Drastically modulating the structure, fluorescence, and functionality of doxorubicin in lipid membrane by interfacial density control

In this work, we report on the observation of a drastic modulation of the fluorescence emission of an anticancer drug, doxorubicin, at the lipid interface during the variation of its molecular density at the interface. The emission efficiency of doxorubicin in the lipid membrane was modulated in the range of less than 10% to above 300% that in the aqueous solution. The corresponding changes in the structure and functionality of doxorubicin on the lipid surface were analyzed with the aid of second harmonic generation and theoretical calculation. It was observed that doxorubicin molecules aggregated on the lipid membrane at a relatively high interfacial density. However, this aggregation may not cause interfacial domain large enough to alter the permeability of the lipid bilayer. At an even higher doxorubicin density, the domain of the aggregated doxorubicin molecules induced a cross-membrane transportation.