Two-dimensional arrays of nanoparticles (NPs) have widespread applications in optical coatings, plasmonic sensors, and nanocomposites. Current bottom-up approaches that use homogeneous NP templates, such as silane self-assembled monolayers or homopolymers, are typically plagued by NP aggregation, whereas patterned block copolymer (BCP) films require specific compositions for specific NP distributions. Here, we show, using polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and gold NPs (AuNPs) of various sizes, that a nanothin PS-b-P4VP brushlike coating (comprised of a P4VP wetting layer and a PS overlayer), which is adsorbed onto flat substrates during their immersion in very dilute PS-b-P4VP tetrahydrofuran solutions, provides an excellent template for obtaining dense and well-dispersed AuNPs with little aggregation. These non-close-packed arrays have similar characteristics regardless of immersion time in solution (about 10−120 s studied), solution concentration below a critical value (0.1 and 0.05 mg/mL studied), and AuNP diameter (10−90 nm studied). Very dilute BCP solutions are necessary to avoid deposition, during substrate withdrawal, of additional material onto the adsorbed BCP layer, which typically leads to patterned surfaces. The PS brush coverage depends on immersion time (adsorption kinetics), but full coverage does not inhibit AuNP adsorption, which is attributed to PS molecular rearrangement during exposure to the aqueous AuNP colloidal solution. The simplicity, versatility and robustness of the method will enable applications in materials science requiring dense, unaggregated NP arrays.

Dense arrays of well-dispersed gold nanoparticles (AuNPs) on optical fibers are shown to bridge the gap in sensitivity and sensing performance between localized surface plasmon resonance (LSPR) and classical SPR sensing. A simple self-assembly method relying on a poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymer brush layer was used to immobilize AuNPs of different diameters from 10 to 92 nm on optical fibers. In comparison with standard AuNP deposition methods using (3-aminopropyl)trimethoxysilane (APTMS) and polyelectrolytes, the sensitivity with the PS-b-P4VP templating method was found to be 3-fold better, a consequence of the smaller gap between particles and the presence of fewer AuNP aggregates. Hence, the sensitivity of the LSPR sensor for IgG was comparable to a classical SPR, also on optical fibers, and about 68% of that for a prism-based wavelength-interrogation SPR instrument. The reproducibility and the detection limit of the LSPR sensor were about the same as the SPR sensor. The enhanced performance of the LSPR sensors using the PS-b-P4VP block copolymer fabrication method paves the way for use of these LSPR biosensors in a smaller and more cost-effective platform.

A nanothin block copolymer (BCP) brush-layer film adsorbed on glass nanofibers is shown to address the longstanding challenge of forming a template for the deposition of dense and well-dispersed nanoparticles on highly curved surfaces, allowing the development of an improved nanosensor for neurotransmitters. We employed a polystyrene-block-poly(4-vinylpyridine) BCP and plasmonic gold nanoparticles (AuNPs) of 52 nm in diameter for the fabrication of the nanosensor on pulled fibers with diameters down to 200 nm. The method is simple, using only solution processes and a plasma cleaning step. The templating of the AuNPs on the nanofiber surprisingly gave rise to more than 1 order of magnitude improvement in the surface-enhanced Raman scattering (SERS) performance for 4mercaptobenzoic acid compared to the same AuNPs aggregated on identical fibers without the use of a template. We hypothesize that a wavelength-scale lens formed by the nanofiber contributes to enhancing the SERS performance to the extent that it can melt the glass nanofiber under moderate laser power. We then show the capability of this nanosensor to detect the corelease of the neurotransmitters dopamine and glutamate from living mouse brain dopaminergic neurons with a sensitivity 1 order of magnitude greater than with aggregated AuNPs. The simplicity of fabrication and the far superior performance of the BCP-templated nanofiber demonstrates the potential of this method to efficiently pattern nanoparticles on highly curved surfaces and its application as molecular nanosensors for cell physiology.

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 THF 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 (μm 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.

A crystalline-coil block copolymer with an amphiphilic corona-forming block affords a variety of different 2D structures in different self-assembly media.