Multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films

Abstract

In this work, we demonstrate a cascaded, multiplicative electromagnetic enhancement effect in surface‐enhanced Raman scattering (SERS) on periodically micropatterned films made of colloidal gold nanoparticles, prepared by a self‐assembly approach, without implying lithography procedures. The multiplicative enhancement effect is obtained by combining surface plasmon near‐field enhancement due to nanoscale features with far‐field photonic coupling by periodic microscale features. The effect is observed for both internal Raman reporters (molecules attached to the Au colloids before their assembly) and external Raman probes (molecules adsorbed on the samples after film assembly). The ability of the patterned films for far‐field light coupling is supported by reflectivity spectra, which present minima/maxima in the visible spectral range. Finite‐difference time‐domain computer simulations of the electric field distribution also support this interpretation. The fabricated dual‐scale SERS substrates exhibit a good spot‐to‐spot reproducibility and time stability, as proved by the SERS response over a time scale longer than 1 month. The experimental demonstration of this cascaded electromagnetic enhancement effect contributes to a better understanding of SERS and can affect future design of SERS substrates. Moreover, such dual‐scale colloidal films prepared by convective self‐assembly can be of general interest for the broader field of nanoparticle‐based devices. Copyright © 2014 John Wiley & Sons, Ltd.

Synergetic Light-Harvesting and Near-Field Enhancement in Multiscale Patterned Gold Substrates

“…In fact, studies on films patterned into cavity shapes and made of colloidal gold nanoparticles suggested the existence of an increased electromagnetic enhancement, presumably caused by the combination of optical interactions on two different scales: surface plasmon-enhanced near-fields due to nanoscale features and far-field photonic coupling by periodic structures at the microscale. 23 Recently, the incorporation of Au nanoparticles into the voids of SSV arrays has been explored, showing also an important increase in field enhancement at the particle-cavity junction. [24][25][26] These results reinforce the idea that electromagnetic fields in SSV arrays may be further confined by smaller metallic features at the nanometric scale.…”

Silver CD-R based substrate as a SERS active material

“…The EF that confirms the efficiency of SERS signal has been estimated using formulae: EF = (I SERS /N ads )/(I bulk /N bulk ), where I SERS is the intensity of selected vibrational mode in the SERS experiment, I bulk is the intensity of the same Raman mode in the spectrum recorded for bulk material, N ads is the number of molecules adsorbed and probed in SERS experiment, and N bulk is the number of molecules probed in confocal volume of the optical system of Raman experiment [28][29][30]. The estimated number of R6G molecules on the area of laser spot N ads assuming close packing is equal to [28][29][30]. The obtained results proved usefulness of CD-R based substrate containing silver nanostructures for enhancement of Raman signal.…”

Advanced Colloidal Lithography Beyond Surface Patterning

“…Yang and coworkers reported shape control of Ag bowls for practical SERS Substrates . Farcau and coworkers reported multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films …”