Hi Aya,

You might try putting a drop (~10-20-50 microL) onto a surface of a ZnSe glass disc (you can purchase them) and dry in an oven at ~45 oC for 2 h (or in air for a day), then use transmission FTIR. The best way would be to remove PBS, as it adds a number of its intrinsic bands to a FTIR spectrum of your liposomes. If the presence of PBS is necessary (e.g., the liposomes are unstable without it), then first take a FTIR spectrum of a similar dried drop of pure PBS at the same concentration that you have in your liposome suspension, and then, by comparing your two spectra, using PBS's strongest line, identify the amount of PBS in your liposome spectrum. (Regretfully, to simply subtract the PBS lines from your mixture - to leave the FTIR spectrum of pure liposomes - would need strictly standardised measurements by the thickness of the samples, which is not feasible with sucg a simple "drop-&-dry" methos.) If the PBS bands do not overlap with those of the liposomes, it's the easiest case - then just fix all others which refer to liposomes. If some overlap - you will see it by comparing the relative intensities of the PBS bands (they will differ in the mixture spectrum from those in the pure PBS). Then compare one of the strong PBS bands which does NOT overlap with liposome's bands and identify those which overlap (they will have a higher intensity, as they overlap with an additional liposome line) - then you will identify at least the positions of other liposome-related bands.

We use this "drop-&-dry" method for our bacterial and other bio-samples (our recent related papers: https://doi.org/10.3390/molecules28041949 , Article Specificities of the Fourier Transform Infrared Spectroscopi...