Templating Gold Nanoparticles on Nanofibers Coated with a Block Copolymer Brush for Nanosensor Applications

Surface enhanced Raman spectroscopy (SERS)-based nanosensors that offer high spatial and temporal resolution as well as high sensitivity are promising for cell endoscopy studies. This requires fabricating glass nanofibers with a dense but well-dispersed monolayer array of gold nanoparticles (AuNPs), which is a challenge on the highly curved nanofiber surface. We showed previously that this can be achieved with dip-coated block copolymer (BCP) templates, hypothesized to be brushlike. Here, we demonstrate, using small AuNPs and a concentrated THE solution of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), that the effect of decreasing fiber diameter (increasing substrate curvature) on the AuNP deposition pattern parallels the effect of decreasing BCP solution concentration using flat surfaces, allowing the definitive conclusion that the BCP template at small fiber diameters is indeed in the form of an adsorbed brushlike layer. Notably, when dip-coating the fiber from concentrated BCP solution followed by incubation in a AuNP suspension, SEM images show dense clusters composed of two to four AuNPs at high fiber diameters (mm range) that transition into dense but mainly isolated AuNPs at low diameters (mu m range), where the transition range depends on the BCP solution concentration and dip-coating rate. The nanothin brush-only layer at low fiber diameters down to the sub-micrometer range provides an effective template for optimal AuNP deposition that is both simple and robust against changing experimental conditions, such as BCP solution concentration and dip-coating rate, while allowing tunability of the AuNP density and gap sizes through the AuNP diameter (10-100 nm studied) and, more mildly, BCP molecular weight characteristics. These features are ideal for nanosensor applications.