Ferrocenated Au Nanoparticle Monolayer Adsorption on Self-Assembled Monolayer-Coated Electrodes

Abstract

The robust, irreversible adsorption of omega-ferrocene hexanethiolate-protected gold nanoparticles (composition ca. {Au(225)(SC6Fc)(43)}) on electrodes provides an opportunity to investigate their submonolayer and monolayer films in nanoparticle-free solutions. Observations of nanoparticle adsorption on unmodified electrodes are extended here to Au electrodes having more explicitly controlled surfaces, namely self-assembled monolayers (SAMs) of alkanethiolates with omega-sulfonate, carboxylate, and methyl termini, and in different Bu(4)N(+)X(-) electrolyte (X(-) = C(7)H(7)SO(3)(-), ClO(4)(-), CF(3)SO(3)(-), PF(6)(-), NO(3)(-)) solutions in CH(2)Cl(2). The nanoparticle surface coverage (Gamma(NP)) and the stability of the adsorbed nanoparticle film to repeated ferrocene/ferrocenium redox cycling decrease in the order of sulfonate > carboxylate > methyl terminated SAM, with increasing hydrophobicity of X(-) and with increasing alkyl chain length. The results are consistent with the proposal that the strong surface adsorption is jointly associated with the polyfunctional character of the nanoparticles, analogous to entropically driven adsorptions of polymeric ions on charged surfaces, and with lateral, ion-bridged nanoparticle-nanoparticle interactions.

Persistent Multilayer Electrode Adsorption of Polycationic Au Nanoparticles

“…This is a lower ligand count than seen for fully ferrocenated Au 225 NP, presumably reflecting a combination of steric and electrostatic effects. [30][31][32] Three different mixed monolayer NPs were prepared by ligand exchange between Au 225 (TEA-thiolate + ) 31 and HSC6Fc using 1:0.5, 1:1, or 1:2 mol ratios of HSC6Fc:TEA-thiolate + ligands, producing respectively, mixed monolayer NPs of average composition Au 225 (TEA-thiolate + ) 27 Fc 4 , Au 225 (TEAthiolate + ) 22 Fc 9 , and Au 225 (TEA-thiolate + ) 18 Fc 13 . The exchange involved stirring a 50-mL ethanol solutions of ∼0.20 g of Au 225 (TEA-thiolate + ) 31 and 0.042 g of HSC6Fc for 4 h at room temperature, followed by addition of 0.10 g LiClO 4 , which precipitated the NPs as a black solid.…”

“…Ideally, for surface confined, noninteracting electroactive sites the theoretical E fwhm for a monolayer is 90.6 mV and is based on a linear relationship between surface coverage and activity. 38 We have discussed [30][31][32] this wave-narrowing effect in terms of various kinds of interactions between the ferrocene ligands on the NPs, both laterally between NPs and intraligand shell, but further work 33 has brought out phase-like behavior that may reflect some more coherent film organization. Figure 4 shows that for a given NP, the E fwhm varies with the electrolyte anionsthe PF 6 -anion promoting narrow peaks and the tosylate anion the opposite.…”

Probing Individual Redox PEGylated Gold Nanoparticles by Electrochemical–Atomic Force Microscopy

“…Functionalized gold nanoparticles have also found many applications in the emerging field of medical imaging and therapy . For these applications, gold nanoparticles are typically protected from the immune system by a polyethylene glycol (PEG) coating. , Redox functionalities can also be incorporated into the layer coating the gold nanoparticles for their use as faradaic electron reservoirs for electrocatalysis; , these redox-functionalized nanoparticles can as well be adsorbed onto surfaces in view of making high charge storage devices. , No matter the targeted application, it is of course indispensable that the properties of the molecular coating of functionalized nanoparticles are fully characterized. Of particular interest is the assessment of the number of copies of the functional molecules introduced on the surface of the nanoparticles.…”

Stepwise Solid‐Phase Synthesis and Solid‐State Electrochemistry of Redox‐Active Viologen Core/Shell‐Structured Modified Silica Materials

“…As a general strategy for the bottom‐up synthesis of functionalized materials, the immobilization of redox‐active compounds on particles, resulting in a core/shell‐structured system, combines high accessibility and simple separation of the modified material 32. The preparation of ferrocene‐terminated indium tin oxide,33 gold,34 and silica35–37 particles was reported recently. In particular, monodisperse and nonporous spherical Stöber silica particles are well established as solid supports38–42 and provide a defined geometry and surface environment.…”