Detection of Enzyme Activity through Catalytic Signal Amplification with Functionalized Gold Nanoparticles

A cascade of two catalytic events was used to detect enzyme activity: When a peptide substrate acting as an inhibitor for a catalytic gold nanoparticle was hydrolyzed by an enzyme, the catalytic activity of the nanoparticle was restored, and a large amount of a yellow reporter molecule was produced (see picture; S=substrate, P=product). The assay can be made selective for a particular enzyme by changing the inhibitory peptide.