Reversible end-to-end assembly of gold nanorods using a disulfide-modified polypeptide

Abstract

Directing the self-assembly of colloidal particles into nanostructures is of greatinterest in nanotechnology. Here, reversible end-to-end assembly of gold nanorods(GNR) is induced by pH-dependent changes in the secondary conformation of adisulfide-modified poly(L-glutamic acid) (SSPLGA). The disulfide anchoring group driveschemisorption of the polyacid onto the end of the gold nanorods in an ethanolicsolution. A layer of poly(vinyl pyrrolidone) is adsorbed on the positively charged,surfactant-stabilized GNR to screen the surfactant bilayer charge and provide stabilityfor dispersion of the GNR in ethanol. For comparison, irreversible end-to-endassembly using a bidentate ligand, namely 1,6-hexanedithiol, is also performed.Characterization of the modified GNR and its end-to-end linking behavior usingSSPLGA and hexanedithiol is performed using dynamic light scattering (DLS),UV–vis absorption spectroscopy and transmission electron microscopy (TEM).Experimental results show that, in a colloidal solution of GNR–SSPLGA at apH∼3.5, where thePLGA is in an α-helical conformation, the modified GNR self-assemble into one-dimensionalnanostructures. The linking behavior can be reversed by increasing the pH(>8.5) to drive the conformation of the polypeptide to a random coil and this reversal with pHoccurs rapidly within minutes. Cycling the pH multiple times between low and high pHvalues can be used to drive the formation of the nanostructures of the GNR and dispersethem in solution.