Engineered sers substrates employing nanoparticle cluster arrays with multiscale signal enhancement

Abstract

Defined nanoparticle cluster arrays (NCAs) with dimensions up to 25.4 μm square are fabricated on a 10 nm gold film using template guided self-assembly. Structural parameters are precisely controlled, allowing systematic variation of the number of nanoparticles in the clusters (n) and edge to edge separation (Λ) between 1<n<20 and 50 nm≦Λ≦1000 nm, respectively. Rayleigh scattering spectra and surface enhanced Raman scattering (SERS) signal intensities as functions of n and Λ reveal direct near-field coupling between the particles within individual clusters, whose strength increases with cluster size (n) until it saturates at around n=4. Strong near-field interactions between clusters significantly affects the SERS signal enhancement for edge-to-edge separations Λ<200 nm. The NCAs support multiscale signal enhancement from simultaneous inter- and intra-cluster coupling and |E|-field enhancement. Applications include SERS-based spectral identification of bacteria.

What is claimed is: 
     
         1 . A substrate for use in surface-enhanced Raman spectroscopy, comprising:
 a planar substrate layer; and   a nanoparticle cluster array on a surface of the planar substrate layer, the nanoparticle cluster array including an array of clusters of metal nanoparticles characterized by a cluster size n and a cluster separation Λ, n being a nominal number less than 10 of tightly-packed nanoparticles in each cluster determined by a nominal size of the nanoparticles and a deterministic binding site width D, and Λ being a deterministic distance less than 200 nm between adjacent clusters.   
     
     
         2 . A substrate according to  claim 1 , wherein n is determined by the radius of the nanoparticles and morphology and width D of the binding sites. 
     
     
         3 . A substrate according to  claim 2 , wherein the nanoparticles are made of a material selected from silver, copper, silver-gold alloys, and aluminum. 
     
     
         4 . A substrate according to  claim 2 , wherein the nanoparticles shapes are selected from non-spherical and/or hollow, core-shell nanoparticles and multi-scale aggregates of different size/shape nanoparticles. 
     
     
         5 . A substrate according to  claim 2 , wherein the nanoparticles are mixed dielectric and metallic structures. 
     
     
         6 . A substrate according to  claim 1 , wherein the substrate layer includes a functionalizing first monolayer, and the nanoparticles include a functionalizing second monolayer bound to the first monolayer at the binding sites. 
     
     
         7 . A substrate according to  claim 1 , wherein the substrate is a non-conducting dielectric material. 
     
     
         8 . A substrate according to  claim 1 , wherein the substrate contains a conducting film on a non-conducting dielectric. 
     
     
         9 . A substrate according to  claim 1 , wherein the substrate is a metal. 
     
     
         10 . A substrate according to  claim 1 , wherein the substrate is a flexible conducting or non-conducting polymer. 
     
     
         11 . A substrate according to  claim 1 , wherein the nanoparticles are from metal nitrides or germanides.