Fluorescent Detection of Tadalafil Based on Competitive Host-Guest Interaction Using p-Sulfonated Calix[6]arene Functionalized Graphene

A competitive fluorescence method toward tadalafil detection has been developed based on host guest recognition by selecting rhodamine B (RhB) and p-sulfonated calix[6]arene functionalized graphene (CX6-Gra) as the reporter pair. Upon the presence of tadalafil to the performed CX6-Gra-RhB complex, the RhB molecules are displaced by tadalafil, leading to a switch-on fluorescence signal. The observed fluorescence signal can be used for quantitative detection of tadalafil ranging from 1.00 to 50.00 mu M with a detection limit of 0.32 mu M (S/N = 3). The inclusion complex of tadalafil and CX6 was studied by molecular docking and the results indicated that a 1:1 host-guest stoichiometry had the lowest Delta G value of -7.18 kcal/mol. The docking studies demonstrated that the main forces including pi-pi interactions, electrostatic interactions, and hydrophobic interactions should be responsible for the formation of this inclusion compound. The mechanism of the competitive host-guest interaction was clarified. The binding constant (K) of the tadalafil/CX6 complex was more than 5 times greater than that of RhB/CX6.