Monitoring lipid phase transition temperatures using fluorescent probes and temperature-dependent fluorescence spectroscopy

Abstract

The response of fluorescent dyes incorporated in multilamellar liposomes was evaluated for their applicability in monitoring thermal-induced changes in liposomes. Five fluorescent probes, diverse in polarity, lipophilicity, and consequently their position within the lipid multibilayers constituted from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), were used to record temperature-dependent fluorescence spectra of the liposomal suspensions. The responses of the dyes were analysed in a multivariate fashion to determine pre- and main phase transition temperatures of DPPC. Laurdan® and 1-chloro-9,10-bis(phenylethynyl)anthracene register both phase transitions, while 9,10-diphenylanthracene and 9,10-bis(phenylethynyl)anthracene report only pretransition. According to the differential scanning calorimetry (DSC) measurements, all suspensions display both phase transitions that resemble DSC curve of pure DPPC. The positions of the dyes within the bilayers were determined by molecular dynamics simulations.