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Chemical patterns consisting of poly(2-vinyl pyridine) (P2VP) brushes in a background of a cross-linked polystyrene (PS) mat enabled the highly selective placement of citrate-stabilized Au nanoparticles (NPs) in arrays on surfaces. The cross-linked PS mat prevented the nonspecific binding of Au NPs, and the regions functionalized with P2VP brushes allowed the immobilization of the particles. Isolated chemical patterns of feature sizes from hundreds to tens of nanometers were prepared by standard lithographic techniques. The number of 13 nm Au NPs bound per feature increased linearly with increasing area of the patterns. This behavior is similar to previous reports using 40 nm particles or larger. Arrays of single NPs were obtained by reducing the dimensions of patterned P2VP brushes to below ~20 nm. To generate dense (center-to-center distance = 80 nm) linear chemical patterns for the placement of rows of single NPs, a block-copolymer (BCP)-assisted lithographic process was used. BCPs healed defects associated with the standard lithographic patterning of small dimensions at high densities and led to highly registered, linear, single NP arrays.

Reactions of Grignard and organolithium reagents are staple transformations in organic chemistry. However, their use in the chemical functionalization of monolayer-protected metallic nanoparticles is unprecedented. In this letter, we report the reaction of Au nanoparticles bearing a mixed monolayer of alkanethiol ligands that are methyl- and N-methoxy- N-methyl amide-terminated. The latter of these rapidly undergoes reaction with organometallic reagents, achieving high yields (in some cases, nearly quantitative) in only a few hours without the need for high pressure, temperature or catalysts. We assess the feasibility of this reaction with a range of organometallic reagents on the basis of both surface reaction yield and also the stability of the particles (defined as the mass % Au particles recovered vs a control). Demonstrating the utility of these strong organometallic reagents opens the door to a large class of reactions that are underutilized within the field of nanomaterials.