EDS was employed to affirm the presence of PEI and mRNA within ZIF-8, manifested by an increase in the nitrogen: zinc atomic weight percent, as the composite particles contain PEI and mRNA, which add to the nitrogen content of the entire particle. The atomic weight compositions were determined at various locations within the bulk sample (Figure ). Our findings indicate a distinct rise in nitrogen atomic percent when comparing ZIF-8 with mRPZ, signifying the incorporation of mRNA and PEI into the bulk material (Figure ). Other tested composite materials, namely PEI-ZIF-8 and mRNA@ZIF-8, also showed increased nitrogen: zinc weight percent compared to ZIF-8. Qualitative element mapping was performed using an EDS-equipped STEM/TEM (Figure ). Due to the sensitive nature of ZIF-8 to the electron beam damage, the measured atomic percentages obtained with TEM were not consistent with SEM or literature (Figure ). However, there is still a notable increase in the zinc nitrogen ratio of mRPZ compared to ZIF-8 as well as visible signatures of phosphorous in mRPZ. To further establish the incorporation of mRNA-PEI within ZIF-8, a molecular probe assay utilizing an intercalating dye was employed, emitting fluorescence upon contact with free mRNA or bound mRNA which is not blocked from the intercalating dye (Figure ). By treating mRPZ, mRNA-PEI, and mRNA@ZIF-8 with EDTA and heparin, followed by probing with the intercalating dye, how mRNA is incorporated into mRPZ could be elucidated (Figure ). EDTA served to exfoliate ZIF-8, while heparin displaced or released mRNA from electrostatically binding surfaces or molecules, the surface of ZIF-8 (+45.6 mV) or PEI in this case. Briefly, particles were suspended in PBS and treated with EDTA and heparin, separately or together, or received no treatment. The suspension was probed with dye and then centrifuged to pellet any suspended particles. After centrifugation, the supernatant fluid, which could contain free mRNA, was probed with dye. By probing both the suspension and the supernatant after centrifugation, it was possible to determine if mRNA was released from the particle or bound to the particle. The data (Figure ) indicate that mRNA is encapsulated within mRPZ, as treatment with heparin alone did not fully release RNA into the supernatant or suspension, akin to mRNA-PEI. Conversely, treatment with EDTA alone did not cause the release of mRNA from mRPZ, as observed with mRNA@ZIF-8. Only the combined treatment of mRPZ with EDTA and heparin resulted in the unbinding and release of mRNA into the supernatant. Interestingly, mRNA@ZIF-8 did have a signal without treatment and with heparin treatment. This alludes to some mRNA loosely associating with the surface of mRNA@ZIF-8, which could explain its larger hydrodynamic diameter. Additionally, this loosely associated mRNA appears to dislodge from mRNA@ZIF-8 when treated with heparin, explaining the signal increase in the heparin-treated suspension and supernatant fractions. Controls confirm no fluorescence is caused by interactions with ZIF-8, PEI, EDTA, and Heparin (Figure ). The mRPZ particles, with a polymer-RNA core and ZIF-8 shell, exhibit unique properties distinct from ZIF-8 and ZIF-8 composites. With a particle size of 107 nm, they are within the ideal range for delivery applications. The crystallinity of the ZIF-8 shell remains intact, confirmed by matching diffraction patterns with standard ZIF-8. The higher zeta potential of mRPZ, compared to mRNA-PEI alone, and the requirement of EDTA and heparin for mRNA release, further validate the core-shell structure. Enhanced mRNA loading, evidenced by an increased zinc-nitrogen ratio in EDS analysis and a 5.3% loading capacity, surpasses previous ZIF-8 nucleic acid delivery systems, showing promise for both in vitro and in vivo application.