The bioavailability represents the location in which the mRNA preferentially expresses luciferase compared to PEI N/P=9.3 and PBS. Briefly, mRNA expressing firefly luciferase was encapsulated in mRPZ or delivered with PEI to Balb/c mice intravenously, after 12 hours, mice were injected with luciferin and sacrificed, their organs harvested, and imaged (Figure ). The luminescence of the organs was measured with the IVIS imaging system, and the log mean radiance was compared. In comparison to PEI N/P=9.3, mRPZ resulted in significantly higher expression in all collected organs, well above PBS background. These findings are consistent across sex (Figure ). PEI N/P = 9.3 mRNA was only expressed above background in the lungs and spleen. Toxicity of the particles was assessed using the collected serum from the sacrificed mice 7 days after injection, measuring the Urea, Creatine, and Zinc (Zn 2+ ) concentrations as well as the Alkaline phosphatase (ALP), alanine transaminase (ALT), and aspartate transaminase activity (AST) (Figure ). These serum factors are a measure of mouse health. Based on our observations, mRPZ, PEI N/P=9.3, and JetRNA caused no statistical difference in the serum factors measured compared to a healthy control (PBS). Of particular interest was the serum zinc concentration, as mRPZ would theoretically release zinc ions upon degradation of the ZIF-8 Coating. Not only was the zinc concentration of mRPZ lower than the healthy control, but it was also equivalent to PEI N/P=9.3 which contains no zinc. Overall, the mice showed minimal signs of toxicity when compared to a healthy control and are within healthy standards. It is important to note that mice being injected intravenously were very sensitive to the concentration and degree of resuspension of the mRPZ particles. Some mice were visibly lethargic after injection but recovered quickly. We note that high concentrations of the mRPZ caused the death of 4 out of 6 mice at a 24-µg dose and mRPZ particles that were poorly resuspended caused the death of 2 mice at a 12-µg dose. The colloidal stability of the particles stands to be improved. The long-term stability of the particles was assessed at room temperature for one month, given the success of tested particles in vitro. Particles were synthesized and stored at room temperature under vacuum and injected intravenously in mice. The resulting luciferase activity was measured between 12 and 24 hours, capturing the maximum expression time range identified in Figure . The integrated mean radiance was used to find the luciferase expression at that time point and compared to mRPZ stored at -80˚C for a month and mRPZ freshly synthesized. A PBS control was included to determine background radiance (Figure ). As expected freshly synthesized mRPZ performed equally to mRPZ stored at -80˚C for one month. mRPZ stored at room temperature produced luciferase expression that was significantly less than -80˚C stored mRPZ, but still significantly above background (PBS) over 5-fold. With the application of mRPZ in vivo, we found that many of the characteristics witnessed in vitro are translatable in vivo. We witnessed a delay in luciferase expression compared to the commercial lipid reagent and improved luciferase expression compared to PEI N/P=9.3. Interestingly, mRPZ was taken up more and expressed more in the lungs compared to PEI N/P=9.3 alone. We found many of the trends to be consistent across mouse sex. We also note, that based on the dosage response, less mRNA can be used to achieve a similar expression level. No toxicity was evident based on the blood chemistry checked, even Zinc ion levels were within a healthy range. Additionally, the storage of mRPZ at room temperature displayed expression after a month of storage. Collectively, our findings in vivo represent an exciting first step for future applications of this technology.