Nanoparticles assemblies on demand: Controlled aggregation of Ag(0) mediated by modified peptoid sequences.

Assemblies of metal nanoparticles (NPs) have been broadly used for the construction of materials with distinct spectroscopic properties towards sensing applications. On the other hand, well-dispersed NPs are exploit for applications in catalysis and medicine. Biopolymers or biomimetic oligomers can serve both as efficient stabilizers of NPs and as useful aggregation mediators that can lead to assemblies with unique properties. Controlling aggregation processes, however, is still challenging and often relies on trial and error rather than on defined thumb rules. Herein we develop specific guidelines for the controlled aggregation of Ag(0) NPs at room temperature in water near neutral pH and without any additives. We use short peptide mimics, N-substituted glycine oligomers called peptoids, as mediators, and investigate the influence of sequences variations on the NPs assembly. Spectroscopic and electron microscopy data reveal that both the length of the peptoids and their sequences have an effect on the NPs aggregation. Thus, we demonstrate that we can control both the degree of aggregation and the aggregates sizes by tuning these properties. Specifically we show that longer peptoid sequences as well as sequences consisting of aromatic side chains are required for the formation of uniform NPs assemblies in an average size of 70nm, while a short hydrophilic sequence can stabilize well-dispersed Ag(0) NPs. Moreover, the catalytic activity of Ag(0) NPs towards the reduction of 4-nitrophenol to 4-aminophenol can be also controlled by varying the properties of the peptoid mediators.