The biodistribution of mRPZ, compared to PEI N/P=9.3 and PBS, was determined by injecting particles encapsulating Cy5-tagged mRNA expressing luciferase into mice, waiting 6 hours, then collecting their organs (heart, lungs, pancreas, spleen, kidneys, and liver) and imaging them for Cy5 fluorescence. Biodistribution, as determined by Cy5 localization, represents the location of the mRNA, and hence the injected particle traffics in mice (Figure ). Our findings show the mRPZ particle traffics primarily to the lungs, spleen, and liver in the first 6 hours when comparing the log of the Cy5 fluorescence against the PBS control (Figure ). This distribution pattern is consistent with the distribution of PEI N/P=9.3. Interestingly, we observed mRPZ particles traffic significantly more to the lungs and significantly less to the liver compared to PEI N/P=9.3 particles. This result is consistent across sex for the lungs, but not for the spleen and liver. When comparing the spleen, PEI N/P=9.3 particles trafficked significantly less to the spleen than mRPZ in male mice while female mice showed no significant difference. On the other hand, PEI N/P=9.3 particles trafficked significantly more to the liver compared to mRPZ in female mice, while male mice showed no statistical difference (Figure ).