Synthesis of a Free-Standing Monolayer of Covalently Bonded Gold Nanoparticles

Abstract

We present synthesis of a free-standing monolayer film of gold nanoparticles (AuNPs) which are linked by covalent bonds. In the method developed, the free-standing film is obtained by chemical cross-linking of the AuNPs of the core diameter of 5.6 nm that form a dense monolayer at the oil–liquid interface. As the cross-linking agent, naphthalene dianhydride derivative, which forms amide bonds with the ligand molecules, is used. The AuNPs are coated with aminothiolate ligands that can change their character from a hydrophilic to a hydrophobic one via the reversible protonation/deprotonation mechanism. When adsorbed at the oil–water interface, such functionalized AuNPs display amphiphilic (Janus-like) structure and self-assemble into a highly stable monolayer. To bring the AuNPs at the oil–water interface, an excitation of the system that leads to the formation of the oil-in-water emulsion is required. After the excitation, the AuNPs are transported onto the oil–water interface on the surface of the oil droplets that carry them as their “cargo”. A thermodynamic mechanism explaining this cargo effect is put forward. The as-synthesized free-standing film can be easily transferred from the oil–water interface onto solid support, as well as porous grids, and it is found to be stable in air.

Nanoparticle Assembly at Liquid–Liquid Interfaces: From the Nanoscale to Mesoscale

“…Rotello and co‐workers used terpyridine stabilized FePt or Au NPs as the building block and also obtained robust cross‐linked films by the complexation of terpyridine with Fe(II) metal ions . Fiałkowski and co‐workers described a method to prepare covalently cross‐linked Au NP films using aminothiolalkyl‐functionalized Au NPs, and a naphthalene dianhydride derivative was added as the cross‐linking agent …”

Compartmentalized Thin Films with Customized Functionality via Interfacial Cross‐linking of Protein Cages

“…This integration of functional NPs, large molecules, or bioactive enzymes into thin films offers numerous advantages to tailor the structural and functional properties by well‐defined design. To this date, several strategies have been developed to prepare such hybrid thin films including surfactant templating, spinning‐assisted assembly, layer‐by‐layer deposition, and cross‐linking . These strategies that deal directly with NPs or macromolecules, often suffer from the complex and diverse surface and physicochemical properties of the individual NPs or the substantial loss of enzyme activity during crosslinking .…”

Free‐Standing 2D Nanoassemblies

“…In summary, the chemically cross-linked free-standing 2D nanoassemblies greatly enhanced their chemical and mechanical stability [94,107,112] . The cross-linking nanoassemblies could survice under compression and expansion, solvent fluctuation, and even magnetic stirring.…”

“…[52] Free-standing monolayered gold nanoparticle assemblies were fabricated by employing naphthalene dianyhydride derivative as a cross-linking agent which could form amide bonds with aminothiolalkyl ligands (Figure 4a). [107] The metal ions can also act as linkers between ligands to link the nanoparticles through coordination bonds. For example, a coordination bonding strategy has been developed to bridge FeS 2 pyrite nanoparticles into free-standing nanosheets.…”

“…For example, it can take more than 2 days to synthesize the naphthalene dianhydride derivative cross-linking agent and another 3 days to complete the cross-linking reaction. [107] In addition, chemically cross-linked assemblies has a major disadvantage that they usually don not have a high degree of ordering.…”