Robust and Responsive Dendrimer–Gold Nanoparticle Nanocomposites via Dithiocarbamate Crosslinking

Abstract

Thin films of organically capped nanoparticle (NP) composites have chemical, optical, and electrical properties that can be applied to catalysis, [1] sensing, [2] magnetic recording, [3,4] optics, and electronics.[5] Interparticle spacing is a key element for modulation of the nanocomposite properties. [6][7][8] Various materials have been shown to be effective for controlling interparticle spacing (D) of NP composites including dithiol molecules, [9,10] hydrogels, [11,12] polymers, [13][14][15][16][17] dendrimers, [18][19][20] and biomolecules. [21] These studies explored the optical properties of gold nanoparticle (AuNP) composites [19] as well as the collective magnetic behavior of iron oxide NPs.[20] Among these, the three-dimensional preorganized structure of dendrimers renders them a particularly attractive 'mortar' for particle-based nanocomposites. This control over nanocomposite architecture has been applied for modulation of nonlinear optical properties [22] and can be used for the fabrication of novel sensor devices, [23,24] exploiting film porosity to allow efficient diffusion and uptake of analyte molecules.Recently, we demonstrated a simple approach for immobilizing monolayers of NPs on surfaces utilizing the robustness of the dithiocarbamate (DTC) bond formed by reaction of amines and carbon disulfide (CS 2 ) to thiophilic metal and semiconductor surfaces.[25] The reaction of DTC with NPs as well as surfaces has been shown to provide systems with high stability to organic solvents, water, and high-ionic-strengths salt solutions. [26][27][28][29] Herein, we describe a simple method for the formation of stable dendrimer-NP nanocomposite materials based on direct bonding of dendrimers to AuNPs via heterobifunctional DTC chemistry in a one-step process. Amine groups on the poly(amidoamine) (PAMAM) dendrimers were converted to DTCs in presence of CS 2 and place-exchanged the ligands on the NPs, forming crosslinked nanocomposite films as shown in Figure 1a. By varying the dendrimer generation and dendrimer:NP mole ratio (Den:NP), the interparticle spacing could be systematically controlled in the resulting composite films. The technique was combined with surface patterning using microcontact printing (mCP) [30] to selectively and covalently attach the nanocomposites onto surfaces (Fig. 1b).In our studies, PAMAM dendrimers of each generation (G 0 , G 2 , and G 4 ) were mixed with %6.5 nm AuNPs functionalized with cationic trimethylammonium-terminated ligands at 50:1 mole ratio of Den:NP in the presence of CS 2 . The composites were deposited onto amine-functionalized substrates obtained by backfilling aminosilanes on an n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) printed by mCP. The substrate was then rinsed with water, methanol, and dichloromethane after the assembly process to remove undesirable depositions on the OTS areas (Fig. 1b). A microscopy image of the surface shows direct formation of dendrimer-AuNP composites on patterned surfaces with %0.5 mm film thickness (Fig. 1c).To de...

Gold Nanoparticles in Chemical and Biological Sensing

“…AuNP-dendrimer composites have also been explored in vapor sensing. 437–441 In these layer-by-layer (LBL) self-assemblies, the AuNPs provide the conductive film material while the dendrimers serve to cross-link the nanoparticles and to provide sites for the selective sorption of analyte molecules. An interesting bioconjugate material has been synthesized by simple reaction of the spider silk with aqueous chloroauric acid.…”

Nanoimprinted Polyethyleneimine: A Multimodal Template for Nanoparticle Assembly and Immobilization

“…This chemistry has been reported for the stabilization of NPs, [30] the formation of very stable SAMs on gold, [31] capturing NPs on amine SAMs, [32] and the construction of NP-dendrimer composites. [33] The amine groups present on the surface of the patterned PEI layer were converted in situ to dithiocarbamates by the addition of CS 2 , resulting in the immobilization of trioctylphosphineoxide (TOPO)-coated semiconducting NPs. Fluorescence imaging of the surface showed successful immobilization of NPs utilizing the dithiocarbamate coupling strategy (Fig.…”

Photolithography of dithiocarbamate-anchored monolayers and polymers on gold

“…4 In situ DTC formation has proven useful for anchoring a wide variety of amine-terminated molecules onto Au surfaces, ranging from low-molecular weight species to complex structures capable of biomolecular or supramolecular recognition. 4,5,6,7,8,9,10,11,12, 13,14,15,16,17,18,19 Recently, in situ DTC formation has been extended toward the chemisorptive anchoring of polymeric amines such as polyethyeleneimine (PEI). 20 …”