Brij Niosomes as Carriers for Sustained Drug Delivery─A Fluorescence-Based Approach to Probe the Niosomal Microenvironment.

Niosomes were prepared using a triad of polyoxyethylene alkyl ether surfactants. The focus was to elucidate the effects of varying alkyl chain length and varying hydrophilic headgroups on the structure of the niosomes, with an aim to design niosomes for efficient encapsulation and release of both hydrophobic and hydrophilic drugs. The phase transitions of the surfactants were ascertained by differential scanning calorimetry. It was found that the headgroup has a profound influence on the niosomal bilayer. Fluorescent probes Coumarin 153 (C-153) and 1,6-diphenyl-1,3,5-hexatriene were used to probe the structural integrity of the niosomal bilayer under stress conditions. Other aspects of the niosomes were probed by following the aggregation of the dyes fluorescein (FL) and Nile Red, red edge excitation shift, and fluorescence resonance energy transfer (FRET) between them. Fluorescence lifetime imaging microscopy provides proof of the exact location of the donor and acceptor dyes in the niosomes under FRET condition. It was also shown that the niosomes are efficient "carriers" for entrapment and controlled release of the chemotherapeutic drug 5-fluorouracil. It was found that a rigid niosomal bilayer leads to controlled drug release. The present work is relevant for the future use of these niosomes for cargo entrapment.