In the remaining possible interaction modes, the carbonyl group is directed away from the surface and the weak interaction is mediated by the methyl, H and Cl terminations in the aromatic ring. The distances between the molecule and their closest Ag atoms on the surface are 3.08 Å for Cl, 2.67 Å for H in the ring and 3.16 Å for H in the methyl group. Rotating the MCPA molecule so that the terminating H interacts with the surface at distances between 2.76-3.30 Å, and the O from the -OH of the acid sits 2.89 Å from the surface gives the weakest interaction mode. These results suggest that the interaction of the target pesticide with the SERS substrate is very weak, making detection of MCPA very challenging in agreement with experiments carried out on pristine dendrite substrates where SERS spectra of MCPA were not obtained.