Therefore, MD simulations show that stable molecular binding is essential for eliciting an optical response. In this regard, ssDNA-SWCNT sensors are similar to traditional biosensors that function through molecular recognition and ligand binding. The binding interactions predominantly involve two types: electrostatic interactions through charged groups and π-stacking interactions, the former facilitating and contributing to the stability of the later. However, unlike traditional biosensors, stable ligand binding alone is not sufficient to elicit a response. The perturbation cross section of a ligand depends on the nature of substituents on the aryl ring (electron donating vs. withdrawing) and their proximity to the surface of the nanotube when the ligand is in a stable binding mode (Fig. ).