In terms of the SEM images in Figures S-2a, the polyelectrolyte deposition further ‘removed’ the pore structures, which are discernable in the SEM image for the PAN-O substrate in Figure S-1a. All the polyelectrolyte-modified PAN-A substrates yielded an RMS value of roughness ~3.5 nm (Figure S-2a), which was slightly higher than that for the unmodified PAN-A substrate (~3.2 nm) as demonstrated in Figure S-1b. Despite the marginal difference in the geometrical characteristics, it is interesting to note that the PAN-A substrate modified by PAH gave rise to a slightly high value of the surface roughness; this is consistent with the observation in prior studies42 that relatively high heterogeneity could result from the deposition of PAH.