790323.fig.003a
(a)
790323.fig.003b
(b)
Figure 3: SERS spectra of (a) 0.25 μM 4-ATP and (b) 0.044 μM 4-NTP aqueous solution using gold nanoparticles with the size of 17, 30, 40, 50, 60, and 80 nm, respectively. The arrow of 4-ATP (1079 cm−1) and 4-NTP (1340 cm−1) indicates the peak used for the calculations of the enhancement factor.