The adsorption of a DNA fluorescent probe belonging to the thiazole orange family at the dodecane/water 
and dodecane/phospholipid/water interfaces has been investigated using a combination of surface-
second harmonic generation (SSHG) and all-atomistic molecular dynamics (MD) simulations. Both 
approaches point to a high affinity of the cationic dye for the dodecane/water interface with 
a Gibbs free energy of adsorption of the order of -45 kJ/mol. Similar affinity was observed with 
a monolayer of negatively charged DPPG lipids. On the other hand, no significant adsorption could 
be found with the zwitterionic DDPC lipids. This was rationalised in terms of Coulombic interactions 
between the monolayer surface and the cationic dye. The similar affinity for the interface with and 
without DDPG, despite the favourable Coulombic attraction in the latter case, could be explained 
after investigating the interfacial orientation of the dye. In the absence of monolayer, the dye 
adsorbs with its molecular plane almost flat at the interface, whereas in the presence of DPPG it 
has to intercalate into the monolayer and adopt a significantly different orientation to benefit 
from the electrostatic stabilisation.