Unusual sensitivity of tween20: Cholesterol niosome structure to the presence of sodium dodecyl sulfate: A study using multiple fluorescent molecular probes

This study reports the interaction of submicellar concentrations (0 mM to 2 mM) of sodium dodecyl sulfate (SDS), a biocompatible surfactant with critical micellar concentration (CMC) value of 8 mM, with Tween20:cholesterol(1:1) niosome membranes, using the fluorescence properties of three conceptually different fluorescent probes (solvatochromic interfacial probe: 8-anilino-1-naphthalenesulfonate (ANS), fluorescence anisotropy sensitive hydrophobic probe: 1,6-diphenyl-1,3,5-hexatriene (DPH), and excited state proton transfer (ESPT) probe: 1-naphthol (1-NpOH)). Dynamic light scattering (DLS) as well as scattering intensity studies have also been used for size estimation. Interfacial polarity of the niosomal membrane increases with increase in SDS concentrations, confirmed by variation of ANS fluorescence intensity. There is an appreciable increase in microviscosity value at the niosomal interfacial domain and moderate increase at the core domain with increase in SDS concentrations, confirmed by steady state fluorescence anisotropy (r_ss) value of ANS and DPH (r_ss (ANS) 0.06 to 0.12 and r_ss (DPH) 0.22 to 0.26 with increase in SDS concentrations from 0 mM to 2 mM). Hydrophobicity in the niosomal core domain increases with increase in SDS concentrations as observed from the fluorescence properties of different prototropic forms of 1-NpOH.