In summary, sensitive detection of PDGF-BB through indirect
detection of thrombin is achieved by using the thrombin-linked
aptamer assay (TLAA) on magnetic beads. This assay benefits from
the rational design of a bi-functional oligonucleotide probe that is
composed of an aptamer sequence binding to the target protein
and the second aptamer sequence binding to thrombin. The target-binding
aptamer sequence and the thrombin-binding aptamer
sequence facilitate the recognition of the target and the introduction
of the thrombin label. Thus, detection of the target
protein is converted into the detection of thrombin. As an enzyme,
thrombin can catalyze the cleavage of fluorogenic or chromogenic
peptide substrates to generate detectable products. Because of the
signal amplification from thrombin catalysis reaction, the assay
sensitivity is enhanced. This strategy has potential in bioanalysis
and biosensing of other targets in a variety of assay formats by
using thrombin as an enzyme label or reporter. This approach
provides new applications of thrombin-binding aptamer in assay
developments and biosensors.