accurate answer within several minutes. To achieve this performance, receptors bound to the gold particles must be carefully balanced with paired receptors striped on the nitro-cellulose membrane. Chemically, this process is the molecular equivalent of setting a mouse trap.
