Tuning the phase transition temperature of hybrid Span60-L64 thermoresponsive niosomes: Insights from fluorescence and Raman spectroscopy

Abstract

In this work, we report the formation of hybrid niosome vesicles, prepared using non-ionic surfactant Span60 (S60) and triblock copolymer L64 for the first time, along with cholesterol. The prepared S60-L64 hybrid niosomes with different compositions are compared with pure L64 and S60 niosomes, and they are characterized using Dynamic Light Scattering (DLS), zeta potential, Scanning Electron Microscopy (SEM) techniques. Gel to liquid phase transition behaviour of the niosomes are studied in detail, using steady-state fluorescence and Raman spectroscopy. The phase transition temperature (Tm) of vesicles is tuned sequentially on the addition of increasing mole percentage of S60 to pure L64. 1-Naphthol, a polarity sensitive fluorescent probe, is loaded in-situ and used to study the micro-environmental changes in the niosome over a wide range of temperatures to determine the Tm of the vesicles. The transformations of the niosome bilayer in the gel, pre-transition and liquid phase are schematically shown and discussed elaborately in accordance with the fluorescence behaviour of 1-Naphthol. As a direct and label-free technique, Raman spectroscopy is also used to investigate the bilayer arrangement of the niosome around Tm. The behaviour of different vibrational modes in the hydrocarbon chain of the niosome at different temperatures is successfully used to determine the Tm of the vesicles. Finally, the phase transition temperature of an appropriate hybrid niosome is determined as 40 °C, which can be used as an efficient thermoresponsive drug delivery system within the physiological body temperature limit at local mild hyperthermia condition.