This paper presents electrospin nanolithography (ESPNL) for versatile and low-cost fabrication of nanoscale patterns of polymer brushes to serve as templates for assembly of metallic nanoparticles. Here electrospun nanofibers placed on top of a substrate grafted with polymer brushes serve as masks. The oxygen plasma etching of the substrate followed by removal of the fibers leads to linear patterns of polymer brushes. The line-widths as small as ∼50 nm can be achieved by precise tuning of the diameter of fibers, etching condition, and fiber–substrate interaction. Highly aligned and spatially defined patterns can be fabricated by operating in the near-field electrospinning regime. Patterns of polymer brushes with two different chemistries effectively directed the assembly of gold nanoparticles and silver nanocubes. Nanopatterned brushes imparted strong confinement effects on the assembly of plasmonic nanoparticles and resulted in strong localization of electromagnetic fields leading to intense signals in surface-enhanced Raman spectroscopy. The scalability and simplicity of ESPNL hold great promise in patterning of a broad range of polymer thin films for different applications.

This work reports scalable, low-cost, and simple fabrication of plasmonic heterostructures consisting of gold nanoparticles (NPs) of different sizes to generate intense hot-pots over large areas to serve as substrates for molecular sensing in SERS applications. Our approach involves assembly of massively-available colloidal gold NPs on substrates functionalized with end-grafted poly(ethylene glycol) (PEG) brushes without need for any sophisticated tools and post-modification of the particles and substrates. From real-time monitoring of the adsorption process by using a quartz crystal microbalance, we identified that the cyclic deposition of citrate-stabilized gold NPs on PEG brushes is an effective approach to modulate the kinetics of particle adsorption and greatly improves the surface coverage leading to reduced inter-particle distances. Cyclic deposition of NPs differing in size leads to placement of the small particles in close proximity of the large ones, yielding hot-spots as a consequence of the unique type of interaction between PEG chains and gold NPs. Assembly of heterostructures (60 nm+40 nm and 60 nm+20 nm) at optimized conditions resulted in strong SERS effects with enhancement factors as high as ≈2.0×10 and enabled detection of rhodamine 6G molecules in concentrations as low as 1 nm. The cyclic deposition of NPs also results in increase of the water contact angle without need for any post-modification of the substrate, resulting in ≈30 fold increase in the Raman intensity of aqueous molecules. The insights gained on the adsorption of gold NPs together with the simplicity of the presented approach show great promise for surface assembly of colloidal NPs for a broad range of applications.

F unctionalization of surfaces with polymer brushes shows important promise for a range of applications in materials engineering [1, 2], nanotechnology [3, 4] and biotechnology [5, 6]. A particular area where these end-grafted polymer chains are receiving increasing attention is immobilization and assembly of colloidal NPs [7-9]. The ultra-smooth surfaces, mechanical robustness, long-term durability and ability to tune the chemistry, thickness and grafting density of the brushes present a highly useful platform for benefiting from the interesting properties of NPs that are available in precisely defined size, shape and material composition in massive quantities through wet chemistry approaches [10]. Tailoring the interaction of polymer brushes with NPs through the intrinsic properties such as the length of polymer chains [11] and external stimuli such as pH [12] allows for assembly of particles into specific architectures that can be dynamically tuned. Assembly of NPs into or-Article History: