790323.fig.004a
(a)
790323.fig.004b
(b)
790323.fig.004c
(c)
Figure 4: Experimental enhancement factor of 4-ATP, 1079 cm−1, as a function of size of gold nanoparticles (a) when the number of gold NPs was kept the same, (b) when the surface area of all gold NPs was kept the same, and (c) when the concentration of gold was kept the same. The solid lines are just guiding of the eye. The error bar in -axis is the standard deviation of the size of the nanoparticles while the error bar in -axis is the standard deviation of enhancement factors from three experiments.