There is near zero intensity of the DMG molecules in the first spectrum acquired, represented in the first data point of the profile indicating that the fatty acid hydrocarbon chains are not present at the outermost surface, fitting the standard description that they are oriented inwards. The PEG and FA14:0 profiles cross at approximately the middle of each ion intensity range at 4 -7 nm depth. This measurement can provide an estimate of the thickness of the PEG2k shell. The value is similar to the SANS estimate of a 4 nm thick surface layer of PEG2k assumed to be in a mushroom conformation for similar PEG2k containing particles. A direct comparative analysis of SANS on the same particles would be needed to make a more accurate comparison, but for the purpose of this method development study, the similarity of the value acquired from Cryo-OrbiSIMS depth profiling to that from SANS value reported in previous studies provides a degree of cautious confidence in the secondary ion profile estimated depth values. The adenine profile is presented to reveal the location of the mRNA molecules in Figure .