Controlled Formation of Gold Nanoparticle Dimers Using Multivalent Thiol Ligands

Abstract

Approaches for the controlled formation of gold nanoparticle dimers are investigated. These are based on a locally confined surface modification of gold nanoparticles followed by bridging two particles with an organic linker. A key factor in these approaches is the use of multivalent ligands. Citrate-stabilized gold nanoparticles are immobilized on a glass surface and mono- and multivalent thiol ligands are investigated regarding their ability to inactivate the nanoparticles sites facing away from the glass. A successful locally confined functionalization is only possible if multivalent ligands are used in this step. The application of monovalent ligands results in less stable particles without a permanent regioselective functionalization. This result can be explained by the dynamic equilibrium between bound and free ligands. Subsequently, the sites of the nanoparticles previously bound to the glass surface are functionalized with thiol ligands additionally bearing a reactive group. Approaches using dithiol linkers, diamine linkers, and coupling complementary functionalized particles are investigated. The highest yield of stable dimers is obtained from conditions where nanoparticles which are regioselectively functionalized with an N-hydroxysuccinimide ester are reacted with complementary amino-functionalized particles. The application of nanoparticles with activated carboxyl groups is essential since standard carboxyl activation agents induce an aggregation of the nanoparticles due to a reaction with remaining citrate molecules on the nanoparticle surface which reduces significantly electrostatic stabilization. This versatile approach using complementary regioselective with multivalent ligands functionalized nanoparticles may be also used for the coupling of particles with different size, shape, or composition, as well as a control of the interparticle distance.

Physicochemical properties of surface charge-modified ZnO nanoparticles with different particle sizes

“…Capping nanoparticles with citrate to give them a strong surface charge and colloidal stability is a well-known technique, and is used in the synthesis of gold nanoparticles. 37 L-serine, a zwitterionic molecule, was not expected to significantly change the surface charge on ZnO, and indeed the zeta potential of ZnO did not significantly change upon coating with L-serine. Instead, L-serine modified the surface of ZnO with an organic moiety, making the L-serine-coated ZnO a comparative sample for citratecoated, negatively charged ZnO.…”

Survey of Plasmonic Nanoparticles: From Synthesis to Application

“…However, mixing particles with complementary thiols will result only in particles with a mixed thiol layer, owing to the steady equilibrium of the thiols between the gold surface and the solution. Hofmann et al addressed these issues by attaching gold nanoparticles to a glass slide and subsequent functionalization of the side facing away from the glass with tripodal ligands. The chelating effect leads to an excellent stabilization of the thiol layer and inhibits the subsequent exchange with monothiol ligands.…”

Designing Gold Nanoparticle-Ensembles as Surface Enhanced Raman Scattering Tags inside Human Retinal Cells

“…Therefore we expect that our tags present higher biocompatibility than SERS tags marked with potentially toxic, Raman-active organic dyes. Moreover, our fabrication strategy for the assembly of AuNPs differs from most of the reported techniques which involve crosslinking molecules, like alkanethiols [19,20], surfactants [21], specific proteins [22], and oligonucleotides [23] and most often destabilizing species like salt or ethanol [24], which might further interfere with the intrinsic particles signal. Herein thiol-modified PEG, a nontoxic, hydrophilic polymer, commonly used to improve particles stability, biocompatibility, and their systemic retention [25], is used for multiple purposes: to link the particles between them and stabilize the formed nanoensembles.…”