Gold nanoparticle-based fluorescence quenching via metal coordination for assaying protease activity

We report a gold nanoparticle (AuNP)-based fluorescence quenching system via metal coordination for the simple assay of protease activity. Carboxy AuNPs (5 nm in core diameter) functioned as both quenchers and metal chelators without requiring further modification with multidentate ligands; therefore, they were strongly associated with the hexahistidine regions of dye-tethered peptides in the presence of Ni(II) ions, leading to notable fluorescence quenching over the varying molar ratios of dye to AuNP. Upon the addition of matrix metalloproteinase-7 (MMP-7), the fluorescent intensity was efficiently recovered in one-pot mixture especially at 10:1–100:1 molar ratios of dye to AuNP. Consequently, the dequenching degree was dependent on the MMP-7 concentration in a hyperbolic manner, ranging from as low as 10 to 1,000 ng mL 1. In this regard, we anticipate that the developed system will give us a general way to construct nanoparticle–dye conjugates and will find applications in the analyses of many other proteases mediating significant biological processes with low background and high sensitivity.