Nanoparticle Cluster Arrays for High-Performance SERS through Directed Self-Assembly on Flat Substrates and on Optical Fibers

We demonstrate template-guided self-assembly of gold nanoparticles into ordered arrays of uniform dusters suitable for high-performance SERS on both flat (silicon or glass) chips and an optical fiber faucet Cluster formation is driven by electrostatic self-assembly of anionic citrate-stabilized gold nanoparticles (similar to 11.6 nm diameter) onto two-dimensionally ordered polyelectrolyte templates realized by self-assembly of polystyrene-block-poly(2-vinylpyridine). A systematic variation is demonstrated for the number of particles (N approximate to 5, 8, 13, or 18) per duster as well as intercluster separations (S-c approximate to 37-10 nm). Minimum interparticle separations of <5 nm, intercluster separations of similar to 10 nm, and nanoparticle densities on surfaces as high as similar to 7 x 10(11)/in.(2) are demonstrated. Geometric modeling is used to support experimental data toward estimation of interparticle and intercluster separations in duster arrays. Optical modeling and simulations using the finite difference time domain method are used to establish the influence of duster size, shape, and intercluster separations on the optical properties of the duster arrays in relation to their %RS performance. Excellent SERS performance, as evidenced by a high enhancement factor, >10(8) on flat chips and >10(7) for remote sensing, using SERS-enabled optical fibers is demonstrated. The best performing duster arrays in both cases are achievable without the use of any expensive equipment or dean room processing. The demonstrated approach paves the way to significantly low-cost and high-throughput production of sensor chips or 3D-configured surfaces for remote sensing applications.