Figure 4.

Experimental and theoretical circular dichroism of gold nanoparticle double helices enhanced by silver. Left- (a) and right-handed (c) gold nanoparticle double helices coated with varied thickness of silver exhibit different CD intensities and wavelengths from the typical gold nanoparticle double helices. A significant blue shift of the peaks (from ~560 to ~530 nm) and dramatically increased amplitudes in the CD spectra were obtained by coating gold nanoparticles with increasing amounts of silver (red, no silver shell; yellow, ~0.5 nm silver shell; green, ~1 nm silver shell; blue, ~2 nm silver shell; purple, ~3 nm silver shell). The insets in (a) and (c) are provided for clarity. Simulated CD spectra for left- (b) and right-handed (d) gold nanoparticle double helices coated with varied thickness of silver shells (red, no silver shell; green, ~1 nm silver shell; blue, ~1.5 nm silver shell; purple, ~2 nm silver shell).