Ultrasharp light-scattering resonances of structured nanospheres: effects of size-dependent dielectric functions

Recently, Chen et al. [J. Biomed. Opt. Vol. 10, 024005 (2005)] reported on the concept of multicolor molecular imaging, which uses resonant light-scattering spectroscopy of multilayer nanospheres. They claimed that the resonance scattering peaks of three-layer nanoshells can be designed so that the ultrasharp widths are as narrow as 10 nm. Here we show that such ultrasharp labels cannot be fabricated in reality because the effects of size-dependent dielectric functions result in the five- to tenfold broadening of resonant scattering peaks. Furthermore, contrary to the data of Chen et al., we did not find any significant advantages of three-layer structures, as compared with the usual silica/metal nanoshells.