Highly specific sensing of silver based on aggregation of G-quadruplex-capped gold nanoparticles

A novel, simple, and rapid colorimetric strategy is proposed based on the aggregation of gold nanoparticles (AuNPs) induced by the unfolding of G-quadruplex (G4) in the presence of silver ions (Ag+). AuNPs to which compact G4 structures were attached had higher stability toward salt-induced aggregation of AuNPs than those on which random coil single-stranded DNA (ssDNA) structures were anchored. In the Ag+-free system, AuNPs remained mono-dispersed. In contrast, upon addition of Ag+, the G4 structure unfolded, inducing aggregation of the AuNPs. The linear range of the as-established colorimetric assay for Ag+ was from 2.0 x 10(-8) M to 2.0 x 10(-6) M, with a detection limit of approximately 7 nM. Additionally, the colorimetric sensor showed good selectivity toward Ag+. The proposed method offers a new assay for metal ion-mediated aggregation-based colorimetric sensing and may pave a new way for heavy metal ions detection.