Depending on the nature of the signal amplification system assays may be of numerous types, to name a few:
#Enzyme assay: Enzymes may be tested by their highly repeating activity on a large number of substrates when loss of a substrate or the making of a product may have a measurable attribute like color or absorbance at a particular wavelength or light or Electrochemiluminescence or electrical/redox activity.
#Light detection systems that may use amplification e.g. by a photodiode or a photomultiplier tube or a cooled charge coupled device.
#Radioisotope labeled substrates as used in radioimmunoassays and equilibrium dialysis assays and can be detected by the amplification in Gamma counters or X-ray plates, or phosphorimager
#Polymerase Chain Reaction Assays that amplify a DNA (or RNA) target rather than the signal
#Combination Methods Assays may utilize a combination of the above and other amplification methods to improve sensitivity. e.g. Enzyme-linked immunoassay or EIA, enzyme linked immunosorbent assay.