Analytical Sciences

Morphology Effects of Cap-shaped Silver Nanoparticle Films as a SERS Platform

Hiroyuki TAKEI*,** and Takayuki OKAMOTO***

*Faculty of Life Sciences, Toyo University, Itakura, Gunma 374-0193, Japan
**Bio-Nanoelectronics Centre, Toyo University, Kawagoe, Saitama 350-8585, Japan
***RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

In this paper, we evaluate randomly adsorbed cap-shaped silver nanoparticles for applications to surface-enhanced Raman spectroscopy, SERS. They were prepared by depositing silver on top of surface-adsorbed monodisperse SiO₂ nanospheres, in a manner similar to the method for preparing metal film on nanosphere, MFON, but one major difference lies in the fact that nanospheres are randomly adsorbed rather than as a close-packed MFON. With random MFON, it is possible to incorporate nanospheres with more than one size. Mixing has been found to increase SERS performance. More specifically, by using 50 and 100 nm nanospheres, we found that substrates containing both types outperform substrates prepared from 100% of either 50 or 100 nm nanospheres. As evaluated by spectrophotometry, this increase could not be attributed to an increase in the extinction coefficient of the substrate at the irradiation wavelength of SERS measurements.

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