One-Dimensional Assembly of Peptide-Functionalized Gold Nanoparticles:  An Approach Toward Mercury Ion Sensing

Carboxylated peptide-functionalized gold nanoparticles (peptide−GNPs) were self-assembled into networks of one-dimensional (1D) chains in the presence of mercury ion (Hg2+) at room temperature without use of any template. Transmission electron microscopy (TEM) confirmed the formation of a 1D array of gold nanoparticle (GNP) chains and revealed that the length of the chain can be tuned by varying the Hg2+ ion concentration in the medium. Dynamic light scattering (DLS) measurements showed that the assembly of peptide−GNPs actually occurred in the medium and not during TEM specimen preparation. The assembly of peptide−GNPs resulted in a change of color of the suspension from red to purple to blue. This color change is due to the development of a new surface plasmon resonance (SPR) band at 670 nm. A mechanistic pathway is suggested for this 1D assembly on the basis of some control experiments, and we believe that the main driving force for the 1D array of GNPs is dipole−dipole interactions. The change of color and the absorption spectrum of the peptide−GNP suspension due to this assembly enabled us to sense the Hg2+ ion up to parts per million levels in water by the naked eye, as well as by UV−vis spectroscopy.