Engineered SERS Substrates with Multiscale Signal Enhancement: Nanoparticle Cluster Arrays

Abstract

Defined nanoparticle cluster arrays (NCAs) with total lateral dimensions of up to 25.4 microm x 25.4 microm have been fabricated on top of a 10 nm thin gold film using template-guided self-assembly. This approach provides precise control of the structural parameters in the arrays, allowing a systematic variation of the average number of nanoparticles in the clusters (n) and the edge-to-edge separation (Lambda) between 1 < n < 20 and 50 nm < or = Lambda < or = 1000 nm, respectively. Investigations of the Rayleigh scattering spectra and surface-enhanced Raman scattering (SERS) signal intensities as a function of n and Lambda reveal direct near-field coupling between the particles within individual clusters, whose strength increases with the cluster size (n) until it saturates at around n = 4. Our analysis shows that strong near-field interactions between individual clusters significantly affect the SERS signal enhancement for edge-to-edge separations Lambda < 200 nm. The observed dependencies of the Raman signals on n and Lambda indicate that NCAs support a multiscale signal enhancement which originates from simultaneous inter- and intracluster coupling and |E|-field enhancement. The NCAs provide strong and reproducible SERS signals not only from small molecules but also from whole bacterial cells, which enabled a rapid spectral discrimination between three tested bacteria species: Escherichia coli, Bacillus cereus, and Staphylococcus aureus.

Self-assembled nanoparticle arrays for multiphase trace analyte detection

“…Increasing the signal strength further can be achieved by tailoring the metallic substrate, thereby lowering the limits of detection. Of particular note, are two-dimensional arrays of closely packed metallic nanoparticles (NPs) on a substrate 18 or metallic nanocavities [19][20][21] . These benefit from multiple hot spots being generated in a uniform fashion over a larger substrate area generating high signal enhancement 22 throughout the entire substrate.…”

“…These benefit from multiple hot spots being generated in a uniform fashion over a larger substrate area generating high signal enhancement 22 throughout the entire substrate. Various methods exist to fabricate such structures including lithographic 18,23,24 and chemical approaches 19 . Metallic structures can also be fabricated from self assembled non-metallic scaffolds 25 .…”

Self-assembled nanoparticle aggregates: Organizing disorder for high performance surface-enhanced spectroscopy

“…On the other hand, theoretical calculations and pioneering experimental works have also demonstrated the existence of an additional gain to the plasmonic signal enhancement of single Np or dimers when these are ordered in arrays on a substrate [6][7][8]. This is due to the combined effects of localized plasmonic excitations and diffractive coupling.…”

“…This is due to the combined effects of localized plasmonic excitations and diffractive coupling. For this reason, Np cluster arrays have attracted wide attention as SERS substrates, providing reproducibility in organizing disordered architectures toward potential high-performance sensing [7].…”

Template-Guided Self-Assembly of Discrete Optoplasmonic Molecules and Extended Optoplasmonic Arrays

“…Noble metal nanoparticle clusters are chosen as plasmonic component as they provide much higher E-field intensities than individual nanoparticles. Furthermore, plasmon coupling shifts the plasmon resonance wavelength into the red [41,42], where the slope of the real part of the gold (Au) dielectric function as a function of wavelength is steeper [43,44]. This behavior is beneficial, for example, for the design of sensitive colorimetric sensors [45].…”