Assembly Behavior of Organically Interlinked Gold Nanoparticle Composite Films: A Quartz Crystal Microbalance Investigation

Abstract

Thin films based on dodecylamine stabilized gold nanoparticles interlinked with different organic molecules are prepared by automatic layer-by-layer self-assembly in a microfluidic quartz crystal microbalance (QCM) cell, to obtain an in situ insight on the film formation by ligand/linker exchange reactions. The influence of interlinking functional groups and the length of the organic linker molecule on the assembly behavior is investigated. Alkyldithiols with different lengths are compared to alkyldiamines and alkylbisdithiocarbamates with a C8 alkylic molecular backbone. The stepwise layer-by-layer assembly occurs independently of the linker molecule, while the largest frequency changes always correspond to the gold nanoparticle step. During the solvent rinsing and ligand/linker exchange reaction step, the frequency is almost constant with slight increases or decreases dependent on the molar mass of the linker compared to the exchanged ligand. The assembly efficiency is higher for shorter molecules and for molecules with stronger interacting functional groups. The densities of the composite films are calculated from QCM data and independent thickness measurements. They reflect the higher fraction of organic material in the films comprising longer organic linkers. The plasmon resonance band of the gold nanoparticles in the final assemblies is measured with UV/vis spectroscopy. Band positions in films prepared from dithiols and diamines of comparable lengths are very similar, while the spectrum of the bisdithiocarbamate film exhibits a distinct blue-shift. This observation is explained by the longer molecular structure of the linker due to a larger binding group, in conjunction with a delocalization of particle charge on the organic molecule. Obtained results play an essential role in the understanding of thin film layer-by-layer self-assembly processes, and enable the formation of new gold nanoparticle networks with organic diamine and bisdithiocarbamate molecules.

Chemiresistors Based on Bisdithiocarbamate Interlinked Gold Nanoparticles

“…The layer-by-layer self-assembly revealed a stepwise assembly of the gold particles and the linking bisdithiocarbamate molecules with major mass increase during the gold nanoparticle exposure as shown in Figure 1b as known from thiol based composites [3].…”

“…Chemicals with reagent grade or higher purity were purchased from Sigma Aldrich, VWR and Acros Organics and are used as received. For the layer-by-layer self-assembly, N,N-dimethyl-1,8-octanebisdithiocarbamate (BDTC) had to be synthesized in-situ by a base catalysis induced addition of carbon disulfide in 2-propanol from N,N-dimethyl-1,8-octanediamine as described previously [3]. For the sensing measurements, oxidized silicon substrates equipped with gold interdigitated electrodes characterized by a finger length of 5.2 mm, a height of 100 nm, and a spacing of the fingers of 50 µm (providing 52 finger pairs in total) were used.…”

“…As shown in Figure 1a, the preparation of the sensitive material has been performed in an automated layer-by-layer self-assembly procedure using two microfluidic cells [3] where solutions of Au nanoparticles and BDTC were pumped through, alternating with pure solvents with 14 assembly cycles. While coating of the sensor substrate took place in the custom-made cell, the coating progress was monitored in the QCM cell.…”

“…(a) (b) Figure 1. Layer-by-Layer self-assembly process: (a) automated setup for the nanocomposite preparation as described previously [3]. It includes also the used assembly cycle at the bottom; (b) detailed view of the frequency shift over time during two deposition cycles for the composite.…”

Chemiresistive Properties of a Novel Composite Comprised of ITO-Nanoparticles and 1,8-Diaminooctane

“…The QSM substrates were cleaned by a short ozone treatment, while the silicon dies were cleaned by an oxygen plasma followed by a gas phase silanisation procedure with 3-aminopropyldimethylethoxysilane. As shown in Figure 1, the preparation of the sensitive material has been performed in an automated layer-by-layer self-assembly procedure using two microfluidic cells [5] where solutions of ITO nanoparticles and 1,8-Diaminooctane were pumped through, alternating with pure solvents. While coating of the sensor substrate took place in the custom-made cell, the coating progress was monitored in the QCM cell.…”